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  • MAREN: Back in December of 2015,

  • parties to the United Nations

  • Framework Convention on Climate Change

  • reached a landmark agreement.

  • One hundred and ninety-five nations,

  • practically every country in the world,

  • were going to officially fight against the climate crisis.

  • This is now known as the Paris Agreement.

  • And the main goal of that treaty

  • is to limit global temperature rise

  • to well below two degrees Celsius.

  • But in order to save the Earth from rising temperatures,

  • we need to remove billions of metric tons of carbon

  • from our atmosphere every year.

  • To help accomplish this,

  • countries have been investing in negative emissions

  • and low-carbon technologies,

  • as well as adding infrastructure to support them.

  • And solar energy is already at the forefront

  • of this renewable revolution.

  • Why? Because the sun is the most abundant

  • energy resource we have on our planet.

  • But how much do you know about solar panels

  • and how exactly do they work?

  • Well, let's start with photovoltaic cells.

  • These cells are what convert sunlight into electricity.

  • A single photovoltaic cell, also called a solar cell,

  • can be smaller than a postage stamp

  • and thinner than a human hair.

  • On its own, a solar cell can generate about half a volt.

  • So, to increase this energy output,

  • you can combine these solar cells

  • to create solar modules

  • and even slightly-bigger solar panels.

  • Depending on their size

  • and the materials they're made of,

  • as well as the amount of sunlight that's available,

  • the power output of solar panels can vary.

  • This output, or the amount of energy a panel produces,

  • is measured in kilowatt-hours.

  • So, if a panel generates 100 watts in one hour,

  • that would be 100 watt-hours or 0.1 kilowatt-hours.

  • But you can combine modules and panels even further

  • to create solar arrays.

  • These structures are what are used to power homes

  • and even spacecraft.

  • And if you gather enough solar arrays in one place,

  • you can even power cities.

  • You may have seen swaths of land

  • covered in solar arrays.

  • These are often called solar farms or solar parks.

  • The largest solar park built to date

  • is the Pavagada Solar Park in India.

  • It spans over 53 square kilometers

  • and can produce two gigawatts of electricity,

  • which is enough to power 700,000 households.

  • By the end of 2018,

  • the world's installed capacity of solar cells

  • reached over 480 gigawatts,

  • representing the second largest

  • renewable electricity source after wind.

  • Now, this may seem like a lot of energy already,

  • but researchers are projecting that by 2050

  • the world's solar cell capacity

  • could reach over 8,500 gigawatts.

  • This is the kind of expansion we need

  • to reach the carbon-cutting goals

  • of the Paris Agreement.

  • The big reason why photovoltaic cells

  • haven't taken over the world yet

  • is because the technology is still limited

  • by three important factors.

  • Cost, efficiency and reliability.

  • Efficiency basically just means

  • how well a solar panel is able

  • to convert sunlight into electricity,

  • and cost can be defined by, well,

  • how much goes into making a solar cell

  • like materials, manufacturing,

  • distribution, installation,

  • relative to how much wattage is generated

  • in return for that investment.

  • And lastly, we have to make sure a solar cell

  • can generate power on sunny and cloudy days,

  • which is tougher than you might think.

  • In recent years, advances to solar energy technology

  • have helped it become more accessible

  • to the average person like you and me,

  • and to the teams taking part in the World Solar Challenge.

  • So, basically, the sun provides energy

  • in the form of photons.

  • And when those photons will hit your solar ray

  • when it hits your solar cells,

  • the photons excite electrons

  • and those will jump across the band gap

  • inside your solar cell

  • and they'll basically flow through your circuit.

  • So, you get this flow of electrons.

  • Today, the most popular semiconducting material

  • used in solar cells is silicon.

  • Diving in even deeper,

  • we'll see that crystalline silicon cells

  • are made of silicon atoms connected to one another

  • to form a crystal lattice.

  • Silicon bonds are made of electrons,

  • the negatively-charged particles in an atom.

  • These electrons allow it to perfectly bond

  • to its silicon neighbors,

  • creating this perfectly organized

  • lattice structure.

  • In a solar cell,

  • there are two layers of silicon.

  • One layer, n-type, has a negative charge,

  • and the other layer, p-type, has a positive charge.

  • Now, each charge needs to be enhanced

  • to create the energy we're looking for.

  • And to do that, researchers will dope

  • or add other elements to the silicon material,

  • giving it extra electrons,

  • or creating empty holes for electrons to fill.

  • The negative charge is usually achieved

  • by mixing the layer of silicon with phosphorus.

  • This adds extra electrons to the mix,

  • allowing more electrons

  • to roam freely in the lattice.

  • A positive charge for that p-layer

  • is achieved by doping that layer with boron,

  • causing those spaces called holes.

  • The boundary between the two layers

  • is called the p-n junction,

  • while the area around it

  • is known as the depletion region.

  • So, now for the fun part.

  • When light from the sun hits those layers,

  • the energy from the photons knocks electrons loose.

  • Because the layers are oppositely charged,

  • the electrons want to travel

  • from the n-type layer to the p-type layer

  • to fill its empty holes.

  • The electrons create a voltage difference

  • between either end of the cell.

  • So, by adding an electric circuit to one end,

  • the electrons can travel through that circuit,

  • powering devices along their way

  • and end up in the p-type layer.

  • [EXHALES] Okay, we did it.

  • We made it through the molecular explanation

  • of how solar cells convert sunlight into electricity.

  • But typical crystalline silicon PV cells

  • only convert 18 to 22% of sunlight

  • into electricity.

  • And that's clearly not enough.

  • We want solar cells to be as efficient as possible

  • so they can power as many things as possible.

  • And the teams competing in the World Solar Challenge

  • are already using an advanced material to do so.

  • The typical material to make solar cells out of is silicon,

  • and this is a car covered in silicon panels.

  • They're allowed up to four square meters.

  • But recently a lot of cars air switching over

  • to a different material, gallium-arsenide cells,

  • and they're significantly more efficient.

  • Gallium-arsenide is a semi-conducting material

  • made from the elements gallium and arsenic.

  • Gallium-arsenide solar cells

  • now hold the world efficiency record

  • for a single junction solar cell,

  • with a conversion rate of just around 28.8%.

  • So what's stopping us from using that in everything?

  • Well, making a wafer of gallium-arsenide

  • is considerably more expensive than making a silicon wafer.

  • The size of the gallium-arsenide array

  • was 3.56 square meters,

  • and to cover that size array, you need about 100 grand,

  • um, to cover the same amount of area,

  • actually to cover about four square meters.

  • So even a larger area of silicon,

  • you'll need about 3 grand,

  • so there's a huge price difference.

  • So researchers are still trying to find that perfect solar cell

  • that is both cost effective and full efficiency.

  • Innovations like those used in the World Solar Challenge

  • are going to continue to push the boundaries

  • of renewable solar technology.

  • And now that you have a solid grasp

  • on how solar panels and photovoltaics work,

  • let's take a closer look at how we can apply

  • all of this solar tech to a race car.

MAREN: Back in December of 2015,

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Breaking Down Solar Panels

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    林宜悉 posted on 2021/01/06
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