Planning a Solar PV and Battery system

[SteamyTea]

13 minutes ago, PhilT said:

"C" ratings

C is a coulomb.

 

C = A.s

Or 

6.241509×10¹⁸ e

With e being the charge of a proton.

There are a lot of protons in a battery.

Edited April 28, 2023 by SteamyTea

[Nick Thomas]

9 hours ago, S2D2 said:

What capacity and temp is your battery for this charge?

 

It's a single Greenlinux 3.2kWh attached to an LXP hybrid inverter. I don't have battery temperatures exposed AFAIK, just inverter temps. Probably not what you're after.

 

I assume that if it were conservatively specced, you wouldn't see the same voltage peak at 90%+ nominal SOC (since that would actually be 80%+ real SOC), but don't actually know ^^.

 

They do claim "100% usable capacity", i.e., they're happy for you to take it to 0%, so maybe 100% is the real 100%, and 0% is really 10% or something 🤷‍♂️

 

 

 

Edited April 28, 2023 by Nick Thomas

[Nick Thomas]

.

Edited April 28, 2023 by Nick Thomas
accidental dup

[Dan F]

10 hours ago, SteamyTea said:

C is a coulomb.

 

C = A.s

Or 

6.241509×10¹⁸ e

With e being the charge of a proton.

There are a lot of protons in a battery.

 

I'm pretty sure c-rate is related to coulomb somehow, but when a battery quotes a c-rate, it's the rate of charge/discharge relative to capacity. 

 

[SteamyTea]

7 minutes ago, Dan F said:

I'm pretty sure c-rate is related to coulomb

It is, C for coulomb, named after Charles-Augustin de Coulomb.

It is the SI unit for electrical charge.  

[PhilT]

11 hours ago, SteamyTea said:

It is, C for coulomb, named after Charles-Augustin de Coulomb.

It is the SI unit for electrical charge.  

The "C" used in hobby packs is the multiplier of the Ah rating that the pack can safely discharge continuously, so a 5Ah pack rated at 120C can safely discharge at ( 120 x 5 = ) 600A, which would take around 30 seconds. The electric model car world speed record holder (over 200mph) would be using these crazy kind of packs, and that means wires like lamp posts!

[Rob99]

Hi All

Unfortunately not been responding to anything last month, had a few family issues to deal with so not much free time!!

Also, apologies in advance for the long post (and possibly repeating myself from earlier posts)……..bit of a brain dump!

Anyway, back to questions about PV etc. and thanks again to those who replied previously 👍

 

Panels I’m now pretty much OK with so I’ve been looking at invertors and it’s just a minefield out there. I’ve joined a couple of facebook groups recently thinking it would help but I think I’m suffering from information overload now. As I see it, it seems to be a bit like choosing anything else (houses, cars, TV etc), they all do what they’re supposed to do but you have to delve into the detail to work out if it does what “YOU” want it to do.

It's likely we’ll end up with around an 8.5kWp PV array (split East/West) so I’ve been looking at invertors which will cope with what PVGIS estimates is our maximum PV generation of around 6.5kWp. As you’d expect there are lots to choose from but getting some of the detailed info on them can be difficult.

One of the biggest issues for me is that invertors (even ones stated as 6.5k) often have a maximum pass through rate of 3.6kW. Whilst this appears ok as they will use your max generation to charge your batteries, once batteries are full they will start clipping the output, so even if your panels are generating 6kW you can only use 3.6kW either in your house or for export. I suspect this is to do with the “standard DNO” cutoff point of 3.62kW export and I guess is designed for the hundreds of installers who are just wacking in small PV systems and are probably the biggest chunk of the invertor market.

What I want from an invertor is that it will pass through as much power as my PV generates and will only start clipping output when batteries are full and usage plus export has maxed out. If my system is generating 6kW, my batteries are full and I’m using 3kW in the house, I want the invertor to then export the remaining 3kW. Seems very logical and sensible to me but I’m not finding it easy to identify a range of invertors that work that way.

Following a post by @Nickfromwales I took a look at the SunSynk invertors and so far seem like they might fit the bill, or maybe it’s just there’s more information on them compared to other makes. I was quite impressed with Victron but they seem twice the price of many others so may not be an option.

In addition to not wanting the invertor to throttle my AC power availability I also want to be able to communicate with it through my Loxone system. I’m not expecting a massive level of integration but would like Loxone to be able to control schedules for charging/discharging batteries, heating HW, grid export etc. I don’t particularly want to rely on programming the invertor by hand or through the manufacturers cloud based App as much of this stuff is more than just time schedules. Loxone will be able to do it all in the background, especially when half hourly electricity tariffs become much more common.

Maybe I’m asking too much, but when I’m looking at dropping £15k or so on a PV/Battery system I’d like to think that I will be able to get what I want.
So, at the moment the SunSynk invertor seems to be top of my list (thanks @Nickfromwales), subject to it being “Loxone friendly”, but would welcome any and all comments about what others have or would recommend, especially those of you who have Loxone and may have successfully integrated it with your invertor.

 

[Nickfromwales]

Do you need it to be Luxone (or anything else HA) friendly ? I'll be making mine 'fit and forget' and it'll be accessible via the 'net, so that will be all I need from it.

[Rob99]

11 minutes ago, Nickfromwales said:

Do you need it to be Luxone (or anything else HA) friendly ?

As a minimum I want to be able to pull real time data out of the invertor into Loxone (preferably not via a 3rd party bit of kit e.g RPi etc). PV generation, battery charge level, battery charging/discharging info, house usage and export power feed into the Loxone energy management functions, for example to decide when to divert energy to immersion and how much, all linked to house usage.

 

It would be useful (but not essential) to be able to ping stuff back to the invertor for example to tell it when to charge/discharge the batteries and when to export. With Octopus Flux there are fixed daily periods for low/normal/high rates but in future (already happening in Europe) there's likely to be more tariffs with day ahead half hour pricing and this can be managed with Loxone.

[Dillsue]

You need to look at this in the correct order!!

First off, if you want to have the potential to export all you can generate then you need to speak to your DNO and likely put in a G99 application. No point in looking at inverters until you know what capacity is allowable.

Secondly, look on the ENA inverter type approved database and make sure anything you shortlist is on the database. If its not then you can't legitimately connect it to the grid.

Then start looking at the specifics you want

 

[Rob99]

26 minutes ago, Dillsue said:

First off, if you want to have the potential to export all you can generate then you need to speak to your DNO and likely put in a G99 application. No point in looking at inverters until you know what capacity is allowable.

Already started that process and registered with my DNO (UKPN) to submit a G99 application. They will automatically approve 5kW but I may submit for 8kW anyway and see what happens. I'll be posting seperately about the G99 application in due course as I think I will need some help on some of the questions!!

 

31 minutes ago, Dillsue said:

Secondly, look on the ENA inverter type approved database and make sure anything you shortlist is on the database. If its not then you can't legitimately connect it to the grid.

Then start looking at the specifics you want

Yes, I've been checking the ENA lists but with invertors being added and dropped off the compliance list daily they are a bit of a moving target so checking every possible invertor won't make sense. It doesn't help that some non-compliant invertors are still being sold and installed in the UK. I've seen some posts on FB groups where people have had systems installed by "proper" MCS contractors where the invertor is no longer on the ENA compliance list (as it's an older version) so their DNO is refusing connection. One to watch.

 

[Dillsue]

18 minutes ago, Rob99 said:

It doesn't help that some non-compliant invertors are still being sold and installed in the UK.

?? Why doesnt that help? You either want to stay within the law or not regardless of what others are doing.  ENA database is easy enough to search for compliant kit

[Rob99]

16 minutes ago, Dillsue said:

Why doesnt that help?

I was making a general point. I intend to export so I will only have a compliant invertor installed.

[DougMLancs]

15 hours ago, Rob99 said:

One of the biggest issues for me is that invertors (even ones stated as 6.5k) often have a maximum pass through rate of 3.6kW. Whilst this appears ok as they will use your max generation to charge your batteries, once batteries are full they will start clipping the output, so even if your panels are generating 6kW you can only use 3.6kW either in your house or for export. I suspect this is to do with the “standard DNO” cutoff point of 3.62kW export and I guess is designed for the hundreds of installers who are just wacking in small PV systems and are probably the biggest chunk of the invertor market.

What I want from an invertor is that it will pass through as much power as my PV generates and will only start clipping output when batteries are full and usage plus export has maxed out. If my system is generating 6kW, my batteries are full and I’m using 3kW in the house, I want the invertor to then export the remaining 3kW. Seems very logical and sensible to me but I’m not finding it easy to identify a range of invertors that work that way.

Do you mean it’s the battery charge/discharge rate that you want above 3.6kW? That’s the only difference I can see about the SunSynk inverter. Any hybrid inverter will supply AC at its full rated output to the house and grid as well as charge the battery with excess unless the DNO say it has to be export limited under a g100.

[Rob99]

13 minutes ago, DougMLancs said:

Do you mean it’s the battery charge/discharge rate that you want above 3.6kW? That’s the only difference I can see about the SunSynk inverter. Any hybrid inverter will supply AC at its full rated output to the house and grid as well as charge the battery with excess unless the DNO say it has to be export limited under a g100.

Maybe I'm getting things confused between DC and AC side! (I did say it was a bit of a brain dump - my head hurts with so much information to process LOL)

 

At some point I'll likely have up to 20kWh of storage so I want to be able to charge or discharge within a 3 hour window which with a nominal battery voltage of 55v (if my maths is correct) is around 120A. Of the specs I've seen the limit on most is well below 100A and some as low as 30A. This may seem like I'm over-engineering my requirements but I don't want to get 3 years down the road and find I may need to upgrade the invertor to cope with larger battery storage.

 

42 minutes ago, DougMLancs said:

unless the DNO say it has to be export limited under a g100

How does this work in practice? For example, if I have a 8kW invertor, and DNO export limit is 5kW, is this a setting in the firmware?

[Dillsue]

34 minutes ago, Rob99 said:

How does this work in practice? For example, if I have a 8kW invertor, and DNO export limit is 5kW, is this a setting in the firmware?

Theres a meter installed between your consumer unit and the house meter thats connected to the inverter. The inverter is configured so that when it sees >5kw being exported it throttles production. The config is password protected if its G100 compliant.

 

Let's you use the full 8kw within the house but not pump it into the grid.

[Rob99]

29 minutes ago, Dillsue said:

Theres a meter installed between your consumer unit and the house meter thats connected to the inverter.

Do you mean an actual meter or is this the CT clamp I see on installations?

[Dan F]

8 hours ago, Rob99 said:

At some point I'll likely have up to 20kWh of storage so I want to be able to charge or discharge within a 3 hour window which with a nominal battery voltage of 55v (if my maths is correct) is around 120A. Of the specs I've seen the limit on most is well below 100A and some as low as 30A. This may seem like I'm over-engineering my requirements but I don't want to get 3 years down the road and find I may need to upgrade the invertor to cope with larger battery storage.

 

The "charger" element of the charger-inverter needs to support 130A (20kWh/3hr/51.2v). This can often be a different figure to the "inverter" amps.  You are right that most of the type charge voltage may be closer to 55v, but worth leaving some margin. Would the 6kW Sunsync be a a good fit? The 5.5kW would also work at 120A.

[Dillsue]

1 hour ago, Rob99 said:

Do you mean an actual meter or is this the CT clamp I see on installations?

Yes. Functionally a meter