Hello - firstly I love this community. My first post but all the info and discussion in here is so useful! Thanks everyone.
I've got 10 solar panels on the roof and I just upgraded my battery to 15KW. Enough to cover my house all day outside of the cheap energy at night.
I have a 7p / KW night time purchase and 15p / KW solar selling during the day. You see where this is going...?
I want to tell me house to run purely off the battery throughout the day. It's more profitable for me to sell my solar than store it for later.
How can I tell all of my solar to sell direct to grid and the house to always use the battery if charged?
Thanks in advance
Nick
Prioritising Selling Solar - What Settings Do I Need?
-
Dave Foster
- Posts: 1786
- Joined: Thu Oct 13, 2022 7:21 pm
Hi,
Just a couple of things as food for thought, irrespective of mode the inverter is in, it will always use PV to cover the house loads first (before anything else).
The control you have is whether the PV will be used to charge the batteries or be exported.
The easiest way to achieve what you want is to charge the batteries over night, and leave your inverter in Feed-In work mode - in this mode the PV will cover the house load first (always), then will go directly to export - If the PV is not sufficient to cover the house load the battery will be used. Once the PV has gone, the batteries will be used to cover the house load until they hit minSoC.
In terms of your batteries you can buy power at 7p/kWh but the roundtrip efficiency of putting power in converting AC>DC, storing that in your battery chemistry and then recovering it and converting DC.AC will probably lose a worst case of 15% i.e. for every 1kWh you get from your batteries it would have cost 8.05p (not a big difference but worth noting).
Second thing is the cost of the batteries, you can either choose to write the purchase/install cost off and then work on everything returned is good (but you'll have to buy some new ones in 10-15 years time), or you can work out the cost per kWh - i'll not bore you with the maths but in my case on HV2600 batteries (similar to ECS) the cost per kWh to use the battery when taking into account purchase/installation is approximately 9p/kWh across their lifetime - the EP11 batteries will likely be a bit cheaper because of their cost effectiveness.
If you work on the principle I want to make sure all my costs are covered then actually breakeven cost would be 8.05p+9p = 17.05p, that's why I use the Feed-in method and use the batteries to avoid using peak grid tariff (up to 23:30)
Just a couple of things as food for thought, irrespective of mode the inverter is in, it will always use PV to cover the house loads first (before anything else).
The control you have is whether the PV will be used to charge the batteries or be exported.
The easiest way to achieve what you want is to charge the batteries over night, and leave your inverter in Feed-In work mode - in this mode the PV will cover the house load first (always), then will go directly to export - If the PV is not sufficient to cover the house load the battery will be used. Once the PV has gone, the batteries will be used to cover the house load until they hit minSoC.
In terms of your batteries you can buy power at 7p/kWh but the roundtrip efficiency of putting power in converting AC>DC, storing that in your battery chemistry and then recovering it and converting DC.AC will probably lose a worst case of 15% i.e. for every 1kWh you get from your batteries it would have cost 8.05p (not a big difference but worth noting).
Second thing is the cost of the batteries, you can either choose to write the purchase/install cost off and then work on everything returned is good (but you'll have to buy some new ones in 10-15 years time), or you can work out the cost per kWh - i'll not bore you with the maths but in my case on HV2600 batteries (similar to ECS) the cost per kWh to use the battery when taking into account purchase/installation is approximately 9p/kWh across their lifetime - the EP11 batteries will likely be a bit cheaper because of their cost effectiveness.
If you work on the principle I want to make sure all my costs are covered then actually breakeven cost would be 8.05p+9p = 17.05p, that's why I use the Feed-in method and use the batteries to avoid using peak grid tariff (up to 23:30)
Thanks Dave - this is such a great summary and I really appreciate your time.
I did see the feed in priority, although having called my installers today, they've said that this will prevent the batteries from charging and "confuse the inverter and cause it to wear out faster than expected". It feels very strange to have a setting on there for feed in which could damage the inverter?!
I agree with your maths. I'm a bit nerdy so I am tracking my path to breakeven and upgrading the battery to run the house all day speeds up that recoup. I'm looking at about 8 years. Even today - 30th Jan in the south UK, I'm generating upwards of 10KWs per day. I download both my Fox data and Octopus Energy data to see what I've bought, when I would have bought grid energy without the battery and what I've generated from solar (worth 7p to 8p if it goes into the battery or 15p if sold - hence this setting!).
I did see the feed in priority, although having called my installers today, they've said that this will prevent the batteries from charging and "confuse the inverter and cause it to wear out faster than expected". It feels very strange to have a setting on there for feed in which could damage the inverter?!
I agree with your maths. I'm a bit nerdy so I am tracking my path to breakeven and upgrading the battery to run the house all day speeds up that recoup. I'm looking at about 8 years. Even today - 30th Jan in the south UK, I'm generating upwards of 10KWs per day. I download both my Fox data and Octopus Energy data to see what I've bought, when I would have bought grid energy without the battery and what I've generated from solar (worth 7p to 8p if it goes into the battery or 15p if sold - hence this setting!).
-
Dave Foster
- Posts: 1786
- Joined: Thu Oct 13, 2022 7:21 pm
Feed-in is a legitimate work mode and used by a large number of people with your tariff (such as me), it really won’t damage the inverter or wear it anymore than any other work mode, and yes it won’t charge the battery that’s the whole point of that workmode.
Welcome to the world of solar
Welcome to the world of solar
-
Dave Foster
- Posts: 1786
- Joined: Thu Oct 13, 2022 7:21 pm
Yes that's right, they will charge from grid when you set a charge but not from solar.nick-tea wrote: Thu Jan 30, 2025 11:04 am Just to triple check - when you say it won't charge my batteries... they'll still charge off the grid at night on their timer OK?
The other slight upside to Feed-in work mode is that it changes the inverter's bias ever so slightly and whereas a gird tied inverter in Self Use mode might take between 0.5-1kWh to maintain it's grid syncronisation - in the Feed in work mode that will reduce to maybe 0.25-0.5 kWh (every little helps)