One family's solar story

[Sideways]

Everything is just ticking along with little fuss.
The biggest change recently is that I registered us for export this April. For the first year and more I didn't bother because the export rates are poor, but we switched to Octopus energy and they have an export tarriff that pays around 15p / kWh. 3x most others. They promised 6 weeks to do the admin which involves getting the DNO to issue a second meter number which is used for the export side, and 6 weeks was what they took.
At this time of year we are now earning enough from this to cover our gas and electricity standing charges, this in addition to it heating the hot water and keeping the battery charged so we are theoretically self sufficient.

Also - last year I changed the hot water tank to a modern one with 180L capacity and twin imersion heaters. I let this heat to 60C and it can absorb 8kWh.

We still have an issue where the setting of the local grid voltage and the resistances in it, mean that when other local solar installations are all working hard, the grid can't spread that power around and we see the voltage rise waay above what it's supposed to be. I've measured 260V+. Never for long, but these spikes cause a properly designed solar system to turn off for a while which is plain irritating and means we actually use a few kWh of paid electricity when we shouldn't have to. I'll have a big argument with the power company over this but just now I have other jobs that are more important. If you are in the planning stage, put a logging voltmeter on your mains for a week and see what it looks like before you start. We have a 253V spike in the middle of the night because they bump it up ready for all the EV's doing an overnight charge on the cheap tarriff.

Lastly, we have a good big battery, handy in winter, bigger than needed in summer, so I've tweaked the settings to run it between 20% capacity minimum and 95% capacity max. This is with a view to maximising it's lifespan. We don't need 16kWh storage in summer.

Here are some of the recent graphs.

Elec consumption since Jan £86

Export since 3rd week April £106

Generation by month since installed in April 2022
You can see what we made (orange) vs what we consume (blue)
The battery stores power, gives back overnight and is enough to carry us through a really lousy day to the next one, so as long as orange is above blue on average we're pretty self sufficient.

For the 6 good months, we get a tankfull of hot water daily - 2 tubs or a bath and a shower - from the solar diverter. The myenergi kit gives an additional insight into the system.
Green yellow red is looking at power in and out of the home as a whole

Week and month view

Notice the red blip ? That was a day when the grid got so high for so long that the inverter turned off and needed a manual reset. I didn't notice so we paid for a days power before I spotted it and cycled all the switches.

The little traces of red elsewhere are mostly overvoltage blips where the inverter recovers itself after taking 10 or 30 minutes out. We have a big battery sized to deliver 6.5kW - so unless we turn on the oven, kettle and microwave all at once cooking dinner or same while the laundry is running, we don't need to draw from the grid.

This graph focusses on power used around the home vs "surplus" shunted into the immersion heaters.

We prioritise home and battery, hot water diverter 2nd, export to grid last.
So effectively we are heating water with elec at an opportunity cost of 15p / kWh.
Arguably we could try to export more, earn some more 15p's to pay for heating the and heat the water with gas instead (6p per kWh / 70% efficient boiler). I think that would be the better deal but with the poor state of the grid we have to limit our exports anyway because we just can't push all the power we make out without contributing to this over voltage problem. Ho hum !

Solar is very very variable, with the seasons and as the clouds go by. I'd say battery storage is essential. Oversizing the system means you are less dependent on the grid in the 3-4 cold months and have lots to spare for hot water and export in summer, but genuinely we can't get rid of what we could make in the height of summer. It would be easier if (when) we have an EV to charge with it too.

Hope this helps.

 

[John Brown]

All very illuminating. So, if I'm reading this correctly, I'd probably be better off even with a couple(my 4kw inverter is 24v in)of 50ah LFPs, than I am with my 2 130ah EFBs? Worth considering, especially as I could parallel up another pair, if finances allowed.

Update on my shed: One of the 130ah batteries failed completely after less than 2 years. The other has a capacity of around 35ah, at a 3a current drain.
I gritted my teeth and spent £430 on 24v 100ah lifepo4 battery. So far I am very impressed.

 

[Spectric]

I think that would be the better deal but with the poor state of the grid we have to limit our exports anyway because we just can't push all the power we make out without contributing to this over voltage problem. Ho hum !

The problem is that the grid was never intended to be anything other than generation at one end and demand at the other but now we have a lot of generation being fed in lower down including at the demand end and the control system was not designed for this.

Battery technology will be the key to long term success and maybe to improve transmission efficiency we need to start thinking of moving away from high votage Ac transmission and onto high voltage Dc transmission and only using AC below maybe 33 or 66Kv and this would help with controlling the voltage as you have removed the bigger issues with impedance and phase.

 

[Sideways]

It will be nice when the utility triple the size of the cables. That will make life much easier. In reality it's a big job and will take decades.

 

[Oddbod]

It will be nice when the utility triple the size of the cables. That will make life much easier. In reality it's a big job and will take decades.

It'll be nice when they stop mucking around & take advantage of the ever increasing amount of solar being installed by updating their control system to take it into account.
Heck, there's an aluminium extrusion manufacturer not half a mile up the road from me & their daytime energy consumption must be significant.

 

[deema]

I would be really interested if you’ve looked at layback on better still the Internal Rate of Return versus the life of both the batteries and the solar panels. I am seriously considering batteries and possibly solar, but this is driven by looking at ways to mitigate power outages caused in winter due to storms etc. Looking at my own energy needs, with just two of us in the house and present electricity prices it doesn’t seem to be financially economic to invest in the system. I may not be taking account of everything?

 

[Spectric]

but this is driven by looking at ways to mitigate power outages caused in winter due to storms etc. Looking at my own energy needs, with just two of us in the house and present electricity prices it doesn’t seem to be financially economic to invest in the system. I may not be taking account of everything?

Just buy a generator for those odd occasions.

It will be nice when the utility triple the size of the cables.

What cables are you thinking of, yes if you are still on 16mm supply then having 25mm @100 amps would help but I would think it is the overal network where all the cables are at capacity at peak times is the bigger problem and as you say this is not a five minute job as they need to start at the top and work down. They have been changing some of the 275Kv lines over to 400Kv with some very large new transformers weighing in at 175 tonnes coming in from abroad so things are happening.

 

[Sideways]

I haven't done the numbers. Not because I can't but because any calculation is heavily affected by the assumptions and there is too much uncertainty around those.
I had the system put in while covid supply chain delays were chronic and I overpaid for the panels and battery as a result. Maybe 20%.
I'm confident my break even is more than 10 years out. I'm aiming for this installation to last 20+ years and on that timeframe I will do OK.
We didn't do it to turn a profit. We did it for our own energy security, predictability, to be green, and because we have a slab of roof that is near ideal for a large array of panels.
It's a 20 year prepayment plan.

 

[HamsterJam]

I am seriously considering batteries and possibly solar, but this is driven by looking at ways to mitigate power outages caused in winter due to storms etc.

Research carefully.
It is a requirement that grid tied solar shuts off if there is a power outage.
This is to prevent solar systems feeding power into an intentionally isolated part of the grid and electrocuting someone and/or trying to take on a load it simply cannot manage.
I’m not 100% sure but suspect the same will apply to grid tied battery systems.
Off course this won’t apply if you have an off-grid system or a system that can take itself off-grid in event of a power failure.

 

[Sideways]

Research carefully.
It is a requirement that grid tied solar shuts off if there is a power outage.
This is to prevent solar systems feeding power into an intentionally isolated part of the grid and electrocuting someone and/or trying to take on a load it simply cannot manage.
I’m not 100% sure but suspect the same will apply to grid tied battery systems.
Off course this won’t apply if you have an off-grid system or a system that can take itself off-grid in event of a power failure.

Grid tied are required not to be able to feed back into the grid while it's down, just as you describe, but a minority of systems do have the necessary controls to be able to isolate and continue to run off grid if the mains fails. Others have the facility to power a simple 13A "emergency" socket to keep essential services running during an outage.

Personally I would want enough for lights, media, freezer and to keep the gas heating system running. Nothing else is essential. So 13A is actually plenty.

I'll get round to wiring a socket up one of these days.
I could implement a full off grid type backup with my kit but it would cost £1-2k more which isn't worth it when we only see an hour or two of outages a year.

 

[Stuart Moffat]

Grid tied are required not to be able to feed back into the grid while it's down, just as you describe, but a minority of systems do have the necessary controls to be able to isolate and continue to run off grid if the mains fails. Others have the facility to power a simple 13A "emergency" socket to keep essential services running during an outage.

Personally I would want enough for lights, media, and to keep the gas heating system running. Nothing else is essential. So 13A is actually plenty.

I'll get round to wiring a socket up one of these days.
I could implement a full off grid type backup with my kit but it would cost £1-2k more which isn't worth it when we only see an hour or two of outages a year.

I have a similar list of things I want to keep running in an outage, but have added fridges and freezers to that list. My backup is a generator, but either way, you need to be able to quickly connect the central heating and freezers to your alternative source of power. All of my essentials have a 13 Amp socket I plug in line, including the oil heating so that they can be quickly and safely swapped over to the generator. Our overhead supply has been rather vulnerable over the years, and we have a lot of home grown produce to lose.

 

[johnb80]

I'll get round to wiring a socket up one of these days.
I could implement a full off grid type backup with my kit but it would cost £1-2k more which isn't worth it when we only see an hour or two of outages a year.

I'm not sure what output configuration your Fronious inverter has, I setup my system using an automatic change over switch similar to this:-

Automatic Change Over Switch

In the event of a grid failure, the emergency power output of the Growatt inverter feeds the Victron grid input, this then syncronises to the supply from the Growatt and both inverters then operate to supply my house from the battery's and solar. The one I used changes over in about 500 M/sec, often the TV doesn't even go off when it happens. When the grid supply comes back on after 2 minutes (configurable) it switches back to grid supply.
Some inverters, Victron being one of them, can run almost like a UPS. The grid goes into the inverter and the load is on a separate output. It runs with the house load all of the time being fed from the inverter, with the inverter providing all of the energy or supplementing the incoming supply.
My final cheat in the event of a prolonged power failure is our MG5 has V2L (Vehicle to Load) output, it can provide 3kW of continuous power from it's 66 kWh battery. It's not quite straight forward to use the output directly, it cant be grid tied. What you can do though is to charge your house batteries and thats what I have set up. I purchased a LifeP04 50v 3 kW battery charger from Amazon, that simply connects across the DC terminals of my Battery Bank. Switching on the car supply it then feeds upto a maxim of 3 kW continuously I would guess for 16 hours or so (it wont allow discharge down to 0%). Combined with the car we have some 87 kWh of storage available.

 

[Sideways]

Fronius's full backup implementation is fully documented here...
https://www.fronius.com/~/downloads...es/SE_QG_Symo_GEN24_Full_Backup_EPS_EN_AU.pdf

It's fairly smart for something entirely built in other than a small number of type proven contactors / auxy relays. The focus is on preventing any chance of backfeed to the grid while the grid is down.
A specific detail is that in backup mode, the GEN24 Hybrid inverter generates at a frequency slightly off 50Hz, by enough that any other inverters in the installation (I have a 6kW newer tech GEN24 hybrid plus an older, simpler 3kW inverter) will read this as the grid frequency being out of spec and this causes them to stop generating.

The backup control logic interfaces with an external contactor (63 amp) and auxy relay, and these can switch the tails to the consumer unit over to the inverter, providing whole house backup. Alternatively, a simple 13A socket can be wired directly to the hybrid inverter.

Fronius have type tested relays from a number of mfrs and documented the whole thing so a competent person can build and test the changeover componentry. If you are not that competent person, Enwitek in Germany will sell you the parts installed in a 3 row DIN module box for a healthy profit.

I'm tight. I'll build it myself when I find all the parts at a discount. We don't have the outages so this doesn't offer a lot of value to us.

Here are the operating modes:

"5.1 GRID MODE
This mode denotes that the inverter is AC coupled with the local grid, backup control logic is turned off and backup loads supplied from the grid.
5.1.1 GRID-TO-BACKUP TRANSITION
Successful transition to backup mode requires the following conditions to be met:
1) Grid (via the AC port of the inverter) is monitored by the inverter’s internal protection unit and Fronius Smart Meter.
2) Grid fails (blackout).
3) The inverter carries out measurement according to country standard and then shuts down.
4) The inverter starts Backup mode after a short time window.
5) Backup control logic is switched on and loads connected to the backup power circuit are supplied by the inverter.
5.2 BACKUP MODE
Operation in Backup mode usually means the grid is not available and the inverter is supplying backup loads.
The interlocking mechanism from the backup control components is on/activated.
In backup mode inverter's AC output acts as a voltage source with AC voltage set at 230/400 Vac (L-N/L-L) and AC frequency set at 53 Hz. AC frequency is purposely increased with the intention of disconnecting other inverters connected to the backup circuit if any.
5.2.1 BACKUP-TO-GRID TRANSITION
Successful transition to grid mode requires the following conditions to be met:
1) Inverter operating in backup power mode.
2) The grid is back and stable.
3) Fronius Smart Meter monitors grid voltage values and passes this information to the inverter.
4) Inverter checks if the grid voltage is within the correct range.
5) Inverter ends backup power mode.
6) Backup control logic is turned off and AC loads are reconnected to the grid.
7) The inverter checks if the grid is within specified parameters (relevant standard) and if successful starts producing energy.

 

[MikeJhn]

I would be really interested if you’ve looked at layback on better still the Internal Rate of Return versus the life of both the batteries and the solar panels. I am seriously considering batteries and possibly solar, but this is driven by looking at ways to mitigate power outages caused in winter due to storms etc. Looking at my own energy needs, with just two of us in the house and present electricity prices it doesn’t seem to be financially economic to invest in the system. I may not be taking account of everything?

I am in the same boat, but have taken into account our respective age's, is it worth if for the amount of life expectancy we have left, interest rates being what they are if may be, but I have been getting near enough £150.00/month off the Premium bonds, good investment this year so far.