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Concept Selection

Table of Contents 1 Wind Collection 2 Energy Storage 3 Battery Type 4 Energy Conversion 5 Turbine Brake

After generating a number of concepts in our Concept Generation document, it was time to narrow down the ideas and eventually select the final design. This was done by first automatically eliminating some of the most outlandish ideas that would clearly not be effective, or were out of the scope of the 22 week timeline. The remaining plausible ideas were organized in a series of Pugh matrices. Much like each function had its own concepts generated for it; each function has its own Pugh matrix, shown below.

In the cases of the Wind Collection and Energy Conversion matrices, the columns containing only "0" were used as comparison benchmarks from last years P11401 project. In the cases where no benchmark was used, all technologies were compared relative to each other.

A Pugh matrix is a concept selection matrix in order to narrow down the concepts that best satisfy our customer needs. Some needs were listed as selection criteria, and each concept was evaluated on a scale of +, -, and 0. The concept selection matrices for various essential system functions are below. They are put in separate matrices since the functions are truly independent of each other and have different criteria.

Click on any matrix image for a larger view.

Evaluation scale for Pugh Matrices:

• + = strongly meets selection criteria
• 0 = neutrally meets selection criteria (benchmark level)
• - = does not meet selection criteria

Rating scale for Weighted Matrices:

• 3 = Matches an ideal system
• 2 = Almost meets the specs of an ideal system
• 1 = Does not match an ideal system

Wind Collection

Based on the Wind Collection concept selection matrix, we narrowed down our choices to either a Savonius vertical axis turbine, or a conventional horizontal axis wind turbine (HAWT). Here are some pros and cons of each design.

Savonius:

• Pros:
  • Inexpensive
  • Simple design
  • Easy to install/assemble

• Cons:
  • Unreliable
  • Inefficient (10%)
  • Possible Safety Hazard

HAWT:

• Pros:
  • Safe
  • Efficient (35%)
  • Reliable

• Cons:
  • Difficult Installation
  • Expensive to achieve optimum efficiency
  • More complex design

In order to choose between our final two options, we created a weighted matrix.

Energy Storage

There are many possibilities for energy storage; whether they are electrical or mechanical. The four that we thought were most feasible are below.

Battery:

• Need approximately a 150 Ah battery

Super Capacitor:

• Need over 7,000 Farads

Water Potential:

• Too many mechanical to electrical energy conversions

Air Potential:

• Too many mechanical to electrical energy conversions

Based on the Energy Storage concept selection matrix, we were able to definitively choose a battery as a storage unit. However, this does not dictate the type of battery we must use so another matrix was necessary.

Battery Type

Based on the Battery Type concept selection matrix, we narrowed down our choices to either a lithium-ion, or a lead acid battery. Another option is the sodium-ion battery that we may or may not have the chance to use. We do not have much information on the sodium-ion battery at this time since it is a fairly new technology, but will keep it as a possible storage device throughout the system design. Here are some pros and cons of each design.

Lithium-ion:

• Pros:
  • No memory effect
  • Low standing discharge
  • Environmentally friendly
• Cons:
  • High temperatures reduce battery life
  • Overheating/overcharging can damage cells
  • More expensive than other types of batteries
  • Cannot be stored with too low of charge

Lead Acid:

• Pros:
  • Deep cycle available
  • Constant discharge and recharge
  • Benefits from a slow charge
  • Cheaper than other battery types

• Cons:
  • Can freeze if discharged too low
  • Overcharging can swell cells

Sodium-ion:

• Pros:
  • Have a direct contact with Aquion now. Will research this battery as a parallel effort.
• Cons:
  • See above.

Energy Conversion

Since battery is seemingly the best choice for storage, conversion needs to take place from the wind's collected mechanical energy to the required electrical energy.

Based on the Energy Conversion concept selection matrix, we narrowed down our choices to either an alternator or a brushless/step motor. Here are some pros and cons of each design.

Alternator:

• Pros:
  • Higher voltage due to the way how the alternator is constructed. The current generating wire winding is in the exterior. So the winding can get bigger which would generate higher emf/voltage resulting in less transmission lose.
• Cons:
  • Still have contact (slip ring) instead of rotary transformer
  • Faster rate of wearing down than the conventional stepper motor

Brushless/Stepper Motor:

• Pros:
  • Brushless, no mechanical contact
  • Last longer than the alternator
  • Less cogging torque and frictions -> lower cut in/ start up speed
  • Lighter, smaller
  • Easier to maintain

• Cons:
  • More expensive
  • Some power loss in the rotary transformer

Turbine Brake

While not a fundamental function of a SESE system, the a wind turbine brake is an essential part of our system. Without one, safety of the users would be compromised and one of our top customer needs would not be met. Various solutions for a turbine brake have been analyzed.

Based on the Brake concept selection matrix, we narrowed down our choices to either a dummy electrical load, or a passive wind avoidance system. Here are some pros and cons of each design.

Electrical Load:

• Pros:
  • Inexpensive
  • Safe
  • Easy to implement
  • Reliable/Repeatable
• Cons:
  • Brakes over time
  • Could be over ran
  • Not fail-safe in an emergency
  • Requires power

Passive Wind Avoidance:

• Pros:
  • Inexpensive
  • Easy to implement
  • Reliable
• Cons:
  • Could limit system efficiency
  • Not fail-safe in an emergency

In order to choose between our final two options, we created a weighted matrix.

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Mission Statement | Stakeholders | Benchmarks | Constraints | Objective Tree | Customer Needs | Engineering Specifications

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Work Breakdown Structure | Function Structure Diagram | Concept Generation | Concept Selection | Risk Analysis | Initial Design Documentation | Systems Design | Detailed Design

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