Solar on the Go: Page 2 of 3

Portable solar systems in this midsize range are mounted on a hand cart or suitcase with wheels, as their batteries can weigh 60 pounds or more. Adding an inverter gives the ability to power AC loads. Since a cart-mounted PV system could be in a variety of positions and be used in a confined area, sealed batteries are typically used to avoid spilled acid and vented gas.

Recent electric-vehicle research to reduce battery weight and increase energy density has produced batteries that are also suitable for PV carts. Lithium-ion batteries allow a full discharge and fast recharge time for thousands of cycles. The amazing amount of energy that these lightweight batteries can store means they are ideal for portable systems.

Until now, condo or apartment dwellers have been unable to use PV systems, either due to lease restrictions on installing permanent arrays or having battery banks in buildings shared by others. Now if the grid goes down, they can roll outside a PV cart from the closet and use an extension cord to energize their TV and lights after a power outage.

PV Trailers

If your portable solar power needs are larger, some manufacturers offer PV-powered trailers that can even include a backup generator. The smaller units are usually the size of a pop-up camper.

Smaller solar trailers cost less than $5,000. Their array and battery are sized to be towable by a car or SUV. These trailers are ideal to power smaller 120 VAC loads that may be needed for extended camping trips, remote construction sites, or emergency power for lights and communications equipment.

For heftier needs, there are manufacturers that custom-build solar trailers in sizes that require a large pickup truck to tow and can cost $90,000 or more. They are better suited for commercial and government emergency power needs, or used as rental units which are towed from event to event to help offset their high initial cost.

The largest solar power trailers have tons of deep-cycle batteries and a heavy-duty backup generator to recharge the batteries when the sun is not available. These units are great for emergency communications equipment at disaster areas, remote television broadcasts, or for temporary lighting and audio/video equipment.

Understanding Your Needs

Before purchasing (or building) a portable PV system, it’s important to estimate the battery drain for the loads you want to power. For systems that include a 120 VAC inverter, you must first convert the power requirements from “watts” into a battery “amp” load. This battery draw can be high for a microwave oven or hair dryer. Any electrical load operating at 120 VAC will require 10 times the amperage at 12 VDC, and the inverter’s efficiency losses must be accounted for.

The table provides both the watts and corresponding battery amp draw for the most common appliances, lights, and computer equipment used with portable PV systems. You will find these values to be more accurate for estimating your true solar battery run time, as they are based on real measurements.

For example, an iPad consumes 11 W of 120 VAC, which is a 1.06 A drain on a 12 V battery, the most common battery voltage for smaller portable PV systems. You can divide the amp values by 2 for systems having a 24 V battery, or by 4 for a 48 V battery bank to find their current draw.