UK renewables company Naked Energy has invented Virtu, a hybrid solar panel that simultaneously heats water and generates electricity.
The technology, developed by Naked Energy’s chief engineer Richard Boyle, integrates an electricity-generating photovoltaic cell into a hot-water-generating solar thermal panel. The solar thermal panels are placed into vacuum tubes and are unaffected by ambient temperature.
Nick Simmons, chief financial officer of Naked Energy, told The Engineer: ‘We can create more useful energy per square metre than conventional panels on the market today.’
Through combining the two technologies, Boyle was able to address one of the fundamental problems facing photovoltaic cells.
‘When photovoltaic panels get hot they become less efficient. For every 1º rise in temperature [from 25°C], you lose half a percentage point of efficiency,’ said Simmons. ‘A very efficient photovoltaic panel has a maximum efficiency of approximately 18 per cent. But by the time you get up to 65°C, which is quite a normal temperature on the face of a solar panel, you’re down to something like four per cent efficiency.’
Heat is transferred away from the photovoltaic cells with a patented thermosyphon technology that harvests the unwanted heat from the photovoltaic cell to heat up water.
As a result of taking the heat away and cooling down the photovoltaic cell, it is possible to generate more electricity than conventional photovoltaic cells.
‘We bond the photovoltaic cells to the thermosyphon, so there is a very small temperature differential between the photovoltaic cell and the thermosyphon. This means the photovoltaic cells are maintained at a uniform temperature,’ said Simmons.
Naked Energy has been working closely with Prof Peter Childs, an expert in heat transfer from Imperial College London, to further improve the efficiency of the solar panels.
Childs recently found that Naked Energy’s photovoltaic cells generate 40–45 per cent more energy as a result of the heat transfer method.
‘Sussex University is helping us put the product into production,’ said Simmons. ‘It’s been helping us make dyes and various tools to press the substrate of the thermosyphon, so we now have a way to manufacture the technology at scale.’
Naked Energy is currently on a trade mission to San Francisco that is being run in association with the Technology Strategy Board, UK Trade & Investment and other private sponsors.
Brilliant device. Congratulations to all concerned. Now just build a great big factory to produce them here in the UK and export them round the world. Perfect.
This is an excellent idea if it can be done cost effectively.
For some time I have been suggesting to people who already have Solar Panels that they should rig up a pump to take water from their water butt and feed a sparge pipe which dribbles water over their arrays to keep them cool. It then returns under gravity to their water butt. However no-one takes me seriously.
For ease of installation the pump could be powered from its own small solar panel so that it only runs when there is a high level of sunlight.
There may be a few minor wrinkles to iron out such as melting water butts but hey nothing’s perfect.
All it needs now is the addition of the new see through photovoltaic film for a triple effect. Anyone got any further ideas?
About time too! Having one system on the roof to do one thing when there is a need for two systems, electric and generation and hot water was always half a job and a waste of space. The report is very illuminating where it states only 4% effectiveness when the photovoltaic panels get hot. Companies who supply these systems seem to have forgotten to mention this!!
I hope this product can be produced in, and marketed from the UK; it would be a sad day if we cannot do this and have to sell yet another good idea to a foreign company in order to get it made. Come on local enterprise groups get in contact with Naked Energy.
We have an sub division in Australia and for years I’ve thought why doesn’t someone combine the two. Excellent idea and hopefully durable product we’ll sell them in Australia for them.
Great product but a fully certified hybrid panel (including MCS) can be purchased today! See http://www.volther.co.uk and the manufacturer http://volthersolar.com/
Unfortunately, this system is not so useful in ME or Africa because the excessive heat there does not let any utilization for such accumulated heated water.
Yes !! I have an idea to utilize the product of heated water:
It is the Thermal Desalination, which is most needed in MENA region.
One of the observations about currently available PV installations is the thermal build-up so it was about time that a system to use the heat as well as the electricity generated. Interesting that we now have an indication of the inefficiency levels as the panels heat up.
Fits exactly our need at the summer cottage. Gan we get additional information.
We would also be glad to act ast test & demo site.
This dual generation was done back in the 1980’s on an experimental basis. As far as running water over the cells as suggested by a commentor, there would be mineral buildup on the panels. It would be better to spray it on the back of the panels and have a small solar powered fan blowing over a radiator to cool the recycled water.
I don’t understand how this works. If I want to keep the solar cell temperature to say 30 degrees then the water temperature has to be less than that. What can I do with such low grade heat other than build a cooling tower? In some countries it’s difficult to get cooling water at less than 25 degrees.
Please check my maths. 60 degrees is 35 degrees above Standard Temperature and Conditions (STC at which the efficiency is quoted) hence we have a loss of efficiency of about 35 x 0.47% say 16%
If the efficiency at STC is 18% then isn’t the efficiency at 60 degrees (100-16)*18% ie .84*18 = 15.12% ?
To answer Graham Revill’s point, I think the main objective is to make use of the thermal energy and use it to heat water. The improvement in efficiency of the solar cells is a secondary effect and will only be effective while the water is heating up. Once the water reaches its target temperature the solar efficiency simply returns to its lower value.
In the matter of the reduced efficiency due to heating, I would agree that the figure of 4% given in the article is highly dubious. We all know that the forward voltage of a silicon diode (solar cell) is about 0.6V and that the temperature coefficient is 2mV/deg.C, it’s engraved on my heart. So at 65 deg.C the voltage will drop to about 0.6 – 40 x 2mV = 0.52V, the current will remain about the same. So the power output and hence the efficiency will drop by a factor of 0.52/0.6 = 0.87. So a solar cell which has an efficiency of 18% at 25 deg.C will drop to about 0.87 x 18 = 15.7%.
A similar technology was developed in 2004 at Harvard University. For some reason it never made it to market.
It should be noted that there is an additional advantage to this design. Over time, solar panels break down. They slowly degrade as heat breaks down the catalytic layer. That is why you need to replace solar panels about every 30 years. By cooling the panels, you can slow the degradation, so these hybrid panels should last much longer than conventional solar panels.
correct Graham, the figures given in this story are utter nonsense.
I think what they’ve done is directly taken the percentage figure for the losses off the percentage efficiency figures, so 18% efficiency minus 14% losses = 4% efficiency.
as opposed to the reality of the correct equation being
18% efficiency x (1-14%) = 15.48% efficiency.
it’s a shame that such obvious rubbish should make it onto a website called ‘theengineer’, and that a company with a decent looking product should resort to such low tricks to market itself.
This superficially seems like a good idea, but it doesn’t work as well as it might because the solar water soon gets up over 45C so it’s not cooling the panels very much. And meanwhile the surface area of the PV panels is reduced somewhat.
And combined PVT panels like this tend to be very expesnive. There are some Germans models available too, and they are certainly expensive. It’s _much_ cheaper to just get standard PV and thermal panels, and the efficiency isn’t going to be that much lower.
These panels will make sense in some cases but I’m not convinced it’s worth the money without seeing some data (and prices). It’s a pity because it seems such a sensible idea.
One question, what temperatur will the water get in this example. 25 degrees C is nor very useful for heating anything.
NG Norman. The water temp is controlled by the storage tank temp. So it starts off cold (10-15C?) then heats up over time until it’s useful for DHW at 40C and above. The PV will essentially be help at whatever the tank temp currently is. As I say this only improves your PV numbers when your tank is cool 🙂
Things can be arranged so that the solar heat exchanger temp never gets that hot (really big tank, bottom coil), but that just means that you mave to use some other heat source to raise the DHW to useful temp.
In practice this sort of system gives you an area advantage (use the same area for both PV and DHW, sharing the available energy) and a marginal efficiency improvement in PV, at least at some times of the year. It’s quite hard to estimate the actual gains over a year.
Great idea, cooling and heating combined.
If you got together with Michael Reynolds who builds Earthships, I’m sure he would be interested.
four should read fourteen (65-25=40 x 0.5 = 20% less ….. 18% x 80% = 14.4%)….
But nevertheless a fantastic improvement and all that heat energy as a bonus.
Does the panel get RHI and FITs?
Here’s the thing… in the summer you have way too much heat to use domestically, and have to actively cool it somehow. This is going to be expensive.
But nobody is seeing the problem here, 2 x solar thermal panels spend over 60% of the summer in stagnation at 150+ what ever will happen to a moderate 2.5 – 3.0kWp array?…….end up even hotter than non integrated panels. only use is for a swimming pool,otherwise it’s a nonsense.
I am looking at integrating water cooled solar panels into a home design that will equate to basically having a water cooled roof, so while generating power it will reduce cooling need and costs While using the thermal energy to provide not only hot water but purify that water for consumption and use in alternative fuels.
Sounds interesting.
Personally, I would run the system through a heat pump – that will increase the temperature of the water going to the tank, while cooling the return flow to the panels.
Get a 3000-litre Akvaterm geo/solar tank, and you have a heat dump that will take a fair amount of energy – but also hold on to it. When the tank is full, switch to a cooling circuit with a radiator that simply cools without using the heat pump.
I would be interested in getting involved, but there is precious little information available at this point. Prior to discovering these, I had been looking at a similar PVT product by solarus.se – but despite several trials and university papers, it still does not seem to be available to buy.
PVT panels have abeen around for the past 7-8 years, first one was produced by solar zentrum in Munich.
I have been a designer of solar thermal systems since 1991, which started with the design and development of a Thermal Store, as the perfect water tank for all solar thermal systems, so you can use 100% of solar heat to support day time home heating as I have done for 12 years.
My own designed PVT panel, 100% different to all on the market will be launched this year at a price of £198.00 + shipping for a 250 watt MCS approved PV panel.
My PVT installation kit for the solar cooling part of the PVT costs around £400.00 and separated to your existing potable water tank.
our years of R&D in China (sorry but no interest or money in UK for this) and No interest from DECC or RHI.
Anybody interested, feel free to contact me for the details