A Message from the Guest Editor.

n this special issue, three papers belong to the path 1 , six papers o the path 2 , and two papers to the path 3 . The thermal path to generate electricity is referred as “concenrated solar power” or CSP. The greatly insolated “sunbelt” reions of the world include large Asian regions in China and India s well as the southwestern United States, southern Europe, Ausralia, the MENA regions, etc. There have been no commercialzed CSP plants in such Asian sunbelt regions yet, however, sevral CSP plant demonstration projects are currently ongoing. In his special issue, the readers will learn that a landmark 1 MW olar tower demonstration plant is currently being built in China Wang et al. . Also, a 200 kW solar tower demonstration plant ith air receiver is planned to be built in Korea. The conversion of solar radiation to chemical fuels has the adantage of producing transportable and long-term storable energy arriers. This is important because energy demand is rarely synhronous or geographically matched to incident solar radiation. specially, the conversion to clean hydrogen via water splitting is n engineering challenge. There are two major chemical paths rom solar radiation to hydrogen—one is the thermochemical path nd the other is the photochemical path. In the thermochemical ath, concentrated solar high-temperature heat above 1000°C is onverted to hydrogen via a multi-step water-splitting cycle. In