The lawnmower is the biggest drain (900W) and is really pushing the envelope - but in the summer I can cut 55 sq. metres of lawn once a week without any charge problems. In the winter the grass doesn't grow :) but I can run the other tools just fine. I was very surprised at just how well this system worked, but then I did splash out on a high end 50W Kyocera panel when I designed this. My only alternative would have been to bury an SWA cable across common ground and somehow run it to my consumer unit in a 1st floor flat, so I was prepared to spend £300 (as it was then) on the panel. They're a lot cheaper now.
Note you can now get a 135W panel for £190, which is some indication of the falling cost over the last 24 months - the 50W Kyocera panel is now £80!
Other bits were a Morningstar SunSaver solar regulator SS10 and a Nasa Clipper BM1 Battery Monitor (unnecessary extravagence - don't bother!). I also added a couple of 12V fluorescent lights powered from the SS10 so I didn't need the inverter running just for light.
It's a pretty simple set up, the hardest part is making up the high current battery cables - the clamps, fuse holder and connector to the inverter are pretty substantial to handle 100A.
I mounted the panel on the roof of the Apex shed with simple aluminium brackets. The wiring is pretty simple (more complicated by the battery monitor which has a 100A shunt resistor in the negative lead to monitor the load current).
I uploaded a pictorial wiring diagram at http://i.imgur.com/UX4Y29o.jpg?1 for you.
The concusion of my research:
- Model A uses a way less (about 33%) electricity, because it does not have a lan controller. So it will be useless as a server, but for my application this is the choice.
- The RPi does work with 3.3 Volts, but then the USB does not work. Yet again, for me good enough.
- Undervolting (the core and ram) and downclocking do not make much sense. It does save nearly nothing and make the board absurd slow.
- The biggest powersink seems to be the GPU, but AFAIK it can't sleep.
- The most inefficient component are the voltage regulators. Replacing them with dc-dc converters was discussed, i have no experimental results. The easies way is to convert the input to 3.3V without replaying and board components.
- Displays use very much power. But they can be turned of if not needed.
It seems the solar panel can be significantly smaller, but not for a webserver.
Maybe they could be pointed towards the sun more efficiently, or been a more expensive & efficient model - but the story says why he chose his porch and cheap solar panels.
What about using the RasPi's GPIO pins instead of the Arduino? And why wouldn't an SD card be able to manage that many writes? What about a ram drive?
Also, if you're worried about an application which does a lot of SD writes, you could:
(1) Try it, see if the SD card holds up. If it does, great. If it doesn't, well, SD cards are cheap, and you did make a backup, right?
(2) Write to a RAM disk
(3) Write to a network drive
It's literally the first hit in Google. He probably doesn't explain it because it's a fairly well-known tool.
4) Write to a disposable USB stick. Assuming recovery from lost data is simpler and faster than a complete wipe/install/customize by using disposable sd cards. I my situation the CF root would last forever because of basically no writes, and when the USB flash drive melts down I'd lose some logs and /tmp and some /var/cache/ stuff, oh well no big deal compared to a complete reinstall and reconfigure.
> I decided set up the panels on the deck facing west.
There seems to be some disparity between his goals and the stability of the environment in which he's placed the equipment.
- MintyBoost Kit http://www.adafruit.com/products/14
- USB / DC / Solar Lithium Ion/Polymer charger http://www.adafruit.com/products/390
- Li-Ion Batteries / Solar Panels http://www.adafruit.com/category/67