A sun tracker will increase your ability to capture solar energy. Through the tracker, your panels will constantly adjust to maintain maximum exposure to the sun. Though they cost more than fixed panels, the boost in energy production makes them worthwhile.
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There is really no reason to even consider getting a solar energy system if you live in an area that rarely sees the sun. This does not mean that a less than reputable company will not try to sell you a solar system though. If your roof does not receive at least 6 hours of full sunlight per day, you should not consider solar power.
A solar powered fan for your attic is a good choice if switching completely to solar power is not feasible. The fan will have a temperature sensitive gauge and switch itself on when necessary. This will remove heat and lower the cost of cooling. It's also solar powered, so you don't have to pay to power it.