How many solar panels would you need to equal the energy output of 1kg of U-235?
if 1kg of U-235 can produce 80 trillion joules (8×10^13 J) of energy how many solar panels would you need to equal this amount of energy?
Any info would be very much appreciated!
Unless the student is supposed to be able to calculate how long it takes the U-235 to produce that amount of energy, there is not enough information. If that is within the scope of the course, the question is way out of my league.
But assuming you just left out the time when stating the problem, divide that into 80 trillion to get joules/sec.
Let’s say the time is 40 billion seconds* for the U-235 to generate 80 trillion J. Divide 80 trillion by 40 billion, that’s 2,000 J/sec. You would need 10 panels. (A typical panel produces 200 Joules/sec.)
*That’s a LOT of seconds, even a lot of centuries. By then the solar panels would have worn out and crumbled into dust, so it’s a silly question in that sense. Is the teacher trying to make a point about the futility of solar power?
Unless the student is supposed to be able to calculate how long it takes the U-235 to produce that amount of energy, there is not enough information. If that is within the scope of the course, the question is way out of my league.
But assuming you just left out the time when stating the problem, divide that into 80 trillion to get joules/sec.
Let’s say the time is 40 billion seconds* for the U-235 to generate 80 trillion J. Divide 80 trillion by 40 billion, that’s 2,000 J/sec. You would need 10 panels. (A typical panel produces 200 Joules/sec.)
*That’s a LOT of seconds, even a lot of centuries. By then the solar panels would have worn out and crumbled into dust, so it’s a silly question in that sense. Is the teacher trying to make a point about the futility of solar power?
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That’s a bit like asking how many potatoes in a pound, since solar panels comes in different sizes.
But let’s do a factor-of-10 estimate. Let’s say that the solar panels are 200 watts, will get an average of 5 hours of sun per day, for 30 years before they break. Let’s not quibble over efficency and sun-hours and such.
200 w * 3600 sec / hr * 5 hour / day * 365 day / yr * 30 yr = about 4 x 10^10 joules / panel
8 * 10^13 / (4 * 10^10) = 2 x 10^3 = 2000 panels. This is about the size of array that went onto my son’s high school.
This disregards the energy involved in the panel’s manufacture and distribution, and also assumes that the U-235 just magically appears in its refined state. It also ignores the security costs for weapons-grade fissile material. Also, the solar panels can produce usable energy with very little added cost – not true for the Uranium.
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