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Making the most of your solar panels

If your home has solar panels – installed by you, or your landlord or through a ‘rent-a-roof’ scheme – you may need to re-think the way you consume electricity in order to reap the greatest benefit

Making the most of the free electricity from your solar panels may involve changing your routines and thinking differently about energy use. It may mean planning ahead: for example using your washing machine or dishwasher during the day rather than in the evening.

Solar photovoltaic (or PV) panels convert the energy in sunlight into electricity, and this is effectively free electricity that can be used in your house (once the cost of installing the panels has been taken into account, of course). Surplus electricity is exported to the grid to be used by somebody else.

However, when the sun isn’t shining, or when you’re using more electricity than the panels are producing, the extra will be imported from the national grid, as it was before you had the panels, and you will be charged for it by your energy supplier at the normal rate.

 A typical 2kWp (2000W) household array of solar panels will produce 2kW under optimum conditions, that is:

  • if the panels face more or less south and are sloped at the right angle to receive the most sunlight
  • if the panels are free from shade;
  • if it’s a sunny day.

So, at noon on a bright June day they could generate close to 2000W, while on a cloudy afternoon in December that might be nearer to 100W. To make best use of this free energy, it helps to know how much electricity different appliances use.

Let’s look at some typical power ratings:

  • Low energy light bulb: 15W
  • Fridge: 100W
  • Laptop: 150W
  • Microwave: 750W
  • Washing machine: 2500W (2.5kW)

And let’s assume your solar panels are generating a steady 1000W (1kW). Of this, 100W will be used by the fridge – though not continuously since it switches itself on and off according to need – leaving 900W for other appliances. So based on the ratings above you could use your 750W microwave for free and still have 150W available to run lower power appliances, such as lights. If you wanted to run your washing machine you’d pay for the extra 1600W that you need and that the solar panels can’t generate.

It follows that you should stagger the use of high-wattage appliances to make the most of the free electricity available. This might mean waiting for your washing machine to finish before running the dishwasher.

Check your inverter

Solar panels come with an inverter which converts the electricity generated by the panels into a form that things like TVs or toasters can use. A display on the inverter shows how much electricity is being generated. If you know how much your appliances use you’ll be able to look at your inverter and then choose what you should run in order to make the most of the free electricity being produced. But remember that what you read on your inverter display shows the output at that particular moment in time; this may quickly change according to weather conditions.

It may be worth making a note of the power rating of your appliances (e.g. laptop, 150W; hairdryer, 1300W) and keeping it next to your inverter display to help you make quick decisions about what appliance you want to use.

However, the inverter may be installed in out-of-the-way places like the loft. If this is the case it’s worth thinking about buying an energy monitor that you can put in a more convenient place.

These can be bought for around £100. Some models are straightforward to install but others may need to be fitted by a professional electrician. You can even have your system connected remotely to your computer, allowing you to monitor your panels over time. If you don’t own the solar panels, check with whoever does that it’s OK for you to fit a monitor.

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This information is available as a freely downloadable PDF from this page.

For more domestic energy advice, view all our advice pages.

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