Print this page

Performance

 

Q:

 Do solar water heating systems work well here in Ontario?

A:

Yes! Solar domestic water heating systems work extremely well in Ontario. There are hundreds of installations here. Solar water heating systems have been installed in Ontario since 1975.

 
Note: Solar water heating systems must be installed and maintained properly in order to do a good job and last a long time.

 

Q:

 How large a solar water heating system do I need?

A:

Sizing a solar domestic hot water system for residential use is not that difficult. The CSA standards rate systems for 150, 225 and 300 litres (33, 50, 66, Imperial gallons) per day. These ratings roughly correspond to the daily hot water consumption of 2-3, 3-4, and 5-6 adults.

Another correlation is the number of square metres of solar collector - flat plate or evacuated tube - per adult using hot water. Typically this number is 1 - 1.5 square meters per adult. This is based upon achieving a solar contribution of approximately 50% towards the hot water load. Larger solar fractions can be achieved by adding solar collectors, however the the returns diminish quickly as you try to achieve an annual performance above 50%.

A significant issue with trying to achieve a percentage greater than 50% is the fact (assuming the hot water load is essentially constant over the year) making the solar system larger will over-size it for the Summer, causing it to overheat and potentially damage the heat transfer fluid or the solar equipment itself.

 

 

Q:

 How important is it that the collectors face due South?

A:

Ideally the collectors will face due solar South, angled at the latitude of the location, to achieve the best year-round performance. However deviations of 30 degrees either side of solar South and plus or minus 15 degrees in angle from the latitude will only cause a small loss in performance. Of greater significance is the effect of shade on the collectors four hours before or after solar noon. The position and height of trees and structures must be taken into account when locating the solar collectors. Consideration must be given to the effects of snow accumulation on or around the solar collectors. Evacuated tubes will not shed frozen rain or snow until air temperatures rise above freezing, and if placed close to the roof can allow snow to pack in between and over the tubes - severely reducing their performance.


If an off-optimum orientation has to be used, it often makes much more sense to add another solar collector than it does to build a complex roof rack to face the collectors towards the South. Normally, not only do these racks look ugly and have the potential to cause problems, they also can cost as much as adding another collector. Usually in these situations, you will get more heat by installing another collector than by using a angle-correcting rack.


Remember: Solar water heating collectors must be mounted securely in order to do a good job and last a long time.