SunPower (SPWRA) saw an increase of more than 10% in its stock price on March 15. This trend was seen across almost all companies in the solar industry, including SunPower's competitors FirstSolar (FSLR), SuntechPower (STP), and Yingli Green Energy (YGE).

Our price estimate for SunPower's stock is at $14.41, about 10% below its current market price.

ConocoPhillips (COP), one of the largest oil and gas exploration and production companies in the world, recently announced that it will partner with NRG Energy and GE Capital to invest $300 million in a joint venture that will promote emerging energy technologies. ConocoPhillips has been a leader in development of new energy technologies with several of its activities focused on power generation and new technologies. Its main competitors are ExxonMobil (XOM), British Petroleum (BP), Anadarko Petroleum Corporation (APC) and Chevron Corporation (CVX).

We maintain a $68.44 price estimate for ConocoPhillips stock, which is roughly 10% below market price.

They don't all work out. Suntech Power Holdings Co. Ltd. (STP), first discussed here on July 28, 2009 at a price of $19.24, was stopped-out at $8 in late August, for an 11-point loss.

Suntech's shares, a high-risk stock, had recovered to about $11 in mid-summer after plunging in bear-hug fashion this spring from about $16 to $8.40.

The calculation in the summer was that photovoltaic cell manufacturer Suntech's long-term business prospects in China would offset short-term hits to revenue, due to price declines.

Nissan has launched one of the first interactive iAd mobile marketing campaigns for the new Apple, Inc. (AAPL) iPhone 4, and it's taking the chance to promote its new all-electric Leaf passenger car. Although hybrid vehicles have been around in the U.S. for years (think Toyota Prius), all-electric cars have been limited to those teeny-tiny, mileage-limited vehicles. Nissan wants to change that with the four-door Leaf sedan.

Trina Solar (TSL) has had a rough couple of years. After a $10 IPO in 2006, it flew up to peak at $35 in 2007 only to bottom out under $4 at the end of 2008. It was partially the broader market that held back Trina, but also speculation over the viability of solar power as oil prices softened.

Trina Solar nearly became a bear market statistic. But the company has fought back from less than $3 a share to its current $25 price, and there are a lot of reasons to think that Trina Solar is making a comeback. In fact, it's one of my favorite small-cap stocks to buy this earnings season -- and here are five reasons why:

Geothermal energy isn't a new concept in the United States; it's actually been around for some time, with numerous geothermal power plants in California, Nevada and a few other western states," says David Fessler.

The contributing editor to Money Morning explains, "There are new plants on the drawing board, too. Unfortunately, the recession has stifled the construction progress on many of them. But all that's about to change.

"Thanks to a few key technological developments -- and a big cash infusion from the government -- the stars are aligning to produce the perfect storm for this super-green energy source.

Sunny skies are here for Ausra, the solar thermal company backed by Kleiner Perkins and Khosla Ventures. The company is looking for a buyer, and it's already talking to three, according to a report by Reuters. Everything is up for grabs, from a majority stake in the company to 100% of it, and the back-and-forth going on is at a "very aggressive level."

The businesses looking to pick up Ausra are said to be global power generation conglomerates but haven't been named yet. So, the clean energy company would be a way for one of them to diversify.

"I'm excited about Quanta Services (PWR), a contracting company that specializes in building utility transmission and distribution infrastructure," says Ian Wyatt.

In his Top Stock Insights, he explains, "The current focus in the U.S. of projects that improve energy conservation, utilize renewable resources, and improve air quality make Quanta an excellent long-term growth opportunity.

"Its customers are in the electric power, gas, telecommunications, and cable television industries. These are stimulus spending customers; i.e., big government organizations and utilities companies.

The clean technology private equity momentum continues. In New York, a group of partners has launched NewWorld Capital Group, a private equity firm that will focus on mid-market investments in clean energy infrastructure companies in the United States and selectively in Europe.

The new fund will work closely with Ambienta, a European environmental assets private equity firm in Italy. Both said they plan to collaborate on finding and analyzing investment opportunities -- with NewWorld taking care of the United States and Ambienta addressing Europe.