Dozens of different types of systems that use solar energy to supplement your hot water heater are available, but only a few have stood the test of time. Sticking with proven entities is always a good idea, despite the extravagant claims you may hear regarding new technologies. In the real world, Murphy has a voracious appetite, and until something is tested thoroughly, the jury is still out.
The integral collector system (ICS): ICS is the simplest and cheapest system, and it's ideal for mild climates. But it also has the most potential for freezing damage because the collector holds the water being heated. Big batch collectors, however, can withstand longer freezing conditions than smaller systems.
These systems are passive and are normally plumbed directly between the cold water supply and the water heater, making the plumbing job easy and straightforward. Whenever someone opens a tap in the house, water flows from the collector into the water heater. If the water in the collector is hot enough, the domestic water heater doesn't need to add any heat at all.
Most ICS systems need to be drained of water when in danger of freezing. The systems use manual or automatic valves. A burst collector costs a lot of money to fix. They're big and bulky, and you may end up having to send them back to the factory. But they're cheap and easy to use and install, which is why they're so common. You just need to understand the operational drawbacks if you're going to successfully maintain one.
Drainback systems: Drainback systems (direct, ICS) do exactly that: They drain the fluid out of the collector and exposed pipes when no sunlight's available or when there's no more need to heat the domestic water because it's already at the preset temperature. These systems use a special tank for holding the drained fluid. These types of systems are medium on the cost scale and can be used in cold climates. There is less risk of bursting pipes than a conventional ICS system, but more risk than a closed-loop antifreeze system (see the next section).
Closed-loop antifreeze systems: Closed-loop antifreeze systems use fluids other than water to collect the heat; then a heat exchanger transfers that heat into the domestic water supply. These systems are far and away the most widely distributed type systems in the world because they work in almost any climate. They're the most expensive as well.
These systems aren't entirely free of problems. The antifreeze solution breaks down when the weather gets really hot and then turns corrosive. These types of systems require service, and owners need to stay on their toes in order to prevent big problems.
Regardless of whether you decide to install a system yourself or have a contractor do the job, there are some definite tips you will want to keep in mind.
Opt for a complete system: Mismatched components reduce efficiency and may even void warranties.
Seek out quality parts: Quality parts mean fewer service calls.
Pay attention to contractor quality: The number-one failure mode of all solar water systems is faulty installation.
Understand the contract terms: Every contract specifies the equipment to be installed, but you also want to know what sort of specification performance is guaranteed.
Look out for red tape: Find out whether you need a county building permit or inspections.
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Source:http://www.dummies.com/how-to/content/choosing-a-solar-system-to-supplement-your-water-h.html
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