Grid Electricity Usage

Domestic Electricity Imported from the Grid (Image: T. Larkum)
Domestic Electricity Imported from the Grid (Image: T. Larkum)

Looking at how much electricity our solar array has generated prompted me to look at how much electricity we’ve been using over the last few years. I was able to dig out most of my energy bills back five years and used those in a similar process to graph our usage – see the chart above.

One of the first things that is obvious is that there is only data for the four quarterly bills in a year, there is no data per month never mind per week. This general point highlights how poor are the systems in place for tracking energy usage. I didn’t realise it before this exercise but our meters are only read about twice per year (typically in May and November) so there’s no real indication of how much energy you are using at any time, and the bills in between these readings are just based on estimates.

Of course the government has plans for everyone to get smart meters installed to give better tracking of energy usage. However, the start of the rollout was planned for next year and has just been delayed by a year. They won’t be fully in place before 2020 which is a long time to wait. In the meantime to address the issue of a lack of detailed information on energy usage I have started to manually record the electricity (and gas) meter readings once per week.

Anyway, back to the chart. Given the lack of data, and its questionable accuracy (since it includes estimated readings) it is dangerous to deduce too much from it. It fairly clearly and as expected shows higher electricity usage in winter months compared to the summer – presumably from more use of lighting, and perhaps more time spent indoors watching television, etc.

I would also like to conclude from it that our usage of electricity from the grid has reduced since installing solar, i.e. that the values for 2011 and 2012 are lower than previous years. However, that is not obvious, and in particular the usage for Jan/Feb 2011 is particularly high. It would probably be wishful thinking anyway, since we are often out (and hence electricity usage is low) when the sun is shining brightest. So what can be done to get more benefit from solar?

There are three key income elements to the government’s solar feed-in-tariff system:

  1. You get paid a generation amount for each unit of electricity generated.
  2. You get paid for each unit exported to the grid. However, since there are no smart meters in place yet this is done notionally: you get paid an export amount for exactly half of what you generate as though you exported it.
  3. Given that the export isn’t metered, you can use the electricity you generate for whatever you want for free.

This means that there is a clear economic benefit to using as much of the electricity you generate as it is being generated, since it deemed to be exported but is actually available to use. This ignores, of course, the complex moral question of whether you should just export it anyway so as to reduce your neighbours’ carbon footprints regardless of the economic cost to yourself, and I may return to this question in a future post.

Anyway, assuming for now the aim is to get the best economic benefit from the solar array, I have been considering some ideas on how to achieve it:

  1. We need to defer our electricity usage to the times when most electricity is being generated. This means, for example, operating the dishwasher and washing machine during the day rather than in the evening (and so using their timer functions if we are out during the day).
  2. Use some electricity storage such as batteries. However I believe such systems are still too expensive to be economically justifiable.
  3. Heating our water electrically to save on gas usage, i.e. operate our electrical immersion heater from solar during the day. There are some technically advanced systems for doing this such as Immersun but they are expensive and so payback would take a long time. I am currently looking into simply running the immersion heater from a timer during the summer months so it operates during daylight hours.

As well as economic benefits I am determined to reduce our family’s carbon footprint – getting the solar array and the ZOE are the key elements to this. There are also other approaches and lifestyle changes that I will be investigating; others are further along this road than I am and I recommend anyone interested to research further. I have put some starting links on the Links page, for example the excellent Earth Notes site.

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This topic contains 9 replies, has 4 voices, and was last updated by  Trevor Larkum 6 years ago.

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    Trevor Larkum

    Looking at how much electricity our solar array has generated prompted me to look at how much electricity we’ve been using over the last few years. I [See the full post at: Grid Electricity Usage]



    Interesting 🙂

    I’d love to hear what further plans you have to reduce your carbon footprint. I’ve mentioned before that I am not a great fan of the FIT payments but there are lots of things you can spend the FIT payments on that will have a real impact on your carbon footprint. For me the focus is on gas usage which it sounds like you are starting to think about as well. Be careful about the immersion heater / timer idea though – if it is a cloudy day you could be using more on your 2Kw heater than generating with your solar.

    While I’m still keen on solar heating for hot water and central heating it could never really replace a gas boiler and as air-source and ground-source technologies have improved I have been considering them more. They work like the Zoe heat pump so use some electricity to ‘gather’ heat from your surroundings. With solar panels and/or a green energy provider they will have a 0 carbon footprint and are much more reliable and stable than solar heating .



    Here an interesting mobile battery:

    Also available in UK:

    Here the missing link solution for the bigger grid:


    Trevor Larkum

    @farblue – good points! I’ll be monitoring my combined 6.9kWp system over the next few weeks to see how well it would cope with the immersion heater load.

    @nosig – interesting links. I’m very keen on getting battery storage at home, as soon as it becomes affordable.



    First:Utility have smart meters: I get an online report of usage by hour of day, day of week, and month. I’m not convinced they’re terribly cheap though.


    Trevor Larkum

    I asked my supplier, eOn, about smart meters – they said I could have one except they don’t work with solar. Not so smart, then.



    Have a chat with Good Energy. Their product innovation manager (Will Vooght is in charge of the Smart Meter trial they are organising for this autumn (about november) and was keen for me to be on the trial when I mentioned buying a Zoe. He specifically asked if I was also considering or had solar. To my knowledge I am currently the only EV owner (well, owner-to-be) on the trial so he might be interested in you joining. He said he created a whole new category for me!

    I’d also recommend them as an electricity supplier as they are the only energy supplier who has only 100% renewable sources. They also won Which best energy supplier 3 years in a row for customer service and are extremely pro-solar 🙂


    Trevor Larkum

    I am certainly considering them, but I’m inclined more towards Ecotricity as they put more of their income towards creating new renewable energy systems (mostly wind). Both firms did very well in customer service and FIT payments, whereas my current supplier – eOn – were bottom!

    This is Ecotricity’s view – I haven’t found an independent assessment:

    There is one for supply info (most companies are abysmal):



    Ecotricity is another very good choice – it is really just a matter of personal preference 🙂

    I think the problem with Ecotricity’s investment info is that it only takes into account the money spent directly by the company on renewable projects it owns (and it is happy to shout about it because they’ve recently started a huge investment stage). Good Energy takes a different approach and provides funding to other projects that are working on energy saving, renewables etc.

    For instance, Good Energy has a thing called HotROCs which they came up with before the FIT and RHI schemes where invented. They pay you 4.3p/kwh of renewable heat you generate through solar and other systems – and that’s all funded from their profits.

    They also support renewable generation through FIT and ROC certificate management on behalf of projects and through all of their generation offerings (from home generation to large projects) currently support over 46,000 generators.

    They are also an ‘ethical investor’ and Green Energy Supply certified 🙂

    My personal concerns about Ecotricity revolve around some of its business practices with certificate trading and its historical fuel mix. I know the fuel mix is currently around 60% renewable but only a couple of years ago it was only 24%. They are also a supporter of nuclear which I disagree with 🙂

    Another good site to check out is:

    One definite plus for Ecotricity is the Nemesis electric vehicle 🙂 They also have about 8 service stations with fast chargers (you can sign up for a free rfid card):

    I used to be on Eon’s ‘Go Green’ tariff and Good Energy came out about the same price. Ecotricity was a little more expensive for me – they try to match British Gas rates.

    While I was unable to sign up for it, Ecotricity also offer a limited quantity of ‘green gas’ generated from waste which would be a great way to reduce the carbon footprint of your central heating 🙂


    Trevor Larkum

    Thanks for those comments, farblue – more food for thought for me.

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