In order to convert power from the panels into usable electricity, he implements a system involving an MPPT (maximum power point tracking) controller to charge two 100 amp-hour deep-cycle batteries. An inverter then converts DC power from these batteries into usable AC power, switched on an off via an SSR (solid-state relay).Control and monitoring of the system is via a Raspberry Pi running Apache and MySQL.
This allows him to see stats on the system, including temperature of the Raspberry Pi and batteries through a web interface. Depending on settings, the Pi can turn fans on and off to help control temperature, as well as the power SSR, controlled indirectly via a USB connection to an Arduino Duemilanove. Current monitoring from the battery packs is accomplished via a split core-style sensor and another Duemilanove, however this functionality still needs some work.
You can check out his system overview in the video seen below, and find its code on GitHub.[h/t: Hackaday]
Why don't hotel rooms have ceiling lights?
My hotel building is over 100 years old, so we have ceiling lights. We also need a ladder to change a bulb 11' from the floor. It can take 20 minutes for 1 bulb! This is one reason that we have changed to the longer lasting (and more economical) low-energy bulbs.
I would be delighted to have wall lights instead. Retro-fitting them would however be even less economically sound.
Higher than average ceilings mean ladders to change the bulbs in ceiling fittings, and this extends the maintenance time and convenience for staff enormously. Even normal height ceilings mean that a chair is needed to swap a bulb out. Wall fittings are so much more convenient for both staff and customers, reducing the time taken to get light again!
As Michael Forrest Jones says - anything other than a simple bulb swap requires the power to be cut to the whole circuit (which may be more than just a few rooms). This makes it very awkward to do emergency repairs after dark! -- Been there done that... Go with wall fittings that can be isolated in-room!
I have ceiling lights.
I don't like them, as they are awkward for maintenance.
Replacing them would be expensive and extremely difficult - basically a total rewire of the hotel lighting system.
Design engineers are not stupid. they note the first 2 points!