The Foolies are back in our inboxes — or in mine, at least, and I can’t imagine they’re not plying their promises to the rest of you as well. This time, they’re trying to sell subscriptions to their flagship Stock Advisor newsletter, along with their annual special report on stocks for next year.

We’ve looked at quite a few picks by Dave Gardner in recent months — he’s the more “growthy” brother who tends to have some huge booms and some big busts as he looks for “spiffy pop” or “multibagger” investments, but I tend to be more comfortable with Tom Gardner’s “stodgier” picks as he plies the “value” end of the investing spectrum. And it’s a Tom Gardner pick that’s being teased today, so I thought I’d sniff it out for you.

The basic premise is that alternative energy is filled with fad investments — not only the relatively big blowups like Solyndra or Beacon Power, but lots of companies, large and small, seeking out the holy grail in a business that is almost wholly dependent on subsidies.

Gardner tells us, though, that he has found “The Only Sure Thing in Alternative Energy.” So what is it?

Here’s a bit of sum-up from the teaser:

“It’s true that billionaire investors have piled into alternative energy. But most stand to lose big time. Get Tom Gardner’s ‘The One Energy Play for the Rest of Your Life’ to see the small but wildly profitable energy-efficiency company he’s recommending that you buy today!”

OK, so that’s interesting — instead of feeding the beast by finding clean power sources, how about just shrinking the beast by using less power? That’s certainly a sensible approach, and one that ought to be far easier to implement (though an ancient power grid and a population that’s angry about switching to fluorescent bulbs and not used to not worrying about unplugging transformers are impediments, to be sure).

Which, then is the “energy-efficiency company” being teased by Tom Gardner? Let’s scour this ad for some clues:

“Energy efficiency — the energy we don’t use — is the only viable long-term solution in existence. It’s an inevitability!

“So you can see why I called my analysts’ 21%-per-year growth estimates for this company conservative. It’s the company best positioned to meet $520 BILLION worth of demand!

“Perhaps the most amazing thing is… you can still buy the stock CHEAP because everybody else is still chasing silly “clean, alternative” energy fads.

“That’s right. The little energy company I’ve just been telling you about is trading for just over 14 times earnings… less than $10 a share!”

“In 2009, this company won an $800 million contract with the Department of Energy, the largest of its kind in U.S. history, for instance….

“Not only is this company ‘well run and sustainable’ according to Forbes…

“It’s already providing its comprehensive energy solution to a stunning number of government clients, as well as some of the globe’s most prestigious brand names…

“Heck, it’s even helping to safeguard the Constitution.”

And some more details:

“What’s more, this little energy company is uniquely positioned to benefit no matter whether we experience a ‘double dip’ recession or don’t…

“Do you remember how I described it as both a ‘top dog’ and ‘first mover;? It’s true. Though it has not developed any new technology, this company IS a pioneer.

“Its CEO — truly the godfather of the industry — was the first to develop a special, new kind of contract that guarantees his customers actually spend less on energy. It’s called ‘performance contracting.'”

And a few numbers to help the Thinkolator along:

“Just since 2001, this company’s revenue has increased 28 times. (And that’s organic revenue growth, not just the result of a bunch of acquisitions.)

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“And it boasts a five-year compound annual sales growth rate of 19%… return on equity of 21%… and even an awe-inspiring $1.2 billion backlog of orders…”

The “performance contracting” stuff, in case you haven’t heard of that, is basically financing an energy efficiency retrofit by paying the contractor a portion of your energy savings — it’s apparently big for government agencies, in particular, because it doesn’t require an upfront investment, and we all know that all levels of government would be delighted to become more energy efficient, but that they’re also mostly quite “capital constrained” these days (to put it mildly). So I can see how that’s an appealing business plan that should be relatively recession-resistant.

But I’m putting the cart before the horse — what’s the company Tom Gardner’s picking and teasing?

Well, we toss all those cute lil’ clues into the Mighty, Mighty Thinkolator (which could use a retrofit itself, I’m afraid — it burns four or five baby seals per hour when we’re dealing with the tougher teasers), and our answer eventually comes popping out the other end:

Ameresco (AMRC)

Which has been around since 2000, but just went public in 2010. The shares have jumped up in recent weeks, probably thanks in no small part to Tom Gardner’s “special report” (though having the markets jump 5% in a day on macro news tends to obscure the impact of newsletter publishers), so the trailing PE ratio is no longer at 14, and the stock is no longer at $10.

This is now a $12 stock with a trailing PE of 16 and a forward estimated PE of 13 (using numbers that are more conservative than Gardner’s analysts, the average Wall Street analyst thinks they’ll grow earnings by 18% next year and continue at a similar rate for the next five years — though five-year growth is obviously an almost impossible forecast to have confidence in for any company). It’s also a pretty small company at about $500 million market cap, though large for a stand-alone energy contractor (most companies like this are owned by or affiliated with utilities, which makes sense — and that’s the background of Ameresco’s founder).

And they’ve been riding a nice wave of government spending on energy efficiency and retrofitting and energy management projects, with a focus on this “performance contracting” for a lot of their work — though it’s worth noting that while their founder was reportedly one of the pioneers of this business model, it’s used by essentially all the businesses in this sector now and doesn’t necessarily make Ameresco unique. I presume that they’re selling not just this “no capital” model (which isn’t always “no capital”), but their expertise and independence from the utilities, and there’s probably something to be said for the fact that they have tight relationships with lots of government agencies thanks to their focus on that sector, which probably helps them keep procurement officers happy and generate more business. They did indeed win an $800 million contract (OK, it was $795 million) from the Department of Energy, which was the largest Energy Saving Performance Contract in history, to retrofit the Savannah cogeneration facility (closing a coal plant and opening a biomass facility). though it’s worth noting that it’s a long-term contract, I think I read 20 years but would have to check. I don’t know how these contracts are constructed, but I presume that Ameresco had to pony up the $100+ million to build the plant and do the work and will earn that back through the “performance sharing” contract over the long run. Not sure what the performance risks might be.

So that, anyway, is the idea — Gardner seems almost certainly to be teasing Ameresco, and the stock has recovered nicely along with the market in recent weeks. Will it do better than 20% earnings growth in the years to come and reward investors handsomely as the “top dog” in an increasingly important sector? Well, I dunno — all I can tell you is that he seems awfully excited about it (if you’d like another “bull case” on Ameresco, a Forbes contributor shared one here a few months ago). This is the first I’ve heard of the company, so I’ll have to look into it more before I consider it for my money — if you’ve a yen for Ameresco, or reasons why we should worry, let us know with a comment below.