Ask RiotACT: Switching from gas to solar hot water

We had an electrician install a timer in our fuse box to control the operation of our electric booster. The timer switches the booster on automatically each morning for a set time period. In autumn and spring, we have the timer set to switch on the booster for 30 minutes from 4:30am. In wintertime, the booster comes on for two hours, from 3am to 5am. During summer we don’t need the booster at all. The brand of the timer is Theben and the model number is TR 608 top2 S: https://www.theben.de/en/Products/Time-and-light-control/Digital-time-switches/DIN-rail/Weekly-program/TR-608-top2-S

Continuing from my previous comment.

Without a switch to turn the booster on and off, you would not know if the solar part of the unit is working. You might be using the electric booster as your only heat source. Very expensive electric hot water system that would be. That happened to me with my new solar system. The solar part of the unit had a broken wire and it wasn’t working. The water in the water tank was being heated 100% by electricity. It was only by insisting on a switch to turn the booster off did I discover this. Otherwise I would have had no way to know. When I turned the booster off my water didn’t heat. Therefore I knew there was a problem and had it fixed. It works as it should now. Fortunately I had the switch installed when my unit was new and so I wasn’t using only electricity for long.

Imagine if I hadn’t had that switch. I would not know the solar part wasn’t working and years later I would be thinking I was saving money, using less electricity, when all along all I had was an electric heater.

I do wonder how many people with boosters that can’t be turned off have broken units and are only running on electricity. They wouldn’t know, and this could have been happening for years. If you can’t turn off the booster, don’t be sure the sun is heating the water. You can’t tell if it’s the sun or if it’s only been working on electricity.

I have solar. I only need the booster for about one to two months a year. The sun heats the water for the rest of the year.
My system did not come with a switch to turn off the booster. An electrician installed one for me. The people who installed it argued that not being able to switch off the booster stops the chance of Legionnaires’ Disease and the like. The trouble with not being able to switch off the booster is that the water drops below 50C and the booster comes on; say after evening showers. Then next day is a hot, sunny day and the water would heat up in no time. With a booster that can’t be switched off electricity has already heated the water, defeating much of the reason for having solar hot water. Besides, for ten months of the year it’s rare that the water is not above 50C sometime during the day and for the two months it isn’t, it’s easy to turn on the booster. Make sure you have a switch.

We changed ours over to solar about 5 years ago from a gas system. Our previous system was on its last legs so we had to do something to avoid the middle of the night in winter fail. We weighed up continuous flow gas versus solar over a 20 year period making guestimates for where utility costs could go. Then we added in the warm inner glow factor from being increasingly green. Haven’t noticed an increase in electricity consumption from the booster being on two hours early morning and early evening. The gas useage hardly declined in relative terms – we had an old ducted heating system until recently. Over the recent Christmas we had up to 8 people in the house at any time and had no hot water shortages. On balance, I would do it again if the old system was about to fail.

A few things to note though. Modern solar hot water systems are quite complex compared to earlier models and as such not quite as reliable – expect to make a few warranty claims for small leaks or overflow valve failues etc. Also, once you install your new sysetm, you are subject to all the new plumbing regulations including lower pressure and temperature.

Try mains electric with off-peak. According to the government all our electricity will be renewable in a couple of years so you can still feel warm and fuzzy about climate change without having your own (expensive) solar hot water.

Of course you will save money. The question though is will you save enough to pay for the cost of the new system.

Frankly there are far too many variables to answer that simply.