A solar battery does not come cheap. So, it might be tempting to think you don't need one. A newspaper article I read tried to be clever by claiming batteries were obsolete because, instead of charging the battery, you just sold any surplus power back to the power company. What the writer of the article obviously didn't appreciate was the power companies are there to make profit, so the unit rate they pay you for exported electricity is typically as small as only a quarter or a third of what they charge you for the electicity they supply, in other words not that brilliant.
Is your household a typical one, with adults out at work in the daytime, children out at school? Then you need a battery. In mid-winter on sunny days, the panels will only be generating electricity in a three hour period - between eleven in the morning and two in the afternoon. Even so, in that short time, they can generate significant amounts. If you have a battery, all that nice free electricity gets stored in it, ready for use when the children get home from school and the adults get home from work, the time when you start turning on heavy usage items like heaters, cookers, showers, the immersion for the hot water, and so on. Othwerise, without the battery you're going to be paying the electricity company for that usage and it's precisely those winter bills that add up.
A battery has two other advantages. The first saves you money whether the sun is in or out; in fact, it saves the money at night! If your electricity is on a variable tarrif with a cut-price night-rate (more of that in a future post) you can set the battery to charge at the cheap rate. Then, at eight in the morning, or whenever the rate switches back to the more expensive rate, you will for a few hours be using the cheaper rate electricity you stored over night. You might save at least 500 Euro a year, or equivalent, a sum of money completely independent of the number of solar panels you have.
The second advantage is protection against power cuts. If the battery is charged up and there is a power cut, all you need to do is pull a switch to change over to battery power. The first time this happened in our house, at night, I was tempted to do a "Mr. Bean" by opening all the curtains and turning on all the lights, including the garden lights, just to annoy the neighbours. I restrained myself. How long will the battery last? If you switch off all heavy power items, like space heaters and immersion heaters, and don't use the electric oven, you can probably survive for 24 hours using just electric kettle and microwave and still keep all the house lights, TV, computers, wi-fi, mobile phone chargers and other lower power devices running.
Soalr panels are becoming ubiquitous. You even see them on the roofs of canal barges, talking of which, please visit my sponsoring web site and take a look at this mystery thriller, where a man accused of murder goes on the run by travelling the country in a canal barge, which he figures is the last place the police would think of looking for him!
