Economy 7 is an electricity tariff that means you get cheaper electricity for 7 hours every night. During the day you have a separate higher tariff for daytime (peak) electricity. This idea behind Economy 7 is that you use the cheaper electricity to heat up you water ready for the next day. If you have electric storage heaters you could also use the electricity to heat up you storage heaters so that they release the heat throughout the day.
You can have solar panels with Economy 7 or indeed Economy 10. As far as I am aware this should not affect your application for free solar panels. The only time any electricity tariffs will cause problems with solar is if you are on a credit or key meter where you have to top up a card or a key in order to buy your electricity. With the credit meters you will not be able to get free solar panels. You can however apply to your electricity supplier to have them changed to normal meters. There may be a charge for this and your electricity company may need to de a credit check first.
The main reason for having an E7 tariff is so that you can use the cheaper rate electricity to off peak to heat your water and charge up your storage heaters. Depending on which utility company is providing your electricity will depend on what time of night your 7 hours of cheaper rate electricity starts. It may switch over at midnight, 1am or 2 am so you need to be aware of what hours are covered.
Solar PV works during daylight hours so the electricity that they will be providing will offset the more expensive electricity from your energy provider. With solar panels it is best to use as much of the electricity that they generate as possible during the day because with free solar any electricity that you do not use is wasted as you cannot store it.
If you are on an Economy 7 tariff then your hot water is going to be heated at night to take advantage of the lower cost of electricity. Some people on E7 may also have night storage heaters, these are electrically powered radiators that store the heat in a thermal mass such as concrete or clay bricks so that the heat can be slowly released during the day. This minimises the amount of daytime electricity that you need to use for heating.
With free solar panels installed however you will want to use the free electricity that is produced during the day. One of the best ways to do this is to use the free electricity to heat your water and if you have storage radiators to heat them up as well. To do this you will need to find out whether you can use your electric immersion heater during the day to heat your water and whether you can do the same for your electric storage heater. There may be a timer or just a switch, it may be called a boost switch in some cases.
Unfortunately these systems were not developed with solar photovoltaic systems in mind. There isn't yet an automated way to use solar automatically where you can divert your excess solar power into heating your water in your hot water tank. People who have solar installed tend to change the way they use electricity to make the most of the free power that is generated during the day. You can do this by overriding your water heating system which is usually an electric immersion heater and have it on during the day. The same can be done if you have electric storage heating.
Solar panels produce more electricity during summer than they do in winter where the days are longer and sunlight is more intense. During the long winter months you will not have as much free electricity generated to contribute towards your hot water or heating and you should therefore be more careful about monitoring you use of electricity during the day. If for example you switch on you immersion during the day and your panels cannot meet the power demand of the immersion then the shortfall is going to be met by you electricity supplier at your daytime rate.
If you solar installer installed a monitoring system or have given you access to live data online you should be able to see how much power your panels are currently producing. This will help you decide whether or not it would be worthwhile to switch on your water heating or not. If you can adjust the temperature on your water heater then turn it down during the day so that it does not use as much electricity and then when you switch the immersion off put the temperature back to normal ready to use the cheaper E7 electricity at night.
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