Hello all,
I have seen a lot of posts on solar heating, but unless I missed something I concluded it really depends on many factors which are almost unique to every pool user. I live in San Diego, CA, just a few miles off the coast. Aside from heat waves (which are isolated events) it never gets very hot here due to proximity to the ocean. The image below gives a good idea of the temperature variation over the year. I have only owned this house for less than a year, and just recently started taking care of the pool myself following TFP recommendations (it is going great by the way!!!

). Water temperature this time of the year is between 60 and 67 degees depending on the day. I have not measured the water temperature in the summer, but I remember that even in August the water was relatively cold (pleasant if hot outside, but definitely still on the cold side).
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I have a gas heater (see info in my signature). I made a test a few days ago on its efficiency in raising the pool water temperature. 4 hrs of gas heater raised the pool temperature by 1 degree Fahrenheit and costs me about 4 dollars. As many had pointed out on this forum, a gas heater is not a good solution for extending the use of a pool. It works great for my SPA since it gets it hot quickly (and I could use it for special isolated pool events), but I cannot count on it for extending the pool usage as it would cost me too much. Hence, here I am considering solar and hoping the TFP community can help me with this decision.
1) I am considering DIY. I am pretty good at DYI stuff, and I have some background in hydraulics (I am an engineer), I generally understand concepts around plumbing such as flows, losses, vacuum, check valves, etc. With that said, I am obviously not a professional and I have never done this before. Am I crazy at considering DIY for this?
2) I found solar panels on some pool stores that are incredibly expensive, while some at Home Depot or Amazon are half the price. Is it one of those cases where you pay what you get and it is strongly not recommended to go with the Home Depot/Amazon products?
3) My roof looks towards East, that is the only option I have with roof mounted. I have enough space to get 100% of the pool area if needed. Another option would be to build a little roof to my pool equipment areas, which would face south (which is good) but it would only be 20% of the pool area. I concluded it would be better to have 100% on roof but let me know if you disagree.
4) My plan would be to use the same pump I have and just use a 3-way valve to only open the solar circuit when needed. Pool info in my signature. Seems a powerful enough pump. A bit old (11 yrs old) but when it dies it dies, irrespective of solar.
5) Considering all the above (especially the seasonal temperatures and the direction my roof faces), would you say it could be a good investment? I am well aware that long term I save money with solar versus gas heater, but I am more worried about the actual extent of pool usage (meaning if I spend 2-3k for solar and then I only get an extra week of pool usage because the temperature raises only a couple degrees, then I would call this not a good investment).
As usual, thanks for all the good input. And if the input is "hey, go talk to a professional if you want all of this figured out" thank you anyway as that is also helpful!