Sustainable Energy & Development
July 27th, 2009The Problem
Calculating the price per kilowatt hour of electricity required for wind turbines to power Greenfield, NY.
Greenfield in Upstate New York is considering an environmentally friendly wind farm as a sustainable source of electricity for the community. An engineering firm is hired to research turbines, confirm the needs, and estimate the cost of electricity per kilowatt-hour produced by turbines.
Based on their initial research, the town believes that they need 15 MW to power 2761 homes and want to install 42 HWAT (horizontal axis wind turbine) wind at a cost of $30 million. They also want to ensure that the cost is recovered within 15 years. A mechanical engineer is assigned the task…
Using Knovel
Finding the right type of turbine and the cost per kilowatt hour
The mechanical engineer needs to first look into all the different types of turbines to make sure that a HWAT turbine would be ideal. He looks to see if Knovel can help with this task so he uses Knovel’s basic search function and types in “types of wind turbines.”
He clicks on, Fluid Mechanics, Thermodynamics of Turbomachinery (5th Edition) and scans through section 10.2. This section describes the various types of wind turbines including drag powered ones like windmills, and lift powered ones like HWAT and VWAT (Vertical axis wind turbine.) He learns that HWAT and VWAT turbines can give 3+ MW and Drag powered turbines are much less efficient. He also learns about some of the potential challenges: VWATs are much less common and can have various problems- because they are normally close to the ground where wind speeds are slower, they can’t regulate themselves as well at high speeds, may have trouble starting themselves up, and can have high variations in torque with every turn. HWATs appear to be much more common and more reliable.
The engineer then needs to see what the kilowatt/hr is for the turbine choices. He uses Knovel’s basic search function again and searches for information on maintenance of wind turbines.
He opens Chapter 55.2.8. in Wind Energy Conversion 1996. He finds an equation that will give him the g, the unit cost of energy.
C is the Initial cost, R is annual cost rate, E is the amount of energy, product F is the fuel cost per unit which is zero for wind, and M is maintenance. To find R he uses the equation below:
The variable R is the rate at which the investment will be recovered in N years (15). A rate of 10% is assumed which will allow for a profit.
He then looks for maintenance costs in the same chapter and finds a general maintenance cost of 1 pence/kWh which is 1.5 cents/kWh.
The Solution
Data found in Knovel helps the engineer to choose the right turbine, calculate cost recovery and even saved the town money.
Based on the data from Fluid Mechanics, Thermodynamics of Turbomachinery (5th Edition) it seems pretty obvious to choose a HWAT, if only for the reason that it’s the most used wind turbine and therefore most likely the best turbine.
Time to do the math on the costs:
He uses Equation 2 above with an N of 15 years and a R of 10%. The R is .1315.
Using Equation 1 with C = $30 million, R = .1315, E = 43.8×10^6 kW*yr (found by multiplying the amount of hours in a year by 15MW), and a maintenance cost of 1.5 cents/(kWh) gives us G = 4.5 cents/kWh. This is below 6-7 cents/kWh, the typical amount for New England and comparable with <5 cents/kWh which is typical for Northern Plans (http://www.awea.org/faq/wwt_costs.html).
Using Knovel’s new Sustainable Energy and Development subject area, the engineer quickly solved the problem, saving his firm money and provided a quick response and validation of costs that the town needed.
