KOSTAL Pressebereich
Freiburg, 21/07/2022

KOSTAL – part of a research project

The KOSTAL PLENTICORE plus inverter in the ECOLAR positive energy house at HTWG Konstanz demonstrates how sustainable architecture and solar systems can work together harmoniously and efficiently.

EDITORIAL TEAM: Good afternoon, Mr Heider. In 2012, you scored very highly in the Solar Decathlon Europe 2012 contest in Madrid with the ECOLAR positive energy house, which came an excellent fourth overall out of twenty universities and won two awards in the disciplines of engineering and industrialisation. Now the house is located on the HTWG campus in Constance and is once again the focus of an exciting research project into infrared heating where you are using a powerful photovoltaic system and KOSTAL converter technology with the PLENTICORE plus hybrid inverter. What is so innovative about this house idea and what role does solar power play here?

JAN HEIDER: The remit for the Solar Decathlon Europe 2012 contest was to plan a house for two people and then to also build it ourselves as an interdisciplinary team of students. First of all, the building was to include all the functions needed in a "normal" household. In addition, particular emphasis was placed on energy efficiency and sustainability. For our project, firstly this meant that we constructed the building largely from wood and other renewable raw materials. We also tried to avoid plastics as much as we possibly could. Secondly, we attempted to reduce the power requirement through an innovative building technology concept and to use as much of the building’s shell surface as possible to produce energy by consciously integrating PV modules into the architecture (BIPV).

Our aim was to show that we can already build houses that are able to cover a large amount of their own power requirement with local renewable energy sources (photovoltaics, ambient heat) or to generate more energy than they consume over the course of a year and that the technology used can be well integrated into the architecture's design. Since the amount of space a person uses also has a major influence on overall energy consumption, we opted for a modular building concept. We placed great importance on the idea that "If your life changes, your house changes". In other words, a household can start as one person on a few square metres with two room elements and expand to larger living spaces when the number of residents increases, but it can also shrink again or change when residents, e.g. children, leave the house again.

EDITORIAL TEAM: How much power does the solar system generate and which KOSTAL inverter type is used?

JAN HEIDER: We are currently using the ECOLAR building for our IR-Bau 2 research project. In our first IR-Bau research project, which we carried out between 2017 and 2019, we were able to demonstrate that infrared heating can be a sensible alternative to heat-producing systems with heat pumps in small, well-insulated buildings. In our current IR-Bau 2 research project, we are now investigating in more depth how, for example, we can optimise self-supply with PV electricity but also comfort levels in the room by heating with IR heaters.

On the flat roof of the ECOLAR house, we installed solar modules that are integrated into the building and have three strings that produce 13.3 kW. In terms of dimensioning, we used the PLENTICORE plus with 10 kW as the heart of the solar system, which intelligently produces and also distributes the solar power.

During the course of the IR-Bau 2 project, we have added a laboratory room to our ECOLAR building. Here, we investigate various matters relating to IR heating. Especially when investigating different control strategies for optimising self-consumption and grid-supportiveness, it goes without saying that being able to use real electricity production from the in-house PV system on the roof is of huge benefit in our investigations.

After all, when using direct electric heating in particular, there are great advantages to be gained from both an ecological and economic standpoint if the degree of self-coverage provided by the PV system is maximised as much as possible by using efficient electricity production technology and intelligent control strategies. When it comes to "heating with electricity", many people tend to think of the negative example of night-time storage heaters from the 1950s and 1960s. However, you need to consider that the basic conditions for supplying heat to buildings have changed fundamentally in recent decades. Firstly, heat demand has been significantly reduced in recent years due to the regulations for better building insulation in new buildings. Secondly, the costs of local energy production on the building have also fallen enormously. Therefore, a low heating requirement is now coupled with cost-effective and local, renewable power generation. Therefore, especially for buildings with low heat turnover, it is interesting to consider what potential simple and cost-effective infrared heating systems have in supplying heat to buildings, especially in combination with local electricity generation via photovoltaics.

We have not included the connection of battery storage as a parameter as we are primarily concerned with heating and the storage sizes required for seasonal electricity storage are unfortunately still far too expensive. In order to improve grid-supportiveness, however, in this project we are currently focusing on thermal storage of solar surplus. However, anyone who wants to operate an electric car or powerful consumers using solar power and connects a battery to have power available for consumption later on certainly can't go wrong with this inverter.

EDITORIAL TEAM: What is the energy concept of the house? After getting the test arrangements set up, you started measuring technical events. Have you got any insight yet indicating trends in the areas you are focussing on?


Currently, the building's heat supply is provided by a system of IR heaters, a PV system and a control system optimised for self-consumption. In addition to our laboratory room tests in the ECOLAR building, the IR-Bau 2 project also has measurement technology installed in several residential and non-residential buildings in southern Germany where IR heating systems are used to produce heat. One of these buildings is equipped with a control system from my-pv, which is specially designed to optimise the self-consumption of direct electric heating by the in-house PV system. Instead of a fixed setpoint temperature, the control system uses a temperature range. Inside this range, the room is considered to be a comfortable temperature. By deliberately raising the room temperature during the day, solar surplus can be thermally stored in the building structure, which avoids having to draw electricity from the grid at night in most cases. 

Here, the advantage that electric heaters are infinitely variable and can be put on a timer comes in useful. Evaluation of the measurements indicates a degree of self-sufficiency of approx. 65 % to 75 %. Initial tests in the laboratory room with the control system display a similar efficiency.

EDITORIAL TEAM: What does grid-supportiveness mean in this context?

JAN HEIDER: As Germany converts its energy supply system to renewable energy sources, base load power plants (nuclear power, coal) are increasingly being eliminated. The output of renewable energy generators is subject to the seasons, day/night patterns and the weather and it can fluctuate accordingly. In order to smooth out these fluctuations on the generator side as well as the consumer side, it is advantageous if buildings are no longer understood as pure consumers but can respond to the fluctuations in the electricity grid. In other words, in times of oversupply of electricity, energy is absorbed and in times of reduced supply, either no further energy has to be drawn or energy can even be fed back into the grid. Given the rapid and infinitely variable controllability of electric heaters in combination with thermal storage mass, electric heaters with appropriate control may be well suited to flexibly responding to fluctuations in electricity production in some circumstances. Therefore, in the future it is conceivable that we will see heating controls that not only take into account local production on one's own roof but also the current electricity supply on a regional or cross-regional level.

EDITORIAL TEAM: When will the study finally report on the project?

JAN HEIDER: Our project runs until April 2023, so the project report can be expected around the beginning of July 2023.

EDITORIAL TEAM: Mr Heider, thank you very much and good luck with the new IR-Bau 2 research project.

JAN HEIDER: Thank you. It has been a pleasure.