The Solar Thread

How is that possible with a 3.6kW inverter?

I’m wondering if the figures being produced are for the power being generated by the panels – not what is actually sent out of the inverter.

If so that’s a little bit crafty (you could have a load of panels producing, say, 7Kw but you’d still only get 3.6kW to use)

That’s a good price @Wooksterbo.

The optimisers alone will be ~£1000, the panels around ~£2500, the inverter around £1500, the charger £800, + other materials @ £300-£500.

Totally naive question here, what’s the longevity of panels, inverter, etc. Are they likely to fail before they’ve achieved payback?

@dooosuk Panels I got quoted for have 12 year product warranty and 25 year linear power output warranty.

The most likely thing to fail is the inverter and most have a warranty of 10 years. Panels are cheap. Batteries are the great unknown. MY ROI is 7.5 years with the battery, at the current energy prices and assuming we can charge from the grid, off peak in the winter, but we use 6500kWh of electric per year. So assuming it lasts 10 years, it’ll save me ~£6500 over the same period if nothing goes wrong, but it’ll also be much sustainable and stable than it is now and that’s quite important to me.

I have just received a quote from GenFit

9 grand for 15 Longi all black panels + 15 SolarEdge optimizers + Invertor etc

@wooksterbo that’s a fair price. Genfit did my installation almost a year ago and estimated I’d get 5MWh per year and I’m as near as dammit going to get that. I can also vouch for the competency of their installers. In fact I had no hesitation in going back to them for an additional array

Cheers @uponthedowns
What was the lead time after ordering?

@wooksterbo they had panels and inverters essentially in stock in 2021 and for my second array, installed June this year, which is 6 x Longi black panels with a Solaredge inverter they basically had those in stock too. As for lead time for the installation the first array went into a new roof and the second into a new garage so they worked around my builders schedule. I can’t comment on what they charge for scaff as they used my builders scaff.

Cheers. Scaffolding quote seemed reasonable in all honesty. I just need to get my head around the export to grid percentage vs home use now.

You want to minimise any export as on a normal export guarantee you’ll be getting about 4p per kWh from your supplier who will then sell it back to your neighbours for 30p per kWh. That’s why its worth considering a solar diverter to heat your water and/or home battery storage. If you have an EV parked in the drive during the day that could soak up excess generation too but it sounds from your earlier post that’s not on the cards quite yet. BTW charging an EV at 30p per kWh is still way cheaper than running an ICE car. Even at the 34p per kWh that their suggesting will happen in October its still way cheaper. Oh and I have the Zappi charger and can recommend that also.

Can I stipulate how much goes to the grid, regardless of home battery or water heater? We have a combo boiler so unfortunately we can’t divert energy to a water heater.

Not as far as I’m aware – everything you don’t use will go to the grid.

Unfortunately PV and hot water tanks are a match (almost made in heaven).

Use it or lose it!

Is there any reason why an unvented hot water cylinder (with heating from an immersion heater) couldn’t be used as the water source for a combi boiler? I mean, a combi takes in cold water from the mains at whatever temperature that happens to be and just supplies heat to boost it up to the set temperature. Would it really care of it was receiving its feed at, say up to 60C? Would be important to ensure that the cylinder gets up to temperature once in a while to prevent nasties like Legionnaire’s disease, but that wouldn’t be too hard.

Is that crazy? Obviously an alternative would be to just switch the combi for an unvented system, but there must be loads of people like me who have a modern combi already, but are considering PV panels and have space in a loft that could hold a modest cylinder with just a mains feed and return, and a cleverly controlled immersion. I guess it’s probably just not worth it for the amount we spend on gas powered DHW… OK waffle end.

You can use pre-heated water from a hot water tank to feed a combi boiler. We looked into it when considering whether to install solar thermal when grants were available a couple of years ago.
It depends on your combi boiler. Our British Gas branded Worcester Bosch was OK. There may be a maximum feed temperature.
Solar PV and immersion heater would work similarly.
We didn’t go for it in the end due to the upheaval of finding tank space etc. but not fully ruled it out for future.
Some more info here:

How to benefit from solar hot water with a combi boiler

Can I stipulate how much goes to the grid, regardless of home battery or water heater?

No like sharkbait said any excess goes back into the grid unless you can find a way to use it. For example its nice and sunny here today and my Powerwall will be fully charged by lunchtime, despite the dishwasher running, but after that the Zappi will divert any excess generation into my EV.

I’m getting a little tired of exporting 10kWh to the grid every day in exchange for sweet FA, so have added a WiFi connected smart switch to the immersion heater. When the solar export goes above 1kW, it’ll start cycling the immersion heater on a 30% duty cycle. It’ll tap a bit off the batteries, which will then recharge during the off cycle.

This has a payback time in a matter of weeks, as opposed to the various other solar diverters which are years (if ever).

Also added an intumescent pad to the back box since I trust cheap Chinese-made electrical items about this much 🤏, so that was another tenner.

Is it just me or does that link go to read.amazon.co.uk?

Ok cheers guys. GenFit also quoted for a Solaredge 10KW battery for an extra 7 grand. No idea on whether to get it or not just yet. I’ll also look into a hot water tank and plumbing in to the combi boiler too.

If you can’t time shift your high power usage like washing and cooking to the middle of the day you could well, worst case, lose 50% of your solar generation to grid. Given Genfit are predicting 5.54MWh annual production thats about £800 per year so 9 year payback for battery at todays prices. 10kWh battery is a decent size and would probably cover most of your daily requirements and would let you make use of a time based tariff to charge the battery at night for daytime use bringing the payback period down a bit. Time to get some old envelopes out.

We also inherited solar panels and the FIT payments are about £600. Had anyone had them cleaned and saw an increase in payment? Hard to judge due to the amount of sun, but we’re considering having ours done

Unlimited information and advice on Youtube but I have found this channel helpful, among others.

Gary does Solar

When the solar export goes above 1kW, it’ll start cycling the immersion heater on a 30% duty cycle

Any link @flaperon

When the solar export goes above 1kW, it’ll start cycling the immersion heater on a 30% duty cycle.

@flaperon
Can you clarify this – are you saying that you’re only putting 1kw into the hot water?
(And how?)

I have something similar where the a raspi checks the amount of power being generated and if it’s over a certain level (and the hot water tank is above a certain temperature) then the electric underfloor thermostat is set to 25c using IFTTT. It’s checks every few minutes and sets the thermostat back to 10c when the generation drops.

It only runs at certain times of the day and there’s quite a big margin of error built in to the power level so it shouldn’t pull too much power from the grid of the generation suddenly tanks.
But in only dealing with 800w, not 3kw!

Personally, for hot water diversion, I’d go with a dedicated hardware solution for a few reasons:
They work continuously, rather than a script that checks every 5 minutes or so.
They will put a variable amount of power into the tank dependent upon the spare generation, rather than the full 3kw or nothing.
When the tank is hot some systems will send spare power to a second (and maybe even a third) destination. My Immersun sends excess to a dedicated room heater once the water is hot – and can send it to third destination as well if required.
With regards to payback, according to the numbers it’s supplying, it’s paid for itself many times over.

When the tank is hot some systems will send spare power to a second (and maybe even a third) destination

This is something I am trying to get my head around and a possible supplier is just saying yes, but at the moment not convinced.
For me:
Solar generation is used there and then
Spare goes to recharge battery
After that to recharge EV if connected
After that iBoost to heat water
Only then back to grid

Not sure if this is all achievable particularly as different manufacturers…

Anybody doing the same/similar???

Can I ask a question from you solar experts

I bought a new build house with solar panels on the roof about 4 years ago.  Nothing was really said about them and I wasn’t bothered about what they did.

Now I have an interest in what they do!  I never signed up for any fit tariff and there’s no battery in the house so I’m assuming for the last 4 years everything they have generated has gone straight the grid for free.

What do I need to do to use this capacity for house?  There are panels on the roof, an invertor in the loft and some kind of meter by the fuse board that look like this

Panels are apparently 0.75kw

Complete novice to all this, but if it’s there I’d like to use it.  Cheers

You’ll be using that at source.

The mention of installed under competent persons scheme worries me if you are thinking export as that suggests its not got MCs paperwork which cannot be had retrospectively. (Nor is it a legal requirement but it is required by SEG accounts)

The good news about that is that 0.75 of panels would create about 12 quid a year in payments.

I’m guessing it’s a new build ? – they often fit token number of panels to get the EPC down without putting in the requisit insulation to get to that level. (Ie above building standards minimum) – the panels are cheaper…..

Solar generation is used there and then
Spare goes to recharge battery
After that to recharge EV if connected
After that iBoost to heat water

So an Immersun should do this:
“Heater 1” would be the battery.
When that stopped accepting power it would send it to the car (heater 2) – if that was full or not connected then it would go to the hot water (heater 3)

Great piece of kit if you can get one.

User guide

(They call them “heaters” but it can be anything inductive)

What do I need to do to use this capacity for house?

If you don’t have a hot water tank then there’s not a lot you can do.
If you do then you could fit a diverter to take spare power and send it to the tank – but you’ll not be sending much they’re with 750w of panels 🙁
Is there from for more on the roof?

They call them “heaters” but it can be anything inductive)

Just to clarify this – it can be any resistive load. Do not connect a car charger to this thing, you’ll break it.

Yep, sorry….. Resistive load 🤦🏻‍♂️

But it could feed something like a Zappi car charger that handles variable (solar) feeds and makes up any shortfall from the grid.

@kato, at 0.75kW installed capacity it looks like you have 2-3 solar panels on your roof (?) so I think its quite a small system (I’m doing some maths in my head about installed capacity vs the estimated annual generation) . Your panels should be feeding power initially into your house and any excess is then fed to grid but I would expect at 0.75kW most, if not all, of the power generated would be used by your home and you would still be primarily using power supplied from the grid during the day with the solar adding to this.

You’re correct that, unless you have Smart Export Guarantee (SEG)set up with a power supplier (the FIT scheme is now closed), you would be sending any excess generated power to the grid for free so yes, its worth getting this set up. It looks like you have the installation documents so you should be able to do this (can anyone else confirm that this is correct as I am currently waiting on my installation certificate to do the same)

A battery might help but with a small system I am not sure it would charge enough during the day to be effective, others here would know more than me. You may need a box added to the inverter to allow a battery to be installed too so check with an installer.

However, the thing I would suggest first would be checking with a solar installer about the potential to add more panels to your system. Main question is : does your roof have space for more panels to be installed and does your inverter have the capacity for this?

Sorry my bad. It’s right at the top that is an MCS cert. Missed that.

Mine doesn’t look like that. It’s got a much bigger MCs header like below. It also looks like they have forgot to edit their template and add in the actual details….. I’m still sceptical that’s an actual MCS cert….

So yeah you do have the paperwork for export. It’s a good thing if your out all day. It’s not much but it’s better than giving it away for free. If your an octopus customer you can get 15 p SEG fixed currently.

A 0.75kw installation won’t cover the cost of the inverter!

The inverters have quite a short lifetime and it will probably cost more to replace than the power generated.

Although this may be not be true as their lifetime may be based on much power goes through them.

IANAEE.

Either way, I would be looking at more panels.

But it could feed something like a Zappi car charger that handles variable (solar) feeds and makes up any shortfall from the grid.

The Immersun is, I assume, rectifying AC to DC and then inverting back to AC to control the load via PWM. I don’t know how a car charger would tolerate this but my guess is “not well”.

So an Immersun should do this:

Thanks I will take a look at that. The issue is (and I assume many people have it) that suppliers have a kit list they can source and fit easily, introducing an alternative doesnt appear to be an option. I will discuss it with them at survey.

I’ll find out as a friend has PV and a Zappi which seems to work very well.

I see that the Eddi diverter looks remarkably similar to the Immersun and is probably an updated version.

Ah cheers gents.  Yeah I think there’s 3 panels on the roof.  Every house here has them, I guess all new builds are required to have them.  There’s plenty of space left on the roof, so I might look into the cost of upgrading everything

so I might look into the cost of upgrading everything

Check the capacity of your inverter, it may be able to handle a typical 3.7kw domestic install. If it can then an upgrade will a lot cheaper.

Check the capacity of your inverter, it may be able to handle a typical 3.7kw domestic install.

We have a 4Kw Growatt inverter…. It’s bigger than that.
I suspect it’s a 2Kw model (I think inverters are supposed to be sized to the potential generation – so you probably wouldn’t fit a bigger inverter than necessary.
Costs more too)

Bigger the inverter the bigger the minimum start up needed from the panels so unless you planned an upgrade quickly you wouldn’t do it.

Afternoon ladies and gentlemen, had any one got any company recommendations for installers in the Worcestershire area?