The ill effects of financial illiteracy crop up in many ways. One of them is in boasts about saving money by solarizing homes.

An enthusiastic report about green energy in Hawaii tells of a couple there who have “been scorned for making the switch to clean energy. The couple spent $23,000 to put solar panels on their house . . . . Some neighbors sniffed that only rich people could afford such a luxury.” But “The family’s utility bill dropped from $110 a month to about $23.”

The couple saved $87 a month on electricity. Fabulous!

Or maybe not. At that rate, they’d break even on their investment in slightly over 22 years--before adding the high maintenance costs to keep the solar panels clean and functioning at peak capacity, without which the energy savings will decline.

But there’s more that’s wrong. True financial management will consider the opportunity cost of the $23,000 initial purchase--what else could have been done with that money.

Suppose they had put that money into an investment that returned them even as little as 4%, compounding. In those 22 years their investment would have grown to over $54,508, a gain of $31,508, or an average of $119.35 a month.

In other words, rather than saving $87 a month, the couple is losing $32.35 a month. That means their investment will never pay off. It will impoverish them increasingly, year after year. Forty years down the line, they’ll have forgone $87,423.50 in potential earnings--an average of $182.13 a month.

It may be, as the “neighbors sniffed,” that “only rich people could afford such a luxury.” But those who acquire it thinking it’s going to save them money won’t get rich--they won’t even stay rich for long.