You have your solar panels installed. You have a solar battery. You have a smart meter. Your energy provider provides a cheap rate at night. Now what do you do?
Solar installations will give you an option, either through an app or by pressing buttons on a control panel, to set the hours at which the battery will charge from the mains instead of from the solar panels. So, how many hours should you set it to charge, and which hours?
Let's say you get a cheap electricity rate between 2 a.m. and 8 a.m. Obviously, you will set the battery to start charging from the mains at 2 a.m. An average battery takes about three hours to reach full charge, so you might think it's OK (in this example) to set it to stop charging at 5 a.m. Wrong! As soon as you stop charging from the mains, the battery will start giving out its stored electricity. In winter, that means if you are using electric heaters and immersion heaters and so on, most of that stored electricity will get used up before the expensive rate kicks back in at eight o'clock.
The moral of this story is to always set the battery to charge for the whole of the cheap rate period, i.e. in this example right up to 8 a.m. Then, at the switchover point, when the electricity rate becomes much more expensive, you won't be paying for it, because you will first be using up all that cheaper rate electricity you stored in the battery.
Is there any circumstance where you might set the battery to charge from the mains in daytime? There is one. In winter, when most of your solar will be used directly by electrical items in the house, there won't be so much spare for keeping the battery topped up. Normally, this doesn't matter, but if the weather forecast is giving out a red-alert for high winds, it's always possible you might get a power cut. So, temporarily, it's advisable to set the battery on continuous charge. If and when the power cut does occur, you'll have a fully charged battery ready to keep running lower power items like lights, kettle, microwave, computers, phone chargers and so on.
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