45W sounds like overkill for an RPi - I live in Scotland (55.95N) and I have a 50W panel charging a 110Ah battery in my garden shed. The battery is used to power a 1kW Invertek 250V inverter (150A fuses are impressive BTW) which I use to run a lawnmower, power tools, soldering station and lights (not all at once!).<p>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.
I was investigating today into something similar.<p>The concusion of my research:<p>- 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.<p>- The RPi does work with 3.3 Volts, but then the USB does not work. Yet again, for me good enough.<p>- Undervolting (the core and ram) and downclocking do not make much sense. It does save nearly nothing and make the board absurd slow.<p>- The biggest powersink seems to be the GPU, but AFAIK it can't sleep.<p>- 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.<p>- Displays use very much power. But they can be turned of if not needed.<p>It seems the solar panel can be significantly smaller, but not for a webserver.
I think he could have halved the size of his solar kit and still not have had to worry about power interruptions.<p><a href="http://pi.qcontinuum.com/cgi-bin/rrd/rrdgraph.volts" rel="nofollow">http://pi.qcontinuum.com/cgi-bin/rrd/rrdgraph.volts</a>
Excellent project, but the shading on the solar panels from the railings is more than likely severely reducing the output of the panels at lower sun angles. Even shading a single cell on a series connected panel effectively reduces the output of ALL cells. Also having peak power tracking would increase panel utilization.
I really like the power monitoring using the Arduino though.
This kind of research is nice to see. Too bad your setup needs a less-powerful system (Arduino) and a more powerful system (RRD host) to operate the charging.<p>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?
Network traffic graph currently showing what it is like to be HN'd:<p><a href="http://pi.qcontinuum.com/cgi-bin/rrd/rrdgraph.pi.main" rel="nofollow">http://pi.qcontinuum.com/cgi-bin/rrd/rrdgraph.pi.main</a><p><a href="http://pi.qcontinuum.com/rrd/pi-traffic-day.png" rel="nofollow">http://pi.qcontinuum.com/rrd/pi-traffic-day.png</a><p><a href="http://pi.qcontinuum.com/rrd/pi-traffic-week.png" rel="nofollow">http://pi.qcontinuum.com/rrd/pi-traffic-week.png</a>
I've been wanting to hack on a few projects that involve small amounts of electrical knowledge, but am not sure where to get the bare minimum information to avoid killing myself or others. What is the best way to get practical background knowledge about this type of electrical project?
What are "the RRD tools"? What does RRD stand for?<p>Also, if you're worried about an application which does a lot of SD writes, you could:<p>(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 <i>did</i> make a backup, right?<p>(2) Write to a RAM disk<p>(3) Write to a network drive
Interesting. Looks similar to this project. <a href="http://www.engadget.com/2012/06/20/48-pandaboards-chained-together-in-solar-powered-arm-cluster/" rel="nofollow">http://www.engadget.com/2012/06/20/48-pandaboards-chained-to...</a>
> see how many years I could keep it running without a reboot<p>> I decided set up the panels on the deck facing west.<p>There seems to be some disparity between his goals and the stability of the environment in which he's placed the equipment.