thanks again Jim for taking the time to answer.
Ok, I understand a bit then about the cell. I will talk to some of the manufacturers of cells. There IS a company that markets a DC direct swg, but then it "floats" in the pool under the panel, so there is not much chance of gas buildup. However I've had emails from others that have used normal swg cells, and run them off DC direct. I think that might be the way for me to go. From what you say, the plates in the swg must produce enough Chlorine that if there isn't water flowing by the plates, carrying away the gas, then there MIGHT be a significant enough buildup of the gas to cause an explosion. PROBABLY with a system that was PV direct, this would not happen if both systems were nominally on when the sun was shining but I'll have to try to put them on a timer I guess just as a precaution. As to a DC timer. I imagine they do, but then you have to have a battery system so that the timer has power when the sun isn't shining. Since I already have AC (thru my main energy shed inverters) I think it easier just to get an AC timer, and have the DC current being the one that is turned on and off. (in case you are wondering since I have AC why not just use it? Because changing DC (from panels) to AC is wasteful of energy. And you don't really want to waste energy when you are off the grid. Also since batteries are the things that go bad, by over discharging them, then you want to guard against that. Going DC direct, not thru batteries, is the ideal way to do that, since you don't really care if the system is pumping at night, as long as it pumps well during the daylight hours.
Just for the record, and you can ignore what follows, but since you state you are not too familiar with DC systems, (I'm not a solar engineer, but I've been off the grid for 30 years, and have multiple systems, some with inverters, some not) it is my understanding that most or all swg cells are actually DC. Sure you plug the device into an AC outlet, but then there is an inverter that makes the DC, (sort of like a car battery charger, makes DC from AC) I believe the normal voltage in many swgs is about 27 volts plus or minus, so most panels have a circuit that allows take offs of 12 V, 24 V and often 48V. Since a feed of 24 V would NOT actually charge a system with 24V, (has to be higher than the actual voltage, a 24V feed is actually about 28 to 30 V. I've heard that it works fine. probably more important than the actual voltage is the amperage or wattage available. Don't want too much power or you would burn out the system. My guess is about 70 watts. I guess I'll find out.
As to pumps? Direct DC off PV? Absolutely. I've been pumping water every sunny day for 25 years, and only when the sun shines. No batteries. Batteries are great, I have them in my energy shed. I store energy for the night time, and also for larger power needs, (I run a woodshop with semi-industrial machines, all off solar). But if you can run direct, that is better. (Batteries are the things that go bad the fastest. The best way to destroy batteries? Run them to less than 80% FULL. That means that if a battery system has 1000 amp hours of energy, you should only use the top 200 hours. Every time you discharge the system below 80%, you are shortening the life of the system, the deeper you go, the faster you destroy it) . In the case of a pump for a pool, DC direct, seems ideal. You don't need to pump as much when it is colder or cloudier, or dark out. You don't need to pump as much in the winter. So sounds perfect for a PV direct. Also for the record, DC motors are usually much more efficient than AC, (certainly single phase AC) motors. They are also naturally variable speed. (which is a plus). Also "soft start" which is a big deal for pumps, making less shock on a system, is automatic for a DC direct system. Modern brushless DC motors are even better. No brushes to wear out.
Anyway, So I'm learning, thanks to many folks here on TFC. I hope to have my system in this winter. I'm starting the dozing of the site this next week. It's on a hillside, but fortunately there is a lot of shale under the dirt, so I think it will make a good base for the pool. Maybe eventually I'll know enough to be able to advise others that are off the grid.
best regards
paul
