PROBLEM STATEMENT: To perform a feasibility study on a solar powered refrigerator cooled by Peltier chips compared to traditional refrigeration methods for use in rural Africa.
PROJECT GOALS: Calculate how much solar power we need to reach a temperature below freezing. Determine potential problems of the project. Analyze cost of designing an effective refrigerator.
INFORMATION ABOUT OUR DEMOGRAPHIC:
- Average Yearly Income: $4100
- Life expectancy: 63.5 years
- 3.6% of children under 5 suffer from malnutrition
The average temperature in Ghana is 70-80 deg F. At these temperatures, produce, meat, and dairy spoils incredibly quickly. By providing a method of refrigeration, less food will go to waste because it will no longer rot in the hot sun as quickly. They won’t have to go buy or gather produce every single day. Meat and dairy will not have to be consumed as quickly either. Though there are other groups around the world addressing the problem of medication storage in these areas, this type of refrigerator could serve that purpose as well. Most of the population in Ghana is concentrated around the coast along the Gulf of Guinea.
A typical TEC, shown in the graphic above, is composed of pairs of n and p type semiconductors that are in series, compressed between two thermally conductive and electrically insulated plates. The heat carriers are the electrons and holes in the n and p type semiconductors. The heat moved by a single semiconductor pair is determined by the Seebeck coefficients, resistivities, and thermal conductances of the two materials.
This is a schematic of the experimental set up we’ve been using to test the TEC (thermoelectric cooler). We have a plastic tub surrounded by a styrofoam box to provide insulation to the ice water that the heatsink is submerged in. The heat sink was immersed in an ice bath so that the ice’s phase change could be taken advantage of and the water would remain at a constant cool temperature for the duration of our experiment. We had a water pump to provide adequate circulation of the water so the water surrounding the heatsink wouldn’t be a higher temperature than the rest of the water. The Peltier cooling module, synonymous with TEC, is sandwiched between the aluminum target, which we’re cooling down, and the heat sink, used to keep the hot side at a constant temperature. The vacuum flask was used because it is an extremely good insulator and didn’t allow for much heat to be lost from the target.
Picture of Experimental Setup:
This is what the heat sink and vacuum flask look like when they are not screwed together. We used plastic screws and had a black plastic foam surrounding the Peltier as other forms of insulation.
This is what the experiment looks like when we have everything running. We have a constant current power supply that we use to power the TECand a multimeter to measure the voltage across the Peltier chip, both used to measure the power inputted into the system.
Also, you can see the two temperature readouts, one directly above the cold side of the Peltier and the other just below the hot side. The phone captures a photo every 30 seconds to record the temperatures and voltage until the the cold side has reached saturation. Orion and Evan are currently utilizing this experimental setup as part of their senior project.
The above shows the electrical components involved in the experiment and the how they work together to get the data we need.
We could use ambient air or a fluid for a self circulating system with no pumps and easy repair. (As shown in the image below) The green slide represents the thermoelectric cooling device.
There are two different TEC models that we used in our experiment, the 12715 and 12706. These are the coefficient of performance (COP) graphs for the each thermoelectric cooler. They show how the COP is affected both by the change in temperature between the cold and hot side of the Peltier and the current running through the device. Another aspect of these illustrations to take notice of is that although the 12706 can reach a higher change in temperature with the same current it also has a lower coefficient of performance.
Power from panels (W):
Time at peak power (hrs):
Peltier efficiency (decimal):
Typical power of a fridge is 2kwh/day with 40% efficiency, meaning 800Wh/day useable cooling
We could alternatively use an inverter (95% efficient) and batteries (70% efficient) to provide an AC fridge with its needed surge wattage. Cost is on the order of $1000
var power = document.getElementById(“power”).value;
var time = document.getElementById(“time”).value;
var inverter = document.getElementById(“inverter”).value;
var battery = document.getElementById(“battery”).value;
var refridge = document.getElementById(“refridge”).value;
var wh = power*time
var work_fridge = wh*inverter*battery*refridge
document.getElementById(“fridge”).innerHTML = work_fridge + ” Useable cooling from fridge (should to be >800Wh)”;
]]> The above widget (not visible in edit mode) shows the estimated energy requirement of a thermoelectric system and a traditional compressor based refrigerator. The traditional refrigerator is more efficient, but with 1000 W of power, both systems are sufficient. Given the longer lifetime and lower cost of thermomelectric devices, they would be appropriate for an environment without a grid or readily available refrigerator technicians.
100 W Solar Panel: $75
Insulation: Free (if we use resources found in their surroundings)
Container to be cooled: $5-10
Picture of Group Members:
- Evan Drake
- Edward Donohue
- Jeralyn Gibbs
- Alex Henrikson
We are all 4th-year physics majors, but our specific interests are all over the board. We are planning on going into fields from teaching to biophysics to aerospace.
[Is it currently feasible? If not, what do we need for it to be feasible? (higher efficiency, lower costs?)]
Please copy all the statements in red to the bottom of the page.
You also need to put this into the context of a people… will it be useful? What is the present technology being used, or is there none? What difference does it make?
This is not adequate for this stage of the project. Please put demographic information in and outline the technology. for next week. What is going on in the experiment below? Do you have a schematic to show what you’re doing? Please link this page to our research page and appropriate technology solar ice page.
A little about you guys? Just a line or two please.
-This is an improvement, thanks, and more needs to be done. Please add the following:
– a map of Ghana *
-some information from gapminder or other graphic.
– Discuss what present technology is being used and how this might be an improvement.
– Show heat flow equations determining how quickly you need to pump heat out of the cooler. Include COP considerations and how much solar power you need.
– please put the appropriate links into these experiments we’re doing.
– Please copy all the statements in red to the bottom of the page as you did before.