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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.

-Sixbears

12 comments:

  1. Sounds like you've got some thinking to do. Could you use a ham radio instead of a cell phone at your home, or would that take too much juice, too?

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    1. Nobody I'd want to talk to use ham radio, and yeah, uses juice too.

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  2. The router and WIFI are the tough ones, otherwise you could get one of those small solar battery chargers for a 12V battery and ONE good deep cycle 12V battery to cover all the little stuff easily.

    That set up wouldn't keep up with a constant converter draw though, even a little one.

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    1. Maybe I should just put a wifi booster on my computer and tap into the wifi from the campground across the lake. :)

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  3. You are going to hurt your mind doing all that thinking! You are way ahead of me on this stuff but on the right path, keep working on it, you are close to getting off the grid!

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    1. I look at my house, vehicles, and life for that matter, as a experiment in progress.

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  4. Yep, what Sunnybrook said...I have a headache just from reading of your layout. Then again, changing a spark plug hurts my head.

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    1. You know how stripping down a gun and rebuilding it again can be fun? My whole house is like that.

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  5. You have been thinking about adding to your system for a while.when you get back add a 100 watt seperate 12 volt system with mabe a 150 watt inverter and 12 volt plugs.it should do for a low watt load system.You can even say its to eleminate reconecting to the grid.If it need to be enlarged you get to choose wheather its on 12 or 24 volt side

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    1. Should work for me.

      If the small system isn't quite keeping up, giving it a boost from the big system should be easy too.

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  6. Nothing like having a pending project to pass the time with serious thing!

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