Just a wee bit of background, my property is a 1980's timber-frame detached bungalow of 147sq m. I was initially interested in Solar Energy but through watching many videos I was made aware of battery storage by a Fully Charged article.  I then discussed various options with Home Energy Scotland and my local supplier Solar and Wind Applications and decided to install a Solar array of LG panels with a capacity of 5.3kW and two Tesla Powerwalls with a storage capacity of 27kWh. I also change my supplier to Octopus Energy and signed up for their Agile Tariff for both Incoming and Outgoing Electricity. Now I can buy clean cheap energy overnight and store it in the Powerwalls to be used at peak periods during the day. Also I have power cut protection through the Tesla Gateway 2 which is really the brains of the set up.

As you can imagine living in south west Scotland there is not a great deal of sunlight during November to March but anything that is generated is saved in the Powerwalls and any surplus is exported to the grid.

Octopus and Tesla also offer a new tariff in which Tesla will control your Powerwall and export and import power at a flat 11p per kWh.

Through this setup, during the period of November to March, I have reduced my Grid consumption by 33% and dropped my monthly bill (including gas ) from £132 per month to £73 per month and I'm sure from now till November I will reduce this considerably.

I intend to have a Vaillant 7kw AeroTherm Plus installed in the spring to replace my gas boiler and complete my transition. The 27kWh Powerwall will help store both Solar and cheaper grid electricty to power the ASHP. The AeroTherm uses the R290 refrigerant and is capable of higher flow temperatures and has an advertise SCOP of 3.64 for a flow of 50 degrees C.

Obviously I have to complete the install and run the system for a full year before I can give a full rundown of the running costs.

@duncan-mac Hi you have a similar set up to me ( LG solar (except mine is only 4Kw) Vaillant ASHP and Im with Octopus) When finances allow I will look at a powerwall. So I will be very interested to see how you get on with them. 

Octopus are taking my gas meter out next week (FOC) so that will be another step to a totally renewable house!

I'll be watching out for your posts with interest!

One of the most interesting features of the Tesla set up is the reporting both real time and historic reporting All data , Grid Input, Grid Output, Solar to home, solar to grid and solar to the Powerwall, together with energy to and from the Powerwall.

Data is available in CSV format to download. All this helps me understand where the power is coming from and how its being used. Also you can workout the losses from generation to Powerwall and back to Home use (AC to DC to AC).

@editor sorry I missed this before I posted yesterday. This is the spreadsheet i was talking about. with a little patience and effort it gives a great picture of the system you might have or considering.

I have a similar display with my Victron CCGX and can control everything but the charge rate on the Tesla  and the hot water on the Heat Pump from my phone.

Here's another

And one last view

@chris-in-kemnay consumption of 34kWh already ! 

My lowest thus year was the 27th February  when it was sunny 7.09kWh I charged the car and used the heatpump during the sunny day using the batteries as a buffer. The most I've used this year was on the 7th Feb 87kWh  it was windy and prices were low.

Best solar day was 22 kWh on the 27th Feb. But this year so far is way down on last year 200 kWh less sunshine this year so far

@chris-in-kemnay I blame the pandemic for the lack of sunshine,  or is it the 5G towers ? I get confused 🙂 hopefully the year will become more brighter 

@chris-in-kemnay, the images are so slick. We have a SolarEdge inverter and their app is cool, but the displays are nowhere near as nice. 

I think going back to the original question asked by Bob.. I think calculating heat loss can be very simple. Once your house has reached the target temperature, start recording the time your heat source worked (of course without opening doors/windows) for example if your heat source gives out 24k BTU per hour and came up during the night for 2 hours then your house is losing 48k BTU. Does that make sense?