Question Video: Understanding the Advantages of Photovoltaic Cells

Photovoltaic cells are often used to power satellites. Which of the following are reasons why photovoltaic cells are chosen as the power source for satellites? [A] Photovoltaic cells do not require a solid or liquid fuel that needs to be resupplied in order to keep generating energy. [B] Photovoltaic cells require very little maintenance. [C] Photovoltaic cells provide direct current, which is what most electrical systems need to work. [D] Photovoltaic cells provide alternating current, which is what most electrical systems need to work.

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Video Transcript

Photovoltaic cells are often used to power satellites. Which of the following are reasons why photovoltaic cells are chosen as the power source for satellites?

Now, before we read these answer options, there are, even more than the four listed here. We’ll show those on the next screen. But for reasons of space, before we show them, let’s consider these four choices here.

The first possible reason says that photovoltaic cells do not require a solid or liquid fuel that needs to be resupplied in order to keep generating energy. Option B says that photovoltaic cells require very little maintenance. Option C says that photovoltaic cells provide direct current, which is what most electrical systems need to work. And then option D says that photovoltaic cells provide alternating current, which is what most electrical systems need to work. Before we get on to options E and F, Let’s evaluate these four.

So our situation is that photovoltaic cells are being used as a power source on satellites. And the question is, which of these reasons, if any, help explain why that is? To see which of these reasons are legitimate, we can recall some of the advantages of photovoltaic cells. When we have such a cell, it’s true that the only energy the cell requires is energy from the sunlight it receives. There’s no need for any other power supply or fuel source. This would come in very handy in space on a satellite where power is hard to come by. All the photovoltaic cell needs in order to keep generating electrical energy is sunlight or, specifically, radiant energy. The source could be something other than the Sun.

As we consider option A then, we see that this option does describe a reason why such cells are used as a power source for satellites. It’s true that they don’t require any other power source in order to work. So we’ll highlight option A as one of our answer choices.

On to option B, this says that photovoltaic cells require very little maintenance. This also is true. Once a cell is set up and working properly, not much is needed to keep it going. This, too, is an advantage in space where repairs are not easy to make. So we’ll also choose option B as a reason why photovoltaic cells are used as a power supply for satellites.

Option C says that photovoltaic cells provide direct current, which is what most electrical systems need to work.

Now if we look ahead to option D, we see that this says the same thing, except it claims that photovoltaic cells produce alternating current. We can tell instantly that options C and D can’t both be correct, since they claim opposite things about the current generated by photovoltaic cells. If we were to connect a wire to our photovoltaic cell and monitor the direction of the current, we would see that as this cell works, as it converts radiant energy into electrical energy, the current it produces is always running in the same direction. In other words, it’s generating DC or direct current. It’s this type of current that most electrical systems require in order to work. So we choose option C, which describes the current produced by these cells this way. And we cross off option D. These cells produce direct current but not alternating current.

Now we’re not done yet because as we mentioned there are other possible answer options, options E and F, which aren’t yet on the screen. Before we get to them, let’s record these three answer options which we have identified as correct. Summarizing these choices, we can say that option A indicates that no fuel is needed other than the sunlight. Option B says that these cells require very little maintenance. And option C says that they output direct current, which is useful for most electrical systems.

Okay, now let’s clear some space so we can write in options E and F and evaluate those. And here they are. Option E says photovoltaic cells have always been very cheap to manufacture. And option F says that there are no clouds in space to block the sunlight that the photovoltaic cells need.

Looking at choice E, we can’t say that this is an accurate statement. Even at their current state of development, if someone wanted to put photovoltaic cells on their roof to completely cover their energy needs, doing that would cost over 10,000 dollars. And this option is saying that these cells have always been very cheap to manufacture. But surely in the very early days of this technology, the costs were fairly high. So we won’t choose option E as one of the reasons these cells are used as a power source for satellites.

This brings us to our last option, option F, which says that there are no clouds in space to block the sunlight that the photovoltaic cells need. And this indeed is an outstanding reason why these cells are used as a power source for satellites. The main disadvantages of photovoltaic cells often come down to the fact that the sunlight on them isn’t steady or reliable. But this is true only for cells that are on the surface of the Earth, cells that sometimes face the Sun and sometimes face away from it. And also the cells may have clouds coming in between them and the Sun. But in space, outside of our atmosphere, there are no clouds to interfere. This means that photovoltaic cells are able to be more reliable power sources in satellites.

Altogether, we choose these four answers. Photovoltaic cells need no other fuel than sunlight to operate. They require little maintenance. They generate direct current, which many electrical systems require. And in space, there are no obstructions between these cells and the Sun, no clouds or other atmospheric conditions.

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