The Power Rating of your Solar PV System

The solar PV (photovoltaic) array is where your electricity is generated. It’s always better to have more power than you need, especially when the sun is shining down freely upon us. Make the most of the FREE sun and get a solar PV system that will allow you to use air-conditioning on hot summer days and leave you with enough power to charge your batteries in winter months.

There are many things to consider when selecting a solar PV system. Common questions that come up are:

• How many panels do I need?
• What is the wattage of the panels?
• What is the array size?
• What is the difference?

The power rating of a solar system is measured in kilowatts, or kW. It is a measure of how big your solar generation system is, not how much it will produce. This is similar to a car engine, where the size of the engine gives you an indication of how powerful it is, but it doesn’t tell you how much petrol it will use, although the two are related.

Panel Watt x no of panels = size of your solar PV system (kW)

A 7kW solar PV system consists of 26 x 275W or 23 x 315W panels. However, the panels can never run at 100 per cent efficiency. Losses occur through cabling, connectors and at the inverter. The energy output will also be affected by factors such as your location, climate, the orientation of the panels, the time of year and the angle of the panels.
A well-designed system will minimise these losses to give you the best possible output of your system.

The solar panels (PV) are the main power source when living Off-Grid. The expected energy output of a 7kW solar PV system in your location is calculated by multiplying the size of your system (7kW) by the Peak Sun Hours specific in your area which differs between summer and winter. The generated energy, kWh will first go to the load in the house during daytime and secondly to charge the battery bank.

Size of your solar PV system (kW) x Peak sun hours = kWh

Here’s an example

If a specific location has an expected Peak Sun hours of 5.67 in the summer, the expected Energy production from a 7kW solar PV array is 39.69kWh. However, the size of your solar PV array should be related to the worst time of the year for solar generated energy – in the winter. The same location has an expected Peak Sun hours of only 2.44 which means that the 7kW solar PV array can now only generate up to 17.08kWh on average.

How is the output of my PV array influenced by array tilt and orientation?

In the Winter – High levels of panel tilt will give greater solar production in winter, but this will come at a compromise -with less energy being produced in summer.

In the Summer – Lower levels of panel tilt will produce more solar power in Summer months, but it is important to have a minimum of 5 ° tilt for the self-cleaning function of the panels.

For an optimum all year around the performance of a typical solar PV array the typical angle of the solar panels can be between 15–30°.
This may vary depending on your specific location.

Facing panels East and West – this gives you more solar power earlier in the mornings and later into the afternoons. This can be useful for working families where power consumption is not during the middle of the day but rather in mornings and from afternoon into the evenings.

Solar panels with low light performance

This is especially important on overcast/rainy days to help your battery system cope with your daily power demands. Furthermore, when living Off-Grid you want the panels to start generating energy as soon as possible in the morning and stop using the stored energy in your battery bank. In the late afternoon you can still get a little bit more generated energy from the panels before you start using the battery bank for night use.