I now have my evacuated tube solar water heater disconnected from the house’s plumbing system and in ‘winter mode’ meaning that I am crossing fingers it doesn’t freeze and break the tubes :). It does have electric heater element inside, and I will switch it on, should the water temperature fall bellow 5 degrees. Here are some interestng graphs to show, we had four sunny days last week, though it was very, very cold: down to -12.5 degrees C. Still the solar heater was able to reach 81 degrees C at the end of the fourth day, which is pretty good given the extreme cold outside. If there was another sunny day to follow, I would have boiling water 🙂 Sure, since the water tank is outside, there was notable loss at night, 8 degrees C to be precise.
Here is the rise of temperature and the calculated W/h harvest (or loss at night) over few days, the last one was completely overcast:
And the outside temperature and humidity measured with the Funky+DHT22: