Many of the parks already have electricity in the restrooms (lights & water). Solar panels would augment the existing power. Of course, they could help in less improved road sidings.
I can't say how long solar panels would last. There are traffic signs, both portable and fixed using solar panels that seem to not be vandalized, stolen, or shot. We do get grafitti, but to a large extent it is limited to already painted surfaces. One can clean painted graffiti off of glass. Scratched graffiti could be more problematic. A question might be where one is planning to mount the solar panels. One could mount them on a pole 20 feet in the air, but the coast can get some wicked storms. Mounting them on an outbuilding roof would be more secure as long as angles and sun is right.
Small wind turbines would also be viable.
Even if one wishes to be "Green", one could offset the power of grid attached facilities with a solar or wind installation almost anywhere, and post a sign about the power offset program.
I don't know about vandalism. It happens some places, not others.
I would design any lockers to be reasonably secure. It is a tall order.
I actually bought a retired bike locker from the local recycler. Made of fiberglass. You'd only get one shot at it, but if one saw a $10K bike going in, one could likely break it in seconds.
My thoughts were to make the lockers stronger than the WWII Pill Boxes. The door would still be susceptible to an angle grinder attack, but it would be a major endeavor to open one.
Also the reason for going with a no padlock policy.
They'd be kept normally locked, with the way to determine if something is inside by using an active key.
The tricky part would be to determine the number of lockers. 4? 10? (each capable of holding 2 or 3 loaded bikes). Obviously varying by location & cyclist appeal.
Oh, and the lockers would also double as bear boxes for overnight campers.
I need to research the coastal hiking trail, but something similar could be offered for hikers (backpack size lockers in places where hikers and cyclists intersect).
The relationship between cyclists or other sports enthusiasts and the general population can be fickle. I think there is broad support, but there is likely someone who would think it is funny to make cycling facilities inoperable just to spite cyclists. Building a sand castle out of a bike locker?