How to calculate your solar power requirements

How much solar power do you need?


So you want to set your rig up for Solar but you are not sure what size of set up you need? This blog is designed to give you the tools needed to be able to work out exactly what are you are drawing from your rig's batteries and what type of solar set up you need. Knowledge is key when setting up your rig for solar so the more information you have on each and every one of those home comforts devices you plan to take away with you the better. If anyone has a question pop it in the comment section below. I will try my best to answer everyone.


iTechworld Solar Panel


How to work out Watts, Amps and Volts

A larger solar panle 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 × Volts


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


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 I need a battery?

iTechworld Lithium 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 in to 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. A smarter battery setup would be to use an iTECH120 lithium battery. This new type of battery is a fraction of the weight of old style AGM batteries. AGM batteries usually weigh 35kg but and iTECH120 battery weighs just 13kg. You can also use more of the battery capacity in an iTECH120 - 80% which means its usable Amp Hour rating is similar to a 200 Amp Hour AGM. Read more about the iTECH120 HERE


What size solar panel do I need? 

280 Watt Solar

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, I repeat Solar Panels are not 12v. Any one who works out the Amps of a solar panels 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 of our website or on the unit itself.

Check out the iTechworld Solar Panel range HERE


Power Inverter

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, its 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.

Check out the iTechworld range of inverters HERE

Charge Controllers/Regulators

MPPT Controller

All Solar Panels 30 watts and above need a Solar Charge Controller/Regulator. A Charge Controller/Regulator is necessary to protect the batteries from over charging 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.

Check out the iTechworld range of Charge Controllers/Regulators HERE


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  • Mandy

    Hi I need your help. I have a solar panel which is 250 watts at 18 volts. That is controlled by a 30 amp Mttp epever unit that feeds 4 X 130Ah deep cycle batteries that are connected on parallel. I also have my batteries connected to my van with a split charge relay. My main power draw is my Mobicool coolbox which draws approx 4 amps per hour. The problem I am having is that the batteries do not seem to last very long. Living in the UK sun can be a premium but during really sunny days the solar panel gets the batteries up to 14 volts. The moment the batteries have to supply the load that’s when the level starts to drop. I am new to all this and wonder if I am doing anything wrong. Great site by the way and so nice to find lots of info in one place

  • Randy

    Are there options besides AGM, like Lithium-Ion, that would produce comparable results with less weight? Application is a boat trolling motor array.

  • Daniel

    Hey mate
    I have 2x 120 amp battery’s in parallel and was lucky to be given a 125w solar mat, it has a 12amp solar charge controller with it, Is that ok to charge those 2 batteries or does it need a larger amp controller

  • tomanddawneBowman

    I have just bought a pop top with a new I panel solar fitted could I please ask what wattage it is the sixe is 680mm wide x1368mm long it has some numbers I found underneath LA 8HO 860 thankyou kindly

  • David

    If I have 2 × 100w panels linked, each with 5.46 AH max output what would be the max output in perfect conditions ie: high UV.
    Currently cant get much over 5.46 amps.

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