Naked Energy touts hybrid solar panel in tube design

Apr 12, 2012 by Nancy Owano report
Naked Energy touts hybrid solar panel in tube design

(Phys.org) -- A British company, Guildford-based Naked Energy, has come up with a “hybrid” solar panel that has generated much interest in the past weeks because of its design, function, and test results, comparing favorably to traditional solar panels. The solar panel is of the “hybrid” variety because it does two jobs at the same time. The product, called Virtu, can generate both electricity and hot water simultaneously. The company believes that with Virtu they have invented the right design and process to achieve an effective thermal transfer system.

The panel is in a vacuum tube configuration, The tubes have low thermal losses and will produce regardless of the climate they operate in, hot or cold, according to the company.

“The annual yield depends on the application, local climatic conditions and quantity of panels installed. For installations requiring high temperatures for thermally driven cooling or heat storage we are producing matching ‘thermal only’ vacuum tubes, which will be able to produce significantly higher temperatures.”

Virtu, developed by Naked Energy’s chief engineer Richard Boyle, has brought the company an opportunity to explore combined photovoltaic and thermal actions. The company’s patented “thermosyphon” technology harvests 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.

Naked Energy touts hybrid solar panel in tube design

This is not the only hybrid panel on the market, but the company says its product has adjustable photovoltaic panels that could be placed on flat roofs, opening up opportunities that traditional panels — that need to be at a 45-degree angle — do not have.

Naked Energy, founded in 2009 as a renewable energy business, has been working over the years toward its ultimate goal of developing and commercializing a breakthrough solar technology. In 2012, they have reached a turning point. Reviewing Virtu, the Imperial College London found that the panels they tested can produce up to 46 percent more energy than the typical PV panel when the cells are heated to 65ºC.

Naked Energy is prepared for more turning points. The company is working closely with Prof. Peter Childs, an expert in heat transfer from Imperial College London, to further improve the efficiency of the . Also, the company recently took off on a trade mission to the San Francisco, in association with the Technology Strategy Board, UK Trade & Investment and other private sponsors.

Explore further: Using intelligence to unlock the market for electric vehicles

More information: www.nakedenergy.co.uk/

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User comments : 26

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Eikka
2.6 / 5 (9) Apr 12, 2012
More energy perhaps, but if you cool a solar cell with 65ºC water it won't produce much electricity. Thermosyphons or not, there must be a heat gradient for the heat to move to the water, which means the solar cell itself is significantly hotter - 100 degrees or more.

The problem with cooling is that tess than 55 degrees for hot water isn't really adviced because it won't kill the legionella bacteria that may be present in the pipes, and then you get sick. If you use it only for space heating then that's different, it just has to be above room temperature to work, but who wants to heat their homes in the summer? Much of the energy produced that way is simply unneeded.

Sean_W
5 / 5 (3) Apr 12, 2012
I think that the idea would be to pre heat water that would be sent to the water heater. It would use less energy than heating water from cold source like an aquifer but it would still reach the same end temperature. It would not be used for heating a house.

There would always be a heat gradient due to the sun heating the panel. Warm water moves to the water heater and the pv cells work without over heating as new cool water enters.
English-Scientific
5 / 5 (6) Apr 12, 2012
Eikka, we need power and heat all year round, i certainly don't shower and wash my clothes / pots with cold water during the summer and neither do i sit in the dark in the evening. Great idea from a British company and i wish them every success.
djr
4.5 / 5 (8) Apr 12, 2012
"More energy perhaps, but if you cool a solar cell with 65ºC water it won't produce much electricity. " Maintaining the PV cell at an optimum temperature increases it's electrical output. PV cells lose efficiency when they get hot (25 degrees C will drop the output by 50% according to this article) http://cleantechn...y-naked/ Also you say "who wants to heat their homes in the summer?" - they are looking at thermal cooling of space.
Lurker2358
2 / 5 (4) Apr 12, 2012
I've seen a demonstration that goes like this:

On a hot summer day a solar panel is submerged in an aquarium and there is a "control" panel of the same type beside it, and they've done before and afters both ways anyway.

the submerged panel produces about 10% more power, even after the light passes through the glass and water (which actually reflects and refracts some away).

Now he didn't have any way to further dissipate heat, he was just demonstrating how much more efficient panels are when rapidly cooled.

Now these collectors look like they are thermo-pumping water through copper tubing inside the vacuum tubes.

Personally, I don't think this makes much sense, because you're combining two technologies that have opposite goals: Trap all the waste heat vs dissipate all the waste heat.

The copper heat sink doesn't look like it has much surface contact with the panel, and it's in vacuum so I mean, you have a plane tangent to a cylinder as your point of contact for conduction!!
Lurker2358
1 / 5 (1) Apr 12, 2012
Now I know vacuum boilers and heaters work, obviously, I love the concept.

I just don't know if this is the right way to go for water-cooled PV system, because I'm not convinced the cooling is going to be enough to be worth it, and of course, the amount of waste heat being trapped will be less as well.

Who knows, I guess you'd have to test it to know, but it just seems to me like it's going to be sub-optimal at both jobs (solar PV and thermal,) instead of improving efficiency at both jobs...

There may be better configurations to do this.

===

Like maybe put the PV submerged in water inside a second glass tube, surrounded by the vacuum, and still have the copper heat sink with a separate water bath inside to dissipate the heat.

But again, the whole idea, in theory for water cooled PV panels was you want them to be cooler than the native environment.

The problem with this system is for the water pump to work, the heat inside the vacuum tube will be hotter than native environment..
Eikka
1 / 5 (6) Apr 12, 2012
Eikka, we need power and heat all year round, i certainly don't shower and wash my clothes / pots with cold water during the summer and neither do i sit in the dark in the evening.


Yes, but here's the thing. Hot water for consumption needs to be hot enough so it won't grow bacteria while it's sitting in the boiler and pipes, so the solar cells need to run hot, so they will produce very little electric power.

In order to increase electric power, you must decrease the water temperature until it's no longer fit for domestic hot water, because building codes actually prohibit you from running your water boiler too cool for public health reasons.

they are looking at thermal cooling of space. -djr


For that application, the liquid needs to be hot, which again compromizes the electrical output of the cells.

It's an either-or deal with solar collectors. Either it's cold and you get electricity, or it's hot and you get heat
Lurker2358
not rated yet Apr 12, 2012
Personally, I think you'd be better off using conventional panels submerged in water in a box.

You could run a small cold water line into the box and have a small electrical water pump (something tiny like a few watts, like something you see in a toy or a fountain.) Pump the hot water out of the "top" of the box and let a cold water line pump cold water in the bottom side. The hot water is pumped to your water heater inside the house as any other pre-heated water system would do.

I think this will make the panels 10% more efficient and still be pre-heating water. You'll lose a few watts worth for a water pump, which will easily be covered by the gains of the first panel.
yoatmon
2 / 5 (1) Apr 12, 2012
The problem with cooling is that less than 55 degrees for hot water isn't really adviced because it won't kill the legionella bacteria that may be present in the pipes, and then you get sick.

It depends on how intelligent the design of the boiler circuits are.
If the hydraulic circuit from the panels pass through a heat exchanger in the boiler or the fresh water is passed through a heat exchanger in the boiler, both hydraulic circuits are completely isolated from each other and there is absolutely no danger of contamination.
jet
5 / 5 (1) Apr 12, 2012
If one is going to go PV for electricity then the mounts alone could be made to do double duty as water heater mounts. The argument of cooling the PV array is interesting but at least construction/installation cost could be shared.
Lurker2358
not rated yet Apr 12, 2012
I wonder what it would cost to make enough of the newly discovered copper-graphene composite material to use as a heat exchanger in a conventional vacuum solar collector?

I know production of graphene has been demonstrated for decent sized wafers, so I wonder if they could make a rod or a hollow pipe of the copper-graphene composite material this size?

Copper is pretty expensive, but the carbon for graphene is as common as dirt. It's all in the process, I guess.

Yeah, right now making decent quantities of graphene costs a lot, but in the future I figure the composite might actually be cheaper than it's weight in pure copper, while being a much better heat conductor.

Well, sell price would probably be more than pure copper obviously, but the manufacture price might be possible to get down in the same price range.
pjmurphy123
not rated yet Apr 12, 2012
I am trying to get a project off the ground, and I would be grateful if anyone reading this could help.

I am looking for a solar array of dimensions similar to those in this product. One cell wide by several long. Looking to buy a handful right now to build prototypes.

The output is not the critical factor, but dimension is. They can be no more than 3.5 inches across, including a waterproof housing.

If anyone can help, please PM me
RealScience
not rated yet Apr 12, 2012
@pjmurphy123 - most crystalline solar cells are made on 5" wafers, and a few 6", and most poly-crystalline cells from 6" ingots.
SO most likely you'll have to buy some solar panel (maybe a 3-cell x 8 cell panel), extract a row, and then cut the cells down yourself (at least to get started).
Silicon can be cut with a diamond saw, or even a very fine carbide saw (although that its tricky).
You can also cut crystalline silicon with a diamond-tipped glass cutter.
That will take you less time than hunting down some non-standard size of cells. From what you've described, I'd start with 6" cells and cut them in half.
Vendicar_Decarian
not rated yet Apr 12, 2012
"The problem with cooling is that tess than 55 degrees for hot water isn't really adviced because it won't kill the legionella bacteria that may be present in the pipes. - Eikka

Hot water is recommended to be 140'F (60'C) or hotter to prevent bacteria growth. But if your water is chlorinated, room temperature is fine.

Collecting the waste heat is a very good idea, and the tubes are a good way to do it, but the glass represents a 12 percent loss in ambient light hitting the photocell. The rule of thumb is 6 percent loss on each optical surface.
Vendicar_Decarian
not rated yet Apr 12, 2012
Go to your local hardware store and purchase a bunch of solar powered accent lights. Remove the PV cells and stick them on a thin metal housing.

Typically the PV cells for these garden lights are low efficiency organic cells.

Efficiency 3%

Alternately you could visit your neighbor's garden sometime late at night.

"I am looking for a solar array of dimensions similar to those in this product." - Pim
Lurker2358
not rated yet Apr 12, 2012
Go to your local hardware store and purchase a bunch of solar powered accent lights. Remove the PV cells and stick them on a thin metal housing.


I don't get it.

Those things are pretty waste of money.

He'd be better served just going and buying a full PV panel and sticking it on the roof or a wall or something.

I sent him a PM because I saw a youtube video describing panels about that size, but like I told him, it was "some assembly required". He's going to need to solder everything for himself, etc. Tedious, but not hard I guess.

You can order scores of these things for really cheaper than an actual panel.

Then again, I don't know if those are safe for a water cooled system.

That's why I referred him to the Greenpowerscience guy, because I know he WILL know.
Vendicar_Decarian
not rated yet Apr 13, 2012
"Those things are pretty waste of money." - Lurker

They are, but he specifically said that efficiency wasn't an issue and he can just pick those things up tomorrow on his way back from work.
English-Scientific
5 / 5 (1) Apr 13, 2012
Eikka

Yes, but here's the thing. Hot water for consumption needs to be hot enough so it won't grow bacteria while it's sitting in the boiler and pipes, so the solar cells need to run hot, so they will produce very little electric power.


Most modern solar hot water systems heat a pressurised water tank that in turn feeds a gas powered combi boiler / water heater, the domestic water is always hot regardless as to the heat supplied by the solar panels. The working fluid in the system is usually some kind of glycol based anti freeze with anti bacterial agents.
antialias_physorg
not rated yet Apr 13, 2012
The problem with cooling is that tess than 55 degrees for hot water isn't really adviced because it won't kill the legionella bacteria that may be present in the pipes, and then you get sick.
You dont use he water directly but use it in a heat-exchanger to preheat the water for showering/dishwashing/washingmachines and the water used for heating your home. This saves tons of money (for the same area this saves you more money than the PV makes you in feed-in tarrifs to the grid. The installation of a solar thermal collector of same size has paid for itself in a thrid of the time that the PV panels did).

Making water that doesn't go boiling safe/bacteria-free is also easily possible. What do you think people with waterbeds do? We dump in a small amount (about 200ml) of antifungal stuff once a year. Problem solved.
Eikka
not rated yet Apr 13, 2012
Yes, everyone, I know you don't use the hot water directly for drinking and washing.

The issue is, that the hot water going into the water tank or heat reservoir, no matter what its design is, has to be hotter than what's already in it. Otherwise the system works backwards.

Most water boilers are of the heat exchanger type, and they too have to keep their water over 55 degrees because when you close the faucet the water stops inside the heat exchanger loop and in the pipes leading from your boiler to the tap, and that's where the bacteria can grow.

Most modern solar hot water systems heat a pressurised water tank that in turn feeds a gas powered combi boiler / water heater


It does not "feed" a combi boiler, it is the same boiler, just with multiple inputs for heat, and the tank is always kept hot, which means the water from the solar array must be hotter than the tank.

What do you think people with waterbeds do?


They don't drink their waterbeds, or shower in them.
Eikka
not rated yet Apr 13, 2012
It is perfectly possible to have a second, low temperature heat reservoir before the main water boiler to preheat the water coming from the mains and save energy that way.

But the problem still remains, because if you have water at 30-40 degrees and large surface areas for biofilms to grow, you are going to get bacteria, fungi and algae living inside your heat exchanger. There's always some that find their way in, unless the water is heavily chlorinated. Killing them by pushing the water through the main boiler helps, but you're still drinking dead pond scum, with all the poisons and allergens they have secreted, and some of them may survive the flash heating because the water goes through so quickly.

Which is why such lukewarm water tanks are not used in domestic applications. If you have hot water in a tank, it must be hot - which unfortunately means that the solar cells in this invention must be hot as well, unless you're only going to do space heating with the water.

antialias_physorg
not rated yet Apr 13, 2012
So use the energy for preheating the water circulating in your radiators. That's where the majority of your energy use is going, anyways.
Eikka
not rated yet Apr 14, 2012
So use the energy for preheating the water circulating in your radiators. That's where the majority of your energy use is going, anyways.


If you live in a place where you get solar energy all year round, you won't need the heat. If you live in a place where it gets warm in the summer and cold in the winter, then you won't be needing the heat for half the year, and won't be getting much sunlight the other half of the year. If you live in a place where you need heating all year round, the solar panels aren't cost effective because you are getting little sunlight.

So it still seems like it would be difficult to put the low grade heat from the collectors to any practical use.
PPihkala
not rated yet Apr 15, 2012
Eikka: One could use heat pump to extract heat from that solar water circulation and use the resulting heat for water boiler. That would use less electricity than using electrity directly to heat the water and at the same time keep the solar panels cool.
Eikka
not rated yet Apr 16, 2012
One could use heat pump to extract heat from that solar water circulation


Well, suppose you get 1 kW of radiation per square meter, and your heat pump pumps at a CoP of 4 to raise the temperature from 30C to 70C, and your solar cell is 12% efficient. You get 120 Watts of electricity, 880 Watts of heat, and you need 295 Watts to pump the heat to the higher temperature, consuming all the electricity it produces and then some.

The heat pump would have to have a CoP of over 8.5 before the system would start to make sense, and even at that point you'd be using all the electricity from the panels to keep the panels cool enough to make electricity.

Most domestic heat pump systems have a CoP between 2...5 depending on the temperature difference.
Eikka
not rated yet Apr 16, 2012
There's one great application for low grade heat, which is to keep a greenhouse going through the winter. With LED lighting to convert the electricity to specific wavelenghts that the plants can absorb, you may even be able to grow stuff in it.