That’s left many investors wondering, “What’s next?”

Regardless of how you feeling about socially responsible investment (SRI), there’s a groundswell of support for the SRI trend–particularly as the younger generation comes of investment age but also investors of all stripes are becoming more aware of and concerned by the environmental impact of companies they hold. In fact, almost eight percent of investment dollars, amounting to almost $3 trillion, are now put to work using SRI approaches.

On top of that, President Obama will bring environmental issues to the forefront of his administration. Particularly as economic concerns (hopefully) ease toward the back end of his tenure, he’s already said that he wants to put 1 million plug-in hybrid cars on the road by 2015. In the meantime, I’d expect his administration to push alternative fuel vehicles as an intermediate step and ensure that 10 percent of our electricity is generated from renewable sources.

Whether you agree with the sustainable investment philosophy or not, over the next few years there’s money to be made in the space. That’s why we’ve been devoting a lot of ink to the subject in my newsletters Louis Rukeyser’s Mutual Funds and Louis Rukeyser’s Wall Street. I’ve got three favorite ways to play it.

China-based Yingli Green Energy (NYSE: YGE), which designs, manufactures, and sells photovoltaic (PV) modules and designs and installs PV systems has long been one of my favorite solar energy plays. It’s been absolutely hammered over the past year, as a weak macroeconomic environment and China sell-off last year, has scared off investors. Falling from a high of almost $40 in January 2008 to just $6 today.

Admittedly, as global economies have slowed over the past year profits have taken a hit as Yingli is having to peddle its wares at lower prices, but overall sales are growing even as margins are shrinking.

In 2008, Yingli shipped 281.5 megawatts (MW) of PV modules. Just barely beating its previously estimated range of 270 MW to 280 MW. Even as the economy steadily worsened over the course of the year, in 2009, it expects total shipments to be in the range of 550 MW to 600 MW, of which 317.4 MW of production are already under contract for delivery next year.

Profit margins were squeezed last year primarily because most of Yingli’s business is conducted outside of China, so currency fluctuations weren’t kind to the bottom line. But 2009 should turn out to be a better year as the company’s research and development efforts are paying off in the form of less polysilicon usage per watt. Polysilicon prices are also expected to soften further through the course of the year, so the combination of lower prices and lower volumes being required, margins are expected to come in somewhere in the low 20 percent range.

The company also as an expansion project to add 200 MW of production to its output, which is expected to come online early in the third quarter, allowing it to capture a larger market share in the PV space. That’s a much needed expansion with Yingli already running close to capacity due to its already strong presence in European markets and expected demand growth in the United States.

Another favorite though more speculative way to play green investing is Clean Energy Fuels Corp  (NSDQ: CLNE). The brainchild of energy titan T. Boone Pickens, Clean Energy owns and operates the largest network of natural gas fueling stations in North America. Currently serving primarily the Western US and pockets of the Northeast, it provides NG fueling stations for corporate fleets and municipal buses as well as taxis and private vehicles. It also owns two liquefied natural gas production and storage facilities to supply its chain of refueling stations.

The company has enjoyed rapid growth over the past few years and that should continue, particularly given the expectations that the upcoming 2010 emissions standards will likely push heavy-duty truck fleets to natural gas in order to come in to spec. Already, many corporate fleets are working towards making the transition.

This is obviously a higher risk play, with exceptionally low oil prices likely here to stay for a while. The company hasn’t yet turned a profit, so there’s also the risk that it may not survive. And while Pickens is certainly a savvy businessman, I would stake my investment dollars on the company just because of his involvement with the company.

However, I do expect the current Democratic regime to make tighter emissions and fuel efficiency standards a major plank in its environmental platform, so I think a small bet on Clean Energy would be a prudent speculation.

Finally, for mutual fund investors, there’s New Alternatives (NALFX).

Launched in late 1982 as the first environmental mutual fund in the US, it’s managed by the father-and-son team of Maurice and David Schoenwald, both former attorneys.

The fund’s 48 holdings include names from outside the green energy space. Energy-related stocks account for 35 percent of assets. Other industries represented include organic food production, utilities, manufacture of the component parts of alternative energy installations and infrastructure. The fund is also geographically diversified, as less than 40 percent of assets are invested in North America, the remainder in Europe and Asia.

Its broad, international approach makes it a fund that won’t blow the doors off your returns under normal conditions but circumstances are coalescing that seems set to make 2009 an excellent year for the fund.

Even if you’re not a mutual fund investor yourself, I’d definitely recommend perusing the funds Web site for more ideas on playing the SRI trend.

With a slight variation on the theme, my colleagues Roger Conrad and David Dittman recently examined the impact of energy security and climate change worries on the Canadian oil sands in Maple Leaf Memo:

It’ll be all business when President Barack Obama visits Prime Minister Stephen Harper February 19th in Ottawa—no pomp, no ceremony, no parliamentary address.”

The broad focus of discussions will be the economy; including where we are now and where we’re going. That means efforts to stabilize the financial system, stimulate the economy and “Buy American” will certainly come up.

The drop-in will include a one-hour meeting between Mr. Obama and Mr. Harper. The new US president will also meet briefly with Liberal Party Leader Michael Ignatieff and host a news conference.

While there will be no public address or state dinner, Mr. Obama is making his first trip abroad to Ottawa, which illustrates the importance of the US-Canada relationship. It is, after all, the most significant bilateral trade arrangement in the world; two-way trade in goods and services amounted to more than CAD 700 billion in 2006, an average of about CAD 1.3 million in trade per minute across the border. The combined Canada-US market represents more than 425 million consumers with a combined GDP of more than USD 11.4 trillion.

One particular aspect of the trade relationship that’s also sure to be on the agenda is Alberta’s oil sands. During the 2008 campaign, Mr. Obama pledged to wean the US off “dirty, dwindling and dangerously expensive” oil. Many in Canada are focusing on the word “dirty.” They interpreted the candidate’s statement as a warning shot across Alberta’s bow, an indication that Obama would oppose US importation of carbon-intensive fuel produced from the oil sands.

But a primary foreign policy objective of the new administration is to reduce US dependence on oil imported from hostile regions. Canada is the US’ No. 1 oil supplier. Exporting 1.8 million barrels of oil per day, 20 percent of daily US import, Canada’s proven reserves rank second in the world to Saudi Arabia’s. When we buy oil from Canada, don’t worry about sponsoring dictatorships or sending money to questionable allies.

At the same time, Mr. Obama has also made addressing climate change a top priority. Canada’s oil sands represent an infinitely safer alternative in national security terms, but critics point to the large amount of natural gas burned to process the sands into synthetic oil, resulting in major greenhouse gas emissions, as well as the production of wastewater and the destruction of boreal forests that are habitats for migrating birds.

Reconciling the apparently conflicting environmental and security objectives will test Mr. Obama, who describes himself—and is widely recognized—as a pragmatist. Mr. Obama’s position isn’t clear yet, and environmentalists will surely employ his oil sands position as a litmus test for how serious he is about a switch to alternative and renewable energies.

Click here for the complete article.