CSP Today talks to SkyFuel founder and CEO, Arnold Leitner, to learn how SkyFuel’s technology will reshape the concentrated solar power landscape.

By Rikki Stancich in Paris

When former senior energy consultant, Arnold Leitner, accepted the task to produce a study on large-scale solar back in 2002, his life switched tracks.

The study, “Fuel from the sky: Solar power’s potential for western energy supply,” not only exceeded the expectations of both the U.S. National Renewable Energy Laboratory (NREL) and the nascent solar industry, it also planted the seed for a ground-breaking solar thermal power technology company.

During his research Leitner realised that there would be a growing demand for concentrating solar power (CSP) and companies in the CSP space.

Two years later, he quit his job, sold his house and “did the classic entrepreneur thing”;  he lived in a basement while attending Columbia business school in New York. The aim: to polish his finance and entrepreneurial skills and to gain access to capital.

In 2005, still at Columbia, Leitner started SkyFuel in New York - the least likely place for solar energy. He managed to secure a small investment from the university’s entrepreneurship venture capital fund and went on to raise a further US$1.6 million for his company.

Since then, he has raised $18.6 million (€12.63mn) in private equity, and roughly US$ 925,000 (€628,000) in state and federal grants.

CSP Today’s Rikki Stancich talks to SkyFuel founder and CEO, Arnold Leitner, about market strategy; whether reflective adhesive beats glass; and how SkyFuel's next-generation, high temperature linear tower is likely to postion the technology provider at the forefront of the solar tech race.

CSP Today: How is SkyFuel managing to drive down costs of CSP and how do its solutions differ from the competition?

Arnold Leitner: There are three things that we wanted to accomplish with SkyFuel. One was to deliver solar thermal energy that was ready today at much lower costs.

The second thing was to sell it in a business model that works with the utility industry.

Third was to show a clear and credible path to lower costs and around-the-clock generation using storage. Today, in less than three years, we have substantially completed all of these goals.

First, we’ve introduced an advanced parabolic trough concentrator, called the ‘SkyTrough,’ which is astounding in terms of how it looks compared to other technologies around today.

It uses a large aluminum space frame. From a structural point of view, this aspect is superior to any other design when rigidity is traded off with the amount of materials. It can be quickly assembled and is much lighter than the traditional steel torque-tube support frame designs.

What you’re losing is mass – which is key, given that materials are very large part of the cost. Note that there are tens of thousands of tonnes of steel and aluminum deployed in a solar field. So mass reduction is inherently one of the key objectives, no matter what your system is.  

The other thing you want to get out of the system is the labour. Our design focuses on mass as the primary cost reduction because we know that the labour problem can be resolved more easily.

Our mirrors, for example, slide in, in less than a minute, where other designs have to place and mount many smaller mirrors. With the SkyTrough, you just insert the mirror panels into the runners and pull it in. Before insertion the panel is loose, like a membrane, and you insert it in, and pull it through to form a stiff parabolic shape.

The benefits of this design are mass reduction and durability; for example, the mirrors are unbreakable. The benefit of unbreakable mirrors is obvious but less known is that this protects the receiver tube from secondary glass shards hitting and breaking it.

The reason you would go for this type of solution is because the capital cost and the installation costs are dramatically lowered, as are the transportation costs, because conventional mirrors weigh a lot – roughly sixty percent more. Our panels are, of course, simply light aluminum sheets with a highly reflective film, ReflecTech adhered to it.

CSP Today: How do the reflective properties of the ReflecTech film on aluminum panels measure up to bent glass?

Arnold Leitner: With regard to the reflective properties, there are two aspects you need to distinguish. Firstly, the amount of light bounced back by the surface; and secondly, the accuracy of the shape.

The amount of light bounced back is equal to even the best sagged glass, 93-94 percent hemispherical reflectivity (across the entire spectrum). This not really surprising, because just like in glass mirrors the reflective material of the film is silver (rather than aluminum, for example). But what’s different is that it the film is lightweight and unbreakable.

The shape of the mirror is created by inserting the panels into a runner on the ribs, resulting a rib-and-panel design. The one-piece reflector spans the entire arc of the trough, resulting in extremely high optical accuracy without adjustment – and the most precise parabolic trough contour measured to date.

The flexibility for design, ease of installation and high performance of ReflecTech based rib-and-panel mirrors has the potential of really changing the industry.

CSP Today: What is your overarching business strategy?

Arnold Leitner: Going back to my earlier statement, there are three key things we want accomplish for this industry: One, provide a lower cost alternative trough via the SkyTrough; number two, sell it in a way that partners can participate and spread the technology; and third, have a technology plan that shows a path to low cost power.

So, through the SkyTrough concentrator that we designed, tested and deployed in California, we met our first goal – to reduce cost by around a third compared to the next most competitive parabolic trough concentrator.

We are also developing a next-generation SkyTrough, with which we are aiming to achieve a further 25 percent cost reduction. So we’ll have brought down costs by 50 percent, compared to the 2007 baseline trough. But we know that our competitors are not sleeping.

The second point is that we are selling in a way that is compatible with the US power industry. We are a vendor – this has been our business model from day one. So we concentrate on the technology and let the big construction firms build the power plant. We are simply an original equipment manufacturer, or OEM. We provide the equipment; you build the power plant.

And the last thing is that we want to show a clear, competitive path toward a true alternative power. So we are focused on lowering costs, becoming more competitive, and providing around the clock generation. The next-generation SkyTrough is part of this strategy, but we also have a high-temperature linear Fresnel technology under development which dovetails nicely with the SkyTrough family of parabolic trough collectors.

Fundamentally, lower cost and around the clock power are addressed, in our view, by our high-temperature linear Fresnel system, which we developed with a US DOE grant. We call it the Linear Power Tower, or, LPT for short.

It’s a brand name we chose to hint at its large size and high temperature, usually associated with towers.  The LPT is a little bit like previous linear Fresnel systems, except you have molten salt in the receiver and the aperture is much wider.

Thus a lot of things are fundamentally different but what we all share is the Fresnel geometry. We’ll be introducing the first Linear Power Tower system in 2012.

CSP Today: So, effectively you are saying that a Linear Power Tower could provide around the clock generation?

Arnold Leitner: Yes, that’s our view. There is no long-term viable storage without going to higher temperatures. Alternatively it could be accomplished via a parabolic trough system that holds molten salts, like the one Archimede is working on.

The good thing is that our SkyTrough concentrator works equally well with a molten salt receiver, so we can also serve that market. But it’s our current position that the likely candidate for molten salt is the high temperature linear Fresnel system that we are designing – a linear system using molten salts. The alternative, of course, is the power tower.

The question is, whether a large parabolic trough system with molten salt, a linear Fresnel system, or a tower can best deliver these kind of 550 degree Celsius temperatures that do two things for you: increase efficiency of the power block and allow for much more compact storage – both of which are required for making our goal of making solar a workable alternative. Efficiency means lower costs, and higher temperature means more compact, cheaper storage, which again means lower cost.

So, will the large parabolic trough, high temperature linear Fresnel or power tower deliver that kind of a vision? I’ll have to bet on my company and say it will be a line-focused system and most likely a linear Fresnel system.

CSP Today: How does the Linear Power Tower compare with what Ausra, Solar Power Group and NovatecBiosol are doing?

Arnold Leitner: Ausra has a concept that is similar to NovatecBiosol The variation is that Ausra has fewer rows and pre-bent mirrors to get some partial focusing, while NovatecBiosol relies on primarily flat mirrors with a small bevel.

Compare that to a Solar Power Group, which I believe has also a mechanically slightly bent mirror, which will be more similar to Ausra’s, except that Ausra was going with much larger row widths.

The challenge for linear Fresnel systems, specifically for a high-temperature one, like our Linear Power Tower, is reaching high concentration ratios. For example, say you have ten flat mirrors.

If all ten mirrors overlap their reflection on the receiver, you would have ten times the normal solar radiation, so 10x. A parabolic trough system has 85x. You’re 8 times short the amount of energy flux onto the receiver.

So why is this so critical? As you let the temperature rise on the receiver, you can reach temperatures that would melt salt with 10x. But as the temperature increased the re-radiation, or emissivity, from the receiver goes up with the fourth power of temperature.

It’s a very steep loss curve. So, unless the concentration ratio is very high, the receiver never reaches the needed temperature and/or cannot deliver any power

So if you want to get to a high temperature with a molten salt system, because of the inherent fact that the receiver itself starts being a “sun” and if the amount of energy you are putting on the system is not much higher than what you are losing or trying to extract for power generation, you can see that you are not going to reach that temperature or get any power out. Thus to use molten salt, you need a high concentration ratio and that means having very accurate mirrors.

As I said earlier, the LPT fundamentally shares the design of other Fresnel systems, but in terms of the details, it is very different.