@AAQ –
The early position was that electricity was absolutely prohibited. Chazon Ish prohibited using “Zionist electricity” because he viewed the workers’ actions as intentional desecration. He argued that even if the electricity is necessary for life-saving services (hospitals, security), once there is a “surplus” used for lighting homes, the Jew at home becomes a beneficiary of the worker’s sin. Specifically in Orach Chaim 38:4, he argues that using this electricity involves a Chilul Hashem (desecration of God’s name) because it demonstrates a lack of “pain” over the public violation of Shabbat.
That’s why Charedim made extensive use of genetators or just sat in the dark. BTW, this still goes on today in some areas (I’ve witnessed it in specific neighborhoods in Bnei Brak – and I’ve heard a couple blow up from overuse during a 3 day Chag).
In Minchat Shlomo (Vol. 1, 11:7), RSZA writes: “Technically, one can find grounds to permit [using the grid], as the electricity is being produced for the sick and for security… However, one who is stringent to use a generator is performing a ‘great thing’ (davar gadol) to avoid even a scent of benefiting from Shabbat desecration”. Which is aruging that power plant must run anyway for Pikuach Nefesh so a private citizen drawing a little more current isn’t necessarily causing more “work” to be done in a way that creates a new prohibition.
Today, there is a tendency to use grama technologies (think Tzomet Institute) and batteries.
Rav Shternbuch is opposed to any use (Teshuvos VeHanhagos Vol. 1, 264), arguing even with automation, the “system” is managed by Jews who make decisions based on economic savings rather than Pikuach Nefesh and is also “empowering transgressors”. He basically reinforces Chazon Ish’s ban.
Rabbi Asher Weiss in (Minchat Asher) prohibits on different grounds – Makeh Be-Patish not Boneh (which personally makes more sense to me).
Rav Yitzchak Yosef allows it but those want to truly be “good, frum Yidden” shouldn’t.