Wednesday, August 28, 2013
Off grid tiny loads
One of the really annoying things to deal with when going off grid is tiny 24/7 power loads. In my house I'm not totally off-grid. My cordless phone, cell phone chargers, wifi router, and cable modem all run on-grid.
Big house size inverters, that thing that turns battery DC power in normal house AC, are terribly inefficient with small loads. A lot of precious solar power gets wasted. With the tiny constant loads shunted to the grid, my inverter isn't running all the time. It goes into a highly efficient sleep mode. As soon as a load is detected, it springs back into life, does the job then goes back to sleep.
One way to deal with tiny inverter loads is to bypass the inverter completely. If your battery bank runs at 12 volts, which many do, it's a simple matter of running some 12 volt circuits. For example, instead of charging a cell phone with the AC adapter, use the car adapter on a 12 volt line. There are also power cords for laptop computers designed to run on standard 12 volt cigarette lighter plugs. In fact, there are a lot of small appliances designed for the RV and marine market that run on 12 volt DC.
Another way to deal with tiny loads is to use a second inverter, a small one sized just big enough to handle the small loads. It will run at peak efficiency and the big house inverter can sleep. The little inverter could be tied into the existing battery bank. Another solution is to run a completely separate small scale solar electric system.
That's what I'm tempted to do at my house. Unfortunately my battery bank is 24 volts so I can't run a DC line directly off it. I could tap into just half the battery bank to get 12 volts, but that would drain half the battery bank more than the other half which is bad for the batteries. There are devices to reduce 24 volts to 12, but that also suffers from inefficiencies. Kinda defeats the purpose of going to DC in the first place.
I like the idea of a tiny separate system as it's one more power backup if the main system fails.
Of course, one way to deal with little power draws is to eliminate the devices completely. If I had a good cell phone connection (which I don't) it'd be easy to dump the router, cordless phone, and wifi. Those jobs could be done with one smart phone.
When my lovely wife and I leave for the winter, I'm going to have the grid completely disconnected from my house. No sense paying a monthly bill for a service I'm not using. When we get back in the spring, we'll then decide if it's worth reconnecting or staying off grid. My guess is that it will be really hard to go back to having a monthly power bill, even the tiny bills we have now.