This detailed technical analysis of Paul Salopek’s solar power system supplements the Lab Talk entry Harnessing the Sun for Storytelling.
Calculations on the solar panel:
*I’m estimating the real-world output of the PowerFilm 20W panel to be about 17 watts. The latest tweet from Paul has him in Djibouti and his path shows him headed north toward Jerusalem along the Arabian coast. As he heads north further from the equator the amount of sunlight available to him will get less and less, but in the near future that is going to be offset as the northern hemisphere enters into the summer months.
Total daily insolation measurements from various meteorological stations along his path show 6-7 full-sun hours of sunlight available to Paul. The term “full-sun hour” is used to express the effective amount of time a solar panel will achieve its maximum output, or 17 watts in this case. However, to extract that much solar power would require his solar setup to be positioned and ready the moment the sun breaks the horizon and then be continually adjusted for proper solar alignment until sunset. A much more reasonable and conservative approximation would be to estimate that he can achieve 4 hours of full-sun in the window +/- 2 hours from solar noon. The estimate then of Paul’s possible daily power output is 17 watts x 4 hours, or 68 watt-hours.
Notes on the recommended V60 battery and the adapters and other hardware required to connect the solar panels to Paul’s devices:
**The V60 is a 60 watt-hour power source that has 4 different DC voltage output selections and is optimized for power input from a range of solar panels, including Paul’s PowerFilm panel. Voltaic Systems has details on their site for using the V60 with the PowerFilm devices.
Please note: I have no affiliation with Voltaic Systems. This is a product I found via Google that has the functionality to charge Paul’s electronics and accept input from a solar source. It’s different from some of the other battery pack products in that they provide a MagSafe adapter for connecting to a Mac Air. I’ll add that I was quite pleased the interactions I had with Voltaic Systems tech support. I contacted them both verbally and via e-mail with various questions about the V60 and they were very prompt with responses and provided answers to all of my questions.
Paul has a newer Macbook Air with a a MagSafe 2 connector so he will also need 2 special adapters to connect the V60 to his Mac. A V60 to MagSafe adapter from voltaic systems and then a MagSafe to MagSafe 2 adapter from Apple.
To charge his devices that use 12V he needs the car charger socket.
For the Canon camera he needs a car charger. There are many of those for sale on Amazon or from other online stores.
For the Hughes 9202 there were 2 options. A DC-DC adapter (available from several places) or a direct connection from the V60 to the Hughes 9202 which would be more efficient, but requires a custom adapter. For now Paul is using the DC-DC adapter but plans are in the works to wire up a custom V60 to 9202 adapter.
He also needs the 12V automotive plug charging adapter for connecting the V60 to the PowerFilm panel.
— Richard Smith
Richard A. Smith is the Director of Embedded Engineering at One Laptop per Child Association where, in addition to other responsibilities, he designs methods for powering XO laptops in remote off-grid locations. He can be reached at richard@laptop.org.