I'm starting to collect the pieces I need to switch my few 24x7 loads over to solar power during the day once the batteries are charged. But I have a couple questions that hopefully some here can help with...
Primarily, how fast of a switching time is needed for an operating load? I'm going to do some testing when I get a chance, but would like to hear others' experiences. The main two load types I'll be switching are the fridge and a couple of servers.
The fridge is my biggest worry - if the power bumps while it is running, and the compressor stops, then it won't restart. But how long of a bump is required before that happens? If the 15-30ms it takes a relay to switch isn't fast enough then I'll need to add a time delay during which the fridge is kept off for several minutes or monitor the current draw to know that the fridge isn't running.
I know most computers don't care for power bumps, but have thought about just leaving them on the UPS and switching the input to that. My inverters are true-sine so I don't think the UPS will have a problem with it.
Again, the relays I'm looking at list their action time as 15-30ms (depending on which relay).
Next question, would you just switch the line side (120V circuits) meaning the neutral from the breaker panel would be tied to the neutral from the inverter (these can be properly grounded on the AC side according to their manuals), or would you switch both line and neutral? Not really a big deal either way - the relays I'm looking at are multi-pole and I'm only going to have one load per relay.
And finally, how often could/should I switch? Obviously the equipment already sees bumps and sags from the power company, but how much of a "stress" would switching from one power source to another be? I could make this a one-shot deal, as I get to absorb / float start switching loads over. If the system can't maintain then back off and done. On the other hand, for a partly-cloudy day that could mean losing out on available power later in the day if the sun comes back out. I don't want to be switching back and forth so much that I cause premature failure with anything though.
My idea at this point is to have three roughly 100W (when running) loads to switch on in stages - which lets me make use of available power on overcast days as well - based on available voltage and current as reported by the Outback system during operation. Then, as the system voltage and PV current starts to fall, indicating loss of sunlight, I'll switch the loads back over to grid. Handily, this also means I get an automatic transfer switch for the fridge if the grid fails.
Thanks!
Joe
