# Solar-Powered Classroom

## Summary

## Overview

Would it be possible to power everything in your classroom using clean, renewable solar power? Inspired by Global Problem Solvers: The Series, in this lesson plan, your students will research and design a solar power system for a mobile classroom that can be used after natural disasters or in remote areas without permanent schools.

This lesson is one of three independent lesson plans inspired by Global Problem Solvers: The Series. You can read more about the series and the lesson plans available from Science Buddies on the Blog: 5 Reasons Global Problem Solvers: The Series Will Inspire STEM Interest in Your Students.

## Learning Objectives

- Use problem-solving skills to figure out the electrical power consumption of different devices
- Design a solar power system for the electrical devices in a mobile classroom

## NGSS Alignment

This lesson helps students prepare for these Next Generation Science Standards Performance Expectations:- 3-5-ETS1-1. Define a simple design problem reflecting a need or a want that includes specified criteria for success and constraints on materials, time, or cost.
- MS-ETS1-1. Define the criteria and constraints of a design problem with sufficient precision to ensure a successful solution, taking into account relevant scientific principles and potential impacts on people and the natural environment that may limit possible solutions.

Science & Engineering Practices
3rd–5th grade
Asking Questions and Defining Problems. Define a simple design problem that can be solved through the development of an object, tool, process, or system and includes several criteria for success and constraints on materials, time, or cost. 6th–8th grade
Asking Questions and Defining Problems. Define a design problem that can be solved through the development of an object, tool, process or system and includes multiple criteria and constraints, including scientific knowledge that may limit possible solutions. |
Disciplinary Core Ideas
3rd–5th gradeETS1.A: Defining and Delimiting Engineering Problems. Possible solutions to a problem are limited by available materials and resources (constraints). The success of a designed solution is determined by considering the desired features of a solution (criteria). Different proposals for solutions can be compared on the basis of how well each one meets the specified criteria for success or how well each takes the constraints into account. 6th–8th gradeETS1.A: Defining and Delimiting Engineering Problems. The more precisely a design task's criteria and constraints can be defined, the more likely it is that the designed solution will be successful. Specification of constraints includes consideration of scientific principles and other relevant knowledge that are likely to limit possible solutions. |
Crosscutting Concepts
3rd–5th grade Influence of Science, Engineering, and Technology on Society and the Natural World. Engineers improve existing technologies or develop new ones to increase their benefits, decrease known risks, and meet societal demands. 6th–8th grade Influence of Science, Engineering, and Technology on Society and the Natural World. The uses of technologies and limitations on their use are driven by individual or societal needs, desires, and values; by the findings of scientific research; and by differences in such factors as climate, natural resources, and economic conditions. |

## Materials

## Background Information for Teachers

*This section contains a quick review for teachers of the science and concepts covered in this lesson.*

This lesson is inspired by Global Problem Solvers: The Series. In the second season of the show, the team designs solar-powered mobile classrooms that can be used after a hurricane destroys a school in Florida. Watch the trailer for the second season here:

In this lesson, your students will be challenged to design their own solar-powered mobile classroom. They will decide what electrical devices (like lighting and computers) the classroom needs, and how many solar panels will be required to power the classroom. This section will provide you with the background information you need to help guide your students through this lesson.

Electrical **power** is measured in **watts (W)**. A watt is not very big, so power measurements are frequently expressed in kilowatts (kW) instead. One kilowatt is equal to one thousand watts:

**Equation 1:**

Solar panels are rated in terms of how many watts they can provide. You can buy small, portable solar panels that produce a few dozen watts, while larger rooftop solar panels can produce hundreds of watts, and be combined to produce thousands of watts (Figure 1).

**Figure 1.**Examples of different solar panels available to consumers. (Amazon.com, Inc, 2019)

In order to run a classroom on solar power, the total wattage of the solar panels needs to be greater than the combined wattage of all the electrical appliances (this is for the best-case scenario in full sunlight; for ideas about how to address cloudy days or nighttime power usage, see the variations section). This means your students will need to figure out the power consumption of everything they want to include in their portable emergency classroom. There are several different ways to do this, outlined below and in a student handout, along with some other useful information. Your class will probably need to use a combination of these methods.

### Check the Product Packaging or Label

Sometimes, the packaging or label for a product will directly tell you how many watts it consumes. This is very common with light bulbs (Figure 2). However, be careful with LED and CFL bulbs. They will frequently advertise an "equivalent" or "replacement" wattage in addition to their actual wattage. This indicates the wattage of the (older, less efficient) incandescent bulb they are intended to replace. For example, the LED bulbs in Figure 2 can replace 60 W incandescent bulbs, but only use 8.5 W.

**Figure 2.**Light bulb packaging that tells you how many watts each bulb consumes.

### Internet Search

If you can't find the wattage listed directly on the appliance, try an internet search. Searching for the exact product name or model number along with a phrase like "power watts" might give the best results. If you don't know the exact product name/model number, try a more generic search like "refrigerator power watts." Many websites have information about power consumption for common electrical appliances.

### Direct Measurements

You can use an electricty usage monitor (Figure 3) to directly measure the power consumption of any plug-in appliance.

**Figure 3.**A plug-in electricity usage monitor.

### Calculate Power Consumption (Advanced)

Sometimes, if you look at the labels for an electronic device (like a cell phone or laptop charger), it might list **volts (V)** and **amps (A)** instead of watts (Figure 4). The values might be expressed in millivolts (mV) or milliamps (mA). One millivolt is one thousandth of a volt, and one milliamp is one thousandth of an amp. They will probably also list an "input" and an "output."

**Figure 4.**The label on a laptop charger.

That might seem like a lot of information, but don't worry! Volts and amps are both units used to measure electricity, but they are not the same as watts. Volts measure voltage, or how hard the electricity is being "pushed." Amps measure current, or how much electricity is flowing. You can use the *input* volts and amps to calculate electrical power using this equation:

**Equation 2:**

But wait—the input voltage on the charger in Figure 4 is a range, from 100–240 V. How do you know what voltage to use? This depends on what country you are in. In the United States, use 120 V. If you are in a different country, you will need to look up the voltage supplied at your electrical outlets. So, for example, the power consumption of the charger in Figure 4 is (remember to be careful with units—the charger lists the input current as 2,000 mA, which is equal to 2 A):

**Equation 3:**

With some guidance and help interpreting the labels, your students can do this calculation to find the power consumption of an appliance.

### Heating and Cooling

Depending on the climate where you live, heating and cooling can be some of the biggest uses of energy in a building. However, the electricity used to heat or cool your classroom might not be easy for your students to measure. For example, your school might have central air conditioning (AC) instead of window AC units; or it might be heated by oil or natural gas instead of electricity.

Your students can approximate the power required to heat or cool your classroom based on its square footage. Electrical space heaters and window AC units frequently list the square footage they are intended to cover (e.g. 400 square feet, or a 20×20 foot room). This is easy for space heaters as they usually list their wattage directly (Figure 5).

**Figure 5.**Example of a 1,500 W space heater for sale online (Amazon.com, Inc, 2019).

Unfortunately, in the US, air conditioners are rated in **British Thermal Units (BTU)** per hour instead of watts (Figure 6). You can convert between BTU/hour and watts using this equation:

**Equation 4:**

So, for example, the 5,000 BTU air conditioner in Figure 6 consumes 5,000×0.293=1,465 W, or about 1.5 kW.

**Figure 6.**Examples of air conditioners available for sale online. The air conditioners are rated in BTU/hour, but note that "hour" is not included in the description. (Amazon.com, Inc, 2019).

### Kilowatts vs Kilowatt-hours

If you read your electric bill, you might notice that amounts are expressed in kilowatt-hours (kWh), not kilowatts. A kilowatt-hour is a unit of **energy**, not power. Power is the amount of energy used per unit time:

**Equation 5:**

One kilowatt-hour is the amount of energy used when you use 1 kW of power for one hour. If needed, you can convert between energy and power using Equation 5.