Calculating your potential energy savings from Solar Panels
Calculating your potential energy savings from Solar Panels
At the time of writing the average household cost of electricity is £0.28 pence per kWh with a standing charge of 0.53 pence per day (OfGem, 2024). This is an increase of 125% since 2010 (Nimblefins, n.d.) and costs are only expected to rise due to the increasing demand being placed on the National Grid by the electrification of heating and transport.
Figure 1 – Data from Nimblefins showing the kWh increase in electricity from 2010 to 2024
It is clear that increasing costs and inflationary effects of rising energy prices are here to stay and every kWh which a consumer can self-generate can help off set these costs. Below I will talk you through how you can quickly calculate your potential savings. At Landsmart, our experts have specialised software for calculating your site specific benefits but in the interest of dispelling myths and enabling the consumer to make informed choices, please read my suggestions as a guide. Landsmart prides itself on transparency and helping guide our customers on what is best for them.
Calculate your own solar generation and bill saving estimate
Now, all homes have very different electricity consumption profiles and receive varying quantities of sunlight irradiance on their roof spaces. So for the purposes of this investigation, we will use generalised data. Before we start, we need to know or estimate our electricity consumption. For usage consumption data, we will use readily available Ofgem usage consumption data (Ofgem, n.d.) which is compiled from millions of consumers monthly bills. A link to the average UK electricity consumption data can be found below
Here’s an excerpt which shows the average energy usage per annum of typical UK households. We will use the averages in the red box below for our analysis of a 2-3 bedroom home. We will come back to this later.
For irradiance data, the Met Office and other environmental data software companies have historical weather data which is taken from physical weather stations and via satellite imagery. By summing the hours and intensity of the sunlight received across all areas of Britain, an annual Irradiance Map is created. An Annual Irradiance Map details the number of kWh’s of sunlight which each square meter receives. On the map from Solargis below, we can see that the areas further south and closer to the equator experience more sunshine than anywhere else in the UK. For the purposes of this investigation, lets take the quantity of energy which a roof without any shading would receive per square meter in London. This is approximately 950 kWh p/year.
A link to Annual UK Irradiance Map:
https://solargis.com/maps-and-gis-data/download/united-kingdom
Figure 2 – Annual Irradiance Map of the Uk. Credit: Solargis
When we multiply this irradiance factor by the size of the solar panel system and make corrections for shade, we can get a fairly accurate estimate of the output of a home’s solar panel system. The equation is as follows: system size x irradiance factor x percent shade factor = estimated annual output (in kWh).
Now it is highly unlikely that a roof will have zero shading or will be perfectly south facing. So, I will add a shading factor of 15% to account for nearby trees, buildings or chimney stacks which at certain times of the day will shade the solar panels.
For our example in London: 3.6kW x 950kWh x 85% = 2907 kWh per annum
So, lets recap on both of the estimates we’ve calculated for a 2-3 Bedroom Home in London. Consumption p/annum: 3,900kWh p/annum. Generation p/annum for a 3.6kWp PV System: 2,907kWh. We can see here, that based off our quick estimate that a 2-3 bedroom home can self-produce 74% of it’s annual demand of electricity.
If only things were this simple! Unfortunately, even though it is possible to generate over 74% of the annual demand, the bulk of the generation is produced at times when the household has the lowest demand or during the day when the occupants are not at home. What happens to this excess energy? It is exported to the Grid at a fee which the owner of the solar panel system can collect from their energy provider. This only decreases the payback period for a Solar PV system as the money received for export is offset against the cost of the full installation.
For the simple facts that without a battery storage system and due to the mismatch between the times of day between consumption and generation we must apply a correction factor. At Landsmart, we have specialised software that can more accurately calculate your self-consumption rate and shading but for the purposes of this investigation we will assume that the occupants are in most of the day to utilise 60% of their generated solar energy. As mentioned, this would be much higher with a Battery Energy Storage System (BESS).
The estimated annual annual bill savings would now be estimated as follows: 3.6kW x 950kWh x 85% x 60% = 1744 kWh per annum
Self Generated PV as a % of total demand: 1744/3900 × 100 = 44%
An electricity bill reduction of 44%, would equate to a saving of £488 in year 1. This saving would increase with each expected increase in the cost of electricity.
Summary
In summary, Solar Panels reduce your bills and estimates can be quickly worked out by yourself based off freely available data and using assumptions around your properties roof shading profile, home occupancy and usage profile. Self-consumption for a PV System is key to delivering a net gain as soon as possible when it comes system investment. Battery Energy Storage (BESS) is the proven way to increase a properties self-consumption rate and depending on the size of the battery system, this can be increased to around 70%. Contact us at Landsmart where our advisors can discuss with you how we create for you a tailored proposal using our specialist software and tools.
Written by Ruairi Lynch 30/01/2024
Bibliography
Nimblefins. (n.d.). Retrieved from https://www.nimblefins.co.uk/average-cost-electricity-kwh-uk
OfGem. (2024). Retrieved from https://www.ofgem.gov.uk/energy-price-cap
Ofgem. (n.d.). Usage Consumption Averages. Retrieved from https://www.ofgem.gov.uk/information-consumers/energy-advice-households/average-gas-and-electricity-use-explained#:~:text=We%20estimate%20the%20typical%20household,of%20gas%20in%20a%20year.
