Minimum PV source size
The size of the PV source, which is determined based upon the load evaluation and weather and solar resource evaluation will determine the necessary size of the charge controller. The charge controller must be selected at the same time as the PV source as the charge controller type - PWM or MPPT - will also determine the possible configurations of PV modules.
In this phase of the design process, more than in any other phase, it is necessary to explore different designs using PV module, series and parallel wiring configurations, and charge controllers in order to achieve the highest performance at the lowest cost possible.
An off-grid PV system that depends upon the PV as its single charging source requires an array that is sufficiently sized to be able to generate sufficient energy to both meet the energy needs of the users and to recharge the energy storage system under less than ideal conditions. Any sizing decisions should therefore lean towards an oversized PV source.
Step 1: Determine module size and charge controller type
The advantages and disadvantages of the two - pulse width modulation (PWM) and maximum power point tracking (MPPT)- are detailed in Charge controller types. The main considerations when sizing and selecting a PV source for each type of controller are the following:
PWM:
- Nominal system voltage: 12V, 24V, 48V. The PV array must be sized to operate at the charging voltage of the energy storage system.
- Maximum PV source current: 6A-60A
MPPT
- Nominal system voltage: 12V, 24V, 48V
- Maximum PV source voltage: varies up to 600V
- Minimum PV source voltage: depends upon nominal voltage and charge controller type
- Maximum PV source current: up to 100A+
