Thoughts on Electrical storage

Deep charge Caravan/Marine battery

8 July 2012: The idea of using PV-Thermal on the extension lead to thinking about ways of storing the energy.

• The thermal portion will be added to my existing Surya plumbing circuit. That's been explained in an earlier posting on this website.
• The PV production cannot be added to the Grid, as we have reached our 4 kW limit, and must not risk changing the Feed-in-Tariff. It must be stored in a battery, and then used through an invertor.

If I have two 155W panels on a sloping pitch facing south, I can expect up to 310 Watts on sunny days, and quite a decent amount at other parts of the season. That is about 2000 kWh of solar energy per annum, converting to about 250 kWh of electrical energy. It could possibly be more, as that calculation assumed 10% loss due to temperature, which will not happen with PV-Thermal.

PVGIS estimation of 300W
at 15ºpitch, facing nearly south.

   Not all this energy can be stored. Once a battery is filled, it does not accept more change, so further electrical capture is wasted.
   At time of highest 'capture', there will also be 'demand', as the liquid pumps in the house will be working flat out, but these are low energy demand pumps. I shall also put additional demand onto the battery, such as the laptop, printer, broadband modem, hard disk, cordless phone. All useful in case of a power cut in the grid.
    You have to get the balance right. If demand exceeds supply, then systems do not work, but worse than that, a fully flat lead-acid battery is difficult to restart.