We’ve had our solar thermal panel up for nearly 2 years now, and while it has been great, we always knew it was slightly too small for the size of hot water tank we have. Some time ago our friend John Clementson was kind enough to let us rehome a couple of older evacuated tube panels, but only now do we have a roof to sit them on. Adding them was in theory a straightforward plumbing job, but in the end, involved two days worth of cursing, head scratching and occasionally downright panic.

Having initially plumbed them into the existing setup, I watched expectantly as the temperature began to rise at the panels. And rise. And rise to 120 degrees C – possible because of the pressurised system and antrifreeze (it raises the boiling point). All the while the temperature in the hot water tank remained exactly the same. Not good.

As steam began to issue forth from the joints in the pipework, and I opened the release valve to reduce the pressure, things didn’t look great. Several hours of bleeding air, filling, refilling, pressurising, depressurising, and eventually I admitted defeat and dismantled all the pipework. In the end I found a tiny piece of old insulation had blocked a pipe, and once removed, water circulated, and all was well. It demonstrated that in these systems, it is a relatively small amount of circulating fluid that maintains a balance between functioning happily, and catastrophic overheating.  The additional panels make a huge difference, and even on a moderately bright day we had 200 litres of water at 55 degrees C, which will save a lot of fire lighting.