MagicBox - The project

The Project

MagicBox is an energy self-sufficient solar house located at the Escuela Técnica Superior de Ingenieros de Telecomunicación (ETSIT) of the Universidad Politécnica de Madrid (UPM). It combines bioclimatic design principles, PV solar energy integration, local energy storage technology and the use of Information and Communication Technologies (ICTs) to monitor and control the house power flow.

MagicBox was originally designed to participate in the Solar Decathlon 2005 contest, being the first house from an European university to take part in this event. Solar Decathlon is an award-winning program that challenges collegiate teams to design, build, and operate solar-powered houses that are cost-effective, energy-efficient, and attractive design. After finishing the competition, MagicBox was installed at the ETSIT under the Heliodomo project framework. This house hosted the R&D project GeDELOS-FV that early studied the integration of PV hybrid and load control technologies in order to explore the possibilities of self-consumption using PV technology, local storage and controllable consumption in the residential sector. MagicBox also hosted the project VE2 whose main objective is the development of a software platform to manage the interaction of electric vehicles parked and connected to the electric grid of a building and the electric consumption of the whole building.

MagicBox is currently used as a research laboratory to assess the effect of the combination of PV generation, load management and local storage on the electrical grids. From the electrical point of view, its structure is based on an AC bus topology. It works on 230V and 50Hz because of Spanish grid connection. From an ICT point of view, an embedded system receives information from the elements of the house (generation, storage and loads) and operates as a user interface. This embedded system can also actuate over some elements of the house to control their power flows. An schematic of the electricity and communication network of the house is shown in the next figure.

PV generator: The PV generation system of MagicBox consists of five independent monocrystalline silicon PV fields with 5.55kWp of total generation. This system is set in order to exploit the different tilts of the sun along the year within the operational strategies of the house. To achieve this goal, the fields are distributed in different south-oriented surfaces: 1.45kWp at 12º, 2.7kWp at 25º, 0.8kWp at 39º and 0.6kWp at 90º. Each PV field has an associated string-type inverter.
The photovoltaic system is equipped with a forecast PV generation module that communicates with the embedded system. This system calculates hourly forecasts of irradiation and ambient temperature for the next day. These variables are estimated for Madrid (40.5ºN, 3.7ºW), where MagicBox is located. From these meteorological forecasts, the usable electricity from the PV generators is estimated taking into account site-dependent (i.e. shadowing) and technological (PV modules, inverters, battery, etc.) characteristics of MagicBox. Therefore, the PV generation profile is available for the next 24 hours.

Storage system: The house is equipped with a lead-acid battery stationary bank. The battery bank is divided in 24 cells, each cell has a capacity of 750Ah and a voltage of 2V. Therefore, the total battery bank voltage is 48V with a capacity around 36kWh. The storage system has a bidirectional battery inverter because the battery operates at DC and all energy exchanges are produced through the AC bus.
The battery inverter does not only implement the current conversion, but allows controlling the power flows in the house. This control is implemented through two stream limiters. Thanks to these limiters, high-level software battery controllers can be developed to fulfill different strategies. The limiter A regulates the power flow between the possible generation sources and the consumption and storage. Through this limiter, the local consumption can be isolated from the grid. The limiter B regulates the battery charge power.

Consumption: The house includes typical electrical appliances of a highly electrified house. The fixed appliances are monitored but not controlled: cooking appliances, fridge, freezer, lighting, computers and entertainment appliances. There are also three deferrable appliances: washing machine, dishwasher and dryer. The deferrable loads are integrated in a home automation system which allows the appliances to be monitored and controlled by a remote system. The communication of the home automation system is based on a Power Line Communication (PLC) network.