### Video Transcript

Energy resources can be renewable or nonrenewable. Solar power is a renewable energy resource. Name two other renewable energy resources.

Okay, so first of all, what even is a renewable energy resource? Well, a renewable energy resource is one which we can use to get energy from without
the resource itself being depleted. What do we mean by this? Well, let’s consider coal, which is a nonrenewable energy resource.

The way that we get energy from coal is that we combust or burn the coal. But then, once all of this coal that we have has been combusted, we no longer have
coal and hence this is a nonrenewable energy resource.

On the other hand, solar power — as we’ve been told in the question — is a renewable
energy resource. The way that solar power works is that we have these rather badly drawn solar panels
which absorb light from the sun and then they convert this into electricity. Now, since the light from the sun isn’t running out anytime soon, this is known as a
renewable energy resource.

Anyway, so we’ve been asked to name two other renewable energy resources other than
solar power. Now, in reality, there are lots of other renewable energy resources that we can name,
for example, wind power where wind is used to turn turbines and these turbines
convert the energy from wind into electricity as well as this another renewable
energy resource is hydroelectric power, where basically a big dam is used to contain
a reservoir of water. And when the time is right, the dam is opened and the water is allowed to flow
downstream which then ends up turning a turbine. And this turbine is what generates electricity.

So these are two types of renewable energy resources. There are also lots of other kinds there, for example, tidal power, wave power,
geothermal energy, and even biofuels. And we can choose to give any two of these as our answer to this question. So let’s choose to give wind power and hydroelectric power as our answers.

Okay, now, in this question, we’ve been told that solar power is a renewable energy
resource. Let’s now think about solar panels.

Solar panels are used to generate electricity. Figure one shows how the power output of a solar panel changes over one day. A solar panel does not generate electricity constantly. For how many hours did the solar panel generate no electricity?

Okay, so Figure one shows the power output in watts from a solar panel plotted
against time in hours. Now, this is showing us the power output of a solar panel throughout the course of a
day. And it’s worth noting by the way that when the solar panel has a power output, that’s
when it’s generating electricity.

So what we’ve been asked to do is to find out for how many hours the solar power
generated no electricity or in other words we’ve been asked to find the amount of
time for which the power output of the solar panel was zero throughout that day. So we just need to count up the number of hours for which the power output of the
solar panel was zero on this graph.

Now, we can see that the power output of the solar panel is zero for this entire
length of time, from here to here. And we can see that the power output is also zero from here to here. So we just need to find the length of time that these two orange bars represent and
then add them together to give the total amount of time for which the solar panel
generated no electricity that day.

So let’s go about doing that. First of all, we need to realize that big divisions on the horizontal axis of the
graph represent two hours because we’ve got a big division at zero hours, a big
division at two hours, another one at four hours, another one at six hours, and so
on and so forth.

And then, as well as this, we can see that there are three little divisions in
between every pair of big divisions. Now, if there are three little divisions between every pair of big divisions, then
they divide up the distance between big divisions into four equal-sized chunks. Look here’s chunk number one, here’s chunk number two, chunk number three, and chunk
number four.

Now, this means that a little division represents the same amount of time as a big
division divided by four. And as we said earlier, a big division is present every two hours. And so if we divide this by four, this is equal to a half or 0.5 hours. Therefore, we’ve just worked out that little divisions represent half an hour.

So for example, if this big division represents 12 hours, then the next one is going
to represent 12.5 hours, the next one is going to be 13 hours, this is going to be
13.5, and this one is 14. So that works out quite well. So now that we’ve worked that out, the length of time for which the power output is
zero here and here.

So let’s look at this region first. We can see that starting at time being zero, the power output of the solar panel is
zero for two hours, four hours, and four hours and one division; that’s one little
division. And as we said earlier, a little division represents 0.5 hours. So in total, this length of time represents 4.5 hours.

And then for the other region, we can start at 22 hours because that’s when the power
output becomes zero and then we move along for another two hours until we hit 24
hours. And hence, this period of time is two hours.

So now, the total amount of time for which the power output of the solar panel was
zero is equal to 4.5 hours plus two hours. And 4.5 hours plus two hours is equal to 6.5 hours. Hence, the number of hours for which the solar power generated no electricity that
day was 6.5 hours.

Okay, so we’ve just seen that solar panels can be used to generate electrical
power. But how do we get it from where it’s generated, for example, at the solar panel, to
where it needs to be used, for example, in homes or in businesses.

In order to transmit electrical power long distances over the National Grid, the
current to the power cables must be low to reduce the energy wasted due to heating
the cables. What device is used to decrease the current through the power cables while increasing
the potential difference between the power cables and earth? Tick one box. A transistor. A diode. A transformer.

Okay, now, we saw in the previous part of the question when we were talking about
solar panels that they generate some sort of power output. And it’s this power that they generate that’s transferred as electricity along the
National Grid.

Now, we can recall at this point that the equation for electrical power is 𝑃 is
equal to 𝑉𝐼, where 𝑃 is the power carried by the electricity, 𝑉 is the potential
difference, and 𝐼 is the current. Now, let’s say that we’re considering the power transferred by the National Grid and
this power is coming from the solar panel from the previous part of the
question.

Now, at any given time, the solar panel can only generate a certain amount of
power. So we can take that power to be fixed for that point in time. And therefore, that’s the amount of power that needs to be transmitted over the
National Grid. However, we can choose to do this in multiple different ways.

We can, for example, transmit this power with a high potential difference and a low
current or a medium-sized potential difference and a medium current or a low
potential difference and a high current or of course anything in between either of
these options.

Basically, the point is as long as the values of the potential difference and current
multiply together to give the power output from the solar panel, we can basically
choose to either increase or decrease one of the values and compensate with the
other value. So if we increase the potential difference, we have to decrease the current by the
same factor and vice versa.

Now, we’ve been told that the current through the power cables must be low to reduce
the energy wasted due to heating the cables. And we’ve been asked to state what device is used to decrease the current through the
power cables while increasing the potential difference between the power cables and
earth, basically increasing the potential difference across the power cables.

And that’s exactly what’s going on in this situation: we’re trying to decrease the
current and the reason that we have to increase the potential difference is to keep
the power constant. And so what we’re trying to do here is to transform the power transmitted from being
high current and low potential difference to being low current and high potential
difference.

And the device that does this is a transformer. Specifically, because we’re trying to increase the potential difference, we use a
step-up transformer because the potential difference is being stepped up. But anyway, at this point, we can put a tick in the box next to a transformer.

And this makes sense because a transistor can do lots of different things, but mainly
forms the basis of computers. And a diode is an electrical component that only allows current to pass through it in
one direction. Hence, at this point, we found our answer. The device that is used to decrease the current through the power cables while
increasing the potential difference across them is known as a transformer.

Okay, so earlier, we were considering renewable energy resources. Let’s now think about a gas-fired power station.

Gas-fired power stations can produce a high power output at a low cost. What is a disadvantage of a gas-fired power station? Tick one box. The power output of gas-fired power stations is unpredictable. Gas-fired power stations can only be built in certain locations. Gas-fired power stations produce large quantities of carbon dioxide. Gas-fired power stations are slow to start up.

Okay, so in this question, we’re trying to find a disadvantage of a gas-fired power
station. So let’s go through each option one by one.

Firstly, that the power output of a gas-fired power station is unpredictable: well,
this is definitely untrue. It’s actually fairly simple to control the amount of gas being burned at any given
time so that we can control the power output from the power station. If we aren’t producing enough energy, we can just burn more gas and if you’re
producing too much, we can just burn less gas. so this first option is not the
correct answer to our question.

Let’s look at the second one then: gas-fired power stations can only be built in
certain locations. Now that’s kind of true; you know there are some limitations as to where we can build
a gas-fired power station. For example, we need a fairly large area so we can build the entire plant. But there aren’t anywhere near as many limitations on gas-fired power stations as
there are on some other kinds of power stations.

For example, imagine trying to build a hydroelectric power station in a place where
there’s little to no water; yeah, that’s not gonna go so well or imagine building
lots of solar panels in a region where it’s always raining, UK. But yeah, so this is not the answer that we’re looking for either. Gas-fired power stations have surprisingly few limitations as to where they can be
built.

So let’s look at the third option then: gas-fired power stations produce large
quantities of carbon dioxide. Now, this one is true and it is a massive disadvantage. Gas-fired power stations run on natural gas. Now, this is a nonrenewable energy resource and what’s more is that it’s a fossil
fuel. And burning fossil fuels releases lots of carbon dioxide into the atmosphere. This directly contributes to climate change. So it’s very much not a good thing.

So option three looks like a genuine disadvantage. But let’s check option four just to make sure. Gas-fired power stations are slow to start up. Now, this one is definitely untrue as well. In fact, gas-fired power stations are very quick to start up. They’re one of the types of power stations that are used when there’s a peak in power
demand.

In other words, when lots of people need power in a short period of time, gas-fired
power stations can be started up very quickly because gas is fairly easy to
transport. We could just squirt it along a pipe basically. So if we very quickly need to start up a gas-fired power station, we just send some
gas along a pipe and all is good.

Compare this with something like coal, for example, which is a solid. And so it’s a little bit more difficult to transport. We can’t just send it down a pipe. So this final reason is not a valid reason either.

Hence, we tick the box next to the third option because a disadvantage of a gas-fired
power station is that gas-fired power stations produce large quantities of carbon
dioxide.

Okay, so we’ve just discussed gas-fired power stations. And earlier, we discussed solar panels. Let’s compare the two.

A solar panel has an average power output of 150 watts. A gas-fired power station has an average power output of 45 megawatts. Calculate how many solar panels will be needed to generate the same average power
output as one gas-fired power station.

Okay, so we’ve been told at this question that a solar panel can generate an average
power output of 150 watts and a gas-fired power station has an average power output
of 45 megawatts. We need to work out how many of these little solar panels we would need to generate
the same average power output as this gas-fired power station.

In other words, to generate 45 megawatts of power output — that’s the same as the
power output of the gas-fired power station — we would need 𝑛 solar panels; we’ll
call it 𝑛, where 𝑛 is the number of solar panels and we need to multiply this by
150 watts because that’s how much each solar panel could produce.

So to recap, this is the amount of power produced by the gas-fired power station and
this is the amount of power produced by one solar panel. So what do we need to multiply the power output of the solar panel by in order to
give us the same power output as the gas-fired power station? And we’re calling this number 𝑛.

Anyway, at this point, we should realize that we’ve got the left-hand side in
megawatts and the right-hand side in watts. In order to compare them effectively, we need to convert them to the same unit. So let’s convert the left-hand side into watts.

To do this, we can recall that the prefix mega which is what’s been used here; we’ve
got megawatts. And we can recall that mega is equal to 1000000. And so 45 megawatts is the same thing as 45 lots of 1000000 watts. And then, we can multiply 45 by 1000000 to give us 45000000 watts. So let’s replace the left-hand side of our equation with 45000000 watts.

And at this point, we’ve got the same units on either side so we can compare them
effectively. The next thing to do to find 𝑛 is to divide both sides of the equation by 150
watts. This way, the 150 watts on the right-hand side cancel out and on the left-hand side
the units of watts cancel out. Hence, on the left, we’re just left with 45 million divided by 150 and on the right,
we’ve just got 𝑛.

Then, when we evaluate the fraction on the left-hand side, we find out that this is
equal to 300000. And hence, the number of solar panels that we would need to generate the same average
power output as one gas-fired power station is 300000. That is a lot of solar panels. But anyway, now that we’ve answered that, let’s take one last quick look at solar
panels.

Solar panels are quick to install and cheap to maintain. What is a disadvantage of using solar panels for generating electricity? Tick one box. Solar panels can only generate electricity when very hot. Solar panels can only generate electricity during the day. Manufacturing solar panels releases large quantities of carbon dioxide into the
atmosphere.

Okay, so in this question, we’re trying to find a disadvantage of solar panels. So let’s go through each option one by one.

Firstly, that solar panels can only generate electricity when very hot. Now, this is not true. Solar panels can work quite well in a range of temperatures. As long as it’s fairly sunny or bright out, the temperature of the solar panel
doesn’t have that much of an effect on its electricity production. And certainly, we don’t need solar panels to be very hot in order to generate
electricity. So this answer is not the one we’re looking for.

Secondly then, that solar panels can only generate electricity during the day. Now the way that solar panels work is to take in the light that’s coming from the
sun, use this energy from that light, and convert it into electricity. And of course, it can only be sunny during the daytime because at nighttime, the sun
is not out. So this does look like a valid answer to our question.

And it might seem silly, but it’s actually quite an important point. Well, yeah, obviously, the sun is out during the day only. But when we compare this to other types of power station, like, for example,
gas-fired power stations, we realize that many of these are the types of power
station can produce energy at whatever time of day. So this is a serious disadvantage of solar panels.

Moving on to the third option then, manufacturing solar panels releases large
quantities of carbon dioxide into the atmosphere. Now, this is kind of true. Manufacturing solar panels does release a fair amount of carbon dioxide into the
atmosphere.

However, the amount of carbon dioxide that we end up not releasing because we’re
using solar panels rather than fossil fuels massively outweighs the amount of carbon
dioxide released when manufacturing solar panels. And as well as this, manufacturing solar panels does definitely release some amount
of carbon dioxide into the atmosphere, but definitely not large quantities. And so this is not the answer to our question either.

Therefore, we put a tick in the second box because our final answer is that a
disadvantage of using solar panels for generating electricity is that solar panels
can only generate electricity during the day.