By Rikki Stancich in Paris

By rethinking the conventional support structure for parabolic troughs, the company has succeeded in removing heat transfer fluids from the equation, replacing them with direct steam generation.

CSP Today speaks to the man behind the technology, Oğuz Çapan, oil industry veteren, and CEO of Hitite Solar Enerji, to learn more about the new design.

CSP Today: Hittite Solar Enerji has developed a CSP system that involves parabolic troughs using direct steam generation. Can you explain how it works?

Oğuz Çapan: When I looked at parabolic trough technology from the perspective of a total outsider as a former oil field production station and pipeline design engineer, I saw that some very basic things were done wrong. Therefore, the existing systems couldn’t handle direct steam generation and instead was limited to using heat transfer fluids.

The main problem was that the receiver system was rotating in the air, which meant you have moving parts (flexible hoses, ball bearing joints, etc.) connecting the rotating receiver to the stationary pipelines on the ground. 

Instead, why not keep the receivers stationary like the high-pressure steam pipelines in power plants, petrochemical plants, and so on? When we decided to keep the receiver stable, it led to a whole different support structure for the parabolic trough. 

We designed a semi-circular support system, (instead of poles), which has the stationary receiver at the axis of rotation of the parabolic trough (namely the center of the semi-circular support). When the semi-circle rotates, the receiver remains fixed, because it remains at the centre.

This resolved the pressure problem caused by the flexible joints and moving parts, and so we were able to achieve direct steam generation (DSG) at high pressures and temperatures.

CSP Today: What is the advantage of having stationary receivers, in terms of operational efficiency, O&M, and cost?

Oğuz Çapan: The main purpose of parabolic trough fields is to generate steam to drive a turbine. If you can’t do direct steam generation, you have to use a heat transfer fluid.

The disadvantage of this is that you have to take the heated oil to a central station and run it through the heat exchanger to generate steam. The steam incurs a 15%-20% efficiency loss because the generating steam goes through two steps, each of which causes an efficiency loss.

Direct steam generation eliminates the need for a heat transfer fluid and heat exchanger costs, so you have three main advantages: reduced cost, increased thermodynamic efficiency and reduced operations and maintenance costs.

These represent considerable cost savings. In order to rotate the parabolic trough structure using less force, we came up with the idea for a counterweight above the receiver, which enables the centre of gravity of the system to be aligned with the receiver, making it easier to rotate than current hydraulic systems being used.

This lowers the cost of providing power for rotating hydraulic power – which is expensive. Instead, we use small electric motors, which are cheaper than a vast network of high-pressure hydraulic pipelines. Electric motors also allow for a much more accurate sun tracking than hydraulic pistons can which is critical for the concentration of solar power.

Another key point is that by keeping the receiver stationary, we use vertical loops of pipe, as in traditional refineries, instead of using a number of high-pressure separators located on the ground to separate the water from steam to protect the turbine.

By using the vertical loops, we eliminated the cost of using high-pressure separator vessels, valves, pumps and other related components.

We think by doing it this way, we can lower costs by around 20%.

CSP Today: Hittite Solar Enerji’s DSG system has so far been tested in three consecutive pilots in Turkey (10kW, 30kW, 200kW steam equivalent). What is the optimal operating temperature of this technology?

Oğuz Çapan: There are temperature limitations when using oil as a heat transfer fluid, and molten salts also have disadvantages.

In my opinion, direct steam generation with fixed, welded flanges (similar to those used in petrochemical plants) removes the pressure problem. By eliminating the limitations presented by pressure, you can raise the temperature to the parabolic trough’s limits.

So far, we have achieved 420 degrees Celcius and I am confident we can achieve 500 degrees in the near future.

Since we have eliminated the pressure problem, we can increase the temperature well beyond what has previously been possible.

CSP Today: What is the optimal sized plant for this technology?

Oğuz Çapan: We are currently working on a proposal for a 50MW project in Turkey – we are in the process of preparing the documents. But we do not plan to install the whole 50MW at once. Initially we will begin with a 500kw unit, which is designed to be part of the 50MW plant.

We have already had interesting meetings with TriState company and NREL, looking at how we can collaborate on developing a system in the US. It is important to have a qualified, independent third-party to carry out the testing, and NREL and EPRI fill this role.

CSP Today: Is the technology modular?

Oğuz Çapan: The standard unit is 48 metres with a 6 metre aperture. So it is modular.

CSP Today: Is Hittite Solar Enerji’s technology eligible for funding in the US?

Oğuz Çapan: We would be qualified for a number of financial support schemes. Personally I think the energy situation is so critical now (given the significant, imminent drop off in oil production – as a former oilman, I strongly believe that the “peak oil” is just around the corner. (You can view my Peak Oil presentation here).

Because of the urgency of the energy situation, within a year attitudes are likely to change drastically and renewable energy projects will not be at a loss for funding.

CSP Today: Hittite Solar Enerji is already in discussions with several high profile players. Which markets will you be targeting initially and with what scale of technology? Is it modular?

Oğuz Çapan: Turkey is an important market – it imports 95% of oil and gas and it has a rapidly growing industrial infrastructure to support.

North Africa and the Desertec concept are important. India and China. The Middle East is also interesting, even though it does not have an immediate energy problem.

CSP Today: You have come up with a novel solution to strengthen parabolic mirrors, resolving some durability issues. Can you please explain it?

Oğuz Çapan: Mirrors are an important part of the system, Instead of specially manufactured glass mirrors we use thin strips of flat mirrors stuck onto the parabolic surface. The result is so strong that the workers can walk on the mirrors without breaking them. This has also eliminated the high cost of specially fabricated large parabolic glass mirrors.

Breakage is an important point; in strong winds, large curved glass pannels are is susceptible to cracking. In this respect, we have eliminated a large portion of costs relating to mirror replacement.

CSP Today: How does the reflective performance compare with bent glass mirrors and what is the rate of degradation (of the adhesive, for example)?

Oğuz Çapan: The reflectivity of flat surfaces – in physics – is better than curved surfaces. In fact, it was a physics professor from MiT who noted that the reflectivity of our parabolic troughs was much better than those using bent glass.

We have used 3M’s glue, which has an unlimited life in open atmospheric conditions. In terms of the degradation of the glass, well, glass is glass, whether it is specially manufactured or not. Of course it is also important that the glue we use insulates the silver lining of the flat glass mirror panels from atmosphere, preventing any damage. 

CSP Today: Hittite Solar Enerji has also developed closed loop desalination technology. How easy is this to bolt on to power generators and what are the environmental advantages compared to other desalination technologies out there?

Oğuz Çapan: Our desalination technology won the Development Marketplace 2006 Competition (with a grant prize of US$185,000) run by the World Bank and the Bill Gates Foundation.

It operates at a low temperature and runs off waste heat. We have combined the desalination unit with the parabolic trough system, but in fact it can be bolted on to any system producing waste heat.

We installed a 100Liter/Hr capacity desalinization unit at the steam discharge of our 30kW parabolic solar trough pilot unit to test it successfully. We also did a study for using the waste heat of a hotel’s centralized air conditioning units located at the Meditterranean coast of Turkey and and saw that it would provid 100% of the hotel’s water requirement from the sea.

The environmental advantage is that it doesn’t dump hot water, like other systems. Instead, we reuse the hot water for the CSP system – in this way the closed loop water circuit resolves environmental issues surrounding traditional desalination plants.

To respond to this article, please write to the editor:

Rikki Stancich: rstancich@gmail.com