Standard Renewable Electricity Supply for People in Rural Areas - Mini Grids in Western Provinces of China - Michael Wollny SMA Technologie AG Hannoversche Str. 1-5 34266 Niestetal /Germany Phone: +49/561/9522-4122 Fax: +49/561/9522-304 Email: Michael.Wollny@SMA.de Abstract: The AC coupling has proven itself in different kinds of systems during the last couple of years. Especially in the electrification of remote areas off the grid, this technology ensures a flexible energy supply. Projects all over the world show how important this technology already is and will be for the configuration of well functioning island grid systems. This systems technology will further expand its position in other international projects in the years to come. The modularity of the system made it easy to adjust the systems without any great difficulty to the demands of the energy supplier or of the end-users. System integrators like Shell Solar or Schott Solar connect these new technologies with their long-term experience and implement them successfully. Keywords: Standalone PV System, Rural Electrification, Hybrid, Mini Grid 1. Introduction Due to the dynamic industrialization in China in recent years a long-term and reliable energy supply becomes more and more important. Major parts of the rural population in China cannot be connected to the existing electricity grid. The reason is that remote villages in the western and southwestern regions, in particular Xinjiang, Yunnan, Gansu, as well as Tibet, Qinghai and Inner Mongolia, are too far away from the public grids. Many households will not be connected to the public grid in the medium and long term. Further reasons are unfavorable topographic conditions, low settle-
ment density and a resulting low energy consumption. An extension of the grid system is thus not reasonable from an economic point of view. An estimated 500 million people in China could leave their settlement area within the next ten years. A mammoth process of urban development as well as the complete depopulation of rural areas that would be fatal for China's cultural development are the results. Figure 1: The German Bank of Reconstruction (KfW) supports the development of off-grid electricity supply systems in the provinces of Yunnan, Xinjiang, Qinghai and Gansu. In this context, the Chinese government initiated a program already in 1996. The purpose of this program is to provide the rural areas in the Western provinces with electricity by decentralized power supply systems, mainly by photovoltaic and wind power plants, by 2010. In the framework of the Sino-German Financial Cooperation the Chinese Ministry of Finance (MoF) and the German Bank of Reconstruction (KfW) decided to contribute to the Chinese "Brightness Program" with the "Solar Energy Program" by means of photovoltaic hybrid (PVH) plants for remote villages. 2. Advanced System design of AC Coupling provides Flexibility Within a first batch, more than 120 villages in this four provinces were equipped with PVH village systems up to now. Further more than 200 villages will be equipped with
PVH village power systems in the year 2006/2007 based on the results of the first batch. The off-grid power supplies are designed as AC-coupled mini grid systems allowing simple and cost-effective grid-connection of the energy sources and consumers on the AC side. Due to the modular design other suppliers, such as wind or hydroelectric power plants, they can be integrated in addition to the energy sources of the photovoltaics and generators currently used. The advanced systems technology of AC coupling together with the communication less parallel operation of voltage-controlled energy sources set new standards. Due to parallel operation Sunny Island systems can be freely scaled in terms of their power and simply upgraded in case of increasing consumer power. The power range of these island grids is 3 to 100 kw. Single- and three-phase solutions are possible. The systems have a number of advantages in terms of plant layout, expandability compatibility and design reducing the specific system costs as well. From an economical point of view, small island grids with a battery bank are more cost-effective than plants where diesel sets are exclusively used. Figure 2: AC-coupled power supply structure; largest installation for villages in the west provinces of china.
Even larger PV-Hybrid systems (5-30 kw) using diesel sets in order to avoid a longterm battery storage can be operated at lower costs than stations exclusively using diesel sets. 3. PVH-Power Supply for Village Electrification The heart of a decentralized power supply is the battery inverter Sunny Island 4500. It can be used for single-phase island grids of 4.5 kw consisting of one single Sunny Island 4500 up to systems with a 3-phase supply and virtually all power ranges by connecting several devices in parallel operation. 30 26 26 PV/Hybrid Installation 25 20 15 10 7 8 21 19 9 Qinghai Yunnan Xinjiang 5 3 2 Gansu 0 1-phase without Genset 1-phase with Genset 3-phase with Genset Figure 3: Type of installation in the west provinces of China up to now. The individual PV generators have a power between 4.5 kwp and 18 kwp depending on the size and infrastructure of the village. Three basic systems are installed for the 120 villages up to now. The single-phase PV off-grid systems consists of at least two battery inverters Sunny Island 4500 (9 kw), two or three string inverters Sunny Boy SB 3000 (3-9 kw AC), the battery unit with an energy content of 72-108 kwh and a Sunny Boy Control Plus plant monitoring system. In case of larger villages with more than 30 households an additional diesel set (10-25 kva AC) was installed.
4. Evaluation of data from the operation In all villages, the most important data for the verification of operation is continuously recorded by a plant-monitoring unit designed by SMA. The local installers in each province visit the sides every six months to download data form the monitoring system. 01.12.04 08.12.04 15.12.04 Figure 4: Evaluation of a PVH-village electrification system in Yunnan First evaluation results of a PV system equipped with PV and generator in Yunnan in December 2004 show the principle of operation. A comparison of the solar power (green graph on top) of Sunny Boy string inverters, actually consumed power (blue graph) and the available power of the Sunny Island battery inverter (red graph) reveals that the most of the energy form solar was stored in the battery. The village energy consumption during these 14 days is low. At night, the most energy is taken from the battery. The yellow graph shows the calculated battery state of charge. From 50 % state of charge the Sunny Island stopped the generating of an island grid in order to save battery lifetime.
5. References [1] Engler, A., Hardt, C.; Bechtel, N.; Rothert, M.; Next Generation of AC-coupled hybrid systems 3-phase parallel operation of grid forming battery inverters; 2nd European PV-Hybrid and Mini-Grid Conference; Kassel, Sep. 2003. [2] Cramer, G; Rothert, M.; Die Zukunft der ländlichen Elektrifizierung Feld-erfahrung mit AC-gekoppelten Hybridsystemen; Erneuerbare Energien: Heft:10/2003. [3] Klinghammer, W; Shenghong, Ma; A New Vision for Remote Villages in Western China: Village Electrification by PV Hybrid Plants - The Solar Energy Program of MoF and KfW in China 2 nd European PV Hybrid and Mini Grid Conference Sept. 2003, Kassel, Germany. [4] Wollny; M.; Zeller, V.; Die AC-Kopplung für netzferne Dorfstromversorgung in China; 20. Symposium Photovoltaische Solarenergie Kloster Banz, Bad Staffelstein, März 2005, Germany. [5] Wollny, M.; Mark, P., Off-Grid Electricity Supply with AC Coupling - Further Trend for Solar Village Electrification in Provinces of China - 15 th International Photovoltaic Science and Engineering Conference, & Solar Energy Exhibition, Shanghai, China 2005.