two-speed with solar panels

[semenzato]

I think I have a valve because after the pump stops I can hear water coming down from the panels for a minute or two. When the pump restarts, for the first couple of minutes only air flows down from the panels and into the pool through the jets---and there is no doubt about that! The explanation of why the valve is needed also makes sense, so I have never questioned this.

I switched to time-of-use because that was required by our power utility (PG&E) in order to sell them energy. We just installed 30 Sharp 170W PV panels (which by the way appear to produce a peak of 4300W, according to the inverter).

I like the cost of electric energy in NJ! But at that price I don't think I would have installed the panels.

[cleancloths]

I switched to time-of-use because that was required by our power utility (PG&E) in order to sell them energy. We just installed 30 Sharp 170W PV panels (which by the way appear to produce a peak of 4300W, according to the inverter).

I like the cost of electric energy in NJ! But at that price I don't think I would have installed the panels.

That is interesting, as I think I am the only one in NJ that has time-of-use with solar panels - they actually had a hard time getting my bill right for the first six months because of it. My system is comprised of 54 Sharp 185W panels and we get a similar yield to yours, the max I have seen on the inverters is about 8600W.

You probably would have done it in NJ even with our "low" electric rates. That is because the state has a very aggresive program to promote solar. At the time I installed mine they were offering rebates of up to 70% or $5.50 per watt installed. Add to the the solar renewable energy credits which you can sell each year. Those credits currently sell on the open market for $225-$250, and are set to double in two years. It makes the project very attractive. I have had the system for about two and a half years and figure my full payback will be reached in just under 4 years. Unfortunately for late adopters, the rebates are now 50% or less.

[chem geek]

I don't know what kind of solar panels you have, but take a look at this link that shows the change in efficiency at different flow rates. It doesn't drop nearly as fast as your power consumption will drop at lower flow rates. The tradeoff will be somewhat slower heating of the pool with much larger savings in electric cost. Very roughly speaking, in a variable speed pump, the GPM is roughly proportional to the RPM while the power consumption varies as the cube of the RPM. You can see from the solar panel efficiency graph that going from 4 GPM at 80% efficiency to 2 GPM at 70% efficiency isn't a huge drop in efficiency, but that the power consumption will drop by a factor of 8 (a little less than that due to "fixed" losses). With a 2-speed pump, you may not be at the "sweet spot" of reasonable efficiency and low power consumption, but you just might.

Richard