Business case for a battery

[JamesPa]

I have 4kWp of solar panels from 2011 on which I get FIT and export payments.  Until recently I was self consuming about 50% of the annual production of 4MWh.  I have a solar diverter already.

 

I have not, up until now, been able to make the numbers for adding a battery stack up so I haven't got one (I cant see that they are justified environmentally over simply exporting to the grid).   However I have recently acquired an electric car and, having finally defeated my planning authority over planning permission, will shortly be getting a heat pump, so the situation is about to change radically.

 

Because of the wide range of options on what one might do with the battery, particularly if I opt eg for an agile tarriff, its a bit challenging however to work out how to crunch the numbers.  Has anybody got a methodology for assessing the case that I could steal?  I have all my half hourly electricity and gas readings so can project the demand profile fairly well allowing for the gas boiler->heat pump conversion.

 

[Gone West]

1 hour ago, JamesPa said:

having finally defeated my planning authority over planning permission, will shortly be getting a heat pump

Congratulations, and well done for sticking with it.

[Conor]

We're on economy 7, and our usage is about 70/30 low Vs high rate, and our solar consumption about 65% of what we generate. So easy for us to calculate. Payback close to 20 years for me.

 

Start by taking a simplistic approach, how much do you pay currently, how much do you use, how much can you move to off-peak by timing usage? And how much do you get paid for solar export? Out solar rate is basically the same as our off-peak import rate. We charge our car, run out dishwasher, washing machine and run our heatpump on the low rate only. This works fine for us, so a battery wouldn't do much. 

Edited October 18 by Conor

[SteamyTea]

4 minutes ago, Conor said:

We're on economy 7, and our usage is about 70/30 low Vs high rate, and our solar consumption about 65% of what we generate. So easy for us to calculate. Payback close to 20 years for me.

 

Start by taking a simplistic approach, how much do you pay currently, how much do you use, how much can you move to off-peak by timing usage? We charge our car, run out dishwasher, washing machine and run our heatpump on the low rate only. This works fine for us, so a battery wouldn't do much. 

 

I have the same problem.

Here is when I use power.

 

As I mentioned in my blog, if the inverter needs a minimum power draw, a lot of the time I could not used stored energy.

 

[S2D2]

This may be useful, figures are outdated but the methodology would be the same.

 

 

[G and J]

So is it a good thing to evaluate battery purchase purely on financial payback?

 

I have a nagging feeling that if we looked real hard at it all we might discover that the total number of tons of carbon who’s release into the atmosphere I’m responsible for between now and my demise will increase if I add a battery in.  
 

It might be that the world would be better served for those precious metals used in ‘my’ battery to be deployed in more electric vehicles.    
 

I’m going to cost building in the option of adding a battery in future by hubbing wiring to the key bits into my attached garage.  If it’s not too much we’ll do it and thus maybe add a battery for power cut backup, rather than to save bills. 
 

When/if it’s proven that the new ecobatts (made from recycled pasta) actually reduce emissions overall including the battery production then it’ll be game on.   But not until.  

[SteamyTea]

6 hours ago, G and J said:

precious metals

Not that precious

https://www.bbc.co.uk/news/articles/cm28mg3zkmxo

 

And the misnamed rare earths.  They are 'rare' because they were hard to isolate because of the similar atomic sizes. Or for context, as rare as lead and copper.

 

Edited October 19 by SteamyTea

[gmarshall]

Cobalt is the only real issue rare elements (and geopolitics/human rights) wise, if you use LiFePo batteries (which most fixed systems are now- cheaper but heavier) then that issue goes away as they are cobalt free. 

 

For estimating costs I took an approach of considering a daily saving on a seasonal basis, i.e. 4 months of good solar generation, operating 95% off grid so effectively paying standing charge only, 4 months of poor generation load shifting cheap rate electric each day saving battery capacity x difference between the electric rates, and 4 months of shoulder season, which is a bit trickier to predict and probably depends on your generation and usage on the best model.

 

For us, using that method I came up with about an 8 year payback for a self install 5 kWh system, with a 10 kWh offering no further benefit, and that is working as expected for us 6 months in. 

[G and J]

For home use battery weight isn’t an issue, so it sounds like I don’t need to worry about the using up of rare commodities.  
 

But how about the carbon footprint of the battery with associated bits?  I appreciate by using the tariffs they can save money but will that reduce emissions?

Edited October 19 by G and J
Fat finger typing correction. I’ve not had enough coffee yet.

[SteamyTea]

7 minutes ago, G and J said:

But how about the carbon footprint of the battery with associated bits

The battery embodied CO₂ is very much dependant on where the lithium comes from and where the materials are processed.

But MIT estimate somewhere between 30 kg CO₂ and 200 kg CO₂ /kWh.

This is away above the UK CO_2e Grid Intensity, which today's forecast is 0.231 kg CO₂ /kWh, not an unusual figure.

So somewhere between 130 and 865 kWh delivered, for the battery alone to reach parity, then it becomes the energy supply carbon intensity and local inefficiencies.

I have read in the past, a hand-wavy figure that the inverter/controllers/mountings etc is a similar magnitude.  I shall pick the median point of 115 kg CO₂, inverters can last decades, so not really an issue.

 

 

 

[JamesPa]

12 hours ago, G and J said:

So is it a good thing to evaluate battery purchase purely on financial payback?

 

I think so but would dearly love to be convinced otherwise

 

To be clear I don't evaluate the case for ASHPs, electric cars or solar panels on a purely financial basis, the case is environmental (or, in the case of an electric car, its just a better driving experience all round as well as environmental)

 

However I do for batteries, because I don't see the environmental benefits.  If my PV produces excess it gets exported, which is then used by others so I can discount that potential environmental benefit.  This leaves the question of whether it is better for the environment to do the job of grid balancing locally.  I can see that on the extreme occasions when (until very recently) we fired up coal fired power stations it might have been, but that has gone.

 

TBH the answer is I don't know whether local grid balancing using batteries are good for the environment, but haven't seen evidence that it is.  It may be that ther optimum is just to charge my car, heat my water and do my dishwashing and clothes washing in the 'cheap' periods (which I presume are a reasonable proxy for carbon intensity) and leave it at that.  These things are by and large easy to do and cost nothing (money or natural resources).

 

If I were to see some reasonable evidence that batteries are good for the environment then I would change my assessment criteria for batteries.  Im not a sceptic on this matter, just haven't seen much of a reasoned argument and am conscious that the MCS crowd basically sell them as an extension to solar panels to 'optimise self use' which doesnt confer an environmental benefit.

 

 

Edited October 19 by JamesPa

[SteamyTea]

29 minutes ago, JamesPa said:

  It may be that ther optimum is just to charge my car, heat my water and do my dishwashing and clothes washing in the 'cheap' periods (which I presume are a reasonable proxy for carbon intensity)

Not really for a couple of reasons.

Generation capacity is set for a future date i.e. tomorrow at 3:00.

Any demand is filled with gas generation, so the carbon intensity actually increased during times of low generation and demand i.e. 3:00 when nuclear and wind are doing the bulk of the work.

 

It is a bit of a myth that the generation tracks demand, it is based on predicted demand and pre arranged generation capacity.

When it goes wrong, you see huge price spikes for a short time.

There was a radio show on about dynamic pricing, and how it is not like the old markets and bazaars. 

Rethink 

 

The 'carbon' price is around £40/tonne at the moment.

Maybe that should be taken into account when costing out a system.

[JamesPa]

43 minutes ago, SteamyTea said:

Not really for a couple of reasons.

Generation capacity is set for a future date i.e. tomorrow at 3:00.

Any demand is filled with gas generation, so the carbon intensity actually increased during times of low generation and demand i.e. 3:00 when nuclear and wind are doing the bulk of the work.

 

It is a bit of a myth that the generation tracks demand, it is based on predicted demand and pre arranged generation capacity.

When it goes wrong, you see huge price spikes for a short time.

There was a radio show on about dynamic pricing, and how it is not like the old markets and bazaars. 

Rethink 

 

The 'carbon' price is around £40/tonne at the moment.

Maybe that should be taken into account when costing out a system.

If cheap electricity prices aren't a reasonable proxy for carbon intensity, then the battery environmental argument is further weakened.

 

I was hoping someone would respond telling me why home batteries are good environmentally, perhaps they still will.

[Nick Laslett]

1 hour ago, JamesPa said:

If my PV produces excess it gets exported, which is then used by others so I can discount that potential environmental benefit. 

 

 

On Gary Does Solar YouTube channel he did a recent video about the problem of excess solar, which someone will have to be paid to take. Already a problem in California where there is a flat fee applied to domestic solar installs to cover this cost.
 

 

[SteamyTea]

8 minutes ago, Nick Laslett said:

the problem of excess solar, which someone will have to be paid to take

We already pay to have it taken away, called the daily standing charge.

It is always hard to compare different systems, in different countries, so no point trying in the case of PV.

[JamesPa]

18 minutes ago, SteamyTea said:

28 minutes ago, Nick Laslett said:

the problem of excess solar, which someone will have to be paid to take

We already pay to have it taken away, called the daily standing charge.

It is always hard to compare different systems, in different countries, so no point trying in the case of PV.

Clearly excess isn't currently a problem in much of the UK since we get paid for export.  Judging by how few solar panels there are down my road I don't think it's likely to be a problem even at the local grid level.  So for now I think it's reasonable to assume that exporting it is sound environmentally. 

 

Presumably if we get to the point where too much solar is a problem we will be penalised for export which will improve the battery business case.

[SteamyTea]

6 minutes ago, JamesPa said:

Presumably if we get to the point where too much solar is a problem we will be penalised for export which will improve the battery business case.

That already happens via grid voltage limiting.  So it will depend on the local accumulated generation and how much local diversion can happen.

I think the UK is a long way off.  Would take 25 years of nothing but physics lessons at school before the idea that PV does not work in the UK.

[Simon R]

6 hours ago, JamesPa said:

 

I was hoping someone would respond telling me why home batteries are good environmentally, perhaps they still will.

Hopefully I can help. I'll start by admitting I'm in favour of home storage, so biased in my thinking.

 

This is back of a fag packet stuff....

1kWh requires 58kg of co2

1kWk generation 162g

So it takes about 358kWh of battery use before they are carbon neutral.

Our 4kWh solar installation generated 7mWh last year of which we used 4mWh the remaining 3 got exported.

 

For our 9.2 kWh it took 533kg of co2 to manufacture (lithium phosphate so no cobalt)

To be carbon neutral we need to use 3,293kWh (3.29mWh) of grid generated electricity at 162g/kWh

Based on our usage of 4mWh we are already carbon neutral in the first year ignoring the 3mWh we export.

So if you manage to use all of your PV generation you'll be carbon neutral even earlier!

 

Yes, I've ignored the co2 associated with the inverter as you need one to manage  any PV in the first pace. I think it's two years for a solar panel to be carbon neutral.

 

Financially

Back in December I posted on a thread on battery sizing. Our battery gives us an annual saving in the region of  £1397 given my system outlay was 6.5K that's not such a bad return.Current data on lithium phosphate suggests they are going to last a long time, a 12 year unlimited charge/discharge warranty is not exceptional.

 

[Simon R]

53 minutes ago, Simon R said:

Based on our usage of 4mWh we are already carbon neutral in the first year ignoring the 3mWh we export.

I've just checked my battery discharge figures and I was including electricity directly from solar. The battery data shows a a discharge of 2.8mWh for the year so it's taken me around 14 months to become carbon neutral, still a very positive reason to have a battery.

[G and J]

2 hours ago, Simon R said:

I've just checked my battery discharge figures and I was including electricity directly from solar. The battery data shows a a discharge of 2.8mWh for the year so it's taken me around 14 months to become carbon neutral, still a very positive reason to have a battery.

I suspect it might prove easy to make a purely financial case for a battery system, but I’m with @JamesPa re the non existence of an environmental case. 
 

And I’m the absence of such a case I’m tempted to conclude that as it uses resources then such is likely to be environmentally negative.  
 

I might want one for battery backup (lights, internet, MVHR, freezer, etc) but that’ll be managed in a different way to a save money battery.  So I’ll therefore accept that my battery system will be an indulgence.  
 

Not my only one either. 

[SteamyTea]

9 hours ago, Simon R said:

4mWh

M

or it is milli watt hour.

[Dillsue]

11 hours ago, Simon R said:

Our 4kWh solar installation generated 7mWh last year 

Assuming the "4kWh" is kwp, that's colossal generation. Does your system track the sun?

[SteamyTea]

17 minutes ago, Dillsue said:

kwp

kW_p

 

kwp

[Wil]

30 minutes ago, Dillsue said:

Assuming the "4kWh" is kwp, that's colossal generation. Does your system track the sun?

Agreed! my 5kWp system facing south only managed 5434kWh in '23. 4622kWh so far this year!

[G and J]

1 hour ago, Dillsue said:

Assuming the "4kWh" is kwp, that's colossal generation. Does your system track the sun?

Perhaps they use a sun lamp at night to generate more.   😉