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Comment by jonawesomegreen | Hacker News Reader

I've spent the last couple years working on a very interesting project using ultra-capacitors for energy storage. We are storing 33kWh of energy in ultra capacitors, charging and discharging with a very short period (seconds) for peak-demand shaving. It really is an exciting time for energy storage technology. I think we are going to see a lot of cool innovation in the next few years, even just finding new uses for existing technologies.

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What sort of volume/weight dimensions are required for 33kWh of ultra capacitors?

They are quite large, but in the particular application weight and volume are not a huge concern. All sitting side by side they are about 20 meters long, 3 meters high, and a meter deep. Probably weighs on the order of 15 tonnes.

Wow, how much capacitance is that?

16.3 megafarads, assuming typical cell voltage of 2.7v, and total energy of 33kWh:

http://www.wolframalpha.com/input/?i=33kWh%2F%282.7v%29**2

I don't know much about this field, but how does charging/discharging on the order of seconds help shave peak demand?

Think of a sinusoidal demand for energy, with a period of a few tens of seconds. By charging when demand is low and discharging when demand is high, peak load is lowered.

Sounds like a logical extension to power factor correction. Large consumers have long been installing capacitors to compensate for inductive loads. Although this new tech is over a longer time frame.

To put this in context for others, although domestic customers are normally only billed for real power this is not the case for industrial consumers. Reactive power is significant as they are billed not just for energy used but also for peak power drawn.

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