Solar Battery in Cold temperatures 8 December 2022 at 9:23AM in Green & ethical MoneySaving 11 replies 450 views

vienly

Hello, can anyone tell me if a Solar Battery installed in a cold garage has less stored energy in the winter than in the summer?

I had my Solaredge 10kWh (9.7kWh usable) battery installed recently in November and noticed I get approxtimately 6.5kWh- 7.5kWh of battery power after looking at some charts and numbers.
At a base discharge rate of around 260w-300w through the night I lose 1% every 15 minutes, which would mean about 6.5kWh - 7.5kWh in 375minutes @ 100%.

This seems to be a 30% loss from what is advertised.

Thank you

Magnitio

If you are losing 1% every 15 minutes i.e. 4% per hour, that would equate to an average consumption from the battery of 388W (9.7 * .04). I'm not quite sure what is meant by "6.5kWh - 7.5kWh in 375minutes @ 100%".

The Solaredge battery has a quoted round-trip efficiency of 94.5%. There will also be some losses in the inverter, which at a relatively low load of 300W could by 5-10%. There are also the electronics in the inverter and BMS which need power (say 50W). This gets you nearer the 300W AC from 388W battery output (388 * .945 *.95 - 50 = 298W).

There may be some additional inefficiencies with the battery when it is cold and some of the battery packs have heaters (which obviously consume more energy) though I can't find out whether the Solaredge product has one.

vienly

Thank you, the 6.5kWh - 7.5kWh in 375minutes is a guesstimate of how much battery capacity I have.
According to Octopus energy my consumption was 250-300watts per hour before solar/battery was installed.

I suppose with the additional inverter usage and losses it would add up to 9.7kWh battery capacity

1961Nick

During the 4 hour Octopus Go period I charge around 12.1kWh in summer dropping to 11.7kWh in winter. I suspect that grid voltage & battery temperature are causing the difference. Winter should have an advantage because the battery pack is always operating between 20% & 80% whereas summer it's between 10% & 100%.

vienly

https://realgoods.com/blog/how-to-keep-solar-batteries-warm-in-winter/

This article seems to explain that:

'Most batteries are rated at 77°F (25°C), meaning their technical specs are based on how the battery's cells perform at 77 degrees. As a rule of thumb, batteries lose about 10% of their rated capacity for every 15-20 degrees below 80°F as measured in the cells.'

If I apply that to my Solaredge 10kWh battery in the garage which is currently 0c, but the internals of the battery reads about 3c due to discharging it would mean out of the 9.7kWh 'usable' energy I should be getting 7.7kWh which is close to what I charge from 0%>100%.
I seem to be the only one who has flagged this up, can't seem to see anyone else in UK that has their battery stored outside have this issue so uncertain.....

Grandad2b

1961Nick said:

During the 4 hour Octopus Go period I charge around 12.1kWh in summer dropping to 11.7kWh in winter. I suspect that grid voltage & battery temperature are causing the difference. Winter should have an advantage because the battery pack is always operating between 20% & 80% whereas summer it's between 10% & 100%.

It's a known fact that rechargeable battery capacity and efficiency are temperature dependent so you might expect the battery to have a lower capacity in winter.
I'm puzzled by the idea that winter has an advantage - what advantage is that? 

arty688

vienly said:

Hello, can anyone tell me if a Solar Battery installed in a cold garage has less stored energy in the winter than in the summer?

I had my Solaredge 10kWh (9.7kWh usable) battery installed recently in November and noticed I get approxtimately 6.5kWh- 7.5kWh of battery power after looking at some charts and numbers.
At a base discharge rate of around 260w-300w through the night I lose 1% every 15 minutes, which would mean about 6.5kWh - 7.5kWh in 375minutes @ 100%.

This seems to be a 30% loss from what is advertised.

Thank you

Had mine installed in Novenber to, not really sure how to measure what you are measuring, probably not related but my installer did set up the battery with a 10% reserve to protect the battery and warranty ,which I got removed by SE (as we have no control of the battery settings) as that was nonsense. Having the battery also screws up all the production figures as well

vienly

I am certain my battery is only supplying around 7kWh of energy in Winter, it will probably more in Summer when battery is warmer to charge. If you have yours indoors I would assume it won't be an issue for you.

My first suspicion was when the battery couldn't take me through a whole day use when I averaged about 10kWh a day (19 hours) (5 hours off peak electricity). It kept falling short a few hours before off peak hours.

I then looked at my base usage at middle of night when noone is using power except fridge/freezer/boiler etc which turned out to be about 290watts/hr which it drained 1% every 15 minutes (4% every hour)
Doing the math that would mean 100% = 7.2kkWh

I also had a look at the Solarview app which showed me how much it charged up from 0% > 100%, beween last 'Lifetime charged' and next 'Lifetime charged'. That also showed about 7kWh charged added.

The app also told me I had about 8kWh capacity which seemed optimistic.

1961Nick

Grandad2b said:

1961Nick said:

During the 4 hour Octopus Go period I charge around 12.1kWh in summer dropping to 11.7kWh in winter. I suspect that grid voltage & battery temperature are causing the difference. Winter should have an advantage because the battery pack is always operating between 20% & 80% whereas summer it's between 10% & 100%.

It's a known fact that rechargeable battery capacity and efficiency are temperature dependent so you might expect the battery to have a lower capacity in winter.
I'm puzzled by the idea that winter has an advantage - what advantage is that? 

The battery doesn't charge as quickly at the margins. Running it between 20% to 80% means there's no derating.

Rheumatoid

arty688 said:

vienly said:

Hello, can anyone tell me if a Solar Battery installed in a cold garage has less stored energy in the winter than in the summer?

I had my Solaredge 10kWh (9.7kWh usable) battery installed recently in November and noticed I get approxtimately 6.5kWh- 7.5kWh of battery power after looking at some charts and numbers.
At a base discharge rate of around 260w-300w through the night I lose 1% every 15 minutes, which would mean about 6.5kWh - 7.5kWh in 375minutes @ 100%.

This seems to be a 30% loss from what is advertised.

Thank you

Had mine installed in Novenber to, not really sure how to measure what you are measuring, probably not related but my installer did set up the battery with a 10% reserve to protect the battery and warranty ,which I got removed by SE (as we have no control of the battery settings) as that was nonsense. Having the battery also screws up all the production figures as well

So you now let your batteries discharge completely? That is not good for them. Mine are rated for a DoD of 95% but I have them set to stop discharging at 15% and force a charge at 10%

arty688

They have a reserve you can't access buil in so are designed to be dischrged to 0% (which isn't really 0%).