# Homework Help: Capacitance, Energy, Power

1. Mar 2, 2010

### Hotsuma

1. The problem statement, all variables and given/known data

A wind power plant will not produce as much energy when the wind slows down. In order to provide power during these time periods it is proposed to store some power when it is operating in high winds in a capacitor. If it is desired to store the energy to power a town at 20 MW (20*10^6) for three days, what is the area of a parallel plate capacitor (seperation, d, 3 meters) filled with air if the voltage is 50,000 V? Is there a way to reduce this size? Explain.

2. Relevant equations

K = 1.0006

3. The attempt at a solution

I cannot figure out where to start. I need to relate area to the capacitor, but I don't know if a Capacitor has an area l*w and then there is just a distance d seperating them or what. I'm lost and tired. Can someone help?

2. Mar 2, 2010

### kuruman

Start with the equation that gives the capacitance of a parallel plate, air-filled capacitor. What is that equation?

3. Mar 2, 2010

### Hotsuma

$$C=k\cdot\frac{\epsilon_0A}{d}?$$

4. Mar 2, 2010

### Hotsuma

Thanks for the disappearing act; I was about to go to sleep.

5. Mar 2, 2010

### kuruman

Correct capacitance expression. When you wake up, figure out how much energy the power plant produces in three days. All that energy is to be stored in the capacitor.