I've been thinking some time about energy storage and how one should compare in a competitive manner the different technologies available. Here incidentally, is a very good page on the different technologies and their technological comparisons produced by the Electricity Storage Association.

Still, my blog-sized and financially biased interpretation of what are the 4 performance metrics of energy storage should be are as follows;

1. Watt hours per installed dollar - pretty fundamental, the upfront capital expenditure cost.

2. Lifetime discharge/recharge cycles - this varies hugely from perhaps 1000 for lithium ion based batteries, 10,000 for Vanadium Redox Batteries and 15,000 for some others.

3. Watt hours per kilo - this determines how portable it is. Lithium ion batteries about 200. Petrol or gasoline about 13,000. By the way, laptops are getting lighter, so why don't they just double the size of the battery?

4. Time required for full recharge - 6 hours for lithium ion to 10 minutes for nanosafe batteries.

So there we have it. I also have to say that if Altairnano's nanosafe technology is as good as they say it is, a revolution is in the offing.But only if metric # 1 comes in at a low enough cost.