Support for the European Union's climate and energy policy eroded further Friday as the Czech Republic became the latest member to denounce subsidies for clean but costly renewable energy and pledged to double down on its use of fossil fuels.

It followed Poland's declaration that it would use its abundant domestic coal supplies for power generation rather than invest in costly renewable energy facilities. Spain abolished subsidies for photovoltaic power generation in July and the U.K.'s power markets regulator last month froze...