Saturday, September 4, 2010

Lifestyle 'load shifting'

Did I really have to die for you to run
your washing machine?
4 Sept: I had an email from a reader of this blog asking if a PV roof prompts alterations in lifestyle. Well it does, in summer for sure. The purpose of our PV roof is to reduce the amount of fossil fuel burning in Ratcliffe-on-Soar (coal fired) power station. Our motive wasn't the Feed in Tariff, but it was our catalyst, our enabler to do an action that we had wanted to do for 3 years.
   If we use electricity at night, some poor little piece of coal, far away, grown from a fine forest tree 60 million years ago, is glowing red, and then finally fading to ash... all because of us. It has to be imported - so I prefer to grow my own. Perhaps this is akin to vegetarians not being able to bear the thought of animals being slaughtered for food.... :)
   So if we have to do something that uses electricity, we time our usage to meet the peak of the roof productivity - our peak is 1030-1100 because the roof is east facing. The heat pump is delayed by a time clock so that it cannot start until 0900, even in winter. If we have a clothes wash to do, we will delay the washing machine that till 1000. If the dishwasher needs running, this never goes at the same time (because it might exceed the output of the roof), so that might be timed for 1100. Then if there's a bit of ironing to do, that might occur at 1200. The washing machine or dishwasher also stimulate the heat pump into further action due to the use of Hot Water, but this is when the roof is producing. Always use A-rated appliances if you can.
  At some point, we might want a damn good cup of coffee, so the kettle is on for a minute (actually, when I replace the kettle it will be an 'Eco-kettle' - of course 'elevenses' coincides perfectly with the roof power peak.
  We still turn off standby items, and avoid leaving inessential items powered up - so more gets exported.

What does this all mean? Well, as we are an electrically heated household, due to the heat pump, it means we are using more like 70-75% of what our roof produces, not the normally expected 50% - so our ratio of Saving to Sale is highly advantageous. In the Winter, we use every tiny watt it produces, and we continue to use every kilowatt in the spring Equinox. We are only exporting (big time) in the Summer and Autumn Equinox.
    In the first year, we have generated 3,300 kWh, and in the same time period reduced our annual electricity import by 2,500 kWh from the previous annual average. That suggests a 75% ratio of usage, but if we have got also some saving from tuning of the heat pump (Sunboxes and timeclocks), that figure might be more like 70%. Financially that means that in addition to £1,360 from the Feed in Tariff, estimated Savings are worth £325, and Sales are worth £24. That totals £1,700 a year.

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