Circular reasoning (Rolfe's solar energy system)

But wouldn't it make sense to fill up any battery available with the cheap overnight?

In which case there would still be no capacity available at noon unless some was used (or exported) a little earlier on.
It gives you capacity to make a guess at what the following day can generate. Using Home Assistant I've programmed it to take in the weather forecast and it then decides how much i import from the grid overnight. In your system you could simply add a second battery, charge both to 50% overnight and then you have 50% of storage available for your otherwise lost generation. Just an idea, probably not cost effective, all depends on pricing of the battery I suppose, battery prices have fallen dramatically over the last year.
 
It gives you capacity to make a guess at what the following day can generate. Using Home Assistant I've programmed it to take in the weather forecast and it then decides how much i import from the grid overnight. In your system you could simply add a second battery, charge both to 50% overnight and then you have 50% of storage available for your otherwise lost generation. Just an idea, probably not cost effective, all depends on pricing of the battery I suppose, battery prices have fallen dramatically over the last year.
I do similar with Home Assistant to virtually eliminate clipping. Luxpower inverters have a mode called 'Charge Last' which switches the priority, after house load, to export rather than charge the batteries. In that mode only the solar generation over the inverter AC capacity goes to the batteries. Basically the batteries are only charged by the small amount of power above the inverter limit, the area of the diagram that is clipped once the batteries reach 100%.
Of course you wouldn't want to leave the inverter in this mode so it's only something you would use when you can automate it, which is where Home Assistant comes in. I use PV predictions for the day, Solcast and ForcastSolar, to determine the level of grid charge of the batteries overnight. During the day an automation determines when Charge Last is required, based on PV predicted remaining for the day, whilst still ensuring the battery SOC rises high enough to provide power in the evening until the cheap overnight starts.
It required a lot of tinkering over the first year, is not perfect, and the financial benefits are dubious with cheap EV tariffs, but it satisfies my mild OCD to maximize solar yield:)
 
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I do similar with Home Assistant to virtually eliminate clipping. Luxpower inverters have a mode called 'Charge Last' which switches the priority, after house load, to export rather than charge the batteries. In that mode only the solar generation over the inverter AC capacity goes to the batteries. Basically the batteries are only charged by the small amount of power above the inverter limit, the area of the diagram that is clipped once the batteries reach 100%.
Of course you wouldn't want to leave the inverter in this mode so it's only something you would use when you can automate it, which is where Home Assistant comes in. I use PV predictions for the day, Solcast and ForcastSolar, to determine the level of grid charge of the batteries overnight. During the day an automation determines when Charge Last is required, based on PV predicted remaining for the day, whilst still ensuring the battery SOC rises high enough to provide power in the evening until the cheap overnight starts.
It required a lot of tinkering over the first year, is not perfect, and the financial benefits are dubious with cheap EV tariffs, but it satisfies my mild OCD to maximize solar yield:)
Everyone needs a hobby. :)
 
This is whooshing right over my head again.
Solutions to improve the efficiency of your system. At times your roof can generate more than you can use/store/export so the system is clipping (kind of like the energy price cap), it hits the maximum on all fronts any more energy is lost. By adding more storage, during these times the energy could be put into the battery for later use / export.
 
Those interested in the issue that we are discussing here may like to watch the latest Gary Does Solar video. This explains the issue that Rolfe has of clipping and losing out on potential generation:

 
I charge my 12 kWh battery overnight at 7p/kWh. House runs off that from 6am until the sun comes up and then starts charging the battery back to 100% (normally by 11ish) after that I'm holding the battery at 100% and exporting at 15p/kWh. Sun dips by 6 then the battery depletes until it starts charging again at 23:30. Works well for me, i have a heat pump and 2 EVs. My bills have dropped from £60 week to around £9 this month. Spring/summer i should be in profit most days.
 
I charge my 12 kWh battery overnight at 7p/kWh. House runs off that from 6am until the sun comes up and then starts charging the battery back to 100% (normally by 11ish) after that I'm holding the battery at 100% and exporting at 15p/kWh. Sun dips by 6 then the battery depletes until it starts charging again at 23:30. Works well for me, i have a heat pump and 2 EVs. My bills have dropped from £60 week to around £9 this month. Spring/summer i should be in profit most days.
Do you not increase export in the last few hours until charging starts? earn more export fees.
 
Do you not increase export in the last few hours until charging starts? earn more export fees.
I export for as long as the suns out and then the battery kicks in as soon as sun's away. I'm producing 6kW just now and 5.6kW of that is being exported the rest is feeding the house as battery is at 100%. I've only had the system since January but already I see a huge advantage, summer should be pretty profitable.
 
I export for as long as the suns out and then the battery kicks in as soon as sun's away. I'm producing 6kW just now and 5.6kW of that is being exported the rest is feeding the house as battery is at 100%. I've only had the system since January but already I see a huge advantage, summer should be pretty profitable.
If you work out how energy you need to cover you in the evening up to the time when your off peak starts, any spare capacity you could export to the grid earning more 15p's.
 
If you work out how energy you need to cover you in the evening up to the time when your off peak starts, any spare capacity you could export to the grid earning more 15p's.
Problem is I very quickly use the entire 12kWh of the battery capacity over tea time, family of 5. If it was just the 2 of us I'd certainly be doing that.
 
It goes like this.
  1. I really should get a home charger.
  2. If I get a home charger, I need a variable electricity tariff.
  3. A variable electricity tariff will make my daytime usage more expensive.
  4. The answer is to get a home battery and fill it with cheap electricity overnight.
  5. Look at your roof, if you have a home battery it would be criminal not to install solar.
  6. That will be £13,700 altogether.
  7. But I could buy a hell of a lot of electricity for that. Um.
  8. But I really should get a home charger.
How do you get out of this loop?
Solar and batteries are too expensive for a trickle charge system that I cannot use during the day and only provides a small amount of my car battery supply via a home battery, do the inverters still need replacing every 10 years or so? For me, it is cheaper and easier to buy green electricity from Octopus energy.
 
Solar and batteries are too expensive for a trickle charge system that I cannot use during the day and only provides a small amount of my car battery supply via a home battery, do the inverters still need replacing every 10 years or so? For me, it is cheaper and easier to buy green electricity from Octopus energy.
Ahh, but the circular reasoning goes:
1. You've got cheap overnight power, so you may as well get a home battery to use that cheap energy throughout the day and evening, rather than using the peak rate power.
So you get a battery...
2. You've got a roof which can take solar panels to fill up the home battery during the day.
....


At the moment those of us with EV, solar and battery are exporting like mad during the day and making money off it. 15p per kWh export and buying for 8p (or something like that) overnight.

Make enough money during the summer to cover your heating and EV charging bills over the winter.

In the future the export rates will drop, but for now the logic is there.
 
We haven't used peak energy for 2 years now but, being rural, have the issue that we can produce more than we are permitted to export - so clipping is inevitable once the car is charged up :( First world problems, as they say!
 
I'm back into profit now, in fact I've more or less been there since 21st February. Happy days.

Those interested in the issue that we are discussing here may like to watch the latest Gary Does Solar video. This explains the issue that Rolfe has of clipping and losing out on potential generation:


I saw that video in my YouTube sidebar but didn't watch it, maybe I should have. But someone on Twitter was also trying to persuade me I could use the generation that would otherwise be clipped by having the battery empty when the clipping starts. The trouble is, I didn't really follow him. I should watch that video.

Mainly, though, it has to be a really sunny day before it would be worth it, and I can't really trust the weather to do what the forecast says, so I'm not sure about the practicality of it anyway. This sort of thing (today) is more common.

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I'm not sure I want to keep fiddling with the settings anyway, or to second-guess the weather. But I will watch the video.
 
I'm not sure I want to keep fiddling with the settings anyway, or to second-guess the weather. But I will watch the video.
You perhaps should consider Home Assistant or Solar Assistant to do the fiddling for you, theres a bit of satisfaction seeing your export stop just as the off peak starts. Either of the above programs can take in weather forecasts and with bit of AI type programming can learn what your system does. Maybe a step too far but certainly worth a thought.
 
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