In the previous blog, the innovation behind the Milpa Alta project was explained. Now, an overview of the technology used in the project will be made, pointing out the sustainability, circular economy and innovation behind the project. This blog is based on an interview with Jahir Mojica, CEO of SUEMA, company that developed the project.
The Milpa Alta project, as most of its type, can be divided into two systems, the biodigester and the generation unit. While the biodigester will produce the biogas, the generation unit will create, through the use of the biogas, two types of energy: electricity and heat.
The biodigester from Milpa Alta is thermophilic, meaning that it needs of a temperature of 57°C to allow for a digestion process that turns solid residues, mixed with water, into biogas. The heat needed to reach 57°C in the biodigester is provided by solar thermal collectors, making the project run on solely renewable energies as well as providing for a decrease in operational costs avoiding the need of fuel or electricity.
Once the biogas has been created it is taken to the generation system. To further simplify the system, it can be stated that it consists of a combustion and a generation unit. In the combustion unit the biogas is burnt to produce heat. The produced heat is used to heat up a process fluid that moves a turbine and ultimately creates electric energy. Another way of using the heat produced by burning biogas is to heat up the bio-digesting unit when the solar thermal collectors cannot produce heat, such as in cloudy days or overnight. Having this kind of energy supply allows for an autonomous system that can work regardless of weather conditions.
It is expected that at the beginning of the project the biodigester will produce enough biogas to generate around 150kWh of electric energy per day. All of the produced electricity will be transmitted to the central market of Milpa Alta, where the residues used to create biogas are produced, through an interconnection to the main grid. While for the time being the project will use the net-metering scheme to lower the electricity consumption from the main grid of the Milpa Alta’s central market, it is expected that as energy production stabilizes, and even increases, the net-billing scheme will be more attractive. By using the net-billing scheme, the project will be able to produce a net positive economic inflow for the central market, as all of its production will cover the electricity consumption of the market, and a surplus will be sent to the grid.
While for the upcoming months all the biogas produced will be used for electricity generation, once the production is stabilized and increased to the point where net-billing is attractive, it is expected that some of the biogas will be supplied to small businesses in the surroundings. The first potential users of the biogas are tortillerias located close to the plant. Jahir Mojica expects that by using this approach, the whole process will become as circular as it can possibly be, and the plant will become a full demonstration of the potentials and positive results circular economies can bring o Mexico.
SUEMA, being a social business, does not only focus on the revenues but puts a great focus on the social impact of its business model. Because of this, it has signed a one-year contract for the operation and maintenance of the plant. Once the contract finishes, Mojica expects to sign it again, as it is his company the one who best knows how everything works. Nevertheless, the space is open for competition, and if another provider can offer a more attractive contract, the company is open to accept it.
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