In Japan, solar thermal energy is used more as solar water heaters than for power generation.
Literal
Solar-heat [topic-は] Japan [at-では] power-generation [than-より] solar-heat water-heater [as-として] is-utilized.
Uses the comparative より...として to contrast two applications: power generation vs water heating. 太陽熱 (solar thermal) appears twice — once as the topic and once in the compound 太陽熱温水器. 利用されています is the passive + ongoing state: 'is being utilized.'