My first experience with portable PV goes back to the 1990s, when I was designing off-grid residential PV systems. Most of the installations were in remote areas, and we wanted generator-free temporary power for tools. I took a 6- by 12-foot enclosed utility trailer and installed a 1,000 W PV array on the side with hinges along the roofline, which allowed easy fold down for travel. An interior wall-mounted 2,500 W inverter, charge controller, and eight L-16 deep-cycle batteries completed the trailer. I later added a SunFrost DC refrigerator, microwave oven, work counter, utility sink, and composting toilet. Spending days working on a remote mountaintop suddenly became much more civilized.

Although I only intended to use this solar trailer for temporary power at construction sites, a year later I received a call from an agent of a well-known actor who was hosting a rally at his rural property to protest the utility’s plan to run a high-voltage power line through the area.

The actor and his neighbors understood the irony of using the power company’s electricity to power an event to protest against the same power company and were looking for alternatives. They were also concerned that a noisy generator might interfere with the speeches and live music. They had heard about my PV trailer and called to see if they could use it to power the tent lights and sound system for their two-day event.

The solar trailer was also used to power the public address system at an outdoor energy fair. I recall to my horror how the solar batteries were losing charge much faster than I expected, right in the middle of the featured speaker’s presentation. I feared a total system failure was only minutes away, and headed out to follow the multiple extension cords from the solar trailer to the distant event’s tent. Halfway along this path I discovered a recently added extension cord—heading off in a totally different direction. As I stumbled through the dark following the wire, I finally reached a brightly illuminated doughnut concession trailer. The fry cook was happily making piles of hot doughnuts in the electric deep fryer for the hundreds of attendees, and had no idea he was running off my batteries!

Since this early experience with making solar doughnuts, my PV trailer has been loaned out to national scouting events and energy fairs, and is still used occasionally at remote construction sites. Through these experiences I have learned the importance of identifying the energy and power limitations of a portable PV system.

If you’re planning to purchase or build a portable PV system, first decide exactly what will be powered and for how long. Most organizers will seriously underestimate the event’s actual power requirements so be sure to take a careful inventory of their loads before taking on a project of this kind.