Solar Kent

Going Green: Solar Water Heating in the UK

Its 2007 and this is the third year that I have had solar water heating. Use of the system is balanced by my wife who wants lots of hot water (while saving the planet) and myself who wants to save money, energy (and the planet).

During the long wet period with almost constant cloud cover from early June through to end of July - lets hope its back to a proper summer - the solar panels have performed, though poorly. the odd sunny day and the hot water cylinder temperature gets to a realistic level from the panels, a cloudy day and we have to switch on the boiler to top up the heat.

solar water heating panles

 

During June and July the boiler was set to come on for about 20 minutes at the start (06:00) and end of the day. The very early heating to allow for getting up in the morning leaving a hot tank ready for solar heating. The end of day heating to either top it up or not depending on the solar heating during the day.

The boiler is set to heat if the cylinder is below 55C, the solar panels are set to take the hot water cylinder up to 65C.

2005 and 2006 we had pretty reasonable summers and as expected were able to switch the boiler off in May then back on late September / early October.

I expect that anybody who has installed a solar hot water system at the start of 2007 will have been disappointed,- stick with it, its just a bad year for sun!

Lessons I am learning.

Though the PV is very much a case of install then forget it, any excess electricity is sent to the grid, the Solar Thermal needs a bit more thought.

If the boiler has heated the hot water cylinder, the solar, however hot the sun is, won't get a chance, the solar panels shut down when the tank reaches the preset working temperature.

You need to keep an eye on the amount of solar heating being generated so that as the year progresses, the normal heating can be lowered allowing the solar to take the strain. Towards Autumn, the reverse is true, but its fairly obvious, the hot water is colder and it is clear that more normal energy needs to be apllied.

In a wet and cloudy June, July, August or September , solar heating doesn't quite keep up with the hot water use - (wife not happy). It can be necessary to top up the heat with traditional forms of heating.

(Can't get in to re commission the boiler as swallows have taken up residence and they object to me spending too much time near their chicks - 2nd brood of the year! 2006 and 2007 the swallows are back, they have raised 8 chicks each year, only one fatality so far. )

Where we are its a hard water area, with the investment in a new cylinder and the desire to keep it working at optimum levels, perhaps time to consider a water softener or some kind of water treatment in order to keep the hot water cylinder happy.

But, with a water softner using salt, is there the risk of increasing salinity of our cesspit which is emptied onto a reed pond? - its not easy being green!

Solar Water Heating - Is it worth it?

Month end

Kw Hrs Month

(Cumulative)
Kw Hours

January
9
9
February
51
60
March
230
290
April
510

800
May
540
1350
June
750
2100
July
650
2750
August*
500
3250
September*
500
3750
October*
500

4250
November
100
4350
December
45
4395
January
52
4443

(From the 1st year)

1st indications are amazing with almost 5KWh equivalent generated on the 1st day - Sunday 28th Jan when it was mostly overcast and very cold!

I am expecting that I will be able to switch off my hot water system which is oil fired, during the spring, summer and early autumn. -

I wrote this when I created this page (That being the case I will save at least £300 a year on water heating).

With the recent increases in oil and from my practical experience that I have managed to save a full tank of oil 1,000 litres over the late spring, summer and early autumn - to end of September, my saving excluding any topping up of heat by the solar system from October - April is 1,000 litres * the cost of oil say 37p per litre. Now I expect to save at least £400 per year!

This is now based on experience rather than theory.

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The chart below shows my adaptation of the genersys savings chart, this is oriented towards a typical installation. I have omitted savings on boiler replacement and servicing but added a Hot Water tank replacement at £800.

I now have a new seriously well insulated 300 litre cylinder included within the price. My old cylinder is only 10 years old but full of scale - like most of Kent, I live in a hard water area - and with minimal insulation, it was over due for replacement! see the pictures

Values below are based on: 70% of hot water generated by Solar Heat, 30% of heating bill for hot water, fuel inflation 7% Per year - this last figure has become a bit silly as fuel inflation has been significantly higher than 7%!

Current Costs
Year 1
2
3
4
5
6
7
8
9
Oil
1000
1070
1145
1225
1311
1403
1501
1606
1718
Boiler Servicing
120
123
126
129
132
136
139
143
146
Total Annual Cost
1120
1193
1271
1354
1443
1538
1640
1748
1864
Cumulative Cost
1120
2313
3584
4938
6381
7920
9560
11308
13173
 
Assumed / Actual Cost Savings
Oil Savings
400
428
457
490
524
561
600
642

687
Hot water cylinder replacement
800
Total Annual Saving
1010
                
Cumulative Saving (excludes boiler servicing) 1200
1628
2085
2575
3099
3660
4260
4902
5589

Most installations will be 2 panels with a total of 4 square meters, I have opted to spend a bit more on 3 panels and a larger than normal hot water cylinder.

* If I factor in the new hot water cylinder that came with the system, my existing one had to be replaced anyway as it was thick with hard water scale, the actual cost of my system could be said to have been reduced by the cost of a hot water cylinder! Then take into account probable increases in oil costs, I might expect significantly less than a 10 year payback!

* We have a family of swifts who have a nest (now two nests) close to the readout. The parents aren't a problem, we all pretend we can't see each other, but when they were raising their chicks (two broods) we avoided going near the readout, hence a gap. The total reading so far this year for end of October is accurate (1,500 Kwh equivalent over August, September, October).

Also see Solar Electric or Photovoltaic (PV)