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As cost of solar cell and wind turbine manufacture and installation costs continue to decrease, there is a cost point at which there is an economic justification for replacing an existing oil or natural gas based home heating system with a system that uses 'renewable energy'. The advantage of the existing oil or natural gas system is that there is no capital cost, though there is a substantial marginal cost of the fuel. The advantage of either solar or wind is that the marginal costs of electric generation is near zero, however there is a substantive capital cost to purchase and install. Using the information below, and your knowledge in alternative selection (Chapter 6), select the alternative that offers the better economic justification [MARR = 9%] Existing natural gas heating system: Useful life = 10 years Average annual cost for fuel = $1, 500 per year Expected average annual maintenance = $100 Expected average annual revenue from resale of electric back to grid = $0 Solar: Useful life = 20 years Expected installation cost = $15,000 Expected average annual Maintenance = $300 Expected average annual revenue from resale of electric back to grid = $1,000 Wind: Useful life = 40 years Expected installation costs = $30,000 Expected average annual maintenance = $0 Expected average annual revenue from resale of electric back grid = $2200