San Lorenzo Hydro Plant: Aspects of Energy and the Environment (TSP Case Study)

Impacts on Native Species: 

The hydro plant clearly affects multiple different species in its vicinity. The first and most apparent impact is had on the aquatic life in the San Lorenzo River. The dam creates a blockade so that the fish found in the San Lorenzo are not able to continue their migration. This profoundly impacts fish populations in many different ways. Some aquatic life gets stuck in the dam’s machinery, some predators prey on fish species in the reservoir, and sediment from the river gets trapped in different areas of the plant, which causes a shortage of nutrients for some species resulting in multiple negative impacts. Fish are not the only aquatic species affected by the plant, there is a variety of snakes, frogs, and other water life impacted by this project. 

This hydro plant has a very specific impact on one of its native inhabitants that is not directly related to the project. In the past, monkeys have been able to cross the river at a certain point just before the dam, by using two trees that virtually connected the opposite banks. The trees created a natural land bridge that was crucial to the monkey’s migration. One of the trees that make up this land bridge recently fell into the river causing geographic isolation for this certain species of monkey. The staff responsible for running the hydro plant realized the importance of the trees for the monkeys and made plans to construct a bridge so that they may continue their natural migration. This is an example of a positive impact had on the environment because of hydro-plants presents. 

Issues with Sediment: 

One of the main tasks the employees are constantly dealing with at the hydro-plant is in regards to sediment in the river. Sedimentation is probably the most technical problem dams face today. When a dam is constructed sediment from the river becomes trapped at the bottom of the reservoir. The reason this creates such a large problem is because the sediment takes away from overall water storage space and poses a threat to the turbines and other machinery necessary to operate the hydro plant. At this particular site there is a door located at the bottom of the reservoir, in the rainy season the door opens and filters out the sediment. Even with the sediment door there is still a large amount of labor put forth to take sediment out of the reservoir. 

One special feature about this project is its second reservoir, located past the main dam. This reservoir does not have the sediment door feature and it is required to be cleaned once every year. This process requires multiple workers, tractors, and other machinery. The sediment from the bottom of the reservoir is then taken to a large pile located about 100 meters from where it was taken. The hydro plant has no use for the sediment so it goes unused. One worker told us that it would be extremely profitable to design a business that specializes in the removal of sediment from hydro sites. The nutrients found in the sediment could be highly beneficial to a variety of different agricultural projects. 

Problems with Turbines:

When the plant is not producing electricity at its peak hours, aquatic life has to deal with the river fluctuating between 10-100 percent of its flow based on the amount of water needed to power the turbines. The turbines are responsible for a large amount of the environmental alteration that results from the plant. As the water from the San Lorenzo makes its way through the turbines, it is drastically heated. The fluctuating temperature can take a toll on aquatic life and other species that use the river as their source of water. Many species of fish become stressed and even harmed in fluctuating water temperatures. 

Another environmental threat posed by the turbines is the maintenance that they require. In order to keep things running smoothly the employees of the plant need to pump lubricants into the turbines. These lubricants make their way through the machinery and end up flowing through the turbines. The water then makes its way out into the river exposing the lubricants to all sorts of life. The only positive about the lubricants at this particular site is that they use biodegradable lubricants, which have a much lesser impact. Even though the impact is lesser, unnatural substances are still being put in contact with the river water.

San Lorenzo Design:
          One major aspect to a hydroelectric plant is the plant’s design.  The design of a hydroelectric plant must achieve maximum efficiency and abide by environmental laws at the same time.  The first aspect to a hydroelectric plant’s design is the location.  The San Lorenzo hydro-electric plant was built just down stream from where two major rivers converge, the main source being the Jamaical river.  The whole facility is constructed along a distance of about a mile.  Every component of this mile long facility has a specific purpose for increasing efficiency.  The dam starts with a large reservoir to increase water pressure and slow the flow of the river.  The reservoir is an average of 60m wide and 18m deep.  The large reservoir is then channeled into a canal 4 meters deep, and 4 meters wide.  The purpose of this long canal is to increase what is known as the head.  The head is the elevation change between the main reservoir and the turbine.  The head of San Lorenzo is a total of 91m.  After the canal the water goes into the main reservoir at San Lorenzo.  In the main reservoir water settles and sediment that is detrimental to the turbines is collected.  If too much of this sediment is detected in the turbines two doors at the upper reservoir will shut off the water supply.  After the main reservoir the water gains speed by using the elevation change in the head.  The water enters an intake pipe.  The closer the water gets to the turbine the smaller the diameter of the pipe gets which increases the speed of the water.  The water then passes through the turbine and turns the generator.  The design of the San Lorenzo hydro-electric plant is a display of great design with great efficiency as the result.  San Lorenzo does not have a large inflow of water to use to produce energy. Therefore they needed to use smart engineering to get whatever energy they could.

Energy Output:

            The San Lorenzo hydro-electric plant produces enough energy to power about 29 thousand middle class homes, which translates to an output of power for a minimum of  145,000 people.  The facility relies on two turbines constructed and shipped from France.  The turbines are known as Francis turbines.  The turbines combined produce 8.5 megawatts.  Due to the design described above they are able to achieve this amount of energy.  If the facility only had one reservoir the energy output would be much lower.  To calculate how much energy is being produced at any hydro-electric plant the following equation is used: P = p x q x g x h.  The following factors signify: P = power(watts), p = density(kg/meters cubed), q = water flow(meters cubed/second), g = acceleration of gravity(9.81 m/s), h = falling height, head (m).  The last aspect to the energy output of the San Lorenzo hydro-electric plant is of course the amount of water present in the Jamaical river.  The maximum capacity of the facility is 19 cubic meters a second, which is what the plant runs at for the duration of the dry season.  During this period the plant never stops producing energy because they do not need to wait for the main reservoir to fill up.  During the dry season the plant uses around 4 or 5 cubic meters a second.  

Graph drawn by the head business-man at San Lorenzo.  Graph shows the
peak times of energy use.

Economics:

           Economics is one of the main aspects to hydro-electricity.  Other than the search for other sources of energy, economics is a large reason for hydro-electricity in Costa Rica.  The economic goal of hydro-electricity or any other renewable energy source for that matter is the elimination of expensive fuel.  Each hydro-electric facility has certain factors in which need to be catered to in order to maximize economic output.  The San Lorenzo hydro-electric plant has to plan accordingly to maximize their energy sales.  In the dry season the workers at the facility fill up the top reservoir and the main reservoir in order to produce more energy during the time periods which energy is most desired, therefore they receive more money.  The windows of time in which energy is most desired is 10:30am to 12:30pm and 5:30pm to 8:00pm.  One window in which businesses are all open and people come home for lunch, and one window when people begin to start using more lights.  In the dry season this is when San Lorenzo sells their energy to the power grid through ESA.  All energy sold goes through ESA and straight into the grid.  During the rainy season San Lorenzo is constantly producing energy because the plant is always running at full capacity.  The plant always gains money for their energy but that amount varies depending on the time of day.  

AUTHORS: Matt Richards, Blake Lecroy