Though written in 2007, an analysis by RENEW’s executive director Michael Vickerman may be even truer today an a few years ago, given the risk involved in “traditional” investments. The analysis shows that an investmnet in a solar hot water system generates a better rate of return than putting money in the bank:

I wrote a column which was highly critical of using payback analysis to figure out whether installing a solar hot water system on one’s house makes economic sense. In almost every example you can imagine, the payback period for today’s solar installations ranges between long and forever. For my system, which started operating in January 2006, payback will be achieved in a mere 19 years using today’s energy prices, though by the time 2025 rolls around, half of Florida might be under water and the rest of the country out of natural gas.

But there’s no reason to let payback length rule one’s ability to invest in sustainable energy for the home or business, especially if there are other approaches to valuing important economic decisions. One way to sidestep the gloomy verdicts of payback analysis is to do what most companies do when contemplating a long-term investment like solar energy — calculate the internal rate of return (IRR) on the invested capital. The definition of IRR is the annualized effective compounded return rate which can be earned on the invested capital, i.e. the yield on the investment.

By using this familiar capital budgeting method, I’m able to calculate an IRR of 6.1%for my solar water heater if natural gas prices rise a measly 3% per annum. That yield exceeds anything that a bank will offer you today. It will likely outperform the stock market this year, which is due for a substantial downward adjustment to reflect the slow-motion implosion of the housing market now underway. And, unless you live in a gold-rush community like Fort McMurray, Alberta, your house will do well just to hold onto its current valuation, let alone appreciate by six percent.

While all investments pose some degree of risk, the return on a solar energy system is about as safe and predictable as, well, the rising sun. Fortunately for the Earth and its varied inhabitants, the center of our solar system is situated well beyond the reach of humanity’s capacity to tamper with a good thing.