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Renew | May 2014

Grid management for green players

As the proportion of total electricity generation accounted for by renewable energies increases, what the grid operators demand from the generators is also changing. Dr. Eberhard Ritzhaupt-Kleissl examines some of the latest technologies being utilsed for managing grids

Siemens Energy has developed a solution that meets all the needs of the power grid operators, especially with regard to the volumes of energy fed in. Because it enables a solar power plant to be both monitored and controlled remotely, operators can act quickly to resolve problems and minimise any loss of yield. The solution can be integrated into new and existing plants and monitoring systems, enabling even globally distributed PV plants to be managed centrally.

Reliable operation and dependable yield forecasts
According to a report issued by the European Photovoltaic Industry Association (EPIA) in March 2013, last year saw the world's cumulative photovoltaic capacity break through the 100 GW sound barrier. In 2012, almost one third of this capacity - around 30 GW - was added by newly built PV installations, as stated in the EPIA report "Global Market Outlook for Photovoltaics 2013-2017". Markets outside Europe were at the very forefront of this growth. This is particularly true of China, the USA and Japan, which together accounted for 8.5 GW of new PV capacity, although strong growth was also seen in India, Australia, Korea, Canada, Israel and Thailand. In terms of installed capacity, however, Germany remains the leader, accounting for 32 GW or one third of the world's existing PV capacity. The total capacity attributable to Europe as a whole at the end of 2012 was 69 GW. In other words: the world has woken up to the advantages of generating electricity directly from sunlight. Experts are anticipating an annual growth rate of around 27% between 2010 and 2020.

As the proportion of total electricity generation accounted for by renewable energies increases, what the grid operators demand from the generators is also changing. In future, all power producers will have to play an active role in stabilizing the grid, and the controllability of renewable energy generation will have to be improved. Grid operators require better forecasting of the energy that will be generated so that they can dispatch the individual producers to match the load profiles, which fluctuate from day to day. To this end, the volume of energy that will be generated must be as predictable as possible. This applies not just to the grid operators but depending on the grid code รป especially to the plant operators. Furthermore, PV plants often need to be integrated reliably into existing generation fleets. Many PV monitoring systems currently available on the market do not meet these various criteria to the required extent and depth. Against this background, Siemens has developed a solution that not only satisfies these needs but also enables the efficient control and monitoring of photovoltaic plants. The Siemens PV Monitoring solution is based on the globally successful control system SPPA-T3000, which is implemented in more than 1,700 power plant units and has been adapted for use in the field of renewable energies, including in particular small and medium-sized PV parks.

Real-time monitoring of PV plants
All process data of a PV plant - that is, data from the PV modules or individual strings, the weather station, the switchgear, the fire detection system, the transformer, the ventilation system, and so on - is collected and forwarded to the local automation server. This field level forms the first level of a four-level pyramid that represents the entire Siemens solution. The field data from the individual containers is finished with a timestamp and forwarded to the central SPPA-T3000 Application Server. This second level controls the inverters and the grid parameters - the active and reactive power and the frequency. Any installed tracker systems can also be controlled via this server. At the same time, local key performance indicators (KPIs) and technical reports (performance ratio, generated energy volume, alarm messages, and so on) are calculated from the field data and made available here. At the third level, the Siemens Energy Asset Management (EAM) software SPPA-M3000 evaluates the plant data provided by the application server and, from this, calculates all the economic key figures and provides a yield forecast up to seven days in advance. Such yield forecasts play a particularly important part in ensuring that the grid requirements are met in terms of the volumes of energy fed in. In preparing short-term and medium-term yield forecasts, the Siemens solution considers current weather data as well as forecasts issued by meteorological services, enabling it to provide each dispatcher with highly reliable specifications for grid feed-in and trading. Data is transferred from all PV plants monitored by Siemens via the Siemens common Remote Service Platform (cRSP), a gateway that is secured and encrypted to current NERC standards. The data is archived on particularly secure servers in a data center for at least 30 years, ensuring complete documentation and providing the basis for subsequent detailed fault analysis. The browser-based Siemens PV Portal represents the fourth level - the presentation level - of the PV Monitoring solution. All previously calculated KPIs and trends are visualized here; at the touch of a button, the data from all PV plants can be displayed according to certain criteria (such as performance ratio, CO2 reduction and economic key figures). If several systems are connected to the PV Portal, customers can also compare their systems directly with one another using configurable reports.

The Siemens PV Portal also enables direct access to all hardware elements of the monitored PV plants in real time via the secure gateway connection of the cRSP, for example to perform remote maintenance on I&C and electrical system components. Just like conventional power plants, solar power plants must undergo continuous monitoring and regular maintenance in order to ensure continuously reliable operation. Faults must be identified as quickly as possible in order to avoid consequential damages and minimise any loss of yield. Furthermore, permanent monitoring is important in order to maximise the electricity yield from a PV plant. Dirt or shadows are the main causes of an electricity yield that falls significantly below the plant's rated output. For this reason, regular cleaning of the modules is one of the most frequent PV plant maintenance tasks; failure to carry it out can cause yields to fall significantly, depending on the region.

Optimum energy yield through continuous monitoring and regular maintenance In Germany, PV plants require less frequent cleaning, as regular rainfall rinses the dirt from the solar panels. In other countries, however, climatic conditions often make it necessary to implement a rigorous cleaning program. In the United Arab Emirates, for example, sharp temperature fluctuations and the proximity to the ocean mean that maintenance of this kind must be performed every 14 days to remove the salt encrustations that can form rapidly on the modules. In other regions, vegetation must be removed regularly from underneath and around the modules to prevent it from casting a shadow. Thanks to accurate data collection and evaluation, the Siemens solution makes it possible to determine the optimum cleaning schedule for each individual plant or module, based on the most efficient ratio of cleaning cost to energy yield. Siemens offers flexible service packages to customers who do not wish to carry out all monitoring and maintenance activities themselves: from remote monitoring through to operation of the entire plant. Siemens offers a full service package of this kind to customers who view their PV plants primarily as investments.

Futureproof solution for PV plants with profound benefits
The integrated Siemens PV Monitoring solution offers operators of PV parks and fleets a range of advantages - demonstrated, for example, in projects already completed in Israel (5 MWp) and South Africa (twice 50 MWp):

  • High reliability of I&C system and monitored electrical systems
  • Full compliance with all requirements of the electricity grid operators (grid code)
  • Option of integration into existing power generation fleets (fossil and renewable) and extendability of installed capacity or energy storage devices through implementation of a solution based on the market-leading control system SPPA-T3000 and EAM software SPPA-M3000
  • Dependable predictability of the energy volume generated (up to seven days in advance) through precise data detection and evaluation, reliable operation, and consideration of meteorological information and complex forecast algorithms
  • Secure, encrypted data transfer and remote access to control and electrical systems via NERC-compliant gateways
  • Web-based PV Portal with access to all information and KPIs, anytime and anywhere
  • Customer-specific service packages to maximise energy yield.
  • The author is a Solutions Manager with Siemens Energy
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