Hydroelectricty Potential – Sustainable Energy – TU Delft

Hydroelectricty Potential – Sustainable Energy – TU Delft


Welcome everybody. Last week we have looked into concept of energy
and the energy use of some major sectors. By now it will be clear for you all that our
energy need in the world is significant. So the big question is: Do we have enough
renewable energy sources available on planet earth to sustain our enormous energy need? This week, we will look at the most important
renewable energy sources. We will make rough estimations on what these
energy sources potentially can deliver in reference to our energy needs. We will do this using rough -back-of-the envelope-calculations. This week will give you some first insights
in what are the opportunities and limitations of the various energy source. Be aware that we only make rough estimations
this week. Later on during this course we will look in
more detail to the technological and system aspects of the various renewable energy sources. In this first video lecture we will take a
look at Hydro power. There are many large Hydro power plants around
the world. But most of them look like this. Water that contains potential energy is collected
in a reservoir behind a dam and flows to the intake .
The water is forced through the pipe or ‘penstock’ by gravity. The turbine in the dam is pushed in motion
and the potential energy is converted to mechanical energy. The turbine is connected to a huge electric
generator to convert the mechanical energy into electrical energy. The generator is connected via transformers
to the electricity grid to deliver electricity in the grid. Losses in the system are mainly caused by
friction at the edges of the pipe. The turbine and electrical losses also further
reduce the efficiency. When estimating the potential energy of Hydro
power, the most important factors are the available waterflow, either via melting snow
or rain, and the height difference of the water representing the potential energy to
be converted. As example we take a close look at the Itaipu
Dam on the border of Brazil and Paraguay to get a feeling of how to estimate the potential
of hydro energy. The ITAIPU dam is the second largest hydropower
plant on the planet. It has a total installed generation capacity
of 14GW, and has reached a record energy generation of 98,6 TWh per year or 0.27TWh per day. If we assume the generated energy is solely
used by the 200 million inhabitants of brazil, we arrive at total electricity generation
of 1.35 kWh for every person everyday. Let’s relate that back to the energy unit
of one person as we have discussed last week. One personal unit of energy was equal to 2.9
kWh per day. So, 1.35 kWh/person/per day would equal 0.45
man units of energy production per day. Another way of comparing the yield of any
renewable energy source is to look at the annual energy yield per rate power or in other
words how much kWh of energy is generated per year per Watt of installed capacity. In this case we have to divide 98.6 TWh by
the 14 GW of installed capacity. For the Itaipu dam we arrive at a little more
than 7 kWh/Watt/year. A value expressed in kWh/W/year will also
be used for other renewable technologies we introduce this week for comparison. Another parameter used in the industry to
compare the production of different powerplants is the capacity factor. It is an easy tool to estimate energy production
over a period of time. The Itaipu dam has a capacity factor of 0.80. Which is the annual production divided by
the installed capacity and the hours in a year (8760). So you could say on average the Dam produces
80 % of the time electricity on maximum capacity 80% . For fossil fuel plants like gas and coal plants
the capacity factor can be very close to one meaning it will run almost continuously on
installed capacity. This is something electricity grid operators
are very keen of to ensure stability on the grid. Other renewable energy sources like solar
and wind can have much lower capacity factors. We will look in to those later this week. For now we will make an estimate of the potential
of hydroelectricity W/m^2. Let’s work through an example. Let’s say a certain region has about 500mm
of rain per year and there is no meltwater from mountainsnow or glaciers. 500mm of rain per year, is equal to 0.5 m^3
of water per square meter. By multiplying that with the density of water,
which is 1000 kg/m^3, we get that per square meter of land there is 500 kg of water per
year. To calculate the potential energy of this
amount of water we will use this equation. Where E_pot is the potential energy in Joule,
M is the mass of the water, g is the gravitational constant of 9.8, and h is the height difference
between the source and the outflow of the dam. Which we will assume is 100m. For these numbers we get 490 Kilo Joules of
potential energy per square meter per year which is equal to about 0.14 kWh, so now we
know the energy density in terms of kWh/m^2/year. We can express this in power per area by dividing
by the total seconds in a year to get 0.015 W/m^2. However, this calculation assumes that all
potential energy is converted into electricity. In reality this is not the case and dependent
on the landscape surrounding the Dam. A hydroelectricity dam is usually build next
to a natural lake or water reservoir that collects the water fallen on a large area
through a network of rivers. The total area from which the reservoir collects
the water is referred to as the catchment area enclosed by the red line in this picture. If we know the size of this area we can estimate
the total energy potential of a certain region or dam. Now we are going back to the itaipu dam and
we will make a rough estimation, to verify it’s typical power and yield. The catchment area stretches an incredible
1.35 million square km. In this area the averaged annual rainfall
is 1650 mm/year. About 1000 mm per year of this water is evaporated
before it is passing the dam. The remainder equals a mass of 0.65 m^3 of
water. If we take the height of the dam, which is
196m, using the potential energy formula we arrive at 0.35 kWh/m^2/year. The overall conversion efficiency of potential
energy to electrical energy of this dam is estimated to be about 20%, including the collection
losses as well as the conversion efficiency of the turbines in the dam itself. With this conversion efficiency of 20% we
arrive at an achieved energy density of 0.07 kWh/m^2/year. If we now take a look at the actual data of
the dam, and divide the annual energy production which of the dam by the catchment area, we
find that the they are achieving approximately 0.073 kWh/m^2/year. This is almost the same energy density as
we found a moment ago, when calculating the potential and achievable energy density. However, we can also take the reservoir surface
area of 1350 square kilometers as a measure for the required land. This gives a good indication of the amount
of land that is sacrificed for the hydro power plant, and is often used when comparing the
impact of hydropower plants. When we do this we get a higher energy density
of 73 kWh/m^2/year. It is also interesting to take a look at the
surface power density or specific power for both defined areas. We can find this by dividing the energy density
by all the hours in a year. For the entire catchment area we get a power
density of 0.008W/m^2, whereas for the reservoir surface area we find a surface power density
of 8.3 W/m^2. As you can see, with some fairly simple rough
calculations, a general estimate can be made of the potential energy that can be gained
from this source. However, the energy potential is not the only
factor that should be considered. Also the immediate and long term effects on
the surroundings and the climate should be taken into account. Hydroelectricity mostly requires a dam to
be built, in order to create a reservoir. This reservoir has a huge impact on the local
flora, fauna, and landscape. In case of really large Hydroelectricity projects,
the local climate could even change, due to the change in the water cycle. One of the biggest benefits of Hydropower
is the consistency of the power source because of it’s high capacity factor. Although it is not always free from seasonal
intermittency. Also, because of the scale of the projects
and the lifetime of 30 to over 100 years, the carbon footprint per kWh of generated
energy, as well as the cost per kWh, are low. Typically the carbon footprint of Hydroelectricity
is 24 gCO2/kWh on average, according to research of the Intergovernmental panel on climate
change from 2014. This is much lower than coal fired power plants,
which have an average carbon footprint of 820 gCO2/kWh. However, the carbon footprint of hydropower
does greatly depend on each individual project. As you can see, there are a few major factors
that have to already be in place before hydropower can be considered. The most important factor is the availability
of water, and a mostly natural height difference. Also the environmental impact of a hydropower
plant should be taken into account. Because of the necessity of a natural feature
that allows for the easy implementation of Hydropower and the impact on the surroundings
of a dam, the global potential of new hydropower is relatively limited. In 2015 the estimated global installed capacity
was 1211 GW, producing approximately 3975 TWh of electricity. This represents approximately 16.6% of the
global electricity demand, and about 70% of all renewable electricity. We can also express the production of hydroelectricity
in our own units. If we divide it by the global population of
7.4 billion people and days in a year we get 1.47 kWh/person/day. This is a slightly more then half a human
unit. Estimations for the global potential of energy
for hydro go up to 25% of the global energy use. With these tools you can try to make your
own assessment of hydroelectricity. In the next video we will look into physical
potential wind energy.

Leave a Reply

Your email address will not be published. Required fields are marked *