Liquid cooled solar panel discussion

[Zucca]

As many of you already known, it panel temperature goes up the efficiency goes down.

Theory here:
https://www.pveducation.org/pvcdrom/solar-cell-operation/effect-of-temperature
https://www.pveducation.org/pvcdrom/pn-junctions/diode-equation <-- last graph here is interesting.
https://www.pveducation.org/pvcdrom/solar-cell-operation/fill-factor <--- Fill Factor Calculator 1

There are many papers on this topic, (for example this one).
Interesting here too

Since years I am thinking about getting solar panels for my home, but I am pondering to get hybrid ones (hot water + electricity production).

Main reasons for this is to increase the electrical power output and has a nice side effect, to collect heat in the form of heated water (long discussion here, but I do not want to digress).
I also read that a cooled solar panel will increase the panel operation life.

Let's keep it simple. Let's assume an unlimited water supply at no costs.

A few point that I need to clarify:

1) A small pump is needed to circulate water (a passive convection is not possible in my case, can't place a hot water tank above the panels), I need to design a system that even with that energy loss, the net output will be bigger than no water circulation.
2) I need to deal with the freezing risk in winter.
3) The market for hybrid solar panel is smaller than regular ones. I am facing it is hard to find hybrid panels.
4) The microinverter should handle an higher panel voltage, I need to buy the expensive ones.

I am located in SC, USA. The solar here hit hard, and winter is not too harsh.

what do you think?

Thanks in advance for the discussion.

[f4eru]

it's nice if you get a pool to heat up.
But I'm not sure it's really economical today, compared to putting a few more panels on the roof, with the low price of panels.
Calculate the budget !!

It could be an interesting tech in a few years.
For wintering, it's easy, just empty them.

[Someone]

But I'm not sure it's really economical today, compared to putting a few more panels on the roof, with the low price of panels.

This x100!
Even though plumbing is a commodity product, and there are solar collectors (even already integrated with solar panels) off the shelf. Still they just cant compete with the cheaply mass produced PV panels. Want some DIY action to save money? get second hand panels.

[Kleinstein]

Cooling the PV cells does not increase the voltage very much ( the usual 2 mV/K per cell, like with normal silicon diodes). There are still possible cold, windy sunny days in spring and the inverter have to live with the slightly higher voltage anyway.

Solar heat usually needs a relatively high temperature to be useful. Especially in winter the PV panels would often not reach 20°C or even 10°C - so essentially no heat when you really need it. A swimming pool would be about the only target for the heat.

The extra plumming adds quite a bit to the costs. So cooling is likely not worth the extra effort, especially not in a more moderate climate and small installations. It may help for large scale in very hot climate, if they have a good sink for the heat.

[Siwastaja]

This would also work as co-production of solar thermal and solar PV.

But it does not make any sense financially. The piping with large surface area results in doubling of the PV cost.

Efficiency increase is true; if you want the similar 10% increase in output power, without the 100% cost increase and extra maintenance risk by the cooling system, just install 10% more panels!

For the same reason, efficiency isn't actually the most critical parameter in PV today. Sure, better would be nice, but right now what matters most is $/kWh produced, this is just cost times expected service life per power output. Efficiency only matters in installations where you have limited surface area and still want as much production as possible.

[Zucca]

Thanks for this first round of responses, highly appreciated.

Yes there are some generic rule of thumbs and those needs to be applied to my specific case.

I am in the middle of running the numbers, once I have a clear picture I will report back.

This are the design decisions I have already made (nothing in cement yet, everything is in discussion)

1)
My roof will have only regular PV. The hybrid PV will be installed vertically on the side of my home facing south. It is a pretty large surface with only two windows.
It gets a very good amount of sun with no shade of trees or something else. The idea is to minimize the piping costs. More on this later (crazy idea spoiler alert: water tank as thermal energy storage).

2)
Yes I will have a lot of thermal energy in summer when I do not need it. My goal is only to cut the water heating costs during summer or ideally in sunny days in winter....

This would also work as co-production of solar thermal and solar PV.

Bingo. Exactely this.

Not sure it I could couple this system with the geothermal I am also planning... for heating and cooling my home.
Water heating (maybe with a dedicated water to water heat pump, probably R407 with directly pass system) and electricity production are the PVs job

[Twoflower]

Not sure if you really get an improvement on the PV if you can‘t dissipate the heat somewhere. Normal PV panels are reasonably thin and unless they‘re integrated in the roof there‘s plenty of convection between the module and roof, or wall in your case. This cools the cells reasonably well to ambient temperature.

You should check how well this works on the hybrid modules if you can‘t consume the heat.

Overall that still might get your total energy demand down using this approach. Just as it adds area you collect energry.

[Kleinstein]

If it is about reducing the power needed for heat, it may be more effective to us conventional PV and keep the themal design of the wall in mind.
In summer good ventilation behind the PV could help to keep the temperature down. In winter less ventilation could imporve the isolation and indirectly harvest some of the "heat".  Wall mounted PV will alread get less hot as the sun usually comes at a larger angle.

For the $/kwh comparison one needs to include also the mounting construction, cabeling and cleaning costs, not just the pure panel costs. This is especially relevant for low efficiency panels (e.g. thin film).

[Zucca]

Let's start with some numbers, finally.

This is how much energy I used in my current home last year.



Gas is for cooking , water and home heating. For all the rest electricity (bloody old and inefficient AC).

This is the water heater
BTU Input 40K/hour = 11.7228 KW or wasted energy (efficiency of this thing is laughable).

Let's focus on the energy needed to heat up the water (gas energy in summer time), I would say I need 6KWh/month. Let's say 10KWh/month just to have some room.

Now this is where I want to mount the hybrid PVs (picture taken at sunset):



1) Is the current chimney for a retarded living room gas fire place we never use.
2) Is the magic wall facing 155°SE. Dimension 5.4x14.6 meter total.

Let's assume I have this sun average:



here the crazy idea, convert the chimney in a water tank for heat storage.
How many hybrid PV panels surface I need to cover my 10KWh/month energy need for DHW [Domestic Hot Water]?

I want a good balance between summer an winter.

Sorry I am too tired to continue with the math, I will do the rest of my homework in the next days.

PS: Oh please correct me if I made some mistakes, some units conversions could be wrong.

[Kleinstein]

It looks like the main energy use is the AC in summer. The heat for warm water is more like marginal and if gas is there for cooking anyway I see not much need to change thinge here. Could be different if there is some conversion error with the gas uusage - the number look very low (could be off by a significant factor).

From the economic side it would likely help most to have PV to power much of the AC from that. In most cases the summy days are also the hot days.
Adding PV to the SE facting wall or the roof also has the tendency to add some extra isolation. In most cases the roof stays cooler in summer and warmer in winter nights with the extra PV layer.

As the wall is no facing directly south, the roof may be the better place for PV. There are web pages to calculate the expected return depending on the orinetation and location.

If one really insists in solar hot water, I would consider separate collectors for heat, as they can deliver the needed higher temperature. The vacuum tube types can compensate for much of the angle and work on the wall. Solar-thermal collector really like a good angle, as they can not use low intensity very good.  Chances are still that it would not save money, with only some 3-5 kWh / month to replace (if the numbers are correct). The water tanks are usually in a fixed form factor and may not fit inside the chimney part.

[f4eru]

I installed solar water collectors in 2015 (simple panels, no fancy vacuum tubes)
Today, I would simply go PV with a heat pump water heater.

Installing water or glycol lines to te roof makes no economic sense any more, at least in my case.

[Siwastaja]

Install bog standard PV, and bog standard air source heatpump(s) which can both cool and heat.

In your installation, cooling power dominates; but cooling requirements correlate with PV production nicely, cutting external electricity cost to near zero.

In your climate, air source heatpumps have excellent heating COP as well. You can utilize PV production nicely for this, too. If you install 4kWp of PV, you get 1kW easily during most of the winter time, too, which is 3-4kW of heat after the heatpump.

[Marco]

If you don't want to become independent of natural gas, a hybrid setup seems cheapest. So the heatpump heats the water going into the boiler with a heat exchanger and the boiler heats it up a further 20 degrees or so.

Cooling with an air to water heatpump will require some extra insulated plumbing to Fan Coil Units, which depending on your location might not be easily available (almost unheard of in my country, but they seem popular in Italy). Also any hydronic heating loop needs to be turned off during cooling. I'm not sure if there are any hybrid setups which can work with two buffer tanks, so they can supply both hot water and cold water. Might be easier to just use some minisplits for cooling.

[Zucca]

It looks like the main energy use is the AC in summer. The heat for warm water is more like marginal and if gas is there for cooking anyway I see not much need to change thinge here. Could be different if there is some conversion error with the gas uusage - the number look very low (could be off by a significant factor).

It is way too low for me too. That's way I mention that.

But here

Amount: 1 cubic foot of natural gas (cu ft N.G.) of energy
Equals: 0.29 kilowatt hours (kWh) in energy

here

1 cubic foot of natural gas = 0.293071070172 kilowatt hours

Let me google more:

    100 cubic feet = 1 CCF
    One CCF = 100,000 Btus
    One therm = 100,000 Btus
    One kWh = 1,000 Watts h  = 3,413 Btus
    100,000 Btus/therm divided by 3,413 Btus/kWh = 29.3 kWhs/therm or CCF
    One gallon of water weighs 8.33 Lbs.
    One cubic foot of water = 7.48 gallons, 1 CCF = 748 gallons
    One hundred cubic (CCF) feet of water = 748 gallons

Much like electricity is measured in kWh (a unit of energy), gas is normally counted in Therms (also a unit of energy). But since it is easier to measure a volume of gas (in CCF) than natural gas' thermal energy, your gas meter will count the amount of gas you consume each month in CCF and not in Therms. On your gas bill, you gas consumption will most usually be firstly expressed in CCF, and then converted to Therms. Also, since 1 CCF is equivalent to 1.025 Therms, the conversion is rather simple.

kWh =
Therm(US) * 29.300

ah ahhhhh found it

100 cubit foot natuag gas = 1 ccf!

Lord have mercy I am a sinner:



which make sense, because that boiler is a waste of energy by definition:

about 41C of hot gas at the chimney 

[Zucca]

In your climate, air source heatpumps have excellent heating COP as well.

This! Why I am trying to heat up water to use it as input in a water/water heat pump when I have plenty of hot air in my climate?
Make more sense to use all the surface/sun I have to generate electricity.
Probably also use the geothermal system in winter to generate hot water.
There are air/water to water heat pumps on the market.

Yesterday under the shower I was thinking also this....
Let's suppose I will install n hybrid PV
one hybrid PV will raise the water by △T
Temperature of the water at the input of the hybrid PV array: Tw_in

If I connect the array hydraulically in series I will have at the end △T*n a s temperature raise which is nice but the last panel will have Tw_in+△T(n-1) input  and Tw_in+△T*n output temperature, bye bye PV efficiency.
If I connect them in parallel I will have a lot of water raised by △T... and that is probably not always enough to use that energy....

Thanks to everybody for helping me.

[Someone]

Lord have mercy I am a sinner

how many people reside at that house? Per capita consumption is usually the better measure of "wasteful".

But now you know that energy is flying through your house for heating and cooling, insulation is probably the most cost effective answer.

Willing to show a wide thermal shot of your whole house? Those eaves seem to be well insulated, but what about the rest.

[Zucca]

Since you asked...
Windows are a joke and the walls yeah.... not great.