20 or 30 tube solar panel?

[NickW]

Last year I purchased a 20 tube panel from Ivan which I later installed at my parents house. The particular system I installed involved using a 125 litre horizontal cylinder located in the loft to store the Solar heat. This feeds the cylinder below which is heated by the gas boiler. My parents and I are pleased with the performance of the system having seen the preheated water achieving over 50 degrees on some days. However when the weather is cloudy 30 degrees is more likely. I'm looking at installing a second system - this time in my own home and am considering using a 30 tube panel and 145 litre tank. I would be interested in hearing from anyone who has installed one of these larger panels in an average size home.

[Ivan]

Hi Nick,

We generally recommend using 1 tube for every 6.5 - 8.5 litres of cylinder volume.  Obviously it will depend on orientation of panel (South is ideal), and water consumption. A horizontal cylinder is less efficient than a vertical one, but sometimes it is the only option for loft installations. Also, loft-installed cylinders will tend to lose heat much faster than if sited in an airing cupboard, especially during the winter - due to much lower ambient air temperatures (even in the summer, lofts will be cold at night).

A 30tube panel therefore sounds a little on the large size - assuming you can site it SE, S or SW facing.  If you go ahead with an over-sized system, then it is a good idea to fit the BS3 controller and a heat dump of some kind (it can be 1.a towel radiator in a bathroom 2.a radiator hidden somewhere eg loftspace 3. you can use the second output to turn on the central heating pump which will reduce cylinder temperature by circulating water around the boiler and radiators (you will need to relay the pump from the CH controls to prevent the boiler starting up when this happens). Otherwise, it should be ok. I have the equivalent of 3 x 20tube panels driving a 260litre cylinder on my own house, but it does tend to produce *a lot* of *very hot* water on sunny days

Ivan

[NickW]

Thanks for the reply Ivan.

The horizontal  cylinder in the loft was the only practical and cost effective option.

To address the heat loss issue I have wrapped the cylinder in bubble foil wrap and a couple of old duvets. In April I measured the temp at 10pm and then again at 6.30am. In this time the temp only dropped 1.5 degrees so I dont think heat loss is a major issue providing extra insulation is added to the tank.

Regards

Nick