NEW YORK (TheStreet) -- My favorite Spencer Tracy-Katharine Hepburn movie is their 1957 comedy Desk Set, easily found in IMDb.

Tracy plays an early computer engineer, basically an


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salesman. Hepburn plays a TV network researcher who fears her department is about to be replaced by the new computer whose installation he's supervising. It's a major undertaking, and it's obvious Tracy's character is well-paid.

That's the way it was throughout the industry for its first 30 years. If you could convince someone to buy a computer you made a very good living. Margins were simply enormous.

The PC represented a tipping point. The PC sold itself. You didn't have to adapt to the PC, in time its abundance adapted to you. So today a computer thousands of times faster than the ones Tracy sold is cheap as chips, its margins wafer-thin.

Renewable energy today is where computers were right before the tipping point, the year I entered college. To make money, you want to be Spencer Tracy. You want to be selling solar or wind or biomass systems, not making them.

This is bad news for investors. You can't really make money. The main solar ETFs,

Market Vectors Solar Energy


and the

Claymore/MAC Global Solar Index

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, are down almost 80% over the last two years.

First Solar

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, which once sold for over $300 in 2008, is now down to under $30.

Wind is just as bad. If you bought the

PowerShares Global Wind Energy Portfolio

( PWND) ETF five years ago, you will feel pawned because you're down 77%.


was an industry leader at over $23/share in 2009 -- it's now in the pink sheets at $1.69. Suppliers are doing just as badly.

Like biomass?



just opened its first big plant, in Columbus, Miss., and has plans to build more. But the stock is at $6 a share, down from over $20 in 2011. Technology players such as




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have done no better.

Companies including


Sungevity, and

SunRun, which sell and finance solar systems, are in the Tracy role right now. If you can convince someone to buy a renewable energy system, if you can find financing for that deal -- in short, if you can make that pay -- you're making money. But these companies are private, you're not going to get into them.

The recent recovery in First Solar shares is due to its success in selling utility-scaled systems to companies such as

Berkshire Hathaway's

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Mid-American Energy

. The same can be said for


( SPWRA), now 66% owned by


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of France. They both make and market solar systems, and their shares are up 20% since Nov. 21.

The tipping point, the point at which these systems become more like PCs, comes when they can deliver power for less than the price of the electric grid. When solar is the cheap power it sells itself.

Hawaii, which has already passed grid parity, finds that utilities are now unwilling to connect systems to their grids, although a commercial installation there can now pay for itself in less than a year, writes

John Farrell of the Institute for Local Self-Reliance.

As parity becomes more common on the much larger U.S. grid, this resistance will only grow. But opportunities will also grow in storing the excess power for use by generators, electric cars, or hydrogen.

Once parity happens -- and

General Electric

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Clean Technica

last year it expects this in 2016 -- then suppliers of renewable energy become great investments.

Just not before. Until then you want to be the salesman.

At the time of publication the author had a position in GE.

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This article was written by an independent contributor, separate from TheStreet's regular news coverage.