Talk:Deployment Guide/Power Infrastructure

Alternative Power Sources

We should consider at least the following possibilities in terms of practicality and environmental impact.

• Solar is well covered on this page.
• Wind.
• Water. The beaver is the MIT mascot. Can we put a beaver-cam on a beaver dam with a microhydro unit and show how many XOs it can power?
• Ethanol, in Brazil, at least
• Biodiesel, using palm oil, for example, in areas of recent glut, such as Nigeria. Soap is a valuable byproduct.
• Biomass (methane).
• Animal power. Cow power is under development. I (--Mokurai 14:51, 22 March 2008 (EDT)) would like to invite MIT engineers to create a hamster-powered system with a hamster-cam. Then we can ask how many hamsters it takes to power an XO. ^_^Guinea pigs ("cuy" in Spanish) are widely raised for food in the Andes. Burros are common in many countries. Both might have potential for generation.
• Child power is where we started. How viable is it? I hear that children can generate power faster than the battery can absorb it. Perhaps children can take turns on a gang charger.

---These ideas are already detailed on numerous pages tagged with Category:Battery & Power, I'll add that category to this article as an aid to navigation for wiki readers. It looks like one intended purpose of this guide is for it be useful in hard-copy form at prospective sites/locales and so I imagine it should stay focused on the most likely questions that will arise. Solar is definitely the number one alternative to mains power generally considered (although microhydro may be making some in-roads in mountainous areas). Philosophically, I agree that power sourcing issues need to be explored, but not necessarily in this guide. In this context, it should certainly be secondary to the more mundane, but still important, deployment-site specific and highly pragmatic questions such as: will there enough total electrical capacity (regardless of source), are there enough outlets, and so forth. Cjl 15:59, 12 April 2008 (EDT)

Watt-hours

I think I fixed the watt-hour terminology. Although I don't think watt should usually be capitalized. (It should not -- nicabod) I also did the math in the example. I don't think that the example is a good one though. Although the server and the modem may be active for the full day or more, the laptops may not be in use every minute they are at school. Also it is probably more cost-effective to run a smaller generator for a longer period of time and not rely on running on lead-acid batteries most of the time.

Another thing to think about is what happens when students come to school on a Monday morning with their laptop batteries discharged. If all 500 plug in at once, you will probably be drawing on the order of 500 laptops * 20 watts/laptop = 10,000 watts or 10KW. You will probably limit the number of users that can charge their laptops at once.

This surely suggests schemes for charging an home. Nicabod 19:44, 10 June 2008 (EDT)

It would be good to get some feedback from the pilot schools to see how many hours a day students use their laptops, both in school and at home. -- Tef

A natural limit here is on the number of outlets one has. --Sj talk

Solar set up notes

Talking with Richard at lunch today, he mentioned some issues with setting up power at deployments - specifically for a solar setup.

• How do you find out how much power they need? (Are they trying to discharge their laptops slower, or actually recharge them - which would imply a higher wattage need)?
• How do you find out how much sun they get, how much space they have for panels, etc?
  • http://www.kmitl.ac.th/~kswichit%20/solarserver/solarserver.htm
• How do you get solar panel materials out to them (logistics of shipping, prices, etc)?
• Mounting solar panels to roofs, etc. in the optimal orientation - how to figure that out?
  • Suggestion: Midsummer noon, set up something like a pencil stuck through a piece of cardboard. Tilt the pencil so it's pointing directly at the sun. There's a lot of info. around about setting up solar power.Nicabod 20:03, 10 June 2008 (EDT)
• If you're powering a large number of laptops at once, you'll be dealing with quite a bit of wattage - but if you run them at relatively low voltages (20, 30V) for more than 10-15 feet, you run into huge resistance losses. So you need to step up the voltage to 120V or so, but then you get an electrocution hazard... and then you have to step it down again before putting that into the XO...
  • I doubt it, but a battery bank for storing power during the day? That, and the power-conversion electronics are costly, but the technology is probably well worked-out. Better to choose a voltage for the battery bank that can be fed directly to XOs, instead of synthesizing the local AC mains power. Try to use car batteries? Busbars from the batteries could be aluminum "[Al]", if copper continues to be costly (as it probably will). However, connections to [Al] absolutely must be gas-tight; air instantly oxidizes [Al]. (Check into household fires caused by [Al] wiring, before the EEs learned how to connect [Al] wire safely. [Al] has a different thermal coefficient of expansion, so a connection that begins gas-tight might cease to be, when the temp. changes.Nicabod 20:03, 10 June 2008 (EDT)
• How to wire cords in the classroom so kids don't trip?
  • Try to set up the charging station against a wall? Otherwise, try to be neat about a "bridge" to carry cords overhead, high enough for adults. (Cost of extra cordage not quite trivial)Nicabod 20:03, 10 June 2008 (EDT)

• There's a new solar-cell technology, non-silicon: copper indium diselenide ("CIS", apparently CuInSe₂), said to be quite efficient (relatively). It might well be worth looking into. Googling on ["copper indium diselenide"] (with quotes) gave some hits that looked good. I don't think OLPC would supply solar-cell chargers -- (or would they?)Nicabod 20:09, 10 June 2008 (EDT)

These are examples of some of the unresolved issues at each pilot, and the process of thinking through these questions is something that should be put into a deployment guide. Mchua 14:01, 9 June 2008 (EDT)