On-grid domestic battery storage

zeupater

Coastalwatch wrote: »

I did some simple calcs on the EDF offering, in our case and without taking battery degradation into account the 4kWh offering would take 16.4 years and the 8kWh 17.1 years before breaking even. By then of course it's beyond the guarantee period and probably at the end of it's useful life, if it, and we get that far!

Hi

In addition to the above ... It's noteworthy that the above repayment period estimate is based on a PV system which is atypical (as in huge compared to UK average!) and likely reflects atypical consumption patterns including heatpump heat provision etc, the combination of which would help improve investment recovery! ...

HTH
Z

mmmmikey

Hi again
All interesting stuff. As with many emerging technologies there are still a huge number of unknowns but the various theories and speculation around this make interesting reading, particularly as the discusion becomes progressively more informed.
I certainly agree with what appears to be the the general sentiment that battery storage for solar energy is not yet viable for most people/systems from a purely financial perspective. I have, however, just ordered a Powervault system based on the following reasoning:
1. I'm looking at this from an environmental as well as financial perspective and happy to spend some money to "save the planet", but my green and ethical money saving ideals mean that I want to minimise the cost of doing this. That is, this isn't just about saving money so I can spend more in retirement or whatever. For me, batteries don't have to turn a profit in the long run to be worth it. If investing in batteries has a reasonable chance of breaking even in the lifetime of the system I would see that as an excellent result, and even if I don't break even I wouldn't see myself as having "lost" money - rather having spent it on doing something worthwhile in itself.
2. The biggest financial benefit I anticpate in my circumstances is on saving cheap rate E7 electricity overnight for use during peak hours, rather than just storing my own solar energy. This works for me because the difference between my E7 night and day rates is 16.85p per kWh. I also suspect that the cost advantage of using off peak energy will increase over the years as (a) we become increasingly dependent on renewables such as wind, and (b) smart meters encourage the introduction of more competitive time of use tarriffs (but this is just speculation of course).
3. Assuming (i) I can use an average of 3 kWh per day from a 4 kWh battery (ii) the E7 saving is 16.85p per kWh from doing this (which goes up by 3% a year due to inflation) (iii) the system costs £3,300 (after the £1500 grid services contribution), according to my calculations the system would pay for itself in about 14.5 years. This doesn't factor in any solar savings on top of this or the impact of the grid services contract and I am making the simple assumption these will cancel each other out over the course of a year. This is longer than the guarantee (at 10 years) but less than the quoted life of the battery if you assume 1 cycle per day (6600/365 = 18 years). Obviously this is very simplistic and there are all kinds of reasons why this could be better or worse in reality, but it meets my criteria of having a reasonable chance of paying for itself in it's lifetime, or at least not costing too much.
Time will tell of course - I'll let you know how I got on in 15 years or so!
In the meantime, I'm expecting installation late Feb / early Mar and should have some initial data to post here in about 6 months. Mike.

Exiled_Tyke

Factor in the cost of capital and the benefits are wiped out. For example currently 2.7% interest is available on savings (five year fixed). After the 14 1/2 years the £3,300 investment would be worth £4,800.

Also take into account efficiency losses and battery degradation and I really can't see this adding up.

zeupater

Hi

Have you looked into the level of intelligence employed by the energy management system you've been offered?

If you're expecting to charge from both PV & E7, depending on the daily demand and PV generation, you may find that the E7 charge will limit the charge capacity for the next day ... for example, if the battery is fully charged overnight and the house only needs (say) 1-2kWh of imported electricity during daylight hours, then the maximum PV contribution to the battery is limited to 2kWh ... this can be overcome by the management system having a degree of intelligence or variable charging schedule by month, but it's not necessarily a standard capability ...

I've come across a number of examples where energy £savings have been based on unrealistic assumptions of storage energy source mix and the ability to meet domestic demand ... for example, a 3kW kettle will still create an import demand if it plus other demand is greater than the storage system's maximum power supply threshold ... basic stuff, but you'd be surprised how many times that it's overlooked!

HTH
Z

pile-o-stone

zeupater wrote: »

I've come across a number of examples where energy £savings have been based on unrealistic assumptions of storage energy source mix and the ability to meet domestic demand ... for example, a 3kW kettle will still create an import demand if it plus other demand is greater than the storage system's maximum power supply threshold ... basic stuff, but you'd be surprised how many times that it's overlooked!

This is what I was alluding to earlier in the thread where I said my own ambition is to be fully off grid during peak times. Given that battery systems are limited to sometimes only 1 or 2 kw of energy, people will not only have to fit low energy kettles (or boiler taps) they would also have to manage their usage so that they don't use multiple electrical devices at once. My morning routine is to turn on the kettle and toaster for breakfast. These alone would exceed the maximum output from a battery by quite a way, without the other electrical loads like the central heating pump, fridge, freezer, TV, etc. also being on at the same time.

In summer it might be possible because you have the output from solar and battery combined, but obviously this is dependent on daylight.

zeupater

Hi

Agreed, we switched to a 1kW kettle years ago to help maximize PV self consumption.

Regarding the battery system itself, the majority of people don't seem to understand that whatever size battery is being considered -or- whatever size PV system you may have -or- whatever time your low cost off peak tariff lasts for, the rate of charge is limited by the capability of the storage charging circuit, therefore the maximum energy storage from each energy source is also limited ... just over the units discussed recently there's a ~600% range in charging rate & up to 800% on supply capability ... of course, many suppliers select a product to sell and push that product regardless of whether it actually provides the most appropriate solution - yes, in general terms, talking about battery storage is like talking about fruit, the problem is that there's a distinct difference between apples & oranges and there aren't many that currently recognise the case!

HTH
Z

mmmmikey

Hi - yes, above points agreed and understood.



The Powervault 3 I have ordered has a usable inverter rating of 5.5kW and usable charger rating of 3.3kW - the nominal rating of the charger is 5.5kW but presumably the lower usable rate is due to the batteries' ability to accept charge. I think it is doubtful that I'll exceed 5.5kW often, as I've also developed habits to minimise peak usage for the reasons you've described. (The exception being using the storage heaters overnight which I'd never do from the batteries anyway).



Taking the tea and toast in the morning routine as an example, I first switch on the kettle and whilst it is boiling I get the bread out, slice it and put it into the toaster - by the time I've done this, the kettle has boiled so I only have one of them on at a time. I find that in practice once I've established this kind of habit I don't have to think about it any more. I'll see how it goes, my aim too is to get import as close to zero as possible in the summer months.


As far as using both PV and E7 for charging is concerned, that's a bit more complex. In answer to your specific question as far as I can tell the system intelligence is very limited. However, in the summer it's easy - I just won't use E7 as May to Aug I generate way in excess of what I use (the panels were on the house when I bought it and way over-specced for my use) so expect to keep the batteries well charged on solar. In the shoulder and winter months, I'll charge the battery fully using E7 overnight (at 6p-ish per kWh). If there's spare solar power during the day after I've topped up the battery, I'll use it to pre-heat the water via the solar immersion controller, saving 6p-ish per kWh on the water heating, so other than efficiency losses I won't waste too much of the solar power. Keeping in mind as well my sums are based purely on E7 charging due to my high day-night differntial and any solar charging is a bonus. That's the theory at least.....



On the other points raised above, re: battery capacity tail-off and system efficencies, I've factored that in to a degree by assuming I'll get 3kWh usage from a 4kWh system. This at best a very rough and ready approximation - it will be interesting to see how this works in practice. On reflection, I may have underestimated the effect of this but let's see.



On the "cost of capital / savings interest" argument, I absolutely agree this needs consideration. However, one of the risks associated with saving is that inflation can make your money worth less rather than more at the end of the period. Having recently retired, I have a fair chunk of cash savings so I'm quite exposed to this risk. If inflation rises, it zaps these savings but conversely it improves the case for investing in batteries (if energy prices go up you save more per kWh). So to some extent, using some of my existing savings to finance this mitigates the risk of them being devalued due to inflation - i.e. the batteries become a sort of insurance policy against energy price inflation. There's no way I'd ever borrow money for them, and I'd even think twice about buying them if they represented a big proportion of my savings.


So you get to the point where the financial case for buying batteries is heavily dependent on the state of the UK and global economy over the next 15 years - discussion of which is well beyond the scope of this forum, I would suggest


Finally, I would re-iterate my view that the purely financial case for batteries isn't there in the majority of cases. My rationale for diving in (after a year or so of deliberation) is based on having a fighting chance of recovering my investment due to my particular load profile and circumstances, and being prepared to take the hit if this doesn't work out. I would caution anyone against buying now based purely on return on investment.


Thanks to all the regular and occasional contributors to this thread which always makes interesting reading, Mike

orrery

mmmmikey wrote: »

H... as I've also developed habits to minimise peak usage for the reasons you've described. (The exception being using the storage heaters overnight which I'd never do from the batteries anyway).

Taking the tea and toast in the morning routine as an example, I first switch on the kettle and whilst it is boiling I get the bread out, slice it and put it into the toaster - by the time I've done this, the kettle has boiled so I only have one of them on at a time. I find that in practice once I've established this kind of habit I don't have to think about it any more. ...

Me too! Mind you, it is a damned long wait for a cup of tea after I've put the dishwasher on for a 3 hours 45 minute programme!

mmmmikey

Dishwasher - that's outageous - wash your cup in a cold puddle at the bottom of the garden like I do and stop complaining!

Martyn1981

mmmmikey wrote: »

Dishwasher - that's outageous - wash your cup in a cold puddle at the bottom of the garden like I do and stop complaining!

Puddle .... garden ....... we havt make do wit pothole in't road!