Design Sessions

Sesotho word of the day: Phula - rain

The Solar Turbine Group has spent the last few weeks up in the mountains putting out heads together to improve the design of our system. During this time, we were inondated by typical thunderstorms that roll through the country, and sneak up out of no where. It really is true that the weather in the mountains can change in an instant! (even more suddenly than even in michigan or in boston!) According to Tumelo, the Basotho are afraid of the rain -- i can see why: it seems that rain in Lesotho is ALWAYS accompanied by thunder and lighting, and in a mountainous country like Lesotho, with no trees or tall things around, you definitely feel like you are inside the storm!

So, where we left off with the design of our system can be summarized by the following pictures and descriptions.

System Protoype at MIT, August 2006

As shown above, the system is made up of two basic components: an array of 4 parabolic mirrors and the Organic Rankine Cycle (ORC).

Parabolic Mirrors

The parabolic mirrors track the sun and focus the sun's energy onto a focal point inside the parabolas. Through the focal point of each parabola runs an absorber pipe that absorbs this concentrated energy. All of the absorber pipes are connected to eachother in series to form the thermal fluid loop. A thermal fluid (this summer we used glycol) travels through the thermal loop and gets hot. The figure above shows one parabola that is turned toward the East to capture the morning sun. The silver wheel at the far end is part of the tracking drive train, the black pipe is the absorber, and the valve at the close end is for draining the thermal fluid loop of its fluid. You can also see the absorber reflected in the mirror, and the strip of light that is focused on the bottom side of the absorber.

Organic Rankine Cycle

After the thermal fluid runs through the thermal fluid loop and is heated up, it enters into a heat exchanger, where it transfers its thermal energy to the working fluid of the ORC. In the ORC, the hot working fluid exits the heat exchanger and enters an expander. The expander spins an alternator (from a car) that charges a deep-cycle battery. The working fluid then exits the expander and goes into a condenser. This summer, we had a two-stage condenser: the first stage was another heat exchanger with a gas-fired fridge, and the second stage was an air-cooled radiator. (In lesotho we will use water to cool the system, so the system will also provide hot water)

ORC

Fridge and Radiator

After the working fluid goes through the condensers, it enters a pump, then returns to the thermal fluid heat exchanger to get heated up again. And around and around we go.

This prototype was built by our group this summer (shown below) in a parking lot at the West end of the athletic fields at MIT. The system is run intermittantly by our team members at MIT as they perform tests on the system.

From Left to Right, Alex, Libby, Perry, Sam, Sorin, Matt, Amy, Simmons Hall