Step 1 - Determine the requirements

We need to determine the customer's daily energy consumption and their peak power demand.

It can be useful to put together a list of appliances and total the requirements.

Step 2 - Size the PV system

The PV system should be sized to balance performance and cost.

A good starting point is a PV system where the average daily generation is equal to the average daily requirement.

The PVGIS tool is helpful for a quick calculation of the energy the panels will generate.

Step 3 - Size the Battery

The battery capacity is determined by the formula:

Battery capacity (kWh) = Voltage (V)  x  Battery size (Ah)

The battery is only cycled to the 'Depth of Discharge' - typically 50% for a lead-acid battery and 80% for a Li-ion battery

Useful battery capacity (kWh) = Depth of Discharge (%) x Battery capacity (kWh)

A good starting point is to consider a battery with enough capacity to store the average daily surplus generation.

The battery must also be able to handle the peak power demand.

This is more important for lead-acid batteries which lose performance if they are cycled too quickly.

For a lead-acid battery ensure that:

Battery capacity (kWh) * 0.2  >=  Peak power demand (kWp)

Step 4 - Choose the Victron Energy charger

The Victron battery charger must offer a sufficient charge rate so that it can store all the energy generated and meet the peak demand.

BlueSolar MPPT  *** / ***

The first number is the maximum PV Open Circuit voltage, the second number is the rated Charge Current.

Victron Energy have published a sizing tool for the MPPT which you can download here

MultiPlus ** / *** / **

The first number is the battery voltage supported by the charger.

The second number is the maximum power output from the unit (combining power from the generator and the charger).

The third number is the maximum current provided by the battery charger.

Charger Voltage (V) x Charger max. current (A)  =  Max charge rate (VA)

Step 5 - Model the system

The 'Solar Fraction' is a measure of the fraction of the energy requirement which will be met by the solar battery system. This can be estimated using a simulation program such as PV*Sol.

A well designed system will have a solar fraction of around 60% or more, the rest of the demand being made up by a back-up generator.

Need more help? Please feel free to give us a call on 01404 891 693 or write us an email