Homeowner Blog

Upgrading Your Home Battery to Backup

Mark Golding · 25 Mar 2020

In light of the recent news, the idea of being grid independent with your own power cut protection has become a lot more attractive. 

We have had a number of customers interested in upgrading their solar PV or battery systems to protect them from power cuts. As we mentioned in a previous blog, a solar PV system alone will not protect you from an outage. With no batteries, if the power goes out, your PV system will switch off. This is a safety mechanism so that you do not discharge any excess PV energy to the grid and seriously injure someone if they are working to repair the grid near your house!

Even if you have a battery, some of them will not be able to island your property from the grid, which is the crucial step needed to have a backup system. Batteries need to follow strict DNO regulations to operate during a power outage as well, and will always need prior grid permission before installing.

Tesla Powerwall

We recommend Tesla Powerwall 2 and Gateway 2 as the most straightforward form of domestic backup. It will back up all single-phase loads on your main house distribution board, or a single phase of your 3-phase supply. Other battery systems are a lot less sleek and sometimes only provide a socket to plug in devices you want to run - not the neatest of solutions!

You can also scale the batteries into sets of 13.5kWh with 5kW of charge/discharge each. So you can have up to a formidable 40.5kWh of backup with 15kW of discharge on a single-phase supply with 3 Powerwall units installed (subject to grid approval!). Each battery has its own inbuilt inverter charger which enables an extra 5kW charge/discharge rate and saves installing a separate external bulky inverter charger unit.

How long can the battery last?

This depends on how full it is, what your loads are and if your solar PV is producing energy or not. If your power cut happens at night, when the battery is completely full after charging from the grid, you would have 13.5kWh of support. This would run a 1kW heater for 13.5 hours or a 0.75kW fridge for 18 hours, all assuming no other loads are on.

So if a power cut happens once you’ve had the battery fitted, what would you notice? Most of the time, you will notice nothing. The Tesla app will inform you after 6 minutes of no grid power that you are in an outage. If the power cut was very drastic (such as a tree falling on your line) there may be a few seconds of an outage while the battery figures out what has happened. This means it is certainly not designed for life support systems or critical data backup (i.e. a UPS), but it will cover everyday household loads up to 5kW.

Tesla app backup

Fridges, freezers, lights, computers and your burglar alarm will all run fine, but the really big loads like air conditioning, hot tubs and EV charging points will have to go off! It will also keep up to 7kW of solar PV energy up and running if the power cut hits when it is sunny.

You can set the percentage of charge you want to keep as a reserve from the app, and Tesla also has a ‘storm watch’ function that predicts when outages are more likely, and aims to charge up the battery as much as possible beforehand.

Tesla Powerwall 2 will back up your main board as standard; we just need your main board to be fully RCD protected before we install it. If you have an older version Gateway 1 but would like power cut protection, you can get this upgraded to a Gateway 2 while keeping the existing battery unit the same.

Gateway 1 Single PW2 & Gateway with Inverter & Meter Box
Gateway 1 (top right) Gateway 2 (top left)

Find out more

We can provide a cost for a new battery system, a retrofit on an old system, or we can even apply speculatively to the grid for your DNO permission if you want to know if the upgrade would be allowed on your supply. Just get in touch for more details!

Request a quote

Or download our free guide to residential battery backup:

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Topics: Battery storage, Tesla Powerwall