Saturday, December 6, 2008

Why on-site renewables don't add up

Straight up, I want to say I love renewables, and I believe that we should have a massive increase in renewables as part of making a sustainable energy plan that adds up (as explained in my book Sustainable Energy - without the hot air, now available on paper).
This is an article about on-site renewables. Imagine a developer is making a new urban development. Offices or homes, perhaps. A three-floor building. Under some planning regulations, new buildings must get some fraction of their energy consumption from on-site renewables. Now, these regulations have some undeniable benefits: if it is expensive to install on-site renewables, the developer may modify the building so as to reduce its energy consumption, thus making it less costly to reach the required renewable fraction. Having local renewable energy production may also increase awareness about energy consumption among the building's users. And some local renewables are no-brainers - making hot water using solar panels, for example, makes complete sense, providing roughly half of the hot water consumption of an average home.
But here is the problem:

200 kWh per year per square metre = 23 W per square metre

On the left, 200 kWh per year per square metre is the typical total energy consumption of many homes and offices, expressed as energy per year per square metre of floor area. In terms of energy rating bands, 200 kWh/y/m2 is the boundary between bands F and G. Many government buildings use twice as much as this. (The Home Office uses 400 kWh/y/m2, for example.) The Passivhaus standard, at 120 kWh/y/m2, is not much better than this 200 kWh/y/m2 benchmark.
On the right, I've converted this quantity into watts per square metre, which are the unit in which I prefer to express renewable power production. Sadly, most renewables have powers per unit land area that are substantially less than 23 W per square metre. Wind farms generate 2 W/m2. Energy crops generate 0.5 W/m2. Solar photovoltaic panels generate 20 W/m2. And remember, we're imagining a three-floor building. So the power required per unit land area occupied by the building is not 23, but 3x23 = 69 W/m2.
On-site renewables are an interesting gesture, but if we are serious about renewables making a big contribution, they have to be big - they must occupy a land area much bigger than the land occupied by the buildings we are powering. If you want to completely power a three-floor 200 kWh/y/m2 building from energy crops and wood, for example, then the land area required for the energy crops and wood must be roughly 140 times as big as the land footprint of the building.
The response of an angry green campaigner to what I have just written can be predicted: "But we could make the buildings far more efficient!" Could we? I'd love us to build more-efficient buildings, but show me data. Not wishful thinking, but NUMBERS. The Elizabeth Fry building at UEA is often held up as an example of a state-of-the-art eco-friendly building. And here are the numbers for that building (from page 299 of my book). It consumes 96 kWh/y/m2, which is 11 W/m2, which is only about 50% better than the Energy-Rating-Band-F/G benchmark from which I started.
The bottom line: if you want to completely power a typical building, or even an amazing eco-building, from renewables, most of those renewables have to be offsite. There isn't room on-site! And it's probably a better use of resources to accept this fact up front, rather than force developers to squeeze uneconomic figleafs (such as micro-turbines) into their developments. We should modify the planning regulations for new buildings so that developers are still required to build renewables, but are encouraged to build new renewable capacity off-site.


EWB.USF said...

Yes, I agree 100% on that, if you are having all this renewable resources for your singled-floor house, rather than a 3 story office building, you are still privately consuming the energy somewhat efficiently. Your point on the numbers seem to be good rough estimates of what would be required to supply these homes. The interesting part is that the Dept. of Energy Office of Fuels Development, Aquatic Species Program, found that with only 200,000 hectares of land (about 0.1% of climatically usable land in the US), microalgal bio diesel could produce a quad of energy. 1 quad = 10^15 BTU's, which is incredible in my opinion. Yes, fossil fuels produce 3-4 Quads of energy, but with the amount of land the algae grows on. In W/m^2, I'm not sure on those numbers specifically, but if one can produce enough energy of lets say a large city of lets say the size of Miami or NY or LA, presuming the USA uses 100 Quads of BTU's. Hopefully energy consumption can be brought to industrial scale for public consumption.

David MacKay FRS said...

The alleged production of microalgae above is 17 watts per square metre. This is way beyond anything I have read for unaided plants. Perhaps the algae are being aided by some sort of input from fossil fuels. (eg concentrated CO2 input or nutrients or heat).

Mark Brinkley said...

Important points you make. I just wish that the DCLG would understand this, and drop their insistence on micro renewables in the Code for Sustainable Homes.

One technical point about Passivhaus. The 120kWh/m2/a is higher than you might anticipate because it counts electricty at 2.5 times CO2.The raw figure it is aiming for is 50kWh/m2/a, of which 15kWh/m2/a is space heating.

David MacKay FRS said...

@Mark, thank you very much for the PassivHaus detail - that's important. Please could you point me to a pdf file where I could have found this out? Thanks! David (

Unknown said...


I agree that in *urban* environments with high density per m^2 of ground space then 100% local supply of energy renewably in northern Europe is mainly wishful thinking and the CSH / Merton Rule value mainly arises in forcing the developer to calculate and reduce/minimise future energy demand for tenants. (I read that equally effective might be to force developers to build a brass statue on the grounds whose height/volume was proportional to future per-annum heat demand: brass is expensive, so...)

But in my own little council-estate house we're hoping to go electricity neutral (year round, not day-by-day in winter) from the start of next year with PV, and our gas-fired water and space heating demand is already ~50% of the UK household average even with 2 adults and 2 young children, and *before* installation of solar DHW. (Our space-heat demand is about 50kWh/m^2/y, ie about three times Passivhaus...)

So I don't think that it's quite as bleak and nonsensical as you have it.



Mark Brinkley said...

I'm not sure that I can point you to a pdf that explains the Passivhaus standard so simply. Indeed, it's a point which seems to have caused a deal of confusion over the years and is partly accounted for in the way Germans account for energy use in kWh, whilst we have tended towards using units of CO2.

If you go to the website
you will see that the 120kWh/m2/a is referred to a "primary" energy use. It's part of the problem of using kWh as an energy unit, as a kWh of electricity has much greater embodied carbon than a kWh of almost any other fuel. Passivhaus's are mostly electrically heated (via air source heat pumps), hence the distinction between energy and primary energy.

James Lee Vann said...

One advantage to producing at least some of your power on premise-

Thanks for the great blog!

Robert Waldrop said...

This is very interesting and introduced (to me anyway) a new method of calculating efficiency and potential for renewals. However, as a non-scientist, I was initially confused about the conversion of the kwhs. The text said "on the right" but my view of the page didn't show any calculations. After some trial and error, it seems to me that you are talking about "watts per square meter per hour". Clarifying that in the text would help us non-scientists understand this concept.

David MacKay FRS said...

To understand what a "watt per square meter" is, please read my book. The book is available free online and also on paper, if you like paper. Please, please stop saying "watts per hour". The watt already has the "per unit time" built in, just a like a horse-power. 1 kilowatt is roughly the same as one horse power. And finally, just to clarify, when I said "on the right", I was talking about the EQUATION that the article was discussing.

Ecorenovation said...

The DCLG look like the've got the message on this. Their latest "consultation" document point in this direction. On site renewables have only a relatively small part to play.

Andrew Smith-Gibbs said...

The NASA (eosweb) figures show that for a roof inclined at 36° and south-facing, average insolation for 51°N, 0E (London) is 3.11kWh/day/m², or 1135kWh/y/m². So, for a one-storey building getting energy equivalent to 100% of its usage from on-site renewables, or a 10-storey building getting the Merton-Rule 10%, (conservatively using the full 200kWh/y/m², not the Passivhaus standard) then a mean system efficiency of 18% would be required for a solar power system, which is within the reach of current technology.

Take a five-storey building at 10% on-site renewable supply, and you need a system efficiency of 9%, which should be achievable with bog-standard current technology (say panels @ 12% yield, and 25% system losses).

Andrew Smith-Gibbs said...
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Andrew Smith-Gibbs said...

[edited and reposted to fix broken DOI link]

Now let's look at the Elizabeth Fry building, with its four storeys and its 96 kWh/y/m² total end-point energy consumption. That's 384 kWh/y consumption per m² of building footprint.

It's roughly at 52°N, 1°E, and NASA tells us that the average insolation on a South-facing roof at 37° is 3.03kWh/d/m², or 1105kWh/y/m². From the satellite photo, the building comfortably has at least as much land again around it again, as it occupies, so there's incoming energy of 2210kWh/y for each m² of building footprint. Hence, for the equivalent energy provision of 100% of consumption, from on-site sources, we'd need a system efficiency of 17.3%. Again, this is feasible given current technology, with best-of-breed silicon PV now getting 25% efficiency, and exotics getting 42.8% .

Similarly, the numbers work if you specify that the building must get one-third of its power from on-site, and is restricted to a bog-standard PV system and inverter from 2002: a system within which we observe 6% mean annual efficiency.

In conclusion, when we run the numbers, we see that on-site renewables do add up

Unknown said...

Andrew, if your numbers are correct, you may have a point, although I think you mistakenly multiplied 96 x 4 when actually 96 kWh/y/m2 is the normalised figure for the whole building (not per storey). No need to multiply by 4. (But I think that helps your case!). By the way, do you by any chance work for Solar Century?! :-)

There are of course some challenges worth considering. One is that the Elizabeth Fry Building is a special case. Most offices are much, much worse. So first we need to make all offices as good (or better) than EFB. Another is the whole storage issue - both night/day and summer/winter.

It is perhaps a little unfair to consider the land footprint around the building because this will be different for example in cities so for comparison purposes we should consider only the building footprint itself. Also, importantly, you're assumming that the entire site is one giant south-facing surface angled at 37 degrees to horizontal, which it isn't. This will change things..

Generally though, even if you do have a point, we should not kid ourselves into thinking that onsite renewables will sort out our total energy needs for transport, food, stuff etc. Onsite power and heat are but a smallish part of the problem.

Dave Howey

p.s. as a slight aside, we should note that the energy requirements of offices versus homes are fairly different. In the UK, homes are dominated by heating and power - therefore can be helped by more insulation, solar conservatories, A rated appliances etc. Offices usually have many more internal heat sources and modern glass ones have a lot of solar gain and therefore hardly need any heating at all even in winter. They are dominated by a huge need for power (eg for lighting) and if there are too many internal heat sources, cooling in the summer.

Andrew Smith-Gibbs said...

No, I don't work for Solar Century. FWIW (not a lot), and in the interests of open disclosure, I was a PV system designer between 1992 and 1994, for Solapak. I do not currently work in the PV industry.

Re the land footprint around the building: as our host had talked about a specific building, it seems entirely reasonable to use the specific circumstances.

According to the Building Services Journal, the EFB energy consumption is 96kWh/y per m² of floor space, not per m² of building footprint, so the calculation of 4 storeys x 96 is correct to get the energy use per m² of building footprint. Unless I'm having a brainstorm. Please do double-check my numbers - we all make mistakes.

The electricity storage issue in this case is a red herring, because the building is connected to the grid: we are not looking for standalone sufficiency, but to generate energy onsite that's equivalent to a share (10%, a third, 100%) of annual consumption. If you want to include efficiency losses due to dispatching unused electricity, you need to know where it's being dispatched to: the grid generally, other local buildings - a full system model, requiring much more data than is easily accessible here. Pipe the weekend electricity to student dorms, and you cut out one large potential efficiency loss from the supply / demand mismatch

As for the large continuous south-facing area, no, that's not really necessary either. The panels can to an extent be staggered without much loss, because very little of the annual yield comes from when the sun is very low in the sky. You'd need to model a specific configuration to get the real figures, but please bear in mind that the system I outlined yielded 100% of the building's energy demands if a system efficiency of 17.3% were achieved: EFB could romp home if you work to a Merton Rule 10% of energy demands.

Combined photovoltaic-thermal systems have had huge efficiencies reported for them, but again you'd need to model the useful flow of energy, because heat generated wouldn't follow the same temporal pattern as demand, so you've have thermal storage with an efficiency hit that depended on how mismatched supply and demand were.

The issue of onsite renewables solving transport energy or stuff energy is an aunt-sally argument, so let's leave that. Onsite heat is a big part of the problem, but one of the easiest (technically) to solve.

Regards, Andrew S-G

pete said...
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pete said...

Going way back to Mark's comment about Passivehaus and Dr. MacKay's search for a source: both the 120 kWh/yr/m2 and the 42 kWh/yr/m2 numbers can be found here ( right from Dr. Feist's keyboard. However, it is not entirely clear to me whether or not Mark's interpretation is correct.

But if Mark's interpretation is correct and the passivhaus standard is 42 kWh/yr/m2 for all energy consumption within a building, the point is not merely "technical." It changes the whole discussion. It means that if you built a 1,200 square-foot, home to passivhaus standards, you could achieve "net-zero" status with a mere 4kW of PV in Central Illinois (where i live... not known for having a particularly mild or sunny climate... calculated using NREL's PVWATTS calculator). 4kW of PV fits easily on the roof of a 1-story 1,200 square-foot house and with some clever design, it could probably fit on the roof of a 2-story 1,200 square-foot house as well!

Andrew Smith-Gibbs said...

As far as I can tell, Mark's comments are broadly correct - the exact values depend on which version of GEMIS or the PHPP dataset you use.
For example doi:10.1016/j.solener.2008.02.014 uses a factor of 1.1 for gas, and 2.7 for electricity.

This CEPHEUS doc from Passivhaus has factors of 1.15 for gas and 2.5 for electricity.

2.5 seems about broadly right, implying an overall system efficiency for grid electricity of 40%; i.e. of the total energy input, 40% ends up as electricity with the consumer.

DanH said...

Does anyone know what controls the diameter of the spot of concentrated light in a concentrator photovoltaic system? Is it the Rayleigh criterion applied using the system aperture, or is the semiconductor element held far enough away from the focal plane to make the spot much broader than the Rayleigh limit?

(Not as off-topic as it sounds; I think this bears strongly on the power per unit land area of concentrator PV systems).



Unknown said...

I just found an interesting article about passivhaus here:

check it out.

David MacKay FRS said...

Andrew discusses the Elizabeth Fry building and seems to think that he has demolished my argument. Please stop being so confrontational and let's try and be consensual, mature and constructive, hey? The Elizabeth Fry building has a power consumption of 11 W/m**2 of floor area. Say that it has three or five floors; then the power per unit roof area is 33 or 55 W/m**2. We all agree on this, right? So my message is, you can't supply this power from even the best PV panels completely covering the building's footprint. Andrew says "you could fill the surrounding site with solar panels too". Yes, you could. There is no disagreement, and you have not disproved me. You have said exactly what I was saying, in another way: namely, you have to have renewable devices much bigger than the footprint of a typical building, to match the consumption of that building - even if it is the famous "low energy" Fry building.

Andrew Smith-Gibbs said...

Professor MacKay,

I'm glad to have been able to take this opportunity to show that on-site renewables within a building's footprint (either the EFB or a PassivHaus) can make a substantial contribution to a building's energy demands. After all, the Merton Rule requires matching only 10% of a building's consumption from renewables.

For a not-particularly-cutting-edge system with a yield of around 12%, then a third of the EFB's energy could come from within its own footprint: that seems pretty substantial.

For a 2-storey Passivhaus, a yield of 8% would be sufficient for 100% of the building's needs:
Consumption=2 x 42kWh/m²/year =84kWh/m²/year

Available power =
8% x 1105kWh/m²/year = 88.4kWh/m²/year

Above, I used kWh/m²/year. Let's do the same calculation in watts/m² for the EFB. The EFB is on average 4 storeys (source BSJ as above), so we've got 44W consumption, per m² of building footprint. From the NASA insolation database, we've got insolation of 3.11kWH/m²/day = 129W/m² (=3110/24) So we need a system yield of at least 44/129 = 34.1% to get a mean power purely from within the building's own footprint.

Currently, AFAIK, the best yield on a PV cell (not PV-thermal, just PV) is 42.8% (again, source as above).

Andrew S-G

DanH said...

I didn't seem to get any takers for my previous question about what controls the spot diameter in concentrator PV systems. Perhaps I can whet people's appetite by explaining fully why I asked.

Imagine that, instead of swivelling a whole concentrator system to track the sun, you keep the big mirror/lens/Fresnel zone plate still, and just move the small semiconductor element to track the focal point. Unless I'm missing something fundamental, this would enable you to get the aperture to land-area ratio up from the 1/3 reported in the SEWTHA book to something close to unity. This effect in isolation would increase the power output per unit land area by a factor of 3.

Of course, this has a down-side, too. The time-averaged insolation projected onto the normal to the aperture is decreased by a factor of 2 by being at an acute angle to the sun. But we're still ahead, with a net factor of 1.5 improvement over the power per unit land area achieved with a swivelling concentrator system.

If the spot diameter is controlled by the semiconductor element being out of the focal plane, then that's that. I'd imagine the factor 1.5 improvement could make a substantial difference to the debates in this thread.

(If, on the other hand, the spot diameter is controlled by the Rayleigh criterion, then all the advantage is killed off by the broadening of the spot associated with the reduced projected aperture diameter. In which case, I've just wasted everyone's time ;-).)

Chris said...
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Chris said...
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Chris said...
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DanH said...

Someone, trying to calculate a financial payback time for solar energy, left a (now deleted) comment on here that mentioned a cost of £5000 per peak kW for solar photovoltaic systems. Just thought I'd mention that the manufacturing cost is more like £1300 per peak kW (Rohatgi et al., 2003).

Unknown said...

Dan. True, but once you take into account the cost of the inverters, cabling, installation etc it rockets up, believe me.

Chris said...
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Chris said...

First I would like to say what a great book you have written and hope all the below doesn't come across badly, right or wrong as it may be (just say as text communication is fraught with misinterpretation). Also I hope it is ok to post another comment here ! I deleted the above comments as it is the first time I have used blogger and am used to another site where you can edit comments until you are happy with them and didn’t realize you couldn’t on blogger !

So combining everything into a more coherent whole...:

Q : Can solar PV make a useful contribution on-site or not ?It really does seem that the answer is yes to this:

just using the figures in the original post

"200 kWh per year per square metre = 23 W per square metre
Solar photovoltaic panels generate 20 W/m2.
And remember, we're imagining a three-floor building. So the power required per unit land area occupied by the building is not 23, but 3x23 = 69 W/m2. "

so a Solar PV system operating at 20 W/m2 = ~ 30% of what you need, which is a useful amount.

a practical example:

a 1 kwe solar PV system can produce ~ 700-850 kwh/yr using ~ 7-8m2 of roof space. (many examples of such system installed on existing houses in the UK)
A gas heated 4 bed/7 person 3 storey terraced house (built to 2002 Building Regulations) uses approximately 2,500kWh/yr (for lights and appliances), so a typical 1kWp system would provide approximately 30% of the dwelling’s electricity needs.

Here is a table showing what % contribution to total energy demand on-site solar PV could make, assuming you can use all the roof space

1. Total energy demand -
floorspace kwh/yr/m2
2. Total energy demand -
footprint kwh/yr/m2
3. W/m2
4. % provided by 20W/m2 PV
5. % provided by 14W/m2 PV

Home Office Building
400,1200,137,15% ,10%
Typical Office
200,600 ,68 ,29% ,20%
96 ,84 ,44 ,46% ,32%
57 ,171 ,20 ,102%,72%

These figures are pretty good and even if we divide by two we still get a useful/substantial contribution.

The 14 W/m2 is for a UK system that produces 850 kwh/yr (which is what some installers quote for Solar BIPV)
Of course installers tend to overstate figures. So one practical measured example in the UK is the Suncities Solar Village in Kirklees
They say: "A number of the systems were monitored for their performance over a 2 year period. Over 80% of those monitored performed to 80% or higher
against the predicted performance for the sites of 780kWhrs / kWp installed per annum. Several systems achieved a performance above the prediction. It was identified that the properties with low performance may have been switched off, either unwittingly by the tenant or because the electricity supply had been suspended in void properties, a small number (around 5%) reported system faults." (project installation was years 2000-2005). Here are some more casestudies from the same project
they expect (and seem to have achieved) ~ 20% of electricity demand through solar pv where installed, and 50-60% of hot water demand through solar thermal where installed. I don't think they installed both systems on the same homes however.

Carry on the good work, but it does seem that on-site solar PV can make a practical contribution to partially meeting domestic electricity demand based on the above figures. Although your argument that in most cases a large amount will have to be off-site is also true, so no real disagreement with that statement, rather I guess the title that on-site renewables don’t stack up is too strong a statement.

Costs and financing are the real issues to tackle with solar PV. This is improving with time and on site and offsite solar PV have strong potential in the coming years. of course energy efficiency first and then renewables ! Also new build is the not the main issue, rather tackling existing buildings. Passivhaus buildings seem to be able to be 100% self sufficient if done well.

Q: a planning policy favouring on-site renewables or an off-set fund for off-site renewables ?Lets compare the £/tCO2-LT for various on-site and off-site renewables, using .527 kgCO2/kwh for displaced grid electricity

onsite-Solar PV £5000 for 1kwp, producing 850 kwh a year, saving 0.45 tCO2/yr , gives £11162 £/tCO2 or £446 £/tCO2-LT if 25 year life time

offsite-Wind £1000000 for a 1MW wind turbine, produce 2MWh a year, saving 1200 tCO2/yr gives £826/tCO2 or £41/tCO2-LT if 20 year life time).

Biomass, GSHP, Solarthermal, CHP examples add another time.

so the argument that instead of a Merton rule of encouraging onsite renewables we allow off-setting through say paying into a large scale wind turbine project has the merit that it would in fact be cheaper for the developer when comparing PV against largescale wind, although not necessarily biomass vs largescale wind. Of course Solar PV and wind have unlimited resource whereas the sustainable biomass resource has a limit.

Also the offsetting argument is not new; by making it cheaper you reduce the incentive to build more energy efficiently, you have to audit the offsetting scheme to avoid it being a waste of time, and since we need an 80% cut eventually you will need later to consider whether you want to come back to that development and install a microgeneration device anyway, you could argue by the time you get to this point microrenewables will have matured and costs come down, but not if there isn't a market for them in the meantime.

The Merton rule in effect encourages energy efficient design and creates a market for microrenewables thus encouraging their R&D and production improvements leading to an acceleration of cost reduction, so we need to factor that in as well.

After some research: the experience curve for solar PV and large scale wind both seem to give a progress ratio of 80% (meaning that every time you double world cumulative installed capacity the price per kwp drops by 20%). However wind is closer to becoming competitive with fossil fuels. Therefore, as a policy maker, if you had only a few billion pounds to invest you should put it into largescale wind as it is closest to becoming self-sustaining, then having done that put it into the next nearest to commercialization renewable and so on.

So...your argument is correct, lol (as I disagreed with you at start), from this point of view of PV vs offsite wind (but still disagree for various practical reasons as we can't ignore politics and evolution of understanding amongst decision makers).

So what policy should we use for developments ? :

we could have:

1) x% requirement for onsite renewables

and/or £Y/tCO2 offset option to pay into fund that finances either

-2) nearby energy efficiency measures, nearby microrenewables and good quality CHP
-3) offsite large scale renewables

policies 1), and 2) exist in various Local Authority incarnations of the Merton policy, but not 3) that i know off for the practical reason that you need to find a large scale renewable energy developer that you feel you can trust and who can spend the money in a reasonable timescale and who uses the money for additional projects rather than doing what they were going to do anyway and bank the profit and also because the money is now leaving the local authority area, and so you are losing investment in your area, and practically hard to audit. Still you probably could get round this by finding an appropriate large scale renewable energy developer and thinking altruistically.

however..., we need to obtain an 80% cut in CO2 emissions, so basically we need everything we can get. As such I think, given the scale of the problem, that these arguments are a bit academic as basically we need to invest in all renewable technologies, trying to take them all down the experience curve to commercialization (i.e. they get get cheaper the more we produce). If Solar PV cost £1000 or less a kwp then on-site solar PV would start to happen without too much encouragement.

So really we have choice of:

a) looking from the small point of view of what money is currently available for doing things in the current policy environment for which we can say that the Merton policy has the advantage of actually being here and in operation rather than being just an idea and so isn't a bad thing, especially as it covers all renewables and good quality CHP rather than just solar PV (which is the most expensive right now), so costs are not unviable for a developer.

b) or looking from the larger point of view of what we really need to do, so basically we need large sums of money invested into all renewables technologies across the board so as to take them to commercialization from which point no subsidy is required. Such an investment would eventually pay for itself both through helping to prevent dangerous climate change, and through renewables eventually paying back into the overall system when they become cheaper than fossil fuels and so reducing energy costs and paying back from then on.

If climate change will cost 5% to 20% of World GDP, then spending 1% of world GDP on prevention is a good investment (as per Stern Review). This would give us £440 billion pounds from the year 2008 alone, to invest in all renewables to take them all to commercialization, which should go a long way to doing so if not covering the whole policy cost.

Some books / sites you might like if you haven't come across them or involved in writing them !

Sustainable Solar Housing
- Book 1: Strategies and Solutions
- Book 2: Exemplary Buildings and Technologies
- Edited by Robert Hasting and Maria Wall. (although expensive ...)

as they take a detailed numerical approach considering a range of technologies and approaches with real case studies (energy conservation, onsite renewables, building envelope, ventillation, etc..)

you probably already have this document, but it has some useful figures in for domestic consumption if not

This document is very interesting concerning the experience curves for technologies and how policy makers can use this to take technologies to commercialization, which is what we should do, and seem to be doing for renewables through the feed in tariffs and ROCS:
This document is well worth the read I would say.

The thing is that there is more than enough money out there for tackling climate change. It is a question of making the arguments to mobilize policy makers into redirecting funds into this area until the markets take over and solve it for us.

I think a good figure to work out is the total buy down cost to take all the renewables we need to commercialization i.e. how much total subsidy in £bn do we need to give to the renewable energy market so that sufficient volume is produced to allow their production costs to decrease to the point that no subsidy is required for investors to prefer renewable installations to fossil fuel power stations.

Chris said...

With regard to current Solar PV prices, if buying in bulk you get £5000 per kwp, otherwise it is higher.

However as i understand it alot of the cost for Solar PV is the frame, putting all the bits together by hand in a factory etc.., so there is room to produce them cheaper if enough volume is needed by using mass producing robot factories for example.

Plus there are other types of PV being researched, organic dyes, plastics that might turn out to be alot cheaper.

I am sure solar PV will keep getting cheaper as it is such a promising technology.

Also if you are reroofing you can offset some of the costs.