I am new to all this and looking for feedback on my 'off grid' system

[Joeboy]

Sorry if I, or anyone else, came across as unnecessarily blunt! I hope you've spent enough time lurking here to understand that, as a group, we have real knowledge and experience and we were not ripping your plan for the sake of it or to feel superior. You'd gone down the wrong alley, so making the post and sharing your plans has saved you a lot of: time, money and heartache!

Don't worry, it wasn't. I made the post to get advice, and I got the advice I needed!

Everyone and his dog has gotten interested in solar/battery systems in the last 6 months, so getting bits can be tough, you might have to chose equipment based on what you can get ahold of rather than on the specs. But here is what I'd suggest as a starter:

• Inverter - SOL-3.6K-RHI-48ES-5G-DC - £1200

• Batteries - 2x Pylontech US2000 @£1000 ea - £2000

Thanks, I've been looking at those products on the Bimble web site, they do sound like what I need.

More questions, if I may:

For the inverter, the 3.6kW in the description refers to the grid output power? Why not save a few quid and get the 3kW version, if I only have 2.4kW of PV? Then again, it really is only £35 difference.

Why not buy a single Pylontech US5000, which has the same capacity but lower price compared to 2xUS2000?

Can I mix and match the batteries? For example use a US5000 and a US2000 to give a total of 7.2kWh?

Are Bimble a good place to buy from, generally?

You don't really want to limit yourself to 3kW as the combined battery and PV output will easily exceed that. Go for the 3.6kW and your system will go to grid less. Bimble are excellent. Yes to mix and match batteries. Although it would be prudent to query the supplier or Pylontech themselves as there are multiple series of Pylontechs now. Batteries are a bit like beer, you start off fancying one and before you know it.... Check the spec details of any proposed hybrid inverter to see what it's battery volume and charge/discharge limits are. No benefit in assuming.

[Oldgreybeard]

More questions, if I may:

For the inverter, the 3.6kW in the description refers to the grid output power? Why not save a few quid and get the 3kW version, if I only have 2.4kW of PV? Then again, it really is only £35 difference.

Why not buy a single Pylontech US5000, which has the same capacity but lower price compared to 2xUS2000?

Can I mix and match the batteries? For example use a US5000 and a US2000 to give a total of 7.2kWh?

Are Bimble a good place to buy from, generally?

You most probably need to size the inverter around the battery to house load, rather than the capacity of the solar panels, as you may well want to pull more than a couple of kW in the house, for example boiling a kettle, using a microwave, etc.

The US5000 is fine, but it is a heavy beast to move around. This is one reason I mentioned looking carefully and adding bounds to requirements. I have six US3000C packs and they were as heavy as I'd want to lift on my own. The US5000 pack weighs 39kg and is a pig of a thing to lift into any sort of confined space. The US2000C packs are only 24kg and that makes them a lot easier to move around.

Yes, the Pylontech's now all mix and match OK, so you can add to the system with extra packs.

[Countrypaul]

You should also bear in mind that multiple batteries allow for lower current draw on each one, this can be a limit if you expect to try and draw the headline figure (which is often time limited e.g. 1 minute, 5 minutes, etc) for a continuous period. Might not be an issue at present but smething to beware of if you want to change tings in the future. You could of course buy another battery - but who would want to that

[dangermouse]

You don't really want to limit yourself to 3kW as the combined battery and PV output will easily exceed that. Go for the 3.6kW and your system will go to grid less.

You most probably need to size the inverter around the battery to house load, rather than the capacity of the solar panels, as you may well want to pull more than a couple of kW in the house, for example boiling a kettle, using a microwave, etc.

Have I misunderstood? Both the RHI-3K and the RHI-3.6K have "Output AC (back up)" rated at 3kW. This is the power the inverter will supply to the house, isn't it? The "Output AC (grid side)" is rated at 3kW or 3.6kW depending on model, so the only difference between these models is the power they will export to the grid?

The other thing in favour of the 3kW version is that it's in stock

Yet another question ... if I disable grid export in the inverter, do I need to notify the DNO, submit a G98 form etc?

[Joeboy]

You don't really want to limit yourself to 3kW as the combined battery and PV output will easily exceed that. Go for the 3.6kW and your system will go to grid less.

You most probably need to size the inverter around the battery to house load, rather than the capacity of the solar panels, as you may well want to pull more than a couple of kW in the house, for example boiling a kettle, using a microwave, etc.

Have I misunderstood? Both the RHI-3K and the RHI-3.6K have "Output AC (back up)" rated at 3kW. This is the power the inverter will supply to the house, isn't it? The "Output AC (grid side)" is rated at 3kW or 3.6kW depending on model, so the only difference between these models is the power they will export to the grid?

The other thing in favour of the 3kW version is that it's in stock

Yet another question ... if I disable grid export in the inverter, do I need to notify the DNO, submit a G98 form etc?

The 3 or 3.6kW limit denotes export limit to grid or home but as I said double check with supplier.

[marshman]

Yes the Solis RHI inverter allows you to set up so you can charge from the grid at specific times to take full advantage of E7 or other TOU tariff, only niggle is you have to do it on the inverter panel which is a pain at this time of year when some days you want to charge from the grid and others you don't due to the weather.

Go for the Solis 3.6kW over the 3kW. OK they both have a max of 3kW from the battery but battery + solar will give you the full 3.6kW even with 2,4kW of PV. Also 3.6kW won't give you any grief with the DNO, as far as I know it is install and inform!

The Solis inverter house two "outputs", the grid tied output which is in parallel with the grid connection, this will out put a max of 3.6kW on the RHI 3.6 inverter. The other output is the EPS or Emergency Power Supply which you do not have to connect if you don't want to. It is this output for use when there is a power cut that is limited to 3kW on both inverters.

[Oldgreybeard]

Yet another question ... if I disable grid export in the inverter, do I need to notify the DNO, submit a G98 form etc?

You still need to notify the DNO, even if the inverter has a G100 export limit set to zero and is G98 compliant. The rationale behind this relates to surges on the local distribution network as no inverter, AFAIK, limits instantly, they can take anything up to around 4 to 5 seconds to adjust to sudden demand or generation changes. This means that even with zero export set, if the inverter is running at full power supplying a load like a kettle, say, then when that kettle turns off the inverter won't instantly reduce it's output to zero. It will export the full 3kW to the grid for a short time, with this export reducing over a period of a second or two. The DNO need to be aware that there will be a device doing this, although the reality is that variations as small as this aren't really an issue for the local distribution network 99.99% of the time.

[Joeboy]

Yes the Solis RHI inverter allows you to set up so you can charge from the grid at specific times to take full advantage of E7 or other TOU tariff, only niggle is you have to do it on the inverter panel which is a pain at this time of year when some days you want to charge from the grid and others you don't due to the weather.

Go for the Solis 3.6kW over the 3kW. OK they both have a max of 3kW from the battery but battery + solar will give you the full 3.6kW even with 2,4kW of PV. Also 3.6kW won't give you any grief with the DNO, as far as I know it is install and inform!

The Solis inverter house two "outputs", the grid tied output which is in parallel with the grid connection, this will out put a max of 3.6kW on the RHI 3.6 inverter. The other output is the EPS or Emergency Power Supply which you do not have to connect if you don't want to. It is this output for use when there is a power cut that is limited to 3kW on both inverters.

Interesting on the 3.6kW limit, assuming this is a combined hybrid inverter doing the PV and batteries too?

I ask as our primary system has its own solaredge inverter rated to 5kW, alongside that ws have a 3.6kW hybrid inverter. This means that on a peak June day I will have 5kW incoming from PV and 3.6kW discharge rate from the battery, allowing a whopping 8.6kW demand at home before the hybrid inverter brings in grid power.

By using a single 3.6kW inverter the OP has lost the capacity to have say 2.2kW incoming from his PV and also the 3.6kW discharge from the battery... This may seem obvious but worth bringing to attention?

If I was going through this and using a single inverter I'd be aiming for a 5kW one. That 3.6kW total would quickly become a pita IMHO.

[Oldgreybeard]

By using a single 3.6kW inverter the OP has lost the capacity to have say 2.2kW incoming from his PV and also the 3.6kW discharge from the battery... This may seem obvious but worth bringing to attention?

That's a good point. I remain convinced that there is merit in considering using two inverters, one solely for the PV, the other for the battery system. We ended up with this arrangement only because the battery system was added several years after the solar panels went in, but it does mean that with the batteries charged and the PV generating the house can pull the combined output of both for a time without pulling from the grid. Right now, for example, the cooker and hob are on and the sun is shining. We're generating about 4.2kW and if need be the battery inverter can deliver another 3kW, so in total we can pull around 7.2kW without importing from the grid at all.

[Stinsy]

More questions, if I may:

You may!

For the inverter, the 3.6kW in the description refers to the grid output power? Why not save a few quid and get the 3kW version, if I only have 2.4kW of PV? Then again, it really is only £35 difference.

The 3.6kW one is the biggest you can have without asking permission form the DNO (power company). 3.6Kw is the maximum power the inverter can inject into the grid, this can come from solar or batteries or a mixture of the two. Imagine your panels are producing 2kW and your house load is 4kW. Then you would get 2kW from the solar, 1.6kW from the batteries, and 400W from the grid. The extra 600W will significantly reduce how much peak grid power you consume.

Why not buy a single Pylontech US5000, which has the same capacity but lower price compared to 2xUS2000?

US2000 seem to be in stock at the moment whereas US5000 seem to have a long lead-time. The US5000 are exceptionally difficult to manoeuvre because of their weight. However, if you can find them in-stock for a reasonable price and heave 2x bags of cement around without flinching, go for 1x US5000.

Can I mix and match the batteries? For example use a US5000 and a US2000 to give a total of 7.2kWh?

You can!

Are Bimble a good place to buy from, generally?

Yes. See also ITS and TradeSparky.