Help Needed in Solar Pool Heating Experiment
This is my first experience working with solar, so thanks in advance for your patience. I have a lot to learn!
I’m trying to setup a pool pump that will be used to send pool water through coils of irrigation hoses that get heated by the sun to give a boost to the pool heating system along with solar rings. I’m starting with one set of coils as a proof of concept and plan to scale it out so that it’ll actually make a difference. Perhaps I’ll just limit the heating to the spa portion, which is much more manageable in terms of volume of water to heat. There are many DIY projects out there that I’ve looked through that have a similar setup, but not many where the pump is powered by solar. I thought I’d give it a try as a fun way to learn about solar systems and how they work, and if it helps heat the pool more efficiently, then all the better.
In terms of requirements, I just need the pump to run when the sun is strong – late morning to mid afternoon (I live in California) – so I didn’t think that there was a need to have a charge controller and a battery as part of the setup. But I’m running into an unforeseen issue (at least to my amateur mind) that I need help resolving. Let me first explain the setup I have so far:
100w solar panel -> low voltage disconnect -> buck/boost converter -> motor pump speed controller -> DC motor pump. I also have a 3 pin switch hooked up that can turn off the system manually. Specs of each component are listed at the bottom.
When the sun is bright, everything works well. LVD is set to switch off at 11V and switches on when it hits 17V. Buck boost converter outputs voltage at a steady 13V and output current is limited to 2A at the moment (don’t need full power of the pump for now). I can adjust the pump speed through the pump speed controller by turning the dial.
This breaks down however, when clouds pass by or late afternoon comes by when the panel isn’t providing enough juice. I would be ok with the system just shutting down (no sun, no need to run the water through), but the LVD and/or buck boost converter keeps on switching on and off repeatedly every second under low light, and that cannot be good for the circuitry. From my reading, it seems that under weak sun, the pump tries to pull more watts than can be supplied, which causes the panel voltage to crater and the whole system crashes. As soon as the motor stops, the panel recovers and delivers enough watts for the LVD and buck boost to operate again a second later. Then the motor starts up again which starts the whole crash cycle over again. Did I get that right? For any given sun intensity, I can dial down the speed controller to keep the system from crashing, but it’ll happen sooner or later as the sun weakens at the end of the day.
Is there a no-battery/no-charge controller solution to resolving this behavior? Not sure if there’s an issue with my settings on the LVD or buck boost converter that is causing this. I haven’t dabbled with capacitors yet, but not sure if those will do anything more than just delay the inevitable crashes for a few moments.
If the battery+charge controller is the only way to fix this behavior, then what do you recommend for PWM vs MPPT charge controller for my case? MPPT will get the most out of my panel, but do I really need that for a simple setup like mine and will a simple PWM controller suffice? Something basic like this one from Renogy: https://www.amazon.com/Renogy-Wanderer-Amp-12V-24V/dp/B07MVZ777D/ref=sr_1_3?keywords=renogy+wanderer&qid=1556829793&s=hi&sr=1-3-catcorr For battery sizing, I think the standard answer to a 100W panel is something like 25-35ah, but provided that I don’t need this to be running in low/no light conditions, do I need that large of a capacity? For this use case, I would have to hook up the motor pump to the load terminals on the controller (and not to the battery terminals) for the pump to shut down properly by the controller? And the controller would basically replace the LVD and buck boost converter? I think I can still have the pump speed controller connected so I can adjust the pump intensity. Any recommendations?
Thanks again for the learning opportunity.
Specs of the components:
100w 12V monocrystalline, Maximum Power at STC:100 W, Optimum Operating Voltage (Vmp): 17.9 V, Optimum Operating Current (Imp): 5.72 A, Open Circuit Voltage (Voc): 21.6 V, Short Circuit Voltage (Isc) 6.24 A, Maximum System Voltage: 600 V, Maximum Series Fuse Rating: 15A
Low voltage disconnect: https://www.amazon.com/gp/product/B07929Y5SZ/ref=ppx_yo_dt_b_asin_title_o09_s00?ie=UTF8&psc=1
12-36 input voltage, 20 max amps before breaker trips
5.5-30V input voltage range, 0.5-30V output voltage range, 0-3A output current range, ability to adjust output voltage and current
Motor pump speed controller: https://www.amazon.com/gp/product/B07H2YP7C6/ref=ppx_yo_dt_b_asin_title_o00_s02?ie=UTF8&psc=1
6-90V operating voltage, continuous operating current: 9A, overload and short circuit protecting current: 15A
1100GPH, 12VDC, 3A draw, 13ft head
I know a bilge pump might not last very long in these conditions but it’s relatively cheap and serves its purpose for this experiment.