The concept of Smart Green Tower goes along with the objectives of the Green City and offers much more than just energy self-sufficiency. Furthermore, this battery-operated office and apartment complex is not merely a paper tiger – it is planned to become reality in the German city of Freiburg im Breisgau. Designed by Frey Architekten, with support of Siemens and Fraunhofer Institute for Solar Energy Systems (ISE), the energy concept of Smart Green Tower differs from other self-sustaining buildings producing clean energy for own needs.
Temporarily generated energy surpluses can power neighboring buildings within the smart district
According to the architects, high-performing photovoltaic panels with fabulous low-light performance were developed to cover the façade. They entire module area, consisting of panels on the roof and on the façade, has a power output of about 400kWp. On the one hand, the generated electricity based on renewable energy sources can power the building and charge the planned lithium-ion battery with a capacity of about 0.5 MWh. On the other hand, temporarily generated energy surpluses can be used by other neighboring buildings.
As if that were not enough, the idea of a flexible energy storage with higher capacity makes it possible to connect further energy producers within the quarter. It is possible to handle the energy in an optimal way depending on the current offer, demand but also from a cost perspective within the Smart Green Tower. The aim is to assure balanced energy loads within the urban district through the intelligent connection of the building and the surrounding district. An energy management controls and operates the smart grid in order to become reality.
The 51 meters high main building, including solar panels, with a total gross floor area of approximately 15,000 square meters plus garage offers 70 one to four-room apartments with a gross floor area of about 4,500 square meters. The proposed office space and boarding accommodation cover 3,200 square meters. The western wing of Smart Green Tower will only measure a height of 16 meters. The northern wing with seven stories will be nearly 22.5 meters high. Additionally, the complex provides 250 parking spaces.
The façade solar modules are not just generating clean electricity. They also protect the building from overheating and thus reduce the need of cooling energy. This kills two birds with one stone.
PowerManager will provide “a targeted recording and control of the electrical energy producers, consumers and storage”
It does not suffice that the required energy of Smart Green Tower will be generated from renewable resources. In the best case scenario, the consumption only takes place when the clean electricity is plentiful and available at low costs.
In order to converge towards this objective and provide targeted energy flows, depending on power supplies by renewables or storages and demands to charge the battery or power the tower or adjacent buildings, an energy management system called PowerManager from Siemens will be applied. It enables to analyze and adapt the individual energy consumptions support of installed measuring devices. An Ethernet connection sends the measured information to the designated computer.
The system also allows to deduce measures for energy savings, indicate leaks or failures immediately and increase the energy awareness. The stand-alone power management software collects, monitors, evaluates, presents and archives the data. To put it concisely: the chargeable battery and the energy management system are indispensable components to realize a smart grid and practice self-consumption optimization, load shifting and peak load reduction. The result: greater energy efficiency, reduction of energy supply costs as well as carbon dioxide emissions.
Power supply over a DC-intermediate circuit reduces energy losses
The innovative energy supply concept should not be forgotten. DC-loads are continually increasing. For this reason, the developer decided to operate the building management system with a direct current (DC) transmission and distribution of electric energy, apart from a few exceptions of alternating current (AC).
“In the case of a predominant supply over an AC-coupled photovoltaic battery system, this means that the generated direct current of the PV generator is non-rectified, and subsequently in the case of an intermediate storage rectified again in the battery, then if necessary reconverted again in alternating current and distributed, in order to again be rectified in many devices – with correspondingly high efficiency losses.” Frey Architekten states.
In the case of Smart Green Tower, the battery storage and the photovoltaic system is planned to link with a direct current. It is intended to connect heating, ventilation, air conditioning, elevators and lighting to the DC intermediate circuit, too.