Bluetooth geocache

So far the arduino forum has been helpful for me being so new but I would to pick the brains of the forum for an idea for a paperless geocache. I ant to construct a cache using an arduino and with bluetooth connection. Cachers would arrive at the GZ and log into the cache via bluetooth and 'sign' the log paperless by leaving a note on an SD card, is this feasible?

How will you power it?

The plan is to power the system using rechargeable batteries and solar panel. Although the British Weather may play a factor in where the cache would be located. I am sure on Dartmoor there is enough places to hide the cache/solar power. More research needed on Solar panels though!!!

Won't the PV array be a bit of a giveaway?

Yes it will be so I need a good spot to hide the the small array I could even place it on a building and let users assume it is part of that said building. I am looking for yes it can work and then locate a spot and then build the arduino. Hoping I do not bite off too much as I am an electronics engineer and not a programmer. Any of the forum readers who give me tips/reading material would also be handy.

You may wish to research Bluetooth Low Energy, and the protocols used for iBeacons.

Here is an excellent overview of a solar powered Arduino, with low power operational tricks.

I'm working on a solar powered pi for something a little more diverse at the moment. You can get lipo solar modules off ebay in the $3-8 range for charging 1.7v systems. Couple them to 6-7.5 solar panels and it works find for charging lipo cells. That of course either requires that you use a 3.3v arduino board or get a step-up buck converter to get you to the 5v needed by standard arduino boards. (what you find out though, if you look deeper into most modern electronics is that their internal IC chips use 3.3v anyway. And things like the pro-minis are available in both 3.3v models and switchable models. The switchables are especially handy in that their pins aren't as delicate and sometimes you can get 5v devices to still work -- assuming you have a separate 5v power for the shield/module/sensor -- even with the arduino running 3.3v. Of course, this would defeat the purpose of having a 3.3v arduino though, but I've been able to use this 'ruggedness' for example, to monitor the voltage on the lipo pack which can get up to 4.2v. Since the 3.3v mode of the mini-pro can use a v-in up to 9-12v on any pro-mini with it's own regulator, you can connect it straight to the lipo with no need for a separate regulator/buck-converter)

I would be curious to know how you got along with your project though, for as my RPi system is still ongoing in development as a non-connected hotspot/access-point information page type experiment, I'm thinking of playing with intelligent geocaches using the same basic concepts. I stumbled on your link when it occurred to me that while trying to scale down a wifi may be too much for an arduino platform, bluetooth (especially using something like the built-in business-card obex exchange protocols built into many things like smartphones) would be ideal, low power and would work find on an arduino.