Solar Panels UK - is it worth it?

[PITA]

If wanting to receive green energy, it may be better to allow the large scale grid operators to achieve that while using a 100% renewal electricity tariff, rather than materially rolling out solar to millions of homes. I've yet to see a true EV-specific energy offering where my own net annual saving is any better than ~£100 (4%). If you already have solar, a battery system is useful if power cuts are relatively frequent. Currently solar adds little to home valuations, but that may change as new buyers value this more over time. Solar panels themselves can be detached/reattached during a house move, but by that time there'll likely be newer, more efficient panels. There is one positive aspect though, in that if you are able to afford both then you can personally contribute to a cleaner grid that bit sooner, but still likely at lower cost effectiveness than grid-scale providers can achieve in the near term.

People talk about Solar Arrays and Battery Storage as being ideal during Blackouts...

... BUT in the UK most systems are Grid-Tied which means they all shut down if the grid fails, leaving the home owner without any power.

An exception is our system, which uses the Tesla Gateway 2 unit. This automatically 'islands' our house from the grid, and our Solar Array & Battery Storage remains operational.

I don't know of any other system that does this??

 

[roadcred]

Most of the subscribers here are so wrong.....the doubters inevitably have neither panels or a powerwall. I have both and had them for 18 months now. I unfortunately do not qualify for FIT but I am on the TEP. Throughout the summer months Octopus pays me. The average I paid in last winter was just £30 per month. This winter the tariff has increased to 11.1p instead of 8p and there is a standing charge. However I assess my average in winter will still remain at £60 pm and Octopus will still be paying me for my summer surplus at 11.1p next summer!
Prior to installing solar my bill was £120pm year round. It would be even more now. When thinking of payback I add this saving to the huge savings I make running 2 EVs as approx £1500 pa. So currently my bills are about £3000 a year less than before 2019. My total installation was about £20k. Payback therefore less than 7 years. No payback required on the EV investments as they do not depreciate at all where my 2 diesels used to depreciate by thousands each year.
A much more worrying scenario is with gas where my fixed rate of 3p has increased to 4.3p variable due to the liquidation of my supplier! There is no simple way around gas when you live in a non passivhaus.

 

[PITA]

...... There is no simple way around gas when you live in a non passivhaus.

We don't live in a passivhaus... but have decent insulation. It's a 1996 built 3 bed detached.

The simple answer for us was to find an alternative independant heating system that meant we used the Gas Boiler less often. A lot less as it turns out.

I ripped out our Gas Fireplace and Gas Hob, capped them off... Replaced with a Toshiba Haori Air to Air Heat Pump and Induction Hob, plus 3 kW emersion heater.

So now we can heat the house & hot water with either Grid Electric, Solar, or Gas... or all of them at once. Plus we can cool the house with air conditioning in Summer, powered entirely by Solar even during the night time.

I've proven you can still get a UK Energy Performance Certificate at an 'A' rating, on a 1996 built house AND keep your Gas Boiler... we did it with a score of 107. Smashed it.

Simple.

 

[dakaix]

People talk about Solar Arrays and Battery Storage as being ideal during Blackouts...

... BUT in the UK most systems are Grid-Tied which means they all shut down if the grid fails, leaving the home owner without any power.

An exception is our system, which uses the Tesla Gateway 2 unit. This automatically 'islands' our house from the grid, and our Solar Array & Battery Storage remains operational.

I don't know of any other system that does this??

Victron MultiPlus-II, it holds the requisite G98 & G99 certification for islanding in the UK. Doesn't require an external gateway, as the PowerWall does.

I am planning an install of one in the new year, along with ~20 kWh of PylonTech batteries (plus PV). The "ESS" system will act in an identical manner as a PowerWall, allowing for charging from/discharging to the grid, providing UPS to "protected" house loads (up to ~3.7kW cont, 5kWp)... and when combined with PV and an MQTT controller it acts as the inverter for the entire system - so it's more efficient overall. You can even discharge it to unprotected loads (such as an EV or heat pump) while maintaining a zero grid import/export if you wanted.

More importantly from my PoV though, it provides fully local control & API's so you can do everything from within the home... I'm planning on controlling it through Home Assistant. They also offer their VRM Cloud tool for those that would prefer not to DIY their controls.

Excluding the PV, it should work out cheaper and with significantly more capacity than a single PowerWall!

 

[PITA]

Victron MultiPlus-II, it holds the requisite G98 & G99 certification for islanding in the UK. Doesn't require an external gateway, as the PowerWall does.

I am planning an install of one in the new year, along with ~20 kWh of PylonTech batteries (plus PV). The "ESS" system will act in an identical manner as a PowerWall, allowing for charging from/discharging to the grid, providing UPS to "protected" house loads (up to ~3.7kW cont, 5kWp)... and when combined with PV and an MQTT controller it acts as the inverter for the entire system - so it's more efficient overall. You can even discharge it to unprotected loads (such as an EV or heat pump) while maintaining a zero grid import/export if you wanted.

View attachment 745784

More importantly from my PoV though, it provides fully local control & API's so you can do everything from within the home... I'm planning on controlling it through Home Assistant. They also offer their VRM Cloud tool for those that would prefer not to DIY their controls.

Excluding the PV, it should work out cheaper and with significantly more capacity than a single PowerWall!

That looks good, but definately not for me.

With 20 kWh of battery storage, you can only discharge up to 3.7 kW continuous. Sorry but thats nowhere near enough. Everytime your house demand loads up over that, it'll need Solar Excess or Grid Support. No good at Night, Winter, or avoiding peak-cost grid demands in daytime.

Our Powerwalls have 27 kWh storage and 10 kW continuous (15kWp)

This means you can still run your house during a blackout and at nightime. Electric Shower (8kW), Induction Hob (7kW), Heat Pump (8kW), Emersion Heater (3kW), Cooker (3kW) etc etc

We had a blackout recently on a Sunday, at Lunchtime in Winter (when your most likely going to get a blackout). My Wife was Cooking our Sunday Dinner when all the street alarms were going off. Our house 'islanded' and I went in to see how she was getting on... hadn't even noticed and we were pulling 6kW at the time and nothing much from Solar.

Your proposed system would've shut down... so no, sorry. It does not maintain a zero grid import outside of 3.5 kW without solar, or during dark hours.

If you're going to store that much energy, why restrict your power access to it at 3.5 kW? ... you'll just be pulling grid power at peak rate for anything over that, especially in Winter when electricity demands are usually highest.

Also, is all your battery kit, inverters, and ESS waterproof for external installations? All the Powerwall kit is... so in the event of any 'rare' battery fires, ours is outside the house. Where do you plan on installing your batteries?

I am interested in your API control. As the Tesla APP already gives me full control over the battery, gateway & car outside. What can your API do, that the Tesla App can't?

It does look like a capable 'small damand' system, but the capacity, safety and convenience isn't there, not for our requirements in a busy family home.

 

[scdoubleu]

The 3.68 kW limitation stems from G98. Unless you have a 3-phase supply, most domestic solar/battery combinations are going to have G98 restrictions applied. In our case, our two solar inverters can put out a combined total of 6 kW, but the battery is limited to 3.68 kW charge/discharge, and there's nothing we can do to change it, short of spending a load of cash for 3-phase. Configuring the battery inverter to never export is not sufficient; the inverter takes a finite time (few tens of mS) to switch off/around when a house load disappears. During that time, it'll be exporting to the grid.

With single phase, the DNO will determine if your local infrastructure (cabling/substation/local demand) can support G99, allowing more kW local generation.

Other than @PITA's example of power cuts, G98 has not really been much of an issue for us.

 

[Dilly]

The 3.68 kW limitation stems from G98. Unless you have a 3-phase supply, most domestic solar/battery combinations are going to have G98 restrictions applied. In our case, our two solar inverters can put out a combined total of 6 kW, but the battery is limited to 3.68 kW charge/discharge, and there's nothing we can do to change it, short of spending a load of cash for 3-phase. Configuring the battery inverter to never export is not sufficient; the inverter takes a finite time (few tens of mS) to switch off/around when a house load disappears. During that time, it'll be exporting to the grid.

With single phase, the DNO will determine if your local infrastructure (cabling/substation/local demand) can support G99, allowing more kW local generation.

Other than @PITA's example of power cuts, G98 has not really been much of an issue for us.

Mine’s uncapped (G99 I think) 10kWh charge/discharge. Not allowed to export though. I’m better without Tesla Energy Plan but couldn’t have it. Local infrastructure isn’t up to it.

 

[PITA]

Mine’s uncapped (G99 I think) 10kWh charge/discharge. Not allowed to export though. I’m better without Tesla Energy Plan but couldn’t have it. Local infrastructure isn’t up to it.

It has been a journey of discovery, that's for sure.

People need to be prepared, even if you want it, and have the money... you may still be denied through product availability, resource availability or application refusal.

Ours is based on 15kW power generation and 5kW export. Took months to sort it all out.

 

[Dilly]

It has been a journey of discovery, that's for sure.

People need to be prepared, even if you want it, and have the money... you may still be denied through product availability, resource availability or application refusal.

Ours is based on 15kW power generation and 5kW export. Took months to sort it all out.

Yes. It’s a complete minefield. When power prices went through the roof I wrote to my DNO and asked if the local export situation had changed. It hadn’t. I then wrote to my MP, who is very keen on green, and he followed it up but to no avail. The local infrastructure cannot cope with the potential solar/wind power being generated locally. My secondary panels like other sources locally, have to shut down when my export limit is reached.
I don’t even want payment for the excess!
Presumably the upgrade cost exceeds short term benefit.

 

[PITA]

Yes. It’s a complete minefield. When power prices went through the roof I wrote to my DNO and asked if the local export situation had changed. It hadn’t. I then wrote to my MP, who is very keen on green, and he followed it up but to no avail. The local infrastructure cannot cope with the potential solar/wind power being generated locally. My secondary panels like other sources locally, have to shut down when my export limit is reached.
I don’t even want payment for the excess!
Presumably the upgrade cost exceeds short term benefit.

In our situation, there must be about 80-100 houses on our local estate.. most of them are on looped supply. I've seen the DNO mapping of the area.

How on earth are they going to unloop all those houses? Individually, as and when they need an EV Charger fitted?

Or all together in some sort of co-ordinated bombing of all the streets.

Dread to think of what the costs will be, whichever way they do it. Our single house was estimated at £7,500 and took a week of labour.

 

[PITA]

Oh... and here's a little Gem of advice..

Don't get your Smart Meters until your EV Charger has been authorised by the DNO.

In our case, the DNO had to move our meter box to another location (as we'd agreed to a 3 phase cable upgrade, as part of the unloop)... but if we'd had Smart Meters fitted, they couldn't have moved it all.

DNO's are not allowed to touch Smart Meters... only your Utility Provider can... which seriously compromises any DNO work if they want to upgrade you to 3 phase cabling.

So luckily we still had the old meters in place, and upgraded to Smart Meters afterwards

 

[dakaix]

That looks good, but definately not for me.

With 20 kWh of battery storage, you can only discharge up to 3.7 kW continuous. Sorry but thats nowhere near enough. Everytime your house demand loads up over that, it'll need Solar Excess or Grid Support. No good at Night, Winter, or avoiding peak-cost grid demands in daytime.

Different solutions fit different people, I wasn't specifically providing a design to meet your use-case - rather I was offering an alternative not often discussed and one that I'm persuing. I'm glad you're enjoying the benefits of your PowerWall!

The 5kVA unit I mentioned is the one appropriate for my domestic peak load, they have models up to 10kWp (which will easily do 7.5kW cont).

Should that not be sufficient you can also parallel MultiPlus units (up to 6, for 60kWp) to provide additional single-phase capacity, or create a three-phase supply (max 2 per phase).

Also, is all your battery kit, inverters, and ESS waterproof for external installations? All the Powerwall kit is... so in the event of any 'rare' battery fires, ours is outside the house. Where do you plan on installing your batteries?

Installation location is obviously site specific, not everyone wants, or has space for, things hanging on the outside of their house. You're correct that my solution isn't IP rated. Fortunately though since PylonTech's chemistry is LiFePO4 (aka LFP) they are far less likely to conflagrate!

I am interested in your API control. As the Tesla APP already gives me full control over the battery, gateway & car outside. What can your API do, that the Tesla App can't?

To be pedantic a moment Tesla's mobile app is not the same thing as a local API, their App works through Tesla's own cloud-based services - as many discovered during the recent outages. PowerWall 2 does have an undocumented & unsupported local API (see here), that's far better than many of their competitors (e.g. GivEnergy, Sonnen etc).

Speaking more generally, the fundamental problem with a cloud only approach is that you're beholden to the provider to continue supporting that feature or service over time, you're only ever 1 software update away from losing something. Companies are acquired or go bankrupt all the time, their priorities change at whim. I've had my fingers burnt several times in the past (e.g. Pebble, Nest, Ring). Having that local API means the cloud/app service can go away entirely and you're not impacted at all.

Personally I'm no longer willing to tolerate manufacturers closed-minded approach. I want the intelligence of my system within my walls - and fully under my control - because I want that functionality to still be there in 15-20 years time. At the moment only Victron has anything even approaching an Open-Source ethos, and while they're not perfect they've done enough to meet my acceptable criteria. I'm glad you found a solution that meets yours!

 

[Peter 224]

The last few posts make me wonder how the domestic green dream will actually happen...
I also don't understand why, if a house can draw 80A at 240v = 19kw it can't export at up to that level.... clearly I'm missing something.

We have a single phase none looped supply, I think: power comes to the house from a cable that goes back to a box on an electricity pole, the cable on the poles goes to a transformer on a pole about 200m away that drops the voltage to 240v.

 

[PITA]

Different solutions fit different people, I wasn't specifically providing a design to meet your use-case - rather I was offering an alternative not often discussed and one that I'm persuing. I'm glad you're enjoying the benefits of your PowerWall!

The 5kVA unit I mentioned is the one appropriate for my domestic peak load, they have models up to 10kWp (which will easily do 7.5kW cont).

Should that not be sufficient you can also parallel MultiPlus units (up to 6, for 60kWp) to provide additional single-phase capacity, or create a three-phase supply (max 2 per phase).


Installation location is obviously site specific, not everyone wants, or has space for, things hanging on the outside of their house. You're correct that my solution isn't IP rated. Fortunately though since PylonTech's chemistry is LiFePO4 (aka LFP) they are far less likely to conflagrate!


To be pedantic a moment Tesla's mobile app is not the same thing as a local API, their App works through Tesla's own cloud-based services - as many discovered during the recent outages. PowerWall 2 does have an undocumented & unsupported local API (see here), that's far better than many of their competitors (e.g. GivEnergy, Sonnen etc).

Speaking more generally, the fundamental problem with a cloud only approach is that you're beholden to the provider to continue supporting that feature or service over time, you're only ever 1 software update away from losing something. Companies are acquired or go bankrupt all the time, their priorities change at whim. I've had my fingers burnt several times in the past (e.g. Pebble, Nest, Ring). Having that local API means the cloud/app service can go away entirely and you're not impacted at all.

Personally I'm no longer willing to tolerate manufacturers closed-minded approach. I want the intelligence of my system within my walls - and fully under my control - because I want that functionality to still be there in 15-20 years time. At the moment only Victron has anything even approaching an Open-Source ethos, and while they're not perfect they've done enough to meet my acceptable criteria. I'm glad you found a solution that meets yours!

Yep, good points and agreed.

I rarely have anything for 15-25 years without upgrading it to newer stuff in the meantime.

I'd never expect to still be using the same batteries & car or even Solar Panels in 10-15 years. I'd have swapped them out long before.

Never knew the Powerwall had a hardwired API

 

[phil4]

The last few posts make me wonder how the domestic green dream will actually happen...
I also don't understand why, if a house can draw 80A at 240v = 19kw it can't export at up to that level.... clearly I'm missing something.

We have a single phase none looped supply, I think: power comes to the house from a cable that goes back to a box on an electricity pole, the cable on the poles goes to a transformer on a pole about 200m away that drops the voltage to 240v.

I'm with you 100% here. Surely the very local infrastructure (cable to substation) can cope, as that's what it sends out in the first place. Indeed we've a 100A fuse... don't use that much 99.99% of the time, but surely everything is sized to allow that.

So why on earth they limit to a poxy 3.68Kw is in place is beyond me.

If I had to guess, it's a big protection racquet.... the energy companies and DNO don't want everyone powering their own homes and generating power left over. If they did, then the power company wouldn't be able to sell you much power, wouldn't make the markup they do, and would lose business. Carrying on my cyncial thoughts, that's why the govt aren't doing much any more to get people with Solar. No, instead they're helping with offshore wind, owned by the energy companies.

Adding solar is doing your bit to democratize power, and that's not what big power companies want.

Now where did I put my anti-5g tinfoil hat?

 

[Dilly]

I don’t know how electricity management works but I’d guess that someone somewhere opens the tap and doesn’t want to find that the populous is generating enough for their needs and no one wants it!

 

[dakaix]

The issue for the DNO's is not so much the local cabling (unbundling aside), but rather the aging transformers they often have. There was a guy from Western Power Distribution at Fully Charged Live in September who explained this better than I can, but in effect the LV networks weren't designed (20 years ago) with equipment that could support large amounts of local generation.

From what the guy was saying WPD were trying to do as much as they can to help, but ultimately there's no quick fixes here.

 

[scdoubleu]

There's no conspiracy theory. It boils down to physics. I'm no expert, but as I understand it, grid tied inverters export by raising their output voltage until current flows towards the grid. The more current available from the array, the higher their output voltage. The required rise in voltage depends on the local loop impedance. As in, how readily can the local loop absorb the exported energy.

The DNOs want to avoid the situation where too much solar (over multiple solar-equipped properties) raises the line voltage so much that it's out of spec (>253 V).

Also, while your DNO fuse might be rated for 100 A, the infrastructure is sized on the basis that no property will import/export anywhere near that amount of power continuously. This is why EV chargers and grid-tied solar are notifiable. The infrastructure may be unable to cope with every house on a street charging an EV simultaneously for hours at a time. Even at only 7 kW each!

 

[phil4]

That's what they'd like you to think

 

[PDB33]

The 3.68 kW limitation stems from G98. Unless you have a 3-phase supply, most domestic solar/battery combinations are going to have G98 restrictions applied. In our case, our two solar inverters can put out a combined total of 6 kW, but the battery is limited to 3.68 kW charge/discharge, and there's nothing we can do to change it, short of spending a load of cash for 3-phase. Configuring the battery inverter to never export is not sufficient; the inverter takes a finite time (few tens of mS) to switch off/around when a house load disappears. During that time, it'll be exporting to the grid.

With single phase, the DNO will determine if your local infrastructure (cabling/substation/local demand) can support G99, allowing more kW local generation.

Other than @PITA's example of power cuts, G98 has not really been much of an issue for us.

I assume that the DNO response to my prospective installer’s application for 18 panels and a Powerwall on a single phase supply “Reduce PV and Battery system to 7.36kW (32A) installed capacity but limit the export capacity to 3.68kW (16A)” reflects the local infrastructure in rural Oxfordshire.

My installer says that PV export limitation would be achieved by installing a 3.68kW inverter, but that would clip any generation over 3.68. Is there an option to have a higher capacity inverter with export limitation in the event that generation minus battery storage and house consumption exceeds 3.68?