A typical solar thermal system is designed to handle 50-70% of the yearly hot water demand which means that the cost of heating hot water is reduced by this same amount. This means that the bigger your hot water heating demands are, the more money can be saved on energy (you would of course need a bigger solar thermal system).
Solar thermal systems are by nature very passive and thus require very little maintenance. Because solar thermal systems typically require a backup boiler system, the maintenance costs compared to a larger boiler system are expected to be smaller, but not significantly so.
While this answer obviously depends on the size and type of system being installed, because of the currently low price of natural gas, payback periods are typically in the 15-20+ year range. In situations where natural gas is not available, the payback period can be drastically reduced. In both cases, the payback period can be significantly improved by taking advantage of the accelerated capital cost allowance for clean energy generation, as discussed below.
While in Alberta there aren't any government rebates or grants available to help pay for solar thermal systems, Canada does have a special CCA Class (43.2) available for depreciating clean assets. It is called the "Accelerated Capital Cost Allowance (ACCA) for Clean Energy Generation" and it allows the depreciation of green assets (Geothermal (including heat pumps), wind, solar thermal etc...) on a 50 percent per year declining balance basis. Basically, the capital cost allowance allows clients to depreciate their assets much quicker than normally allowed under the tax code. If we take for example a $100,000 solar thermal system, under normal tax codes, after 3 years, only 10% of the asset would be depreciated (2% in the first year, 4% every year after), equating to a tax credit of approximately $3,400. Under the CCA Class 43.2 however, 25% of the asset is depreciated in the first year (first year rule) and then 50% every year after, meaning after 3 years, 81% of the asset is depreciated, equating to a tax credit of $28,400! We have found that the accelerated capital cost allowance can sometimes halve the payback time period and we strongly recommend taking advantage of it. Clients should speak to their accountants, but more information can be found here.
Assuming a proper installation with regular maintenance, a flat plate collector system should last in excess of 30 years, even up to 50 years. Evacuated tube collectors would be expected to have a slightly shorter lifespan as they are inherently more complex. As with any asset, proper maintenance and care are essential for the longevity of the system. We also cannot stress enough how important the proper design and installation are to the success of the system; even simple design errors can have a strong effect on the life of the collectors.
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We very much welcome furthering the discussion on these topics so please feel free to post comments and/or questions below and we will be happy to respond to them.