Challenge: Design a solar Hot water heater.
This is a challenge to design and build a solar hot water heater out of of recycled materials commonly found around the home. As an objective measure of the performance of your heater we will use the formula,
where mass is the mass of water heated in 30 minutes of direct sunlight, DT is the temperature increase from start to finish after 30 minutes of direct sunlight, and the heater volume is the (length)(width)(depth) of your solar heater. The idea is to get as much water as hot as possible after 30 minute with the smallest sized solar heater, i.e. try to maximize the Heater Performance. The idea here is to build a relatively small solar hot water heater (no more than 1 or 2 ft on a side) for concept testing not practical function. A holding tank may be use for heated water and it's volume does not count toward the heater volume. Use units of grams for mass, oC for temperature, and cm for length measurements (cm3 for volume)
Your report should include:
A detail materials list
A careful sketch of the design with a detail explanation as to the function of each component
A photo of your final solar water heater
The results of at least 3 30-minute tests of your Heater Performance. A careful explanation of the procedure used to make each test is essential.
A bar graph showing the Heater Performance for each trial.
An estimate of absorbed solar energy for each trial. The absorbed solar energy in calories is simply the numerator of the Heater Performance, (mass in grams) (DT in oC)
An estimate of absorbed solar intensity for each trial. Since 30 min is equal to 1800 sec, the absorbed solar intensity in calories/cm2/sec is simply
where Area is the (length) (width) of the side of the heater facing the sun in units of cm x cm=cm2.
To maximize Heater performance, your test should be done under clear sky conditions with bright sunlight typical of mid-day. Avoid performing trials when the sun is low in the sky. When the sun is low in the sky the solar radiation has to travel through much more air before reaching your collector and hence much more of this radiation is absorbed by the atmosphere; see diagram on the left below.
Other things to consider: You want to absorb the maximum amount of energy for a given heater volume --> make your collector as thin as practical. Use insulation appropriately to minimize heat loss. The greenhouse effect may help give you ideas.