NTT DOCOMO is testing a base station with dual power-source control technology that uses more than 95% reduced-impact (solar and off-peak) electricity.
The idea is to avoid the use of on-peak electricity as much as possible. The proto type base station leverages lithium-ion batteries to store excess solar electricity generated during the daytime and off-peak electricity generated during the nighttime. Stored electricity is used as the primary source between dusk—once solar-electricity generation becomes unavailable—and 11pm, when off-peak electricity becomes available.
https://www.nttdocomo.co.jp/english/info/media_center/pr/2015/0306_01.html
