Source: Wikipedia.

Solar energy is a relatively young industry, and those who invest in it the right way could make some serious money as the industry and technology continue to mature. And, the good news is that you don't necessarily need to take on a lot of risk to invest in solar. Here are several good ways to invest in solar energy whether your risk tolerance is high or low.

Solar companies: Lots of risk, but could pay off tremendously
When it comes to investing in a young industry like solar, it's generally a good idea to go with the largest and most experienced companies. I would avoid investing in any small solar companies (with a market cap below $500 million) at this stage, because these are the ones least likely to stand the test of time.

Some of the larger names are looking promising right now. In no particular order, these two companies are my favorite ways to directly invest in solar energy. In the brief description of each one, I have included a link to a more in-depth article about each company.

First Solar (FSLR -2.02%) -- The solar panel manufacturer's stock has performed well lately on the heels of a joint project with Apple (AAPL -0.53%), but it could still have a lot of room to the upside. The company's backlog of business has been building up, margins are expanding, and the company's products are becoming more and more efficient. Finally, the company has an incredibly strong balance sheet with $2 billion in cash and just over $200 million in debt that should allow it to survive any more "growing pains" the industry experiences.

SolarCity (SCTY.DL) -- In my opinion, this is the riskier of the two companies listed here, mainly because it isn't profitable, nor is it projected to be within the next few years. A somewhat different way to invest in the industry than First Solar, SolarCity is focused on the engineering, sales, and installation of solar energy systems to residential and commercial customers. The company has a unique strategy of financing solar systems to customers, which results in recurring payments over a long period of time, so there is definite potential for the company to build a massive revenue stream over time.

Indirect investment in solar could be the way to go if you can't handle high risk
If you don't have the risk tolerance to invest in solar companies directly, you can still get in on the action. There are many large, stable, and diversified companies that have significant operations in solar power. And, while these may not have the explosive growth potential of the purely solar-oriented companies mentioned above, they could see a nice boost as the profitability of solar energy grows.

Just to name a couple of the companies with large solar operations...

General Electric (GE -1.20%) -- General Electric has a substantial solar operation, producing solar panels and a variety of other solutions for the solar power industry. The company also invests heavily in solar power plants, including some made by First Solar. The company has said it plans to invest more than $1 billion per year in renewable energy projects going forward.

3M (MMM 0.26%) -- 3M produces a variety of adhesives, tapes, and films specifically for use by the solar industry, and it has done so for more than a decade. This could be a good way to benefit from the growth of the solar power industry without being exposed too heavily to any individual solar company.

Solar has massive potential
World energy demand is expected to increase tremendously in the coming decades, and there are few technologies both cost-effective and scalable enough to keep up with it. Solar energy is continually becoming more affordable, and it can be produced at a large enough scale to meet growing energy demand all over the world.

The solar industry today is quite similar to the computing industry of the 1980s and 1990s. And, just like the early computing industry, the investors who get into some of the winners on the ground floor could potentially make a lot of money.