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Author Topic: Rethinking cost/benefits of solar and domestic batteries  (Read 743 times)

steve_pr

  • Joined Mar 2012
  • Carmarthenshire/Pembrokeshire Borders
Rethinking cost/benefits of solar and domestic batteries
« on: November 04, 2019, 08:49:00 pm »
Pricing in this area has changed a lot over the last 12 months or so.  The FIT on new solar installations is no more, and the 5% VAT has also been ended so new solar installations are a whole new set of economics. Fortunately uf you already have installed then the FIT goes on for a good few years.


Big change is the price drops in domestic batteries. Be careful on capacity though, many are only 3-4Kw which isn't going to get you very far.  The Tesla powerwall appears to be the best value in terms of £/kw capacity - we are looking at £7-9000 installed for the 13kw unit. OK - a lot of money, but there are other factors at play here. The latest model includes the ability to continue to supply power (from the battery) when your grid connection fails (eg. powercut) so you get standby power which is a benefit in remote parts of the world like SW Wales. Then add the new tariffs and smart meters to the mix and a whole new world opens up. We signed up to Octopus' recently introduced electric car tariff, which needs a smart meter to record half hourly usage (which they kindly paid for and the installation). We now get 4 hours of power between 00:30 and 04:30 at the ridiculous price of 5p per unit. So charging our electric car now costs under £1 rather than £3 or so before. Most modern appliances (dish washer, washing machine, tumble dryer etc) can be set to start at a preset time in the future, so they all work at the same 5p/unit overnight.


Having done the calculations I reckon I can use the low rate power to charge the battery overnight (probably about 50p) then run off the stored power (along with any solar generation if the rain ever bloody stops) all through the day until it's time to charge again. Most solar generation not immediately used will go to charge the battery (free electricity) and reduce the amount i need to fill the battery at night. I still get paid FIT for 50% of my generation, even though I will probably barely export anything at all - so money in the bank on that one.  Bottom line I can go from buying any power over and above solar generated for 5p rather than 15p per unit and avoid "wasting" power by storing in the battery rather than exporting for a pittance. This looks like a pretty useful confluence of technologies to me.  Warranty is 10 years and payback should be less than that (we are heavy electricity users) without factoring in the inevitable increasing on electricity prices, I have standby power (just sold the 5kw generator we had) without the hassle. OK you have to invest, but then you should save.


Will report more once all installed and operational
Voss Electric Fence

regen

  • Joined Jan 2013
Re: Rethinking cost/benefits of solar and domestic batteries
« Reply #1 on: November 05, 2019, 08:39:05 am »
will be watching this with interest. Current usage is around £450pa from the grid so payback does not look too good at around 14 to 18 years but if the EV became a reality then may improve things. Currently the panels produce around 3650kwh PA and we use around 1600 with the balance going into the thermal store significantly reducing the number of times the oil boiler fires up during the summer when we do not want to light the WBS.

cloddopper

  • Joined Jun 2013
  • South Wales .Carmarthenshire. SA18
Re: Rethinking cost/benefits of solar and domestic batteries
« Reply #2 on: November 23, 2019, 01:50:58 am »
Thanks for that Steve,  I came to similar conclusions as you .

 Can you set things so if neeeded the EV is charged off the Powerwall in day rate hours , instead of having to wait for night rates to recharge ..

Whilst not yet having a Powerwall  I have our EV on an over rideable time clock to charge in the day if needed ( rarely ) .

 Spent the powerwall savings on triple glazing & high spec door for the bungalow instead .. ( due to be fitted any day now ) .
 :thumbsup:Powerwall … 2021...... perhaps .
Strong belief , triggers the mind to find the way ... Dyslexia just makes it that bit more amusing & interesting

 

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