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What is possible with FIT, SEG, Hate Pumps and Batteries?

 
Solar Photovoltaic (PV)
Last Post by David999 7 hours ago
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 ian33a
(@ian33a)
Eminent Member Member
Joined: 4 years ago
Posts: 25
Topic starter 03/07/2026 9:41 pm   [#3082]

Hi everyone,

 

we're in the very early stages of getting a heat pump and are exploring ways to load shift.

 

Our existing set up is a 4KWp solar array (circa 2013) on a generation FIT. The inverter is G98, so 3.68KWp. It is a DC/AC unit with no batteries.

We also have an AC coupled battery, set as G100. It has a 3KWp AC/DC inverter and 15KWh of batteries behind it.

 

If we install a heat pump, it will have to be substantial - probably 14 -18 KW , as our house is large and has a significant heat loss. The age of the house and the character makes massive improvements in insulation impractical. We have what we have.

 

Load shifting is essential, but a 3KWp inverter, to my mind, is not enough to drive a heat pump as well as a reasonable house load.

 

So, we are considering adding additional batteries, all behind another inverter - effectively, increasing the peak power capability of the stored power and thus giving the heat pump and house load as much headroom as possible.

 

Our FIT "partner" Scottish Power, has said that any changes that we make to the existing FIT hardware must not allow us to export any energy that we do not create on site. Fair enough.  Everything that goes through the generation meter must be self generated. I can't see a way that we can change the DC/AC inverter to a hybrid, add batteries to it and keep within the rules that they have stipulated. Perhaps you can?

So, my thought was that we add an additional hybrid inverter with batteries behind it and, if funds permit, some additional solar panels as well. This becomes a second solar array (we have space) as well as an energy store that we can fill either by solar energy or by purchasing energy when prices are cheap or both. This gives us a second repository for storing energy as well as a second inverter to provide a larger instantaneous power output to drive a heat pump and house load. We also have an opportunity to export excess charge too, in theory.

I'm wondering if we could set this second array up as a SEG based system (assuming G99 approval) but a problem comes in measuring exported energy. The original PV system may be exporting (and we are being paid for deemed export) as well as the planned second system which may be exporting under SEG. We are already being paid deemed export on the existing system.

Am I correct in thinking that I could surrender the deemed export section of the existing array (which is generation FIT) and, instead, seek to be paid for all actual export from the existing system and a new system under a SEG associated with the new array - all measured with the smart meter that we have at our property? 

What I don't want to do is lose the generation based FIT payments as they are quite decent , especially as we are paid for pure generation and not just for actual export.

 

If this isn't possible, is there another way to make this all work nicely together and still be financially decent?

thanks

 



   
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Topic Tags
Generation FIT SEG Batter
 David999
(@david999)
Reputable Member Member
Joined: 2 years ago
Posts: 347
03/07/2026 9:57 pm  

Posted by: @ian33a
↑

Hi everyone,

 

we're in the very early stages of getting a heat pump and are exploring ways to load shift.

 

Our existing set up is a 4KWp solar array (circa 2013) on a generation FIT. The inverter is G98, so 3.68KWp. It is a DC/AC unit with no batteries.

We also have an AC coupled battery, set as G100. It has a 3KWp AC/DC inverter and 15KWh of batteries behind it.

 

If we install a heat pump, it will have to be substantial - probably 14 -18 KW , as our house is large and has a significant heat loss. The age of the house and the character makes massive improvements in insulation impractical. We have what we have.

 

Load shifting is essential, but a 3KWp inverter, to my mind, is not enough to drive a heat pump as well as a reasonable house load.

 

So, we are considering adding additional batteries, all behind another inverter - effectively, increasing the peak power capability of the stored power and thus giving the heat pump and house load as much headroom as possible.

 

Our FIT "partner" Scottish Power, has said that any changes that we make to the existing FIT hardware must not allow us to export any energy that we do not create on site. Fair enough.  Everything that goes through the generation meter must be self generated. I can't see a way that we can change the DC/AC inverter to a hybrid, add batteries to it and keep within the rules that they have stipulated. Perhaps you can?

So, my thought was that we add an additional hybrid inverter with batteries behind it and, if funds permit, some additional solar panels as well. This becomes a second solar array (we have space) as well as an energy store that we can fill either by solar energy or by purchasing energy when prices are cheap or both. This gives us a second repository for storing energy as well as a second inverter to provide a larger instantaneous power output to drive a heat pump and house load. We also have an opportunity to export excess charge too, in theory.

I'm wondering if we could set this second array up as a SEG based system (assuming G99 approval) but a problem comes in measuring exported energy. The original PV system may be exporting (and we are being paid for deemed export) as well as the planned second system which may be exporting under SEG. We are already being paid deemed export on the existing system.

Am I correct in thinking that I could surrender the deemed export section of the existing array (which is generation FIT) and, instead, seek to be paid for all actual export from the existing system and a new system under a SEG associated with the new array - all measured with the smart meter that we have at our property? 

What I don't want to do is lose the generation based FIT payments as they are quite decent , especially as we are paid for pure generation and not just for actual export.

 

If this isn't possible, is there another way to make this all work nicely together and still be financially decent?

thanks

 

big house, poorly insulated V heat pump sounds like big bills does it not.  The batteries don’t last long trying to keep a heat pump going.  I have a 16kw heat pump, a well insulated large old house and during winter it’s quite greedy. And the solar is basically worthless in winter. 

 



   
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