A few weeks ago I met with a student team to coach them on their final report for their senior design project. The students were discouraged because they’d spent two semesters on it and hadn’t met their client’s objectives. We talked about how to get the most out of the experience for themselves and their client. Just as we can learn from our mistakes, we can find value in failure.
It’s important to keep in mind that at the proof of concept stage, it’s not clear whether it’s even possible to make it work at all. That’s the question the students were investigating. Still, it’s disappointing when the result indicates that the answer is “no.”
The project goals
The students sought to harvest waste energy from a process that uses a lot of electricity. Other industries have used this principle to save energy in energy-intensive processes. For example, a cement plant may recycle waste heat from the kiln to preheat the kiln feed. That reduces both the cost of fuel and the carbon footprint.
Here, the students wanted to use the air flow from their process to drive a wind turbine. However, as is common in making use of a byproduct, the primary process was, well, primary. Generating electricity had to take second place.
We see this in the concrete industry with byproduct materials. For example, fly ash is a solid waste that comes from burning coal to generate electricity. The utility adjusts the process parameters to meet the energy needs of its customers, not to make good fly ash. In a base load plant, steady-state operations will generate both electricity and consistent fly ash to use in concrete. But if it’s a peak load plant, they’ll switch it on or off depending on demand. The fly ash will vary wildly, particularly in its carbon content. Variable materials are hard to deal with; you’re constantly making adjustments just to keep your concrete consistent.
The students were dealing with similar constraints. Their design couldn’t interfere in any way with the operation of the facility. Because of the direction of the air flow, they would need to orient the turbine mounting horizontally. To withstand the moments from the wind forces on the turbine, the mountings would have to be quite robust. And the facility would generate energy only intermittently, as it operates as needed. That is, the capital costs would be high relative to the value of the energy it generated.
The analysis
In their draft report, the students had estimated a rate per kWhr for the electricity and performed a return-on-investment calculation. I encouraged them to do some additional analysis to extract more value from the failure to meet the client’s goal of a 5-year return period. After all, the client installs these facilities in many countries around the world. The cost of electricity varies with both time and place; at a high enough rate, it might be worth it. It seemed to me that a sensitivity analysis, assuming a series of rates, would be a good way to gain value from failure.
Other variables include the initial capital investment. Electric utilities or governments sometimes offer rebates for capital investments that save or generate electricity. A large enough rebate might make the project worthwhile for some customers.
It would also be helpful to compare the cost and rate of return for an alternative such as installing a turbine in the facility parking lot or on the roof. This turbine would not have the constraints of coordinating with a primary process; it would be a primary process all by itself.
Even knowing by how much they missed the goal would be useful to their client. If they missed it by a little. it’s likely that tweaking their design would get them there. Or it might be worth revisiting later on as conditions change. New technology could reduce the cost enough to make the difference. On the other hand, if they missed it by a lot, they probably need to start from scratch.