Green Building Forum - Is this Solar spec right for us?

Is this Solar spec right for us?

zak99 — Sun, 16 Jan 2022 15:25:51 +0000

Is this spec right for us please ? (hopefully can see attachment?)

Have gone for a local authority group buy scheme on solar and now wishing I'd had time to investigate more about it. At a rough level have we gone for enough panels and battery please? It's a 3 bed detached bungalow currently on oil central heating. Roughly half panels on east no shading, other half west facing with some tree shading hence i went for optimisers. There is a small south facing roof on the garage that I wonder should I have had some panels on. Theres also a south steepish sloping corrugated roof on workshop at end of the garden but planner didn't seem interested on putting panels there. Two of us retired living there. Bound to get an EV at some point in the near future. Not at all sure about changing to heat pump in the forseeable future.

(EDIT. DC optimisers on every panel add roughly Â£700 to below.)

May be too late to ask for changes now but at least worth enquiring if though necessary.

Thank you

Is this Solar spec right for us?

zak99 — Sun, 16 Jan 2022 15:27:12 +0000

Solar performance estimate

Is this Solar spec right for us?

zak99 — Sun, 16 Jan 2022 15:34:15 +0000

Other thing I wanted to ask about please was the planner said that above a certain energy input the energy would be lost to heat as the grid capped it at a certain level. Seems crazy. Sorry for my limited understanding of terminology and figures.

Is this Solar spec right for us?

Nick Parsons — Sun, 16 Jan 2022 16:37:49 +0000

Reading your intro I was expecting you to say you'd got a 2kW array! 6.6kW is reasonably big for a domestic set-up. Many are kept just under 4kW (3.8?) so that they get through under the ?G83? rule (may have changed name now) which says that systems under the relevant size (?3.8kW?) must be *notified* to the DNO, but the DNO *must* give permission. Above that size it's not always the case (for example 'near the end of the (elec) line' where allowing a few too many large arrays might necessitate equipment upgrades).

D.N.O = distribution network operator: ''the company that owns and operates the power lines and infrastructure that connect our network to your property'' says National Grid.

Looks like not a bad price, though I know zilch about batteries.

I initially wondered why you'd want to generate 78% more than your annual consumption but I note your point re EV, and I take it it's in part to optimise your 'shoulders-of-the-year' generation. Still seems you're paying for a lot of kit in order to export 58% of your generation for 5p/kWh. I failed Maths O level first time round!

Is this Solar spec right for us?

DamonHD — Sun, 16 Jan 2022 18:01:50 +0000

G98 replaced G83 on 2019-04-27. (And G99 replaced G59 for larger generators.)

Rgds

Damon

Is this Solar spec right for us?

philedge — Sun, 16 Jan 2022 18:04:25 +0000

With such a surplus of generation you might want to look at a PV diverter to heat your hot water rather than export it. As youre in a bungalow and likely to be able to see under the panels from the ground, Id not bother with bird protection and spend the money saved on a PV diverter. Weve not had any birds under either our PV or ST arrays.
With having your system split fairly evenly east/west you might not be wasting much generation to heat as the split should give you a longer but lower generation rate rather than a bigger peak over a shorter period if they were all facing the same way

If the "electricity cost" is the import cost it maybe wants updating with something quite a bit higher than 18p/unit! Id be working on 25p+/unit!!

Is this Solar spec right for us?

WillInAberdeen — Sun, 16 Jan 2022 18:29:07 +0000

You can export for a lot more than 5p/unit at the moment. Today Octopus were paying 19p/unit for daytime solar exports, or 30p/unit if you store it in a battery and export at 5pm when the grid really needs it. Tomorrow evening they are offering over Â£1/unit which is much better than self consumption. (!) Is this price a blip, or the new normal, who knows?!

The financial numbers are a bit misleading IMO - they are forecasting it takes well over 10 years to recoup the cost of the installation, so the return on investment for that period is going to be nil (or less). Over 20 years they forecast a Â£8386 return* on Â£9478 investment, which is 3% pa if you still own the kit and it keeps working for that long, but that will depend what happens to energy prices and usage, and on the cost of tying up the capital to buy the kit. Can't see where the quoted 14% return could possibly come from.

*Edit: the projected income is Â£552pa, which would actually take 17years to break even and add up to Â£11k income over 20 years. Less the Â£9.5k install cost, leaves Â£1.5k profit over 20 years, or 0.8%pa, miles less than the projection. Some alarm bells there... If the financial aspect is important then do your own sums and take financial advice from someone qualified!

Is this Solar spec right for us?

Ed Davies — Sun, 16 Jan 2022 19:44:27 +0000

Posted By: Nick ParsonsMany are kept just under 4kW (3.8?) so that they get through under the ?G83? rule (may have changed name now) which says that systems under the relevant size (?3.8kW?) must be *notified* to the DNO, but the DNO *must* give permission. Above that size it's not always the case (for example 'near the end of the (elec) line' where allowing a few too many large arrays might necessitate equipment upgrades).

As Damon says, G83 has been replaced by G98 and G59 by G99.

The actual rule is in the The Electricity Safety, Quality and Continuity Regulations which says the maximum you can put in to the grid by â€œrightâ€ is 16 amps per phase which at the nominal 230 volts comes out at 3.68 kW.

https://www.legislation.gov.uk/uksi/2002/2665/regulation/22

The bit about â€œhas the necessary and appropriate equipment to prevent danger or interferenceâ€, etc, is spelled out in practice in G98 and G99.

It'd be interesting to know how zak99's system will be set up to comply with this. There are two options:

1) Limit the inverter to a maximum of 3.68 kW total output (from PV or from the batteries) or

2) Allow the inverter to output more power but limit it using a current sensor by the entry to the house to a maximum of 16 A of actual export (G98 allows this if certain conditions are met - basically, that the connections to the current sensor are all done with pre-wired plugs).

E.g., the batteries are full, the PV is generating 5 kW (probably about the peak it'll actually manage) and 1 kW is being used in the house. Is the inverter allowed to put 4.6 kW into the main wiring so 3.6 kW is exported or is it limited to 3.6 kW so only 2.6 kW is exported.

Perhaps more commonly, more than 3.6 kW are being used in the house: can the inverter provide more than 3.6 kW or does the rest have to come from import.

Is this Solar spec right for us?

WillInAberdeen — Sun, 16 Jan 2022 20:26:07 +0000

Not sure how it works if you have both a PV inverter and a battery system (which also includes an inverter) - G98 would consider the sum capacity of both inverters (s2.5).

If there's a safety system to monitor the overall combination of PV generation, battery dis/charging and home consumption and limit the net result to <3.8kW, it would have to be a quite smart system and type-tested. So it didn't end up charging the battery at times when it would be advantageous to export more; or cutting back the PV because the battery is taking up all the export capacity (for example). Might be better just to apply G99 for the PV+battery capacity, then the PV and battery can each do their own thing?

I have no experience so sorry if this is dumb! Damon do you know?

Is this Solar spec right for us?

djh — Sun, 16 Jan 2022 21:36:52 +0000

Posted By: WillInAberdeenNot sure how it works if you have both a PV inverter and a battery system (which also includes an inverter) - G98 would consider the sum capacity of both inverters

AIUI a hybrid inverter such as Zak has seemingly been quoted for interfaces to both the PV panels and the batter(y/ies), so there's just one inverter.

@Zak, your system sounds a lot like one I was quoted for by a similar council-organized initiative. It would probably be helpful to quote the actual part numbers of whatever you've been quoted for. As others have said your system on the face of it exceeds the capacity that's allowed to be connected without special approval. Maybe because you have an east-west system the peak generation is less, but I was concerned by what you said about "the energy would be lost to heat", but it sounds like some brute force mechanism to avoid breaching the regs. I'm also a bit nervous about "optimisers", they can cover a multitude of sins, though they might be OK. Our system uses microinverters, which could be an alternative. So more details would be helpful.

Is this Solar spec right for us?

revor — Mon, 17 Jan 2022 10:24:38 +0000

I have a 6kW system SSW with a 10kW battery. Based on my experiences I would say that you could do with a bigger battery. This time of year in full sun at around mid day it throws out about 3.2kW (had 6.5 height of summer)so charges the battery in no time at all. Given you are differently orientated to my set up guess you will have a more levelled output over more hours. I would check out the spec of the inverter and battery combo particularly the inverter in terms as to what power it can supply on its own and how much the battery can supply. My set up the inverter can supply 32 amps and battery 20 amps. If I have capacity in the battery I can run an electric shower or oven and top up with solar if producing, or from the grid. The system looks to solar first then battery then grid and combination of them ensuring minimum from grid. Don't understand the bit about heat if grid limitation kicks in on my system the inverter controls the solar input throttles it back then when you draw power in the house ups the solar to match.

Is this Solar spec right for us?

zak99 — Mon, 17 Jan 2022 14:37:55 +0000

Thank you all for the input, apologies for not being up to speed with all the jargon.

I asked the installer and the panels will be JA Solar 370-watt panels, fitted with Tigo optimisers with a PylonTech US2000 battery system. The inverter is a Solis Hybrid 6kW Inverter.

As I understand from their description - ""electricity will only ever be exported to the grid after powering the house and filling the batteries. Throughout the summer months will be when you are most likely to exceed this limit, especially if you go on holiday. A hot water diverter would help in reduced the amount of electricity exported."

The batteries they install are modular and allows for an increase in batteries if needed.

They say "The batteries have a predicted lifespan of fifteen to twenty years. At todays prices it would cost Â£2,000 to replace the battery system".

I'll do a bit more reading !!

Is this Solar spec right for us?

zak99 — Mon, 17 Jan 2022 16:04:34 +0000

Posted By: Nick Parsonsand I take it it's in part to optimise your 'shoulders-of-the-year' generation

I'm intrigued Nick, what does 'shoulders-of-the-year' mean please?. I feel it should mean something to do with the guilt I feel for the environmental mess oldies like me have left for the young. My main reason for getting solar was to try and do something right, so its frustrates me that energy is capped going back to the grid but I do understand it would fry in the summer if uncapped !!

Is this Solar spec right for us?

bhommels — Mon, 17 Jan 2022 16:46:13 +0000

It might be helpful to put your prospective system through PVGIS to obtain a month-by-month estimate of the yield:
https://ec.europa.eu/jrc/en/pvgis
it would help optimising battery capacity or hot water tank size, etc.

I found https://www.comparemysolar.co.uk/
useful as it has a Google maps based tool to identify your roof, giving its exact orientation.

Is this Solar spec right for us?

philedge — Mon, 17 Jan 2022 17:27:40 +0000

Posted By: zak99 so its frustrates me that energy is capped going back to the grid but I do understand it would fry in the summer if uncapped !!

Personally I wouldnt be to worried about your export being capped as its not likely to happen often with the east west split youve got. Panels only generate at max capacity with full sun beaming square(ish) onto them which isnt going to happen with your split. Assuming 3.7kwp facing east the sun will be sideways onto them at its peak and then move round to the partly shaded 3kwp array. Both the arrays will generate without direct sunlight but your not likely to get anywhere near the 6.6kwp of the panels youve got. I think theres software available to model split systems like yours and might be worth asking your installer if they can model it for you??

If you want to do the best for the environment rather than ROI, it might be worth putting in a G99 application, binning the batteries and use a slow cooker for evening meals

Is this Solar spec right for us?

djh — Mon, 17 Jan 2022 17:30:56 +0000

The products all look sensible to me; similar to what was proposed to me. We have a solar diverter and it is indeed very useful. It depends whether you want to use as much as possible yourself, or export as much as possible.

I think by 'shoulders-of-the-year' Nick was meaning spring and autumn, when your panels won't generate as much as in high summer, so extra capacity will allow you to generate the maximum allowed to be exported for more of the year.

Is this Solar spec right for us?

Nick Parsons — Mon, 17 Jan 2022 22:26:42 +0000

Ah thanks djh. Only just come back to this. That's exactly what I meant. Accepting that however many sunny days you get winter yield will be proportionally low, but exactly what you've said relating to spring and autumn.

Zak, I think you are doing something right - it's just getting the balance I am not sure about.

For similar reasons (it feels right) I'm putting around 2200W split E/W on a small extension this year. I don't expect pay-back. I just want to do something a bit right (along with the extensive EWI we're planning).

Is this Solar spec right for us?

bxman — Tue, 18 Jan 2022 12:30:15 +0000

Hi Zac

IMO there is no benefit in fitting Optimisers on any panel that is in a string that is free of shading.

Do not be worried by exporting the community needs ever bit of carbon free energy it can get as others have said an East/ West system of that size will not cause harm .

The problem for the DNO is when there is a number of neighboring properties all with identical orientation when there is a danger of the local voltage going over limits . However before this happens all approved Grid Tied Inverters should shut down automatically.

Is it a Solar Edge system ? because I believe they are best at managing any excess generation and possibly mange
the battery charging schedules to avoid putting to much power back into the grid .

Do not believe those figures on self consumption ratios .

You will find that what you generate in Nov, Dec and Jan (when your need it) there is almost nothing

In my case 90% of consumption is in those 3 months and my guess is that 90% of my annual generation comes in the other 9 months

You say there is shading on the west orientation.
Is that through out the year ? Are they unaffected in summer ? If it is there in summer it will be so much worse in winter.

As there is room for panels with a southerly aspect they could be incorporated into the string with the Optimisers
those panels will do more work , What time of day do you need the power? lots of things to consider

Is this Solar spec right for us?

zak99 — Wed, 19 Jan 2022 14:36:23 +0000

Thanks again for the very helpful answers.

The optimisers are tigo not Solar edge, there are many similarities I believe (in my limited understanding).
I doubted and questioned the need for optimisers in the non shaded string and have asked that question again before committing to install but i may be pushing the go/no go timescale limits now.
I've also asked about apps etc for monitoring as they may perhaps be dependent on optional sender modules (?).
Also asked about possibility of moving a couple of panels to the small south facing roof, looking at the quote I'm not clear if the 10/8 split of the 18 panels is East/West or West/East. The West side has large trees in our garden roughly SSW aspect on the westside, in summer in full leaf and dense of course but the sun is higher. I raised my concern about this repeatedly. The sun clears the trees later in the day depending on time of year. Perhaps this is why they didn't move some of the panels to the small south roof (on the west side). I was assured they felt the gain will still be worthwhile but I elected for optimisers because of it.

A curious question is how do panels, batteries etc work out as far as carbon neutral, at what point roughly does an installation if ever offset carbon from manufacturing. I guess the batteries are not so good? I've been nagging a little my local council in Maldon district why new builds are not with solar and high levels of insulation so would be good to know re neutral timescale in that nagging !!

Is this Solar spec right for us?

philedge — Wed, 19 Jan 2022 19:18:12 +0000

Remember that shading comes in many forms all of which impact string output- a dollop of seagull s**t, passing clouds, uneven build up of dirt, growth of neighbours trees a decade away. On top of that a failing module will bring a whole strings output down.

Im not sure how the Tigo optimisers work but the Solaredge units report individual panel performance so you can see at a glance if theres a problem with a panel/optimiser. Without individual panel reporting any faults can take hours to identify whilst potentially every panel is removed for testing. Quite possible that you could blow a significant chunk of the addtional cost of optimisers fault finding on a system without individual reporting.

Is this Solar spec right for us?

djh — Wed, 19 Jan 2022 19:48:26 +0000

Posted By: philedgeIm not sure how the Tigo optimisers work but the Solaredge units report individual panel performance so you can see at a glance if theres a problem with a panel/optimiser. Without individual panel reporting any faults can take hours to identify whilst potentially every panel is removed for testing. Quite possible that you could blow a significant chunk of the addtional cost of optimisers fault finding on a system without individual reporting.

I was impressed by our Enphase microinverter system at the beginning of last year. Out of the blue it/they sent me an email saying two panels had faults; luckily a quick visual check showed the nature of the fault - a whole load of snow on those two panels. But still demonstrated that the system works.

Is this Solar spec right for us?

DamonHD — Wed, 19 Jan 2022 20:06:29 +0000

Posted By: WillInAberdeenNot sure how it works if you have both a PV inverter and a battery system (which also includes an inverter) - G98 would consider the sum capacity of both inverters (s2.5).

If there's a safety system to monitor the overall combination of PV generation, battery dis/charging and home consumption and limit the net result to <3.8kW, it would have to be a quite smart system and type-tested. So it didn't end up charging the battery at times when it would be advantageous to export more; or cutting back the PV because the battery is taking up all the export capacity (for example). Might be better just to apply G99 for the PV+battery capacity, then the PV and battery can each do their own thing?

I have no experience so sorry if this is dumb! Damon do you know?

(Had not checked in here for a bit.)

I was allowed to put in a system under G83 with inverters totally a nominal 4.5kWp and panels feeding them at a little over 5kWp, but E/W facing split so that exceeding 3kW is fairly rare and full whack would basically be impossible to sustain.

I have subsequently by degrees put in Enphase "AC Batteries" with a nominal max charge or discharge of ~1kWp, and no eyelids have been batted:

https://www.earth.org.uk/Enphase-AC-Battery-3-4.html

I suspect because G100 in its case ensures that the battery will not itself cause an export that wiuld take it over 16A.

Rgds

Damon

Is this Solar spec right for us?

zak99 — Sun, 30 Jan 2022 15:43:46 +0000

Install happened last week, happy so far.

Posted By: zak99 JA Solar 370-watt panels, fitted with Tigo optimisers with a PylonTech US2000 battery system. The inverter is a Solis Hybrid 6kW Inverter.

The Solis inverter iPhone app is very poorly rated at the download page but it seems OK to me so far. Although I enquired, no monitoring of the Tigo optimisers was provided, the install planner has unexpectedly left the company now. (this was done under a LA Solar Together scheme). From reading it looks like monitoring the optimisers should be possible with the addition of something called a TAP and a CCA (Tigo Acces Point with Cloud Connect Advanced) for parts around Â£300. I'll see where I stand with install costs next week

Based on Phils comment below I think it will be worthwhile

Posted By: philedgeWithout individual panel reporting any faults can take hours to identify whilst potentially every panel is removed for testing

Is this Solar spec right for us?

zak99 — Sun, 30 Jan 2022 15:58:58 +0000

Following helpful discussion above I was supposed to have a Solar Hot Water - Power Diverter (Solar iBoost) installed but for some reason (faulty unit cited) that did not happen. That was going to cost Â£427 + 5%, I've put that on hold for now as 1) I'm not sure how often I will have surplus energy given I have batteries and 2) it seems to be less than Â£300 online and allegedly an easy install !

Is this Solar spec right for us?

bhommels — Mon, 31 Jan 2022 16:27:10 +0000

For loft-installed inverters, the summer temperature is a concern. Some inverters start to derate the output from 45 C upwards, so better keep an eye on the temperature in the loft. And perhaps look up the derating data on this particular inverter.

Is this Solar spec right for us?

jamesingram — Thu, 03 Feb 2022 21:39:24 +0000

Re Pv immersion dump.
Once your batteries are charged it'll export to the grid.

Your estimates suggest 58% of generation with be exported =3002 kWh = @ 17.8p = Â£534 per year
(this figure should be consider a very rough estimate)
This will mostly happen in the summer months.
The diverter immersion dump with heat your hot water 1st using some of this potential export, then export.

Average uk home use
"A typical household uses on average around 360 litres of water each day. About 20 per cent of a typical gas heated householdâ€™s heating bill is from heating the water for showers, baths and hot water from the tap. According to the Energy Saving Trust, this costs about Â£140 a year."

What you want to avoid is your boiler firing up to heat water when your exporting electricity

Yes they're easy to fit, they just fit in series with your immersion feed after the fuse spur , just look into how they interact with your battery system before purchasing.
ebay has some good offers and an alternatives.

Ive an iboost plus+ feeding 2 immersions in 2 storage tanks. 7kW PV no batteries to charge.
winter on a sunny day i get a tank, cloudy day I get very little , summer i get 2 tanks and then export.
my guess is itll give you a tank of hot water ++ every sunny day 2 months either side of mid summers

Is this Solar spec right for us?

revor — Fri, 04 Feb 2022 12:51:50 +0000

Posted By: jamesingramjust look into how they interact with your battery system before purchasing.

In my experience getting info on how an inverter and battery interact is like getting blood out of a stone. There seems to be a lot of secrecy presumably designed to protect the detail of the algorithms involved w.r.t the BMS.
I was thinking of a diverter for my immersion but don't think will be worth my while as have solar thermal and suspect the Inverter /BMS may not allow it anyway but I would like to know at some point.

Is this Solar spec right for us?

jamesingram — Sun, 06 Feb 2022 16:59:02 +0000

Revnor, I think as long as the dump sensor measuring export is set higher than the battery set up its ok. You just need to make sure the battreries take priority
in this case of the iboost its possible to set up an adjustable offset to insure this.

in your case im sure the ST system would be doing the job well, but if youre exporting and it viable it may be better sending the power to the immerion first. depends on set up and costs.

if you're one of this people exporting for profit then heating water at a low night rate and exporting solar at higher day rate might be more profitable.