Solar PV: More harm than good?

I recently saw an interesting idea in an in-coming e-mail.  I believe the idea may have originated in the book “Freakonomics”.  It points out that solar PV panels are black, so they absorb in-coming radiation very effectively.  But they convert only about 15% of that solar radiation into electricity.  So where does the rest go?  Obviously it becomes heat.  It warms the panel.  And where does the heat go?  Partly it will be convected by adjacent air.  Partly it will radiate.  But as a (relatively) cool object, radiation from a solar panel will not radiate back to space — it will be trapped in the atmosphere.  All this heat, therefore, will be trapped on the earth and arguably contribute to “global warming”.

Of course we need some caveats here.  The theoretical “black body” beloved of physicists has a matt finish.  But solar panels tend to be shiny.  Some of the radiation incident on them will be reflected straight back into the sky.  And then of course solar panels sit on roofs which may have been dark or light to start with.  My own 2.4KW system replaced dark grey slate tiles, so may well absorb no more heat than previously.  But panels on lighter roofs will undoubtedly increase energy absorption.

I wasn’t sure of the answer to this complex question, so in a spirit of innocent enquiry, I asked the question on Twitter.  And I was astonished by the instant and vituperative response.  Most seemed to assume that I’d made an assertion, rather than asking a question.  Most pretended to assume that because they disagreed with the assertion they thought I’d made, I must be ignorant of science.  Sorry, guys, but we Cambridge maths graduates do know a little bit about physics, generally speaking.

Here are some examples: Rachel Pearce ‏@rachelpearce  @RogerHelmerMEP Your pitiful grasp of physics makes me utterly ashamed that you are my MEP.

Voting Floater ‏@VotingFloaterUK  To be fair, it’s a valid question. Although the answer is clearly a resounding NO!  (“Clearly”, floater?).

Dr Matthew Aylott ‏@renewablewriter “Do solar panels add to global warming?” I hope this is a parody account because that is a very silly thing to say otherwise.

John Russell ‏@JohnRussell40  I’m sure you’re a man of principle, Shame they’re not scientific principles > …

Davis Carlton ‏@DzCarlton  What happens to sun energy that does not hit solar PV?! Why not ask someone with a clue instead of speculating nonsense?!  (But I thought I was asking, Carlton).

One idiot even suggested that the excess heat would dissipate at night, and therefore didn’t matter, as though heat at night were different from heat in the day.

Of course the short format of Twitter leaves room for vituperation and ridicule, but not much for developing an argument.  So I was grateful to Simon Evans, who at least posted a link to an article on the Real Climate web-site purporting to refute the case against solar PV.  Read it here.    I read it with great interest — though it’s couched in patronising and dismissive terms.

The nub of it seems to be just two points.

The first is that the total area of solar PV panels compared to the area of the earth is trivial, so we need not worry about it.  But that wasn’t the question.  We didn’t ask if there were too few solar panels to contribute much to global warming.  We asked whether any given square metre of solar panel would increase, or mitigate, warming.  And the answer will not depend on the total installed area of solar PV panels in the world.

In this context, I was interested to see that the article’s own estimate of the additional “waste heat” generated by solar panels came in at 125 watts per square metre.  My own back-of-a-fag-packet calculation suggests that my own solar panels, under ideal conditions, generate about 80 watts per square metre. So the additional waste heat exceeds the electricity generated.

But the key point in the Real Climate piece is that any excess heat generated in the solar panel will be outweighed by the saving in CO2 emissions that would otherwise have occurred (if the electricity had been generated from fossil fuels).  This is a highly contentious area, with the climate debate dominated by the feed-back issue.  There is no doubt that atmospheric CO2 tends to increase temperatures.  The IPCC postulates additional positive feed-backs that would triple the effect of CO2 alone.  But some sceptical scientists argue that there are also negative feed-backs (increased cloud cover/albedo for example), and that net feedbacks may be negative overall.  Certainly the total absence of further global warming this century strengthens the case for negative feed-backs.

But the Real Climate case also relies on the implicit but facile assumption that every KWh generated by wind or solar means one less KWh generated by gas or coal, with a corresponding reduction in fuel consumption and emissions.  This assumption (on which the whole of the renewables industry depends) is demonstrably false.  Several recent papers, most notably that of Professor Gordon Hughes of Edinburgh University  points out that renewables are intermittent and unpredictable.  They therefore require conventional back-up, usually gas, to be held as “spinning reserve”, able to cut in at a moment’s notice when the wind drops or a cloud obscures the sun.

But keeping this capacity going as spinning reserve is a bit like running the engine on a stationary vehicle.  It burns fuel and creates emissions without going anywhere.  More generally, gas power plants are much less efficient when constantly turned on and off, than when run consistently.

Professor Hughes concludes that when you look at the whole system, renewable plus back-up, the emissions savings achieved by renewables are somewhere between trivial and zero.  Of course Professor Hughes’ work pertains specifically to wind power, but the same considerations apply to solar.  Both wind and solar are intermittent and unpredictable.

So the fundamental point of the Real Climate rebuttal is open to question and probably wrong.  And the whole question is much more complicated than the facile responses on Twitter try to suggest.  I don’t pretend to know the answer to this rather complex issue, but I’m inclining to the view that solar PV is a waste of money, even for those who believe in anthropogenic global warming.  Unless, of course, you’re making whacking subsidies out of it.

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22 Responses to Solar PV: More harm than good?

  1. Ask yourself what would happen to the sun’s rays if the panels weren’t on your roof, Roger. Where would they go? Would they for instance hit the black slates or tiles on the roof below? So what would the net effect of that be, do you think?

  2. James says:

    John Russell, if you had read Roger’s article, you might have noticed that he discusses exactly this point.

  3. John, Why don’t you read the piece? I discuss that in some detail. I agree that if the panels replace a dark roof, there will be little effect. But if they replace a lighter roof, they will increase heat absorption. And I quote the Real Climate web-site, which suggests that solar panels will increase the additional waste heat by 125 watts per square metre. I could hardly have been more specific on the point!

  4. neil craig says:

    Not only are you broadly right but the opposite of this – a worldwide programme of painting roofs white (also tarmac) has been proposed by Stephen Chu (Lawrence Berkley Lab) & Richard Muller. (check Google)

    If CAGW were ever to actually turn out to be a problem this would indeed work. All that is required is that all new roofs and roadsw be this cover, which would cost virtually nothing since they have to be some colour anyway. Of course would take decades but we are talking about a decadal proble. Only a few % of the world is covered by buildings but by the calculation this could mean cutting heat from the Sun by about 1% which is plenty.

    Your Twitterers reactions typically how (A) the ignorance of the ecofascists, (B) the way they always rely on vituperation as a substitute for intellectual process & (C) that nothing scares the proponents of eco scare stories more than solutions for the alleged “problem”, which would deprive them of their morasl weapon against the rest of us.

    I suggest you inform your twitter critics of this. Obviously, being owed one, you willreceive a grovelling apology from every single remotely honest “environmentalist”. If, as I expect, that turns out to be absolutely none of them you wil br at liberty to let them know that any statement made by any part of the movement may safely be ignored as the lies of people without the slightest trace of personal integrity.

    • Brin Jenkins says:

      Lets just accept the Carbon Theory is correct! The aim therefor is to cut down its production, thus achieving the stated objective of less carbon.

      I can all accept true efficiency is in all of our interests, use less, cleaning up wastage, and materials, fuel will last longer saving CO2 into the bargain, the objective achieved.

      However buying Carbon Credits, and uplifting low carbon economies is counter productive. More energy and resources will be consumed, adding to the overall carbon production by the recipients. No carbon gain, in fact the longer term more will be produced, and resources consumed faster. The objective is failed.

      If Carbon Tax spent on War and War machines, again carbon is moved to another area and not reduced.

      If this is not agreed, then perhaps the stated objective is inaccurate and there is another, please tell us what it is?


  5. David W. says:

    I pray for the day genuine scientists finally admit what intuition and even basic knowledge compel us to conclude; that climate dynamics are influenced by so many intra- and extra-atmospheric variables, phenomena, and aberrants that it is impossible to conclude the influence man’s activities and obstructions could have on the climate, as a whole; solar panels, SUVs, smokestacks or not.

    • Solar NJ says:

      Just please, stop talking before you make an ass out of your self on a topic you know clearly less then everyone else here about

      -Sharone Tal

      • Brin Jenkins says:

        Don’t be so hard Solar, the point is unclear perhaps but he has a point of view not to be shouted down. Science is made more complicated than needs be, computer models are not data, and clever programming can produce what ever answer you like. An aircraft simulator might be persuaded to fly backwards, the aircraft will of course crash due to massive reversals of feedback. All computer models need to be evaluated by peer review, not just run as though the results are proof of a flawed theory.

      • Brin Jenkins says:

        I understand now, you have a vested interest! Consider perhaps that by the time 10% of generation was green, the carbon levies had doubled the cost to all other consumers!

        My conscience stopped me participating, how could I ignore that the profit for me was being obtained at the expense of rising electricity prices for everyone else?

        Now we are told it must be more than 10% and we now are looking at 20%. This is not cost free and the poorest pay the most doubling the unit cost yet again.

  6. Phew, a well-calculated blog. The panels don’t capture enough of the sun’s energy to make them really worth turning one’s house into a Lego lookalike. If it was 50% then maybe there might be something in it, but it is rather painful to see traditional terracotta coloured roof- tiles being smothered with acres of featureless black tech.
    As for the idea of painting roofs white; let’s not encourage such ideas, because it’s more than likely some loony in Brussels would make it law. Can you imagine the dreadful glare there would be from thousands of white roofs?

  7. Ammonite says:

    This is what I have gleaned from a relative who was a lecturer in surveying.

    The energy transmitted to the surface of planet earth is 125 Watts/Square Metre (on average – varies depending on season, latitude and associated declination).
    With half of planet earth being lit by the sun at any time that gives us about 31,500,000,000,000 kilowats at any time.
    That energy is absorbed by the atmosphere, the earth and the sea.

    Solar panels make zero nett difference because what they do is absorb a percentage of the available total solar energy that otherwise would be absorbed by the land or the sea. All the solar panels do is capture a percentage of that overall solar energy ‘compress’ it in various ways that allow us to use it in confined spaces e.g.buildings which in turn lose it back to the atmosphere. How we use it does not add to or subtract from the maximum available solar energy within earth’s atmosphere. The technology alters the total amount by zero.

    The environmental and financial efficiencies are the factors that need to be established and improved.
    1. the energy of construction versus the energy produced in a usable form.
    2. the cost of construction and operation versus financial benefits gained.
    3. the depletion of natural resources (often rare earth minerals) versus their potential use in another technology i.e. what is the highest, best or most sustainable Return On Investment, financially, technically and sustainable efficiency.
    As has been recorded ad nauseam, the weak link is the intermittency of such energy resources. For industries that operate mainly in daylight hours, solar energy can be beneficial. Night time obviates any chance of its practical use (solar). Until we devise a way to efficiently, store and reuse daytime solar power its general use for 24 hrs/day applications is but a distant dream. The cost of construction, installation and maintenance is, at present, a factor that mitigates against its use in practical terms. However, home-made/DIY installations can be very beneficial in terms of cost -v- benefit because labour can be counted at zero cost.

    There are ways of storing such energy in high thermal mass buildings but such ways are still expensive in terms of cost -v- benefit.

  8. mikestallard says:

    This really does go beyond parody. No wonder the BBC is so short of comedians! (Sorry, funny comedians).
    You must feel like the small boy who shouts that the Emperor is naked!

    There is not much sun in UK, especially in December when you need a nice hot bath.

    Also that even here in the flat fens, the windmills do not turn all the time because “the wind bloweth where it listeth”. (My wife thinks they have been switched off for maintenance!)

    There! I have said it!

  9. Ammonite says:

    Regarding roof colours and solar panels:
    • The colour has a marginal effect when considered alongside all the other variables;
    • The whole point of solar panels is to capture solar radiation and then pump it into the house. The whole point of that would be lost if the roof (biggest source of heat loss from most buildings) is not adequately insulated. In the case of inadequate insulation all that would happen is that solar energy would be captured, pumped into the building and lost at a rate that would make the whole operation an expensive and very low efficiency exercise. Of course, windows, doors, walls, ground floor and draught ingress will all lose the heat pumped into a house that is at a lower temperature than the outside air. Outside wind speed also affects the overall heat loss (higher wind speed = higher rate of heat loss).
    Let’s put it this way. If we ignore the:
    1. costs of installation,
    2. environmental effects re depletion of rare resources,
    3. the embedded energy of materials harvested, processed, packaged, transported and installed,
    4. maintenance
    5. intermittency of operation (no output at night)
    …then the solar panels are great, marvellous…but only during daylight hours.

    The embedded energy (item 3. above) is significant and can exceed the total energy that the final product will ever produce (like wind turbines). The pollution is significant in production and transportation.

    There are situations where solar panels can be effective but in most cases they are not because of the variables previously mentioned.

    You are at the risk of being misled and it seems seems you are unable to sort out the wheat from the chaff at present.

    • Brin Jenkins says:

      It’s might be likened to examining the complexity of perpetual motion, one gets bogged down in inconsequential detail when it can’t ever function without an extra energy input. Embedded energy in the manufacturing and construction process nullifies any benefits obtained.

      Development before committing to massive investments would have seemed common sense to me, not subsidies/rewards to all who subscribed early like pyramid schemes.

  10. Repro Munchkin says:

    “My own back-of-a-fag-packet calculation suggests that my own solar panels, under ideal conditions, generate about 80 watts per square metre. So the additional waste heat exceeds the electricity generated.”

    Well of course it does. Solar panels are only 15-20% efficient. Think it through.
    And Pierrehumbert’s figure of 125 Watts is the *extra* energy absorbed by a perfect black body panel compared with a patch of hypothetical desert. As you say yourself you’ve put your PVs on a slate roof so the change in heat absorbed is probably very much smaller and quite possibly negligable.

    Lastly, for the record, are your PVs in the UK and do you receive the Feed-in-Tariff for them?

    • I do indeed receive the feed-in tariff. That’s the only reason the system is there. I calculate that after tax I get about double the return that I would get for an annuity bought for the same capital outlay.

  11. Malcolm Edward says:

    I don’t know the answer, but here’s my thoughts …

    The difference between the radiation characteristics (reflection, absorption and re-radiation, across all wavelengths uv to infra-red) of a solar panel and the underlying material it shades, depends very much on the underlying material. If the underlying material is manmade, then this is very much an arbirary choice.
    However I think from the “green” point of view we should compare solar panels to the situation without interference by man, ie. compare to natural vegetation at that location. (In much of the UK the natural vegetation would be tree cover, or if we allow the presence of pre-industrial man, a mixture of grass, crops and trees). In principle one could measure and agree on an average vegetative radiation profile for a region and compare this with the measured characteristics of a solar panel. (Then compare with the atmospheric absorption profile to see the proportional effect it has on the atmosphere).

    In practice most solar panels seem to be mounted on pre-existing rooves, such as red tiles or dark grey slates; so I suggest one needs to measure and agree standard radiation measures for each roof type in order to find the de-facto effect of a solar panel at its location.

    An interesting point is that both a solar panel and vegetation both perform energy conversion of some of the incident radiation, one into electricity and the other into forming biochemicals (plant growth). Electrical energy is released elsewhere immediately and generally ends up as surface heat, whereas plant growth is stored until the plant dies and decays but much of the energy is again released as heat.

  12. David C says:

    Re Solar PV being a waste of money. This is incontrovertible in the UK, even George Monbiot agrees, IIRC. Massive subsidies however make them an attractive proposition for the middle classes on their extensive roofs. In special circumstances, e.g. on islands in Lake Titicaca providing power for radios etc., they do make sense.

  13. Jake Speed says:

    what about LENR? it was said in 1989 junk science after Pons and Fleischmann presented it to the Science community, but NASA are talking about it, That will keep the lights on Roger! look here


    CBS 60 minutes

  14. Dr Green says:

    With solar energy being talked about worldwide the discussions about its effectiveness are but normal. It is however very important to make sure to use the products and that the rooftops are properly insulated in order to generate energy in an effective manner.

    • Brin Jenkins says:

      Dr Green, are you considering photovoltaic or hot water panels here?

      I agree on insulation as it’s less wasteful. However insulation under photo panels is counter productive, increasing panel temperature reduces the output efficiency. Under hot water panels it increases efficiency, this suggests to me that a hot water systems with efficient storage is a sounder proposition.

  15. What’s up, its nice piece of writing about media print, we all be aware of media is a enormous source of facts.

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