Where will you find the best solar plays? Motley Fool CAPS ranks the top five thusly:

Solar Power Stocks

CAPS stars

(5 max)

AXT (NASDAQ:AXTI)

*****

ReneSola (NYSE:SOL)

*****

Amtech Systems

*****

FPL Group (NYSE:FPL)

*****

Yingli Green Energy (NYSE:YGE)

*****

Note: Data current as of Aug. 8, 2008.

Notice which companies don't make this list. Suntech Power (NYSE:STP), a top growth stock and a Motley Fool Rule Breakers pick, rates five stars in CAPS but isn't in the top five here. LDK Solar (NYSE:LDK) reported outstanding quarterly results earlier this month but merits only four stars.

So be it. In investing, where you look is just as important as what you find. And I think I've found something interesting: An up-and-coming solar play in a British defense contractor called QinetiQ Group (OTC BB: QNTQY.PK).

QinetiQ on Sunday said that its unmanned propeller-driven aircraft, the Zephyr, had flown uninterrupted for 83 hours and 37 minutes. That's more than double the record set by a Northrop Grumman (NYSE:NOC) aircraft in 2001. Here's the catch: Zephyr is a solar-powered plane; its wings are covered in silicon arrays. Collected energy is stored in lithium sulfur batteries, News.com reports.

Interestingly, this isn't the first time QinetiQ has been involved in a solar project. The company's most recent financial report provides details of a solar-powered rocket engine created for the European Space Agency (ESA). This "ion" engine, as it's called, will help propel the ESA's soon-to-be launched GOCE Earth explorer into orbit for a detailed study of our planet's gravitational field.

Best of all: QinetiQ sells its American depositary receipts on the Pink Sheets -- a perfectly reasonable place for finding top foreign bargains -- and has a history of producing generous amounts of free cash flow, a rarity for most of the young solar pure plays.

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Fool contributor Tim Beyers didn't own shares in any of the stocks mentioned in this article at the time of publication. He hunts for the best of tech as a contributor to Motley Fool Rule Breakers, which counts Suntech Power among its holdings. The Motley Fool's disclosure policy is still flying high after all these years.