Solar 101- our resource for the basics of solar systems

Solar system basic setup

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This is a basic DC solar system, which consists of a solar panel, a regulator and a battery. Remember you ALWAYS need a regulator between your battery and panel.

NEVER CONNECT A SOLAR PANEL DIRECTLY TO A BATTERY.

Unless you use an MPPT regulator, you will need to match your panel voltage and battery voltage (see below). This system is mainly used for 12V DC lighting. However, any other 12V DC appliance (such as fridges) can be used on this type of system.

This image is courtesy of Victron Energy B.V. from their Off-Grid Brochure (www.victronenergy.com)

Matching panel and battery systems

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Many customers come to me with mismatched solar system. For example a 245W panel linked to a 12V system with a simple PWM charge controller.

Essentially, the power from the panel is composed of Watts, Amps and Volts where W = V x A. The PWM can only send out the same Amps as it receives. For example a 240W panel produces around 8A at 30V. However if you linked this to a 12V battery, the PMW will produce 8A at 12V (only 96W). However, linked to a 24V system it would produce the same 8A at 24V = 192W.

If you used an MPPT charge controller and the same 245W panel on a 12V system, the MPPT would take the 8A (at 30V) and reduce the voltage down to 12V (2.5 times less) and at the same time increase the Amps by a similar factor of 2.5, producing around 20A. This means that the MPPT can produce 12V x 20A = 240W, essentially making the system a lot more efficient.

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The watt (W) is the amount of power an appliance uses. This is equal to the Volts (V) multiplied by the Amps (A). The watt-hour (Wh) is the amount of energy an appliance uses over a period of time. For example a 5W light bulb will use 10Wh if it runs for 2 hours (5W x 2h = 10Wh)

Now, when you run these lights, you should not let your battery run down more than 50%. A 12V 40Ah battery has a capacity of 480Wh (12V x 40Ah). So, we can only use 240Wh from the battery. If we are drawing 4 x 5W = 20W, we should be able to run those lights for 12 hours (12h x 20W = 240Wh).

Now, can we refill the battery with a 50W panel? Usually, on a good sunny day, you can get about 5 hours of sunlight. So in 5 hours we can generate 250Wh (50W x 5 hours). This is more than we used, which was 240Wh.

This is a very simple example, but can be extended to more items, just add up the Wh used for each appliance to get a total Wh used and you can then size the battery or batteries needed and the panel size needed