Solar Geysers In Winter.
(By James Green; MD ; Ubersolar)
Solar water heating works almost as well in winter months as the rest of the year.
Surprisingly ambient air temperatures make relatively little difference to performance as glass evacuated tubes absorb UV and infrared frequencies as well as normal sunshine. The outside of the tubes are cool to the touch at any time of year.
The difference in performance from winter to summer is attributable to shorter days and the sun being lower in the sky. Consequently, the solar irradiation is lower in the winter than summer.
In the table the solar irradiation is shown in the yellow block, taken at April 30th 2019.
In summer days that would be both higher and wider across the time period.
Screenshot from the Ubersolar Geyser App…
The solar geyser water temperature is shown with red line climbing throughout the day and with heat continuing to go into the geyser even when the solar irradiation levels are falling away at 5 o’clock in the afternoon. In the summer that would be at 7 o’clock in the evening.
In winter the solar geyser has to work harder to generate hot water as the cold water being heated will have a start temperature as low as 11°C. In the table, the cold water at April 30th, 2019 is still at 19°C. By August the mains water going into the geyser will be colder, so taking the same performance as in the table the hot water temperature in August would be at around 45°C rather than 52°C. Consequently, in cold winter months electrical back up maybe needed to boost the hot water to higher temperatures to guarantee enough hot water.
In summer months the opposite is true and the hot water temperature would be around 65°C.
The solar water heater performance will always depend on the power output of the solar collector. A bigger solar collector or bigger engine will generally result in more performance or put another way more electricity savings and more hot water.
It is important to understand that it is the solar collector not the tank size (which is doing nothing more than storing hot water) that determines the performance of the solar system.
Solar water heating is the number one priority for saving energy in the home, working all months of the year, winter and summer.
Ubersolar
May 1st 2019