Over the recent decade, long-term investors have grown interested in solar energy stocks, as the alternative energy segment is projected to become the world's largest source of energy by 2050.

As the global economy shifts away from fossil fuels and other polluting energy, solar has taken the lead ahead of a surge of new alternative industries such wind and hydrogen systems. While many may bundle solar companies under one umbrella, the solar segment itself is comprised of companies of different sizes, offering a large variety of products and services.

Different Kinds of Solar

Two competitive solar technologies on the market include photovoltaic (PV or light) and thermal (heat) solar power. In terms of pricing, some firms offer higher quality more-efficient rigid solar panels while others specialize in cheaper, less-efficient thin-film collectors. While some firms sell solar through distributed channels, other use centralized outlets such as large solar farms or fields for utility. Other firms on the supply chain come into play as well, such as the manufacturers of the batteries that store solar energy when the sun is down.

A Cheap Long-Term Pick?

A short-term decline in the industry was partially attributed to slowing Chinese demand driving solar panel prices down, along with other short-term shocks including the surprise election of Donald Trump, who has characterized climate change as a “hoax.”

In particular, First Solar Inc. (FSLR) a leader in both the production and installation of photovoltaic systems, saw its stock lose more than 50% of its value of the course of 2016. The Tempe, Ariz.-based firm has sacrificed its short-term profits in order to restructure its business and streamline the production of its more cost-efficient Series 6 module. (See also: Can First Solar Rebound After 2016's Decline?)

Along with First Solar, SunPower (SPWR), Vivint Solar (VSLR) and Tesla’s (TSLA) SolarCity should interest investors seeking to gain exposure to the industry while the stocks are relatively cheap.