The rads in a room should be sized according to the heat loss calculations and the target room temperature for the room. The water flow temperature (aka weather compensation) can then be used to compensate for different outside temperatures. TVRs aren’t usually recommended. Room stats really need to be slow/insensitive to small changes. I prefer to overheat during the day when the air is generally warmer. HPs are like supertankers.
Phil
Radiators in series went out in the UK more than 50 years ago. It was only ever a measure to reduce the amount of copper in the system to make it cheaper to install. If anyone contemplating the topic of this thread has radiators in series, then that has to be changed first, for a start.
I agree. A lot of people never know how their radiators are connected, nor care.
I have been considering a heat pump to replace my gas boiler. But the few potential installers I have had around to discuss installations and prices do not, for me, ask the right questions about my existing installation.
Ok, so what would actually happen if you were to turn the TRV down on the bedroom radiator for example? The TRVs are quite progessive so flow through the rad will gradually reduce. With a 50-100 litre buffer there should be little or no change in load.
This is not something we need to do. Also we don’t have a buffer as it is just extra water to heat up. The rooms are nicely balanced. It simpler for heating to go off when the house is warm enough. As our running costs for a 300m2 home are low I can’t knock the way it works.
Phil
Yes, I thought the buffer was maybe heating a lot of water unnecessarily.
Hi Johns,
Maybe I can help by explaining it like this :
Your first point - “it wouldn’t be worth it if the tariff was lost” - yes absolutely, you want to keep that historic price per kWh generated. (key is not only the price, but also based on generation and not exporting to the grid)
New System ?
If I was putting in “solar panels” right now (in 2025 - no feed in tariff) then I would install solar panels, and an inverter, but also batteries. The inverter (just one inverter) that is receiving the solar panels power would also control / manage the batteries for storage (charging during the day and then providing power when the sun goes in / overnight).
This new install would be simple with panels and just one inverter and batteries.
Feed in Tariff - adding batteries ?
As we have older systems that benefit from the feed in tariffs set at the date of install, yours 2010, mine 2016, then I could not add a battery to that system without fundamentally “changing it” from its original specification (which we have to certify when we provide generation readings)
So, to keep the original system unchanged, I have simply added a 2nd inverter and 2 batteries.
This 2nd inverter simply charges and discharges the batteries.
It has no connection to, and operates completely separately from the original Solar PV system.
In fact it could be used on its own without a solar PV system to simply store cheap overnight electricity (I pay just over 5p p kWH) and use that in the day when prices are higher.
Hopefully that makes more sense / a clearer explanation ?
FIT T&C’s - This is from my EON-Next FIT agreement:
11. Changes to Your System
11.1 You must let Us know in writing if You make any modifications or changes to Your System (including any extensions, installation of any Storage Device, changes to meters, including if a smart meter has been installed and/or the installation of an Export Meter) as this may affect its eligibility and capacity calculations which, in turn, may affect Your Tariff Code, Generation Tariff and Export Tariff. Let us know immediately after any modifications or changes have been made.
11.2 If you don’t tell Us and we then discover or are made aware that modifications have been made then We’ll notify Ofgem who will take appropriate action which may include changing Your Tariff Code, changing the amount of any FIT payments payable and/or recovering from You any amount of a FIT Payments that should not have been paid. As such We reserve the right to suspend, withhold or recoup any FIT Payments in accordance with Ofgem’s instructions.
11.3 If the change to Your System impacts Your T ariff Code and/or Generation T ariff unit rate, Ofgem will notify Us of any change and We will in turn update You of the change to be made and may send You a revised FIT Plan by email or post. Any such change will take effect from the point at which the Central FIT Register is updated by Ofgem.
11.4 Any extensions commissioned on or after the New Rules Date that increase Your System’s capacity will not be eligible to receive FIT Payments.
11.5 Any Meter Readings received by Us from a System that has had an ineligible extension (as described at clause 11.4 above) will be prorata if the System and ineligible extension share a Generation Meter and/or an Export Meter.
11.6 We shall have the right to request any more details for the Meter Reading received and referred to in clause 11.5 above if We or Ofgem believe or consider the said Meter Reading does not fall within the “expected tolerances” for electricity generated and/or exported by Your System.
11.7 If You have a Storage Device connected to or installed for Your System You must notify Us at the start of this Agreement and provide Us with a copy of the schematic diagram of the Storage Device which will need to show the installation, the Storage Device and the metering arrangements. If You don’t have this, You will need to contact Your Storage Device installer to obtain a copy.
11.8 If You have a Storage Device installed at any point after the start of this Agreement, You must notify Us as soon as possible and provide the information referred to at clause 11.7. If this information is not provided as requested, We reserve the right to notify Ofgem who shall take the appropriate action it deems necessary.
11.9 Where there is a Storage Device present and You do not have an Export Meter, You shall only be entitled to receive FIT Payments for electricity generated by Your System and deemed exported electricity if Your Generation Meter is capable of isolating the amount of electricity generated by Your System. If You have an Export Meter, You will only be entitled to receive FIT Payments for electricity exported to the local electricity network if Your Export Meter is capable of isolating the amount of electricity exported by Your System.
Thanks Pete - useful and probably saved me time. If I can’t add a battery without losing the existing tariff (which I think goes on until mid 2030 or so) it doesn’t work financially so good job you raised the point.
Hope your new installation goes well.
I’ve started using the SolarEdge battery pause facility, mostly because I don’t need to charge the battery and it’s cheaper to run off the grid during a cheap Cosy period.
Interestingly the solar gets diverted to the grid and the house in this mode which means the battery is not being charged by solar as the priority. Next day of full sunshine I will see what happens when there is more than 4kW of solar. Hopefully the excess solar above the export limit of 3.68kW will go to the battery. This will mean that I can avoid wasting the excess solar by storing it on the battery at least until it is full. The only situation to avoid is having some cloud cutting the solar below the house demand and importing from the grid at a higher rate.
I’n’it fascinating!
Phil
I guess it depends on rates… I earn more per kWh in export than it costs me to charge my battery in the off peak rate…
Also I am not sure you can limit the amount you can export other than the limit of your inverter… at least on my system.
I had 4.5 kW of generation the other day for a short time on my modest system… about 320W of internal use, battery was idle at 100% … and just under 4kW was exported… there were some inverter losses.
Can you not get your export limit increased from the 3.68kW? SSE have approved us exporting the full 6kW.
I contacted Our DNO who said our local infrastructure is not able to accommodate the extra.
Phil
That’s a shame. I was told that a network survey would be done as part of the G99 application, so your local situation makes complete sense.
Now I believe I can manage the battery better I feel ok about it.
Phil
I suppose they have to envisage that more people may go Solar, and they have to be careful that they dont reach saturation
It may be worth repeating the application in a year, for a couple of reasons:
I’ve now switched the inverter settings from G98 to G99. We have a few sunny days ahead and it will be interesting to see what difference it makes.
It will be a nice feeling. What are you going to spend your fortune on?
My application seemed a simple rubber stamp excercise, but I have a 100 amp house fuse and over head wiring from the local 11kv transformer which is up a pair wooden powerline supports…and my inverter is rated at 5kW so perhaps my infrastructure was more straight forward.
My inverter is rated at 5kW and we have had a few days where we have exported greater than 4kW pk … though on forced battery discharge and solar for when there is later free electricity, the inverter maxes out at around 5kW and exports 5kW minus house consumption at that time… so it’s been about 4.5kW
I understand that being permitted to export more than 5kW on a G99 is more unusual.
It does beg the question why you can’t apply for a G99 in the first place, and then if there are issues they can just respond with a G98 instead
I looked at my approval document from Jan 2019. It is called an MCS Installation Certificate and states “Declared Net Capacity (kW): 5.40”. No mention of G98/99 so something must have changed since then. I certainly didn’t apply for any extension.