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Why solar?

This is where you can discover how solar works and how to calculate your power requirements

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How solar works

Solar is the world's fastest growing energy technology. As a tried and tested power source, it is used around the world for numerous commercial, industrial, government and domestic applications. It is powering water pumps in African villages, weather stations in the Antarctic and satellites in space! As its potential becomes ever more important to our lives, the UK's solar power industry reported its highest ever production of electricity (9.68GW) in April 2020.

Smart solar generates power from daylight

A solar panel works by transforming the energy from the sun into a reusable form of electricity, a process known as Photovoltaic (or PV for short). The panel acts as a collecting tray to catch the sun’s rays. The bigger the panel, the more energy you can collect. The energy is then stored in a battery for future use. Sometimes more energy is collected than needed so with larger panels a voltage regular is fitted to control the flow of energy and prevent battery damage.

It would be hard to find a more environmentally friendly power supply!

Clean and green, solar power is a renewable, sustainable and non-polluting source of energy. It is easy to see the appeal of solar power for domestic and commercial use. Low maintenance and long lasting, it is a highly cost-effective and reliable energy supply.

Calculating your solar panel requirements

The power of three!

There are three main things to consider when choosing a solar panel, or creating a solar system.

1 : How much energy can your battery store?

2 : How much energy will your appliance(s) use and how long will they use it for?

3 : How much energy can a solar panel generate?

1. How much usable energy storage do I have?

Working out what goes out, and what you need in

Firstly you need to know how much energy your battery can store. Then you can select a solar panel that can replenish your ‘stock’ of energy in the battery in line with your pattern of use.

Battery capacity is measured in Amp hours (e.g. 17Ah). You need to convert this to watt hours by multiplying the Ah figure by the battery voltage (e.g. 12V). this is just the simple calculation below.

X (battery size in Ah) x Y (battery voltage) = Z (power available in watt hours

So, for a 20Ah, 12V battery the watt hours figure is 20(X) x 12(Y) = 240(Z)


This means the battery could supply 240w for one hour, 120w for two hours or even 2w for 120 hours i.e. the more energy you take, the faster the battery discharges.

Getting to grips with rated power

However, you are never really able to take all the power from a battery as once the voltage drops below your equipment’s requirements it will no longer be able to power it. There is a simple rule of thumb for this but please check your battery’s specifications to make sure.

Lead acid batteries will give you around 50% of their rated power (depth of discharge) (i.e. a 10Ah battery has 5Ah of usable power)

Lifos, our advanced lithium iron phosphate battery, will give you 90% of their rated power.  For example, the Lifos 68Ah battery has 61.2Ah of usable power). To find out more about the advantages of our lithium iron phosphate batteries visit our Lifos page.

2. How much energy will you use?

Adding up the the energy sums

The power consumption of appliances is generally given in watts. So, for example, a small portable TV is around 20w. This information can be found on the data sticker that most electrical items have.

To calculate the energy you will use over time, just multiply the power consumption by the hours of intended use.

Calculating your power use

If the 20w TV is on for two hours, it will take 20 x 2 = 40WH from the battery.

Repeat this for all the appliances you wish to use, then add the results to establish total consumption like below.

  • TV 20w on for 2 hours per day = 40w per day
  • Radio 10w on for 5 hours per day = 50w per day
  • Water pump 20w on for 20mins per day = 6.66w per day
  • Main Light 30w on for 3h per day = 90w per day
  • Spot lights 10w on for 1h per day = 10w per day

Total = 196w per day

Get energy smart

An easy way to lower your power usage is to swap out halogen lights for LED lights. LED lights generally use 80% less energy for a similar light level.


3. How much energy can a solar panel generate?

Sizing up your solar panels

The final part to sizing your solar system is the solar panels. The power generation rating of a solar panel is also given in watts.

Theory vs practice

In theory, to calculate the energy it can supply to the battery, you multiply watts (of the solar panel) by the hours exposed to sunshine.

In practice it’s not a great way to calculate the output from a solar panel so we work to a few simple rules.

Seasonal differences

We would generally advise that an average UK winter's day will only give you one hour of sunshine

An average UK summer's days will give you six hours of sunshine

So in winter a 10w panel will provide 10w worth of energy back into your battery. (10w x 1 = 10w)

In Summer a 10w panel will provide 60w worth of energy back into your battery. (10w x 6 = 60w)

Using the above calculation takes into consideration any losses in the system from the regulator, cables and battery you may be using.

Go premium

For your caravan, motorhome or campervan we can supply you a range of solar panels from a small 5w unit all the way to 200w units. Plus you can mix and match panel sizes to create the power generation you want.

For more information and details about the benefits of our range of premium solar panels visit our PV Logic page. 

If you are looking for a solar system for your home or commercial premises take a look at our PVE page.

The finishing touch

The final piece to complete your solar system is the charge controller, or voltage regulator. It's basically the same thing with just a different name. This essential piece of your solar system controls the charge put into your battery, stops overcharging and prevents the solar panel pulling power from the battery at night.

Shop our PV Logic solar panels and accessories  ›

Get in touch

We hope this guide has helped you understand how solar power works and how you can size up your own energy generating systems.  If you have any other questions, or you would like our help in deciding what solar system is right for you do call us on 01684 774000 or email hello@solartechnology.co.uk