Friday, October 15, 2004

Where Do Batteries Fit?
I ran across an article (subscription may be required) a while ago that has had me thinking about the future role of batteries in adapting renewable energy sources for power generation. Last Tuesday I talked about overcoming the intermittent nature of solar power by putting the solar collectors in orbit where the sun shines all the time. Another way, of course, is to store the energy generated when the sun shines or the wind blows, for later use.

There are already applications for which this is attractive, in places not currently connected to the electric power grid. Elsewhere, developers must contend with the cost and efficiency of storing electricity. A wind generator that nearly competes with electricity generated from a natural gas-fired turbine doesn't look nearly as cost-effective if you must pay for batteries to store some of its output before delivery.

The efficiency problem is less obvious. Storing electricity in a battery and retrieving it later is not a free ride. Some of the energy will be lost as heat, at too low a level to recover cost-effectively. That's just the Second Law of Thermodynamics in action, but it has implications for sizing a wind farm or solar collector array, if the power is going to be stored rather than delivered right away. And as battery arrays get bigger, managing the heat byproduct becomes a more important issue.

It's also important to think about how this stored power will be used. If the goal is to enable solar collectors to deliver power day and night, batteries may be a good choice, but so might reversible fuel cells. And if eliminating short-term fluctuations in wind is the issue, or covering brief periods of peak demand, then other technologies better suited to discharging large amounts of power in a short time, such as ultracapacitors, may be more appropriate.

In any case, what we are beginning to see is the shattering of the old paradigm that electricity must be generated as needed, or used as generated. Perhaps, like rainfall, it can be stored cost-effectively for delayed distribution.

No comments: