Additional solar and battery storage

[Ronski]

We currently have a 4kw Solar Edge system installed on our house roof in sunny south east Kent, which was installed in 2015, so earn reasonable FITS from it. We have a detached double garage with flat roof, which is 5.7  x 5.93 meters south westerly facing, dependant on spacing of the panels we could fit at most 12 panels on it. There are two tree's that would cause early morning and late afternoon shading, which is obviously worse in the winter, but for the main part of the day it is unshaded and gets direct sun.

We also have a large NW facing roof at 30 degrees pitch, where there is room for at most 12 - 14 panels, there is also a chimney that would cause shading, and possibly next doors roof, but the roof shading would be close to the end of the day anyway.

We would like to add a solar array to either the garage or the other roof, and also a decent sized battery, without an additional array, there won't be enough solar except on very good days to charge a decent size battery.

Requirements:

• Additional solar array on the double garage or NW roof

• Decent sized battery – either in the garage or the house

• Able to use excess from existing array to charge battery

• Able to charge the battery from off peak electric when solar production is poor

• Whole house battery backup would be useful, although not essential (a nice to have) - see notes below

 

Existing power usage.

• We use 10,000kwh a year (includes what we use from existing solar)

• We generate on average 4350kwh a year, and export roughly half

• We don’t have an EV, and currently no plans for one – too expensive to buy - our cars are old, but bought and paid for, not leased.

 I've got quotes from quite a few companies (still a couple to come, but they are busy), they either come in expensive with poor system specs (£9250 for 9 x 370w panels & 2.4kWh battery)

to systems that use DC coupled batteries, and therefore wastes the excess power from our existing array - I would be correct in thinking we need AC coupled batteries to use the excess electric from our existing array wouldn't I?

Another complication is that I think we need planning permission if the panels exceed 200mm in height from the roof of the garage, is that correct?

Our existing array uses optimisers, and given the shading on either of the two roofs, I feel this would be the way to go, but obviously complicates things.

Our house is split in to three ring mains + the garage, the kitchen and utility room are on there on ring, so all the juicy appliances could be disconnected easily when on battery backup so not to risk overloading the inverter.

As you can see from my introduction post I'm quite capable, but I am not an electrician, ironically when at school many many years ago that is the trade I wanted to go in to, I did a day release college course, even work experience, but couldn't get a job when I left school as a trainee and ended up being a mechanic instead. So I'd like to do the labour intensive side of the install, but have an electrician, preferably MCS registered to do the electrical work and over see the system design.

So what's peoples thoughts?

[SteamyTea]

Punch the numbers into PVGIS and see what comes out.

Then divide the price of the best estimate by the PV production to get the price per kWh.

Then decide.

[ProDave]

Before you get too excited adding more to your existing 4kW, check with your DNO id they will allow more or if they will hit you with a network upgrade cost to add more?  That could change the ballance.

 

If you are only using half what you currently generate then you have not learned the art of time shifting big loads to the middle of the day and excess diverted to an immersion heater.

 

Probably your best bet is an ac coupled battery system to self use 100% of what you generate now.   If that works then subject to what the DNO says think about adding more PV.

[Nickfromwales]

Ok. So how do you envisage the batteries knowing that you have excess, and for the software of the BMS to initiate charge for those specific / sporadic pockets of opportunity?  
 

If you’re already getting FiT then you have your cake. Divert excess into hot water and you get the cherry.

 

If the other areas for PV are not optimal, and you factor in scaffolding, wiring to / from etc, the economics soon head for the nearest window. 
 

If you wish to pursue this, then I’d recommend a dual input hybrid inverter, set to zero export, with your new panels feeding into input 1, and your batteries on input 2. That will put all the new micro generation on the D/C side this not upsetting the DNO when you register. Also, you can put as much battery storage on the D/C side as you like as the A/C side ( grid ) never ‘sees’ it. The biggest issue you’ll have is with finding equipment that will communicate with / support optimisers. That’s the current issue with the system I take delivery of shortly has, but I will likely just add further inverters to take each effective string. Puts the cost up, and elongates the payback, but I’m owed a lot of favours so am getting my equipment for a song ( thankfully ) otherwise I doubt I’d have gone for so much battery storage ( 24kwh intended at this time but will likely double that to 48 in the near future after 12 months of statistical data had been recorded / reviewed ). I’m putting panels  on a lot of outbuildings +newly ( purpose built ) “solar gazebo” , as well as the rear of the roof. 

Do as @SteamyTea says, and work out what the new arrays will likely produce. Then the cost of all the equipment, and have a good think. Optimising your use of peak solar / high load devices and divert to hot water may mop up all of your current excess   

[Dillsue]

If youre happy with the SE system you have, Id be looking to install a Storedge system. They can charge from the grid or the AC output of another inverter like your existing FIT system. I think you can connect additional PV to the inverter doing the battery charging but thats worth double checking with SE.

 

If you really want to add PV and storage but your DNO says no or upgrades are prohibitive, you could add export limitation to stay within the 16A limit  you already have.  With batteries and maybe a PV diverter youll not want to be exporting much anyway.

 

The NW facing roof would help with late afternoon/ teatime production but if youve got batteries youre probably best getting max daytime production on the garage to charge the batteries and draw on the batteries later in the day

[Ronski]

Thanks to all those that have replied, have only just seen the replies as I didn't get an email notification - I'll have to find that setting.

 

To answer some questions/suggestions in no particular order.

 

We don't have a hot water tank/immersion heater, it was removed circa 2005 as gas was cheaper for heating, so a condensing combi boiler was installed.

Shifting large loads, large loads are only washing machine, dish washer and electric oven, we both start work early, so washing/dish washer tends be go on to suit our work schedules, so its only really weekends we could do that. We have a tumble dryer but it is very rarely used.

Most of the power usage is an always on server and other computer equipment such as networking stuff, two fridge freezers.

 

How do I envisage the batteries knowing how to charge, well I've been wondering just that. The solar arrays connect back to the CU, the AC coupled batteries connect to the consumer unit, but how do they know to charge/discharge? I thought perhaps they use a CT clamp to measure flow of power in/out to the grid, but that would only tell you how much, not which way it flows, so perhaps some other measuring device is used. Any body know what the correct answer is?

 

I've worked out what the arrays will likely produce using https://easy-pv.co.uk/ but I don't understand the shading/sun path bit works, so both have a shading factor of 1

 

Garage with 12 x 415w  panels is an estimated 5174kWh annual output (15 degree pitch)

N/W roof with 13 x 415w panels is estimated at 4370kWh annual output

 

I was also looking at sending a G99 application, but obviously have no installer at the moment, can I just put TBC for the installer section? Actually do I even have the correct form - see attached?

 

Best I get to bed, its late.

 

 

 

 

 

 

 

G99 form.pdf

[Dillsue]

With an SE Storedge system theres a CT on the grid connection so the charge controller knows if theres generation going to export and then diverts excess to battery charging. As far as I know any decent PV charge controller would need a CT to govern whether to charge or not??

 

The G99 need for installer details is a stupid requirement! Until you get your G99 approved you dont know what youll be installing... if approval needs an export limitation system with a commissioning demonstration thats likely a specialist system outside the abilities of your local part P spark whose details youve put on the application. I put TBA on our applicatiion and the DNO wouldnt process it. I then told them I was installing myself with a test and inspection carried out by our local Building Control department...that was accepted.

[Nickfromwales]

3 hours ago, Dillsue said:

I then told them I was installing myself with a test and inspection carried out by our local Building Control department

Yup. You could also state "by a competent registered installer", but you'd be fully entitled to choose either route retrospectively  Box-ticking exercise.

 

3 hours ago, Dillsue said:

With an SE Storedge system theres a CT on the grid connection so the charge controller knows if theres generation going to export and then diverts excess to battery

The Solarwatt BMS is a very clever bit of kit and monitors the house / PV / consumption patterns and 'learns'. It then decides when it is optimal to charge or discharge.

 

9 hours ago, Ronski said:

Garage with 12 x 415w  panels is an estimated 5174kWh annual output (15 degree pitch)

N/W roof with 13 x 415w panels is estimated at 4370kWh annual output

Not insignificant then. I would put all of this into hybrid(s) and batteries, as you'll need to conserve outgoings to make this cost-effective. FYI, Solarwatt are soon to release a panel with an output of 540w !!

And yes, we install a LOT of Solarwatt, plus Fronius and Solaredge, but I am looking longer and harder at the cream of the Chinesium offerings atm as maxing out on the D/C side is the future ( until th DNO's give everyone 3ph or a more realistic limit of 1ph at least ).  

[Ronski]

Thanks both, I'll fill out the G99 and see what happens. Don't know if it makes any difference but we are right next to the one of the estates two substations - an 11kv transformer.

 

I bet that 540w panel will be large and expensive though?

 

 

 

[Nickfromwales]

5 minutes ago, Ronski said:

I bet that 540w panel will be large and expensive though?

Would be no point in producing a higher output panel unless it kept to the typical panel sizes  so I assume it'll be kept down to the 'normal' size, or as very near-to as damnit.

 

I have no idea on costs, but will update as soon as this information gets released from he UK reps for Solarwatt.

[Nickfromwales]

8 minutes ago, Ronski said:

Don't know if it makes any difference but we are right next to the one of the estates two substations - an 11kv transformer.

Ironically, it could make you worse off, due to being closer to the grid max voltages for the inverters to shut down at ( 253v ).

[Ronski]

I've had to contact UK power networks a couple of times over the last decade as our voltage went above 253v, but this was usually very early in the morning (my UPS records this info), when there was very little demand and of course no sun. The lady that visited last time told me they have to change the transformer tap twice a year to allow for the solar in the summer.

 

PS. What's the power factor box for on the G99, no idea what to put in there?

 

 

Edited May 2, 2022 by Ronski

[Dillsue]

2 minutes ago, Nickfromwales said:

Ironically, it could make you worse off, due to being closer to the grid max voltages for the inverters to shut down at ( 253v ).

I think shutdown voltage is a fair bit higher than the UK max of 253v....262v? Our supply is at 250v and our existing PV pushes us over 253v on a sunny day, but inverter keeps churning out the kw.

[Dillsue]

4 minutes ago, Ronski said:

PS. What's the power factor box for on the G99, no idea what to put in there?

 

 

Should be on the inverter spec sheet but 1 is likely to be accepted.

[Nickfromwales]

2 minutes ago, Dillsue said:

I think shutdown voltage is a fair bit higher than the UK max of 253v....262v? Our supply is at 250v and our existing PV pushes us over 253v on a sunny day, but inverter keeps churning out the kw.

An interesting comparison to what others have said, but a very relevant consideration if maxing out on grid-tied PV. The OP may be in a better position due to the split arrays producing steadier all-day-long output vs a huge south facing array peaking at midday.

[Dillsue]

Other manufacturers may have different settings but the UK spec SE inverters we have are set to shutdown at 262v

 

Yep spreading the array round will help but I guess a battery bank is going to put a fair load on the PV which should keep things in check.

 

On an SE inverter there is supposed to be a power control feature that you can use to throttle production as voltage rises and so keep household voltage sensible. Im waiting to hear from SE as to where in the menu it is as Ive not been able to find it despite installing the latest software!!

[SteamyTea]

42 minutes ago, Nickfromwales said:

Would be no point in producing a higher output panel unless it kept to the typical panel sizes

Could just be two old 275W ones Bosticked together.

[Nickfromwales]

9 minutes ago, SteamyTea said:

Could just be two old 275W ones Bosticked together.

Dragons Den moment there 🙄

[Ronski]

10 minutes ago, Dillsue said:

Should be on the inverter spec sheet but 1 is likely to be accepted.

 

Yes it is, thank you. For this box ticking exercise I'm listing a Solar Edge SE5000H, which lists a power factor of 1, but adjustable -0.9 to 0.9, so I'll just enter 1

 

Now just to work out a inverter/charger to put some specs on the sheet - I'll aim for one with a 5kw capacity.

 

Just took a look at what Solarwatt have to offer, and I really like the look of the Solarwatt Flex AC-1 battery, it wouldn't look out of place in our hallway (Mrs Ronksi will disagree though!) or it would even fit in the server room.

 

Only downside (ignoring price which I cant find - anyone know the price?) is it looks like it has quite a low power output/charge rate, and to get the best you need many packs, but even the base system would have enough output to cover our base load and a little bit more, and should be OK charging off peak in the winter months.

 

I'll list a Victron Multiplus-II 48/3000/35-32 as that has a peak power of 5500W

 

JA Solar do a 545w panel, but its 1134 x 2279, and £192 each excluding VAT, but all depends on what fits better and kWh and price per square meter.

[Ronski]

What does this bit mean on the G99 form, its just above the signature box?

 

Quote

Balance of Multiple Single Phase Generating Units – where applicable

I confirm that design of the Generator’s Installation has been carried out to limit output power imbalance to below 16A/phase, as required by EREC G99.

 

[Dillsue]

Thats for 3 phase systems to declare there wont be more than 16A per phase difference in export on each phase

[Ronski]

Thanks, I was reading it as multiple units on a single phase, rather than multiple single phases.

[Dillsue]

Just looking at your figures, youre listing a 5kw SE inverter, a Victron 5.5kw charger and the 4kw existing system which totals up 14.5kw of potential export. Thats a fair bit of export to get approved so might be worth having an informal chat with your DNO to see what they think before you submit the G99??

[Nickfromwales]

11 minutes ago, Dillsue said:

Just looking at your figures, youre listing a 5kw SE inverter, a Victron 5.5kw charger and the 4kw existing system which totals up 14.5kw of potential export. Thats a fair bit of export to get approved so might be worth having an informal chat with your DNO to see what they think before you submit the G99??

Yup, hence my suggestion of hybrid and D/C for the new additions. Needs no begging / going on bended knee. One less A/C to D/C to A/C conversion also, so more efficient charging the D/C batteries from the D/C from the roof.

[Dillsue]

11 minutes ago, Nickfromwales said:

Yup, hence my suggestion of hybrid and D/C for the new additions. Needs no begging / going on bended knee.

Still needs a a bit of G99 begging for the inverter unless the new system is off grid