FoxESS Community - Owners & Installers Forum

A major driver for installing a solar system is to reduce energy bills, whilst also reducing carbon footprint. However, whilst odd snippets exist on the form relevant to optimising system design for saving money, I think it would be useful to put in one place how to estimate the optimum system size for a house and how to design to maximise how much money you save.

I am willing to kick this off, but any input and different perspectives welcome.

Step 1 has to be estimating about how much power you consume at what time of year.
A Secure SMETS1 meter conveniently gathers and displays on screen your kWh consumption per month - other meters may also do this and it is worth checking, but I don't believe our current SMETS2 meter makes this available on screen. However, reading data off a SMETS 2 meter via your utility company, or via the apps Hugo or Loop Energy may be a solution. Otherwise its careful reading of historical bills. If you can only gather an annual figure, then I would assume Winter (December) consumption to be about 60% higher than Summer (June) consumption.

Step 2 is looking at where the solar panels could be sited, and estimating:
a) how many (remembering that generall panels cannot go closer than 300 mm to a roof edge to minimise damage risk from wind, and the roof wants to be as free as possible from shadows for the majority of the day, ideally for the whole year ),
b) what orientation from North (Google maps is good enough for this), and
c) what pitch, or angle from the horizontal.
This data can then be used on sites such as:
https://globalsolaratlas.info/map?c=52. ... l,160,45,5
to calculate the likely output by month of year and for the total year.
As a rule of thumb 1kWp gives about 1000 kWh/year.

Step 3 is comparing the annual and month by month figures for generation and consumption, and considering what system will give you the best advantage. A good starting point is a system that generates in a year what you use in a year, but of course you will not use all the energy you generate because you generate more in Summmer, when your use is lower, and less in Winter. The problem with going for a system much larger than this is that generally the capital or purchase cost rises faster than the savings, so the return on investment (ROI) falls, although the absolute savings may rise. A more detailed look would look month by month, and ways of maximising self-consumption (using power you generate) which will come in the next post.

It would be wise, when designing the system to allow for growth energy use, as in the future, more and more electricity will be consumed by households, as heat pumps and EVs are more widely taken up.
Also consider a growing family. Very young children will not present the same energy demands as teenagers, for example.

Another consideration is energy storage. Expensive as it may be, one will ideally require a battery system with enough capacity to run the house for a day, to be able to make use of cheap rate (time of use) energy tariffs. Something to bear in mind if choosing to buy an EV at some point, is Vehicle2Grid technology. EVs are a more cost effective way to increase battery capacity for a house because they are cheaper Kwh/Kwh than batteries alone.

Using solar to run the house loads, charge an EV and household battery storage and heat hot water via a solar diverter to an immersion, will allow most, if not all energy generated to be used. It is inevitable that there will be a shortfall in the winter months, but the additional energy costs will be greatly mitigated by the 'free' energy generated in the summer.

I am still running some calculations for my immersion use and will post these on the forum for those interested when they are complete.