Circular reasoning (Rolfe's solar energy system)

[Bam Bam]

Thanks for all the input. Could anyone specifically clarify two things.

First, how come the projected payback time is less than the time it would take me to pay the capital cost for electricity at my current direct debit rate, and

Second, given that solar generation only really happens in the summer, how is it possible not to rack up a lot of expenditure from the grid in winter?

Not sure I've understood your questions.

1. Does the projection assume that you will cash in some of the credit? You can get an income during the Summer from selling the electricity, though if you keep it as credit you won't have to declare it for tax purposes (at least that is my understanding).

One company was convinced we should get much more solar and battery than the others. I looked through their spreadsheet and they were assuming that energy prices would continue to rise at pandemic rates forevermore. Perhaps they will but it seemed like a big assumption to me! I now wish I had got as many panels as they suggested, though not the expensive powerwall.

2. We built up around £300 credit last summer and gradually got through it over the winter. Having the battery is great for savings sessions in the winter as well - full export and you are paid handsomely.

 

[Rolfe]

What you have said has answered the second question, I think. I'm still a bit hazy on the first.

If I go for this, and it's looking more likely than not, I will get the 18 panels suggested by the installer.

 

[Bam Bam]

What you have said has answered the second question, I think. I'm still a bit hazy on the first.

If I go for this, and it's looking more likely than not, I will get the 18 panels suggested by the installer.

18 panels is a very decent amount if south facing. We have East-West so get about 80% of a South array over the year.

You could interrogate their numbers if they haven't provided you with the full breakdown:
1. Are they assuming you will be selling your summer surplus and getting an income from it?
2. Are they assuming future increases in energy prices in their calculation? (That might happen for various reasons like devaluation of the pound, but who really knows?)

 

[Rolfe]

Honestly, there's pages and pages of technobabble there. This is the relevant page I think. They're only talking about the payback time for the panels themselves. The installer says the standard calculations for the full system don't cover systems expected to generate over 6,000 kwh pa, but he estimates the payback for the full system (including battery etc) to be 6-7 years. The array is to be on a roof that faces slightly east of south.

As my current electricity use is about 6,000 kwh pa another thing I'm struggling with is how it works when I'm generating more than I use from solar alone, but of course mostly in summer when I'm using less. I suppose there are some big assumptions about getting paid to export surplus to the grid in the summer, building up credit, and living on that over the winter as Bam Bam said.

 

[salty]

Honestly, there's pages and pages of technobabble there.

On this thread, agreed, I'm totally lost.

 

[Bam Bam]

Honestly, there's pages and pages of technobabble there.

Well we contacted 6 or so companies and three quoted. Was hard to get quotes at the time as the companies had big backlogs and there were supply chain problems.

Went for the cheapest option and they delivered - eventually.

Your quote sounds reasonable to me, but you could seek out a few more and see what they suggest.

 

[Rolfe]

This guy did my next-door neighbours in an identical (mirror-image) house a year ago, and they're happy with him. The quote is about par for the course. I'm inclined to go for it, as my neighbours did all the multiple quotes and so on, and picked this one. Why keep a dog and bark yourself?

 

[SimonS]

When spec'ing a new install I would insist on the following:

1. A charger that is compatible with IOG (currently the Zappi and Ohme).
2. The charger to be wired from its own separate consumer unit which is fed direct from the supply meter.
3. All communications from charger/inverter/battery etc to be hard wired via ethernet.

Reasons. Do some reading around Forums, Facebook etc and you will soon realise that there are way more issues with vehicle to IOG integrations (and with other electricity suppliers) than with the charger. If you integrate the car you are adding two extra layers of complexibilty. Firstly the control needs to go via the car manufacturer's servers and secondly from these servers to your car via mobile data or your wifi. The one plus side to this is that you can use any charger.

Integrating with the charger means the control signals either go from the supplier to the charger direct or via the charger manufacturer both of which have a vested interest in keeping your systems working and with ethernet to the charger the mobil network and wifi are eliminated from the system.

On Forums/Facebook you will see with monotonous regularity people ask why their charger 'stole' all the electricity out of their battery. Having the charger on its own consumer unit means the Grid CT clamp can be placed between the two consumer units so that a house battery system (if fitted) will not see any current drawn by the charger and you with avoid the house battery being drained.

NB You can ignore this is you have a Zappi/Libbi system as they will communicate with each other to avoid this draining the battery.

Again, comments about communication problems usually come down to owners being overly optimistic about the quality and range of their wifi signals. Wire everything back to your router with ethernet if you want a trouble free installation.

 

[GaryMG4]

Honestly, there's pages and pages of technobabble there.

As my current electricity use is about 6,000 kwh pa another thing I'm struggling with is how it works when I'm generating more than I use from solar alone, but of course mostly in summer when I'm using less. I suppose there are some big assumptions about getting paid to export surplus to the grid in the summer, building up credit, and living on that over the winter as Bam Bam said.

I've had a look at our quarterly generation figures for a sample year.
Spring 700kWh, Summer 1800, Autumn 1000 and winter 300. So, sadly it is probably the inverse of your consumption.

 

[Bam Bam]

I've had a look at our quarterly generation figures for a sample year.
Spring 700kWh, Summer 1800, Autumn 1000 and winter 300. So, sadly it is probably the inverse of your consumption.

I put the stats of our first year here and you are right there is a slight inverse of consumption (though we got a dehumidifier and EV in January which account for an increase in consumption).

First year of solar generation

We had out solar and battery system installed a year ago and so I thought I would share the stats! Yes, we generated 4.64 MWh and we use...

dougstaxappeal.blogspot.com

If you are getting credit for the Summer generation that you can use in Winter it doesn't really matter if they don't match up.

This guy did my next-door neighbours in an identical (mirror-image) house a year ago, and they're happy with him. The quote is about par for the course. I'm inclined to go for it, as my neighbours did all the multiple quotes and so on, and picked this one. Why keep a dog and bark yourself?

That is reassuring if the company did a good job with your neighbour and your system would match theirs. Ours were the cheapest quote but poor communication/customer service.

 

[Rolfe]

When spec'ing a new install I would insist on the following:

1. A charger that is compatible with IOG (currently the Zappi and Ohme).
2. The charger to be wired from its own separate consumer unit which is fed direct from the supply meter.
3. All communications from charger/inverter/battery etc to be hard wired via ethernet.

Reasons. Do some reading around Forums, Facebook etc and you will soon realise that there are way more issues with vehicle to IOG integrations (and with other electricity suppliers) than with the charger. If you integrate the car you are adding two extra layers of complexibilty. Firstly the control needs to go via the car manufacturer's servers and secondly from these servers to your car via mobile data or your wifi. The one plus side to this is that you can use any charger.

Integrating with the charger means the control signals either go from the supplier to the charger direct or via the charger manufacturer both of which have a vested interest in keeping your systems working and with ethernet to the charger the mobil network and wifi are eliminated from the system.

On Forums/Facebook you will see with monotonous regularity people ask why their charger 'stole' all the electricity out of their battery. Having the charger on its own consumer unit means the Grid CT clamp can be placed between the two consumer units so that a house battery system (if fitted) will not see any current drawn by the charger and you with avoid the house battery being drained.

NB You can ignore this is you have a Zappi/Libbi system as they will communicate with each other to avoid this draining the battery.

Again, comments about communication problems usually come down to owners being overly optimistic about the quality and range of their wifi signals. Wire everything back to your router with ethernet if you want a trouble free installation.

Perhaps I should bounce this off the installer. He is quoting for a Zappi and it is a Zappi that my neighbours have, but I don't know what a Libbi is.

 

[Archev]

Perhaps I should bounce this off the installer. He is quoting for a Zappi and it is a Zappi that my neighbours have, but I don't know what a Libbi is.

I think the Libbi is the storage battery made by Myenergi.

 

[GaryMG4]

I put the stats of our first year here and you are right there is a slight inverse of consumption (though we got a dehumidifier and EV in January which account for an increase in consumption).

First year of solar generation

We had out solar and battery system installed a year ago and so I thought I would share the stats! Yes, we generated 4.64 MWh and we use...

dougstaxappeal.blogspot.com

If you are getting credit for the Summer generation that you can use in Winter it doesn't really matter if they don't match up.

My panels have been in for 9 years now so I'm fortunate to be on the FiT scheme. because the panels were there when we moved in I don't have an idea of our actual consumption, only what I have to pay for. When we moved here the FiT payments covered our total electricity bill but the hike in prices means it was less than half at the peak closer to 3/4 currently.

 

[SimonS]

Perhaps I should bounce this off the installer. He is quoting for a Zappi and it is a Zappi that my neighbours have, but I don't know what a Libbi is.

As Archev has said, the Libbi is Myenergi's battery system. Having a battery and inverter from another manufacturer is not a problem and long as the charger and CT clamps are installed correctly to avoid battery drain. The installer should be aware of this.

https://support.myenergi.com/hc/en-gb/articles/4716922623633-Hybrid-PV-Battery-Set-up-Avoid-Draining

 

[Rolfe]

I've pretty much made up my mind to accept this quote, as it seems reasonable, the installer seems knowledgeable, my neighbours are happy, and he says he can start work in 4-5 weeks if I order now.

He was showing me his phone with current prices from Octopus Flux while he was looking at the job, and is quoting for a Zappi.

The panels are Trina Vertex S
The battery is GivEnergy Giv-Bat 9.5
The inverter is also GivEnergy hybrid inverter 3.6
There is also a MyEnergi Eddi microgeneration energy diverter

If anyone has any experience of these things, or any comment, fire away.

 

[Bam Bam]

I've pretty much made up my mind to accept this quote, as it seems reasonable, the installer seems knowledgeable, my neighbours are happy, and he says he can start work in 4-5 weeks if I order now.

He was showing me his phone with current prices from Octopus Flux while he was looking at the job, and is quoting for a Zappi.

The panels are Trina Vertex S
The battery is GivEnergy Giv-Bat 9.5
The inverter is also GivEnergy hybrid inverter 3.6
There is also a MyEnergi Eddi microgeneration energy diverter

If anyone has any experience of these things, or any comment, fire away.

Oooh you're getting an Eddi as well - that increased our quote substantially so I didn't bother with it. We came up with our own hot water solution which is working as intended but probably not worth the hassle we had to go through.

Givenergy works well for us.

The only thing I would query is whether you will get much clipping with the 3.6kw inverter.

Installers like the 3.6kw because they don't have to do as much paperwork.

I asked for a 5kw (it is only £40 more expensive) but that created a lot of extra delays! If there were delays then you'd then be missing out on the fantastic generation over the Spring and Summer.

On the other hand, in the winter the 3.6kw might be better though and in the Summer you'll have loads of generation so I doubt it is a major issue.

So I would say go for it, but check you are getting a recent generation (ie Gen 3) GivEnergy inverter.

 

[SimonS]

Two suggestions. Firstly, I would go for a 5kW inverter which will only add £150 or so. With a 3.6kW you will be drawing from the grid when you turn on the oven and the hob or kettle. We have a 5kW and it's very rare that we exceed that during the day when drawing from the battery but regularly get above 4kW.
Secondly I would question if you need the Eddi. We have one and before we were registered for export we used the Eddi to divert solar to the immersion rather than giving it to the grid. Now we have the battery and an export tariff. we send as much solar as possible to the grid as Octopus pay us 15p/kWh. We rarely use the immersion now as it is more cost effective to use gas. If you are not on mains gas then your priorities might be very different.

Something else to add... Do you have a smart meter? If not, it's easy to get one fitted (usually no cost) but allow a couple of months as there is a backlog.

 

[Bam Bam]

Two suggestions. Firstly, I would go for a 5kW inverter which will only add £150 or so. With a 3.6kW you will be drawing from the grid when you turn on the oven and the hob or kettle. We have a 5kW and it's very rare that we exceed that during the day when drawing from the battery but regularly get above 4kW.
Secondly I would question if you need the Eddi. We have one and before we were registered for export we used the Eddi to divert solar to the immersion rather than giving it to the grid. Now we have the battery and an export tariff. we send as much solar as possible to the grid as Octopus pay us 15p/kWh. We rarely use the immersion now as it is more cost effective to use gas. If you are not on mains gas then your priorities might be very different.

Snap!

Eddi ?
I know what you mean about the Eddi, I didn't go for it myself, but in the future I think there will be more of the 'free green electricity sessions' where you get free energy at times of plenty (windy and/or sunny).

A smart device like an Eddi could potentially just dump some of that lovely free electricity in the hot water and save the need to buy gas.

5kw?
You've also given @Rolfe another reason to ask for a 5kw inverter, though that would cause delays.

You might be right about the extra cost being more than the difference (£40) - it might require thicker cabling as well for all I know.

Worth asking the installer what the pros and cons are of going for the 5kw instead I think.

 

[Rolfe]

Thanks for all that. I already have a smart meter.

The Eddi, with built-in wifi and ethernet, is only adding £410 to the cost. I wasn't sure about it, but it's not a huge amount, and another neighbour (not the neighbour who recommended this installer) spontaneously said to me that his installer had fixed it so that excess solar went to his immersion heater and he thought it was a great idea.

The inverter is a Gen 3. I can ask about the 5 kw part.

I'm not on mains gas, my heating comes from a tank of kerosene, and sparing the usage of that would probably be worth it both in terms of saving a bit on the oil bill and enhancing my green credentials. I'm also going to look at some way to use some surplus to heat somewhere, maybe the main living room, though I don't know the practicalities.

 

[SimonS]

Thanks for all that. I already have a smart meter.

The Eddi, with built-in wifi and ethernet, is only adding £410 to the cost. I wasn't sure about it, but it's not a huge amount, and another neighbour (not the neighbour who recommended this installer) spontaneously said to me that his installer had fixed it so that excess solar went to his immersion heater and he thought it was a great idea.

The inverter is a Gen 3. I can ask about the 5 kw part.

I'm not on mains gas, my heating comes from a tank of kerosene, and sparing the usage of that would probably be worth it both in terms of saving a bit on the oil bill and enhancing my green credentials. I'm also going to look at some way to use some surplus to heat somewhere, maybe the main living room, though I don't know the practicalities.

Without mains gas then I agree that the Eddi is a good idea.

Re the inverter, 3.65kW would be a 'G98' approval which basically means that you only have to tell your DNO that you are installing it. For a 5kW it becomes a 'G99' which means you have to ask permission which can take a bit longer. Your install can give you more details.