April 19, 2017
Watering the world
New design cuts costs, energy needs for drip irrigation, bringing the systems within reach for more farmers.
Jennifer Chu | MIT News Office
Many farms in drought-prone regions of the U.S. rely on drip irrigation as a water-saving method to grow crops. These systems pump water through long thin tubes that stretch across farm fields. Hundreds of dime-sized drippers along the length of each tube trickle water directly onto a plant’s base. A farmer can control the timing and amount of watering, delivering only as much water as a crop requires.
Drip irrigation can reduce a farm’s water consumption by as much as 60 percent and increase crop yield by 90 percent, compared with conventional irrigation methods. But these systems are expensive, particularly in off-grid environments where they cost farmers more than $3,000 per acre to install.
Now engineers at MIT have found a way to cut the cost of solar-powered drip systems by half, by optimizing the drippers. Furthermore, these new drippers can halve the pumping power required to irrigate, lowering energy bills for farmers. The team modified the drippers’ dimensions in a way that significantly reduces the pressure required to pump water through the entire system, while still delivering the same amount of water.
The team, led by Amos Winter, an assistant professor of mechanical engineering, plans to further modify the system upstream, optimizing the tubing, filters, pumps, and solar power system to ultimately make drip irrigation affordable for farmers in developing regions of the world.
“Many small farmers in India make only a few hundred dollars a year, so a drip irrigation system is way outside their price point,” Amos says. “Low-cost drip systems could help them increase their yield and income, so they can get out of the cycle of poverty.”
The team has published its engineering theory on dripper design in PLOS One. The paper’s co-authors are lead author and graduate student Pulkit Shamshery, former MIT postdoc Ruo-Qian Wang, and undergraduate Davis Tran.
“The silver bullet”
Today, farmers in India and other developing parts of the world mainly grow crops using flood irrigation, an ancient, low-tech method that involves flooding fields with redirected river or groundwater. While this method is inexpensive, farmers have little control over when and how much to water their crops. Flood irrigation is also inefficient, as most of the water not taken up by plants either evaporates or drains away.
“The silver bullet here is drip irrigation … but it’s exorbitantly expensive,” Winter says. “The main cost driver is the pump and power system. That laid the foundation for our research project: Could we make drippers that operate on much lower pressures, and thus cut the pumping power and the capital costs?”
To do this, the researchers set out to characterize the behavior of existing “pressure compensating” drippers — drippers designed to maintain a constant flow rate, regardless of the initial water pressure that is applied. Such a feature enables every dripper along a tube to deliver the same water flow throughout a farm field, regardless of how far away an individual dripper is from the central pump.
Most conventional drip irrigation systems are designed to operate the drippers at a pressure of at least 1 bar. To maintain this pressure requires energy, which constitutes the main capital expense in off-grid drip irrigation systems, and the primary recurring cost in on-grid systems. Winter and Shamshery aimed to design pressure-compensating drippers to operate at 0.1 bar — one-tenth of the pressure of commercial systems. This reduction can halve both the power required to pump water through the drippers and the capital cost of an off-grid drip system.
The team set out to characterize the features in drippers that produce a pressure-compensating effect. To do this, they first generated a model of a conventional pressure-compensating dripper in MatLab, a numerical computing program that enables researchers to change the dimensions of a model to produce a change in behavior. In this case, Shamshery studied the dynamics of water flowing through the modeled dripper, and then came up with a mathematical description to explain how a dripper’s internal features affect fluid flow and water pressure.
Shamshery then coupled the mathematical model with a genetic algorithm — a computer program that simulates evolution of, in this case, various parameters in a dripper. For instance, the team selected a range of dimensions for certain features and tested their flow behavior in simulation. They discarded those dimensions that produced undesirable water pressure, and kept the better performers, which they fed back into the algorithm with a new set of dimensions.
“We let this evolve through multiple generations,” Shamshery explains. “You end up expressing the features and geometries that give you good performance, and you kill off the features that give you bad performance.”
They evolved the dripper’s dimensions to a geometry that produced an optimal flow rate with an initial pressure as low as 0.15 bar. Using these optimal dimensions, the team fabricated a few dripper prototypes and tested them in the lab, with results that matched their simulations.
Winter is now working with the United States Agency for International Development (USAID) and Jain Irrigation, a major manufacturer of drip irrigation systems, to test the optimized drippers in Morocco and Jordan, where he says there is a push to shift farmers to drip irrigation.
“With these drippers, poor farmers can now grow higher-value crops, like off-season crops that they couldn’t grow unless they had rain, and make more money to try and get out of poverty,” Winter says. “In places like California, with a history of blackouts, this means not only less water consumption, but less energy [used] for agriculture.”
Next, the team plans to optimize the rest of the drip irrigation system, which will further reduce the system’s cost. The researchers will pilot solar-powered drip irrigation systems in Jordan and Morocco with USAID in the coming two years.
“It turns out there is a massive untapped market in off-grid situations,” Winter says. “If you look at the developing world, there are about half a billion small farms with 2.5 billion people. For them, this technology could be a game-changer.”
This research was supported in part by USAID, Jain Irrigation, and the MIT Tata Center for Technology and Design.
Imec Develops Bifacial n-PERT Solar Cell with a Record Percent Front-Side Efficiency
Imec announced it has realized bifacial n-PERT solar cells using an industrially-compatible process with a record-setting front-side conversion efficiency of 22.8 %. Used bifacially under standard front illuminations conditions in conjunction with an additional 0.15 sun rear illumination, these cells can produce the equivalent energy of 26.2 % monofacial cells, as the research and innovation hub in nano-electronics, energy and digital technology and partner in EnergyVille points out.
With a projected potential low cost-of-ownership at module level (< 0.30 $/Wp), Imec’s newly developed bifacial cell technology allows a further reduction of the levelized cost of electricity (LCOE) of large photovoltaic (PV) installations.
Featuring a transparent backside and comparable front- and back contact schemes, bifacial solar cells capture light on both sides of the cell. As a result, they also profit from indirect light, light reflected by the ground and buildings, diffuse light on overcast days, and even direct light at sunrise or sunset, incident on their rear surface.
Tests indicate that, over the course of their lifetime, cells like the one introduced by Imec may generate 10 – 40 % more electricity than traditional monofacial cells, depending on their bifaciality, the PV installation properties and the reflection or albedo of the location. This may result in an estimated LCOE reduction for PV installations of 10 up to 30 percent.
Imec’s bifacial n-type PERT cells (Bi-PERT) have thin and narrow (< 20 µm) nickel-silver (Ni/Ag) plated fingers on both the n+ and p+ side of the cell. The cells’ contacts were fabricated in a patented process of simultaneous plating both cell sides. This cell plating is performed on cassette level (simultaneous plating on a full cassette of wafers in a chemical bath) without the need for an electrical contact to be made to the substrates. This resulted in a solar cell batch with an average conversion efficiency of 22.4 percent, with the best cell topping 22.8 percent, which is a record for this type of cell. These outcomes were measured internally, based on an ISE CalLab calibrated reference cell, with a GridTOUCH system under standard test conditions using only front side illumination and a non-reflective chuck.
Filip Duerinckx, principal engineer at imec, said: “Our Cost-of-ownership calculations indicate that this new cell technology has the potential for an exceptionally low cost-of-ownership at module level (< 0.30 $/Wp). This results from the low-cost patented metallization, the fine finger contacts, and the potential of multi-wire interconnection schemes. Especially the very limited use of silver compared to traditional screenprinted bifacial cells has a beneficial impact on the cost. As for the bifacial aspect: our cells have a near
100 percent bifaciality, which maximizes the bifacial gain. We are now working to demonstrate this technology on full 60-cell modules with wire interconnection, which we expect will reveal the full potential of this promising bifacial technology on an industrial level.”
Imec will showcase its silicon and perovskite photovoltaic technologies at SNEC, the biggest PV trade show worldwide, April 19-21, 2017 (Shanghai New Int’l Expo Center, Shanghai, China) Booth E2.573
Front and rear-side of imec’s Bi-PERT bifacial cell with up to 22.8% front-side efficiency and near 100% bifaciality.
SOLAR POWERED SMART FENCE
Equipped with high-tech versions of common city fixtures — namely, smart benches and digital information signs — and fueled by a “deploy or die” attitude, MIT Media Lab spinout Changing Environments is hoping to accelerate the development of “smart” cities that use technology to solve urban challenges.
“The idea is to bring simple technologies to the streets,” says CEO Sandra Richter, a former Media Lab researcher who co-founded the startup with Nan Zhao, a Media Lab PhD student, and Jutta Friedrichs, a Harvard University graduate. “When it comes to smart cities, there’s been a lot of talking, but not a lot of doing. If you don’t want this [smart city] concept to die, you need to bring real-world examples to the places where we live, work, and play.”
The women-founded startup is the brains behind the Soofa Benches that have cropped up around Boston and Cambridge, including on MIT’s campus. The benches contain an embedded charging station powered by a mini solar panel, with two USB ports for plugging in mobile devices. They also connect to wireless networks.
First installed in Boston in June 2014, the benches are now in 65 cities across 23 U.S. states, including in New York; Washington; Los Angeles; Boulder, Colorado; Oklahoma City; and Austin, Texas. Cities in Canada, Costa Rica, Saudi Arabia, and Germany have adopted the benches as well. The startup also sells a Soofa charging station independently, which can be integrated into existing city infrastructure.
Recently, Changing Environments starting deploying its second solar-powered product, the Soofa Sign, in Metro Boston spots including in Kendall Square in Cambridge, Samuel Adams Park in Boston, and Porter Square in Cambridge and Somerville. Each sign has apps installed that display public transit times, weather, and events, among other information. This month, the startup will select three additional cities where it will pilot the Soofa Sign.
Each Soofa product comes equipped with sensors that gather pedestrian-traffic data for cities, and can be considered part of the “internet of things” (IoT), in which many kinds of everyday devices are wirelessly connected and exchange data. This data can be used by cities to make decisions about funding city developments, events, and other initiatives that impact the public.
Deploy or die
Richter and Zhao came together in the Media Lab after realizing they shared similar interests in developing “persuasive” technologies that helped people live healthier and more sustainably.
Richter studied in the Changing Places group led by Principal Research Scientist Kent Larson, where she designed technologies and apps that encouraged people to bike more, use electric cars, and maintain other healthy practices. (Richter was named one of the most creative people in business by Fast Company in 2013 for her work at the lab.) Zhao, a student in the Responsive Environments group led by Joseph Paradiso, the Alexander W. Dreyfoos Professor in Media Arts and Sciences, develops technologies that help people save energy by using less light. The startup’s name, in fact, is a combination of the two group names.
Many of Richter and Zhao’s projects centered on building for smart cities, in which IoT devices would collect data to help improve efficiency of services and meet residents’ needs. As a side project, in 2013, they decided to build an IoT fixture that could be easily deployed in urban areas and would benefit the public.
“And what is better than a park bench?” Richter says. “It’s something we have all around the globe, has existed for centuries, and is a place for people to connect with each other. For us, that was the ideal platform to start introducing sensors into the public environment.”
From there, things moved quickly. Influenced by the Media Lab’s oft-repeated motto, “deploy or die,” Richter and Zhao, then joined by Friedrichs, developed a concrete prototype of the current Soofa Bench model, “every now and then turning the Media Lab into a concrete mess,” Richter says, laughing.
Thanks to a meeting facilitated by Larson with Boston’s Mayor’s Office of New Urban Mechanics, the first Soofa Bench prototype was installed in Titus Sparrow Park in June 2014. One week after, Richter took the prototype to the first White House Maker’s Faire, where she sat down with then-President Barack Obama to discuss the bench and the future of smart cities.
Upon returning to Boston, the three co-founders embarked on a “crazy summer where everything happened,” Zhao says.
Verizon and Cisco — which invests in IoT technologies — had funded the students to develop more Soofa Benches. But the students didn’t even have a company bank account. “So literally a couple days before Cisco transferred money, we said, ‘Alright, we need to start a company,’” Richter says.
Naming themselves Changing Environments, the students cranked out about 10 benches in the Media Lab as part of a pilot launch for spots in the Boston Common, the Rose Kennedy Greenway, and other Boston locations. In mid-2015, Changing Environments opened headquarters in East Cambridge and brought its first commercial Soofa Bench to Central Square, in Cambridge, before spreading to dozens of other U.S. and international cities.
An icon for IoT
Today, the Soofa Benches are certainly seeing use. Charging activity is tracked at headquarters where, in a lighthearted competition, the office has a “bench leadership board” with benches that see the most charging activity. Currently holding the top spot is “Amelia,” the startup’s first commercial bench in Cambridge’s Central Square, with 1,817 total hours charged over a total of 3,571 charging sessions, as of mid-January. (Soofa encourages cities to name each bench to keep things amusing and engaging.)
Benches in Harvard Square and on the Rose Kennedy Greenway have logged around 2,500 charging sessions. Some newly installed benches in New York City, which were just implemented in May 2016, already have more than 2,000 sessions charged.
On the back end, Soofa fixtures collect valuable data for the city governments that purchase them. The sensors count the wireless signals emitted from pedestrians’ mobile devices and assign an activity level for the location. Cities can use Soofa software to check if activity was high or low in certain areas at certain times. A city may note, for instance, that a certain event drew a big crowd and may decide to host similar events.
More broadly, Richter says, installing Soofa Benches — often a publicized event — can open discussions about smart cities. When benches are installed in a new city, the mayor or other city official usually meets the co-founders at the bench to discuss the technology and its benefits and limitations. In that way, Soofa serves as “an icon for internet of things in cities,” Richter says.
The MIT connection
Now a thriving startup, Changing Environments owes some of its success to MIT’s entrepreneurial ecosystem, the co-founders say, including an early investment from the Media Lab’s E14 Fund, which provides stipends, mentoring, introductions to investors, and basic legal and accounting services to recent MIT graduates such as Richter.
The E14 Fund, Richter says, gave her a great “runway” for transitioning from student to entrepreneur. “It’s like you’re still under the wing of the lab, but you’re just learning how to fly,” she says.
The newly deployed Soofa Sign, Richter adds, came about through a collaboration with MIT spinout E Ink — which invented electronic ink for e-readers and other devices — that was initiated by Joi Ito, director of the Media Lab. “It’s beautiful to see two MIT companies working together to push the envelope on a product,” Richter says.
This winter, MIT professors also helped the startup recruit interns for the Institute’s Independent Activities Period. And mentors still offer advice when needed. “It’s been great to continue the relationship with professors, students, and the MIT community as a whole,” Richter says.
17.08.2011 Suntech Power
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13.07.2011 by Andrew Galligan
DC Passes Bill to Revitalize Solar Industry
In a major victory for the DC solar market earlier this afternoon, the Council of the District of Columbia unanimously voted in favor ofThe Distributed Generation Amendment Act of 2011. This bill is expected to be signed by the mayor within the next 10 days, and its passage will significantly improve the market for DC Solar Renewable Energy Credits (SRECs) and solar energy generally. The legislation will amend the District of Columbia’s Renewable Energy Portfolio Act to significantly increase the demand for solar energy and ensure the RPS benefits the residents of the District.
The Distributed Generation Amendment Act of 2011 is expected to create over 1500 new green jobs and direct around a billion dollars in investment into the District of Columbia over the next 10 years. This investment stream will generate revenue opportunities for the city and mitigate up to 53,000 tons of carbon dioxide, making for a cleaner, safer, and healthier Washington, DC. Perhaps most importantly, this legislation will facilitate innovative business models that will allow District residents and businesses of all economic backgrounds to adopt solar energy that will provide them with reduced energy bills over the next 30 years.
The legislation comes at a time when the substantial decrease in SREC prices coupled with the exhaustion of the DC Renewable Energy Grant program appeared potentially fatal to a previously booming DC solar market. Energy suppliers (who are mandated by the RPS to procure a certain percentage of solar electricity or pay an alternative compliance fee) could easily fill their quota for solar electricity by purchasing SRECs from systems in states outside the District. This oversupply drove down prices, which led to DC solar businesses and potential customers losing faith in SRECs, one of the key financing tools for a solar system (Income from SRECs typically covers 20 to 40% of a solar system’s cost).
The passage of the Distributed Generation Amendment Act will catalyze the DC solar market. Starting in 2011, the solar requirement for energy suppliers in DC will increase annually to higher percentages than the original RPS. Furthermore, energy suppliers will no longer be able to purchase out of state SRECS to meet their demand. With solar module prices continuing to drop, the passage of this amendment puts DC in a great position to take advantage of one of the fastest growing industries in the country. Solar energy businesses in the District can rely on SRECs for financing, which will lead to significant employment opportunities, stimulate direct commercial investments in the city, and raise the profile of Washington, DC as a leader in green industry.
"This is a huge victory for DC and the solar industry at large," notes Yuri Horwitz, CEO of Sol Systems, a solar finance company based in the District. "This legislation is a direct result of the hard work and dedication of the local solar community working in concert with District’s City Council to craft a piece of legislation that is both realistic and game changing. We have all seized the future."
Photovoltaic (solar cell) Systems
Solar cells convert sunlight directly into electricity. Solar cells are often used to power calculators and watches. They are made of semiconducting materials similar to those used in computer chips. When sunlight is absorbed by these materials, the solar energy knocks electrons loose from their atoms, allowing the electrons to flow through the material to produce electricity. This process of converting light (photons) to electricity (voltage) is called the photovoltaic (PV) effect.
Solar cells are typically combined into modules that hold about 40 cells; a number of these modules are mounted in PV arrays that can measure up to several meters on a side. These flat-plate PV arrays can be mounted at a fixed angle facing south, or they can be mounted on a tracking device that follows the sun, allowing them to capture the most sunlight over the course of a day. Several connected PV arrays can provide enough power for a household; for large electric utility or industrial applications, hundreds of arrays can be interconnected to form a single, large PV system.
Solar shingles are installed on a rooftop. Credit: Stellar Sun Shop
Thin film solar cells use layers of semiconductor materials only a few micrometers thick. Thin film technology has made it possible for solar cells to now double as rooftop shingles, roof tiles, building facades, or the glazing for skylights or atria. The solar cell version of items such as shingles offer the same protection and durability as ordinary asphalt shingles.
Some solar cells are designed to operate with concentrated sunlight. These cells are built into concentrating collectors that use a lens to focus the sunlight onto the cells. This approach has both advantages and disadvantages compared with flat-plate PV arrays. The main idea is to use very little of the expensive semiconducting PV material while collecting as much sunlight as possible. But because the lenses must be pointed at the sun, the use of concentrating collectors is limited to the sunniest parts of the country. Some concentrating collectors are designed to be mounted on simple tracking devices, but most require sophisticated tracking devices, which further limit their use to electric utilities, industries, and large buildings.
The performance of a solar cell is measured in terms of its efficiency at turning sunlight into electricity. Only sunlight of certain energies will work efficiently to create electricity, and much of it is reflected or absorbed by the material that make up the cell. Because of this, a typical commercial solar cell has an efficiency of 15%-about one-sixth of the sunlight striking the cell generates electricity. Low efficiencies mean that larger arrays are needed, and that means higher cost. Improving solar cell efficiencies while holding down the cost per cell is an important goal of the PV industry, NREL researchers, and other U.S. Department of Energy (DOE) laboratories, and they have made significant progress. The first solar cells, built in the 1950s, had efficiencies of less than 4%.
Photovoltaic (solar cell) Systems content for this section provided in part by the National Renewable Energy Laboratory and the Department of Energy.