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Wednesday, May 7, 2008

Cheap Energy Storage is Here Now

In answer to a question from William Hughes-Games from New Zealand
Hi William,
You wrote:
I'm not sure how one can only buy from the power company as a back up when home generation is low. No problem if you have your own batteries but the common (possibly incorrect) wisdom is that batteries are an economic no-no.
Actually, I would say that the conventional wisdom is wrong. This is why. The economic choice in batteries is flooded lead acid at this point. (However that may soon change.) By my calculations these batteries cost approximately $US 0.15 per stored kilowatt hour. (also by my calculations, the new Altairnano batteries will cost only $0.03 per stored kwHr but they will seem expensive because with 15,000 deep cycles, you buy a lot of storage in advance).
But, that is a lot, you might say. What is not recognized by those who have not lived with these systems is that only a fraction of the energy you use needs to be stored as electricity. So while you may need to store enough to meet your nightly use for a few days, most of your energy is or can be scheduled to be used during the day, directly from panel to inverter. This greatly reduces the amount of storage required. And by the way you don't have to disconnect the batteries to do this. The AC inverter will have first call on the generated energy - only what's left over goes to the battery.
For instance the largest energy user in my system is my refrigerator. I run it a bit cooler than I would otherwise and then it turns off with a timer during the night after the normal use period. This way, energy is being stored as cold. In an efficient modern appliance, little cold is lost when no one is opening the refrigerator.
I try whenever possible to run my washer and dryer during days with bright sunlight. This way I am storing energy as clean clothes. The same can be said for food processing, and other energy intensive activities. In the end, electricity is useful because of the function that it allows. If you maximize your energy-use timing, you get the same function at the at a much lower cost because then the kwHrs are not stored.
This is why there is a lot of room for smart energy use systems. With a system in which instrumentation can activate on-off timers or switches, you can even do some chores like laundry while you are away, to optimize energy-use timing.
So, say you might use an average of 5kwHr/day. By maximizing energy use timing, you may only need to store 1-2 kwHr. So total cost of your battery storage is much lower on an averaged kwHr basis. From my experience it is not an issue, especially for retired persons with flexible time.
This also means that all the energy you produce is tax free except for the tax on the original equipment purchse. Over a 20 year estimated system life, this can be a huge saving.
At any rate, with batteries you can still be grid inter-tied if you choose to. It actually makes more sense to only sell to the power company in the summer when you are likely to have a surplus. If your average stored energy cost is $0.05/kwHr used and your generation cost is $0.08/kwHr, the total of $0.13/kwHr is not bad, especially if you sell your surplus in the summer, to defray these already low costs. And what value can you place on a green conscience, knowing that your energy footprint is not destroying the environment?

PS. Also noteworthy is that by buying your system now, you are locking in rates for years to come.