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Written by Ulrich Bonne, Kailua-Kona, HI, ulrichbonne@msn.com
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Sunday, 12 September 2010 16:38 |
Batteries are readily available for use as a means to even out the variable output of clean energy sources powered by sun, wind or ocean, and to provide power when the grid goes down, after a quick switch to “off-grid” operation. But one wonders about the proper size of such a battery, which clearly would depend on home load, its relation to the energy output of a PV system, with or w/o an EV or PHEV, the day-to-day variability of available sun and PV energy, and of loads; how battery size influences the annual NEM (Net Energy Metering) dollar balance with the utility or positively contributes to grid voltage stability, and last-not-least the economic benefits of permanent off- vs. on-grid operation of such a small but about 2x oversized 2-kW PV system.
The over 300-days of recorded daily PV output data were the basis of this analysis. The data not only show that the PV output cycles are over 300 days in length, but that they may not even follow the expected seasonal variations expected from the sun's elevation.
To see the data and read the full paper, click here.
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