In my last post I talked about some seemingly off the wall, but doable, energy storage contrivances. As for the compressed air storage, apparently some pretty clever people have already thought about this. Follow this link to a pretty thorough discussion of the subject.
There are some pretty neat pages at Low Tech Magazine and No Tech Magazine. Speaking of energy storage and No Tech, how about storing energy with NO equipment? This is coming out of the solar air conditioning research. First, it is a no-brainer to state that your solar electric electrical system works best on a sunny day, right? Well, fact is, it doesn’t really draw in useable energy at night, even though a full moon might make the green light come on on your system. So, it makes sense to use the energy when it is being made, rather than tax the batteries so severely at night.
Here is what I am doing and it is so simple. During the day, my programmable thermostat is set to a fairly cool temperature, within the limits of what the array can supply. Usually, that is around 76 degrees. I am looking into building a smarter thermostat that will take into account the state of the battery charge and the weather, so that I can squeeze out a little more performance without being here to manually manage things. At night, the thermostat gets set to 79. Some folks could not go for that range, but as a native Southerner who grew up without a/c, no sweat. Literally. The reduced humidity of the a/c is as big a factor as the temperature on one of those hot, muggy days.
Ok, so where’s the storage? What’s the medium. Look around your house. Sheetrock walls, tile floor, pots and pans, that cast iron bathtub, brick or stone fireplace…anything and everything with some thermal mass. You’ll have the cooler temps when you are stirring about and need it cooler for comfort, but at night, when you are reading, watching the tube or sleeping, the temperature will slowly creep up as thermal mass will slowly absorb the heat seeping in. At a high in the high 70s should be fine, especially with a ceiling fan. I still have the a/c running some during the night, especially those nights, but not nearly enough to run down the battery bank.
Just leaving the thermostat at one temperature has its merits, but for using the power when you are making it, changing temps makes for longer run cycles to optimize efficiency. I know from observation that my PV is putting out enough power to run the a/c without getting into the battery about 9:30 a.m. in the summer. Having the program go into cool-down, starting then, means I can run the a/c without taking the battery down any lower and any time after that I am building power to fully recharge by the end of day. In the late afternoon, I cross that threshold again around 5 p.m. The frequent afternoon thunderstorms can play havoc with that, though, hence the quest for a smarter thermostat.
My house is powered by a hybrid system, part on and part off grid, so I still get a power bill. I suspect some of my neighbors have cooler homes than mine, but I bet they have bigger power bills, too.
—Neal