Poor Planning! - Solar & Battery Install

[BenY]

Dear Forum.

 

I'm looking to do a new solar install and add some battery storage as well.  Some background.  I live in a mid terrace house which is four storeys high with a flat roof.  I've just completed a complete retrofit on the house with a 5kW ASHP, lots of insulation, good airtightness etc.  I kind of half planned a solar install at the beginning of the project (January 2020) but didn't put much effort into it.  I realise this was a big mistake and I've left myself with a heap of unknowns that I can't seem to find answers to.  Hopefully the forum can help.

 

I got my electrician to install a thickish cable (6mm2 cores) from the roof to the consumer unit in the basement telling him it'd need to cope with 5kW max @ 240v and the cable runs around 10m distance.  I had a quote from pluginsolar which suggested using microinverters so this cable seemed to be the right decision for my install.  I can only fit 7 large (2.3m x 1.3m max) panels on my roof and the realistic max output was  ~3kW.  7x445W panels.  In addition some of the panels would be closer to my roof parapet walls (<1m high) than is ideal so would suffer from shading at different times of day/year again pointing to microinverters being ideal.  What I didn't take into account even back then was my roof buildup might be a problem.  I have a compact roof design, insulated below the roof deck (between the joists) with wool and above the deck with PIR panels (150kPa compressive strength).  As part of the calculations for the roof design, it was recommended not to install a wooden layer over the top of the PIR panels and just to glue the EPDM roof covering direct to the insulation which we have done.

 

I also didn't at the time consider a battery solution as I didn't really see the need, in summer I could use any excess power from the PV to run the ashp in cooling mode and in winter I'm fairly sure there will never be any excess power.  This was of course before the price of electricity went through the roof.  I now don't have a place to install a normal inverter or for that matter any place to put the batteries except for in my utility room which is in the basement.   Inconveniently this is not near the consumer unit (or the roof either) but at least is close to the main electricity supply, meter and isolator for the house.

 

I've spoken to a couple of suppliers but I'm not getting any good answers on what system design I could have and my knowledge is still pretty limited.  So this all raises a number of questions for me. 

 

1.  Firstly is it worth having batteries installed at all?  I'm not really concerned about power cuts, my electricity service is buried and I can't remember an unplanned power cut in 15 years.  I don't really have any historic power consumption data for the house btw, since we only moved in this June.  If I switch to Octopus Go with 10kWh of batteries installed I'd save ~10 x £0.25 = £2.40 per day on my current electricity rate (£0.12 vs £0.36) by charging the batteries at night but given I'm using ~30kWh a day currently, the other 20kWh (@ £0.44) would cost me an extra £1.60 each day.  A saving on a cold day of £0.80.  In the summer, using PV to charge the batteries best case I could get and use 10kWh of free electricity from the batteries or £3.60 a day saving.  Average this out (not very scientific I know) at £2.20 a day and you save £800 per annum.   Cost of 10kWh battery install~ £5,000 (2 x 5kWh batteries + inverter + electrician) = 6 years payback.  Not awful but I could be making bad assumptions anywhere in this calc?    

 

2.  The solar panels I can get have got more powerful/bigger and ITS recommended a 545W JA Solar panel which appears too powerful for any of the Enphase microinverters which top out at 460Wp (what is the lower case "p"? panel?) so would I need a normal inverter vs microinverters?  Am I misreading the microinverter specs? https://enphase.com/en-gb/installers/microinverters/comparison

 

3.  If I need a normal string inverter are there any waterproof ones I can install on the roof or could I install it 10m of cable away next to the consumer unit?  If the inverter was in a cupboard would you hear it?  Are they noisy enough to hear if you were sleeping next to the cupboard?  My consumer unit is in a cupboard in the room we use when guests stay.

 

4.  It's possible I'd need a second inverter for the batteries as cabling from the consumer unit location to the battery location might not be possible.  Are there any manufactures who are set up for this double inverter scenario and if so who is best?

 

5.  I have a loxone system so in theory I can control disparate systems easily enough as long as I can talk to them.  Anyone got any experience in this area?

 

6.  Will the strength of my roof be enough to support the solar panels which will need weighting down as there is nothing to fix the fames too without puncturing the waterproof roof and through 120mm of insulation to the ply. I've done a mounting report on the Van Der Valk calculator and it says the overall system would weight 600Kg but maximum point load would be 40kPa (vs 150kPa compressive strength of the roof insulation) so I'm pretty sure the roof would be ok? 

 

 

Thanks in advance for any comments.

 

 

 

 

 

 

 

 

 

 

 

 

[Nick Thomas]

Hey,

 

I've recently done the whole ASHP, panels, batteries thing ^^.

 

1) Payback of ~6 years on the batteries for you isn't bad - at current electricity prices, my panels have a payback of 7 years, for instance. Calculation looks fine, but worth keeping in mind that power costs will change over time - how upset would you be if off-peak tariffs disappeared completely, for instance?

 

2) The "p" means "peak". It's actually "peak at standard operating conditions", IIRC - not an absolute number. Other than that, I have no experience with microinverters. Regular string inverters allow you to install more panels than the inverter capacity (e.g. 6kWp of panels on a 3.6kW inverter), but I don't know if microinverters permit that.

 

3) Regular inverters are rated for external installation as long as certain conditions are met. Mine (LuxPower 3600 Hybrid) is IP65 but contraindicates direct sunshine and snow, and it needs to be installed either vertically, or with a slight backwards tilt - so on the wall, not on a flat or pitched roof. They're also bloody heavy.

 

Out-of-date manual: http://www.pvpro.co.uk/wp-content/uploads/2018/07/Lux-Power-Hybrid-Manual.pdf . It generates a good deal of heat, and also contraindicate being installed in enclosed spaces - I suspect a cupboard would count as that. Mine's in the loft, but I've not heard it make any noise while I'm up there; it's passive cooling.

 

I don't think the batteries like to be installed externally, they stop working below a certain temperature. I think mine is just IP20?

 

4) An inverter for the panels and an inverter for the batteries is not unusual when you install the batteries *after* the panels; the batteries tend to be called "AC-coupled" in this configuration and you can get inverters that have no capacity for solar panels at all (e.g. LuxPower 3600 ACS). However, it's a bit of a pain with G98/G99 (you have to sum the export capability of the two inverters together), there are (minor) transmission/conversion losses, and it doesn't work as well in the event of a power cut (which you're not worried about). 

 

5) Inverters vary massively in how automatable they are. Generally they punt all their data to a random cloud service and allow control from there, local tends to be a bit of an afterthought. I'm currently using https://github.com/celsworth/lxp-bridge on mine, it's still pretty skunkworks. No experience with loxone specifically.

 

6) Not a clue

Edited December 12, 2022 by Nick Thomas
over-panel info

[Dillsue]

I wouldnt beat yourself up with a 'poor planning' title!  In the thick of a whole house refurb youve managed to get one of your bigger PV problems sorted by running a cable through the house.

 

With a circa 1 metre parapet wall youll likely be able to mount the inverter on the inside of the parapet if you needed to, but..... think hard about maintenance access on a 4 storey house before committing to putting the inverter on the roof. If you do go for a roof mount get a louvred canopy to go over the inverter to keep the worse of the weather off it

 

 

[JohnMo]

Only thing come into my head after reading lots of threads.

 

Above 16A so 3.6 kWp you move from G98 (tell DNO after install), to G99 ask DNO for permission before connection. 

 

Depend on where the batteries are in the system DC part or AC after you PV inverter, this either increases or doesn't change the kW you could export. 

 

Export potential is the measurement the DNO are interested in, not that you do or don't want to export.

[BenY]

7 hours ago, Nick Thomas said:

3) Regular inverters are rated for external installation as long as certain conditions are met. Mine (LuxPower 3600 Hybrid) is IP65 but contraindicates direct sunshine and snow, and it needs to be installed either vertically, or with a slight backwards tilt - so on the wall, not on a flat or pitched roof. They're also bloody heavy.

 

4 hours ago, Dillsue said:

With a circa 1 metre parapet wall youll likely be able to mount the inverter on the inside of the parapet if you needed to, but..... think hard about maintenance access on a 4 storey house before committing to putting the inverter on the roof. If you do go for a roof mount get a louvred canopy to go over the inverter to keep the worse of the weather off it

 

Ok so based on this I could install the inverter a few metres further away just outside my bathroom windows which will make access simpler and put a canopy on it.  I think I'd still prefer to go for a microinverter solution if I can.  I'll try and get more information about the power rating.

 

9 hours ago, Nick Thomas said:

I don't think the batteries like to be installed externally, they stop working below a certain temperature. I think mine is just IP20?

Yes that's fine they will be indoors.

 

13 hours ago, Nick Thomas said:

An inverter for the panels and an inverter for the batteries is not unusual when you install the batteries *after* the panels; the batteries tend to be called "AC-coupled" in this configuration and you can get inverters that have no capacity for solar panels at all (e.g. LuxPower 3600 ACS)

OK that's great I can just treat them as two different systems and then hopefully make them work harmoniously with Loxone.   

 

13 hours ago, Nick Thomas said:

However, it's a bit of a pain with G98/G99 (you have to sum the export capability of the two inverters together)

 

10 hours ago, JohnMo said:

Above 16A so 3.6 kWp you move from G98 (tell DNO after install), to G99 ask DNO for permission before connection. 

 

 

OK so if I have 2 inverters one for then panels and one for the batteries, I could in theory export 7.2kW and hence I need to get permission to add this to the grid.  Hmmm that's a pain and I don't imagine there is anyway to wire everything up to ensure the batteries cannot export?

 

[joth]

7 hours ago, BenY said:

Hmmm that's a pain and I don't imagine there is anyway to wire everything up to ensure the batteries cannot export?

There is a way, in effect by taking your house (or a subset of loads) off grid and powering them only from the battery. But this is more expensive and less flexible than doing the DNO permission.

 

Regarding Loxone inverter integration, I have solaredge DC coupled inverter for PV and batteries (under a single 8kWp G99) and the Loxone integration works ok. The template on their library is a bit naff, so I rewrote most of it to avoid glitches then discovered the German Loxone forum has copious pages explaining how to make it work well. 

 

[Dillsue]

9 hours ago, BenY said:

OK so if I have 2 inverters one for then panels and one for the batteries, I could in theory export 7.2kW and hence I need to get permission to add this to the grid.  Hmmm that's a pain and I don't imagine there is anyway to wire everything up to ensure the batteries cannot export?

 

Youve got a few options. First and obvious one is speak to your DNO as they can be surprisingly helpful and may have capacity to take your full potential output.

 

2- agree a lower export limit with your DNO and implement an export limitation system. Fair chance your DNO will want to witness a limitation system operating so in addition to extra equipment there could be a charge for a witness test.

 

3- go partly off grid as already suggested. Likely a few bits of extra kit to be housed indoors and a second consumer unit with some circuits being moved to the new CU.

 

4- get an integrated battery system that manages PV generation and limits export from both PV and/or battery. I've no experience with batteries but I beleive the latest Tesla powerwall have an integrated PV inverter and if you get the G98/3.68kw limited version you don't need DNO approval to connect, just notify them once its installed. Victron do a big range of battery/PV management kit so they may do something similar???

 

5- put in a DC coupled battery system where the inverter limits output. Similar to 4 but separate units so doesn't have to be a big cash outlay all at once. Solaredge do an energy bank and I think others do similar modular DC coupled systems.

 

Speaking to your DNO first seems the obvious way to go so you know what constraints youre up against

[BenY]

On 13/12/2022 at 10:20, Dillsue said:

Youve got a few options. First and obvious one is speak to your DNO as they can be surprisingly helpful and may have capacity to take your full potential output.

Thanks I've made an appointment with them to talk about it.

 

On 13/12/2022 at 10:20, Dillsue said:

4- get an integrated battery system that manages PV generation and limits export from both PV and/or battery. I've no experience with batteries but I beleive the latest Tesla powerwall have an integrated PV inverter and if you get the G98/3.68kw limited version you don't need DNO approval to connect, just notify them once its installed. Victron do a big range of battery/PV management kit so they may do something similar???

I think once I've spoken to the DNO this is hopefully where I will end up.

 

On 13/12/2022 at 08:00, joth said:

Regarding Loxone inverter integration, I have solaredge DC coupled inverter for PV and batteries (under a single 8kWp G99) and the Loxone integration works ok. The template on their library is a bit naff, so I rewrote most of it to avoid glitches then discovered the German Loxone forum has copious pages explaining how to make it work well. 

Great thanks I'll have a look at that.

[Marvin]

On 13/12/2022 at 08:00, joth said:

There is a way, in effect by taking your house (or a subset of loads) off grid and powering them only from the battery. But this is more expensive and less flexible than doing the DNO permission.

What about a split power supply using a relay? battery supply inverted to 240v

 

 

 

 

Edited December 18, 2022 by Marvin

[joth]

6 hours ago, Marvin said:

What about a split power supply using a relay? battery supply inverted to 240v

 

 

 

 

Yes That's what I mean by "a sunset of loads".

 

[Nick Thomas]

Sounds like the "level 3 manual whole-house backup" in https://www.deegesolar.co.uk/eps_for_solar/ (I found this link very useful when trying to understand my own options).

 

Another possibility when you have two inverters is to make the PV inverter's output a dedicated input to the battery inverter. Then, you only have the battery inverter's capacity to worry about for G98/G99 purposes. They need to be compatible with each other, though - there's a standard involving frequency shifting that the battery inverter can use to tell the PV inverter to reduce its output,and that's quite important.

 

I didn't keep notes but I do remember concluding that a https://www.victronenergy.com/inverters-chargers/multiplus-ii combined with a Solax X1 Boost G3 would work. Expensive, though.

 

A single inverter with both batteries and panels DC-side is so much better for me.

 

 

[Marvin]

8 hours ago, Nick Thomas said:

Sounds like the "level 3 manual whole-house backup" in https://www.deegesolar.co.uk/eps_for_solar/ (I found this link very useful when trying to understand my own options).

 

Another possibility when you have two inverters is to make the PV inverter's output a dedicated input to the battery inverter. Then, you only have the battery inverter's capacity to worry about for G98/G99 purposes. They need to be compatible with each other, though - there's a standard involving frequency shifting that the battery inverter can use to tell the PV inverter to reduce its output,and that's quite important.

 

I didn't keep notes but I do remember concluding that a https://www.victronenergy.com/inverters-chargers/multiplus-ii combined with a Solax X1 Boost G3 would work. Expensive, though.

 

A single inverter with both batteries and panels DC-side is so much better for me.

 

 

Hi @Nick Thomas

 

Thanks the info. Very interesting.

 

Our setup using excess PV power is slightly different:

 

Dedicated EPS sockets for use only in a power cut. Level zero type system? ( can be used for a small heater assuming a short scheduled power cut)

A level 2 type system for battery power for overnight use of lighting, MVHR, Fridge Freezer.

A combination of both the above for use in a power cut. (Assuming a short scheduled power cut)

We have calculated and monitored our PV excess power produced in the summer days and are aiming to use about 5kWh a night about 200 days of the year.

This will be completely isolated from the mains and we hope to have the system up and running once we get on and install it.

 

 

[joth]

10 hours ago, joth said:

Yes That's what I mean by "a sunset of loads".

 

Thank you autocorrect 🤣

Subset of loads

Edited December 19, 2022 by joth

[Marvin]

2 minutes ago, joth said:

Thank you autocorrect 🤣

Subset of loads

Oh! sunset worked for me! 

[Nick Thomas]

Currently I just have a double socket attached to the EPS... in the loft 😬 .

 

Next time I'm making changes, the plan is to replace it with a consumer unit and at least get the lights shifted over. Probably a dedicated socket on each floor too, so we don't have to let all the warm air out through the loft hatch. Taking a bit of a breather at the moment though 😅

 

 

[BenY]

I have now managed to DIY my solar installation on the roof. In the end I managed to squeeze 8 panels on my flat roof in an East West configuration, 3.3kWp, using Enphase microinverters.  The shading isn't as bad as it looks on the picture although I could have done without the satellite dish being right there.  The Enphase install was very simple as both the DC cables from the panels and the AC cable they provide simply click into the microinverters.  I might need to add some pigeon protection before they start nesting under the panels.

 

 

 

Everything is working very nicely and I have had my G98 application approved by UK power Networks but they are now asking for commissioning documentation.  My understanding is there is a G98 commissioning form to fill in and I need to provide them with an electrical diagram.  Will this diagram suffice, I've seen examples and this seems ok?

Also has anyone actually done this application with UK Power Networks specifically? They have an online portal for the application and I think you don't need to fill in a commissioning form as it's been replaced by their website.  They haven't been clear in their communications exactly what they are asking for.

 

 

Finally anything else I might have missed?  

 

 

Thanks

 

[Dillsue]

You keep mentioning "application" but if you're under 16amp max export its a G98 notification.

 

All the DNOs should be working to the ENA G98 specs so there should be little difference in what you submit. For us, SPEN wanted-

Single line diagram of the house wiring specifucally showing the location of the lockable PV isolator, which is what youve got.

Completed commissioning form with the signature of whoever checked the install which should be your spark although thats not always the case.

Details of the ENA type test certification for your inverter(s)

 

BTW your roof install looks neat

Edited September 15, 2023 by Dillsue