Parabolic trough solar power plants possess inherent thermal inertia in the circulating heat transfer fluid (HTF) that provides a 30-45 minute buffer against the transient effect of clouds on electricity production.

Wind generators and photovoltaic systems have no such buffer; they produce power that varies widely as the weather changes. Our more uniform output is highly valued by electric utilities.   The addition of thermal storage, available only in concentrating thermal solar systems, allows electrical production to be shifted by several hours and match the customer load demand profile. The market value of the electricity is increased.  Lifecycle Cost of Electricity (LCOE) may also be reduced because electricity production (hence utilization of power equipment) occurs for more hours per day.
All of the 1200 MW of parabolic trough solar plants in commercial operation today use synthetic oil as the HTF.  These plants typically operate at a maximum temperature of 400°C because the oil degrades at higher temperatures.  As the industry looks for ways to reduce costs, one option is to increase the collector operating temperature.  For a given storage volume, more energy can be stored when the temperature difference is larger.  Consequently, molten salt is getting attention as an HTF that withstands higher temperatures.
SkyFuel is engaged in a US Department of Energy funded research and development program on two concentrating collectors that will operate at higher temperatures.  The DSP is a parabolic troughsimilar to SkyTrough, except twice as large and with greater sun concentration.  The LPT is a completely different  style of concentrator:  a linear Fresnel with a fixed receiver.  Both of these new collectors will operate at higher temperatures and can use molten salt as the heat transfer fluid.

By David White, Chief Engineering Officer,