back to article Graphene solar panels harvest energy from rain

Solar panels could generate power at night and during inclement weather by harvesting energy from raindrops, research finds. The panels are built from highly-conductive graphene. In the presence of water, the material binds positively charged ions with its electrons. It is difficult to mass produce. Key to the operation of …

  1. Anonymous Coward
    Anonymous Coward


    When its just a typical british day, that is, cloudy but dry then the entire system is buggered.

    1. tiggity Silver badge

      Re: But,

      Your typical British weather must be better than mine!

      Seriously, there is quite a lot of geographical differences in UK rainfall.

      Solar cells work when cloudy, just get significantly less power generated

    2. AndrueC Silver badge

      Re: But,

      Oh it would've done well enough this year. I'm old enough (nearly half a century) to be used to the British weather but I am getting sick and tired of the rain now. I don't think we've had a week since October when there wasn't significant rain on at least one day or overnight. Almost all our local golf courses have been partially closed in the last few months and normally there's only one that suffers and that was built half on a flood plain.

      1. Sir Sham Cad

        Re: local golf courses have been partially closed

        So it's not all bad then.

  2. Paul Crawford Silver badge


    My own concern is how long would such a system continue work given the presence of various contaminants in the air, lichen, bird crap, etc.

    1. Anonymous Coward
      Anonymous Coward

      Re: Lifetime?

      With nano-particles a surface becomes self-cleaning - apparently.

      1. Anonymous Coward
        Anonymous Coward

        Re: Lifetime?

        When I was a student, I had one of those self-cleaning ovens. It was very effective. Strangely though, it seemed to stop working about the same time as my flatmate moved out.

      2. Chemist

        Re: Lifetime?

        "With nano-particles a surface becomes self-cleaning - apparently"

        Certainly I've seen examples of titanium dioxide nano-particles being used for self-cleaning ( in sunlight) - not sure of anything else unless they have some with non-stick properties.

        1. Arthur the cat Silver badge

          Re: Lifetime?

          Certainly I've seen examples of titanium dioxide nano-particles being used for self-cleaning ( in sunlight)

          I've got self cleaning glass in a dormer that would otherwise require the window cleaner to have scaffolding or a cherry picker. It works - but slowly, and needs both sun and rain. The TiO + sun encourages the contaminants to oxidise and unstick, the rain then washes them off. Fine for small things, but large bird droppings(*) can take 3 months or so to disappear, and during long dry spells(**) everything just sits there slowly turning grey.

          (*) Parenthesise as you will.

          (**) I'm in East Anglia, we get them(***).

          (***) Although not this winter.

  3. Anonymous Coward
    Anonymous Coward

    "All-weather solar cells are promising in solving the energy crisis"

    Come on - what exactly is the energy density of impure rainwater? Pretty low I'd expect.

    Furthermore: if it's the chemical energy which is useful, there seems no particular reason to combine it with expensive solar cells. You can just collect it in a barrel and have a separate system for extracting the energy.

    1. Anonymous Coward
      Anonymous Coward


      I wonder what the difference is between the amount of power generated by this and putting a turbine in your downpipes......

  4. AMBxx Silver badge

    Measuring the efficiency

    I understand that you can measure the efficiency of the solar cell part - it's just how much of the potential energy from sunlight that's converted.

    How do you calculate the efficiency of the rainwater bit? What is the potential energy of rainwater?

    1. This post has been deleted by its author

    2. JeffyPoooh Silver badge

      Re: Measuring the efficiency

      In terms of solar power for wide application, the only efficiency that matters is 'watts per $£€'.

      By that measure, this is a stupid concept.

  5. Sam Liddicott

    Roof tank?

    Catch the water on a roof tank and then let it through a low-speed turbine... how would that compare to the panels?

    1. Esme

      Re: Roof tank?

      Nope - not cost-effective. Apologies, but I can't find the relevant bit from the xkcd site, but Randall Munroe looked at this idea (which many, many people think of at some point in their lives) and IIRC fount that it'd take decades if not centuries to recoup the costof installation.

      Right, I'm off (out) tolunch...

      1. JeffyPoooh Silver badge

        Re: Roof tank?

        Esme "...decades if not centuries to recoup the cost..."

        Actually, it's common for 'Green' projects to require MULTIPLES OF INFINITY to achieve breakeven of either fiscal or embodied resources. In other words, a 'Green' system might require FOREVER to earn back just A FRACTION of its cost.

        The concept of 'multiples of infinity' payback for 'Green' investments is both hilarious and massively tragic.

        Innumeracy is a much bigger issue than the 'deniers'. The airheads in the Environmental movement do far more harm than the daft but mostly-harmless skeptics.

        1. Anonymous Coward
          Anonymous Coward

          Re: Roof tank?

          The solar PV panels on my roof have significantly reduced my carbon footprint in the year since they were installed. some of the energy produced goes into charing my Hybrid Car. So for short journeys (< 20 miles round trip) I run totally on battery. No petrol consumed. I've not had to fill up since March 17th.

          The rest is fed back into the grid for which I do get paid.

          I estimate that the ROCI for the panels is around 3 years at current usage (fuel costs and ££ income from feedingthe grid).

          1. Killing Time

            Re: Roof tank?

            It's commendable if carbon footprint is your principle concern however the finances would be mine.

            I would be interested to know if you factored in the additional cost of purchasing a plug in hybrid? At my last investigation there was a significant cost uplift in comparison to a straight forward hybrid or combustion model.

          2. Doctor Syntax Silver badge

            Re: Roof tank?

            "I estimate that the ROCI for the panels is around 3 years at current usage"

            That's because everyone without solar panels is subsidising you.

            1. AMBxx Silver badge

              Re: Roof tank?

              You could always just use mains water to fill a tank in the roof void. Each time the tank fills, just release the water through a mini turbine.

              Mines the one without a water meter!

            2. Nigel 11

              Re: Roof tank?

              That's because everyone without solar panels is subsidising you.

              That's partly because everyone without solar panels is subsidising you.

              Anyway, money is a poor guide to sustainability. When you are doing anything that requires burning fossil fuel, where does global warming feature in your rate-of-return calculations? It's worse than saying that vandalism increases the country's GDP. (Which it does, if/when the damage is repaired). When the sea rises and swamps much of the World's most desirable farmland and real estate, the damage will be irreparable.

              A better measure is EROEI (Energy return on Energy invested). Solar panels now score well, even using a 20-year life expectancy for panels which I suspect will be lasting a century or more once any 20-year design "bugs" have been ironed out of their design, and even if sited in a seriously sub-optimal climate such as the UK's. In the best locations for solar panels (sunny dry places) it now takes just over a year for a panel in an optimal location to generate enough energy to generate another panel from raw materials. That number is still improving quite rapidly. (To say nothing of the potential of perovskite panels replacing silicon ones. Watch that space).

              The energy storage problem does urgently need a solution, though.

              1. StudeJeff

                Re: Roof tank?

                I'm all in favor of energy and recycling ideas that make economic sense. If something has a reasonable payback or (in the case of recycling) recycling a material is cheaper than making it new I'm all in favor of it. In fact there are some really interesting products, such as deck planking, that are made almost entirely from recycled material that otherwise would have just gone into a landfill.

                However global warming does not figure into my rate of return calculations at all. I'm REALLY skeptical about the notion that we are having a significant effect on the climate of a whole planet, and even more skeptical that anyone can come up with accurate figures on how much impact any single project would have on the Earth.

                1. M man

                  Re: Roof tank?

                  Estimates are that Humans are releasing the carbon that took a million years to lay down in ONE year......if that not a big enough number for you.

  6. Alister Silver badge

    lightbulb moment...

    OK, so here's an idea that's just come to me...

    Would it be possible to use piezo-electric devices to generate electricity from the actual force of the rain drops falling on a surface?

    1. Brewster's Angle Grinder Silver badge

      Re: lightbulb moment...

      But how much energy would it generate? My guess is there's more chemical energy that gravitational energy and that's its easier to harvest. (A raindrop will bounce so it will retain most of its kinetic energy.)

    2. JeffyPoooh Silver badge

      Re: lightbulb moment...

      Perhaps possible, but it should be criminal to pursue 'Green' energy projects that would never recover enough energy to recoup their embodied resources.

      A simple legal solution to this huge problem might be that any manufacturer of such systems must, within one year of startup, power their entire 'Acme Rain Drop Energy Harvester' factory by the very same technology installed on their roof. Fail to do so, Life in Prison.

      1. Mark 85 Silver badge

        Re: lightbulb moment...

        Fail to do so, Life in Prison.

        That should fill up any unused prison space pretty quickly. While you're at it, why not give them a treadmill or stationary bike with a generator on it. Then they can put power into the grid for x hours a day. Oh wait.. that might be considered "cruel and unusual punishment" or even "slave labor".

    3. Bill Gray

      Re: lightbulb moment...

      Dunno how much _chemical_ energy would be available (seems to me as if it would be peanuts), but both the "gravitational energy from impact" and the "gravitational energy as it drains off the roof" ought to be easy enough to figure.

      says raindrops hit at about 10 meters/second.

      I live in Maine (northeastern US). It's not a rain forest, nor is it arid. We get about 1.5 meters of rainfall per year.

      We have a medium-size, maybe largish, house, with a footprint of about 80 square meters. Over the course of a year, we accumulate 1.5*80 = 120 cubic meters, or 120 metric tons (or tonnes... just remembered this is a UK site), or 120000 kilograms, of water.

      The energy from impact is 1/2 mv^2, or (120000 kg) * (10 m/s)^2 / 2 = 6 million joules, or a bit under two kilowatt-hours. We have rather high power rates here in the Great State; that would cost us about thirty (US) cents. (I'm assuming 100% efficiency in harvesting the energy.)

      However, we _did_ build a rather high house. The drainpipes let those 120 ton(ne)s just drop two stories plus a bit to the ground, about six meters, currently harvesting none of that valuable energy. Rounding 'g' to 10 m/s^2, that's 120000 * 6 * 10 = 7.2 megajoules, or two kilowatt-hours, or about ten cents worth of electricity, completely gone to waste.

      The energies involved are not very different, which makes sense now that I think of it. Falling off a five-meter roof would result in hitting at "raindrop speed" of ten m/s.

    4. Pirate Dave

      Re: lightbulb moment...

      "Would it be possible to use piezo-electric devices to generate electricity from the actual force of the rain drops falling on a surface?"

      When I clicked into the story, that's what I thought it would be about - a new use for that "generate electricity from people walking across a pad" thing that came out a few years ago. It's an interesting concept, but it might require a hail storm to generate any significant electricty.

  7. Anonymous Coward
    Anonymous Coward

    I remember back in the '80s some English electrician came up with a way to tap the hysteresis curve and even had a working proof of concept that gave a tiny amount more energy out that in that he hoped would scale up, whatever happened to this?

    I would have thought given all the RF being pumped out for comms in the UK that some efficient leeching system to tap it would have been made by now

    1. ARGO

      Power from radio

      Like this you mean?

    2. aelfric

      I can only imagine it was revealed for the scam that it was. Or else it wasn't revealed but still sank without a trace because it was just a scam. Whatever happened, it was a scam. It cannot work. I don't even need to know the details of this particular scam but I can say with absolute certainty that it was a scam. Aside from anything else, including the laws of physics and thermodynamics, if it actually worked in a provable fashion, it would be the biggest news in the whole of history, both past and future. It would mean pretty close to as much free energy for everyone as they wanted. Materials costs would drop through the floor.

      1. Anonymous Coward
        Anonymous Coward

        Yeah there is no way an EM source could be tapped for energy

        like the sun for example, there is absolute no way to tap that and wireless charging is a scam.

        This electrician had exactly your problem when trying to patent it because it was immediately identified as a perpetual motion machine and his education was not sufficient to actually describe the systems involved nor say where the extra energy came from.

        As to things disappearing there have been many inventions that never went anywhere for reasons other than being scams, double key encryption and electronic computing were both blocked under the official secrets act not to mention those inventions that got blocked in case they change the market too much like stainless steel razor blades or why we are still using internal combustion engines when we know how inefficient they are.

        Given that our fossil fuels are still running out then being less blinkered might be a good idea, the problem with energy transfer via EM is from memory that power decreased by the square of the distance but when you don't have to pay for the initial energy then any for free is a good thing.

        1. Anonymous Coward
          Anonymous Coward

          Re: Yeah there is no way an EM source could be tapped for energy

          "... the problem with energy transfer via EM..."

          "The" problem? Just one?

          Pigeon lover Nikola Tesla knew how to power the entire world with a handful of towers. Unfortunately the margin was too small...

          " from memory that power decreased by the square of the distance..."

          The Inverse Square Law, from memory. Like, Wow...

          1. Anonymous Coward
            Anonymous Coward

            Re: Yeah there is no way an EM source could be tapped for energy

            I am interested what then in your opinion is more of a problem to EM energy transfer than the inverse square law, please quote percentage losses involved because distance is "THE" limiting factor of EM transfer.

            As to the inverse square law I didn't bother to look up, I just remember the equation hence "from memory".

            This discussion is about solar power which is in case you were unaware IS a form of EM energy transfer, one which is quite profitable mostly because we do not have to pay for the sun to provide the energy in the first place.

            So since you are so knowledgeable what are typical comms flux densities and power from adjacent to 1 mile from source, baring in mind some people live next door to all sorts of transmitters

  8. BurnT'offering

    Not solar cells

    Solar-pluvial cells, perhaps

  9. Anonymous Coward
    Anonymous Coward

    Wait, the internet is always telling me that the Chinese don't invent anything...

    1. Anonymous Coward
      Anonymous Coward

      Chinese invented loads of things but the English re branded them

      That 'ill server 'em for getting invaded

  10. TRT Silver badge

    The sun and the rain?

    That's madness!

  11. I Like Heckling

    Rain water into Hydrogen

    I was just reading a news article about a farmer who has converted his farm to be as energy efficient as possible. One of the things he has installed is a rainwater collection system that converts into Hydrogen which in turn powers a fuel cell. He's also got solar and wind energy system with battery storage.

    Considering this is a large farm, it's not suitable for the average person... and they didn't mention the cost... But as a person who is interested in these types of things and who hopes to one day build their own home complete with as many energy saving systems as is reasonable. I'm definitely intrigued by some things... Just not this one, which @ a little over 6% efficient is next to useless and wouldn't even generate enough to power some lights at night (depending on the KW rating, and the max for a residential home is 4KW).

    If.. and I admit it may take a little lottery win to accomplish what I want.. I'd be having solar built into the room, a ground source heat pump (powered by solar and with battery storage for low sunlight days) for a virtually free running cost heating system. Solar hot water system and larger cavities with extra insulation and triple glazed windows to maximise thermal retention. This will keep the house warm in winter and cool in summer.

    If space allows I'd also have some kind of wind turbine to add extra capacity... even if it's just a small one to power some exterior lighting in the garden.

    The cost would be a little higher... but as you are building these things into a new home, it's actually a lot cheaper to build in underfloor heating throughout as you build.

    As a backup I'd have a wood burning stove centrally located in the home which would help heat the home during the winter, and to fuel that (space permitting of course) I'd plant some fast growing trees that could be cut back after a couple of years to provide most of my own fuel.

    Some sewerage could be treated through a gravel and reed bed into a pond.

    I have actually done a lot of research into it, and could build a small and very sustainable home for about the same cost as a normal 3/4 bed home but with about 20% of the running costs. Given that I'm spending around £1300 a year on my current inefficient (old 50's built) for all utilities and have gone almost as far as I can with insulating it (walls, roof, windows, flooring underlay) and underfloor heating and solar panels are not an option (roof faces wrong way, and concrete floors)... that's a saving of almost £1000 a year. So all of that would pay for itself in 10-12yrs when you factor in what you'd get back from FiT (if they still exist).

    If local councils and housing associations installed solar panels on every suitable roof of their properties... low incomes families would benefit from lower bills and HA/LA would benefit from the Feed in Tarrifs creating an extra revenue stream to pay for local services... I've been advocating this for the last 10yrs and it's only in the last few that I've heard of it happening.. although it's rare.

    I'm not some raving greeny, hippy, peace loving beatnik... But I do think that everyone should be using technology to reduce our personal consumption of energy... I think electric cars are a waste of time and are nothing more than a stop gap. Investment should be made into building the infrastructure for fuel cell vehicles... In 10yrs there should be a fuel cell filling station within every town with more than 20,000 people. Hydrogen is after all the most abundant gas in the universe (aside from what comes of of any politicians mouth... although that's probably mostly methane based)

    Long post I know... but if everyone did something... it would make a massive difference.

    1. Lee D Silver badge

      Re: Rain water into Hydrogen

      I stopped reading at:

      "One of the things he has installed is a rainwater collection system that converts into Hydrogen which in turn powers a fuel cell."

      The energy (electrical, chemical or otherwise) to convert even the purest water into hydrogen is at best precisely equal (but probably, with losses, much more) than that which you can generate from a hydrogen fuel cell based on that hydrogen. And will give you a ton of oxygen too which he's presumably wasting as that isn't used in fuel cells. Even with the oxygen, the total energy from using the hydrogen and oxygen will be limited to precisely the energy used to separate them in the first place from the water.

      At best, it's an inefficient energy STORAGE mechanism. We have pretty good batteries already.

      Precisely the same problem as all the other "green" methods - sounds great, fails to completely describe the system and/or understand that a closed system like that it still ultimately dependent on the same energy inputs and outputs.

      Solar panels? Only valid in certain parts of the world, with subsidies, en-masse, using rare materials, with a lot of storage and infrastructure to use them.

      Wind turbines? Only valid in certain parts of the world, with subsidies, en-masses, using large structures (usually built with plastics that "could be built with other biomaterials" but never are), with a lot of storage and infrastructure to make them viable.

      Sure, you can "profit". In dribs and drabs, here and there. Or you could just stop building primary school projects and getting those kinds of energy returns and build one big huge nuclear station out in the middle of nowhere and operate it for several thousand years without having to do very much at all (in comparison to several thousand years of solar cell and wind turbine maintenance in bright sun / high winds).

      1. Charles 9 Silver badge

        Re: Rain water into Hydrogen

        "At best, it's an inefficient energy STORAGE mechanism. We have pretty good batteries already."

        Pretty good? They're not really all that efficient, they don't scale well, they don't really last that long under prolonged use, and many have an issue with spontaneous combustion. We REALLY need something better.

  12. DougS Silver badge

    How much energy comes from the rain?

    There are no figures here, if it generates an extra 0.1% compared to regular solar panels then this is pointless. If it generates a significant fraction of water a solar cell does, then why not station a bunch of these at Niagara Falls to catch all that spray coming off it?

    I suspect the energy recovered is so tiny it is just a press release opportunity but not anything that will ever be practical to include in a solar cell. They want to counter the dumb "but what about when it is raining" objection to solar cells, but if you say "yeah, now when it rains we generate a couple watts an hour" that will just make people laugh at the absurdity of it all.

    Unless the paper's mention of hundreds of microvolts and microamps is actually more impressive than it sounds to me...why that's almost a milliamp at a millivolt, if they could boost it up to those levels that would equal a whole microwatt! Assuming that's per raindrop, that's only a million raindrops to generate a whole entire watt!

  13. Anonymous Coward
    Anonymous Coward

    "professor Peizhi Yang of Yunnan Normal University". I wonder what they study at Yunnan Abnormal University?

    1. Pirate Dave

      I work at a University that was originally called "<snip> Normal College" (snipped for obvious reasons). My understanding is that it's an old-ish name for a 2-year school that trains elementary school teachers.

  14. hoola

    Difficult to produce

    I would bet a large doughnut on the fact that from an energy perspective it will never be viable. For something like this to actually have an impact there has to be the possibility that you get more energy out than went into making the thing in the first place. This is where so much of the PV solar industry falls down. The embedded CO2 in the panels is horrendous and you really have to question if we would be better off just burning the coal, oil, gas or whatever to make more electricity or petrol in the first place.

    It does however give the greens a warm fuzzy feeling and the PVs bandits a license to print money, ripping bill payers off in the process. But his is a Government scheme so it must be okay.

  15. NohSpam

    Is solarPV a waste?

    My understanding is that:

    1/ Solar thermal has a longer generating opportunity than solar PV, because it can exploit radiation that passes through clouds, which PV cannot match.

    2/ The larger a Stirling engine is the more efficient it is (and I believe a large thermal gradient helps too)

    So I don't understand why Solar farms use PV when they could use solar thermal to create a significant thermal gradient to a large (and pretty efficient) Stirling engine, to turn its kinetic energy into electricity directly or for example, store the heat in an aquifer to help drive the Stirling engine at other times.

    I realise energy conversion losses will be in play here but I understand PV isn't very efficient, particularly in a cloudy country like the UK?

    1. Anonymous Coward
      Anonymous Coward

      Re: Is solarPV a waste?

      I'd need to check, but I suspect part of the answer to (1) is that despite its wavelength limitations, PV can do better as a whole than solar thermal because while solar thermal can pick up infrareds and so on, it can exploit less of the higher wavelengths.

      As for (2), even with a large thermal gradient, what is its mechanical capability? How much torque can it produce? I would suspect that if it were truly worthwhile, Stirling generators would find a home in a place like Iceland, home to perhaps the largest temperature differential in nature (volcanic heat right next to the Arctic Ocean).

      1. StudeJeff

        Re: Is solarPV a waste?

        In Iceland isn't the temperature difference enough they can use turbines?

        1. Charles 9 Silver badge

          Re: Is solarPV a waste?

          Meaning turbines are more efficient than Stirling engines?

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