Everything you want to know about using Solar Energy is here!

Knowledge – as well as solar energy – is power! I'm very proud to announce the publication of not one but two new titles that I've been working on for a long time.

These distil much of my learning over this period about two essential topics that will help us fight climate change:

1. Passive Solar Architecture Pocket Reference
2. Solar Energy Pocket Reference

Get 20% off! E.g. paperback or e-book would be £20.79! Just enter code FLR40 on checkout. Order here:

• Passive Solar Architecture Pocket Reference
• Solar Energy Pocket Reference  

Passive Solar Architecture covers: the principles of passive solar building and passive house, a ten-step design and build strategy, calculating solar irradiance, factors affecting the choice of building materials, passive heating and cooling principles and techniques in different climates, the Passivhaus Standard and natural and augmented lighting and notes on technology and building occupation.

The book also includes conversion factors, standards, resources and is peppered throughout with helpful illustrations, equations, explanations, and links to further online resources.

Passive Solar Architecture is ideal for practitioners, architects, designers, consultants, planners, home builders, students and academics, and those working in development contexts.

This book is intended to act as an aide memoir, a reference supplement, a resource and an overview of the field. Rich in background detail, the book also includes at-a-glance tables and diagrams, equations and key definitions.

Solar Energy covers: solar radiation and its detailed measurement, the emissivity and absorption properties of materials, solar thermal energy collection and storage, photovoltaics (both at all scales), solar cooling, and the use of solar energy for desalination and drying.

The book also includes conversion factors, standards and constants and is peppered throughout with helpful illustrations, equations and explanations, as well as a chapter making the business case for solar power.

Solar Energy is for anyone with an interest in solar energy, including energy professionals and consultants, engineers, architects, academic researchers and students.

They will find a host of answers in this book – a practical assimilation of fundamentals, data, technologies and guidelines for application.

They're available in hardback, paperback and as ebooks.

Get 20% off! E.g. paperback or e-book would be £20.79! Just enter code FLR40 on checkout. Order here:

• Passive Solar Architecture Pocket Reference
• Solar Energy Pocket Reference  

Bitcoin is the future of local and community renewable energy trading and EV charging

Dr Jemma Green, co-founder and chair of Power Ledger.

A new bitcoin company has raised AU$17 million (£10.3m or $13.7m) in 72 hours to support a revolutionary technology platform that will allow electricity producers and consumers to trade directly with each other in tiny units of power.

This article first appeared last week on The Fifth Estate.

Power Ledger is at the forefront of a disruptive wave affecting the energy market that will see the end of the dominance of centralised generation and the increasing participation of building owners, smaller renewable energy suppliers and electric vehicle owners in a peer-to-peer marketplace, all made possible by the new, internet-based encrypted currency, bitcoin.

Consumer are the ultimate disruptors, David Martin, Power Ledger’s co-founder and managing director says. “Consumers have said, ‘I don’t want to buy energy from a coal-fired station’, instead saying this model of energy transaction is what they want to participate in’.“The concept of peer-to-peer [energy] trading is something that has universal appeal to customers … it’s a demonstration that the community wants to be part of the power economy of the future.”

“The concept of peer-to-peer [energy] trading is something that has universal appeal to customers … it’s a demonstration that the community wants to be part of the power economy of the future.”

Dr Jemma Green is the other co-founder and chair of Power Ledger. Her background is in financing and accounting at JP Morgan in London but also financing environmental sectors. In 2013 she returned to Perth and did a PhD in Energy Markets and Disruptive Innovation and also featured as a member of our Sustainability Salon for Perth and WA.

In a podcast with bitcoin.com website she explains how she came by the idea for Power Ledger. She saw that in Australia 20 per cent of houses have rooftop solar but hardly any are on high-rise apartment buildings. She saw the potential for these buildings acting as energy retailers, supplying their residents, and designed a system for a building in Perth.

However, she was unable to find software that allocated the electricity to each apartment until she met some blockchain developers in January last year, and realised blockchain was perfect for her needs.

A problem was identified with the power grid, which is that if some apartment residents are using local energy, fewer are using the grid and so those consumers will pay proportionately more. Power Ledger was formed in May last year, just after the birth of her daughter, to explore how blockchain could circumvent this problem by allocating small transactions to each apartment.

A pilot project in a retirement village south of Perth from August to December 2016 proved the success of the concept. A second trial was conducted in Auckland with the local network operator and linked up with the banking sector to complete the loop.

Sell your solar power when you’re out and don’t need it

“It means that I can sell to others the electricity I might have utilised when I’m not in my apartment,” Green says.

“Schools and any partially occupied building owners can do the same. If I’m not using that electricity, then it can be spread equally across everybody in the apartment block or network. This also incentivises people to use less electricity as they can sell their unused power and make money.”

Power Ledger’s platform connects to smart meters to tally how much power is generated and how much is used. Its software is installed and the revenue information is extracted into the blockchain. It is priced differently according to the time of day and the laws of supply and demand.

The blockchain can be used to fractionalise the power stored in the battery or that is directly generated, and allocate it.

Some of the power may be owned by a third party. For example, a solar farm can be part owned by investors, say a pension scheme, which recoups the revenue from sales.

Presently, if an apartment has rooftop solar and is selling its surplus back to the energy company it will typically not be paid for 60 days. With Power Ledger’s system, participants can monitor their revenue in real time.


“You could also have a marketplace, and this could bring the price down,” Green says. “Supply and demand would set the price. The cost curves for batteries and solar are coming down. It’s low cost electricity.”

Power Ledger issues tokenised values called Sparkz for a unit of electricity, representing one low-value unit in the host country. Electricity is priced in the local currency. Suppliers will be paid in Sparkz at the local cost of power. If the unit price is 30c/kWh they will receive 30 Sparkz. E.g. 1 Sparkz = 1 AUD.

POWRs are another token, which represent investments in the company. Their price can vary, but this does not affect the cost for electricity for the everyday consumer. It is these tokens which are being offered on the market.

“The more application posts offer these, the more competition there is. We’ve created one billion and are selling 350 million at the moment in an initial coin offering (ICO),” Green says.

“We sold 190 million of these last week to raise 17mAU$ in 72 hours in a public pre-sale of 100 million Power Ledger tokens — called POWRs — and a discounted private pre-sale of 90 million POWRs.

“On 8 September we open the public sales and our supporters and platform users say they want to have the option at buying at a market price. This will be determined by the number of tokens left divided by the amount of money pledged in the sale.”

This sale will last for four weeks. Tokens can be bought from the website tge.Power Ledger.io. David Martin believes it is “not unreasonable to expect” that this next offer will raise $20-30 million.

The Sparkz power tokens are effectively a means for markets to trade and self-regulate, says Green. Utilities will purchase the tokens and use them as bonds to trade with customers.

People in the banking industry are a little sceptical of blockchain. This is because there is much vapourware out there, Green believes. “A country’s laws needs to be attached to a project in order to support and validate it,” she explains.

“Power Ledger has a platform, the first in Australia. Our lawyers say our tokens are not a financial product as such, but they are designed to the same standard, with a constitution, shareholders and rules under national corporate law, in order to provide confidence.”

The second pilot was across networks and included banks, which it was really hard to persuade to be involved.

Use bitcoins to pay for charging electric vehicles

In the future Power Ledger hopes to use the experience in a project involving solar-powered apartments in Fremantle, Perth. One of these will possess a shared electric vehicle (EV), charged from the panels, which any member of the public can use.

They will be able to pay for it with the bitcoin platform. They will also be able to charge their own electric vehicle on the charging point. All of this gives the building an income stream on the sale of their generated electricity to EV owners.

This means of selling investment in energy projects could replace power purchase agreements in the future. Instead of a generator selling to a small number of large customers they could sell to many small consumers.

Therefore a developer of a community energy project could sell small amounts to purchasers and in so doing provide liquidity by using the tokens for trading the assets. Power Ledger calls this “fractionalised ownership” or “asset germination”. Green says that this approach will be deployed on a project in the near future and that they are in conversation with financial exchanges that could partner on this.

“Not everyone can afford solar panels,” she says. ‘The people who are paying for it are those who can afford it the least. So our platform will provide low cost renewable power to people who don’t have solar panels while utilising the grid and maintaining its relevance.

“It will also work for any type of electricity. It’s ambivalent about the source, so could be used for wind. Wind and solar are good partners as one is often providing power without the other, lessening the need for storage.”

Green recently attended a gathering hosted by Richard Branson about blockchain on his island where she heard about other social uses for blockchain. For example blockchain is being used to eliminate land theft in places like Georgia and Afghanistan where it’s being used to update the land registry.

“It’s about the democratisation of power,” Green says. “We see ourselves as being a distributed ledger for distributed energy markets. It’s a revolution, away from the one way street of the century old system.

“The old centralised system will continue but we will have a hybrid one. This disruption is happening with our without Power Ledger but what I think our system offers is to do this without the destruction of value.”

David Thorpe is the author of Solar Technology and The One Planet Life.

How to use solar energy for air-conditioning, save billions and cut emissions

Question: if you can use solar power for cooling and air conditioning then why doesn't everybody do it? After all it's a match made in heaven: just when it's so hot you need the aircon, there's lots of solar energy around.

Answer: it's fairly new, not well known and there is a relatively high upfront cost. This makes it a candidate for some sort of net metering or feed in tariffs to kickstart the market, if ever I saw one.

Yesterday I wrote about how architects can use passive solar techniques to design zero carbon buildings and/or drastically cut the need for air-conditioning in warm/hot climates.

In this article I'm going to run you through the technology principles and alternatives for active solar cooling, but first let's look at the problem.

The problem: we want to be cool

It's hot. You turn on the aircon or the fan. Your energy bill goes up

According to the NREL, "air conditioning currently consumes about 15% of the electricity generated in the United States. It is also a major contributor to peak electrical demand on hot summer days, which can lead to escalating power costs, brownouts, and rolling blackouts".

The picture is the same in Europe. For example, according to a national market survey by the Hellenic Ministry of Commerce, about 95% of air-conditioning sales in Greece occur in the period of May-August and reach about 200,000 units (primarily small-size split-type heat pumps) every year. The use of air-conditioning units in summer causes peak electric loads that periodically result in power shortages in large areas of metropolitan cities like Athens.

In southern European countries there is a well-established connection between the growth of peak power electricity demand in summer and the growth of air-conditioning sales in the small and medium-size market.

The picture is the same throughout the world whenever there is hot weather. It leads to ugly city views like this one (right).

The fact that peak cooling demand happens at the same time as high availability of solar energy offers an opportunity to exploit solar thermal technologies that can match suitable solar cooling technologies (i.e., absorption, adsorption, and desiccant cooling), cut emissions from the burning of fossil fuels and in the longer run save billions of dollars in fuel costs.

The technical solutions

Space cooling uses thermally activated cooling systems driven (or partially driven) by solar energy. The two systems are:

1. Closed-cycle:  a heat-driven heat pump that operates in a closed cycle with a working fluid pair, usually an absorbent-refrigerant such as LiBr-water and water-ammonia, or an adsorption cycle using sorption such as silica gel; two or more adsorbers are used to continuously provide chilled water;
2. Open-cycle: solar thermal energy regenerates desiccant substances such as water by drying them, thereby cooling the air. Liquid or solid dessicants are possible. a combination of dehumidification and evaporative cooling of air.

Desiccant cooling system assisted by solar energy from air collectors and PV moduls. Pompeu Fabra Library (Mataró, Spain) | Source: AIGUASOL

More case studies below the techy section, next.

Absorption NH₃/H₂O

The single stage, continuous absorption refrigeration process works as follows: The working fluid (WF), mainly ammonia and water, is boiled in the generator, which receives heat from the solar collectors at 65–80°C. Mainly ammonia, but some water leaves and is condensed at the water cooled condenser (25–35°C). The boiling working fluid in the generator has therefore to be exchanged continuously using the pump to deliver strong working fluid with a concentration of 40% ammonia, from the absorber via the working fluid heat exchanger, which heats it to 50–65°C taken from the weaker fluid leaving the generator.

The latter, now cooler, is led to the absorber, and leaves the absorber at c.35°C. Meanwhile, the condensed refrigerant ammonia has left the condenser and is injected into the evaporator by the refrigerant control valve. This works at low pressure level (2–4 bar), and the refrigerant boils and evaporates. The cold vapour flows into the absorber which absorbs it, combines it with the working fluid, and sends in back to the generator.

The thermal coefficient of performance (COP_thermal) describes the relation between the profit (cooling capacity) and the expense (heat from the collectors): COP_thermal = Q_cooling / Q_heating

Absorption H2O/LiBr

This system employs a refrigerant expanding from a condenser to an evaporator through a throttle in an absorber/desorber combination that is akin to a “thermal compressor” in a conventional vapour compression cycle. Cooling is produced through the evaporation of the refrigerant (water) at low temperature. The absorbent then absorbs the refrigerant vapour at low pressure and desorbs into the condenser at high pressure when (solar) heat is supplied. In this a single-effect absorption system liquid refrigerant leaving the condenser expands through the throttle valve into evaporator taking its heat of evaporation from the stream of chilled water and cooling it.

The vapour leaving is absorbed by an absorbent solution entering dilute in refrigerant (strong absorption capability) leaving rich in refrigerant (weak absorption capability), where it is pumped via a heat exchanger to a desorber which regenerates the solution to a strong state by applying heat from the solar-heated water stream, causing the desorption of refrigerant. It condenses in the condenser to liquid, then expands into the evaporator. The absorber and condenser are cooled by streams of cooling water to reject the heats of absorption and condensation respectively.

Adsorption

Adsorption substances are working pairs, usually water/silica gel. The solid sorbent (gel) is alternately cooled and heated to be able to adsorb and desorb the refrigerant (water). A sequence of adsorbers in deployed to use the heat from one to power another. The cycle is (refer to the schematic diagram, right): refrigerant previously adsorbed in one adsorber is driven off through the use of hot water (may be solar-heated) (right compartment).

It then condenses in the condenser and the heat of condensation is removed by cooling water. The condensate is sprayed in the evaporator and evaporates under low partial pressure, producing cooling power. The refrigerant vapour is adsorbed into the other adsorber (left) where heat is removed by cooling water.

Open cycle liquid desiccant cooling

Humidity is removed from the process air by the desiccant, which is then regenerated by heat from an available source, e.g. solar. Both solid and liquid hygroscopic materials may be used in the dehumidification of conditioned air.

Liquid desiccant systems can store cooling capacity by means of regenerated desiccant. Solar thermal energy is used whenever available to run the desorber and its associated components (hot water-to-solution heat exchanger, air-to-air recuperator, pump) to concentrate hygroscopic salt.

Later, when needed, this is used to dehumidify process air. This method of cold storage is the most compact, requires no insulation and can be applied for indefinitely long time periods.

Solid desiccant air handling unit 

Here, two air channels are mounted on top of each other. The outdoor air enters (A) where the sorption wheel with a silica gel surface dehumidifies is (B) and transfers heat from the outgoing air (C), rehumidifies it to the correct level then enters the conditioned space, increases its enthalpy by internal heat sources and moisture, and leaves as return air (G) where moisture (H and J) and heat (I) are removed as necessary and it is expelled (L).

Highly effective solar collectors should be used for the heat regeneration. The Middle European climate allows an enhancement of the adiabatic cooling mode.

Relation between the cooling capacity and the regeneration heat: COP_{thermal, plant} = Q_c,plant / Q_heat

Relation between the cooling load and the regeneration heat: COP_{thermal, build} = Q_{c, build} / Q_heat

Desiccant-Enhanced Evaporative (DEVAP) Air Conditioner

NREL, AILR Research, Inc. and Synapse Product Development have developed the DEVAP air conditioner. This consists of two stages: dehumidifier and indirect evaporative cooling.

Water is added to the tops of both; liquid desiccant is pumped through the first. Some outdoor air is mixed with return air from the building to form the supply air stream, which flows left to right through the two stages. In the dehumidifier, a membrane contains the desiccant while humidity from the supply air passes through it to the desiccant, which is also in thermal contact with a flocked, wetted surface that is cooled as outdoor air passes by it, causing the water to evaporate and indirectly cooling the desiccant.

In stage 2, the supply air passes by a water-impermeable surface that is wetted and flocked on its opposite side, providing indirect evaporative cooling. A small fraction of the cool, dry supply air is then redirected through the second-stage evaporative passages to evaporate water from the flocked surface and is then exhausted.

Evaluation

More information and a simplified evaluation tool called "Easy Solar Cooling" can help assess the cost performance of different technologies and system designs under different operating conditions. See: http://www.solair-project.eu/218.0.html

Two examples of solar cooling in practice

Video of a large scale solar cooling in South Africa:



Solar cooling in Italy

Solar cooling for a department store in Rome: The 3,000 m^{2</"600"sup> of collector area run a 700 kW chiller. Photo: Metro Cash & Carry} 

The Italian minister for economic development, Claudio Scajola, inaugurated this innovative, energy saving project in Rome on a Metro Cash & Carry building. The installation uses solar energy to cool down the wholesale outlet during summer and to heat it in winter. With its 3,000 m² of solar collectors – provided by the Italian Riello Group – this system on the store's roof is one of the biggest in Italy. It reduced the store's energy consumption by 12%, Dominique Minnaert, managing director of METRO Cash & Carry Italy, was quoted saying in the press release.

The system was designed by the British company AP Engineering Services. The chiller, with a power of 700 kW, was provided by the US-American Carrier Corporation, a leader in the areas of heating, ventilation, air conditioning and refrigeration systems. The cooling tower came from Evapco Europe, a specialist for industrial and commercial cooling equipment with headquarters in Belgium and Italy. The installation in Rome is part of Metro´s project “Energy Saving Today”. Its goal is to optimize performance of storage technology and therefore reduce energy consumption.

I fervently hope that many companies and organisations, not to mention individuals take up this exciting range of technologies.

David Thorpe is the author of 

• Solar Technology: The Earthscan Expert Guide to Using Solar Energy for Heating, Cooling and Electricity 
• Energy Management in Buildings: The Earthscan Expert Guide
• The 'One Planet' Life: A Blueprint for Low Impact Development
• Sustainable Home Refurbishment: The Earthscan Expert Guide to Retrofitting Homes for Efficiency, and
• Energy Management in Industry: The Earthscan Expert Guide

How to save millions on air conditioning by designing passively cooled buildings

Air conditioning is by far the greatest consumer of electricity in buildings in hot countries, but it needn't be so.

Architects designing buildings for regions that otherwise would require air conditioning can use passive solar techniques to keep them cool, and in many cases successfully eliminate the need for expensive air conditioning.

Right: A design for a mosque using passive solar and evaporative cooling.

Passive solar cooling operates in two stages:

1. Do your best to prevent the sun from reaching the building or gaining the interior of the building during the periods when it is in danger of overheating.
2. Then employ passive techniques to remove unwanted hot air.

Different techniques are available depending upon the climate, i.e. whether it is dry or humid.

Passive cooling for warm/hot, dry climates

Here is a summary of the techniques available for hot, dry climates with a large temperature variation from day to night use:

• high interior thermal mass;
• exterior superinsulation;
• highly-reflective OR green roofs, with insulation and a radiant barrier beneath;
• night ventilation;
• phase change materials;
• air vents;
• diode roofs;
• roof ponds;
• wind towers;
• ensure correct exterior shading on windows;
• closing windows and deploying shutters at sunrise to keep out the hot daytime air;
• direct evaporative cooling.

Above: How a wind tower on a building is used for cooling cooling.



Cooling is provided by radiant exchange with the massive walls and floor plus optional techniques explored in more detail below. Open staircases, etc. may provide stack effect ventilation, but observe all fire and smoke precautions for enclosed stairways.

Curved roofs and air vents are used in combination where dusty winds make wind towers impracticable: a hole in the apex of a domed or cylindrical roof with a protective cap over the vent directs the wind across it and provides an escape path for hot air collected at the top.

Arrangements may be made to draw air from the coolest part of the structure as replacement, to set up a continuous circulation and cool the spaces.

Passive cooling for warm/hot and humid climates

This is a summary of the techniques available for warm and humid climates, with little temperature variation from day to night:

• airtight and superinsulated construction;
• a radiant barrier beneath the roof deck;
• highly-reflective or green roofs, with insulation beneath;
• phase change materials;
• daytime cross-ventilation to maintain indoor temperatures close to outdoor temperatures.
• fresh air brought in through a dehumidifier through the crawlspace or basement by using underground pipes or use solar-powered absorption chillers;
• avoid drawing in unconditioned replacement air that is hotter or more humid than interior air;
• avoid open areas of water such as pools;
• the Passivhaus standard permits 15 kWh/m².yr of cooling energy to be used, which has proven to be sufficient in almost all cases because the Passivhaus system is highly effective in reducing unwanted heat gains;
• As above, curved roofs and air vents are used in combination where dusty winds make wind towers impracticable.

Large buildings will require detailed modelling. Power may be required for anti-stratification fans and ducts.

Shading tactics

Some tactics for providing shading to prevent the sun from reaching the building are:

• Covering of rooves and courtyards with deciduous vegetation (allowing winter access) such as creepers or grapevines permits evaporation from the leaf surfaces to reduce the temperature. At night, this temperature is even lower than the sky temperature.
• Green rooves, earthenware pots laid out on the roof, and highly-reflective surfaces (e.g. painted with titanium oxide white paint/whitewash) are all techniques practiced widely.
• Coverings that in the daytime insulate the roof but automatically withdraw at night exposing the roof to the night sky, allowing heat to leave by radiation and convection.
• Horizontal overhangs or vertical fins prevent overheating while preserving natural daylighting.
• For east and west walls and windows in summer: vertical shading and/or deciduous trees and shrubs.
• For south-facing windows: horizontal shading.
• Shutters, closed in the day.
• Highly textured walls leave a portion of their surface in shade.

Right: A summary of different shading types.

Natural ventilation

The design of natural ventilation systems varies on building type and local climate. The amount of ventilation depends on the careful design of internal zones, and the size and placing of openings.

Wind-induced ventilation is helped by siting the ridge of a building perpendicular to summer wind direction, with minimal obstruction to the wind.

In a multi-storey building, the rooms or zones on the outside faces may be separately controlled, depending upon the degree of sophistication present in the building, its size and location. If hot air is present above a set temperature, it is allowed to escape at whatever rate is necessary to preserve the comfort of this zone’s occupants, via controlled venting into a vertical space – atrium or stairwells/lift shafts – positioned centrally or on corners (with glass sides to aid the process).

At the top of this space, louvres, perhaps in clerestories or skylights, allow a controlled amount of hot air to escape, again, at whatever rate is necessary for comfort of the whole building’s occupants. Basement windows allow cool air in.

• Offset inlet and outlet windows across the room or building from each other.
• Make window openings operable by the occupants but controlled by the building management system.
• Provide ridge vents at the highest point in the roof that offers a good outlet for both buoyancy and wind-induced ventilation.
• Allow for adequate internal airflow.
• In buildings with attics, ventilate the attic space to reduce heat transfer to conditioned rooms below

It's not always possible for a building to be completely natural ventilated. In such cases fan assistance is required. Thermostats, dampers and fans would be connected to a building energy management system.

Ventilation chimneys include caps to prevent backdrafts caused by wind. These adjust according to the wind intensity and direction and increase the Venturi effect.

Turbines may be deployed to increase ventilation. Self-regulating turbine models are available. There are several styles of passive roof vents: e.g., open stack, turbine, gable, and ridge vents, which utilise wind blowing over the roof to create a Venturi effect that intensifies natural ventilation.

Bernoulli's principle

This uses wind speed differences to move air, based on the idea that the faster air moves, the lower its pressure. Outdoor air farther from the ground is less obstructed, with a higher speed, and thus lower pressure. This can help suck fresh air through the building.

Bernoulli’s principle multiplies the effectiveness of wind ventilation and is an improvement upon simple stack ventilation. However, it needs wind, whereas stack ventilation does not. In many cases, designing for one effectively designs for both.



The BedZED development in south London (above) utilises specially-designed wind cowls which have both intakes and (larger) outlets; fast rooftop winds get scooped into the buildings. The larger outlets create lower pressures to naturally suck air out.

Solar chimneys for cooling

Solar chimneys are employed where the wind cannot be relied upon to power a wind tower. The chimney's outer surface (painted black and glazed) acts as a solar collector, to heat the air within it. (It must therefore be isolated by a layer of insulation from occupied spaces.)

Pre-cooling air with ground source intakes

Right: Earth-air tunnel.

Also known as an earth-air tunnel this is a traditional feature of Islamic and Persian architecture.

It utilises pipes buried a few meters down, or underground tunnels, to cool (in summer) and to heat (in winter) the air passing through them.

They can lower or raise the outside replacement air temperature for rooms which are buffer zones between the interior and exterior temperatures.

Trombe wall effect for cooling and heating

A double skin façade is employed, the outer skin of which can be glass or PV panels. The cavity between the array and the wall possesses openings to indoors and outdoors at both high and low levels. operate more efficiently anyway).

Evaporative cooling

Evaporative cooling is used in times of low or medium humidity. As water is evaporated (undergoing a phase change to water vapour), heat is absorbed from the air, reducing its temperature. When it condenses (another phase change), energy is released, warming the air. This is the same for all phase change materials.

Right: passive solar cooling with a courtyard.

Evaporative cooling can be direct or indirect; passive or hybrid.

• Direct: the humidity of the cooled air increases because air is in contact with the evaporated water – can be applied only in places where relative humidity is very low.
• Indirect: evaporation occurs inside a heat exchanger and the humidity of the cooled air remains unchanged – used where humidity is already high.
• Passive: where evaporation occurs naturally; incoming air is allowed to pass over surfaces of still or flowing water, such as basins or fountains;
• Hybrid: where mechanical means are deployed to control evaporation.

Phase change materials (PCMs)

PCMs utilise the air temperature difference between night and day. In the daytime, incoming external air is cooled by the PCM-storage module, which absorbs and stores its heat by changing its phase state (e.g. solid to liquid).

At night-time the substance reverts to solid form, releasing its heat by being cooled by the now cooler external air. Commercially available PCMs are chosen based on the temperature of their phase change relative to that required in the space to be moderated.

Night cooling

Night ventilation, or night flushing relies upon keeping windows and other openings closed during the day but open at night to flush warm air out of the building and cool thermal mass which has heated up during the day.

It relies upon significant temperature differences between day and night time (which must be below 22°C / 71°F) and some wind movement.

The above combines edited extracts from one of my published books, Solar Technology, and a forthcoming title: Passive Solar Architecture Reference Pocketbook.

David Thorpe is the author of 

• Solar Technology: The Earthscan Expert Guide to Using Solar Energy for Heating, Cooling and Electricity 
• Energy Management in Buildings: The Earthscan Expert Guide
• The 'One Planet' Life: A Blueprint for Low Impact Development
• Sustainable Home Refurbishment: The Earthscan Expert Guide to Retrofitting Homes for Efficiency, and
• Energy Management in Industry: The Earthscan Expert Guide

4 Ways to Plan Neighborhoods and Buildings to Minimize Energy Use

Conventional buildings consume much energy for heating and cooling to protect them from the temperature effects of climate and seasons. But some basic thought and planning, in combination with these 10 passive solar building design techniques, can help to radically reduce these energy costs. Here's 4 key ideas:

1. Optimize the spatial layout

 

Inappropriate (left) and appropriate (right) spatial layouts for settlements in hot climates. Grid layouts borrowed from other climates, and wide spacing of buildings, do not provide shade or wind shelter. Organic, non-grid layouts do provide shade and can be designed to block winds, preventing issues with wind funnelling. Credit: author.



Right: Sample layout for housing estate in higher latitudes such that each property has both privacy and an equator-facing aspect and roof to maximise potential use of solar energy. Grey circles are trees, grey lines are hedges (preferably) or fences. Credit: author.

2. Optimize the building form and layout

A low surface area to volume (S/V) ratio is optimal for a passive, low-carbon building. This is the ratio between the external surface area and the internal volume.

Compactness C = Volume / Surface Area

Size is also a factor: a small building with the same form as a larger one will have a higher S/V ratio. Buildings with the same U-values, air-change rates and orientations but differing S/V ratios and/or sizes may have significantly different heating demands. This has the following consequences:

• small, detached buildings should have a very compact form (square is close to the perfect optimum, the circle);
• larger buildings may have more complex geometries;
• high S/V ratios require more insulation to achieve the same U-/R-value.

In temperate zones, aim for an S/V ratio ≤ 0.7m²/m³.

Form factor

The ratio of the usable floor area, F, to above-grade enclosure area E is more useful, because it favours buildings that require less floor-to-floor height.

Form factor = F/E

The more compact the form, the higher the ratio, which is better. Large buildings (e.g., 172,800 ft² over 12 stories) have a much more efficient form than small buildings or large high-bay buildings for heating load (but not cooling, where the opposite is true).

This metric permits comparisons of the efficiency of the building form relative to the useful floor area. Achieving a heat loss form factor of ≤3 is a useful benchmark guide when designing small Passivhaus buildings. This also reduces the resources required and the cost. Most building uses do not require volume but floor area. This metric also does not include the ground contact area, but does include the roof.

A building with a more complex form is also likely to have a higher proportion of thermal bridges and increased shading factors that will have an additional impact on the annual energy balance.

The effect of form on total energy consumption for a given floor area is reduced as buildings increase in size. Besides permitting greater design flexibility, this lets designers use daylighting and natural ventilation cooling strategies also to reduce energ demand, as these require one dimension of the building to be relatively narrow (between 45 and 60ft (14–18m).

Example:

For a small office of 20,000 ft2 (1800 m2) a narrow two-storey form, ideal for natural ventilation and daylighting, may have a form factor ratio of 0.88, whereas a deep square plan have one of 1.02. For the former to have the same enclosure heat loss coefficient as the latter, its overall average enclosure R-value would need to be 1.02/0.88 = 16% higher. This would require a significant increase in the opaque wall area R-value, a reduction in window area, or a more expensive window.

 

An increase in the S/V ratio of 10% (the building in the middle) would require 20mm of insulation more than the good form on the left to achieve the same level of insulation. The one on the right (a 20% higher S/V ratio) would require an extra 40mm of insulation.



Optimum room layouts in dwellings according to the climate.

3. Adapt the dwelling forms and room layouts according to latitude

For latitudes above 25°: the sun-facing glazing area should be at least 50% greater than the sum of the glazing area on the east- and west-facing walls. Orientation is long on the east-west axis, which should be within 15 degrees of due east-west. At least 90% of the sun-facing glazing should be completely shaded (by awnings, overhangs, plantings) at solar noon on the summer solstice and unshaded at noon on the winter solstice. The room plan should – if it is a dwelling – incorporate the main living rooms on the equator-facing side, with utility rooms, less used rooms and garage if any on the north side. Morning rooms are typically bedrooms. On the side away from the equator windows should be kept to a minimum and as small as possible for lighting to minimise heat loss. This wall should also have high thermal mass or/and be externally insulated, to retain heat in the building.

For latitudes less than 25° or where topography significantly impacts insolation, the opposite should be the case. Bedrooms, for example, need light in the morning. The whole building needs to be protected from low angle heat.

Around 25° there is some leeway depending on local conditions. In these mid-latitudes different parts of a building may be used in the winter and summer, as equator-facing rooms become too hot and occupancy is switched in summer to rooms on the non-equator-facing side (not shown in the above left plan).

Table: The shape of the building has different requirements according to the local climate:

Climate	Elements and requirements	Purpose
Warm, humid	Minimise building depth	for ventilation
	Minimise west-facing wall	to reduce heat gain
	Maximise south and north walls	to reduce heat gain
	Maximise surface area	for night cooling
	Maximise window wall	for ventilation
Composite	Control building depth	for thermal capacity
	Minimise west wall	to reduce heat gain
	Limited equator-facing wall	for ventilation and some winter heating
	Medium area of window wall	for controlled ventilation
Hot, dry	Minimise equator-facing and west walls	to reduce heat gain
	Minimise surface area	to reduce heat gain and loss
	Maximise building depth	to increase thermal capacity
	Minimise window wall/window size	to control ventilation, heat gain and light
Mediterranean	minimise west wall	to reduce heat gain in summer
	Moderate area of equator-facing wall	to allow winter heat gain
	Moderate surface area	to control heat gain
	Small to moderate window size	to reduce heat gain but allow winter light
Cool temperate	Minimise surface area	to reduce heat loss
	Moderate area of pole-facing and west walls	to receive heat gain
	Minimise roof area	to reduce heat loss
	Large window wall	for heat gain and light
Equatorial upland	Maximise north and south walls	to reduce heat gain
	Maximise west-facing walls	to reduce heat gain
	Medium building depth	to increase thermal capacity
	Minimise surface area	to reduce heat loss and gain

4. Optimize the roof shape and orientation

In hot climate zones, vaulted roofs and domes dissipate more heat by natural convection than flat roofs. They give greater thermal stability and lower daytime temperature. The best orientation requires that the vault form receive maximum daily solar radiation in winter and minimum in summer.

A north-south axis orientation for a vaulted roof is better for winter heating, receiving the minimum direct solar radiation in the summer, while an east-west axis orientation will maximise summer heating, receiving the most irradiation in the morning and evening. The results are summarised by example for a 30° latitude site below.

Table: The effect of vault orientation on seasonal direct solar radiation.[i] CSR = Cross Section Ratio. This is the ratio between vertical height of the vault and the horizontal width.

Orientation	Season	Loss of direct solar radiation (%)
		CSR1 = 0.5	CSR1 = 0.8	CSR1 = 1	CSR1 = 1.25	CSR1 = 2
W-E	Summer	12.4	20.1	23.9	29	37.8
	Winter	9.8	17	19.6	23.2	30.4
N-S	Summer	17	28.6	35.1	42.1	56.4
	Winter	6.3	7.1	8	8.9	10.7
NE-SW	Summer	14.7	23.9	29.3	34.8	45.6
	Winter	8.9	13.4	16	18.8	24.1
NW-SE	Summer	14.7	23.9	29.3	34.8	45.6
	Winter	8.9	13.4	16	18.8	24.1

The effect of vault orientation on received seasonal direct solar radiation.

See this related post on passive solar building design techniques.

David Thorpe is the author of 

• Solar Technology: The Earthscan Expert Guide to Using Solar Energy for Heating, Cooling and Electricity 
• Energy Management in Buildings: The Earthscan Expert Guide
• The 'One Planet' Life: A Blueprint for Low Impact Development
• Sustainable Home Refurbishment: The Earthscan Expert Guide to Retrofitting Homes for Efficiency, and
• Energy Management in Industry: The Earthscan Expert Guide

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[i] Mashina, GA and Gadi, MB; Calculating direct solar radiation on vaulted roofs using a new computer technique, Nottingham University Conference Proceedings, 2010. Available at: http://www.engineering.nottingham.ac.uk/icccbe/proceedings/pdf/pf196.pdf

10 stages to a passive solar building from design to build

Some aspects of a zero carbon building in the northern hemisphere, temperate zone.

Passive solar architectural principles have come of age. They have given rise to thousands of buildings of all sizes and purposes around the world, in all climate types, to demonstrate how buildings don't need to consume fossil fuel energy to support their occupants. They can even generate more power, or absorb more carbon, than they use. Below is a ten-step guide to how to go about designing and building one.

But  first, the benefits of passive solar architecture:

• Saves energy and running costs from the start;
• Comfort in all seasons and climates;
• Safe investment and resilience into the future;
• Added value every year through decreased operation costs;
• Longer useful life with high quality standard;
• Contributes to climate change protection.

Thanks to experience of the last 30 years, we know what works in different climates in the world and build costs have reduced to the same or just slightly higher than conventional builds. But lifetime costs are considerably cheaper – on average (dependent on purpose/design) being 87.5% savings (1/8 less to run) on heating and cooling.

Sustainable solar building is also known as passive house (Passivhaus in German), although this is also a strict standard.

There are currently 30,000 Passivhaus structures built around the world. The principle is that the architecture is designed to provide comfort for the occupants with minimum need for additional energy. This is achieved using design tools to establish the needs and requirements of all functions in the building and their inter-relationships. Energy savings are maximised by placing spaces in the most advantageous position for daylighting, thermal control, and solar integration.

This process may also reveal opportunities for multiple functions to share space and reduce the footprint of the building.

General principles of a passive solar building

Buildings should be at least zero carbon on balance, when totalling the impacts of materials, construction, use and demolition. Features of this are to:

• minimise the use of fossil fuel energy during the supply chain and process of construction;
• encourage the use of materials which store atmospheric carbon in the fabric of the building;
• encourage the generation and even export of renewable energy by the building;
• construct and manage it in such a way that it minimises the emission of greenhouse gases during its lifetime and eventual demolition.

Right: possible building designs for maximising the use of daylighting.

Such a building could, over its lifetime, become zero carbon, or even negative carbon by generating enough power to more than make up for the fossil fuels it has used.  To achieve this, the following features are needed:

• favouring the use of ‘natural’ and cellulose-based materials (timber products, and other products made from plant-originating materials);
• making the structure very airtight;
• making the structure breathable;
• making it durable, resilient, low-maintenance, fire- and weather-resistant;
• incorporating a large amount of insulation;
• taking advantage of free, renewable energy. 

10 steps to a zero energy building

So here, now is a summary of 10 steps in the design and build strategy of a zero-energy passive solar building, averaged for any climate zone in the world.

1. Site selection

• Secure optimum location, as free as possible from non-useful shading relative to the seasons and time of day. 
• Research the available solar resource and wind factors for the site using local and freely available data.
• Orient optimally.

Example of a sun chart to view the azimuth angle through a year at a building location.

2. Concept development

• Minimize shade in winter, minimizing parapets, projections, non-transparent balcony enclosures, divider walls etc.
• Choose a compact building structure with low skin to volume ratio. Use opportunities to combine buildings. 
• Use a simple shell form, without unnecessary recesses. 
• Survey and model the expected internal and external heat gains and cooling requirements, and other building energy loads.
• The following energy performance targets and air changes per hour define the Passivhaus standard and must be met in order for certification to be achieved:
• Specific heating demand ≤ 15 kWh/m²/yr
• Specific cooling demand ≤ 15 kWh/m²/yr
• Specific heating load ≤ 10 W/m²
• Specific primary energy demand ≤ 120 kWh/m²/yr
• Air changes per hour ≤ 0.6 @ n50.
• Optimize glazing, shading and aspect/form according to latitude and climate zone, to maximize the use of daylighting, balancing against the appropriate heat gains.
• Concentrate the utility installation zones, e.g. bathrooms, above or adjacent to the kitchen, in coolest areas in summer (temperate zones) or hottest (hot zones).
• Model and decide on the ventilation scheme making best use of the stack effect and Bernoulli principle. Is additional mechanical ventilation (with heat recovery) needed?
• Thermally separate basement from ground floor (including cellar staircase), make airtight and thermal bridge free. 
• Derive an initial energy use estimate.
• Evaluate the potential for renewable energy technologies: solar thermal, PV, wind, heat pumps, etc.
• Consider use of underfloor heating to save energy (water or electric).
• Check the possibility of government subsidies.
• Commence consultations with the building authority.
• Contract agreement with architects, including a precise description of services to be rendered.

3. Construction plan and building permit planning

• Select the building style – thermally massive or light. Sketch out a design concept, floor plan, energy concept for ventilation, cooling, heating and hot water. 
• Floor plan: short pipe runs for hot/cold water and sewage.
• Consider the space required for utilities (cooling/heating, ventilation etc.).
• Short ventilation ducts: cold air ducts outside, warm ducts inside the insulated building envelope.
• Further calculate and minimize the energy demand, e.g. with the Passive House Planning Package (PHPP) available from the Passivhaus Institut, Darmstadt. Climate data sets are available for most areas in the world which plug into this.
• Plan the insulating thickness of the building envelope and avoid thermal bridges.
• Calculate cost estimate.
• Negotiate the building project (pre-construction meetings).

4. Final planning of the building structure (detailed design drawings)

• Insulation of the building envelope: the absolute U-values will vary according to context (location, form etc), but in general aim for: 
• walls, floors and roofs ≤ 0.15 W/m²K; 
• complete window installation ≤ 0.85 W/m²K.
• Design thermal bridge free and airtight connection details.
• Specify windows that comply with passive house standard: optimize type of glazing, thermally insulated frames, glass area, coating, shading.
• 5. Final planning of ventilation (detailed system drawings)
• General rule: hire a specialist.
• Ventilation ducts: short and sound-absorbing. Air flow velocities below 3 m/s.
• Include measuring and adjusting devices.
• Take sound insulation and fire protection measures into account.
• Air pathways: avoid air current short-circuiting.
• Consider the air throws of the air vents.
• Provide for overflow openings.
• If MHVR/cooling is used, install in the temperature-controlled area of the building shell.
• Additional insulation of central and back-up unit may be necessary. Soundproof the devices. Thermal energy recovery rate should be > 80 %.
• Airtight construction to be checked at every stage.
• The ventilation system should be user-adjustable.
• Optional: ground or water-source heat pump (air or water as medium) and/or air pre-cooling/heating pipes; may be reversible for summer cooling and winter heating.

6. Final planning of the remaining utilities (detailed plumbing and electrical drawings)

• Plumbing: Install short and well-insulated pipes for hot water in the building envelope. For cold water install short pipes insulated against condensation water. Use no greater bore than needed to conserve water and heat.
• Use water-saving fittings.
• Sub-roof vents for line breathing (vent pipes).
• Plumbing and electrical installations: avoid penetration of the airtight building envelope – if not feasible, install adequate insulation.
• Use the most energy-saving appliances/equipment.
• Situate switches for ring mains alongside light switches to enable easy switching off of phantom loads when leaving rooms/building.
• Plan installation of (perhaps wireless) building energy monitoring system.

7. Call for tenders and awarding of contracts

• Plan for quality assurance measures in the contracts.
• Set up a construction schedule.

8. Assurance of quality by the construction supervision

• Thermal bridge free construction: schedule on-site quality control inspections. Take photographs.
• Check of airtightness: all pipes and ducts must be properly sealed, plastered or taped. Electrical cables penetrating the building envelope must be sealed also between cable and conduit. Flush mounting of sockets in plaster and mortar. Take photographs.
• Check of thermal insulation for ventilation ducts and hot water pipes.
• Seal window connections with long-lasting adhesive tapes or plaster rail. Apply interior plaster from the rough floor up to the rough ceiling.
• n50 airtightness test: Have a blower door test done during the construction, when the airtight envelope is complete but still accessible, i.e., before finishing the interior work, but after completion of the electricians' work (in concert with the other trades), incl. detection of all leaks.
• Ventilation system: ensure easy accessibility for filter changes. Adjust the air flows in normal operation mode by measuring and balancing the supply and exhaust air volumes. Balance the supply and exhaust air distribution. Measure the system's electrical power consumption.
• Quality control check of all cooling, heating, plumbing and electrical systems.

9. Final inspection and auditing.

10. Conduct post-occupancy monitoring

...to determine if building performs as expected.

David Thorpe is the author of 

• Solar Technology: The Earthscan Expert Guide to Using Solar Energy for Heating, Cooling and Electricity 
• Energy Management in Buildings: The Earthscan Expert Guide
• The 'One Planet' Life: A Blueprint for Low Impact Development

He is currently working on a Passive Solar Architecture Pocket Reference Book. Acknowledgements to Isover, St Gobain.

How WW1 Killed a Dream of a Solar-Powered World

The world is marking the 100th anniversary of the start of World War I. This was not only the bloodiest war the world has ever seen but it saw the start of the West's involvement in carving up the Middle East and interfering in its politics for the sake of oil. We are still mired in the bloody consequences of this.

WW1 also marked the end of the world's first solar power station, which was operating only for one year, in Egypt, before the outbreak of hostilities caused it to be abandoned.

As I explain in my book Solar Technology,  a Swedish-American inventor and mechanical engineer, John Ericsson, working for the British and Americans, pursued pioneering solar work in Egypt, a British colony then, where the first parabolic trough – and the first utility scale solar technology – was developed as long ago as 1883.



John Ericsson’s design focused sunlight from a curved silvered window glass surface (called a heliostat) onto an 11-foot long iron tube central receiver to generate steam to mechanically drive a Stirling engine. The heliostat was 16 feet wide and 11 feet tall, and tracked the sun across a north–south axis. It had a maximum output of 3 horsepower (2.24kW) and was able to pump 500 gallons (2,273 litres) of water per minute.

Inspired by this, American engineer and inventor Frank Shuman commissioned the first large-scale solar power generator in Maadi, near Cairo, in 1913. Schuman dreamt of a completely solar powered world. It was theoretically possible then, as indeed it is now.

With a solar collector area of 1240m², his array powered a pump that irrigated elevated farmland with water from the River Nile.



The world's first solar power plant in Cairo 1913.

This consisted of five rows of parabolic mirrors with a total output of 88kW. This power station was more cost-effective than a similarly sized coal-based plant would have been at the time, and would have recouped its investment in four years. However, despite its success, it was only used for one year, as the First World War intervened and the Turks battled the British for control of the nearby Suez Canal.

WW1 and oil



The location of the oil fields in 1914.

This war began the worldwide predominance of oil as an energy source, as one of its causes was competition for control of the Middle Eastern oilfields. By the end of the war, British forces had secured the entire oilfields of Mesopotamia in a new League Protectorate called Iraq. This put a provisional end to any attempts of pursuing the development of solar energy on a large scale.

The British feared that the Ottomans might attack and capture the Middle East (and later Caspian) oil fields. Their Royal Navy depended upon oil from the petroleum deposits in southern Persia, which the British-controlled Anglo-Persian Oil Company owned the exclusive rights to exploit throughout the Persian Empire except in the provinces of Azerbaijan, Ghilan, Mazendaran, Asdrabad and Khorasan. To secure the oil, the British even worked with Russian Communist troops to prevent the Turkish leader Enver Pasha's goal of establishing an independent Transcaucasia.

Oil was already the lifeblood of the British Empire as the British Navy had converted from coal to oil a few years previously. British and French trucks and aircraft also ran on oil.

On November 6 1914, the day after war was declared on the Ottoman Empire, the British landed ships at Abadan, on the shores of Iraq, with a mission to protect the oilfields and make sure production was not affected. Both the French and the British had invested much money in developing these oil fields.

In March 1915 General Townsend took 30,000 troops up the Tigris to attack the Turkish army and protect the oilfields. He succeeded and continued to march onwards with the intention of attacking and capturing Baghdad. By November, 25 miles away, they battled the 25,000 Turkish army for four days. They lost, and retreated to the coast where they were beseiged for five months before 13,000 troops surrendered.

But the British hatched another plan. They captured Baghdad eventually, on March 11 1917, having marched across Palestine from the Suez Canal. The French and British sealed an agreement to share the oil and protect the oil line from Basra.

After the war, agreements were made, mostly between between France and Britain, which resulted in the carving of the old Ottoman Empire into artificial nations - Iraq, Iran, Jordan, Lebanon, Saudi Arabia, Palestine, and Syria.

The struggle is documented in the film "Blood and Oil - The Middle East in World War I" (below), which examines how this conflict laid the foundation for all the wars, coups, revolts and military interventions in the Middle East ever since, all ultimately on the need for oil.







Oil also figured in a major conflict between the Ottoman Empire and the German Empire at the strategic port of Batumi on the Black Sea and Baku on the Caspian Sea, with the arrival of German Caucasus Expedition. This was established in the formerly Russian Transcaucasia around early 1918 during the Caucasus Campaign. Its prime aim was to secure oil supplies for Germany and stabilize a nascent pro-German Democratic Republic of Georgia.

The century of conflict over oil

Oil was the black gold that motivated, and still motivates the West to constantly interfere in the Middle East, without taking into account its widely diverse population, without seeking to understand the complexity of its many cultures and ethnic composition. This is well told in William Engdahl's book `A Century of War'.

After the defeat of the Ottoman Empire, the Arab population was betrayed by the British who were their allies at the time. The British and French agreed a secret treaty to partition the Middle East between them and the British promised via the Balfour Declaration to create a Jewish homeland in Palestine.

It not until 1947 that the UK withdrew its forces from Iraq.

As long ago as the 1870s, visionary solar pioneers such as Augustin Mouchot (right) foresaw the time when the coal would run out and began to develop alternatives that could deliver the same benefits from solar power.

Mouchot, demonstrating a solar powered device that made ice at the Universal Exposition in Paris in 1878, said:

"Eventually industry will no longer find in Europe the resources to satisfy its prodigious expansion... Coal will undoubtedly be used up. What will industry do then?"

It is a great tragedy that the Earth's crust contains so much fossil fuel; not just because of global warming, but because of the millions upon millions of lives that have been lost in the wars that have been fought over access to oil in the last 100 years.

On 6 August 1882 this printing press produced copies of Le Chaleur Solaire (Solar Heat) by Augustin Mouchot, a newspaper that he created in the Tuileries Gardens, Paris, for the festival of L’Union Francaises de la Jeuenesse. It printed 500 copies an hour, using solar thermal technology.

The competition between nation states for access to these resources has time and again over the last century brought violent conflict, suffering, widespread destruction and loss of life. The presence of oil, coal and gas in a territory has been a curse as much as a blessing.

Nowadays, the phrase ‘energy security’ is being used by those who want to see local, sustainable sources of clean energy replace dirty fossil fuels. This is because the sun, wind and other renewable sources of energy are available abundantly, everywhere on the planet, with no need for conflict over their use.

Looking at the history of solar power it is clearly obvious that its development has suffered as a result of the abundance of fossil fuels. The world’s economy is currently predicated upon their use. Despite all the scientific evidence of the imminence of catastrophic climate change as a result of our continued use of these fuels, the companies and economies which rely on them are as enthusiastic as ever to exploit them.

Humanity – or its leaders – are now faced with a clear choice: whether to stick with the status quo and vested interests that aggressively promote as inevitable a continued dependence on fossil fuels; or whether to accelerate the deployment, research and development into solar and other renewable, sustainable technologies and practices.

The potential of these technologies is completely clear and proven. The scientific case for the likelihood with business-as-usual of a runaway greenhouse effect, has been conclusively established. The stakes could not be higher and the choice more stark.

Energy storage: the next growth market in US and Europe

Energy storage is the currently missing link that will enable the intermittent renewable energy sources like wind and solar to play a much greater part in the future grid mix.

Now that more homes and businesses are installing photovoltaic systems, a new trend for combining these with battery backup is emerging.

Previously, battery storage systems were only thought necessary with solar PV and wind in stand-alone systems, separate from any grid connection, but as the grid supports more and more PV and wind systems, which can supply power only at certain times, the need for storage backup is becoming more apparent.

For large commercial installations this is especially attractive because, although they may have negotiated contracts with utilities that bring down their overall electricity rates, the fees that they are charged for the times when they do draw power, which can be based on their highest peak energy use during a month, have been rising as much as 10-12% per year.

According to Marcus Elsässer and other executives attending the Intersolar North America 2013 trade show held over the last three days, large commercial electricity users can reduce their peak demand and lower their demand charges by installing a storage system alongside a PV system.

Last month California set a proposed 2020 procurement target of 1.3GW of battery storage for network operators.

In Germany, grants from a scheme with a total value of €25 million are being offered to offer storage to existing solar installations.

Last month's Intersolar Europe trade show consequently saw over 200 exhibitors, including major brands, presenting their storage and smart grid solutions.

There, energy storage systems had their own dedicated section for the first time in any global energy trade fair. This particular show, the largest in the world for the solar industry, was attended by over 50,000 visitors from 47 different countries.

Energy storage plus PV was a key topic, with reference to many different types of storage, not just batteries, including flywheels, capacitors, heat storage and compressed air.

The German support scheme is managed by the state KfW Group bank, which provides a 600€/KW grant for new PV systems and 660€/KW grant for older systems. To receive support, systems must be in Germany, have a duration of at least five years, and no more than 60% of the installed power can be fed to the grid.

According to ">Ash Sharma of IMS Research, by 2017 the storage market is projected to be worth $19 billion, mainly due to the German scheme being taken up by residential system owners and operators of small systems up to 10 kWp.

As a whole, photovoltaic storage installations will, on average, he says, grow by over 100% for the next five years, up to nearly 7GW, rising to 40GW of battery systems by 2033.

Will this catch on here? The UK Department of Energy and Climate Change (DECC) is currently reviewing energy storage demonstrator proposals entered into a £17 million procurement competition.

There is a wide variety of entrants including some seemingly bizarre technologies: hybrid batteries to grid, smart energy storage, a radical proposal for using surplus energy to lift heavy aggregates that would be allowed to descend and generate energy at times of peak demand, flywheels, the use of electric vehicles for storage, liquid air, the conversion of surplus electricity into methane, cryogenic liquid nitrogen energy storage, and industrial scale lithium ion batteries.

A further potential winner under this scheme is Moixa Technology, an EU pioneer of smart direct current (DC) technologies, which has submitted a bid to install Maslow storage technology across 750 homes.

It works by shifting DC (direct current) loads from lighting, communications and electronic devices, to batteries during low tariff times, charged using local renewable sources such as solar PV, or at times of excess, wind power.

Simon Daniel, the CEO of Moixa, commented on the need for storage: “Just this week, the volatility of solar and wind resources created negative electricity prices and renewable curtailment in parts of Europe".

He says British distribution network operators face similar issues, especially at times of high sunshine, as now, or high winds. Daniel says that without using energy storage "considerable infrastructure upgrade costs, to reduce voltage issues caused by rising solar PV adoption" could result "which could otherwise lead to local blackouts or lost renewable revenue”.

He continued: “We’ve estimated that by using Maslow distributed energy storage systems with local solar PV, excess wind supply and low overnight energy prices, energy bills could be reduced by up to 30%, and keep essential consumer devices online if the grid fails”.

According to Anthony Price, director of the Electricity Storage Network, Britain should aim for an energy storage target of 2020MW (2.02GW) by 2020.

Speaking at the recent energy storage conference organised by the Institution of Mechanical Engineers, he said: “Meeting Britain’s power requirements requires energy storage as well as generating capacity. The expected shortfall in reliable generating capacity has been caused, in part, by a lack of commitment to a balanced portfolio of generation, storage and network investment.

"Adding more electricity storage into the power system will bring real long term benefits."

Sounds like a good bet for investors to me.