My year with a battery - A year of savings.

Waywardmike

Hi All, the numbers are in… 

I have an old FIT system from 2014 and am currently in my 9th year.  It paid for itself in FIT payments alone a couple of years ago, so decided to fit an AC coupled Battery and inverter. This was fitted in April last year, 6.5kWh battery, so not huge but a good useable amount.

I got a much better monitoring system in May last year, Solar Assistant on a Raspberry Pi, so although I’ve had the battery for over a year, I now have a full years data.

House Load                                   5457.5 kWh      

PV Generation                               4436.44 kWh    

Battery Charged                            1634.8 kWh      

Battery Discharged                       1459.9 kWh                     89.3%  Round trip efficiency

Exported                                        616.7 kWh        

Imported                                        2159.27 kWh    

iBoost                                            380.26 kWh

Consumption                                 86.1% (71.1% Aug, 98.9% Dec)

Consumption without battery        49.2%

So how does this stack up in terms of money?

FIT payments                   £954.46

Used Savings                    £573.22

Battery Savings                £467.59

iBoost Savings                  £? (Not really sure how to calculate the gas offset savings)

Meaning a total of £1995.28 made/saved + iBoost savings.  Not bad at all for a single year…

My total energy bill for the same period was £1170.96.  It looks like the good years may be gone as the FIT payments used to completely cover our annual energy bills.

If energy prices stay high, here’s hoping they don’t, the battery should pay for itself within the 10 year warranty period, but the ‘system’ should pay for the battery in less than two years, so even if doesn’t directly pay for itself I’m not too bothered.  The system is now much more ‘useable’ with a battery, gone are the days of staggering appliance usage to minimise grid draw, the battery will cover any shortfall from the PV so no worries.  Also my wife will probably say she LOVES the battery, I’m not sure I’ve asked her once in the last year to delay doing something, laundry, dishwasher etc, as it’s going to be sunnier in the afternoon…

If I was starting again and the calculations were looking like 8 years payback without a battery and 10 with, I’d choose the battery every time.

Another thing to note is that I've been part of the 'onboarding' process for Octopus Go for the last 8 months.  Have currently had 3 failed attempts at installing a SMETS2 meter and am now currently waiting for my DNO to change the fuse before I can go for my 4th installation attempt.  Once I'm able to take advantage of the available smart tariffs, there are even more savings to me made load shifting as my battery did almost nothing over the month of December.  

Mikeyboy01443

My install is just over a year old now too, and my savings calculated so far is just over 2k, so about the same! Pretty pleased with that

EcoScruples

Well thats got me thinking, im a few days away from having my first years data.
Is that the way to calculate your round trip efficiency? If so mine is 97% (it's a DC coupled battery).

I'll be doing some calls and will post something in here next week.

Waywardmike

EcoScruples said:

Well thats got me thinking, im a few days away from having my first years data.
Is that the way to calculate your round trip efficiency? If so mine is 97% (it's a DC coupled battery).

I just used energy out vs energy in, not sure if there's a better way?

Interestingly, if there's a lot of energy going in and out my efficiency is better, 93.63% for last May, whereas in December it's a very low 80.86% because very little went in so the battery was generally just hovering around the 10% charged mark, the inverter using the energy to power itself presumably.

michaels

Isn't your saving (from the battery system only) energy out of battery x rate you would have paid for that energy?

1459.9 x 32p = £467

Less any of that energy that might otherwise have heated hot water via the iBoost (worth say a saving of 11p per unit of gas water heating costs)

Edit to add : So this is the saving you need to compare vs the cost of the battery system.


You might be able to improve on this using a TOU tariff over the winter and/or Octopus Flux over the summer.  Should also compare vs agile export with and without battery.

Waywardmike

michaels said:

Isn't your saving (from the battery system only) energy out of battery x rate you would have paid for that energy?

1459.9 x 32p = £467

Less any of that energy that might otherwise have heated hot water via the iBoost (worth say a saving of 11p per unit of gas water heating costs)

You might be able to improve on this using a TOU tariff over the winter and/or Octopus Flux over the summer.  Should also compare vs agile export with and without battery.

Exactly that... Which is what I wrote, 467.59? Although I had 4 months at 28p and 8 months at 35p a kWh. 

I wasn't sure how to calculate how much of that battery energy would have heated water, we're very low users of hot water it would appear, but It's offset by the iBoost savings which I didn't add.  It's safe to say I made/saved £1995.28+

If I go to flux or another TOU tariff I would have to opt out of 50% deemed export, I have that calculated for the previous year at £111 deemed export and ~£98 if I was on Octopus 15p a unit export.  Flux would probably be more and maybe exceed my deemed export, but isn't guaranteed whereas my deemed exports are for another 11 years.

michaels

Waywardmike said:

michaels said:

Isn't your saving (from the battery system only) energy out of battery x rate you would have paid for that energy?

1459.9 x 32p = £467

Less any of that energy that might otherwise have heated hot water via the iBoost (worth say a saving of 11p per unit of gas water heating costs)

You might be able to improve on this using a TOU tariff over the winter and/or Octopus Flux over the summer.  Should also compare vs agile export with and without battery.

Exactly that... Which is what I wrote, 467.59? Although I had 4 months at 28p and 8 months at 35p a kWh. 

I wasn't sure how to calculate how much of that battery energy would have heated water, we're very low users of hot water it would appear, but It's offset by the iBoost savings which I didn't add.  It's safe to say I made/saved £1995.28+

If I go to flux or another TOU tariff I would have to opt out of 50% deemed export, I have that calculated for the previous year at £111 deemed export and ~£98 if I was on Octopus 15p a unit export.  Flux would probably be more and maybe exceed my deemed export, but isn't guaranteed whereas my deemed exports are for another 11 years.

For example if you were on the Octopus export getting 15p per unit then you would probably want to turn off the iBoost as exporting those units that are saving you about 11-12p of gas would instead net you 15p - would agree with your current plan keeping the deemed export sounds like a winner given the certainty on export value.

EcoScruples

My year with a battery and solar.

I've been on various tarriff since joining Octopus but I'll use Flux for the coatings as the agilè rates last summer were extraordinary and compatible.

Just over 4mw of solar produced against my installers prediction of 3.8mw so very good.
We consumed 3.8mw in total for the year of which around 2.8mw was from solar PV and the battery. The other 1mw was exported to the grid.

My apps costings are pretty close to my calculations with £1.3k revenue (kw avoided + kw exported - kw used from grid)

Battery charged 1.6mw and discharged the same so without the battery that would have all went to the grid.

That's worth £368 On flux

So please feel free to pick through and point out anything that's not corr3ct but the battery side isn't exactly going to pay for itself very quickly. Definatel3y would have went more solar and no battery had I known then what I know know.

Doesn't mean I won't enjoy the battery though as current projection is an 8 year payback for the whole system.

1961Nick

Savings so far this year:

Direct use of solar: £439
Solar & off peak battery charging: £551
FIT: £443

Total £1433 & forecast to be close to £3000 by the end of the year.

(All data from meter readings rather than apps.)

EcoScruples

3k is a hearty sum, good going, I'm going to use off peak during the winter as it'll save me about £200 at current rates.
I should end up paying Octopus £100 per year inc the standing charge too.

Screwdriva

EcoScruples said:

So please feel free to pick through and point out anything that's not corr3ct but the battery side isn't exactly going to pay for itself very quickly. Definatel3y would have went more solar and no battery had I known then what I know know.

Thanks for sharing! With Flux, we've experienced a ~45% net increase in PV export earnings without a battery, at an average tariff rate of 25.5p per kWh.