The past 12 months has seen some successful IPOs from across the clean tech sector, including electric vehicle firm Tesla and biotech fuels company Amyris. But it has also seen some duffers, such as Solyndra’s failed IPO attempt, and the IPO partnership between Goldman Sachs and oil-from-pond scum firm PetroAlgae, the company that revenue forgot. Announced last August, that IPO has yet to happen.

Like many others, clean tech is still a difficult market to operate in given the economy’s gradual and fragile recovery. As such, hopes that 2011 could prove to be a big year for clean tech IPOs look increasingly optimistic.

It is likely to be a mixed market for a while yet, warns Peter Fusaro, co-founder of the Energy Hedge Funds Center, a web community designed to help people understand hedge funds in the energy sector. “Our strategy isn’t wired for IPOs any more, it’s for trade acquisitions. The public market has been closed. There have only been a handful of IPOs,” he points out.

It’s going to be hard for that market to open up again in a clean tech economy muddied by a mixture of artificial stimulus and paranoid US customers, warns R. Paul Herman, chief executive of HIP Investor, an information and advisory service for clean tech investors. “The government will play a larger role in this, and when that goes away, share prices could get ripsawed,” he warns.

The problem for many clean tech companies is that the sector often requires large amounts of up-front capital expenditure, especially in areas such as utility-scale renewable energy projects. That makes it difficult for cash-constrained customers to invest in such projects.

“I would say the underlying fundamentals are: can you get cost reduction without up-front capital, and where is the company selling?” muses Herman. “In China and Europe, you’ll have a more stable base than in the US.” The Chinese are ready to make multiple-year commitments, he explains. That could also mean that the market sees more clean tech IPOs from Chinese companies in the coming year or two.

The need for up-front capital means that much of the big money is going into project financing, says Fusaro, leaving high net-worth investors rather than institutional market watchers to analyse the innovations happening in clean tech. He also warns of a dearth of expertise in the market which could hinder big-ticket investments in clean tech IPOs.

“It will come roaring back,” he says, “but I don’t know when.”

While we wait, and hope, here are some of the possible contenders that will break the IPO window when the market does start to pick up.

Automotive

Following in Tesla’s footsteps, Fisker Automotive is said to be gearing up for an IPO this year. The firm raised $150m (£92.9m) in February, ahead of shipping its long-delayed Karma electric vehicle. Senior executives have gone on the record predicting that shipping a car in commercial production will come before any IPO.

Fuel cells

Bloom Energy is one of the most promising fuel cell companies around. It already has several big-ticket customers for its Bloom Energy Server – a 100kw box of low-cost solid oxide fuel cells powered by natural gas or biogas. But despite its high profile there has been relatively little speculation about a possible IPO.

Lighting

LEDs are one of the most promising clean tech sectors, given that municipalities are itching to save money by refitting swathes of government buildings with more energy-efficient lighting technologies. Bridgelux, said to be enjoying revenues in the tens of millions, is targeting the commercial market with its energy-efficient LED systems, prompting rumours that it may seek an IPO in order to help accelerate its expansion.

Smart Grid

Smart grid technology is an area of huge interest as utilities look for new ways to regulate demand. Silver Spring Networks handles IP-based networking systems for metering and distribution automation. The market has been waiting for its IPO after rumours suggested it would offer its shares to the public last year. Perhaps this year could see the company deliver its long-awaited floatation.

Solar

Unlike photovoltaic solar projects, Brightsource Energy’s solar tower technology makes use of thermal solar power, using mirrors to concentrate the sun’s rays on a central tower. The company is currently pursuing a number of projects including a 370MW plant in California’s Mojave desert. While it waits for those to come onstream – and as legal battles over the project’s location and effect on the environment play out – it is also exploring thermal-enhanced oil recovery as a stopgap with Chevron commissioning the firm to explore the technology’s potential. The firm’s high-profile, big-name backers, and capital-intensive business plan have all fuelled speculation that an IPO could come within the next year or so.

Unlike its competitor Solyndra, thin-film solar module maker MiaSolé kept its IPO powder dry last year. Solyndra announced and then canned its IPO, whereas MiaSolé, which also makes thin-film photovoltaic solar panels, continued to concentrate on private funding. Chinese manufacturing efficiencies are putting American firms such as these two under pressure, but they continue to drive efficiencies in solar materials. MiaSolé reportedly just raised $125m to continue its development and manufacturing. Solyndra may have been on the ropes last year, but it still enjoys more than $500m in government loan guarantees. Which of them will come to market first?

Renewable energy

Could Ice Energy be a candidate for IPO in 2011? The firm provides ice-powered air conditioning systems, which sit atop commercial roofs and freeze water overnight when electricity is cheap. They then run coolant into air conditioning systems during the day as they melt the ice, thus saving peak-time electricity costs. The firm closed $24m in Series C funding in October suggesting an IPO may be a way off, but longer term the company’s innovative technology makes it an intriguing IPO prospect. 

Construction

Green construction materials firm Serious Materials started out with eco-friendly drywall, and then moved into super-insulating windows. Last September it expanded into cloud-based building energy management software. The company’s revenue has already topped $50m, and it could no doubt employ the cash raised by any IPO to fuel its continuing category-by-category expansion, while also funding its commercial production.