Solar Quiz: In which month do solar hot water systems harness the most energy?

As we reach the end of August and finally have some nice weather to enjoy in Nova Scotia, it is easy to assume this time of year has the most solar energy potential.   Sunny days are more frequent and the days are still longer than average. 

However, the answer isn’t as obvious as you may think!

While PV energy generation potential is directly proportionate to solar radiation, solar thermal energy potential also depends on the starting temperature of the cold water it is heating.  Colder starting temperatures allow for more energy to be transferred as well as the efficiency of that transfer to be more efficient (due to higher deltaT).

So far in 2011, many of the solar hot water systems installed by the team at Doctor Solar have harnessed most energy in the month of March.

Parker St in Dartmouth, NS  Parker St. Annual Savings Graph

The Royalton in Bedford NS  Royalton Annual Savings Graph

While there are many variables that could contribute to this variance, the most likely cause is the temperature the cold water supply.  The amount energy harnessed is calculated by the difference between temperature of solar pre-heated water and the original temperature of the cold water supply (the status quo).  In March the cold water supply averages close to 5C, while in August it averages 21C.