On-grid domestic battery storage

Starfrog

So I finally got my smart meter installed for octopus yesterday and its working great so I have the solar and battery setup as per my signature file and I am currently on a loyalty tariff till march 2023 at 27.94p per unit kWh and 27.39 daily standing charge. So now that I have a smart meter what tariff (if any) should I move to to obtain the benefit of cheaper charging of my batteries 12kWh overnight due to there being much less solar production now as the winter comes. Not really really thinking getting money for exporting as it’s going to be very very small during the next few months. I dont have an EV so that counts out GO I guess ? Thanks for help  

Petriix

chamelion said:

Petriix said:

Here's why I didn't get batteries:

With 6 months of smart meter combined with solar generation and grid export data I was able to model what my optimal savings would have been with an infinite sized battery. It turns out that I'd have only been able to save £20 per month on average.

Ultimately, since moving to Octopus Go, our peak usage is only ~ 20% of our total. Broadly speaking we use:

5000kWh per year total; of which
1000kWh comes free* from solar
1000kWh is peak rate at 24.25p
3000kWh is off peak at 5p

That's ~ £392.50 (plus standing charge) at an average of under 10p per unit.

At current Go rates it would increase to £625 at 15.625p per kWh.

Optimistically I could save £400 per year at these higher rates, if they stay high. I could have had an 8.2kWh Givenergy battery for about £4k this summer. It's more like £6k for a 9.6kWh now.

So roughly a 15 year ROI before making any savings. On the other hand, overpaying my mortgage by £6k will save me about £4k in interest (on top of the capital repayment).

While the headline cost of 5000kWh is £1700 at the new price guarantee, the reality is quite different for many people. You obviously need to do your own sums. 

It boils down to a few things - your upfront cost, the delta between high and low, if you have solar, what type of payment you receive for solar (i.e deemed? Agile outgoing? Fit?), and ultimately your usage and usage profile. My newly purchased 2x us3000c last year have an roi of just over 2 years in my situation.

I don't want to dismiss your calculations. It's possible that you have sufficient peak usage which you couldn't possibly load shift into the off peak window to reach such a short ROI. Assuming your US3000Cs were only £1200 each and incurred no installation costs or other equipment then you're suggesting a saving of £1200 per year. That means 3500kWh of usage at 34p per kWh completely avoided or closer to 4000kWh load shifted into the off peak window on Go.

However, even at 100% DOD, the total capacity of those batteries is 7kWh which only totals 2555kWh if cycled fully every single day for a year. So I'm really struggling to work out how you could genuinely make such a saving and would be really interested to see your calculations.

What I regularly see is people multiplying the maximum hypothetical throughput by their peak unit rate to reach their 'savings' figure. In reality you need to calculate how much unavoidable peak usage you can save. That's a much harder thing to work out. My original calculations for savings were hugely optimistic because I couldn't envisage how low my peak usage would really be once I started load shifting. It turned out that it was cheaper to stop trying to use so much of my solar generation because it was more expensive to supplement it from the grid at peak times than to draw the whole load from the grid off-peak. 

shavy65

Powerplant – Premium Lithium Limited

How do these look? Price reduces if your willing to wait 

chamelion

Petriix said:

chamelion said:

Petriix said:

Here's why I didn't get batteries:

With 6 months of smart meter combined with solar generation and grid export data I was able to model what my optimal savings would have been with an infinite sized battery. It turns out that I'd have only been able to save £20 per month on average.

Ultimately, since moving to Octopus Go, our peak usage is only ~ 20% of our total. Broadly speaking we use:

5000kWh per year total; of which
1000kWh comes free* from solar
1000kWh is peak rate at 24.25p
3000kWh is off peak at 5p

That's ~ £392.50 (plus standing charge) at an average of under 10p per unit.

At current Go rates it would increase to £625 at 15.625p per kWh.

Optimistically I could save £400 per year at these higher rates, if they stay high. I could have had an 8.2kWh Givenergy battery for about £4k this summer. It's more like £6k for a 9.6kWh now.

So roughly a 15 year ROI before making any savings. On the other hand, overpaying my mortgage by £6k will save me about £4k in interest (on top of the capital repayment).

While the headline cost of 5000kWh is £1700 at the new price guarantee, the reality is quite different for many people. You obviously need to do your own sums. 

It boils down to a few things - your upfront cost, the delta between high and low, if you have solar, what type of payment you receive for solar (i.e deemed? Agile outgoing? Fit?), and ultimately your usage and usage profile. My newly purchased 2x us3000c last year have an roi of just over 2 years in my situation.

I don't want to dismiss your calculations. It's possible that you have sufficient peak usage which you couldn't possibly load shift into the off peak window to reach such a short ROI. Assuming your US3000Cs were only £1200 each and incurred no installation costs or other equipment then you're suggesting a saving of £1200 per year. That means 3500kWh of usage at 34p per kWh completely avoided or closer to 4000kWh load shifted into the off peak window on Go.

However, even at 100% DOD, the total capacity of those batteries is 7kWh which only totals 2555kWh if cycled fully every single day for a year. So I'm really struggling to work out how you could genuinely make such a saving and would be really interested to see your calculations.

What I regularly see is people multiplying the maximum hypothetical throughput by their peak unit rate to reach their 'savings' figure. In reality you need to calculate how much unavoidable peak usage you can save. That's a much harder thing to work out. My original calculations for savings were hugely optimistic because I couldn't envisage how low my peak usage would really be once I started load shifting. It turned out that it was cheaper to stop trying to use so much of my solar generation because it was more expensive to supplement it from the grid at peak times than to draw the whole load from the grid off-peak. 

My man math is here: https://forums.moneysavingexpert.com/discussion/comment/79469833/#Comment_79469833

Note this is just the added delta of the 2 us3000cs that I picked up. Had them shipped over, plugged in myself - no added install cost which was already all done up with my original 3xus2000B and lux inverter set up. 

Happy to recalculate if there's something ridiculously glaringly obvious i've done wrong here  

For the full package, I paid £2500 for lux inverter + 3xUS2000B + install. So my entire setup was £4,220 for 13.2kwh usable. Charging at 7.5p + 10% loss = £1.09 for the full bank. 13.2kwh at peak would be £5.19. That's a £4.10 saving per cycle, which I do daily = £1,496.50 per year = 2.8 years ROI. 

Note 1 - I have a high base load throughout the day - constantly over 2+kw. Shifting stuff like washing machine or dryer loads etc barely make a mark. 

Note 2 - conscious there is NO way to get pricing anything like this today.

Petriix

@chamelion if you're cycling them every single day for unavoidable peak usage then 2.8 years seems about right. That's for some exceptionally high usage which is pretty unusual. That's why I always say people have to do their own sums. 

chamelion

Petriix said:

@chamelion if you're cycling them every single day for unavoidable peak usage then 2.8 years seems about right. That's for some exceptionally high usage which is pretty unusual. That's why I always say people have to do their own sums. 

100% agree That's why I mentioned usage / usage profile as some of the key variables that can impact your ROI calcs. 

Also this is based on current rates, but that's only effective last week - before that I was paying 5p offpeak / 15.9p peak - at those rates my full bank charged at 66p and saved me £2.10 of peak usage, saving me £2.09 per day - resulting in ROI of 5.5 years, which is still awesome. 

However, my base load is going to significantly drop down to approx 1/2 kw soon - this alone will massively spike my ROI as I'll be swimming in excess energy in the summer (thanks, Solar) and barely making a dent on my capacity (and hence ROI) in winter when generation is low. 

Solarchaser

I think I'd say, not to wee wee on your parade, but 3x 2.4 + 2x3.5 at 
@ 90% useable and 80% round trip efficient is only 10.2kwh
I'd suggest running calculations again going by that.

However as I've said probably a few times on this thread, a low user will struggle to make batteries work financially  (leccy price increases aside) but if you use 4500+ they can easily make sense.
Add in solar, and you are onto a winner imo.

But you really need to do the calculations for you, and your usage.

Edit. Idiocy

chamelion

Solarchaser said:

I think I'd say, not to wee wee on your parade, but 3x 2.4 + 2x3.5 at 
@ 90% useable and 80% round trip efficient is only 10.2kwh
I'd suggest running calculations again going by that.

However as I've said probably a few times on this thread, a low user will struggle to make batteries work financially  (leccy price increases aside) but if you use 4500+ they can easily make sense.
Add in solar, and you are onto a winner imo.

But you really need to do the calculations for you, and your usage.

Edit. Idiocy

I consistently get more than 12.5kwh out of a single charge from 100% down to 10%. Measured by two devices...

Solarchaser

I'm intrigued,  tell me more.

orrery

I've just ordered. I've gone for the Lux 3.7kW AC coupled inverter and a single Pylontech US5000 5kWh (nominal) battery, installation and a large cabinet to eventually take a total of x4 US5000's.

I could have got a basic install with x2 US2000 for about £3,700 (fully installed) but I've managed to talk the price up by insisting on the US5000 and 19" rack and will have to pay about £4,600 as the US5000 is special order and not available until November. Ho Hum, but saw no point in not going for the US5000 and making it expandable. I'm estimating that my optimum will be about 15kWh of capacity (my peak tariff usage is commonly 15kWh if the house is occupied, neglecting solar contribution and car charging), but I know that I'll end up with 20kWh to maximise the amount from solar PV in summer). I can buy the additional batteries discount and add them myself.