Technical Papers

The Spanish company Bornay Aerogeneradores has specialized in the construction of small wind turbines primarily for private use. To increase economic effectiveness and efficiency of its installations Bornay uses feed-in converters of SIEB & MEYER AG.

Besides China with installed wind capacities of about 45 GW, the USA (40 GW) and Germany (about 27 GW), Spain is one of the largest producers of wind-generated electricity[1]. In 2010 the share of wind energy was 14.4 percent of the national electricity consumption (with regard to an average wind year) – the 3rd place behind Denmark (24 percent) and Portugal (14.8 percent). In the statistics Germany is ranking 5th.

The political will to expand wind energy contributed to the development of a new industry in Spain, Germany and Denmark and opens up new markets. The Spanish manufacturer of wind turbines Bornay Aerogeneradores is one of the companies operating in this new business sector and benefiting from the growing markets, just as SIEB & MEYER AG with its feed-in technology products for renewable energies.

Clean Energy

Since 1970, the Spanish company has been developing and producing wind turbines. Today, Bornay is one of the world's leading manufacturers of small wind turbines. "Our target is to bring clean power  to areas which are not electrified today", says Juan de Dios Bornay, CTO at Bornay and son of the company founder. Today his company produces five variants of small wind turbines with rated powers up to 6 kW in series and has installed more than 4,000 wind turbines in over 50 countries. Combined with control system, inverter and storage batteries, all these small wind turbines serve primarily for power supply of private homes as well as agricultural and small or medium-sized commercial buildings.

The larger turbines Bornay 1500, 3000 and 6000 however, can also be used for feeding power into the public grid. To make power generated by wind energy available for own power needs or feed surplus energy back into the 230 V grid, these small wind turbines require a special grid-tie inverter transforming the three-phase alternating current produced by the generator of the wind turbine into  grid-compliant single-phase current. Changing wind conditions require a special control system, allowing optimal controlled operation and power feed-in during different wind conditions. Until now, Bornay used modified photovoltaic inverters, but was not satisfied with this suboptimal solution. "In search of more economic solutions, we came across the aeocon feed-in converters by SIEB & MEYER some years ago", says Vicente Martinez, head of the technical development at Bornay. "These devices are specially conceived to the needs of small wind turbines and offer many advantages to us", he adds.

Smart All-rounder

The feed-in converter aeocon for small wind turbines unites all components required for operation in one compact housing. The combination of rectifier, inverter including galvanic isolation and ballast circuit in one device allows minimizing the time and effort for installation as well as initial operation. In addition the required installation space is considerably smaller than that of conventional devices. "The specific construction of aeocon allows for direct control of the switchable external ballast resistor, which is required during startup and as overvoltage protection", says Ralph Sawallisch, key account manager for feed-in technology at SIEB & MEYER. The control of the feed-in converter is especially adapted to the requirements of small systems allowing excellent control of the different operating states under consideration of the characteristic curve of the system: This ensures smooth startup of the small wind turbine and selection of the optimum operating point during different wind conditions. Thus, aeocon compensates for mechanical construction tolerances of the small wind turbine. By means of the wide range power input and the control along the optimum characteristic curve of the system the best possible efficiency is reached particularly during partial-load conditions. This has positive effects on the energy yield.

Besides the control tasks the maintenance-free device fulfills various protective functions during operation, for example the deceleration of the wind turbine in the event of a power failure. During this process the rotor is loaded controlled by the external brake resistor. "The integrated brake function was especially important for us in order to achieve better control of the wind turbine", says Vicente Martinez. If the wind turbine generates more power than can be supplied to the grid, the feed-in converter activates the integrated ballast resistor control. Excess energy up to five kilowatts is discharged securely and the thermal heat produced could be used e.g. as support for the heating system.

30 Percent Surplus

The device is to be connected single-phase to the 230 volts grid. Depending on the used aeocon – SIEB & MEYER offers the series 4000 and 5000 – the grid feed-in power is 4 or 5 kilowatts. The integrated galvanic isolation allows parallel connection of several devices. In this way three-phase small wind turbines up to 15 kilowatts can also be equipped with the devices. By means of the COM-Box the feed-in converters communicate with each other and are able to react accordingly in the event of an error. In addition the devices provide potential-free relay contacts for a higher-ranking control of handshake signals. Thus, the control of the small wind turbine is permanently informed about the operating status of the aeocon. "Especially the new series aeocon 4000 and 5000 stand out for their increased braking power and greater operating safety. The control characteristics are improved further compared to former device versions. In times of strong wind the devices supply more energy for a short time, now", Ralph Sawallisch explains. All devices come with protection class IP 54, which makes operation in covered outdoor areas possible. The connection area of the feed-in converter aeocon can be accessed easily making the work of the engineer more comfortable. "The SIEB & MEYER inverters can be combined with devices provided by various manufacturers. Operation and monitoring via computer are less complicated compared to other feed-in converters", Martinez confirms. By now, he employs the aeocon devices for half a year. His experience: With the new feed-in converter the energy yield of the small wind turbine is about 30 percent higher than before. "We need more knowledge though to confirm this value for sure. But at any rate the systems run more efficient and longer than before, since the wind turbine is able to produce power even at low wind speeds with aeocon. In addition the devices are maintenance-free", says Vicente Martinez.