Solar Panels UK - is it worth it?

[Zakalwe]

I think to stop the battery contributing, I need to set it to charge mode, at whatever %its at, then the Andersen solar mode will take care of charging. I think I'll leave the car set to over night charging, but manually initiate a charge when needed.

I need to run the faffing around a few times manually to work out the algo I want, and will then slowly pick bits to automate as best I can. So many different bits of tech involved I'm worried I'm going to need some kind of windows GUI automation solution with a virtual phone running some of the apps. Only the Tesla really has a proper API access .

Personally I think that it's easy to fall into the trap of over-thinking these things and adding too much complexity. I found myself falling into a deep, dark hole this morning looking at Pi servers for Home Assistant before I realised that spending a couple of hundred quid and hours of frustration learning and setting up a system to monitor PV output and automate routines was a fool's errand. The pennies saved will not recompense me for the hours of messing about.

As we are in Summer, I let the system charge the 8.2kW battery to 35% on overnight cheap rate power. That then sees the house through the night and the battery ends up at about 10-15% charge in the morning. I then let the PV charge the battery (on a good day its at 100% by 10:30AM). The solar diverter then puts the excess into heating the water cylinder. By then, again on a good day, its probably 1PM. If I am at home I then plug the car in and let the Andersen charger push the excess into the car. Again, on a good day, I can get maybe 10kW in there.

My PV system has generated 40Kw at peak in a day. Normally it's lower than this, but that gives an idea of what I'm playing with (May's total generation was 696kWh, June was 756kWh) . Getting the panels and battery in was the big jump. Everything after that is a game of diminishing returns.

 

[Battpower]

The DNO's are an absolute pain in the a**e, it's no wonder installers want to stay under the 3.68 limit.

There is no joined up thinking - how the net zero will ever be achieved when there are so many restrictions in place by the DNO's - and if there is an upgrade required on the infrastructure somewhere - they want the individual customer to pay for it!

I agree 100%.

Almost to the point that this thread could be 'is dealing with DNO's worth the hassle to install solar PV?’

The only genuine concerns I can come up with for DNOs are

1) Multiple solar inverters make load disappear from the network, and I read that DNOs get paid based on energy flow.

2) large loads supported by home owner inverters could cause momentary power surges when the loads turn off and on.

But DNOs treat this kit as though it could randomly dump random amounts of power on their network. They don't even use peak inverter power, just rated.

I realised that spending a couple of hundred quid and hours of frustration learning and setting up a system to monitor PV output and automate routines was a fool's errand.

Yes. And it only takes the smallest change to render all your work pointless.

The hardest thing I find is how much to charge batteries over night. Likewise, if using battery power during the day, are you going to charge over night, or leave the battery discharged in the hope of being able to charge from solar before you need more battery energy.

While you are down the rabbit hole, it's easy to lose the plot and miss far more obvious 'big picture' opportunities.

 

[Battpower]

Forgot to mention that (especially in summer) the picture becomes even less clear if you have a diverter to heat water and have to decide how hot and when to heat. I regularly end up with a tank of very hot water that just sits and cools down over night.

If you have a heat pump, you could opt to run the heat pump before immersions have heated the water too much (above 50deg ish) and then have more PV to charge a car.... but only if there is a car that needs charging.

Having simple operation algorithms that stand a good chance of getting most of the low hanging fruit makes most sense.

 

[Avendit]

Forgot to mention that (especially in summer) the picture becomes even less clear if you have a diverter to heat water and have to decide how hot and when to heat. I regularly end up with a tank of very hot water that just sits and cools down over night.

If you have a heat pump, you could opt to run the heat pump before immersions have heated the water too much (above 50deg ish) and then have more PV to charge a car.... but only if there is a car that needs charging.

Having simple operation algorithms that stand a good chance of getting most of the low hanging fruit makes most sense.

I've not managed a full trial of this yet, being away, but our plan (with a heat pump) is

• Base plan is HP runs once at solar max, and once over night cheap rate for hot water. Our default HW temp is 48 as this is good for the HP apparently. This isn't isn't quite enough for the HW usage we have over an evening, so an extra cycle kicks in late evening. This neither takes advantage of high day temps, solar or cheap rate power. Grrr.
• On a good solar day I will (manually initially, through some kludgy automation later) increase the HW temp to 65, which is as high as it can go. Up to 55 is HP, beyond that is supported by an immersion. This will hopefully give us enough to get through the evening.
• Any left over will go I to the car.

It will be much harder on marginal days. I suspect the car will just be de prioritised and filled up on cheap rate of it's actually needed. It rarely needs urgently charged tho. Will see how hard this all is in practice over the next few weeks.

 

[Dilly]

I've also recently pulled the trigger on solar, hopefully getting installed in 3 weeks time. I'm fortunate enough to have quite a large (almost) directly South-facing roof even so when I started getting quotes almost everyone was coming back suggesting 8-12 panels. It seems the installers are really trying to stick under the 3.68kw limit to avoid a DNO application. As others have suggested I want to max the system out so I persevered, had some installers just stop speaking to me, but now have 20 panels being installed for somewhere around 8kw total. I realise this is going to be above my inverter max output and it'll get "clipped" however for the rest of the time/year I'll be generating more overall so I think it's worth it. The panels after all are not particularly expensive.

Battery storage I think is entirely down to your household usage. I worked out that I needed somewhere around 14kwh of storage to maximise how much of our own solar we could use in the house, however with a couple of cars I can also dump excess power into I've gone for 10kwh of battery initially.

I had 28 panels installed with 2 inverters in 2015. There are 4 strings of 7 with 2 strings to each inverter. It’s 7KW array but maxes out at 7.3.
2 inverters would solve the clipping problem

 

[WannabeOwner]

First step is installing a Shelly EM with CT clamps to start collecting usage data for the whole house

You might be able to get that from Tesla APP (assuming PowerWall rather than A.N.Other battery)

Bit fiddly to download, as have to do one day at a time, but that gives recorded history readings every 5 mins of Home consumption, Solar production, Battery kW (Plus/Minus) and Battery SoC%

looking to manage it between the house battery, immersion, and two cars.

Might be worth getting some AirCon? Ideal bedfellow for PV in the summer ... particularly in a well insulated house with good thermal mass. The "cold" generated will be stored in the fabric of the building.

The pennies saved will not recompense me for the hours of messing about.

Very true ... and I don't have the time, hence why, personally, I was hoping to find someone had already built something ... but ... I think the planet would benefit from some efficiency gains spread across the whole fleet. I suppose much the same as fixing a dripping tap, or turning off things instead of using standby.

I then let the PV charge the battery (on a good day its at 100% by 10:30AM

In my case that will charge my PowerWalls at 10kW (the max), which is a lot above their best-longevity charging rate. Unlike my EV car I'm not passing-on my House Batteries every few years ... so longevity more of a concern for me (than the car). So I'm trying to start my alterative load when the sun is strong enough to generate way above "optimum" for PowerWall (in my case the PV will generate about 14 kW - so that's 4kW exported (or used elsewhere) when the batteries would still be charging flat-out). But 14 kW max is only for a couple of hours "peak" and only on good-sun days - so in my case I find it worth delaying any car charging so as to be available as a peak-drain at that time.

I've been doing this manually, mainly to figure out what's going on ... but it is something that a software APP could do, and I think would benefit battery longevity as well as give me a good chance of finishing the day with battery at 100% ready for overnight drain.

The hardest thing I find is how much to charge batteries over night

If you are trying to predict how much PV generation you will have tomorrow? (and thus how low the battery should be at sun-up) the best resource I've found is Solcast - Solar Forecasting & Solar Irradiance Data but its a lot better at "next 3 hours" during the day, than "tomorrow" at around midnight.

if using battery power during the day, are you going to charge over night, or leave the battery discharged in the hope of being able to charge from solar before you need more battery energy

I drop my reserve from 10% to 5% at around 5:30AM (about when my battery will hit 10% if it was only at 90%, or a bit lower, yesterday at sundown) providing that the PV generation prediction is good for the day ahead. I figure I can take the risk of 5% for an hour or so until the battery starts to climb back up to 10% ... but then I have to remember to reset it to 10% to stop it falling below that. Something else for a software solution to do more reliably than I am every likely to do on "Manual pilot"

But that's because my setup will only get from sun-down to sun-up, on battery alone, if the battery is very close to 100% at sun-down (I'd like to take credit for planning that, but I just went with "Probably need two")

 

[JaseW]

Just to add a couple of thoughts. I have a 3.6KW system facing SW near the coast and it has been in operation since 2011 and the one thing I have learnt is it doesn't matter how you consider economizing on export you will hit a brick wall on investment return whether its batteries(high cost) heating water (limited storage) and numerous other schemes. I have yet to find a suitable cost effective way of storing power from PV and I have been looking at this for 11 years and have come to the realization that a bit of export is OK and not to sweat over it. Its way too easy to overthink solar installations and get carried away with plans and schemes to minimize export. I would have to add we do not get power cuts in our area.

I hope to have a 3.6kw system installed soon but the battery is only 2.4kw. Did you go for a battery? I’m wondering if 2.4 is too small (south facing roof down south)

 

[Avendit]

I hope to have a 3.6kw system installed soon but the battery is only 2.4kw. Did you go for a battery? I’m wondering if 2.4 is too small (south facing roof down south)

It would be for my usage. You need to understand your usage and see how that interacts with the solar and battery to decide. At 2.4 that is really just helping you stay grid free while using a high draw appliance (eg kettle) that is beyond the panels output. There will be a reserve at the bottom you can't use too.

2.4kw would get me to about 9pm this time of year, but I'm all electric, so HW is coming out of that (via a HP).

I'd say for a low power user you need 5kw, really more. Is that one of the Costco kits btw?

 

[Battpower]

the battery is only 2.4kw

Kw or kwh?

2.4 Kwh (of stored energy) is still very useful as a small buffer to keep you running off your own energy during intermittent sun. But also consider what the max rated power from battery is. I have some old Pylontech batteries that are 3kwh (energy stored) but can only output 1.5kw max power.... So if I had one of them on its own, it couldn't provide enough instantaneous power to boil a kettle (and so you would have to draw something from the grid to make up the difference.)

However, with a smaller (cheaper) system, it doesn't have to 'work' as hard to justify the system cost. So it could still be a cost effective purchase.... just not as capable.

There is quite a lot to take into account, especially if your expectation is to generate a significant amount of your own electricity needs!

If you are on a budget and still have a hot water tank with an immersion heater, a small / inexpensive device called a solar PV diverter would use any surplus PV during the day (once your battery it charged) to heat your water - which would likely be better than just exporting the energy.... and still contribute to reducing your energy bill.

With any system, all that really matters is if the savings on your energy bill justify the expense of the solar PV gear.

That said, 2.4kwh sounds a bit on the small side. I'd guess upto 5kwh would still justify the additional cost. Check if the inverter / charger allows you to charge the battery from the grid over night if you are on an appropriate tariff.

 

[Avendit]

That said, 2.4kwh sounds a bit on the small side. I'd guess upto 5kwh would still justify the additional cost. Check if the inverter / charger allows you to charge the battery from the grid over night if you are on an appropriate tariff.

Without this my battery would not be worth the cost btw.

 

[JaseW]

Thanks it’s a Pylon 2.4kwh US2000 C Li-ion Battery and 9x Trina Vertex S 400W Black Framed Mono panels

You can stack the batteries, I have some extra budget so I may ask them to add another one on and then have 4.8kwh.

Also do you know anything about these brands?

 

[HenryT]

Thanks it’s a Pylon 2.4kwh US2000 C Li-ion Battery and 9x Trina Vertex S 400W Black Framed Mono panels

You can stack the batteries, I have some extra budget so I may ask them to add another one on and then have 4.8kwh.

Also do you know anything about these brands?

We have 3 of those batteries and a 3kWp 8 panel system - apart from the odd peak draw it's enough to keep us more or less off grid on most bright days, given the battery tops up overnight.

Yesterday as an example;

 

[JaseW]

We have 3 of those batteries and a 3kWp 8 panel system - apart from the odd peak draw it's enough to keep us more or less off grid on most bright days, given the battery tops up overnight.

Yesterday as an example;

View attachment 833301

Oh I have some questions as my setup may be similar to yours

What octopus tariff are you on? I’m currently on Go but I don’t know how it works when I add PV to the mix. Do I stay on Go and use something else for FIT.

It looks like you’re mainly using the battery to charge with Go, are you also charging them from the panels too? If so how much?

 

[Zakalwe]

Oh I have some questions as my setup may be similar to yours

What octopus tariff are you on? I’m currently on Go but I don’t know how it works when I add PV to the mix. Do I stay on Go and use something else for FIT.

It looks like you’re mainly using the battery to charge with Go, are you also charging them from the panels too? If so how much?

You can stay on Go, but for export you will be limited to SEG (4.1p per kWh). The best is to try and limit your export and consume the generated power yourself.
A solar hot water diverter can be a good option as it heats the water instead of exporting (you'll obviously need a hot water cylinder and immersion heater in your plumbing setup)

 

[HenryT]

Oh I have some questions as my setup may be similar to yours

What octopus tariff are you on? I’m currently on Go but I don’t know how it works when I add PV to the mix. Do I stay on Go and use something else for FIT.

It looks like you’re mainly using the battery to charge with Go, are you also charging them from the panels too? If so how much?

Yep, I'm on Go too.

We have the battery set to charge up overnight at the cheap rate and also charge one of the cars (we have 2x EVs) overnight in the 4 hour window when needed. We charge the system battery to 100% every night but could do less as we have some surplus from solar on sunny days. My view is that it is so cheap to fill the battery anyway, little point in not doing so as we would risk using more peak rate electricity if it was a cloudy day. We also have timers on the washer, dryer and dishwasher so they only run during the cheap rate.

We do lose some surplus solar back to the grid on sunny days while the battery is at 100% and the house draw is too low. I've now got the info needed to set up an export tariff. Not rushed to do it though as its only about 4p a kWh and in reality wouldn't add up to too much anyway - I will get it done at some point.

We have toyed with the idea of trying to use the surplus to charge the cars but our charger (WallBox) doesn't have the sophistication needed to manage the surplus itself in the way some (Givvi) can. I have used the granny charger on really bright days when we have been pushing more than 2kWh back to the grid, but even that runs the risk of cloud cover or the odd boiled kettle meaning that we have some peak draw so we've abandoned that idea.

 

[cryo]

I hope to have a 3.6kw system installed soon but the battery is only 2.4kw. Did you go for a battery? I’m wondering if 2.4 is too small (south facing roof down south)

No I have full FITT so have not bothered with a battery. South facing roof with 3.6kw will provide a fair amount of KWhrs on a sunny day so I suspect 2.4kw battery is a bit small. On a sunny day you will get anywhere up to 3kw an hour with a south facing system.

 

[RedMod3]

We have 5.1kW max net generation capacity and being all electric we use up to 2kW with all air-con units running when it gets very hot (or very cold), 2 Tesla PWs are a minimum in summer giving us 27 kWh of storage but from October we will have 3PWs, giving us 40 kWh of storage that should keep most of our consumption at the lower GO rate. I don't export anything to the grid as the cars and immersion heaters can always do with topping up.

 

[ACarneiro]

I’ve had 2 more PWs or order for 14 months now. Maybe October time, they say…

 

[PITA]

I’ve had 2 more PWs or order for 14 months now. Maybe October time, they say…

I'm holding off now until the Powerwall 3 comes out...

Two Powerwall 2's will keep me ticking over until then

 

[RedMod3]

I’ve had 2 more PWs or order for 14 months now. Maybe October time, they say…

For orders not placed, I've heard extra PWs are now over £9k. Heard Tesla are managing demand with price.