Estimation of the Nominal PV System Power
Influencing factors
The nominal PV system power depends on the following factors:
Energy consumption per year (EAnno)
System efficiency (ηSys)
The system efficiency is approx. 0.7.
Solar fraction (SF): Amount of PV energy as a proportion of the total energy supply in an off-grid system
The solar fraction depends on the amount of PV energy typically available at the installation site.
Specific PV energy yield (EPV)
The specific energy yield depends on the amount of energy typically available at the installation site and on the nominal PV system power.
Energy yield from PV energy and reasonable proportion of PV energy in the off-grid system:
Region (examples) | Specific energy yield per year1) | Solar fraction of the energy supply |
|---|---|---|
Germany | 800 kWh / (kWp × a) to 900 kWh / (kWp × a) | 50% to 70% |
Southern Europe | 1300 kWh / (kWp × a) to 1450 kWh / (kWp × a) | 60% to 90% |
North Africa, South Africa or South America | 1450 kWh / (kWp × a) to 1700 kWh / (kWp × a) | 60% to 100% |
Saudi Arabia | 1800 kWh / (kWp × a) | 60% to 100% |
1) Example: 1000 kWh / (kWp × a) corresponds to a specific energy yield of 1000 kWh in 1 year per 1 kWp of installed nominal PV system power.
Calculation:
An approximation of the nominal PV system power can be calculated using the above listed values.
Information on design
The design of the PV array and selection of the PV inverter is based on the required nominal PV system power.
The nominal PV system power results from the rated powers of the PV inverter used ( > Selecting the PV Inverter).
In off-grid systems, the nominal PV system power may not be more than double the total nominal AC power of the Sunny Islands inverters ( > Sunny Island and Multicluster-Box Design).
When using lead-acid batteries, the battery capacity per installed kWp of the PV array must be at least 100 Ah. Example: The minimum battery capacity is 500 Ah in case of a PV array with 5 kWp ( > Battery-Storage System Design).
When using lithium-ion batteries, the battery capacity per installed kWp of the PV array must be at least 50 Ah. Example: The minimum battery capacity is 250 Ah in case of a PV array with 5 kWp ( > Battery-Storage System Design).