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What types of systems are available?

 

Q:

What types of systems are available?

A:

There are several different arrangements available. The first choice is between systems that are designed to operate all year or only during the non-freezing months - called "seasonal" systems. Seasonal systems can be more cost-effective than full-year systems as they are less complex.

If year-round usage is required, then the method of freeze protection will determine the next choice of products. Drainback systems drain the water from the collectors and plumbing to provide freeze protection. Antifreeze systems use a non-freezing fluid in the collectors and piping to prevent freeze damage. Most systems sold in Canada use antifreeze. However, drainback systems tend to be more efficient, require less maintenance, are potential less expensive and don't have the toxicity concerns of antifreeze systems.

Note: "drainDOWN" systems are not the same as "drainBACK" systems. DrainDOWN systems, commonly used in the Southern United States, have a poor record of reliable freeze protection. DrainDOWN systems depend upon the operation of electric valves to drain the collectors and piping. DrainBACK systems rely upon gravity - a much more dependable force.

After determining the method of freeze protection, the type of solar collector is next. Two types are available for solar hot water systems. Flat-plate collectors are the most common. Evacuated tube collectors are also available. (Concentrating collectors may be available shortly.)

Flat plate collectors are available from many manufacturers in several different configurations and sizes. Their performance is very good for the temperatures associated with domestic water heating, and they are tough and long-lasting.

Evacuated tube collectors are now available from many (Chinese) suppliers in several different configurations. Most require the use of antifreeze. Their performance is very good for the temperatures associated with domestic water heating. They are not nearly as tough as flat plates and are not as long lasting. The pricing ranges from significantly more to less than than flat plate collectors. There is little or no performance advantage from using evacuated tube collectors over flat plate collectors.

Seasonal systems come in four styles. 1.) "Breadbox" where the solar absorber and water storage tank are the same item. 2.) Thermosyphon, where the solar absorber is place below the storage tank, 3.) Direct, where the solar collectors are on the roof and water is pumped from a tank - usually inthe basement - below the collectors,  4.) Direct, where the solar collectors - typically evacuated tubes - and the tank are on the roof and city water lines are run from inside the house to the tank on the roof. They all work, but they all must be shut down and drained before experiencing freezing conditions,

For a given solar collector area, seasonal systems will save 20-25% less money than a year-round system (over a whole year). They typically cost 50% less because they usually use less collector area.

 It is a dangerous practice to try and use a seasonal system all year. Unfortunately there are a number of companies selling seasonal sysetms and heat-tracing the piping to try and prevent in from freezing. Not only does this not work reliably, the energy consumed to prevent the system from freezing is more than the energy delivered by the solar system - so it costs money to operate the solar system. The other issue is that if the system or its piping does freeze it could do significant damage to the home it is mounted upon - potentially flooding the house or collapsing the roof.