in turn, influence the selection and placement of the individual components which include the PV arrays with their solar modules, inverters and wiring, not to mention access roads. Until now, engineers have designed solar power plants using CAD programmes, with every layout and every variation painstakingly generated separately. This is a very time-consuming approach. To improve a planned power plant in terms of certain criteria or to compare different concepts with one another, often the entire planning process has to be repeated. Now Fraunhofer Institute for Industrial Mathematics ITWM in Kaiserslautern, in collaboration with Siemens Energy Photovoltaics, has developed new planning software that tackles these woes. “Our algorithms, programmed exclusively for the Siemens PVplanet (PV Plant Engineering Toolbox) software, provide engineers with several hundred different plant designs in a single operation. It takes less than a minute of computation time,” said ITWM researcher Dr Ingmar Schüle. The only user-inputs are parameters such as the topography of the construction site and the module and inverter types that will be used. The user can also change a number of parameters – such as the orientation, spacing and inclination of the solar arrays – to study the impact on the quality of the planning result
Cost estimates and income calculations included
To evaluate the designed PV power plants, an income calculation is performed that includes a simulation of the weather in the region, the course of the sun throughout the year and the physical module performance including shading effects. With the results of this computation and an estimate of the investment and operating costs, the planning tool can come up with a figure for the LCOE (Levelised Cost of Energy). By comparing the plant with a
New ‘microbial fuel cell’ cleans municipal sewage and generates electricity at the same time. Credit: Orianna Bretschger, Ph.D.
large number of similar configurations, the planners can investigate the sensitivity of the various parameters to find the right solution from a large array of options. Dr Martin Bischoff, project manager at Siemens Energy Sector, added: “More than anything else, the planning tool provides an overview of the scope for optimisation. This provides the best possible support for planning the most cost-efficient systems. There has been no other planning software with this scope or level of detail until now.”
Cleaning sewage while making electricity
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cientists have described a new and more efficient version of an innovative device the size of a home washing machine that uses bacteria growing in municipal sewage to make electricity and clean up the sewage at the same time. The report was presented at the 243rd National Meeting & Exposition of the American Chemical Society (ACS) in San Diego. Orianna Bretschger, Ph.D., who presented the report at the ACS meeting and her team at the J Craig Venter Institute, is developing one version of a so-called microbial fuel cell (MFC). Traditional fuel cells, like those used on the Space Shuttles and envisioned for cars in the future ‘hydrogen economy,’ convert fuel directly into electricity without igniting the fuel. They react or combine hydrogen and oxygen, for instance, and produce electricity and drinkable water. MFCs are biological fuel cells. They use organic matter, such as the material in sewage, as fuel, and microbes break down the organic matter. In the process of doing so, the bacteria produce electrons, which have a negative charge and are the basic units of electricity. Electricity consists of a flow of electrons or other charges through
a circuit. The new MFC uses ordinary sewage obtained from a conventional sewage treatment plant. Microbes that exist naturally in the sewage produce electrons as they metabolise, or digest, organic material in the sludge. Bretschger found that microbes exist in the MFC community that might even break down potentially harmful pollutants like benzene and toluene that may be in the sludge. An MFC consists of a sealed chamber in which the microbes grow in a film on an electrode, which receives their electrons. Meanwhile, positively-charged units termed protons pass through a membrane to a second, unsealed container. In that container, microbes growing on another electrode combine oxygen with those protons and the electrons flowing as electricity from the electrode in the sealed chamber, producing water or other products like hydrogen peroxide. Bretschger said the MFC also is quite effective in treating sewage to remove organic material, and data suggest a decrease in diseasecausing microbes. “We remove about 97% of the organic matter,” she said. “That sounds clean, but it is not quite clean enough to drink. In order to get to potable, you need 99.99% removal and more complete disinfection of the water.” Still, she suggested their MFC might one day replace some of the existing steps in municipal wastewater treatment. The group presented their first MFC last year. Since then, they increased the amount of waste their device could handle each week from 20 gallons to 100 gallons, trucked in from a local treatment plant near San Diego. They also replaced the titanium components with a polyvinyl chloride (PVC) frame and graphite electrodes. Because of that, the new fuel cell costs about $150 per gallon, half as expensive as their previous prototype. The group hopes eventually to bring the cost under $20 per gallon or less to be cost competitive with existing water treatment technologies. July2012
thehub FEATURE
In the future, large PV plants such as the Siemens solar farm that went into operation in 2011 in Le Mées, France, can be planned quickly and efficiently using the PV planet software solution. © Siemens AG.
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