What makes solar panels work?

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  • What makes solar panels work?
  • andrewh
    Member

    Not as daft a question as it sounds, hopefully.
    If a solar panel is running off sunlight is it the visible-light bit of the sunshine which is doing the work or is it something else in the sunlight which powers it, like the IR or UV rays for example?

    Aidy
    Member

    Good question!

    I had to look it up, but a quick google suggests that wavelengths longer than about 1.1 ?m will not have sufficient energy to be useful to solar panels. So IR is probably out, but visible, UV and other shorter wavelength light will be effective.

    [Edit] But the shorter the wavelength, the less efficient the solar panel is at converting that light into electricity. [/Edit]

    Bear
    Member

    How efficient are solar panels at converting light to electricity too?

    DrP
    Member

    There’s a new Generation of PV panels that utilise a wider spectrum of the light…

    DrP

    TooTall
    Member

    Flexible panels IRO 8% efficient, current rooftop panels IRO 15-18% efficient, some of the advanced triple junction panels (these are the broader spectrum panels DrP mentions – there re others in development )are getting IRO 37% but the higher figures tend to be in labs as the technology is so expensive. There are one or two getting higher than that but they are very experimental materials.

    irelanst
    Member

    How efficient are solar panels at converting light to electricity too?

    Within reason the efficiency isn’t really an issue, as long as you have enough surface area to provide the output that you need then who cares? you aren’t paying the heating bill for the sun.

    TooTall
    Member

    efficiency isn’t really an issue, as long as you have enough surface area to provide the output that you need then who cares?

    Well – given that you would be paying for the solar panels, you care. Given that there are probably very few buildings in the UK with sufficient suitable roof area to provide all of their energy with solar, increasing efficiency (and driving down cost) is of interest. Lots of other reasons, like rising energy costs etc.

    Bear
    Member

    I just find it interesting that people assume they are a real energy efficient product when generally they are around 20% efficient. And to get that much higher is proving difficult and very expensive.
    I would also like to know what happens to all the waste product from their manufacture, mainly in China, so I imagine it is just dumped?
    As with all the renewable technologies there is another story to them.

    But we have to do something with our energy use and solar is potentially a very good provider of a lot of our energy.

    allthepies
    Member

    The sun.

    </thread>

    piemonster
    Member

    I just find it interesting that people assume they are a real energy efficient product when generally they are around 20% efficient. And to get that much higher is proving difficult and very expensive.
    I would also like to know what happens to all the waste product from their manufacture, mainly in China, so I imagine it is just dumped?
    As with all the renewable technologies there is another story to them.

    Out of sight out of mind, I heard questions raised about turbines as well. That said, coal etc is hardly going to be any better.

    Interesting thread, I shall lurk with intent.

    irelanst
    Member

    You quoted all of my reply except the significant caveat at the very beginning which stated “within reason”.

    Of course cost of panels, available area etc. are significant when considering the ROI but the actual efficiency of the panel isn’t the key concern – people are looking to save money, that’s the bottom line. If a panel cost X pounds and generates Y Watts and a panel that is more efficient may cost 1.6X pounds and generate 1.4Y Watts, it is just a case of maximising Watts per pound coming out of the panel.

    To expand my original statement;

    As long as the capital investment and energy saving potential of your system is sufficient to provide an acceptable return on your investment and as long as you have enough surface area to provide the output that you need then who cares what the individual efficiency of the panel is.

    piemonster
    Member

    Whoah, thought that was me for a minute.

    #returnstolurkermode

    Bear
    Member

    irelanst – but that is the point though, without subsidy or a return on investment very very few people would ever install them.

    I suspect the majority of households they are installed on are affluent with disposable income, possibly under performing investments that they take their money out of and invest in a solar array.

    I have nothing against that, but it is not really the principle of being green as they probably have two or three cars, holiday abroad, big houses, inefficient heating etc. It is purely a money making exercise.

    I’m convinced that we could really reduce emissions by people actually using there heating correctly, updating controls etc.

    scruff9252
    Member

    The current efficiency of 17-30ish% is not too bad. You have to bear in mind that a current combustion power plant, be it coal or gas is, at best 35% efficicienct. That figure too is before a further 12% is lost as distribution losses.

    Bear
    Member

    Scruff – there are a few that would challenge that efficiency of a combustion plant, have seen claims of upwards of 60%.

    Although I sit more in your camp with about 30%

    ohnohesback
    Member

    Subsidies from poor people.

    irelanst
    Member

    Bear – you are probably right, all the people I know who have them fall into that category to be honest.

    All I am saying is the efficiency isn’t the key factor, people who are looking at PV panels only have a choice of whats on the market, if they are 20% 40% or 99% efficient it matters not a jot, what matters is that for an investment of £4k you can get 2kW system. If you don’t like that then you don’t have the choice to buy a significantly more efficient system because there aren’t any available.

    TooTall
    Member

    irelanst – you assume we’re all just interested in slapping them on a roof in the UK. We’re not – and I am very interested in the efficiency (and related whole life costs) of solar for far more than UK house bling. Driving efficiency up and cost down is very important to the (global) future of solar PV.

    I work for a company which supplies solar powered variable message boards for traffic management, events etc. Therefore we’re all experts (all 4 of us). Allthepies is correct – it’s the sun what works ’em. when the sun’s rays strike the panel, the little Chinese pixies inside collect them and mix them up with some electrickery and then squirt it down some wires and stuff and then store the resulting mixture in some batteries. Sorted.

    Premier Icon slowoldgit
    Subscriber

    What Bear said. And us poorer folk are subsidising them to make power in the summer, not the long dark nights of Dec and Jan.

    Now solar hot water would interest me except that I have cold-fill dishwasher, washing machine and shower.

    irelanst
    Member

    I am very interested in the efficiency (and related whole life costs) of solar for far more than UK house bling. Driving efficiency up and cost down is very important to the (global) future of solar PV.

    Yes OK, I think were bordering on semantics now; the majority of people specifying a PV panel would be interested in size, cost and output. Efficiency is the driving factor behind the size/output/cost ratio of course.

    The vast majority of people would also like a smaller cheaper panel with a higher output, but those aren’t available yet because the efficiency has a ceiling which is limited by current technology at < <40%.

    Which was my (obviously badly made) point, the efficiency has reached a ceiling (for the time being), it doesn’t matter what you want; you aren’t going to get a panel with an efficiency of 99%. So for the moment if you can specify a panel which fits in the size you have, has a usable power output and comes in under budget then that’s all you can hope to achieve, the fact that it’s not very efficient at converting a free source of power into something more usable is mute.

    klumpy
    Member

    I suspect the majority of households they are installed on are affluent with disposable income, possibly under performing investments that they take their money out of and invest in a solar array.

    I have nothing against that, but it is not really the principle of being green as they probably have two or three cars, holiday abroad, big houses, inefficient heating etc. It is purely a money making exercise.
    Exactly so. The feed in tariff basically takes money from the rest of us, including POOR people(!) to pay three times the going rate to affluent upper middle class types for electricity that can’t be used. (Interestingly, the Tories of all people tried to axe the FIT.)

    This was covered on page two of this thread:
    http://singletrackworld.com/forum/topic/if-everyone-in-britain-stuck-solar-panels-on-their-roof/page/2

    Premier Icon molgrips
    Subscriber

    I just find it interesting that people assume they are a real energy efficient product when generally they are around 20% efficient.

    Lol.. 20% of free solar energy – yeah terrible.

    if they are 20% 40% or 99% efficient it matters not a jot, what matters is that for an investment of £4k you can get 2kW system.

    It does matter – the stuff you need to make panels doesn’t grown on trees.

    irelanst
    Member

    It does matter – the stuff you need to make panels doesn’t grown on trees.

    It doesn’t because you don’t have the choice of different levels of efficiency vs. environmental impact, you either accept the current level of environmental impact to produce the panel vs. the level of performance and buy some panels, or you don’t.

    You can’t pop into PV panels’r’us and choose between a panel thats 18% efficient but killed 15 fluffy bunnies or one thats 22% efficient and killed 20.

    Premier Icon richmtb
    Subscriber

    What makes solar panels work

    The photoelectric effect.

    Einstein won a Nobel Prize for his work on the photoelectric effect – he was a smart chappy

    Premier Icon molgrips
    Subscriber

    It doens’t matter if you purchase now, no. But it matters in the long run – which is why people are working on it.

    Premier Icon AlexSimon
    Subscriber

    I don’t get your line of argument irelanst.

    As a designer of consumer electronics, of course efficiency is important. Mainly because size is one of the most important aspects.

    Also, as a specifier, of course I have the choice of efficiency vs environmental impact vs cost. It might not be measured in fluffy bunnies, but it’s definitely measurable and is measured.

    One could also argue that if I could do the maths, I could consider domestic PV vs Passive with a consideration for environmental impact vs efficiency too.

    irelanst
    Member

    OK, I’ll run through my logic,

    The efficiency of a PV panel is a measure of the panels ability to convert solar radiation to electrical energy. The more efficient the panel the higher the power density. The power density of the panel is governed by the power density on the cell, the power density on the cells is determined by the density of the circuit on the chip, the density of the circuit on the chip is determined by the lithography and that’s where I come in, I design lithography tools.

    The resolution of the lithography doesn’t develop linearly over time, there are step changes due to new technologies, followed by a period of time where gradual developments improve productivity and reliability. At the moment we are in a period of gradual development of production tools, the tools which will make the next step change are in our and our customers R&D labs. Until this step change is possible, manufacturers are limited in what they can achieve and can only tweak their process to eek out the fractions in efficiency and improve production yield to lower their costs.

    What happens once the cells leave the fab, I don’t know, I assume that different panel manufacturers have different design and production methods which will add or subtract to the overall panel efficiency which admittedly fuzzies the edges to a certain degree.

    The result of this is that there isn’t a linear price vs. performance product range in PV panels (or semi-conductors on the whole), there are discreet jumps in terms of technology. You can’t pay a bit more and get a bit more efficiency, you have to jump up to the next rung on the technology ladder and then you get a discrete increase. When the next step change takes place then one of the major players will have an advantage because they will be able to produce panels which are significantly more efficient for a brief period, and then the competitors will catch up and the market will stagnate at that level for a time, before the cycle is repeated.

    I think I’ve gone too far OT now, so will leave it there.

    maxtorque
    Member

    It seems to me that actually ALL forms of energy are free, and it’s just the cost to leverage those reserves that matter? i.e oil is “free”, but you have to buy the land underwhich the field exisits, build a drilling rig, refinery, and distribution system to actually leverage that energy. Same with wind (land + turbines + power grid), wave, solar etc etc

    So efficiency does matter. However, the chances are, that for the consumer, who primeraily worries about the cost, the chances are a more efficient system will not be any cheaper (because the people developing/selling it will want to make money from it). At this point market forces dominate, rather than pure physical ones.

    One question i have, is why is Solar PV not combined with solar TH? PV cells loose efficiency when hot, so cooling them with a TH system will improve both power output and efficiency massively? Use the electrical power to drive heat pump to leverage the low level heat, or perhaps “store” heat in a fluid accumulator for release over night etc?
    I guess it’s just economics that prevent this being feasible?

    Premier Icon DavidB
    Subscriber

    Here is my stupid question.

    Why can’t we replicate photosynthesis? Surely we should be ripping off the plants’ ideas as they have this totally nailed?

    oliverd1981
    Member

    I think UK domestic solar is really just a scribble in the margins of the energy story it doesn’t matter how efficient the cells are -they’d produce a lot more power for the same amount of environmental impact if we put them in a sunnier part of the world. Unfortunately some of these places have a vested interest in continuing to sell us fossil fuels.

    I’m still not convinced about the longevity of the panels – I know the old generation cells had a tendancy to die after a few years.

    is it feasable to make a solar powered co2 > methane process? that would be a good idea IMHO

    Premier Icon molgrips
    Subscriber

    Unfortunately some of these places have a vested interest in continuing to sell us fossil fuels.

    Actually most of them are trying to find alternatives to selling oil because they know theirs is running out.

    Why can’t we replicate photosynthesis?

    Cos this is easier. Leaves are complex, and would be quite hard to make. And photosynthesis makes carbohydrates, which we’d have to somehow burn.

    Afaik people are trying to get stuff like algae to produce hydrocarbon fuels via photosynthesis, and also to use great big seawater algae farms, with the algae itself being harvested, dried out into bricks and used as fuel.

    TooTall
    Member

    It seems to me that actually ALL forms of energy are free

    Depends whether you want to think about carbon deposits being finite – too many people think that what comes from the eco system is ‘free’ but it is limited capital.

    Solar PV not combined with solar TH?

    There are many examples of this. Lots of people making them. You just end up combining inefficiencies.

    I’m still not convinced about the longevity of the panels – I know the old generation cells had a tendancy to die after a few years.

    Got a reference for that? I’ve seen far more working 25 year old panels than non-working. They tend to lose about 1% efficiency per year as they degrade, but they still work.

    irelanst – how do the triple junction cells that are 37% efficient get that sort of output without your personal intervention then? There must be something out there that is either better than you say or bypasses your little bit of it.

    Premier Icon molgrips
    Subscriber

    seems to me that actually ALL forms of energy are free

    Well obviously the monetary cost of a resource includes all costs associated with it. The difference between solar/wind etc and coal/oil is that the input cost per unit of raw material is zero throughout the supply chain, as opposed to quite a lot with oil etc.

    Nice thing about solar is that the maintenance cost is pretty low, the real-estate is also very easy to come by. Since almost all of us have a good few square metres of it over our heads right now.

    Mugboo
    Member

    So having said all that, are we saying that Solar power is not worth buying into yet? When I had the house rewired I ran an SY cable just in case..

    Premier Icon molgrips
    Subscriber

    I think it’s already worth it. It just depends how long you want the payback to be, and if you can afford the outlay.

    klumpy
    Member

    Here is my stupid question.

    Why can’t we replicate photosynthesis? Surely we should be ripping off the plants’ ideas as they have this totally nailed?
    Plants use photosynthesis to build organic carbon structures, so to “rip off” photosynthesis in an effective way we would grow plants and burn them.

    Premier Icon molgrips
    Subscriber

    so to “rip off” photosynthesis in an effective way we would grow plants and burn them.

    An excellent idea!

    klumpy
    Member

    so to “rip off” photosynthesis in an effective way we would grow plants and burn them.

    An excellent idea!

    But biofuels made babies starve, or something, apparently.
    They’re out of favour, anyway – possibly for a good reason.

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