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. This phase may have to be performed several times.
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 a charge controller type
There are two different charge controller types - pulse width modulation (PWM) and maximum power point tracking (MPPT) - each of which has advantages and disadvantages that are are detailed in Charge controller types.
Step 2: Deteremine a PV module size
The PV module size that is ideal for the system design will depend upon the amount of energy required each day, the type of charge controller chosen, and what module sizes are available in the market. An MPPT charge controller can function with any module size as long as the series configuration of modules meets the minimum voltage requirement for the charge controller so that it can properly charge the batteries.
PWM:
The PV source must be configured to operate at the charging voltage of the energy storage system and below the maximum PV source current rating of the charge controller.
- Nominal system voltage: 12V, 24V, 48V.
- Maximum PV source current: 6A-60A
MPPT
The PV source must be configured to operate below the maximum PV source voltage rating of the charge controller, above the minimum PV source voltage based upon the maximum charging , and below the maximum PV source current rating of the charge controller.
- 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+
