Solar Power from Space

If you haven’t heard yet, Caltech launched and tested a prototype from its Space Solar Power Project. Conceptually, they launched solar panels into Earth’s orbit, and received the collected energy back on campus. Why is this important? Well, the sun is a constant source of renewable energy for Caltech’s satellite, which can then beam the energy anywhere on the planet. That means sustainable energy for anyone with a special kind of receiver, regardless of their current living situation. Sustainability is extremely important to us at theDIHEDRAL, so I, your resident astrophysicist, would like to explain how Caltech’s contraption prototype works.

The prototype component that was tested by Caltech is called the Microwave Array for Power-transfer Low-orbit Experiment (MAPLE). Simply put, MAPLE has arrays of panels that are made of a special type of conductive material (e.g., silicon). The sun, as you might know from ever being outside on a hot summer day, constantly produces a lot of electromagnetic (EM) radiation. EM waves are just light waves, so during the day you see the waves from the sun, feel the radiation as heat, and see the waves’ energy or frequency as color. When MAPLE’s arrays are hit by these EM waves from the sun, their electrons absorb the waves’ energy in a particular way so that it can be converted into DC power (battery power). This process is one of the reasons why MAPLE’s arrays are much more efficient than those on Earth. MAPLE’s arrays have unadulterated access to the sun’s EM waves, but Earth’s do not. Solar EM waves can’t reach arrays on Earth during the night, and many of these waves get reflected back into space by clouds before they can even reach Earth’s arrays during the day. That essentially means that even if we got rid of every cloud in the sky, MAPLE’s arrays would absorb at least twice as much energy per day as those on Earth. That’s a pretty good start!

Once MAPLE has the DC power ready (like a charged battery), it makes a few calculations to determine how and when it will send the power to a specific receiver. Remember those electrons that were really excited by the EM waves? Well, they can also release that excitement back as an EM wave. MAPLE converts the DC power into microwaves (lower energy waves than light waves we can see, but higher energy waves than radio waves) to send back to Earth. I’m sure you guys are all thinking, wait, High-Clip, according to what you said in Physics of Rock Climbing: Part III, Physics of Rock Climbing: Part IV, and Physics of Rock Climbing: Part V, shouldn’t relativity come in here somewhere? Absolutely, it does! Good catch, guys. Feel free to ask for more clarification, but essentially light has a funny way of stretching and compressing in the presence of gravity. Well, really it’s the spacetime that stretches in different ways, but it’s easier in this case to think of the EM waves losing or gaining energy based on gravity. This means that if a receiver needs a microwave at a frequency A at time B, MAPLE can’t just send a microwave at A frequency right before time B so the light has enough time to travel. Because of relativity, time doesn’t pass the same way on MAPLE, so it would need to adjust when it sends the microwave. Similarly, MAPLE would need to send a slightly different microwave so that by the time it reaches the receiver it is at frequency A. Caltech has fantastic scientists, however, so they designed MAPLE to account for these small discrepancies. In fact, during MAPLE’s test, the receivers powered LED lights to demonstrate that MAPLE sent them the exact frequency they needed, when they wanted it. Success!

To learn more about MAPLE, visit Caltech’s website, and be sure to check out this and this!

Please comment your thoughts and reach out with any questions!