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Summary:

Saul Griffith, the president and chief scientist of Makani Power and founder of WattzOn, gave a fantastic presentation at our Green:Net conference. We also sat down with him at the show to chat more about his projects: What has he learned from WattzOn users through managing […]

Saul Griffith, the president and chief scientist of Makani Power and founder of WattzOn, gave a fantastic presentation at our Green:Net conference. We also sat down with him at the show to chat more about his projects: What has he learned from WattzOn users through managing energy consumption online? The typical average user under-reports their footprint (a problem with all carbon calculators). Makani Power, the Google-backed high-altitude wind startup, is still more than a year away from deploying its kites commercially, but Griffith says initial data has found that the kites can hit a capacity factor (a measure of how reliable it is) of 60 percent — that’s about double the reliability of traditional wind turbines.

By Katie Fehrenbacher

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  1. Careful not to confuse Capacity Factor (CF) with Reliability Factor.

    CF isn’t necessarily a measurement of reliability (although very often, reliability measurements are rolled up into capacity factor measurements). Capacity factor is a ratio of the actual output of a machine over some period of time, to the theoretical maximum amount of output that machine could produce over that period of time.

    So, if I have a 500kW fuel cell, the most production I could expect from it in the course of one day is 50024=12,000kWh. That would be a capacity factor of 100%. In reality, however, maybe the load profile for the building its serving isn’t so great and I can only run it at an average of 65% capacity factor. So my output is only 50024*.65=7,800kWh.

    Over a longer period of time, reliability measurements are typically included in the capacity factor — so that same fuel cell may be available 92% of the time over the course of the year.

    For distributed generation and on-site power, capacity factor is intimately linked with the users Load Factor (which is kind of the demand-side version of capacity factor). The fuel cell, or turbine, or pv panel will only produce power to meet load or store energy – net metering aside for the moment. This is why capacity factor is such a critical number for distributed power systems – including small-scale renewables. Its the only time when capital investments are being repaid!

    When a relatively small generating source is tied into the grid, it more or less can assume infinite load – so it can produce as much as possible, trying to approximate its capacity factor as close to 100% as it can.

    Finally the other number –specifically relevant to renewables — is the utilization factor (I think this is probably more appropriate than capacity factor in this case). The energy sources that solar and wind use are only available a certain amount of time per time period – there are only so many hours of sunlight each day. This is whats exciting about the high-altitude wind projects…they dramatically increase the utilization factor.

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  2. guess the comment system didn’t like asteriks for mathematical equations…the 50024 above should be “500 x 24″

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