Friday, 10 June 2011

I'm in "hot water".....

We've heated hot water in the past using our gas central heating boiler either as a by product of the heating in the winter or as a stand alone program during the summer.  We’re very fortunate as when the heating engineer installed the heating system some years ago he provided us with a back-up electric heater in the top of the immersion tank.

I wanted to use the solar power to heat the water, but I realised that unless I timed the heating cycle to coincide with energy generation I’d possibly be adding to my costs rather than reducing them.

After some research on the internet I decided that my local branch of Screw-Fix had just what I was looking for. I paid £21.00 for a timer unit which I then added to the wiring circuit. It was a simple task which I managed to make difficult by pushing the tails from the wire too far into the holes, I’ve never come across the situation before as they are normally ‘blind holes’ which don’t allow you to push the wire in beyond a certain point. Anyway, I managed to tighten the screws down onto the insulation on the wire rather than the bared metal tails. It took me a certain amount of head scratching before I realised my mistake...

The unit provides a multitude of timing options.
  • Specific days/ groups of days.
  • 4 timing programmes within each of the day selections.
I just need it to heat the water once a day. I’m making the assumption that 365 days a year the most productive time for the PV panels will be around midday? The immersion heater element has a thermostat fitted as standard and I’ve initially set it at 40 degrees. I’m hoping that the timer will kick in a the specified time and the thermostat will turn the whole process off once it’s achieved the required temperature.

I’d be very interested in any feed-back from anyone else who’s using PV panels to heat water.



  1. singingshutters8 July 2011 at 14:36

    I was considering a similar scheme. We have an oil fired condensing boiler which presently provides our hot water in the summer. Until Feb 2010 we had a solar panel system that did this job instead but it froze in the winter of 2009/10 and burst and insurers won't pay for a repair. As I am now going for PVs it occurred to me that I could use my "free" electricity to heat the water in the summer and, like you, I thought midday would be the optimum time. My PV system will be a 4KwHP system. As my immersion heater is 3Kw it seems to me that there will be precious few times when I will be generating enough electricity to power the immersion heater and other ongoing equipment (PC, Router, PVR, pumps, kettles etc) and I am likely to end up paying for imported electricity. I need to compare the costs of this against oil and the amortised costs of replacing the parts of the solar thermal system.

  2. @singingshutters
    Hi. I'm in the process of trying to establish the economics of heating water with PV panels. I suspect that my system, (2.66KWh) isn't adequate for the job. I'm currently averaging 1.1KW around midday which means I'm paying for the majority of the power used from the grid. Obviously, this wasn't what I'd envisaged. I suspect you will get closer to the 3KW required with your mega system. I'd be interested in your comments once you're up and running.
    Best regards. Ian

  3. I would also be interested in whether you achieve savings. We don't use the immersion heater as in the summer we've used our gas CH system in mornings and evenings just to heat the water. But now we have a PV solar system we are thinking of using the immersion in 'summertime' (lol) only from 345pm, perhaps for a couple of hours - to cover evenings and the next morning's requirements. I will need to compare gas units with electric units to see whether any savings can be made...

  4. @Chrisso
    Hi Chrisso.
    I personally think with my 2.66kWh system heating water using electricity during the day is a bit of a blind alley. I will be posting my energy usage figures in the near future and how they might influence my usage now that I have "free" electricity during daylight hours.
    Best regards.

  5. this site nay be of intrest to some of you

  6. @Anonymous
    Great site....I suspect the majority of solar panel generators will be looking to optimise the output from their roof tops especially during the cloudier months.I wish I'd payed more attention during my Physics lessons.....

  7. They are harder to find but you can buy 1kW immersion heaters. Also, I have heard it suggested that one can use a step down transformer to lower the voltage to a heater which will lower the power. A 240 V 3kW heater will put out 750 Watts when run through a 240 to 120 Volt step down transformer. This type of transformer is commonly used on building sites for safety so they can't be hard to get hold of. Ideally one wants to monitor the power being used in the house and subtract it from the total power being produced by the PV panels and then dump the difference into an immersion heater. I considered the idea of a high frequency variable power controller which could dump the excess exactly in a similar way to a DC motor controller. Not sure if it's worth getting that complicated though.