What is Hydropower?
Hydropower uses the energy of moving water for many applications. Hydroelectricity is a renewable energy that produces no air pollution or toxic byproducts, but it can have significant negative effects on the surrounding environment.
In Costa Rica, Hydroelectric Energy typically provides about 80% of the countries energy. A majority of this is through large dams controlled by ICE (the Costa Rican Electricity Institute, which we visited during our time in Costa Rica.)
ICE controls three large dams that are connected by the same flow of water. The source of this water is a large artificial lake that ICE created to capture the precipitation that falls over the Arenal mountain/volcano range. This lake holds enough water that it could continue to run the three hydroelectric plants for a year without running out even if there was no precipitation. It is strategically located to move water from the Atlantic zone to the Pacific zone, which would naturally not occur (Source 2).
From this lake, the water travels down a large pipe (5 feet in diameter) to the Arenal plant that we visited. The water in the system has an incredible 100 m/s^3 flow rate (Source 2). The head between the lake and the first plant is 210 meters, then 230 meters from the first to the second, and only about 30 meters from the second to the third (Source 3). The first and second plants use Frances turbines, which are designed for higher elevation changes (greater than 200 meters of head.) The third plant utilizes Kaplan turbines, which is a type that is meant for lower elevation changes (less than 40 meters of head.) (Source 1).
As you can see in the image shown above, a main difference in these two types of turbines is the shape and angle of the blades. Kaplan turbines have fewer blades than Frances turbines, as well as adjustable blades where the Francis blades are not adjustable. Kaplan turbines do however require a more heavy duty generator (source 1).
When dealing with this much water and pressure, it is crucial to design a system that can handle the fluxes in pressure that occur when different valves are opened and closed causing a sudden change in water velocity. ICE does this by utilizing large open cylindrical structures before each of their hydro plants called oscillation towers, or surge tanks (Source 3). These vertical pipes are able to absorb a sudden rise in pressure, as well as quickly provide extra water during any drops in pressure (Source 6).
The first plant produces about 150 megawatts, the second produces 178 megawatts, and the third produces 32 megawatts. This totals to a maximum of 340 megawatts of hydropower produced by ICE with this chain (Source 2). After the water has passed through the last plant, it is then distributed to the irrigation district where it is utilized on farms for crops. This is an example of Ecological Engineering because they have utilized the precipitation and elevation changes Costa Rica has to offer, and implemented the technology to harness it into power, as well as put what would be waste water to good use for crops.
Although Costa Rica has done a good job at creating green energy and leaving minimal waste, there are negative impacts of hydro power plants. Building the man made lake that powers the whole chain was the first negative impact as it had to be built over multiple cities. This forced both the people, and the ecosystems to be severely disrupted, and some parts completely destroyed. For example, we learned that snakes in particular were found all over the surrounding areas were they were not previously found because their homes were flooded by the lake (Source 3).
There are many affects that continue once the hydro system is in place. For example, “reservoir water is usually more stagnant than normal river water. As a result, the reservoir will have higher than normal amounts of sediments and nutrients, which can cultivate an excess of algae and other aquatic weeds. These weeds can crowd out other river animal and plant-life,” (Source 5). Also, reservoir water is usually lower in dissolved oxygen and colder than a normal river. When they release mass amounts of this water into surrounding rivers, it can have significant negative affects on the wildlife downstream as it disrupts their normal habitat (Source 7).
What is Wind Energy?
Wind energy is created when wind flow (kinetic energy) is harvested by wind turbines into mechanical power. Wind turbines are often grouped together to create a wind farm that generates bulk electrical power. This energy can then be distributed just as a conventional power plant would.
In Costa Rica, there are many wind farms present. Costa Rica currently produces about 3.5% of their energy through wind power, and they plan to continue to increase this amount (Source 1). In fact, there are multiple private projects lined up to create new wind farms that will hopefully be executed in the near future when the laws on energy creation are lifted allowing companies other than ICE to be major contributors (Source 5).
We did not get the chance to specifically learn about wind farms in depth like we did hydro power at ICE, but we did get to drive up and see an area of wind farms first hand! This is another good example of ecological engineering as they input technology (wind turbine farms) to take advantage of what nature already had to offer in this area with extreme winds. In fact, wind 10m above ground in an open area like this can be calculated as approximately 145 km/h! (Source 6)
As with hydro, the negative impacts of wind energy must be considered. The main environmental concern is with birds and bats. “Research found evidence of bird and bat deaths from collisions with wind turbines and due to changes in air pressure caused by the spinning turbines, as well as from habitat disruption,” (Source 8). With further research, however, it was determined that wind turbines do not threaten these species populations (Source 8).
Another aspect to consider is the visual and sound pollution cause by wind turbines. This may be very relevant in some areas of the world, but in Costa Rica in particular they are located on mountain tops where the wind is so loud the sound pollution is not relevant. As for the visual impact, this comes down to personal opinion, but I thought the wind farms did not negatively impact the views.
With both wind and hydro, there are positive and negative aspects. Both have effects on the surrounding wildlife and people, but they also both contribute to a significant decrease in carbon emissions in the region. All types of energy have trade offs, and different locations must decide which type makes the most sense in the given environment, what the economic value is, which is the most sustainable, and what has the least impact.
- ICE website: http://www.grupoice.com/
- Top Ten Things you Didn’t Know About Hydropower: http://energy.gov/articles/top-10-things-you-didnt-know-about-hydropower
- Tico Times – Costa Rica Energy: http://www.ticotimes.net/2012/09/07/a-renewable-power-generation-primer
- Wind Energy Basics: http://windeis.anl.gov/guide/basics
- Plant Tour- ICE Location 1
- Plant Tour- ICE Location 2
- EARTH University Presentation
- Marriott, M. (2009). Nalluri & Featherstone’s Civil Engineering Hydraulics. Wiley Blackwell.