Is battery storage all its cracked up to be?

tesla powerwall battery

Battery storage is the big thing in the solar pv world at the moment and like when any new big thing comes on the market there are a number of issues to be sorted through.

The first question people have is can it be retro-fitted? The answer to this is yes. If you have a solar pv system in your property, a battery storage system can be retro-fitted.

Do I need battery storage? This is a really important question and should be considered carefully. If you are exporting more than 40% of your solar pv generation then a battery will be worth it for you. If not, then you’re probably better sticking with it as it is. Just so you know, the average export for a UK household with a 4kW pv system is 75%. So the chances are that unless you have a really good grasp on what you’re generating at any one time and turning things on and off to suit then you are probably exporting above 40%. I would recommend installing a smart meter which will tell you: 1. how much solar pv electricity you are generating. 2. how much you are exporting and 3. how much you are importing. With this information you will have a great idea as to whether you need battery storage.

How big a battery do I need? This is a big question and there a lot of things that need to be considered. Battery storage is measured in kWhours. e.g. a storage capacity of 4kWh. Please note though that this is not the same as a 4kW solar pv system. a 4kW pv system working at full capacity will produce 4kWh of electricity in one hour or 8kWh in 2 hours etc. The 4kWhour battery is capable of storing 4kWh of electricity. So in this example, after the battery is full after one hour, it will stop storing electricity and the electricity will revert to being exported onto the grid. The ideal battery size then is one which will be small enough to be fully loaded by the end of most days and will also be big enough to supply most if not all of the electricity that you need when the solar pv is not generating i.e. in the evening and night time.

On this then there are a number of options available and most jump around the 2-6kWh of storage capacity and price and quality varies with manufacturer. The big thing to remember though is that the vast majority of these batteries cannot be fully drained down. If there is a storage capacity of 4kWh then the drain down limit might be only 3kWh or less. This is a serious limitation on the solar battery storage industry at the moment and serious attention to detail must be paid to this point when purchasing.

There is one big exception to this rule (that I know of!) and that is the Tesla battery. Tesla, as you may be aware, have led the way in the last few years in the electric car industry and they are now clearing the way on the solar battery storage front. Because I am not an employee of the BBC I have no problem saying that the Tesla battery is by far and away the best battery in the industry (other battery storage options are available…they are just not as good!).

The first thing about a Tesla battery is that its a beautiful piece of kit. Its the iphone of the battery world. I don’t know if that is a big deal for you but the battery will probably be stored on an outside wall (mainly for cooling purposes) so having a nice looking battery is quite important.

More important though is how it works. The Tesla battery is bigger than most and has a storage capacity of 6.8kWh. This is huge and will comfortably provide even a large household with all the electricity it needs in the evening. What’s more though, there is no limitation on storage use. So every last drop of your stored 6.8kWh of electricity can be used up. This is a fantastic selling point for the Tesla.

How big are they? The different batteries vary in size but generally they are a little bigger than the inverter that is probably installed in your loft.

Where do they go? Some batteries can be installed in the loft. However, this is not very wise as they will need to cool down and lofts can be very hot and stuffy. This then is also true of understair cupboards and airing cupboards as old coats, towels and old football kits are likely to get thrown on top of them. The best place is on an outside wall as this provides great cooling and you can also boast to your neighbours about it!

How much does it cost? Again, price varies dramatically but the Tesla installed is about £4500 plus VAT. Most other systems are likely to be cheaper but you get what you pay for. If you want the best, you have to pay more.

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