Monday, June 09, 2008

Cucumbers in the Desert

Deep in the heart of Sal’s desolate moonscape, amid boulders and barren sand dunes, you might just come across a 30-centimeter cucumber. A desert mirage? Hardly. Robust cucumbers, tomatoes, lettuce, peppers and other crops are harvested year-round from Milot’s 15.500 kilometer farm thanks to a promising technology called hydroponics.
Hydroponics is soil-less culture (“hydro” water, “ponos”, labour). Developed by Germans in the 1860’s, it features the use of nutrient solution in place of soil, which allows for more robust yields and greatly reduces water use. While hydroponics is practiced widely in Europe, the Americas and the Middle East, it is nascent in Cape Verde, where low rainfall and little arable land (only 10% of total land mass) make it an ideal candidate for the technology. Hydroponic farms currently operate in Sao Francisco (Tom Drescher’s “VenteSol Cultura Hidroponica e Turistica” ) and Sao Domingos on Santiago in addition to Sal, while adult education classes in Santiago aim to expand it.
While techniques vary, one of the most popular is the Nutrient Film Technique (NFT). In this system, a shallow stream of nutrient-rich water flows constantly along a slightly tilted trough, which holds the plants. A non-soil medium like gravel may be used to anchor the plants, while a mechanized pump ensures a constant flow of nutrients, air and water. Usually a mesh enclosure covers the crop, retaining moisture and protecting against insects.
The advantages are tremendous. Water input is reportedly between 1/10 and 1/20 of that necessary for normal agriculture, even less than drip irrigation. That’s because no water is wasted through soil absorption or excess evaporation, and because water can be recycled through the trough. Hydroponics also uses only 1/10 the land required for normal agriculture. Indeed, it can be implemented anywhere, year round, and calls for no weeding or ground preparation. Crops are usually healthy and mature quickly, because the microbes that cause weak plant growth reside only in soil, and hydroponics allows you to control the ratio of nutrients in the solution exactly.
Still, overhead costs are high. One farmer estimated spending 6,000-7,000 euro to set up his 500-meter farm. Nevertheless, monthly yields were so good that he had recouped his investment after only seven months. Operation costs are also a factor since NFT requires constant energy to keep the water flowing. In fact, with no soil moisture reservoir, plants are prone to die quickly if watering ceases even briefly. Certain plants with deeper roots are more challenging if not impossibly to grow hydroponically.
While hydroponics is still novel in Cape Verde, diminishing rains, rising import costs, and a growing tourist market may render it essential. As the technology grows, don’t be surprised to find cucumbers in the country’s most barren landscapes.

The Answer is Blowing...?

Sweeping across the Caribbean and Africa, the alize trade winds have brought ships to Cape Verde’s shores and dust into newly swept homes each summer for centuries. But today, these winds may prove more useful than ever, fueling a clean, renewable energy that powers homes and businesses, and reduces dependence on foreign oil.
Wind energy has a long history. For centuries peoples have harnessed the wind’s power to sail ships, crush grain, pump water, and cut wood. Fossil fuels virtually replaced it by the 1930’s, but oil shortages in the 70’s forced many countries to revisit it. Today, just over 1% of world energy comes from wind, but wind generates 19% of energy in Denmark, while Germany, the U.S. and Spain each produce more than 15,000 Mega-Watts of wind power.
In sharp contrast, only 3-5% of Cape Verde’s energy comes from wind. But with wind speeds averaging 5-9.7 m/s2, and electricity demand increasing by 8-15% per year, wind has huge potential. Electra built its first wind park on Sao Vicente in 1989, and today there are three functioning wind parks on Sal, Sao Vicente, and Santiago. In concert, they contribute 15,000 kW to the electricity grid.
Each of these wind parks is composed of 2 or 3 wind turbines, each with a rotor, a generator, and a tower. The rotor captures the kinetic energy of the wind through blades designed to be lifted by the wind, similar to airplane wings. The motion then drives the generator to produce electricity.
One major constraint is financing. With each turbine costing many thousands of U.S. dollars, and producing at best 322 kWh per month, each one will pay for itself only after 4.5 years. Fortunately, Infraco, a US company, in collaboration with the Cape Verdean government with invest 40 million euros to build new plants on four islands, increasing the power to 17% -25% of total energy production. Wind power will then total 20-25MW.
Wind is highly erratic--changing direction and intensity---wind energy is difficult to store. That makes wind an “intermittent generator”, meaning its guaranteed output must be valued at zero, and therefore that diesel capacity must be able to meet 100% of demand. Wind’s intermittency is what prevents it from supplying more than 25% of any country’s total energy.
Current efforts aim to address these difficulties. A proposed Thermo-Wind-Solar Power Plant could provide constant, storable energy by generating thermal energy. Wind would be used only as a cold source, while the soil, oceans or warm water sources on Santo Antao would provide the warm source.
Proposals like these are promising, but their implementation is urgent, if Cape Verde is to meet its goal of 50% renewable energy by 2020. If they do, it will be worth catching wind of.

A Sip of The Sea

What could be less thirst-quenching than a mouthful of salty seawater? Perhaps nothing, thanks to desalinization plants that are turning salt water into one of the most widespread sources of drinking water for Cape Verdeans. With 965 kilometers of coastline, and dwindling underground sources, the arid nation has reason to seek solutions to its water problem through desalination. Plants on Sal, Boa Vista, in Praia, on Maio and on Sao Vicente--managed by Electra, the state owned energy company, and Aguas da Ponta Preta, a private enterprise--produce roughly 4,109,229 cubic meters of water annually. That supplies almost 30,000 Cape Verdeans with water and means that ocean-bathers are not the only ones drinking seawater regularly.
While plant technologies vary, the preferred, and most pervasive method in Cape Verde is Reverse Osmosis (RO). In regular osmosis, the solvent (in this case, salt) moves from an area of high concentration to a lower one through a semi-permeable membrane, equalizing the substance’s distribution. In contrast, during Reverse Osmosis, the salt water is pressurized to encourage highly concentrated salt water to separate from clean water, which collects on the opposite side of the semi-permeable membrane. Once this water’s salinity has decreased from about 38,500 mg of salt per liter to 400, it is treated and sent to a holding tank. RO Plants in Cape Verde produce between 1,000 and 5,000 cubic meters of water per day respectively.
RO boasts lower installation costs and is cheaper that Vapor Compression Distillation, and Mult-effect distillation, two other desalinization technologies used in Cape Verde. Still, operation is far more expensive than other water collection methods, like drilling and rainwater collection. Even modern RO plants that recycle energy require between 2 and 3 kwh per cubic meter of water. That is an enormous amount of energy for an island nation that must import most of its energy, especially when a single kilowatt hour costs about $0.30 US dollars. For a 1,000 cubic meter capacity plant, that’s about $600-900 dollars a day.
Moreover, because only 43% of the seawater is converted to potable water, the remainder—a highly saline “brine”-- is dumped back into the ocean. Scientists assert this saline concentrate is very harmful to marine life.
Other forms of desalinization are being tested to address these problems. Two Peace Corps volunteers, Brian Newhouse and Nick Hanson, are working with students at Assomada’s technical school to develop solar stills that use sunlight alone to convert seawater into fresh water. As sun light filters through a glass pane, the salt water heats and evaporates within the hot black box. Fresh water condenses on the glass, dripping down into a catch basin. While construction costs are low and materials readily available, so far the prototype produces only about two liters a day.
Nevertheless, Cape Verde is counting on desalinization for the future. Two new RO plants are under construction in Santiago’s Interior, which will produce a combined total of 12,000 cubic meters of water per day. Public-private partnerships modeled on “Aguas do Porto Novo”, established in 2007 on Santo Antao, will likely sprout up elsewhere, while private golf courses and hotels will continue to run their own private desal plants. If all goes according to planned, underground water sources will be left exclusively to agriculture and Cape Verdeans—ocean-bathers and otherwise--will drink seawater everyday.