Types of Solar Water Heaters
Solar water heaters for cold climates require special solar collectors (evacuated-tubes) and pumps, sensors, controllers and antifreezing fluids.
The drainback model is probably the best design for solar water heaters in cold climates (see SRCC: Solar Rating and Certification Corporation).
Solar water heaters for moderate and hot climates are a lot more simple and inexpensive; they are mostly of thermosyphon type (ICS or batch solar water heaters are an older type of solar water heaters, with a small market share).
Thermosyphon Systems: Moderate and Hot Climates.
Cold Climates: drainback and solar photovoltaic systems
You certainly have already seen solar systems mounted on roofs with cylinders on their top... These units belong to the thermosyphon type and are the most common type of solar water heaters worldwide. They are simple, reliable and inexpensive.
But if you live in a climate with freezing temperatures, thermosyphon systems aren't recommended. Consider in this case a drainback solar heater or, perhaps, a solar photovoltaic water heater system.
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Location and Orientation
The number of hours of sunlight and the angle at which the sun hits the solar collectors are critical for performance, and should be carefully addressed when installing a residential solar system.
Types of Panels
Current solar water heaters use two types of panels: flat glazed panels (in hot and mild climates) and tube evacuated panels. Tube collectors are more energy-efficient but also more expensive.
Prices and Paybacks
Solar water heaters for moderate and hot climates are relatively inexpensive, often in the range $1.000-$3.000. In these climates it's possible to have short payback periods.
But things are more complicated in cold climates. Cold-climate solar water heaters may cost you $5.000 or more.
See on these issues:
Solar Water Heaters Prices and Paybacks
The Chinese are installing about 6.000.000 solar water heaters per year, and the Israelis about 70.000 (see: Rocky Mountain Institute), in contrast with what's happening in North America: about 30.000/year new solar water heating systems.
What Should You do In a Cold Climate?
Solar water heaters for cold climates are expensive (USA and Canada: $5,000 to $9,000) and require large backup systems.
Drainback and glycol and other closed loop systems are complex and require regular maintenance.
Hence the increasing appeal of other water heating options, including solar photovoltaic systems designed to meet residential hot water needs.
Solar photovoltaic (PV) systems can be designed to produce electricity to heat water. These solutions can now be less expensive than solar thermal systems. A dedicated 1 kW photovoltaic system may cost you $4.000 (US and Canada).
But the costs can be a lot lower, for PV systems designed for multiple residential uses. Increasing the capacity of such a photovoltaic system by 1 kW (from 4 kW to 5 kW, for instance) in order to also produce electricity to meet hot water needs, may cost you $2,000 or less, which is 1/3 or less of the cost of a solar thermal system for water heating.
Bottom line: in cold climates, it's cheaper to heat water with PV modules than with solar thermal panels.