Solar System to Run Electric Pool Heater Off Grid

For summer, unglazed thermal collectors are probably most efficient (put the most heat into a 60 degree F pool per unit area.)
I don't know the numbers, not 100%, maybe 60% to 80% of sun's energy?

Photovoltaic panels only 20% efficient. So 3x to 4x the area and higher cost for same energy into the pool.

Heating pool to 90 degrees, unglazed collector will fall in efficiency. I don't know how far. They are best with cool water coming in.

For higher temperature water and cold days, "Evacuated Tube" collectors look interesting. As with any thermal collector, if your location can freeze, you need a way to deal with that. Could be propylene glycol loop, could be continuously pumping pool water through collector even at night. I don't see as many evacuated tube systems advertised as before.

What is fairly inexpensive is used PV panels. They can be had for $0.10 to $0.30/W, which might make electric heating cost-competitive after all. But you need mounting hardware and installation, which adds up.

You've got 21 days, maybe only 7 days, to make an NEM 2.0 reservation with your utility for net metering. That would let you install PV panels and inverters to backfeed the grid (assuming you have enough area.) Then you can heat with electric, hopefully heat-pump. Run the heater during off-peak midnight to 3:00 PM, not when rates are higher.

You've got a short time to decide how much area is available for PV panels and get in your reservation.
Gas has gone up and down. If your time window is 20 years, maybe gas will be driven very high, and electric will become more cost effective. Potentially DIY PV is cost effective.

Our grandparents have solar vacuum tube for heating their pool.

Get a pool cover to trap heat by preventing evaporation.

Look into these:
Northern Lights Group SunRain Solar Vacuum Tube Collector- 20 Tube Solar Water Heater https://a.co/d/bZ0LClg

They use 40 tubes (2 units) to heat their pool. It's roughly 9500 gallons I believe.

You will need a circulation motor, like one used for home heating.

sunshine_eggo said:

If you're saying you used 550 therms of natural gas to heat your pool/jacuzzi, I don't think you have a grasp of the enormity of that energy usage.

1 therm of natural gas is 29.3kWh of energy.

The average home in the United States uses about 30kWh/day of electricity. Let's call those equal.

In ONE MONTH, you used 1.5 YEARS worth of equivalent electrical energy that the average U.S. home consumes.

550 therms/month
550/30 = 18.333 therms/day = 537kWh

For perspective, my 2300 sq-ft home in PHOENIX with temperatures that push 120°F never uses more than 120kWh/day, so your energy needs are over 4X the A/C requirement of my Phoenix home.

Let's say you can realistically offset half of this... so 537/2 = 268.5kWh/day.

I expect you have pretty exceptional sun even in Winter, so we'll use 5 solar hours.

You need 268.5/5 = 54kW of solar to generate this much energy daily.

Yes. That's 54,000W of solar panels. This is a huge amount, and you likely do not have enough space on your entire property to accommodate this. You're likely looking at a system that costs $100,000 to offset HALF of your natural gas usage.

Using your pool dimensions, I ran some numbers to sanity check this, and it takes about 633kWh (about 21 therms) to heat your pool volume from 68°F to 90°F. This does NOT take into account any losses to the air or earth, so it's likely low.

I would encourage you to confirm the 550 therms number. Does the house have a leak?

I vigorously recommend you consult a pool pro, plan for solar water heating, and investigate a pool cover:

Flush Track Automatic Cover - Up To 499 SF

Check out the deal on Flush Track Automatic Cover - Up To 499 SF at Royal Swimming Pools

www.royalswimmingpools.com

Click to expand...

Hey thanks for the detailed response. The 500 something therms is for my entire house (gas stove, water heater, heat inside the house AND the pool & Jacuzzi heat. The usage is always this high in the winter- my home is an airbnb, the pool is heated to 90 degrees, the jacuzzi to 102 the majority of the months. No leaks or anything like that. GAs co has been to the house.

LosFelizGirl said:

Hey thanks for the detailed response. The 500 something therms is for my entire house (gas stove, water heater, heat inside the house AND the pool & Jacuzzi heat. The usage is always this high in the winter- my home is an airbnb, the pool is heated to 90 degrees, the jacuzzi to 102 the majority of the months. No leaks or anything like that. GAs co has been to the house.

Click to expand...

Without knowing what the pool consumes, it's extremely difficult to make an estimate. What is the gas usage of similar sized homes in the neighborhood that don't have a gas heated pool?

Even if it's only half your usage, and I suspect it's > 50%, that's a 25kW solar system you need to offset HALF the usage.

dumb to burn that much energy in this way

Why are you allowing airBnB people to crank the pool heat that much? Lock that control down ?‍

LosFelizGirl said:

Hey thanks for the detailed response. The 500 something therms is for my entire house (gas stove, water heater, heat inside the house AND the pool & Jacuzzi heat. The usage is always this high in the winter- my home is an airbnb, the pool is heated to 90 degrees, the jacuzzi to 102 the majority of the months. No leaks or anything like that. GAs co has been to the house.

Click to expand...

Do you have enough space to mount a large number of solar and "water heating" panels?

Fafco panels are about 50% efficiency in a swimming pool application. Fafco does publish much data on panel area vs pool size , efficiency, etc.

That is bare panels only, not encased in a box, not insulated, just the 4’ X10’ panels mounted on the roof as per Fafco specs. I have seen 6 panel array’s (4X10 foot and 4X12 foot) heating a residential pool in many locations here.

The panels are thin about 5/16 thickness, there have been several changes in design over the years.

They have been around for 20-30 years here in California as you cannot get a permit for a pool heated by gas or electric if it is feasible to use solar. It is legislated here.

Air bnbs are a plague. Turning neighborhoods into commercial zones and reducing the housing stock. Ban them all.

740GLE said:

Why are you allowing airBnB people to crank the pool heat that much? Lock that control down ?‍

Click to expand...

I dunno about how he's doing it, but my neighbor has an AirBnB with a pool/hot tub. $200 charge if you want to heat it.

Bluedog225 said:

Air bnbs are a plague. Turning neighborhoods into commercial zones and reducing the housing stock. Ban them all.

Click to expand...

In dense residential maybe. The only way may parents could afford to keep a family summer home was to rent it. That rent over the summer would cover the taxes (barely). Without AirBnB (or short term rentals in general) a lot of people won't be able to keep places.

Where I agree is that NO ONE should be disrupting the neighbors.

Bluedog225 said:

dumb to burn that much energy in this way

Click to expand...

Which is why the OP is asking about other options. Trust me, lots of people burn more energy than they should as single humans.

There wouldn't have been a post about this if there hadn't been a brutal spike in natural gas prices. The same usage today would have been < $500.

Yeah, I guess because people are dying in Ukraine so they can keep the latte’s warm in berlin. Sorry, this whole thread has me annoyed. I’ll drop out.

People are dying in Ukraine because Putin ordered the attack.

It would seem alternatives to the present situation are 1) submit to being taken over, or 2) counter-attack in such a massive way that the aggressor can't continue. Perhaps the drawn-out conflict is actually the choice of certain governments. Nothing we the people can do about that, unless we unite in directing certain governments to do something different.

People died in Iraq, Syria, other places too.

If the Happy Girl buys used PV panels that would otherwise end up in a landfill and uses them to heat a swimming pool, that doesn't prolong the war. It does reduce consumption of natural gas (as would simply not heating the pool.)

if people have to die in order to heat my pool for airbnb guests, that is a sacrifice I am willing to have them make. o7 o7 o7

LosFelizGirl said:

@Bluedog225 I was under the impression that solar water panels can't get the pool that hot. I have to maintain a 90 degree pool temp in the winter, and 102 for the jacuzzi. My house is an airbnb, this is what I have to supply.
My goal is to supplement the gas heat w/ electric during the day. For example, use the gas to heat the pool up fast and then maintain the temp w/ a separate electric heater, powered w/ an off grid solar system that only feeds the electric pool heater. Meaning, it will have nothing to do w/ my main electric panel in the house. I figured this would relieve me of using gas during the sunny days in the winter to maintain the temps. I'm not interested in storing energy in batteries.
My pool is small w/ an attached spa separated by a wall (i attached a pic in other replies)
Pool measurement: 10' X 35' 3 feet to 6 feet deep
Jacuzzi measurement 10' X 5'

Attachments​

Click to expand...

I live in Maine and I can get our pool up to 87 degrees with 10 4' x 8' solar hot water panels. The water comes out at 130 degrees with a 5/8" garden hose. I calculated out the btu's and I think it was around 160 kbtu per hour. I picked up the panels on the cheap from someone who removed them during a roofing job. It would really save you a lot of money to use solar hot water panels.

They are rather easy to install as well. All you do is find a place for the panels and then divert some of the flow from the pool pump to the solar hot water panels.

I'm thinking about doing this. I have an electric pump and heater, so why not look into converting it to solar. I have a bunch of open land next to my pool, so panels will be on the ground. I'd guess that most expensive part would be the battery. But since I make li-ion batteries for electric bikes, I'll just make one for this purpose. I just need to figure out the calculations, and this will be done in a couple of days.