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Tuesday, September 12th, 2006

trouble with the trees

the shading problem, from the inverter's perspectiveI needn’t have climbed the roof to determine whether the PV array has a shading problem. The kWh meter on the inverter makes it plain; on a sunny day, output drops from 1500 watts to 50 in the space of 40 minutes.

Unfortunately, this happens around 5:00 PM, so there’s over an hour of the daily peak period during which we’re not only not selling power to PG&E at 3x market rate, but in many cases we’re buying power at that rate. Ouch.

I met with an arborist today. He said he could prune the eucalyptus and birch trees that are shading the PV array, but not until December — cutting them now could damage them, and in the case of the birch, possibly kill it. So, we wait.

Unfortunately, the summer rate season lasts until October 31, and I expect the shade to impinge on production progressively earlier in the day (until the Winter Solstice). So we’re going to take a big hit in production this year.

I managed to reduce our peak-period consumption slightly this week — I found that the thermostat on the attic fan was set way too low, to 85° or something, which meant the fan ran for most of the afternoon and into the evening on warm days. I dialed it up to 110°, reducing the runtime by hours per day. A small but welcome victory.

Tags: photovoltaic, solar, shading
posted to channel: Solar Blog
updated: 2006-09-15 05:02:09

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