Sunlight in a tank

Clean, abundant and costing absolutely nothing, solar power may one day prove to be the answer to the world’s energy puzzle. But perfecting utility-scale electricity production has always come up against a fundamental roadblock: when the sun goes down, the power dies. Designers of the Crescent Dunes Solar Energy Plant in Nevada have overcome that hurdle using a first-of-its-kind system that relies on molten salt to store heat, allowing the plant to stay in operation day and night, rain or shine.

 

Taking the heat

Like most plants built on the Concentrated Solar Power (CSP) model, Crescent Dunes consists of a field of tracking mirrors, or heliostats, that focus light onto a central receiver atop a concrete tower.

Rather than using the sunlight to boil water directly as other CSPs do, Crescent Dunes heats a mix of sodium and potassium nitrate to over 600 degrees Celsius and pumps it to an insulated thermal storage tank made of Outokumpu Therma stainless steel. Whenever electricity is needed, the salt is sent through a steam generation system, superheating water to turn a turbine.

For creating the plant’s hot nitrate storage tank, Outokumpu delivered 650 tonnes of Therma 347H quarto plate. Therma range is specifically designed for high temperatures. This grade’s superb corrosion resistance, given the harsh salts it would be exposed to, was also essential in ensuring that the plant can long fulfil its duty, supplying enough power for 75,000 homes.

 

Pivotal, in two ways

Stainless steel was also mission critical to the plant’s more than 10,000 heliostats. These must pivot on two planes as they track the path of the sun throughout the day, keeping the energy-rich rays directed toward the receiver.

Over 60 tonnes of Outokumpu’s Forta LDX 2101 went into their anchoring bolts, which have to function in an atmosphere of wildly fluctuating temperatures, sand, moisture and the corrosion that comes with them. This duplex stainless steel grade was chosen for its ability to withstand these tough conditions, making sure the sunlight never loses focus, nor does the drive toward clean, renewable energy.