Solar Panels UK - is it worth it?

[WannabeOwner]

the limit seems odd

Export limit presumably? Actual generation can be something else.

I had 16 PV panels and a car charger. DNO happy with that (probably only "notification" required at that point)

Added 2x PowerWall ... DNO still happy (their calculations are based on the possibility that I might export the whole lot at "peak" ...)

Added 32 PV panels and a 2nd car charger. Was expecting the DNO to require an export limit (happy with that, not expecting to export anything). DNO were happy with that too.

I think I'll register my house as a Peaker Plant

 

[Avendit]

I guess my beef is with paying for an 8kw inverter when the smaller 3.6kw one would be more appropriate really. Running an 8kw inverter at 3kw most the time will not be efficient.

I can only guess they have come up with different calcs for how much I can generate, but I'd rather have an effective efficient system 90% of the time rather than chasing peak output.

 

[phil4]

I'm not 100% on this, but I think you also need DNO permission if you go big on the batteries. So we're talking above about solar over 3.7kW needing DNO permission... I think the same is true for battery. And that's something you also need keep in mind about battery.

It's all well and good having a 10kWh battery, but if it can only trickle out 2kWh at a time, it won't be "powering your house" when you put the kettle on, toaster etc. etc. Tesla PowerWalls can do 5kWh... buuuuut that's over the DNO 3.7kW threshold. Apparently some installers who didn't ask for permission are knobling the TPW to reduce the output to match the DNO limit.

So my thinking is don't dodge the DNO permission. You might want to feed in from the battery above the threshold even if the solar doesn't provide more.

 

[scdoubleu]

As I understand it, the restriction on battery inverter capacity is because they are (currently) governed by the same regulations as grid-tied solar (G98/G99). That is to say, the DNO adds the battery inverter's theoretical max *output* power to that for the solar inverter(s). The fact that in the vast majority of cases the battery will do its damnedest to avoid exporting more than a few watts to the grid is not taken into account by the regs or DNO.

Basically OFGEM needs to get off its arse and relax the regulations for domestic grid-tied energy storage.

 

[RichardTheKing]

What is there purpose of the DNO? What's does they check and why?

 

[Avendit]

As I understand it, the restriction on battery inverter capacity is because they are (currently) governed by the same regulations as grid-tied solar (G98/G99). That is to say, the DNO adds the battery inverter's theoretical max *output* power to that for the solar inverter(s). The fact that in the vast majority of cases the battery will do its damnedest to avoid exporting more than a few watts to the grid is not taken into account by the regs or DNO.

Basically OFGEM needs to get off its arse and relax the regulations for domestic grid-tied energy storage.

All makes sense - thanks. The battery theoretically counts as generation so a software update could enable batt to grid as a usage model, and that could happen on a max gen day, then you are exporting 4kw from the solar and another 3-5kw from the battery. No one wants that, but it's electrically possible, so it's notification time.

What is there purpose of the DNO? What's does they check and why?

Your Distribution Network Operator - they own everything from the inside of your fuse outwards. It's also their job to balance the grid and keep it in phase and so on. It's complex and hard with AC, and lots of people shoving significant current into the grid at random places and times makes their life's harder. So by default you are only allowed reasonably small amounts of power feeding in.

 

[WannabeOwner]

What is there purpose of the DNO? What's does they check and why?

One of their considerations must be "What happens if everyone in the street starts exporting all their Solar etc." and whether the infrastructure can handle that. I don't know how much of a headache it gives them with load balancing (the fact that all those people MIGHT export .. and then the actual amount that is exported in practice - maybe that doesn't bother them, the "demand" on their generation is just less than it would have been, and they pay the PC exporters accordingly - and presumably at a much lower rate than their generating costs and/or they get some "green credits" for that generation, which gets them some brownie-points at least).

Maybe at some point in the future I will have the ability to export at Peak for a price that suits me. Right now the only one I know of is Tesla, and they want to control my export ... and I have no idea if I will wind up importing power as a consequence in a way that I might not be comfortable with.

I'd be very happy to export for 5 minutes during Coronation Street adverts ... or maybe for 2 hours during evening cooking interval - depending on Export Price ... but until then I'm happy to store and use all my own self-generated power. Once EVs are able to discharge to Home / Grid all that may change, because it will be more cost effective for power companies to pay people with EVs than to build / run Peaker Plants.

 

[WannabeOwner]

The battery theoretically counts as generation so a software update could enable batt to grid as a usage model,

Tesla have that right now I think? When then mailed me (some time ago) their offer was 8p kWh 24/7 and they then control the export. No idea how much export (i.e. at Peak) they would actually have done, which might have resulted in me buying power at some other time in the day, when I would otherwise have had enough battery. Presumably they would then top up my battery at a time when they could buy cheapest.

 

[94jdh]

I'm not 100% on this, but I think you also need DNO permission if you go big on the batteries. So we're talking above about solar over 3.7kW needing DNO permission... I think the same is true for battery. And that's something you also need keep in mind about battery.

It's all well and good having a 10kWh battery, but if it can only trickle out 2kWh at a time, it won't be "powering your house" when you put the kettle on, toaster etc. etc. Tesla PowerWalls can do 5kWh... buuuuut that's over the DNO 3.7kW threshold. Apparently some installers who didn't ask for permission are knobling the TPW to reduce the output to match the DNO limit.

So my thinking is don't dodge the DNO permission. You might want to feed in from the battery above the threshold even if the solar doesn't provide more.

That's why I'm looking at two hybrid inverters, one for each battery. Individually, the batteries are discharged at max 2.5kW but together with the two inverters, max 5kW.
It originally confused me ( and probably still does!) when I was looking at two batteries with one inverter.

 

[Avendit]

I'd be very happy to export for 5 minutes during Coronation Street adverts ... or maybe for 2 hours during evening cooking interval - depending on Export Price ... but until then I'm happy to store and use all my own self-generated power. Once EVs are able to discharge to Home / Grid all that may change, because it will be more cost effective for power companies to pay people with EVs than to build / run Peaker Plants.

Unfortunately it seems like at the moment only Octopus and Tesla are building the structures that allow for this. Even So.Energy, which was set up on much the same premise lacks the data driven back end to be able to time slice to the resolution that smart meters can.

Tesla have that right now I think? When then mailed me (some time ago) their offer was 8p kWh 24/7 and they then control the export. No idea how much export (i.e. at Peak) they would actually have done, which might have resulted in me buying power at some other time in the day, when I would otherwise have had enough battery. Presumably they would then top up my battery at a time when they could buy cheapest.

Yes, tesla with PW's can because they then own the end to end story. I was talking more about my install where it won't be quite so integrated with the puredrive battery, the the capacity to dump power into the grid is still there.

 

[Battpower]

the battery will do its damnedest to avoid exporting more than a few watts to the grid is not taken into account

..... which makes no sense at all.

My battery inverter is set to allow zero export. Its role is solely to power local loads. It is true that during a transition phase it could dump a few kilowatts to the grid for a few milliseconds while one inverter ramps down, but seriously, nothing that would even register at all at a supply network level.

If the Gxx certification of the kit is deemed adequate for anti islanding protection and to limit export to 3.6kw then surely you would 'trust' it to keep export effectively to near zero.

On the matter of 'overloading' inverter inputs with extra panels to compensate for location and low sun days, I'm not sure why that would be a problem and isn't more common. Obviously Vppp / string lengths need to keep the peak voltage within what the inverter can tolerate, but MPPT puts the power / current totally within the inverter's control, so I'd expect that additional panels as parallel strings would just allow MPPT to draw more current under cloudy conditions.

 

[googlepeakoil]

Interesting you say this, I'm getting some push from my supplier to both go for DNO permission for more than 3.7kw and an 8kw inverter (lets leave aside 5g vs 4g just now...)

I don't think this is needed, as although we are getting 22 panels installed, they are split NE/SW. From PVwatts, the combined output of the 2 arrays only pops over 3700w for 28 hours a year, totalling 3kWh lost generation. As I understand clipping of this much is pretty much ideal isn't it?

Anyway, we have accepted the quote for the moment and hope to have a more detailed discussion with the detail designer/installer when they come, and cut the inverter down to size.

The 1kWh generation above 3.7kW is less important than 1kWh generation at the bottom. A bit like the analogy... when really hungry what's the value of 1 mars bar, but if you've just eaten 5 another one looks less appealing!
I think most inverters support a 1.5x multiply (7kW of panels on 4kW inverter = 1.75 would be bad). But if it's an East-West split then you can probably go higher - depending on the inverter. The Youtuber Spectrum Geeks has 9kW (30x300w) array on a 6kW inverter.

 

[googlepeakoil]

With a purely 2.6/2.9kw array facing south (can’t remember which), worth considering a larger one facing north or not really? Even with the lower efficiency using higher power panels should give me similar or higher generation in summer but more drop off in autumn/winter

Maybe better to use the money formore battery and just shift off peak into peak instead?

Are you limited in space on the south side? No flat roofs, no garage. No room for ground mounting? Although if you have panels at a different angle they need to be on micro-inverters or a different string. North is almost as bad as being shaded! You'll get about a quarter what a south facing array will get. When the sky is white and cloudy it'll do better than with blue sky. But the other day, as an example, blue sky, I have some NE panels (rising sun) and I get 0.9 amps from them when it was 4pm and the SW main array is in full sun doing 4-5amps! East/West you lose about a third maybe vs pure south but gain in terms of output in morning and afternoon.

 

[RedMod3]

If you have a properly insulated tank (and don't use it all). Our tank loses ~1degC over 24 hours at its 50degC, although its very new.

We have a 30year old Economy 7 tank and it retains heat. However, a tip, when t was installed, the builders put in a cheap copper immersion heater which failed after 9 months. I had both immersions replaced with titanium coated immersions, and touch wood, used every night for 30 years, they are still fine.

 

[roadcred]

Tesla have that right now I think? When then mailed me (some time ago) their offer was 8p kWh 24/7 and they then control the export. No idea how much export (i.e. at Peak) they would actually have done, which might have resulted in me buying power at some other time in the day, when I would otherwise have had enough battery. Presumably they would then top up my battery at a time when they could buy cheapest.

They do. They fill my powerwall up to 100% during the night and discharge it every evening to 20% between 4 and 6pm. Not ideal as at 4pm when the sun is shining my panels get shut down while the Powerwall discharges. There needs to be a recognition that when my panels are producing surplus that they are used to export until later. Tesla could dump a couple of hours later and still earn a good rate.
However I am happy with the status quo to get my hands on power 24/7 at 11p and surplus export 24/7 at 11p! I would prefer to control the powerwall but I could not return to GO + export at 3p. In an ideal world TEP april through September and Go during the winter.

 

[94jdh]

They do. They fill my powerwall up to 100% during the night and discharge it every evening to 20% between 4 and 6pm. Not ideal as at 4pm when the sun is shining my panels get shut down while the Powerwall discharges. There needs to be a recognition that when my panels are producing surplus that they are used to export until later. Tesla could dump a couple of hours later and still earn a good rate.
However I am happy with the status quo to get my hands on power 24/7 at 11p and surplus export 24/7 at 11p! I would prefer to control the powerwall but I could not return to GO + export at 3p. In an ideal world TEP april through September and Go during the winter.

I asked the question elsewhere but didn't get a reply - do you get all power used in your house at 11p no matter how much you use or is just related the size of the batteries?

 

[Avendit]

They do. They fill my powerwall up to 100% during the night and discharge it every evening to 20% between 4 and 6pm. Not ideal as at 4pm when the sun is shining my panels get shut down while the Powerwall discharges. There needs to be a recognition that when my panels are producing surplus that they are used to export until later. Tesla could dump a couple of hours later and still earn a good rate.
However I am happy with the status quo to get my hands on power 24/7 at 11p and surplus export 24/7 at 11p! I would prefer to control the powerwall but I could not return to GO + export at 3p. In an ideal world TEP april through September and Go during the winter.

If it's 11p/unit all day, that's stunning!

 

[Fred2]

If it's 11p/unit all day, that's stunning!

It is yes. Any unit imported, for whatever reason, is 11p (with the usual regional variations), any unit exported is 11p.

It used to be 8p in both directions, went up to 11p for new contracts/renewals etc around April and I don’t believe has changed since. I renewed at 11p in December.

 

[Avendit]

Wow. If you use a fair bit of power, that would offset the extra cost of a PW pretty pronto. Do you personally get any advantage from the battery at this stage tho, other than the cheap import and good export?

It's almost like you are on net metering like the US, where they basically use the grid as a battery if they export anything?

 

[phil4]

I've said this before, but apart from the fact you have to have a powerwall to be on that tariff there's not benefit to having the battery... the grid is your battery when you're on a matching in/out tarriff.