One family's solar story

[Sideways]

Oversize battery, oversize array.

It's 4th Feb and we've been self sufficient for electricity for the last 6 days ! Even in northwest UK.
The battery may tap out tonight as we are down to 36% and generation today is only enough to keep up with the background demand but the next two days are forecast to be bright.

Running the oven for about 45 mins at 200/180C last night used up about 10% capacity. For a
3.6kW rated oven, 1.6kWh used sounds about right. You can see this really clearly on the right of the consumption / battery SOC graph from 7pm

This stuff is frankly nerdy and I'm sure that we will "grow out of it" but it is very easy to check the app and see where we stand for reserves.
With both of us in our 60's and retired / working part time, we have the freedom to adapt to the weather. Just as gardening and outdoor DIY get fitted around the weather, the laundry is going to wait a day to take advantage of the promised sunshine tomorrow
Small changes to routine like this are proving easy to do

 

[Pabs]

thankyou, @Sideways - you've managed to condense both an involved and evolving technology in a very clean manoeuvre. Definately something wifey and me have been talking about for some time. Even on a mini scale for an occasional garden room at first I think the theory can be adapted.



p.s no pun intended for 'clean manoeuvre' btw.

 

[Sideways]

Nearly three months on since our battery was fitted and the job officially completed,
In January, our generation wasn't quite enough to meet our electricity demand and we had a number of occasions where the battery ran dry overnight, we still achieved 60% self sufficiency for electricity.
Feb we were 98% self sufficient, and in the entire month only used a total of 15kWh of energy from the grid, plus gas for the heating, cooking and DHW of course
Mar has been 96% self self sufficient, but with the weather getting brighter we made 80kWh of additional energy compared to Feb, most all of which went into the solar diverter and gave us 20 baths courtesy of the sunshine.

An interesting, slightly frustrating issue has become clear since January. Locally, the electrical distribution co. run the grid at well above the nominal 240V.
The permitted tolerance allows the grid voltage to be up to 253V but this is exceeded (briefly) most days, usually three or four times. When this happens, my inverters follow their design specifications and shut down because of the overvoltage, then restart. It is all perfectly controlled, but it's a bit annoying as this can happen when we are using 100% of our own energy charging the battery so we know we are not exporting anything and not contributing to this increase in the grid voltage.
I'm licensed to export all of our 9kW generation but as long as the grid is wired "hot" like this, there is no way that the grid can accept it.

A chance conversation with two of the electricity DNO's engineers I saw working on the local substation suggests that this is a widespread problem. They remarked that where customers used to complain about low voltage, they now complain about high voltage and the engineers are having to tweak the substations to try and lower the voltage they produce. People with EV car chargers are seeing the same problem that I do, because their car chargers automatically switch off when the supply exceeds the 253V maximum. I don't know why the DNO have adjusted the network to run (in our area) at an average closer to 250V than 240V, but it can't be an easy fix as they are advising the EV owners to contact their installers and have the overvoltage cut out increased all the way up to 260V to stop them tripping out.

It's not quite that easy for me. If I were to make that same adjustment I could actively contribute to other people's trouble as I generate energy,, I don't just consume it. This is all relatively subtle stuff that normal folk don't have the tools to observe, but it does hint at the challenges the DNO must face keeping the electricity network balanced in the face of the renewable energy changes without / while spending a fortune to upgrade the copper cables everywhere to deliver more and more energy through the grid.

Nevertheless, this is only an inconvenience. The principle of "you make it, you use it" still works for me.

 

[RogerS]

Cracking thread, thank you.

A couple of questions, if I may. I may have missed it but how much has this cost ? Have you calculated a payback time ?

Also, what sort of supply to the grid do you have ? Typically like a 'standard' house or out in the sticks with overhead wires and poles ?

 

[Spectric]

@Sideways for you the increased cost of electricity is a bonus because you will now be saving more and reducing the payback period, as you say the biggest unknown is the battery life which only time will tell.

I can see your issues with the grid supply, 230 volts at -6% to +10% gives you 216 volts to 253 volts and I have seen this problem more often in power supplies and large UPS systems when the voltage dips and you get a brownout but they handled the overvoltage. I can also see why the grid is having issues because originally all the DNO's were supplied by the national grid and now they have local input from windfarms and such so a more complicated setup and it will not just be the voltage but also the phase. I do wonder how much thought has been put into the issues with the added loads of EV chargers and maybe this will bring the voltage down.

 

[Sideways]

Cracking thread, thank you.

A couple of questions, if I may. I may have missed it but how much has this cost ? Have you calculated a payback time ?

Also, what sort of supply to the grid do you have ? Typically like a 'standard' house or out in the sticks with overhead wires and poles ?

Cheers Roger
This is a typical residential setup with the supply coming in on an underground cable, a bakelite termination with the same 60 amp fuse that has been there since '78.
Something I had not realised is that my supply cable loops in from the neighbour's identical house and goes from their garage down the drive to the manhole in the pavement. I discovered this through the G99 application process.

The full system has cost about £24k
£22k to the installer for supply and fit
A couple £k more to cover the myenergi solar diverter components which I bought and fitted myself, the supply and fit of a replacement consumer unit (20x RCBOs) and the G99 application which cost about £450 of it.
The price feels fair for what I have. Covid supply chain issues contributed 10% or so of this cost by inflating component prices and the sizing of the system that *just* pushed me into having two inverters accounts for about £1300 of it that I didn't originally intend.

It's a load of money but a project that we've wanted to do for years and are at the age to do it and benefit from it.
I'm convinced that it will pay back because I bought components built to last, but I look at it more like a 10 - 20 year electricity prepayment plan, not a financial investment. Looking at it this way, the upside is the surplus energy that it provides across 6+ months of the year which equals a lot of hot water and reduces our gas bill, could run a summer air conditioner, that sort of thing.
I don't consider payment for exports at all in my thinking because that pays so little.

 

[Sideways]

@Sideways I do wonder how much thought has been put into the issues with the added loads of EV chargers and maybe this will bring the voltage down.

I am sure there are engineers working hard on a rolling programme of "network reinforcement" to upgrade the grid as we demand more from it. This was inevitable. I've seen estimates that it will need to carry between 300 and 500% more power as we shift to electric cars, heat pumps, etc. That's huge and will limit the rate that we can adapt whatever the politicians say.

There was an expert review into the subject a couple of years ago which made several recommendations including relaxing the voltage limits further than the -10/+6 today as this would allow the grid to be worked harder and a few £bn of upgrades delayed for 5 years.

European harmonisation of voltage is 230V +/- 10%. We don't use that full range of tolerance in the UK but we probably could. If the voltage at our 3 pin plugs were to fall to low 207V the cooker, kettle and microwave would all take a little longer, but our TV's would be happier and with LED bulbs we might not even notice the lights dim the way they did when we were kids.

Interesting geeky fact: the grid adapts automatically to maintain voltage within the permitted range. It has to, ohms law and all that: the more current we all draw out it, the more voltage is "dropped" across the wires from the substation to our houses which takes away from the voltage that we can measure at our 13A socket. The adjustment is made by changing the "tapping" on transformers to alter the voltage into each local part of the grid.
A housing estate like ours is fed at 11kV and a local substation shifts this down to 240.
A larger district is fed at 33kV and a higher level substation drops this down to 11kV to feed many local substations.
Automatic voltage adjustment only happens at the 33-11kV substation covering a huge number of homes, so there will always be winners and losers. I think we find ourselves living at the hot end, nearer the big substation and that's the reason we see such high voltage. One of our regular peaks happens at 1am in the morning. I guess that's a time when the substation "tap changes" to up it's voltage ready for all the EV chargers switching on for their overnight charge. We see more spikes early morning as the EV load turns off before the substation reduces voltage again.

 

[Spectric]

Yes I think most people just see the grid as lengths of wire connecting them to some generating plant somewhere and really have no clue as to the actual complexity of how it all interconnects. The other aspect which is invisible to end users is the protection systems to protect the lines, busbars and transformers which is actually a fascinating subject in itself and mostly only possible because we use an Ac grid. Maybe the future for the high voltage grid is really Dc which reduces the number of lines as you no longer have the three phases. A major project that went for Dc transmission is the Chinese five gorges transmission lines running at plus and minus 500Kv and delivering 3000 Mega Watts so another good example of why we cannot always say that chinese products are tack.

At the moment I think we are just firefighting to keep the lights on but for the grid to handle even 300 % extra load will mean a massive upgrade starting at the top and working all the way down involving new lines and transformers and at what cost, that will be some stumbling block and who is going to pay ! Then in some places do they have the space to accomodate the larger substation footprints, i don't think many of us older folk will see any major changes in there lifetime because there are to many issues all requiring capital expense.

 

[deema]

@Spectric Eddison will have a wry smile in his grave whilst Tesla will be turning at the thought of DC winning through over AC!

 

[Spectric]

This is a good example of how as technology advances what was once thought of as the only option has been superceeded so Tesla was right at the time but Eddison will finally win through . Ac is great for anything needing a time changing magnetic field such as motors but not so good for high voltage transmission but back in the day they had to use it because there was no easy means to convert Ac to Dc and back to Ac. A dc system is much better when you have multiple sources of generation like we are now seeing, you don't have any issues with phase and no parastic reactances on the long runs of overhead lines but gone will be the days of the distance relay that uses impedances to monitor lines for faults.

 

[RogerS]

.....If the voltage at our 3 pin plugs were to fall to low 207V the cooker, kettle and microwave would all take a little longer, ...

Yup. And the Blue Smoke Fairy would wake-up as my motors burned out in my woodworking machinery because they couldn't get up to speed fast enough.

I know what it's like, believe me. Our house is effectively fed by a 1/3 mile extension cable...courtesy of a tight-fisted a*****le of a farmer and his BiL when the place was renovated in 1978. Not helped by them using an undersized cable. They got round it because the transformer on the pole feeding the other two properties up here had very generous tappings and so the voltage at the transformer had been increased to 260v and so my Hammer C3-31 was a Happy Bunny.

Then the ladies in the Lodge renovated their kitchen and installed a Miele dishwasher. Which complained after a few days. When the Miele engineer arrived, he measured the voltage. Formal complaint made to Northern Powergrid. Result ? New transformer. I explained to the linesman as the engineer was elsewhere, my problem and asked if the engineer could increase the tapping to give the allowed 253v which would have given me a fighting chance. When power was restored after the work, to my horror I found that Jobsworth had stuck it at 230v and refused to change it. My nickname for him rhymed with banker.

Took a long time and a lot of persuasion at Director level but eventually got it increased. Thanks to 9fingers I've also put in a 15v boost circuit.

And before anyone asks, no, I do not have £80,000 to run in our own dedicated line.

 

[Sideways]

You need a step up autotransformer or a digital phase converter. Sort out your problems for a few £hundred or < £2k at worst.
I totally sympathise but this shows the difficulty of providing a proper service to everyone without spending a fortune tailoring the network to individual households. The other properties had a legitimate complaint. 260V is out of spec and the DNO had to fix that.
Unfortunately for me, as the spikes above 253V are short and only a few times a day, even though it's a pain and I will complain about it, the DNO can probably argue that it's within spec and it's my problem to live with it.

 

[Jaco]

Cracking thread, thank you.

Agree, well written, a bit over my expertise.

 

[yngndrw]

You need a step up autotransformer or a digital phase converter. Sort out your problems for a few £hundred or < £2k at worst.

There was a bit of a scam going around a while ago, where companies were selling "voltage optimisers" with the promise that you'd save money with a lower voltage. Nevertheless these voltage optimisers are still available for a few hundred today (Both new and used) and I believe they are essentially just a bucking autotransformer. They seem to start at around 60A capacity which is sufficient for all but the largest single phase solar arrays.

Edit: Try this one on ebay, it looks like you can even pick from three tappings:
https://www.ebay.co.uk/itm/155463278458

 

[Sideways]

There was a bit of a scam going around a while ago, where companies were selling "voltage optimisers" with the promise that you'd save money with a lower voltage. Nevertheless these voltage optimisers are still available for a few hundred today.

I have one. I got it free of charge, cosmetically damaged but electrically OK.
Exactly as you say, it is simply a 60A autotransformer with choice of two voltage step down ratios.
Max reduction is 18V on this one.
They are useless for energy saving but I will wire mine in to reduce the voltage of a few of the household circuits where it will reduce stress on my electronic devices.
Normally they should be connected between the meter and the consumer unit to reduce the voltage to the whole house but I see no point in slowing down my oven and kettle
They are of no help with the solar overvoltage tripping as they can only be connected on the household side of the solar, not between the solar and the grid.

A 60A toroidal autotransformer is heavy lump of ferrite and copper. The whole unit weighs 16Kg and comes with sleeve anchors for wall mounting.
A toroid of this size and rating would cost £100 to £200 anywhere.

 

[yngndrw]

I have one. I got it free of charge, cosmetically damaged but electrically OK.
Exactly as you say, it is simply a 60A autotransformer with choice of two voltage step down ratios.
Max reduction is 18V on this one.
They are useless for energy saving but I will wire mine in to reduce the voltage of a few of the household circuits where it will reduce stress on my electronic devices.
Normally they should be connected between the meter and the consumer unit to reduce the voltage to the whole house but I see no point in slowing down my oven and kettle
They are of no help with the solar overvoltage tripping as they can only be connected on the household side of the solar, not between the solar and the grid.

A 60A toroidal autotransformer is heavy lump of ferrite and copper. The whole unit weighs 16Kg and comes with sleeve anchors for wall mounting.
A toroid of this size and rating would cost £100 to £200 anywhere.

Why can't they be connected to the solar inverter? The inverter connects to an MCB like any other circuit, not directly to the grid. (And even if it did connect directly - Say to a switch fuse unit, as you say they are designed to connect before the consumer unit so they are rated sufficiently)

In this case the inverter would see a lower voltage from the grid which should keep it happy. It would also boost the output voltage of the inverter making it compatible with the higher grid voltage.

 

[Sideways]

In this case the inverter would see a lower voltage from the grid which should keep it happy. It would also boost the output voltage of the inverter making it compatible with the higher grid voltage.

That's exactly why you cannot wire it like that. The inverter would be happy but it would overdrive the grid causing problems for other households in the neighbourhood. Such an installation would breach the G98 / G99 license conditions. Inverters are type approval tested and much limit or shut down within a specified timeout if the grid voltage exceeds 253V, whether that is due to the solar installation or the external grid. Put an "optimiser" between the solar and grid and the installation no longer meets the license conditions and the DNO can summarily disconnect you.

There are incompetent electricians who do install optimisers incorrectly with solar so be warned...

 

[yngndrw]

That's exactly why you cannot wire it like that. The inverter would be happy but it would overdrive the grid causing problems for other households in the neighbourhood. Such an installation would breach the G98 / G99 license conditions. Inverters are type approval tested and much limit or shut down within a specified timeout if the grid voltage exceeds 253V, whether that is due to the solar installation or the external grid. Put an "optimiser" between the solar and grid and the installation no longer meets the license conditions and the DNO can summarily disconnect you.

There are incompetent electricians who do install optimisers incorrectly with solar so be warned...

It would match the grid, if they can't be bothered to keep the grid in spec then that's on them. To the best of my knowledge inverters use phase lead / lag rather than outputting at a higher voltage, which means that it wouldn't be overdriving it anymore than it already was.

 

[deema]

I’m obviously have a senior moment, so I’d appreciate an explanation from those in the know. If the max voltage permitted is 253V, why would any transformer have a tap that exceeded it? Each spur from the transformer will have a max length and current carrying capacity to meet the max voltage drop across it to keep voltages in spec, so that’s fixed. Transformers are placed near to the loads and don’t act as power transmission. So to me, naively I can’t see how 253V is exceeded unless independent power generators like PE are pushing higher voltages illegally into the grid? I also can’t see why every transformer would have anything other than a 253V tap as this minimises power lose in the transmission wiring? What am I missing?

 

[Myfordman]

You are missing comprehension that transformer connections use voltage ratios not absolute voltage unless you are referring to specialist constant voltage transformers.