A tankful of sunshine

Wind turbines and photovoltaic plants produce renewable energy. But not on windless days or at night, when continued supply requires storage. Solar thermal power plants in sunny regions are able to combine both energy production and storage.

The technology that makes this possible is known as concentrated solar power (CSP) with integrated thermal energy storage (TES). Most modern CSP plants have tens of thousands of reflectors all directing sunlight toward a receiver atop a solar tower. There, the concentrated solar energy heats a transfer fluid – most commonly molten salt – to a very high temperature. The benefit of this design is that the energy can be stored cost-effectively in tanks and then transferred to a steam generation system for electricity production, even at night.

According to the US National Renewable Energy Laboratory, operational and under-construction CSP capacity worldwide currently totals 10.7 gigawatts. The installed capacity in China alone is projected to reach 15 gigawatts – the equivalent of 15 large coal-fired plants – by 2030.

Solar tower power systems are an engineering challenge in terms of heat, pressure and corrosion. “The hotter the heat transfer fluid, the more efficiently solar energy can be converted into thermal energy and then into electricity,” says Song Li, Power Industry Manager at Endress+Hauser China. Hence the measurement instrumentation, like various other key systems, must be able to withstand temperatures of over 550°C, high pressures and the corrosive properties of salt. “Endress+Hauser is the only producer of measuring instruments for every one of the measured variables relating to the heat transfer fluid and the water-steam circuit,” Song Li says. The biggest such project that Endress+Hauser has equipped to date comprises far in excess of 3,000 sensors – whose job it is to ensure operational reliability and maximum efficiency.