Clean energy has been growing at a fast pace over the past decade. In particular, investments in the industry have ramped up substantially in recent years due to rising adoption of wind, solar and other renewable energy sources. Last year, the U.S. Senate passed a massive $1 trillion infrastructure package, with a major portion of the funding targeting renewable energy. Even the Russia-Ukraine war — which has resulted in an increase in oil and gas prices — is bringing renewables and clean energy stocks into the spotlight.

Like electric vehicle (EV) stocks, though, the market for clean energy stocks has become remarkably frothy. Hence, it’s tough to find undervalued speculative stocks in the sector that could potentially blow up in the coming years. However, after much deliberation, these seven clean energy stocks trading under $5 could be promising picks.

Ocean Power Technologies (OPTT)

Ocean Power Technologies’ (NYSEMKT:OPTT) proprietary systems produce renewable energy by harnessing ocean waves in Europe, Australia and the Americas. Its PB3 PowerBuoy system is essentially an uninterruptable power supply that can be used to generate electricity in remote offshore locations and can consistently recharge itself by storing energy from waves.

The company partnered with SeaTrepid, a robotics firm that can autonomously install a PowerBuoy off the coast of Chile. OPT will relay instructions to SeaTrepid on how to install the equipment. Moreover, if these remote installations continue, they could significantly improve margin expansion. Additionally, it would be a lot easier for OPT to scale its operations and string together several orders with minimal cost implications. If OPT successfully executes its business model, it could become a major contender in renewables.

Broadwind (BWEN)

Broadwind (NASDAQ:BWEN) is one of the leading fabricators of componentry across different energy sectors. It covers both renewables and non-renewables. In terms of renewables, its focus is on wind power, and it claims to be “one of the first producers of 100-meter wind turbine towers in the United States.”

First-quarter revenues came in at $41.8 million, a 27.8% bump from the prior-year period. Its heavy fabrications and gearing segments were the stars, posting 20% and 98% gains from the same period last year. Cost inflation, though, remains a major headwind for wind turbine customers.

Moreover, due to delays in the renewal of federal production tax credits and the higher cost of steel, the wind market should recover beginning in 2023. Non-wind markets remained robust for the company, while labor remains a major challenge.

Enerkon Solar International (ENKS)

Enerkon Solar International (OTCMKTS:ENKS) is an engineering and construction contractor that operates utility-scale PV power plants and renewable energy systems. It apparently operates a wide variety of complex and successful projects. ENKS stock spiked over $2 last year, suggesting that it might be a worthwhile speculative play.

Currently, it trades for a few cents, but if it can push on with its projects, it could potentially be trading much higher.

It recently bought 122 acres of land to build its solar and hydrogen plant. Moreover, these will be its first solar and hydrogen production project catering to the U.S. Also, it will be looking to take advantage of its land area to install an agritech pilot project using hydroponics and related technologies for indoor food production. Hence, Enerkon stock could potentially be a high-risk, high-reward play.

Solar Integrated Roofing (SIRC)

Solar Integrated Roofing (OTCMKTS:SIRC) operates a successful solar power and roofing systems installation business. Additionally, it’s building a highly diversified asset portfolio across EV charging, roofing, solar and related verticals through its aggressive merger and acquisitions strategy.

Perhaps the highlight of SIRC is its ability to acquire other competitors. The number of acquisitions signed over the past couple of years has been staggering. Consequently, the company will report higher revenue growth due to inorganic growth. In its most recent quarter, it made $84.2 million, representing a 386.7% bump on a year-over-year basis. If it can continue to acquire smaller competitors, the stock price could trend in an upward direction.

FuelCell Energy (FCEL)

FuelCell Energy (NASDAQ:FCEL) produces carbonate fuel cell products that can generate energy from natural gas and biogas. Fuel cells convert the input fuel into hydrogen, which produces power through an electrochemical process. The company currently targets stationary power markets, with customers being utilities, commercial, and industrial players.

Recent results, though, have been a step back for the firm. It made $16.38 million in sales during the second quarter, a 17.4% increase from the prior-year period. Unfortunately, the top-line results missed by almost $16 million.

However, its backlog remains at an impressive $1.33 billion compared to $1.32 billion in the same period last year. According to FCEL’s CEO, the total addressable market opportunity is at a whopping $2 trillion through 2030. He believes the operations are on track for over $300 million by 2025 and revenue of $1 billion by 2030.

Orbital Energy Group (OEG)

Orbital Energy Group (NASDAQ:OEG) is an infrastructure services business that offers services in three main segments: electric power, renewables, and telecommunications. Moreover, its projects include public utilities, solar farms, and other related offerings.

2021 was a year of acquisitions for the company, which is already showing results. Its total sales have jumped 1,154% in the first quarter this year from the prior-year period. Results across its three segments have been solid, while its solar segment has exhibited 6 times growth from $2.4 million to $14.5 million. It expects a fivefold increase in sales from $83 million in 2021 to a whopping $400 million at the midpoint this year.

Fuel Tech (FTEK)

Fuel Tech (NASDAQ:FTEK) develops systems for air pollution control. It is involved in the application of a variety of water treatment and pollutant emissions control technologies. The company has a list of high-profile blue-chip clients, having completed over 1,000 installations across 26 countries. 75% of its sales are from natural gas projects.

2021 was a strong year for Fuel Tech, with sales rising by 7.60% to $24.3 million. Moreover, it became profitable for the first time since 2013. It’s an asset-light business with cash accounting for the bulk of its assets. It aims to pursue a global revenue pipeline of $50 million to $75 million.

It’s on the right track and is looking cheap due to its substantial cash balance. Revenues are rising and have significantly decreased operational expenses.

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On the date of publication, Muslim Farooque did not hold (either directly or indirectly) any positions in the securities mentioned in this article. The opinions expressed in this article are those of the writer, subject to the InvestorPlace.com Publishing Guidelines