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If I have a 15kwh battery, how big an inverter?
If I have a 15kwh battery, how big an inverter?
Hello everyone,
I’m glad I found this forum, so much great information. My question is: if I have a 15kwh battery, how big the inverter should be to optimise storage as well as export? -
13 Replies
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About a MW should do it, you coild charge and discharge thousands of times a night then and make a fortune.
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It depends on your house load and to some extent your tariff. Most houses a 5kW inverter is sufficient and will charge your battery from flat in 3hrs.
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Beware : suppliers are getting wise to brown exports. OfGem say they need pay nothing for such so unless you are planning on using a tariff like Octopus Flux that actively encourages brown export by its structure, focus on your battery as an average tariff reduction device not an brokerage device.
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Don’t forget, your inverter will limit how many Kw you can draw from your battery at any one time.
A 3.6 is basically a kettle and a bit.
If you need to draw more the rest will come from the grid.
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The selection of inverter will be based on the anticipated peak demand, ability to charge fully in a low rate period and the charge/discharge rate of the battery itself.
For example. If you have a four hour window to charge the battery, the charge rate is going to need to be around 4kW. If it’s three hours it’ll be more like 6kW.
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Different batteries will have different charge rates so you need to look at that as well as inverter charging rate.
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You need to think about consumption as much as storage/export. And think ahead to future needs. A few years ago we went with a couple of Powerwalls. Oversized for our needs at the time but conscious we were moving towards full electrification. We’re now all electric and are hitting the limits occasionally. Here’s a screenshot from Monday 5th. Got down to -4°C, heat pump was busy, I was off work doing a fair bit of baking and we were hitting about 6kW – we can go up to ten with 5kW from each Powerwall. The 5kW for each Powerwall means we can make the most of charging opportunities on Intelligent Octopus Go. Note the car doesn’t charge from the batteries.
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Hi, similar advice to the above. My batteries discharge at 5kw, my inverter is 6kw. You will be limited by your battery and inverter so aim for as much as you can. 5kw suits my household but all the ovens and hob on will draw more.
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Boil a kettle – that’s 3kW – add the toaster, 1.5kW – the microwave 2kW – the oven 3kW – the rest of the house 0.5kW – ok, you won’t fire them all up at the same time, but you’ll understand why a 3.68kW inverter is a waste of time. Get a big inverter, but you’ll probably find the limiting factor is how much max can a 15kWh battery discharge…. I initially had a 6kW inverter but upgraded after a year, as it was undersized….
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Tbh I’d get a bigger inverter than you think. The cost difference it a tiny contribution to the total cost of the system.
We have an 8kw inverter (and 20kwh of batteries) – it’ll run the cooker, kettle and a bunch of stuff like electric showers all at once. They only run for a few minutes at a time so the total taken from the batteries isn’t an issue, but it means even in winter we only draw from grid in the cheap rate overnight (keeping the average price we pay for electricity below 8p per kWh and therefore minimising the bills)
When I was looking the price for a 3.6kw inverter was around £1100, a 5kw unit around £1500 and an 8kw one £1800. If doing it today I’d buy a 10kw unit. I bought a Sunsynk unit which is certified to run with a limit on export meaning (other makes can do this as well – just make sure you check). if the G98/99 process imposes a lower export limit you can use a large inverter an just cap how much it exports
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The powerwall 3 has an 11kw inverter for provision of a near full home solution a 3.6kw can just about power a kettle using those as your guidance think about how often you will want to run a kettle – oven – immersion etc ( assuming they are electric) and work it out accordingly me personally I would look at min 6kw probably 8kw as a minimum
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Great post. I’ve currently got an issue with my setup. Has 2 10.2kw batteries but upgraded to 4, was told it would be ok. 6kw Inverter. However I can rarely charge overnight at cheap rate (00.00 – 07.00) and I believe this might be down to the fact my ASHP is running overnight and limiting charge ability. This sound right ?
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Depends on the load on your house, but I would choose 5 or 6 kw to minimise you pulling power from the grid.
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