Money,money,money.... if it's gas or electric you'll pay thru the nose.

I dunno about your location,you must have SOME partial of full sun,even if you have to locate a panel 20-30feet from the pool.

First of all a solar panel or 3 of the right size with a decent storage tank is ridiculously easy to fabricate,did it myself,get some 3/4 marine grade ply,giving you 4by8collectors,4by8 sheet of 1/4"thick lexan,3/4i.d.PVCpipe with plenty of 90degree ells,space your pipes 4"apart,spray everything inside flat black,screw your 1 1/2"high wall strips on the base,cover with the lexan and screw framing strips to hold it down,not forgetting plenty of black tar for the joints{silicone is worthless}.
Your main concern is the velocity with which the water is circulated thru the collector,slower is hotter,30psi pressure relief valves in line are good.

You wanna go crazy?get a 12 volt circulator pump with a photovoltaic array to charge the batteries that power it.
It's all so damn easy.
First cost in materials was under $600.00,can't calculate the savings though

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