You are here: Home Housing Danfoss Inverter Produces Energy for Denmark’s First House with an Energy Surplus
Danfoss Inverter Produces Energy for Denmark’s First House with an Energy Surplus Print E-mail
Friday, 06 August 2010 18:21

danfossA pleasant indoor climate and no energy costs. The ZERO+ house in Sønderborg is the first residential house in Denmark to produce more energy than is consumes, thanks to a range of energy saving initiatives along with a PV installation with a Danfoss ULX 5400o inverter.

Danfoss provides fresh air, ground heat and electricity
The unique house is the result of a collaboration between different companies that all specialise in energy efficiency

Power generation
All the electrical power is supplied by 46m2 of roof-mounted solar cells connected to a ULX 5400o inverter running in parallel configuration. The panels face south, providing optimal utilisation of the irradiation levels, which in DK correspond to approx. 850 kWh/kWp.  The PV panels are of the make Schüco SPV 175 SME-1, monocrystalline with a module efficiency of 13.7%.  
During the first year the PV installation produced 5,160 kWh, despite the fact that the solar cells were covered by snow for 2 ½ months this winter. Seeing that the family only consumed 5,133 kWh, this left them with a surplus.
The PV panels are integrated into the roof by means of an indent into the roof’s surface in-lining the panels with the rest of the roof. The panels are therefore virtually invisible. Underneath the panels a 10 cm cavity ensures adequate cooling.

Energy conservation measures - all from Danfoss
As the vision for the house is to be a surplus house, it is predominantly the size of the PV installation which determines the energy levels. It is hence required pay careful attention to the consumption; however, using a combination of technologies this poses no problems.
The living space of the house is 200m2 and is state-of-the-art and extremely comfortable.
The technical solutions for most of the heating and power supply are supplied by Danfoss. This includes the air conditioning system with heat recovery, the geothermal heat system along with the energy-efficient heat pump that produces the necessary heat and utility water, and the inverter for the PV system.

Top insulation
The house is a passive-house designed with the method ”line of the pencil” in mind. This implies that you have to be able to draw a continuous line in the insulation layer around the house. This means that thermal bridges and other insulation weaknesses are avoided. Among other things it proved necessary to make a special foundation design to avoid a thermal bridge.
The walls of the ZERO+ house consist of a light exterior structure with heavy brick interior walls. This ensures the best possible insulation of the exterior walls as well as heat accumulation in, and sound proofing of, the interior walls.

Air Conditioning
In a superbly insulated house like the ZERO+ house a ventilation system is of the utmost importance to maintain a nice and healthy indoor climate. Focus has been on the interaction between ventilation and heating in order to achieve optimal utilisation of the energy.
The air conditioning system includes heat recovery, which ensures that half the air inside is replenished automatically every hour while transferring the heat from the exhausted air back into the intake. A geothermal system in the ground surrounding the house adds preheating in the winter and cooling in the summer.

The geothermal system consists of an approx. 100 m long hose filled with a frost-proof fluid that via a heat pump transfers energy from the surrounding ground to the house.

To achieve as low electricity consumption as possible the geothermal heat system is combined with a fast-reacting floor heating system, which is placed just below the floorboards, above the concrete floor. Consequently, the heat pump only needs to produce heat at 23-27 °C as opposed to the higher temperatures required by central heating, air heating or traditional floor heating, conserving energy. 
The system is called SpeedUp and it reacts and regulates the temperature in just 15 minutes.

Passive Solar heating
By using the heat of the sunrays to warm up the building the need for additional heating is also limited. To exploit the heat emitted by the sunrays the varying angle of the sun according to season has to be taken into consideration. In the winter, when the sun is positioned low in the sky, all the heat the sun emits is required. However, during summer, when the sun is high in the sky, overheating must be avoided so that excessive energy is not spent on cooling (the aim is to have no more than 25 °C in more than 10% of the time).

Due to the combination of the glass facades, the air conditioning and the heat pump as well as the heat accumulating interior walls, the south facing windows of the house have become an energy source in themselves.

Making modern living possible
Previously, saving energy and the production of green energy has been synonymous with living an alternative lifestyle. However, it is not so anymore. The ZERO+ low-energy house in Sønderborg is the house-concept of the future.

“We do not compromise on quality of life. We wash and tumble-dry as much as we’ve always done” says Lone Midtgaard Wrang, the owner of the house.    

The ZERO+ house is part of ProjectZero, which aims at making Sønderborg CO2 neutral by 2029

Contact details

electrical industry renewable energy news,


To include news or advertise your product or service on the electrical digest - Call: 07530 871 673 or Email:



Newsletter and magazine Sign-Up

Subscribe to the 'electrical digest newsletter and magazine' for all the Latest Electrical Industry News

Click a logo below to find out more.


Featured Manufacturers