How To Calculate Your Solar Power Requirements

Knowledge is key when setting up your rig for solar, so the more information you have on each and every one of those home comfort devices you plan to take away with you, the better.

Calculating Your Solar Power Needs

Working out Watts, Amps and Volts

A larger solar panel will collect more energy in less time, but just how big does the solar panel need to be?

The power consumption of appliances is usually given in Watts. To calculate the energy you will use over time, just multiply the power consumption by the hours of use. For example:

10 watt device used over 3 hours equals 10 x 3 = 30 Watt.

How to convert Amps to Watts

The energy in Watts is equal to the electric charge in Amps times the voltage in volts:

Watts = Amps Ã— Volts

Example: If your device doesn't have the Watts labelled on it, then it should at least have the input Volts i.e. 240V and the Amps AC it draws such as 240V 1.5A. You can then use the equation Watts Volts x Amps so 240v x 1.5amps = 360 Watts.

How to convert Watts to Amps

The electric charge in Amps is equal to the energy in Watts divided by the voltage in volts (V):

Amps = Watts / Volts

Example: Find the electric charge in Amps when the energy consumption is 300 watts and the voltage is 240 volts. 300 Watts / 240 volts = 1.25 Amps.

Do you need a battery?

Solar panels are commonly used to charge a battery not to charge a device directly. There are a couple of reasons for having batteries. Solar panels might not generate enough wattage to directly power an appliance, but they can build up a higher wattage via a battery.

Secondly a battery can regulate the power going into the appliance at a constant rate. When solar panels are charging a battery it is usually at a varying rate which could harm an appliance if not regulated.

Battery capacity is measured in Amp Hours (e.g. 120Ah). You need to convert this to Watt Hours by multiplying the Ah figure by the battery voltage (e.g. 12V) see calculations above.

AH refers to amp hours. This rating is usually found on deep cycle batteries. If a battery is rated at 100 amp hours it should deliver 5 amps of power for 20 hours or 20 amps of power for 5 hours.

When choosing a battery, keep in mind the equipment you will be powering and the time in which they will be running. Theoretically a 100Ah battery can deliver 5 amps over a 20 hour period (and so on).

Taking into account the average small campsite - with a small 45W fridge running for 6 hours, 3 hours of 15W lighting and 20W of other electronic equipment - the minimum consumption to be expected is 335W. Take this wattage and divide it by the voltage, 12V, gives 28Ah. With the aim of leaving 50% in the battery brings the requirement to 56 Ah per day.

What size solar panel do I need?

Solar Panels power generation is commonly given in Watts e.g. 120 Watts. To calculate the energy it can supply the battery with, divide the Watts by the Voltage of the Solar Panel.

120 Watts / 18V = 6.6 Amps

Please note that Solar Panels are not 12V. Any one who works out the Amps of a solar panel using 12V as the voltage calculation does not understand solar or has been misinformed. All solar panel voltages should be marked in the item description either on the website you got it from or on the unit itself.

What about Inverters?

The power inverter converts your storage battery power into the 240 volts AC that runs your appliances. Unless you only run 12 volt DC appliances you will need a power inverter to supply your AC.

There are 2 types of Inverters: pure sine wave and modified sine wave.

The Pure Sine Wave matches the power to that of which you get from your electricity supplier, it's clean and you can run any appliances safely, even sensitive equipment.

The modified sine wave used to be considered a dirty power but some aren't as bad as they used to be, you can use this inverter type for things that don't have sensitive electronics for example fridges, cookers, pumps, You may have to be careful with some appliances such as laptops and TVs so check first.

What about Charge Controllers/Regulators?

All Solar Panels 30 watts and above need a Solar Charge Controller/Regulator. A Charge Controller/Regulator is necessary to protect the batteries from overcharging and supply them with the proper amount of energy to promote long battery life. If the charge isn't regulated it can have a damaging effect on the battery being charged.

Got any more questions about setting up your solar panel system? Give us a call today and let us know how we can help!

About the Author

Megan Thicke Megan is a researcher from Canberra who has dedicated her time to writing articles for outbax in order to help educated readers about the proper ways to handle generators and lithium batteries. She provides content about picking the right hardware for its specific purpose and how to take care of them properly. As a writer for 7 years already, her articles are witty, smart, and absolutely informative.