On-grid domestic battery storage

joefizz · 6 October 2020 at 6:37AM

Solarchaser said:

You know that I've had batteries for a while now, so surely you know.... that I know... how a battery inverter works based on loads, but you explain it anyway, this perplexes me.

Because Im not explaining it for you. Im making the same point I make in a lot of my posts that when people make assumptions based on their own experiences there are lots of scenarios out there that prove the opposite. Yours is obviously one, mine another. We make our purchase decisions based on a lot of things and its only when we tie things together that anomalies and 'features' come to light. So my theories are about my equipment and if I test my theory then its no longer a theory. That never implies it applies to anyone else but is something that may occur that we all wouldnt necessarily have considered at initial purchase.

You have to remember this is not just a discussion between two people but for all the lurkers and people who only reply via PM that its also an information resource. By explaining what I know we both already know it helps to explain it to others who may not know or who may just see price point as the only selection method.
So for example my hob is a zanussi one with hobs running from 2.7kw to 3.7kw and almost 5 years old now, so is going to be different from yours.

Regarding the three stage charging, its common across chargers but thats not really what interests me, its the discharge rather than the charging that we have been talking about.

Exiled_Tyke · 4 November 2020 at 9:56AM

Should I be force charging my (Solax) battery?
With the gloomy days recently the batter is very rarely getting above 20% full. (That may change this week mind). I've noticed that the BMS is occasionally 'deciding' to add a bit more juice by charging up to around 15% overnight. Would it benefit the battery if topped it up for a longer charge?

I am hoping to move across to Octopus Agile in time. In which case I plan to force charge in the very early morning and early afternoon. However right now I'm on a fixed term tariff with exit fees and don't yet have a smart meter so it isn't really worthwhile.

Your thoughts would be appreciated. Thanks

chamelion · 4 November 2020 at 10:34AM

Exiled_Tyke said:

Should I be force charging my (Solax) battery?
With the gloomy days recently the batter is very rarely getting above 20% full. (That may change this week mind). I've noticed that the BMS is occasionally 'deciding' to add a bit more juice by charging up to around 15% overnight. Would it benefit the battery if topped it up for a longer charge?

I am hoping to move across to Octopus Agile in time. In which case I plan to force charge in the very early morning and early afternoon. However right now I'm on a fixed term tariff with exit fees and don't yet have a smart meter so it isn't really worthwhile.

Your thoughts would be appreciated. Thanks

I'm using the 'octolux' script to charge up my batteries to 100% overnight using cheap energy. We're now at a stage in winter that my max generation for solar doesn't cover the baseline for the house, so instead what I do is trickle the battery input to the house based on agile electricity prices. i.e. if it's 10p, I contribute 10%, if it's 15p, I contribute 15%, during peaks I contribute 100% from the battery etc etc.

Ultimately it means that despite agile tariffs being quite expensive last few months (albeit, big declines last few days) I'm paying less than half as I'm relying on battery power to supplement expensive daytime / peak grid energy.

I have a very high baseline in my house, so with the contributions above I do have a depleted battery by end of day, ready for another round of topping up with cheap(er) overnight energy.

EVandPV · 4 November 2020 at 4:40PM

Exiled_Tyke said:

Should I be force charging my (Solax) battery?
With the gloomy days recently the batter is very rarely getting above 20% full. (That may change this week mind). I've noticed that the BMS is occasionally 'deciding' to add a bit more juice by charging up to around 15% overnight. Would it benefit the battery if topped it up for a longer charge?

I am hoping to move across to Octopus Agile in time. In which case I plan to force charge in the very early morning and early afternoon. However right now I'm on a fixed term tariff with exit fees and don't yet have a smart meter so it isn't really worthwhile.

Your thoughts would be appreciated. Thanks

From a battery health point of view, you don't want it sitting at only 20% for long periods. I'd top it up from the grid to around 50% and perhaps set the minimum discharge level to around 40% while you're not getting enough pv to fully charge and don't have a cheap rate leccy tariff.

joefizz · 10 November 2020 at 8:41AM

Exiled_Tyke said:

Your thoughts would be appreciated. Thanks

In addition to the previous posts, check your warranty. Some specify that they cover only one charging cycle per day (usually solar). So worth checking that out and weighing it up. To be fair though, if Id charged from the mains this weekend it would only be one charging cycle per day!

joefizz · 10 November 2020 at 9:12AM

joefizz said:

Exiled_Tyke said:

Your thoughts would be appreciated. Thanks

In addition to the previous posts, check your warranty. Some specify that they cover only one charging cycle per day (usually solar). So worth checking that out and weighing it up. To be fair though, if Id charged from the mains this weekend it would only be one charging cycle per day!

Bad form to reply to your own post but...
I forgot to mention that if your warranty does exclude more than one charging cycle per day it would be worthwhile topping up during your daily charge cycle (although that would get round the cheap at night stuff) or only charging from the mains and disconnecting the solar aspect during low output seasonality.

Exiled_Tyke · 10 November 2020 at 6:57PM

joefizz said:

joefizz said:

Exiled_Tyke said:

Your thoughts would be appreciated. Thanks

In addition to the previous posts, check your warranty. Some specify that they cover only one charging cycle per day (usually solar). So worth checking that out and weighing it up. To be fair though, if Id charged from the mains this weekend it would only be one charging cycle per day!

Bad form to reply to your own post but...
I forgot to mention that if your warranty does exclude more than one charging cycle per day it would be worthwhile topping up during your daily charge cycle (although that would get round the cheap at night stuff) or only charging from the mains and disconnecting the solar aspect during low output seasonality.

Thanks. Solar at this time of year is not an issue - it all get's used as it comes in!

JKenH · 22 January at 9:24PM

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Dave_Fowler · 30 January at 5:51PM

I'm getting quotes for a retro-fit battery system to operate with my solar panels.

So far I've had a quote of £5700 inc VAT for a Sofar ME3000SP inverter with 4 x 2.4kWh Pylontech batteries fully fitted and installed.

I have a problem that I've two solar panel systems. One system is on the house and the other on the garage and workshop which is out in the garden. The one on the house is connected directly (via the usual inverter, switches and generation meter) to the house consumer unit. The one on the garage and workshop is connected to a consumer unit in the garage. It has its own generation meter etc. Whilst I can connect a CT clamp to measure the generation of the house system, the cable from the garage and workshop to the house carries the nett current of the garage system and power consumption. A CT clamp on this cable will have little meaning.

I raised this problem when asking for quotes. When speaking to the company that has given this first quote they told me the Sofar inverter will still operate correctly even if there are no clamps on the generation cables. It would just measure the power to grid and use that to decide what power to take to charge the batteries. The only downside would be that the monitoring system app would give strange results. The Sofar installation manual makes no reference to this mode of operation.
Has anyone had experience of this set-up?

TIA
Dave F

Solarchaser · 30 January at 10:15PM

Hi David, you have basically described my system.
I have the main house system and then my garage system.

For me, what I did was rewire the garage incoming cable to go through the main house solar CU as it is 63a.
Note the CU, not the gen meter, so the gen meter doesn't see the extra usage/solar, only the CU after it.
I then put the ct between the CU positive and the main house CU.

So the positive of this is that the solar ct sees all the solar, and the other CT goes on the incoming mains, and so the sofar is happy.
The negative is that when I use power tools in the garage the ct sees as extra solar, however because the mains ct does not see export, it will not charge the battery.

I ran this was with an me3000sp and 3x 2.4 pylontech for over a year.

However if I can be so bold, I'd suggest that me3000sp is old tech in comparison to the lux 3600.
If you went with parallel lux you could run as I do now which uses one ct on each of the solar inputs, and one on the mains.

This would give you more output capabilities and far better monitoring than the me3000sp.

The lux and sofar are both around £750, and batteries are about the same.
So what you are paying for is about £3750 worth, so I'd say 2 grand to install is.... excessive

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On-grid domestic battery storage

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