Eco Renovation Strategy - opinions please

[bontwoody]

Hi

I have purchased a new home and am looking to improve its eco-credentials in the most efficient /cost effective way. My previous home was a well insulated self build 3 bed bungalow with 4 kW of Photo-voltaic (PV) panels, Air Source Heat Pump (ASHP), Thermal store and Under floor heating (UFH), which worked well, but Im starting from a different base and would like to tweak a few things.

The new place is a 2 bed bungalow and its original building is stone. However the kitchen and living room are later additions and have cavity walls. It has 3kW of PV on its main roof which benefits from the highest FIT tariff. It has recently had a new mains gas combi-boiler installed. I’ve attached a plan of its orientation.

My first job is to sort out its loft insulation, but the walls are more problematic. External insulation is possible, but may have to wait. The floors will probably have to stay as they are. Fortunately the oldest walls are in the bedrooms where I prefer it colder anyway.

The property has a chimney in the living room and I intend to put in a small wood burning stove for the winter evenings.

My initial thoughts are as follows:

• I want to keep the FIT payments but would also like some battery storage, from what Ive read, the best way of doing this would be by putting the batteries on the AC side. Ideally Id like to add some more PV, but the best roof space is all used, also I might be limited to 4kW grid linked maximum anyway.
• The living room does have some available roof space in the SE direction and Im considering adding some solar thermal evacuated tubes there. Its something Ive always wanted because of its increased conversion efficiency compared to PV, although I appreciate its not as flexible as PV and wont be of a lot of use in winter.
• Id like to eventually use another ASHP or GSHP to heat my DHW via a tank and the space heating directly, probably using oversized radiators. However it doesn’t make financial sense to rip out the new combi-boiler, so Im thinking of how to utilise it in the meantime.
• Having previously had a thermal store, I appreciate its ease of installation and inherent Legionella protection, but due to the fact that I had to heat a larger body of water to a higher temperature, Im persuaded that an unvented twin coil cylinder will be a better way to go this time with a heat pump, even if I have to instigate a Legionella purge occasionally. For two people I was thinking 150-200 litre size at 50C would be about correct?
• To make use of the gas combi, I intend to install the cylinder underneath it and preheat the water using the solar thermal panels via the solar coil. Leaving the heat pump coil temporarily unconnected. The warm/hot water from the tank will then feed the cold water inlet of the combi-boiler. I’ve read that most modern combi’s can accommodate this type of top up heating, but in the event mine cannot my fallback position will be to connect the combi to the heat pump coil until I install an ASHP in the future.
• At some point in the future, I intend to add an extension that will give me additional South-ish facing roof space. Would it be possible to add additional PV panels there that only charge the batteries and are not grid connected. Thereby avoiding issues with the FIT payments and export limitation?

So there are my thoughts so far. I would welcome any suggestions as to its feasibility.

Cheers in advance

Edited June 16, 2022 by bontwoody
Correction