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Short Title: EAHplus-Monitoring: Entwicklung einer neuen Generation energieautarker Häuser - messtechnische Überwachung -
Running Time: 08/2012 bis 01/2018
Topics: Construction of individual buildings, Heating, ventilation and cooling, Decentralised energy generation, Energy storage, Operational management & energy management, Solar heat, Solar power, Biomass, Heat from soil, groundwater and sewage


  • Solar energy use for electricity and heating combined with large storage capacities designed to enable self-sufficiency
  • Over 70% of the heat is supplied using solar energy, supplemented with stoves
  • Independence from the electricity grid during operation not yet achieved
  • Electromobility increases the self-consumption rate by about one third
  • Use as a family home or office makes no difference in the energy balance

In Freiberg, the performance of two single-family homes conceived as energy self-sufficient buildings is being scientifically investigated. The buildings’ very low heating requirements are met by generously sized solar collectors and heat storage tanks, supplemented in each home with a wood-fired, water-cooled stove. A photovoltaic system in combination with a battery storage unit ensures almost 100 per cent solar power provision.

Project context

The declared goal for the two energy-efficient homes in Freiberg is to achieve complete independence from the public electricity grid and fossil fuels. The building concept is based on the so-called Sonnenhaus (Solar House), which via generously dimensioned solar thermal collectors and heat storage tanks meets more than 50 per cent of its heating requirement with solar thermal heat. In addition, solar power is generated with a large photovoltaic system as in the case of energy-plus homes. In contrast to these, currently unused solar power is not fed into the public electricity grid but is stored in batteries or in electric vehicles. This concept can help prevent the "stress" caused by high solar power capacities being fed into public electricity networks on sunny days.

Two such buildings were completed and occupied in Freiberg (Saxony) in October 2013. One building is inhabited by a family of five and the other is used as an office.

Research focus

The buildings, which are almost identical, differ only in terms of their usage profile as residential and office buildings. Since 2014, extensive measurement data relating to the heat and power supply as well as the indoor and environmental conditions has been gathered during the course of the scientific evaluation and assessed with regard to additional data such as the solar radiation and weather. This is aimed at determining a detailed building energy balance and, where necessary, identifying necessary optimisation measures to the building concept, building technology or operational management.

For this purpose extensive measuring technology was installed in both buildings. Numerous heat meters (oscillation beam principle) as well as humidity and temperature sensors were also installed to balance the heat supply. Additionally installed resistance thermometers (PT100) enable a detailed evaluation of the heat flows. Numerous electro-energy meters are available for balancing the electricity in the standalone network. These meters record the electricity requirements with a high temporal resolution, including to some extent for individual end loads. This enables precise recording according to the system and load groups and makes it possible to assess the user impacts.

In addition, it is also intended to investigate the effect of electromobility on the energy balance, on increasing the self-consumption rate and for relieving the public electricity grid.

Hydraulic schematic showing the heat supply for the energy self-sufficient residential building.

© TU Bergakademie Freiberg, IWTT


Building concept

The buildings are based on the Sonnenhaus-Institut's construction and heating concept that orients the house and large windows to the south. The houses are built using a monolithic means of construction, whereby the walls consist of solid bricks with internal plaster and external render, but without any additional externally applied thermal insulation. Thermo-active building systems (TABS) are used to transfer heat to the rooms. These can also be optionally used in summer via a borehole heat exchanger for cooling purposes to ensure a comfortable indoor environment. The ground is used here as a heat sink.

The schematic shows the building with a) roof-integrated solar thermal collectors, b) solar power modules, c) long-term heat storage tank and d) battery storage unit outside the building.

© TU Bergakademie Freiberg, IWTT

Further images

The long-term heat storage tank is lifted into the building.

© Timo Leukefeld

The topping-out ceremony is ready to be celebrated.

© TU Bergakademie Freiberg, IWTT

The battery storage unit with lead-gel batteries is located behind the house and provides 58 kWh of electricity.

© Timo Leukefeld

The complete technology in the laundry of the energy self-sufficient residential building.

© Timo Leukefeld

The fireplace as additional heating with wood as renewable energy for periods with little sunshine

© Timo Leukefeld

The fact that almost complete energy self-sufficiency is achieved is hardly noticeable when looking around the house. The view from the living room into the open-plan kitchen space.

© Timo Leukefeld

Energy concept

The buildings each have a solar thermal system (46 m²) with a long-term thermal storage tank (9.12 m³). The system is combined with a water-cooled wood-burning stove as a supplementary heating system. This is intended to achieve a solar coverage of at least 65 per cent and an annual primary energy requirement of 7 kWh/m², which is about 70 per cent less than the total primary energy requirement of typical passive houses.

The power supply is ensured by a photovoltaic system (8.4 kWp) and a battery storage unit (lead-gel battery, 58 kWh). The buildings' respective total electricity requirement for both types of usage amounts to about 2,000 kWh (without electromobility). In addition to the depicted energy supply concept, the influence of electric vehicle use on the standalone electrical network has been investigated since October 2014. Although the building is basically independent of the public electricity grid, it is connected to it in order to guarantee the power supply during periods with low solar energy.

Heat balance for the residential building and the thermal solar coverage for the period 2014 and 2015. The storage in and removal of heat from the heat storage tank is balanced, differentiated according to the source and use. The contribution made by additional heating during the winter months can be clearly seen.

© TU Bergakademie Freiberg, IWTT

Electricity balance for the residential building and the electrical solar coverage for the period 2014 and 2015. In August 2015, electricity was drawn from the power grid owing to maintenance work being conducted on the battery (B).

© TU Bergakademie Freiberg, IWTT

Performance and Optimisation

The data analysis shows very high solar coverage levels over the course of two years. In the case of the electricity supply, this amounted to about 92% (2014) and 97-98% (2015) for both utilisation profiles, which did not fully meet the objective of achieving independence from the public electricity grid. In terms of the heating provision, the solar share of the heat supply was about 71% (2014) and 72-73% (2015). Here the target of more than 65% was clearly exceeded.

The outdoor temperatures in the winter months critical for the energy supply were, with the exception of one month, mainly above the German Weather Service's long-term mean for the nearby Chemnitz location. In contrast, the accumulated number of sunshine hours in both years was below the long-term average. Furthermore, the long-term mean value for the incident radiation in the winter months was significantly lower in 2014, which meant that additional heat had to be provided via the stove. This was also the reason why the buildings failed to achieve 100 per cent self-sufficiency in terms of their electricity consumption. The causes can be seen in the very low solar irradiance during the 2014/2015 winter months, where the long-term mean values for the solar irradiation used for the planning were not attained. The planned total electricity requirement of 2,000 kWh/p.a. was essentially able to be achieved with a maximum electricity consumption of 2,144 kWh/p.a. It was also shown that higher self-consumption rates are achieved from spring to autumn with additional loads such as an electric vehicle. The differences in the user profiles for residential and commercial use are present, but have little effect on the overall energy balance.

The low total electricity consumption of approximately 2,100 kWh means that the use of an electric vehicle is also conceivable from spring to autumn without endangering the self-sufficiency. This is being tested with an iMieV vehicle since October 2014. Initial investigations show that the self-consumption rate was able to be increased by about 36% in 2015. In addition, the mobility costs are reduced when considered in the long term. To further increase the self-consumption, an intelligent charging strategy and the storage and use of grid surpluses are currently being investigated.

In both buildings, a renewable cooling system for summer use was integrated via a borehole heat exchanger. The control parameters are being continually developed and compared with real measurement data.

It is intended to transfer the energy self-sufficiency concept to apartment buildings. Here the project partners will work together with the Sonnenhaus-Institut.

Economic viability

An economic viability analysis shows that the additional costs for the self-sufficiency package for the energy self-sufficient house should be amortised after approximately 24.7 years (static) and 34.1 years (dynamic). The data should be considered as a example because it is dependent on the prevailing underlying conditions such as the energy prices (for fossil fuels and electricity) and the location (irradiation and thermal heat demand).

The dynamic amortisation calculation was used for the economic viability analysis, whereby the following was assumed: a calculation interest rate of 4.36%, an observation period of 20 years, 2014 energy prices (electricity 29.14 Ct/kWh, gas 6.81 Ct/kWh), an identical single-family home with gas-fired  condenser boiler technology as the reference scenario and an energy price increase of 5% p.a.

The building concept was co-developed with the prefabricated construction company HELMA Eigenheimbau AG, and is now marketed as a ready-to-build home called the "Energy Self-sufficient House".

Project data

Building data

Who is who?  
Building owner Timo Leukefeld, Stephan Riedel
Occupant Timo Leukefeld
Building type Single-family home / office
Time data  
Year of construction 2013
Start of planning 2011
Completion 10/2013
Inauguration 11/2013
Gross floor area 279 m²
Workplaces 5 persons
Heated living area 206 m²
A/V ratio 0,72 m²/m³

Energy data

Energy indices demand        
New building / after … before refurbishment  
Heating energy demand (Utility energy demand Heat) 40,10 kWh/m²a  
Source energy for heating and domestic hot water (dhw) 7,10 kWh/m²a  
Overall primary energy requirement 7,10 kWh/m²a  
Measured energy indices (demand)        
New building / after … before refurbishment  
Source energy for heating and domestic hot water (dhw) 68,90 kWh/m²a  
Overall primary energy requirement 7,4 kWh/m²a  
More specific consumption data for lighting, air conditioning, ventilation etc.        
New building / after … before refurbishment  
Electricity for building technology 2,83 kWh/m²a  
Electricity for lighting 0,48 kWh/m²a  
Electricity for appliance 4,00 kWh/m²a  
Electricity for communication 0,98 kWh/m²a  
Electricity for office work 0,49 kWh/m²a  
Sockets 1,25 kWh/m²a  

Implementation costs

Building costs or renovation costs        
Costs for the (renovation of) structural design [KG 300] 844 EUR/m²    
Costs for the (renovation of) technical installations [KG 400] 637 EUR/m²    
Usage costs        
Period from... to...    
After inauguration 01.2015 12.2015    
New construction / after … before renovation  
Overall energy costs 1,13 EUR/m²a  
Overall heating costs 1,07 EUR/m²a  
Overall elictricity costs 0,06 EUR/m²a  

Last Update: 21. March 2017

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