Good investments are hard to find in this economy. Housing prices are falling. Spiking oil prices send shock waves through the stock market. Some experts worry about the safety of municipal bonds. It is tough all over.

But one investment is almost a sure bet. It's not a standard investment, such as a mutual fund. And you don't earn money as much as you save money. But the result is the same: more money in your bank account.

What is this sure-fire investment? It is energy efficiency.

Minimum investment can lead to maximum returns. According to this report, every $1 investment in energy efficiency leads to a savings of $4. The consulting firm of McKinsey & Company reports that energy-efficiency programs could save $600 billion by 2020.

Some companies are reaping large returns from energy-retrofit projects. AT&T saved $44 million in 2009, Dow Chemical is investing $100 million in efficiency measures and News Corp has saved a bundle.

More on those efforts is available here, here and here.

The owners of the Empire State Building and University of North Carolina at Chapel Hill also are believers . There is a reason why federal energy officials call efficiency the low-hanging fruit of clean energy.

But, like many investments, there are upfront costs and other barriers to entry.

It has been an uphill slog in many ways. Some politicians propose deep cuts to efficiency programs, PACE programs (which would provide a financing mechanism for property owners to finance energy upgrades) were all but curtailed and budgets are in disarray.

But a potential $600 billion in savings awaits. And a strong energy-efficiency program could have a significant impact in places such as the San Joaquin Valley of Central California. In Fresno, where I live, my summertime power bill can exceed $500, and is my second-largest expense behind my mortgage.

Incomes here are low. The unemployment rate exceeds Appalachia figures. We have some of

worst concentrated poverty in the nation. Lower power bills would enrich residents, provide jobs and potentially stimulate the economy.

Photo of University of North Carolina at Chapel Hill by earthfirst.com