Of course, on the day I visit the sky is covered in clouds. “No electricity will be produced today,“ says Rachid Bayed at the Moroccan Agency for Solar Energy (

Of course, on the day I visit the sky is covered in clouds. “No electricity will be produced today,“ says Rachid Bayed at the Moroccan Agency for Solar Energy (Masen), which is responsible for implementing the flagship project. This is a big problem with concentrating thermal solar power: it requires intense direct normal irradiance to work and performance falls off catastrophically when skies aren't clear. A conventional non-concentrating PV module can deliver about 10% of its rated output if it is illuminated at 10% of standard test conditions, e.g. sun through light cloud cover. Performance falls off almost linearly with decreasing illumination until very low levels. Concentrating solar thermal performance falls off a cliff with insufficient and/or diffused light. You can see this effect in the EIA's data about US solar farms here: https://www.eia.gov/electricity/monthly/epm_table_grapher.cfm?t=epmt_6_07_b https://www.eia.gov/electricity/monthly/epm_table_grapher.cf... In the summer months, PV and concentrating solar thermal plants have comparable capacity factors. In the winter months, PV plant capacity factor falls off by less than half while thermal plant performance tumbles by ~80% (June 2016: 33.6% and 33.5%, January 2016: 17.9% and 6.8%). A decade or so ago, solar thermal was justifiable because PV was so much more expensive. Even after PV matched and then beat solar thermal costs for instantaneous generation, thermal still had a value proposition for after-sunset operation via thermal storage (like this Moroccan plant has with molten salts). But as costs of PV and alternate forms of storage continue to fall, while solar thermal costs barely budge, I expect that solar thermal electricity is going to become obsolete even for the very sunniest regions.