Working out what you need.
WHAT TO ESTABLISH FIRST
Your daily consumption in units, for the load you intend to supply.
WHY THAT LOAD RATHER THAN EVERYTHING
Supplying air conditioning and heating from solar is expensive; supplying lights, computers and refrigeration is not.
WHAT TO CALCULATE FOR PANELS
Units needed daily, divided by the effective generating hours you can expect.
WHAT EFFECTIVE HOURS MEANS
Not daylight hours, but the equivalent hours of full output.
WHY THE DISTINCTION
Early and late sun produces far less.
WHAT TO ASSUME CONSERVATIVELY
Fewer effective hours than a supplier's projection.
WHY CONSERVATIVELY
Dust, cloud, heat and ageing all reduce output.
WHAT TO ADD
A margin for losses through the system.
WHAT TO CALCULATE FOR BATTERIES
Units needed overnight and through poor weather.
HOW MANY DAYS OF AUTONOMY
At least one full night, with more for critical loads.
WHAT TO SIZE THE INVERTER FOR
Simultaneous load, with starting headroom.
WHAT TO SIZE THE CHARGE CONTROLLER FOR
The panel array, with margin.
WHAT TO CHECK IN ANY QUOTATION
That each component matches the others That the assumed sunlight hours are stated That expansion is possible
WHAT TO BE SCEPTICAL OF
Systems promising to run everything Figures with no stated assumptions
WHAT TO ASK FOR
The calculation, in writing.
