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Are there solar powered window blinds?
(sh.itjust.works)
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No need to solder.
Someone mentioned battery blinds that charges by USB, lots of small panels provide charge by USB.
I'd say it's worth spending extra on a panel that won't try to charge a full battery just to be safe, but other than that with as little juice as it uses you can buy a very cheap, very small panel and just stick it in an upper corner.