We're thinking of extending our home by adding a single storey 'garden room' to the rear of our home. Whilst many would be thinking of colour schemes and interior design, my thoughts have been whether we could add more solar panels or if we would have space for a heat pump.
Heat Pump
We had gone ahead with approving the Octopus Heat Pump quote and were waiting for the initial site survey. After speaking to Octopus it was decided that we would get the building work done before progressing the heat pump further. What I need to do was ensure we left enough room for a heat pump to be installed.
Thankfully even without the Octopus site survey we could estimate what heat pump would be required by going back to the 'visit a heat pump' we did a few months ago. That house was very similar to ours so I could estimate we may need a 5kW Valiant heat pump. Thankfully Valiant provide their installation manuals online so I could download them.
Using the details below `I was able to suggest an area of 0.8m by 3m running alongside our extension room should provide sufficient space for a heat pump in the future.
Solar Panels
By adding the extension we will be increasing available free roof space. To me empty roof's need filling to make them work for you more than just providing a waterproof shelter. When I see an empty roof I always think about how many solar panels could fit. It makes sense to install in roof solar panels if we installed them as part of the extension, rather install roof tiles then put solar panels on at a later date.
I've always wanted more solar panels but we could only install 9 panels on our entire south facing roof As the other side of the roof faces north there isn't much point installing them on that side as they would be in shade most of the day.
We've calculated our garden room extension will be 3m by 4m. This should provide enough room for 3 off in roof solar panels.
Design of the rear garden room extension
Dimensions of new solar panels
Estimated Generation Increase
I've calculated the estimated generation for our existing 3.69kWp system and the additional 1.23kWp system using the EU Photovoltaic Geographical Information system.
We should see a 31% generation increase from three additional solar panels as long as we are able to increase our export limit via G99 approval to the full 5kW.
When I compare the payback to our existing system it should increase our overall RoI (Return on Investment) by just 5 months at current rates. That's actually better than I thought it would be.
Increasing Battery Capacity
We could also increase our battery capacity by installing another 2 off 5.1kWh batteries for £3000. This price shocked me as our batteries cost £5500 only 12 months ago!
Installing additional batteries would increase our useable battery capacity from 8kWh to 16kWh. Whilst we don't currently use all of our battery capacity (20% daily in summer and 60% in winter)if we were to install a heat pump our electricity use would increase.
We run our heating for about 5-6 months a year (October to March). It's difficult to say how much power a heat pump would actually consume on a daily basis. I suspect much more than the 8kWh capacity of 2 off additional batteries. I do wonder if we would be best to install the heat pump first then decide if we really need additional battery power. We could install the heat pump supply so that it's not seen as a house load therefore outside of the solar and home battery system. We could easily move it back in by moving the position of a CT should we find we do want it to be powered by the home batteries. It would be easy to install additional batteries should we want to in the future.