Refers to a panel of photovoltaic cells used to generate electricity from sunlight. Common in contexts of renewable energy and residential/commercial power generation.
We installed solar panels on the roof.
The power generation efficiency of solar panels is improving year by year.
Compound of 太陽 (taiyō, 'sun') + 電池 (denchi, 'battery/cell') + パネル (paneru, from English 'panel').