Solar Desalination

Activity Source: NASA

 

Grade Levels: 3-10

Background

Desalination is the process of removing salt from water. The process of desalination can serve as a vital tool to bring fresh water to people and communities that may not have reliable access to safe drinking water. Solar stills have been used since ancient times to treat saltwater. In this activity, you will create a simple solar still, and can do calculations of the energy required for the process.

Materials

  • Part 1:
    • Large bowl or bucket*
    • Water*
    • Salt (17 g per 500 mL of water)
    • Small glass cup or jar
    • Small paper weight or rock
    • Cling wrap or plastic wrap
    • Tape
    • Beaker or graduated cylinder

*The time required for Part 1 is dependent on the volume of water the container can hold.  

  • Part 2:
    • Computer with internet access
    • Calculator  

Procedure

  1. Part 1: Solar Desalination
    • Tape the bottom of the glass jar to the center of a bowl.
    • Measure enough water to fill the bowl (record the volume in milliliters, mL). Mix in salt until no more can dissolve.
    • Fill the bowl with the saltwater without getting any in the glass jar.
    • Cover the bowl with plastic wrap and tape it to the side of the bowl to seal it as best you can. Leave it slightly loose so the center sags.
    • Place a small weight in the center of the plastic wrap.
    • Place the bowl in a sunny location and observe what happens.

 

  1. Part 2: Calculations (for grades 7 and up)
    • Multiply the volume of water used in Step 1b by the density of water (0.001 kg/mL) to convert to kilograms.
    • Multiply the mass of water you used by the latent heat of water vaporization (2,260,000 J/kg) to calculate the solar energy needed to evaporate it.
    • To calculate solar irradiance, visit the POWER Data Access Viewer (DAV): https://power.larc.nasa.gov/data-access-viewer/. A tutorial for this site can be found on the lefthand menu.
    • Select the following from the menu:
      • “Single Point”
      • User Community: Sustainable Buildings
      • Temporal Level: Climatology
      • Location: Find your city on the map and click on it
      • Parameter: Midday Insolation Incident (MIDDAY_INSOL)
    • Click submit and a graph will show the hourly irradiance values. Hover over the line and record the highest and lowest values on the graph.
    • To calculate evaporation time: Time = Energy / (Solar irradiance * Surface area of water in the large bowl)
      • Use 0.1 meters squared (m2) if the surface area was not measured.

Analysis

  1. Where did the salt and water end up at the end of the experiment? Explain this by relating to solar energy and the water cycle.
  2. How might the time it took for the water to evaporate differ if you did this activity at a different time of year?
  3. What could a larger solar still do for those that have limited access to drinking water? Where else could it be useful?

Further Steps

Learn more about the data used in Part 2 of this activity from NASA’s Prediction of Worldwide Energy Resources (POWER) project that provides free global solar and atmospheric data collected from satellite missions:

NGSS Connections

  • SEP: Planning and Carrying Out Investigations; Analyzing and Interpreting Data
  • DCI: ESS2.A: Earth’s Materials and Systems
  • CCC: Energy and Matter

SDG Connections