Sunday, 3 July 2011

When's the best time to use electrical appliances when you have solar panels?

We all hope to reduce our electricity bills once we’ve taken the plunge and installed PV panels on our roofs. Its early days, but I’m slightly disappointed by the amount of power I’m still using from the grid. I know that in the 12 month period June 2010 – April 2011 we used 3618 kw of electricity an average of 9.9kw a day. In the 25 days since our installation we’re using on average 6.5kw a day, as we’re in the warmest time of the year and rarely use lights a 33% reduction is worrying.

I installed a timer to heat our immersion tank each day assuming it would be a “freebie”. "Hot Water"  I’m turning it off next week to check if it’s skewing the figures by its heavy power usage.

The Sunny Beam monitor allows me to collate the daily output figures and present them as a graph. Click to view data.
Unsurprisingly, this indicates that in June 2011 the major output is between 11am and 3pm when it averages over 10% per hour. I intend to collate these figures each month to get an indication if mid-day is always the most productive time here in the East Midlands.

Watch this space…



  1. Hi

    I've also taken the plunge and the first thing I've noticed about our usage in the home is this.

    in the month of October, our generation meter has been averaging around 800-900w (6Kwh per day maybe). When I turn on a kettle I use 3Kw. When I turn on the electric shower I use 8Kw. and so on.
    The Oven, the Microwave, the Hoover all similar (2-3Kw).

    So, unless you generate 2Kw (i.e a really sunny day) at any given moment, you are always STILL going to get charges for your electricity.

    My answer to the solution is this. where possible, buy LOW power appliances and use them in series. first make a cup of tea with a 1Kw kettle, then cook with a 600w microwave, turn on a 900w heater in a room for 2Hrs etc etc.

    Nothing in parallel and nothing that sucks massive amounts of juice. Therefore always staying close, to the power you're generating.

    AND do as much as possible in the day.

    I have just purchased a low power kettle and 900w oil filled radiator for exactly these reasons.

    all the best

  2. @Anonymous
    Hi Jonathan. Unfortunately, I don't know how to contact you , but I would like to give you a huge pat on the back for your lateral thinking. I hadn't thought through the implications of having low powered "FREE" appliance usage during the day. I'm intending to research the options available and blog my experience of using alternative items during the winter months 2011/12.

    Thanks again for a great comment.

  3. This seems a tricky question to answer and depends on hours and strength of sunshine of the day. Say you have a 2kw rated dishwasher, and its cloudy and the panels are only generating 500w, then you'd only get 1/4 of your electricity from the panels and have to buy the rest at day rate. But if you have Economy 7 you could run the dishwasher at night and maybe save 2/3 on the unit price which is therefore cheaper than running it in the day.
    I've tried setting the dishwasher to come on at 4am when the forecast is cloudy so as to catch a combination of economy 7 and some early summer rays. :)
    This all assumes a 2kw dishwasher consumes that consistently which it probably doesn't. Each part of the program will be different. I suspect my 4am technique is fairly useless if most of the energy is used at the beginning to heat the water, when its still dark.
    What owners of solar panels really need, is appliances that consume energy slowly. For example weaker heating elements that take ages to heat up and maybe added 40 mins to a wash cycle , would be great for use when we've only got 500w coming out. The only obvious example of that really existing in practice, is a slow cooker which is absolutely ideal for use with solar.

    1. Hi Nick.

      I've looked at your comments regarding Economy 7 and how it could work with PV panels. Take a look at the new post on the subject & let me know what you think.

  4. I use the solar immersion switch mark II from to monitor the PV production and the house hold load to control the immersion and other devices. It monitor both the PV production and house hold consumption to make intelligent decision when to turn on the load via relay.

    Its very affordable too.

    I use it together with the 3 kW power reducer from ( to bring down the existing 3 kW immersion to a 1.5 kW.

  5. I am not quite so technical,but my routine is to load the dishwasher during the day finishing with the pots from teatime.
    In the morning if its sunny the first job is to turn it on unless of course you have managed to do it before 6.00 pm the night before.
    There is only two of us in the houshold but there always seems to be enough in the wash basket to make either a whites or a colours load, so if the suns shining bang it on.
    My fist year generation is 3441KW which is over 9KW per day average, so there is plenty of scope for flexibility without it being too much of a chore.
    One thing I have noticed is that even on the coldest days proving the sun is shining the generation is not too different to warm days.

    1. That's because solar panels are most efficient when they are colder.