Plug-in Solar - How much can you save?

As mentioned previously, savings come from using the solar as it's being generated. Simply put - if you don't use it you'll lose it. 

In the UK a 1kwp array (say 2 x 500w panels) can generate between 800kWh and 1MWh per year. If you used every kWh instead of drawing from the grid that would mean an annual saving of between £200 and £250 (based on a tariff of 25p/kWh). On the face of it that's a lot.

However all of that is generated during daylight hours, with the highest proportion in the brighter months when it's warm and the lowest proportion in the darker months when it's cold. 

So when do you use the most electricity? Generally in the colder months and in the evenings when solar isn't available. So you're not going to use anywhere near all of that. In fact you'll be pushing it to use 50%

Let's run some numbers 

Using an average consumption of around 10kwh per day and a base load of say 150w, a household without solar would have an annual bill (excluding standing charge) of around £912 (365 x 10kwh x 25p).

Using one of the many modelling tools available (eg Solar by Postcode), you can get monthly by month information on the amount of solar generated and then you can work out how much you might use. The table below models an average generation of a 1kWp array against an average household consumption of 10kWh per day

Based on this model, the average savings would be around 19%. That would equate to a saving of around £172 annually.

Now it's important to note that this is just a model and that your mileage may vary 😂😅. But there are ways to increase the benefit.

Over panel the inverter

An inverter (even an 800w one) can usually take more solar input than its inverter capacity. This is called over panelling. Some 800w inverters can take up to 2kWp of solar. On the surface this seems daft as if the panels are generating at their full 2kw capability, the maximum output will be limited to 800w (this is called Capping). However this over panelling can result in better generation in the morning and evening, boosting generation overall and potentially resulting in higher consumption by the household. Increasing your savings to above 30%

Load shift

If you have the ability to move workloads around (ie do your washing when the sun is shining) - also known as load shifting, you can use more of the generated energy. If planned correctly this could increase consumption to 40%.

Get a battery

A battery will allow you to store some of the unused energy so it can be used later. If you also have access to an off-peak tariff it can also store off-peak for use during peak times.

This is a game changer. 

A battery sized correctly (roughly the same size as the households peak rate grid consumption - so in this case 8kwh or there about*), can increase overall savings to 60% or 70%

* If you are on an off peak tariff, then you don't need battery capacity for that period. Similarly you don't need battery capacity to cover the time when solar is generating. So annoying average house with 2kwp of solar and access to an off-peak tariff would only need an 8kwh battery.

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One final note

If this blog has helped and you go on to installing a solar or battery solution, please let me know by leaving a comment and sharing this page as I really like to know I've been able to help. 

If you're considering a move to Octopus to charge your batteries in the darker months, please consider using my referral link below (click on the Octopus) as it will give each of us £50 off our Octopus bill.