Alternative methods to gas over oil actuation

One of our clients has asked us to investigate environmentally alternatives to an existing gas over oil hydraulic actuation system.
These systems are on facilities which have no power generation or instrument air.
I believe this sort of system is in common use throughout the middle east, is anybody aware of alternatives which don't use instrument gas?
Electric actuation via solar power has been mentioned but I don't believe that the necessary power could be generated to actuate a valve electrically.
Any thoughts would be appreciated.
Bryan
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snipped-for-privacy@tinyworld.co.uk says...

Look into high output paraffin (HOP) actuators. These are linear motors that harness the force of expanding paraffin in the presence of a heat source.
--Gene
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