Solar Panel Q&A

[Superspy]

Following me derailing the heat pumps thread (https://www.drfc-vsc.co.uk/index.php?topic=282673.msg1209889#msg1209889) I wanted to start this one to just answer any real-life-usage type questions about Solar as I've had my system in for a few months now, and thought it was quite tricky when I was looking around to find real experiences that weren't driven at sales etc.

When I've had it for a year I intend to come back and report on the generation of the system over the year and compare how it stacks up with the original quote and assumptions.

To start things off:

That's really useful SS.

Question from me if you don't mind. What's the peak wattage output that you get from your battery? Checking my Loop app data, we rarely use above 3kW (usually when the oven and several hob rings are on). I'm wondering if a battery would be able to service that requirement without drawing from the grid (assuming it was sufficiently charged up of course).

Also, when charging your battery from E7, can you program that? I'm thinking that I';d want to fully charge it every night in winter, but probably not in high summer, when the solar panels would do the job.

The timing of the question about peak output is really interesting because of something that happened this week.
Bear in mind not all batteries and inverter systems are made equal, so you have to check the performance capabilities of the specific hardware you would be looking to buy, but for my stuff (up until yesterday) the peak output was 3kWh, and the peak charging rate was about 2 to 2.2kWh. The batteries are marketed with these figures in mind - although they usually are limited by current.

The interesting part is that the engineers who fitted my system came out yesterday to reconfigure a few "dip switches" as part of a firmware update that had been deployed and now my batteries are able to charge and discharge at 4kWh. That was a pleasant surprise. The cynic in me says they just didn't configure it properly in the first place - but actually everything I can find online in the marketing says the old figures were correct. I'll be monitoring for a couple of days to make sure those numbers remain.

With regards to E7 - again I can only speak to my specific hardware - the inverter can indeed be programmed for the charging. Mine is currently configured as follows:

Charge level: 95%
Charge time: 12:31am - 7:30 am

I have a 9.6kW battery, so in practice what happens is
- at 12:31 am the battery starts to charge at full power (4kWh as of last night)
- Once it has finished charging the battery, because I've told it to charge until 7:30, this effectively acts as a "hold this charge" command...so all power required by the house comes from the grid
- at 7:30, the battery takes over the house load and the grid is no longer required

This can be seen in this image of last nights charge. The reason it took less than 2 hours to charge is because the battery still had some juice in it from yesterday.



The inverter I have has 3 charging time periods, so if I wanted to boost the battery again later in the day I could - but the only reason to do this is if you can then export it at a high rate to make money. I've done this a couple of times but not very often. In summer I'll just knock the charge off completely as it definitely won't be needed.

[BillyStubbsTears]

That's really, really useful background stuff SS. Many thanks.

Can I just ask - do you have the Greenlinx batteries?

[Superspy]

You're very welcome.

I do indeed, 3 of the 3.2kW ones.

Having a battery of that size, for my usage, has meant that switching to E7 has knocked about 30 quid a month off my winter bills. The only behavioural change we've done to achieve that, other than charging the battery over night, is putting our dishwasher on a timer to also run during that cheaper period overnight. 

[BillyStubbsTears]

Do you mind if I ask how much each battery unit costs? I've had a quote for a solar PV system with 2x3.2kWh batteries. I was thinking of going for 3, but they didn't itemise the individual components of the quote, so I've no idea how much the batteries are.

[keith79]

I have just got some solar panels (16) and a battery (5.12) for £10,700

[mugnapper]

I've said for years that every new house with a suitable aspect should have Solar Panels fitted as standard.
This would reduce the price through economies of scale, and the price of awful new shoebox houses seems to be heading upwards of £250k, it wouldn't add much to the price percentage wise.

[BillyStubbsTears]

Agreed Mug. It's a no brainer. A sensible Govt would massively subsidise this to make sure it actually did happen. Then pay for it by increasing taxes to reflect the benefit that people got from this subsidised free power.

Instead, this lot cut subsidies to green power 10 years ago.

Then, when the shit hit the fan, they had to pay subsidies straight into the pockets of BP and Norwegian gas producers.

[Superspy]

Do you mind if I ask how much each battery unit costs? I've had a quote for a solar PV system with 2x3.2kWh batteries. I was thinking of going for 3, but they didn't itemise the individual components of the quote, so I've no idea how much the batteries are.

Ask anything you like mate.

When I had them fitted I think they were either 1k or 1.1k per battery, and because they were fitted with the system they were VAT free... I'm not 100% sure but I think the company I used have since upped them to 1250, still vat free with no additional fitting costs if included with a system... but obviously retrofitting makes them much more expensive due to vat and fitting.

If you're a moderate to high user I would definitely get 3 at the point of the panels going in. I certainly don't regret it and could probably have justified 4 for the winter E7 benefits, but less needed in summer due to the longer days.

My system, with 19 panels, was about 13k, for what it's worth.

[BillyStubbsTears]

Who did you get them fitted by?

I had a quote of £10,700 for 10x400W panels and 2x3.2kWh batteries, plus inverter. Sounds like your quote was a good bit less than mine.

[Superspy]

Ask Renewables in Barnsley. Really happy with them throughout the process.

Similar to you...no itemised quote, but I'm pretty sure mine is 19 x 385 panels, across 2 strings (east and west), 3 x 3.2 batteries, and a Lux Power 5kW inverter.

Just bear in mind this was about 6 months ago, before some of the pricing went up.

[Superspy]

They did a quote for my mum in November which was the same batteries and inverter but 17 x 375 panels for 12k.

[Filo]

Who did you get them fitted by?

I had a quote of £10,700 for 10x400W panels and 2x3.2kWh batteries, plus inverter. Sounds like your quote was a good bit less than mine.

Theres a guy I use for all my electrical work that does solar, he’s a real good lad, and takes pride in his work, R S Electricals and Security, he’s on Facebook, but don’t let that put you off getting a quote. He did my 4 camera CCTV for £650 when others were quoting double that


This is what he was quoting last summer:

4kW Solar PV system  + 6.5kW Battery Storage

Supplied and installed

10 x 400w Black Mono Suntech
1 x 3.6kw Growatt Hybrid inverter
1 x 6.5kaw Growatt Battery storage
1 x WiFi Data Logger + Smart phone app
Roof mounting Rail + Clamps
2 X DC Isolators + Cable
2 X AC Isolators + Cable
1 X Generation meter
1 x CT clamp
1 x Battery Lead
Installed to one roof
Roofer + Electrician
G98 forms + RECC + MCS

Fully installed £9850.00

4kW Solar PV system + 6.5kW battery storage

[Spud]

Interesting read this.
I've had solar panels for best part of ten years now, even though I could only get 2.6kw worth on my roofspace they've paid for themselves now. Been thinking of a battery/batteries for a while now, do they work in a power outage still? I read somewhere that not all of them have the smart technology to do so, to do with backfeeding into the grid & potentially electrocuting engineers working on it.

[Superspy]

That's what I was told when I had mine fitted Spud - H&S risk of backfeeding into the grid when they think the power is down. Apparently there was a legal case somewhere (Germany rings a bell) where an engineer did actually die as a result. Either way the point is your system is down during a power outage. Disappointing, but it is what it is. They are able to fit a socket to the battery/inverter (not sure which) to use as a backup with an extension cord I believe, but I didn't ask any further about this with my system as it's not of huge use to me.

[colfromdonny]

I've got a 4kw system that pays approx. £600 per year.

[Spud]

That's what I was told when I had mine fitted Spud - H&S risk of backfeeding into the grid when they think the power is down. Apparently there was a legal case somewhere (Germany rings a bell) where an engineer did actually die as a result. Either way the point is your system is down during a power outage. Disappointing, but it is what it is. They are able to fit a socket to the battery/inverter (not sure which) to use as a backup with an extension cord I believe, but I didn't ask any further about this with my system as it's not of huge use to me.

I'm sure i read the Tesla power wall has the smart technology.
Can't remember too many power cuts, but who knows where we're heading on that score.

[Spud]

I've got a 4kw system that pays approx. £600 per year.

Yeah, I get around £400 from my 2.6kw system, plus what I save when they're generating.
No idea what rates are being offered nowadays, mine is 19p generation & 5p export.

[Superspy]

That's what I was told when I had mine fitted Spud - H&S risk of backfeeding into the grid when they think the power is down. Apparently there was a legal case somewhere (Germany rings a bell) where an engineer did actually die as a result. Either way the point is your system is down during a power outage. Disappointing, but it is what it is. They are able to fit a socket to the battery/inverter (not sure which) to use as a backup with an extension cord I believe, but I didn't ask any further about this with my system as it's not of huge use to me.

I'm sure i read the Tesla power wall has the smart technology.
Can't remember too many power cuts, but who knows where we're heading on that score.

Yeah, it may well have, I'm not sure, but then isn't the power wall something like 10k on it's own? Out of reach for a lot of people. As you say though - not many power cuts round here, that's why I didn't really look into that side of things any further, for me it was all about reducing bills over the long term.

[Superspy]

I've got a 4kw system that pays approx. £600 per year.

Yeah, I get around £400 from my 2.6kw system, plus what I save when they're generating.
No idea what rates are being offered nowadays, mine is 19p generation & 5p export.

These days you don't get anything for the generation directly - that was part of the Feed In Tariff stuff several years ago. Now it's all export.
Export rates vary from as low as 3 or 4p up to 15p with Octopus or 24p (I think) on the Tesla power plan - but you need Tesla hardware for that.

Personally I'm on the "agile" export tariff with Octopus where the export rate changes every half an hour. I've seen it as high as £1.80 a unit when there has been high demand on the grid, but most of the time it is much lower than that. Today for example the price is between 12p and 33p.

Overall, on my 7.3kWh split system, when you factor in the 3 ways of earning with it (export, reduced bills and Economy 7 charging) I've saved about 300 quid between mid September to the end of December - so just over 3 months. However, I wasn't on an export tariff until some time in November so the savings would have been higher than that, as I was exporting more in September/October.

[Superspy]

Thought I'd add a bit of info regarding the savings I'm making and where the numbers come from now that we've rolled into another month.

The image below shows where I've saved as a result of generated power I've used, power I've been paid to export, and the differential between a standard unit rate and what I've saved by charging the battery over night on the cheaper Economy 7 rate and then using that power through the day.



It's not a perfect formula as there are some nuances, but generally the calculations are:
- Generation: (generated units - units exported) * standard price per unit ignoring E7 savings (roughly 33p). September was low because I only got the panels fitted mid-month
- The export saving is simply the amount Octopus have paid me during that month, rather than using a formula, as it will all balance out over time anyway. December is high because there was a bit of energy trading going on where I was force-discharging the battery because they were paying up to £1.80 per unit for it (that was a fun couple of days). September and October show 0 because I wasn't on an export tariff at that time.
- TE7: (total units used * standard unit cost) - ((day units used * day unit cost) + (night units used * night units cost)). Or in other words, the difference between what I would have paid for all my grid usage on a standard rate, versus what I actually paid for the same usage split between the Economy 7 rates (as per my meter readings at the start of each month).

[BillyStubbsTears]

Thanks SS. Really useful stuff again.

Your electricity generation in winter is more than I've been quoted: It's very interesting to see real figures rather than a generic model.

It's all tipping me further towards going for solar this spring.

[Superspy]

Yeah - the biggest problem I had beforehand was finding real-world examples of actual systems rather than just stuff based on predictions and calculators.

For what it's worth, these are my total actual generation figures (in kWh) - so independent of unit prices and before exported units are taken off:

September (2nd half): 189
Oct: 299
Nov: 100
Dec: 69
Jan: 127

As mentioned before, that's on a 7.3 KW system, split between east and west facing, with some some shading on the west. I've nothing to confirm this but I read that the difference in energy that hits a south facing roof versus a 90 degree offset (east or west) is about 15%.

[danumdon]

SS, does force discharging of the battery have the same effect on it as accumulative charging, ie, in wear and tear on the battery over time, im asking because of the way the buy back scheme works with suppliers like Octopus Energy i would imagine this would be something you would do on a regular basis as and when the buy back price is elevated.

I just wondered if this would have a detrimental effect on your equipment or would the additional monies earned add to an overall gain over the lifetime of your generating and storage kit?

[Superspy]

I would assume the wear and tear is the same - in the sense that the battery doesn't care whether it's discharging because the house is demanding power, or because I'm telling the system to discharge to take advantage of higher export rates. I'm not a battery-tech expert, but I'd expect it's all just about the battery having a serviceable life in terms of number of charge/discharge cycles.

With that in mind it makes sense to make those cycles as financially beneficial as possible, so yes, unless somebody tells me otherwise, when the price is energy is high I'll discharge back to the grid and take the money for it.

Octopus release the following day's pricing at about 4 in the afternoon, so I tend to check it after that time to see if it's worth doing anything the day after. There's no point forcing it to discharge if the rates are below about 50p though, as 40p is the day rate so I'd pay that to import it back, and you get some losses over the system. In summer I may change approach as they'll generate so much energy I'll be exporting at some point during the day anyway, so it might be worth me tweaking it to make sure I'm discharging at the best time of day based on the pricing.

Tomorrow the highest rates are about 24p so I don't bother. And during the morning and early afternoon they're around 14p...which is less than I pay to charge the battery during the night, so I'll try to avoid exporting during those times if I can help it and make use of the power instead. Of course this only translates into a cost saving if you're actually using power you would normally use (just at a different time) - if you're using it for the sake of it then you aren't really benefiting.

[BillyStubbsTears]

Update after the first 10 days of my new panel and battery system.

It's still not even the equinox yet, but I've had 2.5kW peak power out of a 4kWh system.

The panels have been covered in snow for three days when they gave only minimal power. And the sun's only been out briefly over the last couple of weeks. But I've had 40kWh of solar production. That's about £13's worth at current rates.

And for the other usage, the batteries and the Octopus Agile tariff are brilliant. I reckon I've paid about 24p per unit on average, and saved about £6 on what I'd have spent on that electricity at a standard tariff.

So, £19 saving in the first ten days. In this weather. At this time of year. When I'm still getting used to running the system.

Very pleased with that.

[albie]

A new report looks at the combined savings from installing solar alongside a heat pump;
https://www.pv-tech.org/solar-pv-and-heat-pumps-can-cut-european-household-energy-bills-by-84/

This summary does not look at UK data, but Germany is included so that is the best for us to compare.

Significant findings, if this replicates across the sector.

[BillyStubbsTears]

03:30-07:30 this coming night, the Octopus Agile rate averages 15p/kWh. So a 10kWh battery can be charged to full for £1.50 rather than £3.30.

Small gains each day but I guess that's the idea. And at that rate, direct heating with electricity is getting close to being down to gas prices. Using electricity at that cost to power a heat pump would be way cheaper than using gas for heating.

[danumdon]

It'll be interesting to find out what sort of savings you start making when you start to plan your energy using activities around the peaks and troughs, could be some big gains to be made there.

[BillyStubbsTears]

It'll be interesting to find out what sort of savings you start making when you start to plan your energy using activities around the peaks and troughs, could be some big gains to be made there.

I think there's more to be squeezed out DD, but we've already started to get the main benefits of the battery by charging it at the times when tariffs are low and using it to power the house when tariffs are high. You can easily shave £1/day, day in, day out off your electric costs by just doing that.

With tonight's really low tariffs, that'll go up to £1.70-1.80, saving just by charging the battery up overnight.

As you say, you could get more out of the deal by setting the washer, dishwasher or even oven to come on overnight. I reckon you could probably work it to be able to save £1.25-£1.30 every day and upwards of £2 when the tariffs were very low. And that's before you factor in the free stuff from the panels and the export to grid payments.

It's not exactly life changing amounts but it's not bad as a constant saving.

[danumdon]

It'll be interesting to find out what sort of savings you start making when you start to plan your energy using activities around the peaks and troughs, could be some big gains to be made there.

I think there's more to be squeezed out DD, but we've already started to get the main benefits of the battery by charging it at the times when tariffs are low and using it to power the house when tariffs are high. You can easily shave £1/day, day in, day out off your electric costs by just doing that.

With tonight's really low tariffs, that'll go up to £1.70-1.80, saving just by charging the battery up overnight.

As you say, you could get more out of the deal by setting the washer, dishwasher or even oven to come on overnight. I reckon you could probably work it to be able to save £1.25-£1.30 every day and upwards of £2 when the tariffs were very low. And that's before you factor in the free stuff from the panels and the export to grid payments.

It's not exactly life changing amounts but it's not bad as a constant saving.

Yes, on those figures you could end up saving up to£100 a month for the winter autumn part of the year, when you compound that over the year on year costs that's some decent saving to be had, if the price cap goes up again next winter then the savings will make a big difference.