The cheap and reliable form of solar energy storage for homes that is already on the market

How should we store solar electricity? How about as heat? A Swedish research team is storing solar energy in liquid form, but it is still a way off being commercially available. A competing technology using molten salt is already on the market and shortlisted for a major renewable energy prize. But there is already a much cheaper and already well-proven solution now being used in a brand new context...

A shorter version of this article has appeared on The Fifth Estate.

The problem

Solar photovoltaic power it is increasingly being installed on buildings but a major challenge is that it is difficult to store so that it can be delivered when needed.

Storing solar electricity as heat is useful because the world uses more than twice as much energy in the form of heat as electricity. So for solar power to become ubiquitous, it needs to be delivered as heat more than as electricity – and round the clock.

Liquid solar energy

The solution of researchers at Chalmers University of Technology in Sweden is a chemical liquid that can tranport solar energy and then release it as heat whenever it is needed. The research, described in March’s edition of Energy & Environmental Science, describes how the team came up with a way of copying the means by which plants store solar energy – in molecules.

Transforming it into bonds between atoms in a liquid chemical makes it possible to transport it as well as store it.

“The technique means that that we can store the solar energy in chemical bonds and release the energy as heat whenever we need it,” says Professor Kasper Moth-Poulsen, who is leading the research team.

“Combining the chemical energy storage with water heating solar panels enables a conversion of more than 80 per cent of the incoming sunlight.”

The research project has come a long way since it began six years ago when the solar energy conversion efficiency was 0.01 per cent and the expensive element ruthenium played a major role in the compound.

Four years later, the system stores 1.1 per cent of the incoming sunlight as latent chemical energy – an improvement of a factor of 100, and ruthenium has been replaced by much cheaper carbon-based elements.

“We saw an opportunity to develop molecules that make the process much more efficient,” Moth-Poulsen says.

“At the same time, we are demonstrating a robust system that can sustain more than 140 energy storage and release cycles with negligible degradation.”

The process is based on the organic compound norbornadiene, which upon exposure to light converts into quadricyclane.

Hybrid panels

The rooftops of buildings can take advantage of the benefits of installing both solar water heating and photovoltaic modules.

Typical efficiencies for photovoltaic modules are now at least 20 per cent. Solar water heating systems have an efficiency of between 20-80 per cent, depending on the application, location and the required temperature.

Solar water heating systems make use of the full solar spectrum, whereas photovoltaics can only harvest a much more limited proportion.

Some companies have used this difference to design hybrid panels which contain both solar water heating and photovoltaic cells, particularly since the water can be used to stop the photovoltaic panels overheating, making them more efficient. The downside is the expense.

The Swedish researchers think that one of the potential applications for their technology, when it has become more efficient, will be a new generation of hybrid panels that utilise the heat, which can be released from the liquid storage medium.

Concept diagram for the hybrid solar panels

They say that combining solar water heating with their system allows for efficient usage of low energy photons for solar water heating combined with storage of the high-energy photons in the form of chemical energy.

Their simulations have persuaded them that these hybrid panels could be up to 80 per cent efficient. In terms of energy density they are comparable to a lithium ion battery.

The team will continue work on the technology to evaluate the potential cost and bringing it down by finding a way to mass produce the constituent chemicals, and to find a non-toxic solvent.

More than a pinch of salt

A totally different technology is from Sunamp, a British company that has developed its technology by collaborating with the University of Edinburgh School of Chemistry. It guarantees low-cost materials, exceptional long life, recyclability, safety and high energy density.

The technology has been shortlisted for the 2017 Ashden UK Awards alongside the work of the Passivhaus Trust and the Carbon Co-op, a community benefit society that helps its members to retrofit their homes.

An engineer installing the solar salt battery.

Sunamp’s form of storage uses a salt as a phase change material. This absorbs and releases thermal energy during the process of melting and solidifying respectively.

Similar technology is used on a large scale with concentrating solar thermal power stations, typically located in hot, arid deserts.

In this case it is used for storing energy from photovoltaic panels, waste process heat, or heat from heat pumps and micro CHP (combined heat and power) systems, in order to increase efficiency.

How does it work? In the case of storing solar electrical energy, an electrical element connected to the solar panels heats up the salt, thereby melting it.

The salt is kept liquid in a vacuum-insulated container. When heat is required, cold water is passed through the liquid in a heat exchanger, absorbing the heat and causing the salt to re-solidify. The heated water passes to the tap and the salt is ready to be charged again.

Sunamp’s batteries come in various sizes and can be used in series, meaning they can be used in anything from small homes to large hotels, for example. They take up much less space than a hot water tank, can store heat for longer and are more efficient.

The battery can store heat at half the weight of hot water in a tank storing the same amount of energy. Whether they are cost-effective depends upon the location and pattern of usage.

The easy solution

Tenants moving into a new passive solar mini-housing estate in Wales – Pentre Solar, Glanrhyd, near Cardigan – have roofs covered with grid-connected solar panels and zero energy bills.

The brand new passive solar homes for affordable social housing, covered in solar panels.

Dr Glen Peters, CEO of Western Solar, which is behind the development, has an ambition for his company to supply 1,000 homes and to work with housing associations and local authorities to provide sustainable, solar-powered social housing.

The occupants of the estate have been given a Nissan Leaf electric car to use collectively, charged by the solar panels on the roofs. So that's one form of storage.

But the homes' heating is provided in a surprising manner, using the best of old technology with new: solar electricity and storage heaters.

An installed storage heater in a passive solar house; proven, old technology meeting the new.

Storage heaters contain thermally massive blocks which are heated up by an element. They then release that heat gradually over many subsequent hours.

This form of energy storage was introduced to British homes in the 1960s and '70s on a special tariff called Economy 7. Since nuclear power stations could not be switched off unlike other forms of electricity generation, these tariffs allowed people to use nuclear electricity at night – at a lower rate when national demand was low – to charge the storage heaters.

The problem was that by the time the heat was needed, the following evening, they were often too cool and many people subsequently removed them and installed central heating instead.

Here, the idea is to let the storage heaters be heated up during the day by the solar panels on the roof, meaning that they are able to provide adequate heating through the evening and night provided that there has been average sunshine (50% of a June summer day) during the day.

This may not be the case in the depths of winter and so the homes are also grid-connected. They export surplus energy when there is some – after the electric car and storage heaters have been topped up – and purchase it when not enough has been generated.

"Storage heaters are incredibly cheap," says Glen, "and a well proven technology. Whereas the storage we had to start with in our prototype house – lithium ion batteries – were designated a fire risk and we had them taken out. They are also much more expensive – a couple of hundred rather than thousands of pounds."

This sounds like a solar energy storage solution that deserves far wider application. Good luck to the other technologies, but if I was looking for energy storage for a house, I know which I would choose.

David Thorpe is the author of a number of books on energy efficiency, sustainable building and renewable energy, including The Expert Guide To Energy Management In Buildings and The Expert Guide to Solar Technology and The Earthscan Expert Guide to Retrofitting Homes for Efficiency. Find out more and buy the books here.

Fact-checking Scott Morrison on affordable housing

The Australian Treasurer Scott Morrison has been seeking solutions to the problem of affordable housing in London. So let’s do some fact-checking on his position.

Australian Treasurer Scott Morrison 

Note: This post first appeared last week on The Fifth Estate.

Australia’s housing crisis

First – the scale of the problem: the thirteenth annual international house price survey by Demographia recently ranked Sydney’s home prices behind only Hong Kong, ahead of London and New York. It concluded:

“Hong Kong is the least affordable, with a Median Multiple of 18.1, down from 19.0 last year. Sydney is again second, at 12.2 (the same Median Multiple as last year). Vancouver is third least affordable, at 11.8, where house prices rose the equivalent of a full year’s household income in only a year. Auckland is fourth least affordable, at 10.0 and San Jose has a Median Multiple of 9.6.”

Whether or not you believe these exact statistics, there is no doubt that there is a supply crisis.

And, as with London, while the obvious solution may be to build more homes, the important shorter-term questions need answering of who owns the homes – occupiers or investors – and whether they are “affordable” or premium. The longer-term solution is: who builds them?

In a tight market, the more homes are owned by investors, the fewer can be owned by occupiers. This simple arithmetic is at the heart of the debate raging in Sydney, which Scott Morrison continues to dodge by refusing to admit that ending negative gearing might be a solution.

Negative gearing

Negative gearing allows property investors who make a loss to reduce the tax they pay on other income. According to ABC there are over two million landlords in Australia, over 60 per cent of whom claimed they made a loss (averaging about $10,000) in 2013-14, and so benefited from this.

Ending negative gearing – critics like Morrison’s own Liberal Party colleagues say – would reduce the incentive for investors to buy properties, easing the supply.

The Capital Gains Tax discount has also been blamed for the housing crisis. This was introduced by the Howard Government and generally results in half the profits from the sale of an investment property escaping tax.

Since being introduced in 1999 buying property as investment has increased substantially.

Whom does negative gearing benefit? Research by the Grattan Institute has revealed that the top 10 per cent of income earners, before negative gearing, get almost half the benefits.

The research body has dispelled the myths propounded by the pro-negative gearing lobby here and here.

The property industry argues that tax incentives for investment housing encourage more homes to be built. But more than 93% of property lending is for existing housing.

The Labor Party has proposed restricting negative gearing to new homes from July 2017, and halving the CGT discount to 25 per cent.

Speaking in London, Mr Morrison said this would not work and that changing negative gearing would make it harder to save for a house, because it would put rents up.

Fact-checking Morrison

Is this true?

No. In fact the opposite is true. While rents rose a little in Sydney and Perth when the Hawke government restricted negative gearing in 1985 they were stable in Melbourne and fell in Adelaide and Brisbane.

The Grattan Institute puts the rise in Sydney and Perth down to population growth and insufficient residential construction due to high borrowing rates and competition from the stock market for funds.

This week in London, Morrison was also quoted as saying: “What’s interesting in the UK is they’ve never had negative gearing. Yet they have the same and worse affordability problems than Australia has.”

That’s not quite true either, because landlords have had other kinds of tax relief. These were curbed in 2015 by the British government, with the then Chancellor George Osborne saying they gave investors buying homes to let a “huge advantage in the market” over people buying homes to occupy themselves.

Morrison also said on Sunday: “They have an even bigger problem than we do here, people pay more of their income in rents there, and they pay more of their incomes on their mortgages than they do in Australia”.

Is this true? According to the Resolution Foundation British high-earners with mortgages pay 20 per cent of their income toward their mortgage, while low-earners pay 28 per cent – and those on benefits are losing more than half their income. (These figures are a year old.)

In Australia, the most recent official data is even older – from 2013-14 – and doesn’t distinguish between high and low earners. It records that on average home owners spent 16% of their gross weekly income on their mortgage (down from 18% in 2011–12), while the figure for renters was 20%.

So Morrison may be right.

How do other countries compare in terms of housing supply and demand? According to the ANZ Bank Australia currently lacks around a quarter of a million homes, or 2.6% of its current housing stock (9.6 million). In the UK, house building is at around half the rate it should be.

In the social sector, there is a severe shortfall. The figure below compares the indexed number of households on social housing waiting lists, the number of vacant dwellings and the social housing shortfall as a percentage of the total social housing stock, from 2010 to 2015 in England alone:

England is not therefore exactly a success story wen it comes to housing. Does this make you wonder if Morrison might be looking for a solution to his problem in the wrong place?

What policies might work better?

In a paper published this month in the journal Housing Studies, the authors, from the universities of Adelaide and South Australia, conclude that “Australian governments need to adopt more effective housing policies if they are to meet the needs of the 700 000 to 1 million households who live in unaffordable housing”.

No surprise there. But what should they be? Morrison favours social bonds as a way of letting investors buy into the provision of affordable housing.

Does this work? In the UK most social housing is provided by housing associations which have charitable status. Most of these do issue bonds to raise finance. Here is a link to a list of the current issues and their returns.

Yet despite this, social renting is in long term decline compared to private renting, according to official statistics. And in the private sector, rents are 50% higher: private renters spend a greater share of their income on housing (30 per cent) than mortgage owners (23 per cent) or social renters (20 per cent) according to the Resolution Foundation.

Bonds may be part of the answer. But it’s more complicated than that.

The Joseph Rowntree Trust in the UK specialises in research into inequality and poverty, including housing and affordability. In 2013 it conducted a major study into how to finance the supply of new affordable housing which Morrison would do well to read.

Analysing innovative policies from the UK and abroad that help to increase the supply of below-market-price housing:

1. It found that a general shift upmarket, lowering subsidies and trying to encourage affordable rather than social housing doesn’t work: it results in higher rents and more limited security of tenure.
2. It cautioned against the use of state-backed guarantees in a climate of low interest rates.
3. And it came out in favour of competition among providers (both for profit and non-profit) because it encourages efficiency and innovation and lowers subsidy costs.

What else works?

Like Morrison, the left-wing think tank the Institute for Public Policy Research (IPPR) (Hull and Cooke, 2012) supports the idea of local authority pension funds investing in housing newbuilds – but unlike Morrison it also supports grants for new home buyers.

But probably the most comprehensive review ever of different funding mechanisms, by the Cambridge Centre for Housing and Planning Research (CCHPR) Funding future homes: an evidence base, found that no one approach wins out. Instead, all the models have strengths and weaknesses.

It also cautioned against importing solutions from one place into another, saying that “any serious cross-national application of innovative models needs to be placed into a suitable context”.

The Rowntree Trust also agrees that you can’t just take a single policy from one country and apply it in another – because conditions are so different.

Morrison therefore needs to take great care if he wants to transplant a policy from the UK to Sydney.

If there is any other single unanimous conclusion it is that the CCHPR and the Rowntree Trust both also feel that the local government level is the one best suited for identifying and driving the most appropriate mechanisms to deliver affordable housing.

“Local fiscal incentives and local institutional structures for mobilising savings or capital set against the local regulatory context for affordable and social housing are important general success factors”, says the CCHPR’s report on page 32.

Perhaps Morrison would have been better off staying at home after all.

PS: Although Morrison himself does not declare any homes he owns for renting out, the Coalition’s MPs own collectively 331, more than double the Labor Party MPs. Turnbull himself owns 4. I wonder how many of them benefit from negative gearing?

David Thorpe is the author of a number of books on energy and sustainability. See my website here.

We need a budget for green homes

New Guardian piece: We need a budget for green homes - Alistair Darling must set up a co-ordinated plan to encourage energy efficiency and refurbish the nation's dwellings.

Local energy, especially renewable heat, needs more support - Gov Committee

The government should do more to support local energy, according to the House of Commons Trade and Industry Committee.

Preferring the term "local energy" to “microgeneration” because it "is easier to understand and less restrictive", it argues that "there is too much emphasis on electricity production and not enough on local heating schemes - household or community-based." Roughly 1.3 million homes replace gas boilers each year, and Centrica estimates that micro-CHP systems could displace as many as 30% by 2015. It suggests that new housing schemes be fitted with CHP district heating. Furthermore it complains that Government payback figures, particularly for solar water heating panels, are far too pessimistic.

It urges energy suppliers to offer local energy systems with energy efficiency measures as part of a package of services to customers. Planning restrictions on rooftop wind turbines and solar panels should be removed, incentives streamlined, and the electricity distribution firms must pay a proper market rate for any surplus produced by such systems.

It acknowledges thast most forms of local energy are not suitable for all locations or uses. Micro-wind power's potential is "in danger of being oversold", according to one witness, so the government must ensure adequate information is available to consumers.

It says smart metering will be an excellent tool for promoting energy efficiency and export measuring, and calls for a deadline of 1 July 2008 for establishing standards and interoperability and a national roll-out scheme as in Italy.

However, local energy "cannot make a significant contribution in the next decade to closing the capacity gap created by the decommissioning of coal-fired and nuclear power stations—local energy is not a panacea that will 'keep the lights on'."

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