What if you were buying stocks that you wouldn't be able to sell until the year 2042 at the earliest? What criteria would you look for before adding them to your portfolio?

When we asked three Motley Fool investors these questions, their picks for top growth stocks to buy and hold for 25 years or more were First Solar (NASDAQ:FSLR), iRobot (NASDAQ:IRBT), and Intuitive Surgical (NASDAQ:ISRG). Here's why they think these particular stocks look like solid long-term investment choices.

Man with hands facing up with dollar signs over one and clocks over the other

Image source: Getty Images.

Scorching-hot growth

Matt DiLallo (First Solar): Solar power installations grew at a blistering pace in the U.S. last year, rocketing remarkable 95% over 2015, according to data from the U.S. Solar Market Insight Report. Furthermore, last year was the first time that solar ranked as the leading source of new electric generation capacity additions in the country, accounting for 39% of the total. While solar isn't expected to grow as fast this year, the future remains bright. In fact, according to the latest long-term outlook from the U.S. Energy Information Administration, solar remains poised for unabated growth over the next 25 years, and is expected to account for 50% of new generation capacity additions after 2030.

A chart showing projected renewable power growth over the next 25 years.

Data source: EIA.

That sunny forecast bodes well for First Solar, which is a leading manufacturer of solar panels for commercial installations. However, unlike most competitors that make silicon-based panels, First Solar uses a thin film of cadmium telluride on its panels, which costs less, is lighter, and works better in low-light and overcast conditions. While those panels aren't currently as efficient at creating power as silicon ones, First Solar is working to overcome that by making its systems more competitive overall. Its newest module, Series 6, has improved efficiency and lower system costs that make them cheaper than silicon panels as well as competitive with fossil fuels in many cases.

That growing technological edge positions the company to thrive over the next 25 years as solar heats up.

The robots are coming

Tim Green (iRobot): Human beings have been using machines to make tasks easier since the dawn of the industrial revolution. Robots are the next step, promising to automate mundane tasks that eat up time. iRobot, the company behind the Roomba line of autonomous vacuum cleaners, has been selling these modern marvels since 2002. But the company may only be in the early innings of its growth story.

iRobot's revenue has steadily risen over the past decade, with the company producing sales of $661 million last year, up from $249 million in 2007. Roomba is its main product line, but iRobot also sells Braava robot mops and Mirra pool cleaning robots. Profitability has risen along with sales, and iRobot enjoyed a gross margin of 48.3% and an operating margin of 8.7% in 2016.

Two megatrends, the smart home and artificial intelligence, are converging to create a major opportunity for iRobot over the coming decades. Some Roomba models are already integrated with Amazon's Alexa voice assistant, allowing owners of an Alexa-powered device to control their robot vacuum with simple voice commands. Artificial intelligence should also allow iRobot's products to become smarter and more efficient in the future. iRobot faces plenty of competition, but the company can carve out a competitive advantage by making its products smarter than the rest.

iRobot is far from a cheap stock, trading for around 40 times trailing-12-month earnings. But the strategy of building products that make people's lives easier will never be outdated. As the smart home goes mainstream in the coming years, iRobot is in prime position to benefit.

Even more robots are coming 

Keith Speights (Intuitive Surgical): I think Tim is exactly right about the rise of robots. Another tremendously promising area for use of robotic technology is in healthcare. And with Intuitive Surgical, the robots aren't just coming: They're already here.

Nearly 4,150 of Intuitive Surgical's da Vinci robotic surgical systems were installed as of June 30, 2017. These robots have been used in more than 4 million surgical procedures to date, roughly 750,000 of which were performed last year. This strong adoption has enabled Intuitive Surgical stock to soar more than 5,600% since the company went public in 2000.

Intuitive Surgical is now trading near its all-time high level. I think the stock remains one to buy and hold for the next 25 years or more. There are two prime opportunities for Intuitive Surgical to sell even more of its da Vinci systems. One is by expanding internationally: Barely over one-third of the da Vinci systems are installed outside of the U.S. Intuitive Surgical also should be able to move into new types of procedures through technological innovation. 

The really great thing about Intuitive Surgical is that it really doesn't have to grow its system sales much to perform well. In the first half of 2017, 74% of the company's total revenue stemmed from recurring sources, including instruments, accessories, and service contracts. 

Intuitive Surgical has a great product and a great business model. Even with competition increasing, the company's customers have high switching costs and are likely to stay with da Vinci. That's exactly the kind of scenario you'd want for a stock to buy and hold for the long run.

Keith Speights has no position in any of the stocks mentioned. Matthew DiLallo owns shares of First Solar, Intuitive Surgical, and iRobot. Timothy Green has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends Intuitive Surgical and iRobot. The Motley Fool recommends First Solar. The Motley Fool has a disclosure policy.