Thursday, June 10, 2010

Hello Darkness My Old Friend

Dark days have indeed returned.  The last couple of days have been a steady deterioration from the wall to wall sunshine of last weekend through the record breaking partial cloud of Monday (when I briefly saw the 1.8kW array spike to over 1.94kW) to today's wall to wall gloom.

Solar cells are temperature sensitive and when in full sun they get hot and lose some power.  But on partially cloudy and cold days, the cells get cold when there's a cloud but when the sun peeks out they put out more power for a short time before they heat up.  Also, as the sun peeks out from behind a cloud a sort of focusing effect happens to the light and for a few seconds it can be stronger than in a clear sky.  Under these circumstances it is not uncommon for solar panels to put out as much as 115% of their rated power for a few seconds.

The new larger battery bank is capable of absorbing a lot more power now and had no trouble lapping up the 73 Amps that the solar chargers blasted out.  Sadly, although these events produce very high rates of charge, they only last a few seconds so don't actually charge the batteries much.  So over the last couple of days the batteries have been slowly fighting a losing battle.

Having increased the capacity from 180Ah to 492Ah has made a big difference though, extending the time that we can survive without a decent sunny day from just one day to maybe two or three, depending on how reckless I am in the evenings.  But tonight after a particularly gloomy day where the PV output never crept above 375W and with the forecast for tomorrow to be non-stop heavy rain all day, the battery gauge is sitting at 69% tonight and likely to fall to below 50% tomorrow night.  We might have to switch the fridge freezer back to mains power at night until Saturday when the forecast is for sunny intervals again.

We'll see.

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