Photovoltaic vs. thermal radiator Solar Panel comparison (using a lens)

[Opera]

I produce domestic hot water with PV. While less efficient in collecting space vs thermal solar, it is far more economical. Supplemental PV water heating on a cost basis can be better than a heat pump. True success in a water heater is it turns off. That PV energy can be used elsewhere like air conditioning. I built my own controller to keep the PV array at optimal voltage for energy transfer to a resistive element making the cost for a system not much more than the panels themselves. This method of water heating is relatively new with the drop in panel prices. This still isn't understood in the solar community, but new products are starting to appear. This is a paper comparing PV against thermal at several locations in the world https://www.hindawi.com/journals/ijp/2017/7540250/
Any questions of my practical experience with PV heating are welcome. I've been experimenting in this technology since 2016.

 

[camerart]

I produce domestic hot water with PV. While less efficient in collecting space vs thermal solar, it is far more economical. Supplemental PV water heating on a cost basis can be better than a heat pump. True success in a water heater is it turns off. That PV energy can be used elsewhere like air conditioning. I built my own controller to keep the PV array at optimal voltage for energy transfer to a resistive element making the cost for a system not much more than the panels themselves. This method of water heating is relatively new with the drop in panel prices. This still isn't understood in the solar community, but new products are starting to appear. This is a paper comparing PV against thermal at several locations in the world https://www.hindawi.com/journals/ijp/2017/7540250/
Any questions of my practical experience with PV heating are welcome. I've been experimenting in this technology since 2016.

Hi O,
After suggestions from here, I've stopped concentrating on this kind of technology, although if I wasn't working on other 'interesting' projects, I would experiemnt, in case something different appeared.

My idea was mainly centred around stroring the energy, in a block, in my case for experiment it would have been water, insulated and underground. I assume it would have been compartmetalised, with high heat at the centre etc.

I think the weak link is converting very hot water, into electric, so if you think of something let me know.

I am a fan of PV, and hope to have an array sometime.

Thanks for the offer of questions.
C

 

[bob012345]

Hi O,
After suggestions from here, I've stopped concentrating on this kind of technology, although if I wasn't working on other 'interesting' projects, I would experiemnt, in case something different appeared.

My idea was mainly centred around stroring the energy, in a block, in my case for experiment it would have been water, insulated and underground. I assume it would have been compartmetalised, with high heat at the centre etc.

I think the weak link is converting very hot water, into electric, so if you think of something let me know.

I am a fan of PV, and hope to have an array sometime.

Thanks for the offer of questions.
C

Just a note FYI that if you do store energy underground in an insulated container, hot sand can be stored at much higher temperatures;

https://www.renewableenergymagazine.com/storage/first-commercial-sandbased-thermal-energy-storage-is-20220707#:~:text=As a material, sand is,8 MWh of energy capacity.

 

[camerart]

Hi B,
I looked into different heat storage materials, and decided on water as the most suitable for experimenting with. e,g, between each sized test, water can be pumped, and doesn't need shovelling, stroring or much cost.

When I'm experimenting with anything, I don't go for the best in the first instance, that would come later if the earlier tests were sucessful
Thanks, c.

 

[solvejskovlund]

Old thread, but still.... I've played with the idea of adding copper pipes on the back of PV panels, and add insulation on the back to keep the heat in. Then circulate water in the pipes. The PV panels do get hot in sunlight. PV panels are more efficient when cold. After all, they have 17-22% efficiency. The reminding energy, that is not reflected, becomes heat. That heat I'd like to collect by circulating the water, and at the same time it provides cooling to the PV panels.

10 years ago solar heat collection was a big thing. In the past years PV panels became cheap and I've seen calculations concluding that PV powering a hot water tank is more economical than solar heat collection.

 

[sophiecentaur]

I've played with the idea of adding copper pipes on the back of PV panels, and add insulation on the back to keep the heat in.

These ideas are always worth playing with but, when you get down to it, it's the numbers that count. It would be necessary to compare the heat that gets to the cooling pipes with what you'd get from black pipes (plus other fancy additions) with what you can expect from your 'in behind' proposal. Then you'd need to look at the economics of installing a solar heat collection system (plumbing isn't cheap). Solar heat collectors work mainly on radiant energy from the Sun and they would be in the shade if behind PV panels. Afaik, thermal solar collectors are not usually a system of choice and PV seems is now the runaway favourite so I'd suggest that keeping them in the shade (albeit in contact with the PV panel backs) would disadvantage them. So I'd guess that any benefit would be marginal.

 

[solvejskovlund]

The main benefit is area saving. If you have available area to install PV or thermal, go for PV. If you've run out of installation area, pipes behind may be worth an experiment

 

[camerart]

The main benefit is area saving. If you have available area to install PV or thermal, go for PV. If you've run out of installation area, pipes behind may be worth an experiment

Hi S and S,
I agree that pipes behind the PV panel would not be good, as they would be in the shade.
I would try to seal the top of the PV panels, so water could flow over them (To keep them cool) and extract any heat, though heat exchanger/heatpump, if economical.
Use plastic or glass for the cover and plastic central heating pipe for transfer.
C

 

[Rive]

I've seen calculations

Entirely depends on the amount of machinery involved.

There were those low emission dream houses a decade (or so...) ago with 1-2 m³ boilers with multiple heat exchangers within, fed parallelly by wood stove or solar heat (gas options and heat pumps are optional) and hooked on a high tech floor and wall heating system... Yeah, no return point is expected within the millennia.

But those simple, straightforward vacuum pipe&boiler on roof kind of systems are still kickin'.

I've played with the idea of adding copper pipes on the back of PV panels, and add insulation on the back to keep the heat in.

The temperature is just too low for any practical usage/return calculation.
Might be OK for a pool heating, but if you have some free area on the roof then utilizing that'll still beat it by far.

 

[camerart]

Entirely depends on the amount of machinery involved.

There were those low emission dream houses a decade (or so...) ago with 1-2 m³ boilers with multiple heat exchangers within, fed parallelly by wood stove or solar heat (gas options and heat pumps are optional) and hooked on a high tech floor and wall heating system... Yeah, no return point is expected within the millennia.

But those simple, straightforward vacuum pipe&boiler on roof kind of systems are still kickin'.The temperature is just too low for any practical usage/return calculation.
Might be OK for a pool heating, but if you have some free area on the roof then utilizing that'll still beat it by far.

Hi R,
This is quite complicated, and what do we know what developments have happened since the decades old house?

I'm always interested in subtleties, and what gets forgotten with long thread. The OP mentioned cooling the PV panels, this must have an added affect along with some heat capture.

I did have a thought about low level heat, as in a warm water tank. If it wasn't circulating and was well insulated, would heat rise to the top for reclaim?
C

 

[sophiecentaur]

pipes behind may be worth an experiment

Entirely depends on the amount of machinery involved.

The temperature is just too low for any practical usage/return calculation.

There is one huge problem in experimenting with this. You can't just go up on the roof with some pipes and even that is inconvenient for most people. You would need the pipes to be installed just before the PV panels and the PV panel fixing brackets would need to be non standard. I can't imagine any installer being interested in doing the job; they like to be up, down and off. This would involve probably double the on-roof time.

The only realistic experiment you could do would be to buy a single panel, mount it in an accessible spot with a home brewed system and play with various piping systems. Actually, you'd really need two PV panels with one as a control.

There must be lots of data about PV performance at different temperatures. That wouldn't require any of one's own experiments. Pipes with various covers would be easy to try . . . .

This is getting out of hand for anyone but the real enthusiast.

 

[Rive]

This is quite complicated, and what do we know what developments have happened since the decades old house?

They pretty much got retired as dream houses by now (except, maybe, for absolute enthusiasts of the 'money does not matter' type).

There is a nice paradox around insulation. The more you spend on insulating a house (bringing down the energy required to run it) the less room you'll have for additional machinery to reach a return point.

In a really well insulated house only (if any...) the cheapest, most direct heating system would worth it.

 

[sophiecentaur]

the less room you'll have for additional machinery to reach a return point.

Predicted return point is only accurate in a lifetime situation of stable prices. Also, the proportion of a person's income that's spent on Energy will be relevant. (Is it actually always worth it?) There's a good parallel with replacing primary cells with re-chargeable cells for small devices. Very often it's pretty marginal when you take into account the drag of managing the system. You have to be a suitable sort of person [this isn't a quality judgement :-) ] to organise it successfully

Imagine how 'smug' could turn into 'sick' when Fusion Power drastically reduces the cost of energy, half way towards your predicted return point. But then, I can't imagine the Energy Companies letting us get away with free Energy!!