Sandia National Laboratories is partnering with Flowserve Corp. and Kairos Power LLC on a $2.5 million, three-year Department of Energy Advanced Valve Project grant to lower the cost and boost the efficiency of concentrating solar power in the U.S.

Control valves are a critical link in managing the solar energy captured by next-generation concentrating solar power plants. They must safely and reliably collect, store and transfer extremely hot and corrosive chloride salt to be used for generating electricity for public use.

A more reliable, higher-temperature molten salt valve is vital in achieving DOE SunShot targets that will lower power-generating costs while increasing production. SunShot aims to reduce the total costs of solar energy, making it cost competitive at large scale with other forms of energy without subsidies by the end of the decade.

The project will investigate a newly designed molten salt valve as part of a complete solar energy management system. If successful, these redesigned valves also can be used for energy transfer in other fields, including nuclear energy and petrochemical industries.

Concentrating solar power systems must handle molten chloride salt temperatures that can reach in excess of 750° C, or nearly 1,400° F.

Concentrating solar power and other energy sources super-heat liquid, which is then pumped through a network of pipes and transported to the power station to generate electricity. Molten salt is the preferred liquid for delivering and storing lava-hot liquid energy because it retains its viscosity, as opposed to water, which converts to steam under such extreme temperatures. Molten salt also provides a more consistent temperature throughout the power plant during energy collection and delivery.

Proportional flow-control valves serve as the piping-system gatekeepers for delivering this harvested energy to the production side of a power plant. These valves are continually confronted with extreme temperatures, pressures and flow rates, and oftentimes, extraordinarily low outdoor temperatures. Valve freezing and thawing due to the vagaries of weather can create expanding and contracting materials resulting in weaknesses in the system, according to a spokesperson from Sandia.

As concentrating solar power plants become increasingly larger and more productive, system components like flow-control valves must withstand even more extreme conditions to perform reliably.

Current molten salt valves require expensive, frequent maintenance. But perhaps a bigger challenge is that molten salt valve failures can occur frequently throughout the system, resulting in expensive downtime to repair or replace the valve and repack and replace the seals.

Add the corrosive properties of salt, and there is a recipe for repeated breakdowns. If a valve failure is happening on a monthly basis in systems with between 10 and 15 valves, the system can be inoperable for days, weeks or even months. The associated loss of revenue can render these systems unsustainable.

Today’s molten salt valves are formed with expensive chromium-based materials that are susceptible to corrosion, and high nickel-based materials generally do not have the strength at these high temperatures. Sandia will focus on developing less expensive base materials for the valve and adding a durable clad composite overlay to withstand corrosion, increasing durability while significantly reducing manufacturing costs.

In addition to the materials upgrade, innovative trim design elements would automatically buffer pressure surges and pulses as molten salt passes through, while dissipating heat to avoid valve damage. The new design also would enable use of reformulated packing materials to create a modular quick-change system for replacing costly bellow seals, which can rupture if activated with frozen salt present.

Another major valve reliability issue is internal salt freezing from low outdoor temperatures, which can cause mechanical stress on valve stems, seals and bonnets. An innovative feature within the valve should address this freezing issue by carrying heat through the valve stem to the packing area, thus maintaining a constant internal temperature and reducing operations and maintenance.

The self-contained thermal management system is expected to reduce material stress and fatigue that can rupture pipe and valve systems and improve component longevity. The advanced valve design also will employ innovative gaskets, seals and packing to reduce maintenance demands.

This self-contained, integrated thermal management system should reduce the levelized cost of electricity — the cost of the system divided by lifetime energy output — which has become increasingly competitive for developers to win solar projects.

These performance upgrades also will address the DOE’s Generation 3 Concentrating Solar Power Systems program, which calls for advancing high-temperature concentrating solar power components and developing designs with thermal energy storage that can reach high operating temperatures.

The partnership, with decades of experience in researching and developing molten salt systems, will examine new control-valve materials, design and modular features to withstand extreme temperatures and pressures associated with costly valve failures.

Sandia will test potential materials using a chloride-salt blend within its chemistry laboratories. The valves will be evaluated for their corrosion resistance, material loss and mechanical strength under several scenarios at Sandia’s National Solar Thermal Test Facility.