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Building a Raspberry Pi based server powered 100% by solar energy (qcontinuum.com)
66 points by 666_howitzer on June 24, 2013 | hide | past | web | favorite | 26 comments

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!).

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.

So if I got a bigger panel and needed more power would you say to buy a second battery? Would I just hook it up in parralel?

If you need more power you have 2 options. You can add more batteries in parallel and increase the size of the cables to take the higher current, or you can go to a 24 volt system which means you can use the same cable. 24 volt components are maybe harder to find though. My system is really intended for short periods of peak power (say 30 minutes a week running the mower). It was harder to find cheap inverters to handle more than 1kW at the time too.

How much did the system cost?

In total about £600 (this was 2 years ago); £250 for the panel, £120 for the battery, £150 for the inverter (Ebay, 2nd hand) and the rest on sundries like cable & connectors (also Ebay in most cases). I used http://www.midsummerenergy.co.uk/ for a lot of the bits.

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!

So what kind of battery is it? I might want to try this. Do you have any other details? A blog post perhaps :-)

It was an Elecsol 100Ah leisure battery. The equivalent would be http://midsummerenergy.co.uk/buy/Sealed-Batteries/PM-110.htm...

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.

That's great thanks! I'll let you know how it goes.

I was investigating today into something similar.

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.

I think he could have halved the size of his solar kit and still not have had to worry about power interruptions.


Evidence shows the solar panels are important: He doubled the number of solar panels in November after the initial panels weren't enough to power the RPi in the winter. http://pi.qcontinuum.com/failure2.html (The graph also shows the voltage dip below 10V in Nov, probably representing that failure, though it's hard to see the details in the "last year" graph.)

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.

Adding some kind of rotation mechanism to the panel would increase efficiency, and I'm sure the Pi or Arduino could handle this.

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.

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?

And the allmighty raspberry pi is surviving traffic like a baws :)

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?

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.

I implemented option 4 on a linux based router a couple years ago:

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.

Round Robin Database.

Interesting. Looks similar to this project. http://www.engadget.com/2012/06/20/48-pandaboards-chained-to...

> see how many years I could keep it running without a reboot

> 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.

I wish there were more pictures and descriptions of how to hook up the battery to the raspberry pi. That is the biggest unknown to me.

I don't know what the author used, but you should be able to build something similar with these products/kits from Adafruit:

  - 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

142 days uptime is pretty cool!

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