Fusion Power

Let’s do the calculation that goes with the question asked in Figure 7.3.2–3. That is, suppose you had a miniature fusion power plant hooked up to your kitchen sink faucet. How much power could you generate from the hydrogen in the water flowing through it? We’ll give you two pieces of data that will be helpful:

• The total amount of energy that can in principle be generated by fusing all the hydrogen in 1 liter of water is approximately 70 trillion joules, or 70 terajoules.
• The average total power requirement for the entire United States is about 3 terawatts.

Solution

Step 1 Understand the problem. The key to solving this problem is to find a simple equation that will tell you the power from information that you have available or can easily figure out. You know that one piece of information must be the rate of water flow through the faucet. That’s easy to measure. For example, if you place a one-liter pitcher under a typical kitchen faucet, you’ll find that it fills in about 20 seconds. Therefore, the flow rate is about 1/20, or 0.05, liters per second. You can then confirm that the following equation will give you what you need:

Notice how the units will cancel to give you an answer in watts, which are the correct units for power. Also notice that besides the water flow rate that you can measure, the only other information you need is the energy from each liter of water, which is given to you above.

Step 2 Solve the problem. You should measure the water flow rate of a kitchen faucet for yourself, but let’s assume it is 0.05 liter per second. In that case, we simply put in that rate and the given data for the fusion energy that could in principle be obtained from each liter of water:

Step 3 Explain your result. We have found that the fusion generator hooked up to your kitchen faucet could in principle produce a power of about 3.5 terawatts. Notice that this is greater than the total average power of 3 terawatts needed for the entire United States. In other words, this single faucet could in principle provide enough power to replace all other power sources currently being used in the United States.