Solar Pool Heater vs PV Panels & Heat Pump

jthacker48

New Member
While building an addition on our home in Phoenix, we are adding a swimming pool. I'm looking for advice on the best overall plan for heating our pool and maximizing pv solar.

Background Details

Our home is currently 1,300 sq ft and we are adding on and additional 700 for a total of 2000 sq ft. Currently, we have a 6.5kw Tesla, Solar City, system that we inherited from previous owner. We've got about 10 years left on the lease and I can't find anyway out of it (believe me I've tried). The system is (28) Yingli 235 panels and a Fronius IG Plus 6.0.

The home was built in 40s and is made of block so insulation is garbage. During addition, we are removing older packaged AC unit and installing a split heat pump which should be more efficient. Our home is completely electric. We moved and upgraded electrical panel to 400A service. We've got a Trutankless hot water heater that should be sufficient for indoor hot water. We are grandfathered into APS net metering plan for installs prior to 2017.

We are adding a pool that is 30' x 12' with a 3/5/3 depth with a couple of small bajas on each end. We're installing a Pentair VS pump with in-floor cleaners. The pool is only shaded minimally but not subject to direct sun all day.

We've got plenty of additional rooftop space to add 30 panels or more potentially. The new roof is flat but not blocked from sun in any direction.

We are looking to add additional PV solar to cover the additional usage from additional square footage and also looking at options for heating and, potentially, cooling the pool. The issue is that we would only heating the pool for 3 to 4 months a year. The remainder of the year, the solar pool panels would be serving no purpose. From what I've read, solar pool panels are more effecient and cost-effective and than using pv panels with a heat pump.

1) Are we better off using pv panels and heat pump, despite the higher upfront and operational cost, than solar pool heater because the pv panels can supply energy 12 months while pool panels would only work for 3 or 4?

2) If we go PV addition, we would need all new system due to Fronius limit, based on my understanding. Is there a better option or should I just look at this as a new install when researching equipment and solutions.

3) If you've got other suggestions, feel free to send them over. I can scrap lots of things at this point if it makes sense.

Thanks and happy to provide any information needed for clarification.
 

snoobler

Solar Honey Badger
Welcome to the forum.

Fellow AZ resident on SRP, but they both suck these days.

I don't know these as hard facts, but it's my understanding based on my research.

Your existing system is grandfathered. If you expand it, that will void your contract, and you would lose your favorable net metering arrangement unless it has a provision for expansion. Best to check with APS. If you expand it, new panels will likely be subject to NEC2017 installation requirements, which drive up cost notably.

PV panels are at best 20% efficient at turning sun into electricity, so that's a big hit. Purpose-built or improvised pool heaters collect far more solar as heat on an area basis, but you have no real option for cooling. We have a ghetto above ground pool, and there is about a month every year where it's like swimming in warm saliva.

Best way to get heat from the sun is to skip all the expensive stuff in between.
 

jthacker48

New Member
Welcome to the forum.

Fellow AZ resident on SRP, but they both suck these days.

I don't know these as hard facts, but it's my understanding based on my research.

Your existing system is grandfathered. If you expand it, that will void your contract, and you would lose your favorable net metering arrangement unless it has a provision for expansion. Best to check with APS. If you expand it, new panels will likely be subject to NEC2017 installation requirements, which drive up cost notably.

PV panels are at best 20% efficient at turning sun into electricity, so that's a big hit. Purpose-built or improvised pool heaters collect far more solar as heat on an area basis, but you have no real option for cooling. We have a ghetto above ground pool, and there is about a month every year where it's like swimming in warm saliva.

Best way to get heat from the sun is to skip all the expensive stuff in between.
Thanks for the reply. Fortunately, APS owes me some favors (long long story) and has no problem with additional solar in my grandfathered plan.

Based on what you're saying, it sounds like 3 to 4x as much pv usage at 20% efficiency is roughly equivalent to the more efficient but less used solar water panels.

All things being equal, I think I'm better off with the pv and heat pump for the following reasons:

- Higher & more flexible temps
- Ability to cool the pool as well as heat
- PV offers flexibility in use cases

I'm sure I'm missing some key points. What am I missing?
 

snoobler

Solar Honey Badger
Glad to hear it. If you can add to your existing system, you're also adding the potential for future savings as well.

Have you verified that you are not subject to NEC2017 with array expansion? That's not necessarily APS's call. That's the AHJ's (authority having jurisdiction) rules if you need a permit to install additional panels/inverter.

Heat pumps are very efficient but incapable of very high temps. The hybrid water heaters with heat pumps must have a traditional heating element to get them to peak temp, so it's not higher, but it might be more flexible.

A solar heater can damn near boil water if you want it to.

Points two and three are agreed.
 

jthacker48

New Member
Glad to hear it. If you can add to your existing system, you're also adding the potential for future savings as well.

Have you verified that you are not subject to NEC2017 with array expansion? That's not necessarily APS's call. That's the AHJ's (authority having jurisdiction) rules if you need a permit to install additional panels/inverter.

Heat pumps are very efficient but incapable of very high temps. The hybrid water heaters with heat pumps must have a traditional heating element to get them to peak temp, so it's not higher, but it might be more flexible.

A solar heater can damn near boil water if you want it to.

Points two and three are agreed.
I've got plenty of roof space to do both if I want. What's the best equipment for solar pool panels? It's a small pool relatively.
 

jthacker48

New Member
Glad to hear it. If you can add to your existing system, you're also adding the potential for future savings as well.

Have you verified that you are not subject to NEC2017 with array expansion? That's not necessarily APS's call. That's the AHJ's (authority having jurisdiction) rules if you need a permit to install additional panels/inverter.

Heat pumps are very efficient but incapable of very high temps. The hybrid water heaters with heat pumps must have a traditional heating element to get them to peak temp, so it's not higher, but it might be more flexible.

A solar heater can damn near boil water if you want it to.

Points two and three are agreed.
I looked for info on array expansion in NEC but didn't see anything that applied. Can provide further detail on what I should be looking into?
 

x4dow

Solar Enthusiast
solar water heaters are extremely more efficient at heating water than PV panels.
However PV panels can still heat the water a little in the winter, while solar water heaters can easily boil water in the summer, theyre kinda pointless in the winter. depends on the weather where you live
 

Mike Jordan

Solar Addict
In my previous house in central Florida, (no pool now) I installed a solar pool heater. Its been a while, but they were 2 panels about 4x12ish feet, with straight straw sized tubes, mounted on a south facing sloped roof. I ran the water in the bottom and out the top. It did a great job at heating the pool, to where you could swim most any day fall to spring.

In the summer the panels had a valve and bypass to keep from heating the pool. But even without heat, in the middle to end of summer the pool was like swimming in a hot bath. Not comfortable

But... I found a pretty good solution. In the summer ran my pump at night, with the solar heater valve open . I set the timer to come on at about midnight after the air, the roof, and panels were cool. This reduced my pool water temp, to make the end of summer days more enjoyable.

I have only visited Arizona. But Florida summer night time temps were always higher than anything I experienced in Arizona. I would guess that would work better for you, than me
 

2009Bounder2020

Solar Enthusiast
back in the 80s my grandpa covered his pool shed roof with black garden hose it was on an endless loop to and from the pool... it kept the pool warm all summer .. .no pv involved. not sure if it meets neighborhood codes but simple works
 

carl2591

New Member
why not just do like they do in florida for pool heating.. get solar water panel on roof with a pump.. would not think in phoenix you need a lot of heat but for just a couple of months in jan feb.. my brother has a pool in glendale and it get too hot in summer. in winter it get cool but they are not using it them..
this is just one system that might be too large for yours..

While building an addition on our home in Phoenix, we are adding a swimming pool. I'm looking for advice on the best overall plan for heating our pool and maximizing pv solar.

Background Details

Our home is currently 1,300 sq ft and we are adding on and additional 700 for a total of 2000 sq ft. Currently, we have a 6.5kw Tesla, Solar City, system that we inherited from previous owner. We've got about 10 years left on the lease and I can't find anyway out of it (believe me I've tried). The system is (28) Yingli 235 panels and a Fronius IG Plus 6.0.

The home was built in 40s and is made of block so insulation is garbage. During addition, we are removing older packaged AC unit and installing a split heat pump which should be more efficient. Our home is completely electric. We moved and upgraded electrical panel to 400A service. We've got a Trutankless hot water heater that should be sufficient for indoor hot water. We are grandfathered into APS net metering plan for installs prior to 2017.

We are adding a pool that is 30' x 12' with a 3/5/3 depth with a couple of small bajas on each end. We're installing a Pentair VS pump with in-floor cleaners. The pool is only shaded minimally but not subject to direct sun all day.

We've got plenty of additional rooftop space to add 30 panels or more potentially. The new roof is flat but not blocked from sun in any direction.

We are looking to add additional PV solar to cover the additional usage from additional square footage and also looking at options for heating and, potentially, cooling the pool. The issue is that we would only heating the pool for 3 to 4 months a year. The remainder of the year, the solar pool panels would be serving no purpose. From what I've read, solar pool panels are more effecient and cost-effective and than using pv panels with a heat pump.

1) Are we better off using pv panels and heat pump, despite the higher upfront and operational cost, than solar pool heater because the pv panels can supply energy 12 months while pool panels would only work for 3 or 4?

2) If we go PV addition, we would need all new system due to Fronius limit, based on my understanding. Is there a better option or should I just look at this as a new install when researching equipment and solutions.

3) If you've got other suggestions, feel free to send them over. I can scrap lots of things at this point if it makes sense.

Thanks and happy to provide any information needed for clarification.
 

GaryBIS

New Member
It seems like for your situation going with solar thermal pool heating would work better.
The pool heating collectors are very efficient (75% ish) and cheap in that they are plastic and don't have to be glazed.
You should be able to use the regular pool pump to circulate solar water as well as pool water (just make sure they size it for this).
The plumbing is cheap PVC.
Add a simple differential controller and that's about it.
Its a simple build if you like to do DIY.

This calculator says you would want about 250 sqft of collector to heat your 360 sqft pool.

The pool heating panels are in the $8 per sqft area, so not a very expensive system -- maybe $3000 for all materials.
I think you get the federal tax credit (26% now).

More on DIY pool heating https://builditsolar.com/Projects/PoolHeating/pool_heating.htm

Gary
 
Top