PV Array Size with Generator

PV Array Size (with a back-up generator)

If we are to incorporate a back-up generator for our system we will be able to reduce the overall size of our array.

Let us presume our back-up generator is rated at 2.5 kW, we could reduce our array size by 2.5 kW, this would equate to 2500/250 (@ Stc) = 10 modules. This would result in an array of 13 modules (12 or 14 modules could provide a balanced system), rated at 4 kWp.

A simplified monthly energy balance in this configuration would be as follows:

	Average daily irradiance	Daily available energy from 12 modules at monthly PSH (kWh)	Daily requirement (kWh)	Average daily deficit (kwH)
January	0.82	2.46	3.78	-1.32
February	1.53	4.59	3.78	0.81
March	2.93	8.79	3.78	5.01
April	4.02	12.06	3.78	8.28
May	5.00	15	3.78	11.22
June	4.90	14.7	3.78	10.92
July	4.80	14.4	3.78	10.62
August	3.93	11.79	3.78	8.01
September	3.05	9.15	3.78	5.37
October	1.92	5.76	3.78	1.98
November	1.08	3.24	3.78	-0.54
December	0.68	2.04	3.78	-1.74
	Annual available energy (kWh)	3156

* The monthly available energy is only a theoretical amount that is available upon the module array, this simplification does not include meteorological losses such as cloudy days, losses due to temperature variations, neither does it account for unused energy when the battery is fully charged. For a more detailed analysis one should simulate the system. See manual analysis simplifications and  assumptions in the note section.

As we can see from the table above we could expect our back-up generators to be utilized during November, December and January.