Generating Electricity & Heating Water With One Technology

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Editor’s Note: We’ve written about hybrid solar panels in the past, but they are clearly far from being mainstream. Below is another company that is selling solar panel systems that both generate electricity and heat water. Check it out:

A Swedish company using technology based on 12 years of research is now marketing a product that can produce both electricity and heat with solar power.


Solar panels don’t work at optimal efficiency when they become too hot, so Solarus has developed a way to keep them cooler and at the same time collect the heat, which can be used in a hot water boiler. The hot water can be run through a tap so people can utilize it.

This hybrid system is more energy efficient because it improves the electricity production of solar panels while heating water. One square meter of a Solarus solar panel can produce 136 watts of power and 400 watts of heat. Solarus says that it can achieve 30 cents/watt with a 40 MW solar power plant, when you include the heat production component.

Imagine a 40 MW solar system for a manufacturing plant and all the hot water that would be created as well.

A standalone product with 300 watts is planned for small households. It will generate electricity and hot water.

Solarus employs blue economy principles, which are based on physics and wasting nothing.

In fact, the founder of the blue economy framework has collaborated with Solarus. “Solarus AB… began manufacturing solar panels out of recycled carbon fibres discarded by the aerospace industry. Today, Solarus AB is able to offer cost-attractive and competitive solar technologies without the aid of government subsidies.

If the thermal part of the equation doesn’t sound too impressive, just consider that most homes in Israel use the sun to generate hot water.

Hot water from solar is not a trivial contribution to a cleaner, greener world. We might tend to think of solar power as only solar panels used for generating electricity, but hybrid systems do exist and they can be very beneficial.

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Jake Richardson

Hello, I have been writing online for some time, and enjoy the outdoors. If you like, you can follow me on Twitter:

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40 thoughts on “Generating Electricity & Heating Water With One Technology

  • Makes sense to me. Why waste free heat? Especially when cooling the panel helps efficiency?

    I know, the devil can be in the details–complexity, cost, and so forth. At a minimum, it requires s a whole other plumbing job! But perhaps Solarus has got the math working out favorably. I’m honestly not sure how to assess the quoted cost.

    • Many people are installing these systems separately – solar PV for electricity and solar thermal for water so combining them while definitely a more complex system, should only require the same endpoint connections – plumbing for water and wiring for the power.

      • Restaurants and bakeries use tremendous amounts
        I have a friend that runs small local very busy bakery, he installed solar hot water and cut his oil heating bill drastically .

        • Did your friend connect the heat to the oven or is it only for hot water needs?

          • He uses massive amount of hot water. Ovens not heated by solar hot water. Saved a lot of money. Also works well crowded city location, solar hot water can heat up without direct sunshine.

  • “Imagine a 40 MW solar system for a manufacturing plant and all the hot water that would be created as well.”

    Imagine an industrial process that has a use for tons of water at 70 deg. Apart from a large laundry or municipal swimming pool, I can’t think of one.

    • This is along the lines of the big CHP – combined heat and power push in the US. There are many industries that generate heat through boilers – whether for facilities or otherwise and obviously need power as well. I have worked in a paper plant and while this wouldnt generate all the steam or power we needed (steam is used to dry the paper and paper machines use TONS of power), it could be used to help increase the input water temp which would cut how much energy would need to be put into the water to make steam. I’m sure there are similar upstream applications – like in most homes.

      For reference, the plant used ~36mw of power which is current generated via natural gas turbines…which we also tapped for heat/steam 🙂

      • Process heat needs the real thing, not the bathwater you get from a solar thermal panel. The saving from part-heating will be rather small. PS: I have two and am glad of them, especially as the Spanish government’s war on pv makes adding it a quixotic gesture.

    • Some industrial biotechnological processes fall into that category, as do several chemical reactions. Reactors need to be kept at a constant, fairly high temperature (usually somewhere between 30 and 70°C) in order to keep enzyme activity and specificity at an optimal level. I’ve seen fermentation units that needed 5MW of heating a piece.

      And we’re not talking about obscure, small scale reactions here. Cellulosic ethanol involves a hydrolysis step at roughly 55°C that needs constant heating. Penicillin derivates require 35°C-ish. Non-cariogenic sugars require 40-60°C. All are produced at a scale of thousands of tonnes anually. And those are examples from biotech, if you look at chemistry the scales are even larger.

      Same story in some types of food processing and pharmaceuticals. Both are examples of large industries that involve processes at modest temperatures.

      It’s of course far from clear if those plants would be interested in solar power. Current heating systems were designed with a small volume of high temperature steam in mind, because that’s what has historically been cheapest and easiest to acquire. There is no technical reason why this kind of reaction couldn’t work well with a large volume of warm water, but it would require converting entire installations.

      The relatively high cost of solar combined with the low cost of gas and the need for converting and redesigning processes will prevent this from catching on in the forseeable future. But who knows.

  • There is an intense discussion going on right now in green building circles. Is solar thermal dead? Has Pv, at the new price, replaced it? It seems it has. Electric water heater and Pv are cheaper, longer lived and much more reliable than solar thermal. So the question remains, why add on solar thermal to a technology (PV) that is superior. Just add more PV and eliminate the plumbing part since it is costly and prone to repair.

    • and dont forget
      a heatpump consumes 1 kwh and delivers 4 times more kw heat or warm water COP 4
      or 5 kw heat with 1 kwh electricity. COP 5
      I use this system in my house for 2 years now.
      it is like 1 dollar in 4 dollars out.
      so imo thermal solar is out

      • Will E, yes, the next discussion is exactly this: heat pump water heater or plain electric tank? Is it better to put more PV on your roof (if you have the room) or pay 2.5 times as much for the heat pump water heater. At American price of $3.75 installed a slight advantage goes to the electric resistance water tank and more PV. At German prices of $2 watt installed, it is significantly cheaper to go bigger on PV and use conventional water heater. I am contemplating the choice right now off grid which has different implications than on grid. Solar thermal is definitely dead, the only choice is between heat pump and ordinary electric. Interesting times we live in!

        • It also has to do with where you live and the cost of laying the pipe. It isn’t the same in all soil/rock types.

    • I remember this study as well. The new piece that this tech introduces is that it also cools the PV component which increases efficiency. Is it enough? Dunno.

      • Kyle, it cools it in the summer which is great, however you have problems with plumbing in cold climates. That is why it is better to have plumbing inside out of the weather. It is easy to access, not prone to stresses. Nothing more of a nuisance to access the back side of roof mounted solar panels in winter looking for a leak.

        • With this company based out of Sweden, I would expect seasonality to be taken into account, but don’t have the details. Maybe it’s an override for winter that bypasses the external plumbing…?

          • The original article on Green Building Advisor, was titled, “Is solar thermal dead?” that was 2011. A new article is titled “Solar thermal is really, really, dead.” All the reasons for this are gone into in the article, along with about a 100 commenters, many of whom install both Pv and thermal for a living. You can see some are just attached to the old thermal technology and are having trouble realizing its limits. The new cheap PV just changes everything!

        • Could be turned to advantage. A closed system would run glycol which wouldn’t have freezing issues, and could be used to deliver heat to the panels for snow melt in Winter.

          • Actually that is a brilliant idea. In fact I have a set of panels that is rooftop and hard to clean snow from. I suggest though, that heat cable on the back side would accomplish the same thing for far less than the plumbing cost. I imagine you all know that plumbers cost a lot of money per hour. I was once crossing the U.S. Border on the train. The customs guy said “what are you?” I said “I am a buddhist monk” he said, “what’s the next thing up from a monk?” I said, ” a plumber”. He laughed and let me through.

    • Vensonata, that is what appears to be happening in Australia. Solar hot water is being squeezed by solar PV thanks in part to low to zero feed in tariffs for electricity from new rooftop solar and restrictions on electricity exports from solar in that hell we call Queensland. Yes, that’s right, in the same state where 47 people died in floods just 4 years ago, a significant amount of clean solar electricity is banned from being exported to the grid and so is simply wasted. This is in a state that has one third the solar capacity per capita as South Australia. Why the difference? I can’t imagine. One a completely unrealated note, South Australia has one small stranded brown coal mine while Queensland has 52 coal mines, some quite massive, and in 2012 produced 194.5 million tonnes of coal.

      But solar hot water takes up less roofspace than an equivalent amount of solar panels, so some people will prefer it for that reason, and in places such as China which has both less roof space per capita than Australia and extremely low installation costs by our standards, solar hot water is still going strong.

      • Yes, solar thermal takes up less space, except perhaps if PV is combined with heat pump. Apparently it still edges out solar thermal in price because of the plumbing and heat transfer coil tanks etc. It wins by a nose at the moment in the U.S. but I am thinking because of the incredible prices in Aus that Pv wins by quite a bit over Solar thermal. Am I wrong?

        • I would have to recommend extra PV panels rather than a solar hotwater system on the basis of cost for most households in Australia. This is despite the fact that in almost all of Australia simpler, lower cost solar hot water systems will suffice as it is warm enough not to require evacuated tubes or freeze protection.

      • Interesting thread! I suspect that whilst the footprint might be less for solar hot water the energy utilisation of the actual space might not be fully maximised because when the water reaches temperature then the system would not output any further energy other than to keep the water at temp. Therefore, I suspect (though I might be wrong) that PV might provide a better ROI for the space taken up in the long run and it would provide better utility for other power requirements, either domestic or for export. Just a thought.

        • A very good point. The most efficient use of roofspace with a solar hot water system requires boosting the temperature of the water with electricity or gas (or potentially something else) in winter or periods of high hot water use.

  • 30 cents per watt is a baloney of a diluted price. It is like diluting a very expensive price per watt of the solar panels with a very large number that is about three times as much.

    So what really is the price per watt of solar PV and the price per watt of “useful” water heating?

    This technology is not new.

    • real price of solar kwh
      installation cost 6000 for 4000 kwh a year
      30 year production is 120000 kwh
      6000 divided by 120000 is
      5 cent a kwh.
      this is a 1 on 1 solar ray index, where I live
      when there is a 2 on 1 solar ray index
      spain, california
      you get a price of 2.5 cents a kwh.

      • The system’s cost are based on peak power rating and not on energy production. A 30 year calculation of energy production in your case, you should factor in the net present value of the 30 year revenue, it is not a simple arithmetic.

        • Hmmm…the calculation is usually quite simple, nothing to do with peak watt power. It is based on annual solar production, which is easy to determine. Just consult the NREL site PV WATTS. There they will give you a very close approximation of how much annual production based on weather conditions of your area and the angle of your array or whether it is a tracking array etc. They calculate efficiency losses and actual cost per kwh, and if you will save over your local utility rates. It is an amazing resource for free and very accurate. More people should be made aware of it.

          • the price per peak watt power is one of the quick basis of comparisons when purchasing solar PV systems.

            As to the multiyear energy production, you don’t seem to get what Net Present Value is, search the term, and especially google for LCOE and then you will understand.

          • I see…perhaps I see… are you talking about taking the money invested in the solar vs investing it in some revenue producing account? That certainly calls for more complex math. I think about investing in solar as something that must be done on ethical grounds even at some loss, although today the loss is small. In my case, off grid, the choice is diesel or PV. The PV wins economically as well as ethically and in reliability. (As I glance at the PV meter on a fairly hazy morning in February at 10 AM the PV array is bringing in 5kw, like a powerful diesel generator roaring away. And I am so glad our powerful diesel generator is just sleeping quietly like a dragon.

          • Just wanted to say that I love your parable, all of the stories make it quite obvious that you don’t want to awaken the sleeping dragon and have to deal with the damage that they cause.

          • How much does it produce on a bright blue sky day?

          • Tim, it is 11.4 kw peak, so anytime after 10am you can get that 11.4 kwh in your battery bank in one hour or usually partially using it to run the house as well. Theoretically on june 21 in cloudless conditions it could generate about 10 times its rated wattage or 110 kwh! I have actually gotten more than 10 fold on spring days with smaller arrays. On the shortest day of the year December 21 if cloudless it can bring in about 40 kwh. In fact we cannot yet use all the electricity since we store it in a 40kwh battery bank. The left over is enough to produce all domestic hot water and charge an EV. And still not used up! We are still trying to figure out how to maximize use.

          • Wow Vensonata! I am not sure about others but I would love to hear a little bit more about your whole set up (if you were willing) and what Electric Vehicle you are charging. I am yet to install a PV system myself (thinking a minimum 10KW array), spec’ed high enough to enable full power for in-slab electric heating, normal electric hot water heating (I would contemplate abandoning off peak) and hopefully an EV one day.

  • Hot water is energy storage. This is a low cost system + energy storage combined. If the water can be heated to high enough temps to generate steam …

  • It’s a relief to know that this combination, maximising the available efficiency from a given area, is in good hands, “simmering away” because, in the appropriate applications,its time will surely come.
    Thanks, Zachary, for keeping the pilot light lit.

  • What about capturing “waste” heat as electricity with an ORC device? Or storing heat e.g. geothermal for recovery and use as needed?

  • I can’t help wondering why this isn’t combined with Building Integrated photovoltaic. There is a lot of scope to slash the price of solar, if buildings are designed with solar in mind rather than retrofitted as a careless afterthought.

  • There is a domestic company in Longmont Colorado with a very similar package. I’ve not seen it personally. Textile Testing & Innovation.

  • Well, you’ve got three years on me but let this young pup put is his two cents. ;o)

    I think the answer is we quit using heat to generate electricity.

    Coal plants? Close them. All US coal plants should be gone in less than 20 years.

    Nuclear plants? Don’t build any more. Most of the US reactors are aging out and I suspect the rapidly falling price of renewables will make it economically unwise to refurbish more of our reactors for another 20 years of performance.

    Gas plants? I suspect we’ll see them run fewer and fewer hours per year which would make their heat a non-reliable heat source for industrial use. NG should be morphing to only a peaking role.

    You missed one massive energy waster – the internal combustion engine. Replace 20% efficient with 90% efficient EVs.

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