Reliable independent figures on cost-effectiveness of low or zero carbon energy generation based on real monitored examples are yet few, and I'm trying to collate them, because this kind of evidence is what we need to help determine policy.
Crucially, page 37 of the 2009 impact assessment of the Community Energy Saving Programme (CESP) (which places an obligation on energy suppliers and electricity generators to meet a CO2 reduction target) ranks the effectiveness of non-large-scale generation measures in kgCO2 per pound sterling spent as follows:
1 Existing community heat to CHP 88 (kg CO2 score per £ spent)
2 Electric to community CHP 39
3 Wood pellet boilers (primary) 24
4 Micro Hydro (0.7kWp, 50% LF) 16
5 Ground source heat pumps 14
6 Air source heat pump 13
7 MiniCHP (revised) 9
8 Mini-wind 5 kW, 20% LF 4
9 Solar Water Heater (4m2) 4
10 Photovoltaic panels (2.5 kWp) 3
11 Micro Wind (1 kWp, 1% LF) 0
From this it is quite glaringly obvious that for both heat and power the community scale is by far the most efficient level for interventions. Right at the bottom are the single-dwelling only solutions (I dispute the figures for wood pellet boilers since data on their carbon content is disputed) except where hydro is available (not many places).
The Electricity and Gas (Carbon Emissions Reduction) Order 2008 (CERT) looked into the cost and carbon reduction effectiveness of various measures. The document Explanatory Memorandum To The Electricity And Gas (Carbon Emissions Reduction) Order 2008 contains a further Evidence Base.
In this community CHP with woodchips comes out at nine times more cost-effective in ££ per tonne of carbon saved than solar water heating and about the same as ground source heat pumps.
The figures are (- with suppliers’ cost to save one tonne C02 (£/tC02) for the Priority Group):
1 Community heating with wood chip 3
2 Ground source heat pumps 42
3 Wood chip CHP 49
4 Wood pellet boilers (primary) 58
5 Micro Hydro (0.7kWp, 50% LF) 60
6 Log burning stoves 110
7 Mini-wind 5 kW, 20% LF 125
8 Wood pellet stoves (secondary) 126
9 mCHP 176
10 Photovoltaic panels (2.5 kWp) 218
11 Solar Water Heater (4m2) 346
12 Micro Wind (1 kWp, 10% LF) 685
13 Community ground source heat pumps 697
The above underscores that renewable energies are frequently site-dependent and sensitive to economies of scale, because you have to cost the whole system.
Only 2% of UK homes can have a small wind turbine. This Energy Saving Trust report suggests the best sites and how to pick them.
In my previous blog I link to actual surveys of real PV installations and the figures show that they do not generate sufficient power in the UK when we need it for the reason that there is not enough sunshine in the winter - unless you have a huge array, which is currently very expensive.
If PVs could become as cheap as a low-e coated window unit, with spray-on or printed nano-scale circuitry or similar it might be worthwhile. This is a technological advance not a deployment advance. They would also need to capture a greater range of frequencies of light.
I would suggest that the standard for measuring and marketing the rated output of a panel or a system is changed to make it more realistic and easier for buyers to understand. As discussed in the blog above, the test conditions are way different from European field conditions and led to unreal expectations, or to potential obfuscation by the industry/ unscrupulous installation companies.
All of this suggests that while renewable heat can work on a community level, only CHP can universally provide electricity, whatever the power source, and then not that much in relation to demand since there is a limit to the available waste, waste heat and biomass.
Therefore we have to conclude that for renewable electricity generation larger scale wind and marine power are what is required at a massive scale. Of these, only wind is currently cost-effective and that is why it is being aggressively pursued offshore and onshore.