This lesson will let students do research to define terms that will be used in this unit. They will record this information in their Journals, which can be scientific or simple homemade notebooks. This lesson will also introduce the multimeter, small solar modules, and how to calculate power. Students will compare the power of the module to its area and create a power/area ratio. This ratio will then be used to check the efficiency of the module using a pyranometer (if available) to measure incoming irradiance from the sun (Power per area, or W/m2). Calculations and practices that students are guided through during this lesson will continue to remain themes throughout the remainder of the “Off the Grid Unit.” This lesson is suitable as a stand-alone lesson.

This lesson is intended as a way to check for student understanding regarding the content presented in the previous lesson of this unit. The assessment takes place in two parts: a written assessment of content-related vocabulary and concepts as well as a hands-on section intended to discern whether they can correctly use a multimeter. Each of these assessments focuses on their understanding of units and their application to circuitry. By requiring students pass this section before moving forward, it ensures that they can efficiently collect data independently in the remaining sections of this unit as well as increase the longevity of the equipment used in this process.

In this lesson students will explore the concept of efficiency, and how to take data in order to calculate the efficiency of various cell phone or USB charging circuits. They will complete this process by using a combination of multimeters hooked into ATC fuse holders as well as USB current/voltage meters, collecting the Power-in and Power-out measurements for these circuits. This knowledge will pull from the initial lessons focusing on electrical units and measurement-taking processes and will be recorded in the journals they have been working with. Students will also be introduced to circuit diagrams, or “schematics.”

This lab uses a variety of voltage conversion devices to output 5 Volts, the requirements for a USB charger such as for a cell phone. Students will take data on these devices and calculate, graph and compare efficiencies of different devices. Devices used in this lab are buck converters, which lower the input voltage and Boost Converters, which raise it (the Minty Boost® and Boost 500® are boost converters from Adafruit). These devices are available on the Internet and can be hard-wired to groups of series AA batteries. These devices frequently accept a range of input voltages, and some offer a range of output voltages. Students will be familiar with data collection from previous Off the Grid Lessons 1 and Lesson 3.

This lesson will continue to deal with efficiency of USB charging devices, but this time we will be using an inverter in order to create AC voltage from a battery pack, and then use a standard AC charger (what you would plug into the wall) to charge a USB device. Students will continue to use USB voltage/current meters to take readings on the charger-side of the circuit. After constructing these circuit components, students will measure the efficiency at which this inverter changes DC power back into DC power (in a DC-to-AC-to-DC conversion), and will collect the data in their journals using the self created tables in their science journals.

This lesson continues to look at the efficiency of USB charging devices, but this time we will be using a commercially available camping stove that uses heat to create electricity in order to charge a phone. This is the Biolite stove that exploits the Peltier Junction in order to generate an electrical current. Students can also attempt to measure power output of the stove by taking data on the heating of water. This is a demonstration activity, as the whole class will be using one stove and recording data into their science journals.

This is the culminating activity for the unit “Off the Grid.” Students will be given some restricted parameters around which to design a solar powered battery operated phone (or other USB device) charger. Students will charge the AA battery packs that have been using throughout the unit using photovoltaics, and then hook these battery packs into their USB charging device (for a phone, bike light, etc.). This process requires that they combine background knowledge such as voltage and current requirements for their devices they are charging, the function of boost and buck converters, and the correct construction of circuits. Included at the end of this lesson is a written assessment for the entire unit.

Drawn on a white board in red marker 12 V CAR CHARGER FOR USB DEVICE underneath is a circuit diagram showing a ATC Holder (empty) to battery pack (12V) with DC female power plugs coming off of it to the right the male plugs connect to a female cigarette socket. A male cigarette plug (car charger) connects to the USB meter with power lines connecting off the bottom of the image. All junctions are labeled as listed in the description.