Help with battery storage - why ??

[oneeyematt]

Hello all. I moved into a property with 1200w solar panel array. I decided to put a growatt inverter on the system with a 5kw battery. So far so good and all working it seems.

My questions / thoughts
1. I haven’t connected my solar array to the inverter to charge the batteries as at 1200w output it would take years to charge ( I have the old export tariff so I get a good FIT fyi ) - do you agree ?

2. I have programmed the inverter for “battery use first” but I don’t see the point of the battery as it never discharges to the house to benefit from the storage so what’s the point ?

I am on octopus agile so I don’t access cheaper off rate electricity, should i now switch to fixed and charge the batteries at night and discharge in the day / when im at home ? ( not sure how to make happen on settings)

Any help would be appreciated .

 

[OffGridForGood]

Is there a potential to add more PV to the system, and take advantage of the full capacity of that inverter?

 

[SeaGal]

I moved into a property with 1200w solar panel array. I decided to put a growatt inverter on the system with a 5kw battery. So far so good and all working it seems.

Can you share a bit more about what your house loads are and the decision behind installing the growatt and battery? I am assuming that it is just AC coupled at the moment, but presumably, that means the growatt can charge from excess PV production (when you have any, assume very little this time of year). 1200W, although not a great deal, will be good to charge batteries on sunny days and increase your own usage vs. export usage of the PV production.

I assume you have made the necessary applications to your DNO for approval of the additional inverter?

Moving the PV to the Growatt could be an option, but suggest you contact your existing FiT provider first, as there are strict rules of what you can change on your system without losing FiT benefits.

The other consideration is, assuming my assumptions in my post below are correct, is that if that 1200W is just those 3 panels I can see, then you would need to check that voltage output from just 3 panels is enough for the startup voltage of the Growatt inverter. Gut feeling is that it wouldn't be sufficient.

 

[SeaGal]

Is there a potential to add more PV to the system, and take advantage of the full capacity of that inverter?

Yes! SeaGal's detective abilities believe he could add more panels to the south-facing aspect of his garage and possibly to what looks like an extension or pergola roof

Am going to suggest mods change the location from being a postcode to just the local town (Portsmouth) as there's only one house on that road that has just 3 panels, which is presumably his 1200W. Safest not to disclose personal information like that IMHO. Or maybe I'm just paranoid about the great unwashed checking stuff out on the internet.

 

[Hedges]

1200W PV, 5kWh battery, not years but 4 hours to charge. Reasonable size, holds maybe 2/3 of a summer day's production.

Graph shows 1.7kW exported to grid? From 1200W PV, or from battery? But 0kWh exported?

PV and battery on a grid-tied inverter would give you backup during power failure.

Do you, or do you not, have rates that vary with time of day? (What I read seems to contradict itself).
With batteries, you can draw from batteries when rates are high.

What are the rates? Chart shows a graph that goes higher 17:00 to 22:00. Table below lists 10.30p to 12.83p at night, looks like peaks are 2x that. So around 20p to 25p during peak?

At such rates, you could save some by running off batteries those hours.

Do you get credit for export of PV to grid? What inverter is the PV connected to? Are you allowed to charge battery from PV then export to grid? If so, you might get to use 2x the kWh off-peak in exchange for having saved PV to export on-peak.

All depending on whether tariffs change when you install or configure equipment differently. In the US we have various rules on what we charge batteries from if we export from battery to grid.

 

[SeaGal]

Do you, or do you not, have rates that vary with time of day?

Yes, the OP has a variable tariff with a different price for each 30 min period.

What are the rates? Chart shows a graph that goes higher 17:00 to 22:00. Table below lists 10.30p to 12.83p at night, looks like peaks are 2x that. So around 20p to 25p during peak?

Can very a lot - today it looks like from -1.8p to +30.1p - see https://agileprices.co.uk/

Do you get credit for export of PV to grid?

The OP has the very lucrative Feed-in-Tariff scheme that ran from about 2010 to 2019. No longer available - paid for what you generate and what you export.

All depending on whether tariffs change when you install or configure equipment differently. In the US we have various rules on what we charge batteries from if we export from battery to grid.

Similar in UK. Minimal changes are permitted to retain FiT payments, will depend on what the provider allows and whether you have bi-directional export meter on the inverter - they don't want you importing when cheap and then exporting it to increase the export payments.

 

[Hedges]

But fair game to charge battery with 100% of PV generation, while supplying load from grid, off-peak?
Then export from battery during peak?

We can't add to PV system (beyond greater of 1kW or 10%) without getting bumped to new tariff. But we can add battery with its own inverter.

 

[SeaGal]

But fair game to charge battery with 100% of PV generation, while supplying load from grid, off-peak?
Then export from battery during peak?

We can't add to PV system (beyond greater of 1kW or 10%) without getting bumped to new tariff. But we can add battery with its own inverter.

Not sure, but from what I read, because you get paid for electricity you generate as well as export, then only AC coupled battery systems can be added to preserve the existing FiT payments (i.e. after the generated energy has been measured by the installed generation meter). Hence my suggestion the OP would need to discuss with their FiT provider before making changes.