UK grid-tie inverter recommendations

[xcentric]

Very helpful thanks. On oversizing the array for the inverter, is there a % Solis recommend? Currently got 3.5-4kW of panels (backside solar generation too hence if it works, maybe 4kW) which is a bit low for the 6kW Solis - I assume it'll run fine on that but allow me to add another 3kW with no problem.

(6kW Solis is the suggested swap for the faulty inverter I have at present - and at times we'd easily need 6kW so that works). Plan is to pair with pylon tech batteries, initially 10kwH but probably expanding to 15kWh quite soon when I see either a decent price one used or new. I assume with the Solis adding more batteries is straightforwards?

For those that install them in the garage, do you have the energy meter installed next to them, or a comms cable to the main consumer unit and the meter installed there?

Other location is a cupboard with my switch rack in it already - less ventilation but it doesn't get hot - does the Solis need a lot of free circulating air or is a roomy understaffs cupboard likely to be okay for it. No point putting it in there if it's too heat sensitive and the fans are always on!

 

[xcentric]

Since we're settling on the Solis, one more q on this thread for the Solis experts - is it acceptable to mix and match batteries on the one inverter, or not? I was going to get another pylon tech 5000 to go with the 2 currently on the order, but have noticed the Frogstar 15kwH for about £2k (with VAT relief) which is 3 x the battery for twice the price..... or would I need a second inverter (which I know is probably ideal).

 

[rpdom]

Very helpful thanks. On oversizing the array for the inverter, is there a % Solis recommend? Currently got 3.5-4kW of panels (backside solar generation too hence if it works, maybe 4kW) which is a bit low for the 6kW Solis - I assume it'll run fine on that but allow me to add another 3kW with no problem.

I've got a 3kW inverter with 3kW of panels as that's all I could fit. I have seen them produce 4kW briefly. My inverter is good for up to 4.8kW, but only 3kW AC and/or 3kW DC (battery charging). I would have gone for a bigger inverter with more batteries if I could. I wouldn't get any extra from the panels, but it could handle more of my load and I could fill up with cheap overnight electricity.

(6kW Solis is the suggested swap for the faulty inverter I have at present - and at times we'd easily need 6kW so that works). Plan is to pair with pylon tech batteries, initially 10kwH but probably expanding to 15kWh quite soon when I see either a decent price one used or new. I assume with the Solis adding more batteries is straightforwards?

Adding more Pylon batteries is pretty easy. Nothing needs to done on the inverter. There is a recommended procedure and wiring order for the batteries.

For those that install them in the garage, do you have the energy meter installed next to them, or a comms cable to the main consumer unit and the meter installed there?

Mine is in my loft, not garage. I've got the RS485 comms cable running down to my consumer uint where the meter is and the CT from that is by my supply meter. The comms cable can be extended as long as you need. The cable to the CT should be kept as it is.

Other location is a cupboard with my switch rack in it already - less ventilation but it doesn't get hot - does the Solis need a lot of free circulating air or is a roomy understaffs cupboard likely to be okay for it. No point putting it in there if it's too heat sensitive and the fans are always on!

I'll quote from the manual for mine:

It is recommended that the inverter is installed in a cooler ambient which doesn't exceed 104℉/40℃

To avoid overheating, always make sure the flow of air around the inverter is not blocked. A minimum clearance of 300mm should be kept between inverters or
objects and 500mm clearance between the bottom of the machine and the ground.

Adequate ventilation must be provided.

 

[xcentric]

Batteries - saw a comment by @SeaGal that you can never have too many batteries - house currently uses ~25kwH per day and with 4kW of panels I'd hope for ~20kWh - so with 10kWh of batteries I'm using about 5kwH of off-peak electricity to top them up, right? So better to put in more panels before I increase the battery capacity, correct? And with the 6kW inverter I can probably put in another 4kW or so into that unit.

 

[rpdom]

I (almost) always fill my batteries overnight. Any surplus from the PV during the day will go as export and my export rate tends to be higher than my overnight rates so I don't lose out.

Check out what tariffs you can get for export and import.

I only have 4.8kWh of batteries. I want to add more when I can. Another 4.8kWh unit or two would be great. I can have up to 16 Pylontech batteries on my inverter. That's a theoretical maximum of 76.8kWh


Panels are fairly cheap, so over-panneling is a good thing if you can do it.

 

[xcentric]

who are you with re tariffs? The ones I've looked at are all more for overnight than export, so I'd be interested to find one that isn't as this would suit me perfectly.

 

[peufeu]

Other location is a cupboard with my switch rack in it already - less ventilation but it doesn't get hot - does the Solis need a lot of free circulating air or is a roomy understaffs cupboard likely to be okay for it. No point putting it in there if it's too heat sensitive and the fans are always on!

Efficiency of 48V <-> grid conversion is a bit better than 90% so at full power it will generate close to 500W of heat.

PV -> grid is more efficient (97-98%) so at full power expect 100-150W losses.

If you put it in a cupboard it will cook (and also cook the batteries).

 

[rpdom]

who are you with re tariffs? The ones I've looked at are all more for overnight than export, so I'd be interested to find one that isn't as this would suit me perfectly.

Octopus. I'm currently on their Agile tariff for Import, with rates that vary every half hour depending on the wholesale costs - tonight is between 7.93p and 13.0p per kWh, and I'm on Outgoing Fixed for export, which is a flat rate 15p/kWh.

The lowest I've seen Agile Import rates are -7.276p. That was a turn all the heaters on and charge the batteries time

Agile can be really expensive between 4pm and 7pm, but I pretty much run 100% on battery or solar at that time.

 

[xcentric]

@rpdom thanks - I'd seen the agile tariff but as it was unclear what it would actually cost I'd been looking at their alternatives. Seems like it's worth another look. Were they bothered about a certified install (my current one is but the replacement inverter will be an, err, replacement, and so not sure if I need it recertified.....

Mind you, it may be the grid operator not the supplier, I guess....

 

[MisterB1959]

FWIW, my inverter and battery are in an outside brick built utility, i didnt want them in the house as i would have felt uncomfortable, though as time has progressed i feel a bit more comfortable about them being in the house, but to be honest it makes more sense to keep everything as it is and im glad i set it up like that.

 

[houseofancients]

Days of negative prices of power here

 

[rpdom]

Were they bothered about a certified install (my current one is but the replacement inverter will be an, err, replacement, and so not sure if I need it recertified.....

Octopus do require an MCS certificate for the install. They have talked about accepting export without MCS, but that area is a bit grey and said they would charge a £250 admin fee for each application to start with.

Mind you, it may be the grid operator not the supplier, I guess....

The grid operator (DNO) are the ones that require the G98 or G99 to connect your system to the grid. I don't think they need MCS.

 

[kommando]

UK DNO's do not ask for MCS, with the right wording you even can get a DIY G98 registered but a qualified electricians sign off works 100%. G98 is an inform process, they cannot stop your install, G99/G100 is a pre install permission process so no work can be started until the approve. So keep to 3.68kw or below and you just inform them via G98. I have a G98 grid install plus and off grid install, in the right weather and season I can disconnect from the grid and then combine both.

 

[xcentric]

thanks for the info. I assume if I have a G98 install and up the power I simply request permission first then connect once agreed?

Out of interest why did you go for the grid-tied, and off grid, as two solutions? What are the benefits (maybe redundancy, I guess?)

 

[kommando]

Before going above 3.68kw you need permission, you cannot install and then apply as they could refuse and you would have to dismantle the additional capacity. Note they are only interested in the inverter capacity, you can over panel to say 6kw or more and as long as the inverter will not blow up then its still 3.68kw system. You lose output 11am to 1pm but get more in the morning and evening over a say a 4kw PV array feeding a 3.68kw inverter.

I did my install as a 2 part so as not to need a G99 application plus the equipment I use on the extra section is either pre G98/99 or off grid only. It all was bought 2nd hand so the lower cost means a faster payback eg 2 years.

 

[xcentric]

Before going above 3.68kw you need permission, you cannot install and then apply as they could refuse and you would have to dismantle the additional capacity. Note they are only interested in the inverter capacity, you can over panel to say 6kw or more and as long as the inverter will not blow up then its still 3.68kw system. You lose output 11am to 1pm but get more in the morning and evening over a say a 4kw PV array feeding a 3.68kw inverter.

I did my install as a 2 part so as not to need a G99 application plus the equipment I use on the extra section is either pre G98/99 or off grid only. It all was bought 2nd hand so the lower cost means a faster payback eg 2 years.

so the off grid part is for stuff that is permanently off grid? I get you combine them when you bring other system off grid. Such as house as grid-tied, garage/shed/outbuilding off-grid?

 

[kommando]

The off grid bit charges batteries and some off grid equipment, when the battery shows its well charged and the weather forecast is good I can go off grid completely for long periods.

 

[SeaGal]

My 2p's worth (feels more like 20p's worth)...

Very helpful thanks. On oversizing the array for the inverter, is there a % Solis recommend? Currently got 3.5-4kW of panels (backside solar generation too hence if it works, maybe 4kW) which is a bit low for the 6kW Solis - I assume it'll run fine on that but allow me to add another 3kW with no problem.

Not so much a %, but a max value, as per Solis Datasheet - the S5-EH1P-6K supports up to 8kW PV input, but you'll also need to check voltage and current of your panels are within range - see:-

https://www.solartradesales.co.uk/Cache/Downloads/Datasheet-S5-EH1P3-6K-L-GBR-V2-1-2022-10-1.pdf

(6kW Solis is the suggested swap for the faulty inverter I have at present - and at times we'd easily need 6kW so that works).

6kW is possible provided you have at least 1kW of PV generation - battery alone is 5kW, probably a bit less if you use Pylontechs due to their lower voltage than most other battery packs.

Plan is to pair with pylon tech batteries, initially 10kwH but probably expanding to 15kWh quite soon when I see either a decent price one used or new. I assume with the Solis adding more batteries is straightforwards?

Yep.

For those that install them in the garage, do you have the energy meter installed next to them, or a comms cable to the main consumer unit and the meter installed there?

In my case, comms to the CU which is 30m away; see also this thread:-

Wireless solution to feed CT clamp data to hybrid inverter

Hi all, I've just found the forum whilst trying to research a solution. I'm looking for some guidance with regards to battery storage. I have a Luxpower 3.6K hybrid inverter with approx ~3Kwp solar panels. I'm trying to figure out if it's feasible to DIY adding battery storage (obviously...

diysolarforum.com

Other location is a cupboard with my switch rack in it already - less ventilation but it doesn't get hot - does the Solis need a lot of free circulating air or is a roomy understaffs cupboard likely to be okay for it. No point putting it in there if it's too heat sensitive and the fans are always on!

That's a no-no, as @peufeu and @rpdom have already advised.

Since we're settling on the Solis, one more q on this thread for the Solis experts - is it acceptable to mix and match batteries on the one inverter, or not? I was going to get another pylon tech 5000 to go with the 2 currently on the order, but have noticed the Frogstar 15kwH for about £2k (with VAT relief) which is 3 x the battery for twice the price..... or would I need a second inverter (which I know is probably ideal).

You cannot match Pylontech with virtually any other battery pack as the cheapskate design only has 15 cells, rather than the usual 16. IMHO I'd cancel the US5000 order and go for Fogstar (not frog!) instead. Or if you are into DIY what about the Seplos / 280Ah or 305Ah cells solution that Fogstar sell instead?

UK DNO's do not ask for MCS, with the right wording you even can get a DIY G98 registered but a qualified electricians sign off works 100%. G98 is an inform process, they cannot stop your install, G99/G100 is a pre install permission process so no work can be started until the approve. So keep to 3.68kw or below and you just inform them via G98. I have a G98 grid install plus and off grid install, in the right weather and season I can disconnect from the grid and then combine both.

True that G98 is simpler, but I found my subsequent G99 approval process to be very straightforward and the DNO got back with approval within a week.

thanks for the info. I assume if I have a G98 install and up the power I simply request permission first then connect once agreed?

You would just complete a G99 application and signal that the existing G98 is being decommissioned. In my case, I was keeping the exsiting G98 installation, so the new EH1P 6kW inverter was an addition via a G99 application.

Before going above 3.68kw you need permission, you cannot install and then apply as they could refuse and you would have to dismantle the additional capacity.

Technically, yes they could refuse. In practice they will tell you that you are restricted to export of <some-number-between-0-and-6> kW of export, so you would just need to install and commission the EH1P-6K with export power limitation to less than its maximum capacity.

Were they bothered about a certified install (my current one is but the replacement inverter will be an, err, replacement, and so not sure if I need it recertified.....

You will just need to get the G99 approval in. However, you will also need to check the internal wiring / fuses etc. are suitable for the 6kW output of your new inverter - i.e. can support at least 32A. If not, wiring will require and upgrade (obviously to BS7671 standards).

 

[peufeu]

6kW is possible provided you have at least 1kW of PV generation - battery alone is 5kW, probably a bit less if you use Pylontechs due to their lower voltage than most other battery packs.

Yes

On S5 EH1P 6k + pylontechs the limit is set by the inverter's maximum current of 100A (or the batteries if they can't deliver more than 100A). Then you have to factor in 90% efficiency of 48V to mains conversion, so the "commercial rating" of "5kW" is more like 4300 real Watts on the AC side. This holds for about 40 minutes depending on ambient temperature, after which it begins to sweat from the effort and throttles down to 3750W until the batteries run out.

Here's my big heat pump running at night, with the inverter supplying a good chunk of the power (about 75% of the total energy).



When PV is producing enough it will hit the rated 6kW output without any issues.

Here's the heat pump running during the day, I also did a wash and ran the dryer, which explains the 8kW peak. Solis maxes out at 6k using either PV only or PV+battery when there's a cloud, and the Fronius inverter (with 3k of panels) adds some more power on top.

 

[SeaGal]

On S5 EH1P 6k + pylontechs the limit is set by the inverter's maximum current of 100A (or the batteries if they can't deliver more than 100A). Then you have to factor in 90% efficiency of 48V to mains conversion, so the "commercial rating" of "5kW" is more like 4300 real Watts on the AC side.

so all the more reason to avoid using 15 cells battery packs with the Solis. I'm getting around 4600W (battery alone) when battery voltage is 52V and have max discharge set to 95A - so that should be about 4800W once I increase discharge to 100A.