There are three types of solar hot water collectors on the market:
1. Unglazed Collectors - Usually made of black polymer, EPDM, or PVC, these panels are designed to deliver high volume, low temperature water. They are only useful in the summer because of the high thermal loss of the collectors from ambient temperatures and wind. Typical applications include fish farms, and pool heating.
2. Glazed Collectors - Usually made of an insulated metal frame with black copper tubing, and a glass cover. They are usually designed as pre-heating systems for DHW, and indoor pools. They can be operated all year, and require freeze protection by using propylene glycol, or a drain-back design.
3. Evacuated Tube Collectors - The pressure within the glass tube is usually less than 0.01 Pascals (atmospheric pressure is 101.7 kPa) creating a well insulated vacuum for the working fluid or copper tube to absorb the sun's energy.
The below graph illustrates the seasonal efficiency of the different types of solar hot water collectors
A typical analysis of the viability of a solar hot water system is to use RETScreen4-1 modeling software. It is free, and can be downloaded at www.retscreen.net
On the start page, change the project type to 'Heating' and the Technology to 'Solar water heater'. The 'Energy Model' tab directs you to the key inputs needed.
ecoENERGY for Renewable Heat is a Government of Canada program offering 25% reimbursement of these systems.
OSTHI (Ontario Solar Thermal Heating Initiative) will fund an additional 25% of the same systems.