http://www.globesolarenergy.com/sales_kit/questions_answers/a_about_working_principle/a4.html

Does a solar water heater work in winter?

No one doubts the potential to use solar energy to heat our hot water in the sunny days of summer. However, most people in Toronto are sceptical that a solar unit can deliver significant amounts of hot water during the cold winters and record snow falls like we have had this winter (2007-2008). The WISE project asked Globe Solar Energy to install a flow meter with two heat probes [ ISTEC 4400 meter] on the system installed at 31 Pinewood Ave. The meter was installed in late December and we now have data from January and February of this year on the winter performance of the IP-195 system. This data reflects the temperature after showers at 7 AM.

Average January/08 solar tank outlet temperature --- 31.8 degrees C [range 20.4 – 45.3]

Average February/08 solar tank outlet temperature --- 35.4 degrees C [range 16.5 – 46.1]

The National Solar Lab test results show that overnight the IP-195 unit loses 1 degree C for every 6.43 degrees difference between the tank temperature and the air temperature.

Jed Goldburg’s household would be considered a conserver household in hot water use -- 3 showers a day, occasional dishwasher use, occasional hot bath and weekly warm water laundry. On average over this period they used 200 litres of hot water daily.