Solar Battery Plans - enough?

Bimbly

I have 3.24KWp solar system consisting of 12 x 270w PV panels. When they were installed in 2017, a battery wasn't recommended. I'm now planning to get a battery installed. I've gone for 6kwh because, at £4.5k installed, it'll be paid for by a recent windfall. And it was recommended by the installers. Now I'm thinking - is the battery big enough?

My logic is, during the winter, I can charge it up on cheap tariff overnight. Then, if needed, I can top up mid-afternoon to avoid drawing from the grid at peak (Octopus Agile tariff). So even if an overnight battery charge won't last all day, I'll be saving money on the bill.

Last year, I used 2,640kWh from the grid. In the darker winter months, it averaged 7-9kWh per day. But usage next year is unknown as I'm due to get a hot tub to help my aching back (only a smaller 3-seater, but decent well-insulated model).

My logic is, it's probably only three months of the year in winter when electric use is that much higher. And, as I say, I can charge up the battery twice in 24hrs over that period. Also, if I get this installed and decide to add to the battery capacity, I can. The installers said the cost of the initial install is a lot higher because of the infrastructure, so adding more battery is not so expensive.

That seems logical - right?

Netexporter

Many people use batteries to arbitrage the grid - buy cheap, sell dear. You get more money for exporting all your solar than it costs to charge the battery at off-peak rates. The limiting factor for the battery size may be the inverter, as you need to be able to fully charge the battery within the 4/6 hour chap window, if you are using an EV tariff.

Reed_Richards

Well I have a 6.5 kWh battery.  It charges at approximately 2.5 kW so goes from 10% to 100% charged in less than 2.5 hours.  It also discharges at a similar power so that isn't always enough to avoid drawing some power from the grid.  Maximum charging and discharging power is certainly something you should check.  I think this is down to a combination of what both your battery and your inverter can do.

Bimbly

Netexporter said:

You get more money for exporting all your solar than it costs to charge the battery at off-peak rates. The limiting factor for the battery size may be the inverter, as you need to be able to fully charge the battery within the 4/6 hour chap window, if you are using an EV tariff.

I receive a feed in tariff, so I will not be using an exporting tariff. I have looked at the EV tariffs which are attractive, but you have to prove you have an EV to get one. As I don't have an EV, this is problematic.

Netexporter

I receive a feed in tariff, so I will not be using an exporting tariff.

You can keep the FiT and convert the deemed export to a SEG, where you could get 15p, or more, for exports.

As I don't have an EV, this is problematic.

But you could use Agile, or some of the other TOU tariffs.

I recommend the Gary Does Solar Youtube series to understand which tariff might suit you best. He explains them very clearly. Also Tim & Kat's Green Walk provides good analysis of various tariffs. Search the the "rule of thumb" video, which may provide a quick guide to what may suit you best.

Bimbly

I didn't think I could get FIT *and* SEG. I think it's one or the other, as you have to notify the relevant authorities (grid or whoever). But I will check.

Yes, as mentioned, I am looking at Octopus Agile. I don't know what TOU is.

pete-20-11

Bimbly said:

I didn't think I could get FIT *and* SEG. I think it's one or the other, as you have to notify the relevant authorities (grid or whoever). But I will check.

Yes, as mentioned, I am looking at Octopus Agile. I don't know what TOU is.

You can have FIT generation payments and opt out of the FIT export payment (getting SEG instead). 

Need a smart meter and need to apply for an MPAN for the export via your electric supplier.

Netexporter

TOU is Time of Use. Agile is an example, as are Flux, Go, Cosy, etc.

Bimbly

pete-20-11 said:

You can have FIT generation payments and opt out of the FIT export payment (getting SEG instead). 

Yes, that's what I thought.

Anyway, none of this is addressing the issue of if my logic of getting 6kWh battery makes sense. Or should I look at bigger.

Screwdriva

Which battery are you considering? 

Newbie_John

2640 kWh at 25p rate is £660.
As you already have freeish energy during the day, your solar won't always charge it so you'll need to top it up at night at cheaper rates, energy loss.. your savings will be like £400 max a year? 
If you put £4500 to a savings account at 5% it will generate £225 interest from year 1, unlike battery from year 10+?