Solar Energy System of the Month:

Electricity and heat from the sun and salad oil:
Combined Vegetable Oil Heat and Power Unit (CHP) and Solar Collectors fully provide a residential house with renewable energy

The engineering graduate from Stuttgart, Martin Bucher, operates a power station, from in his own house, that heats the building as well as the indoor swimming pool throughout the year and, in addition, generates electricity for approximately six families. The combined vegetable oil Heat and Power Unit (CHP) is run with cold-pressed canola (salad oil) from farmers of the region. Additional heat is provided by solar thermal collectors on the roof. The innovative energy supply is not yet a perpetuum mobile but fairly close, says the resourceful Swabian. Electricity not used by themselves is fed into the grid and is remunerated according to the german Renewable Energy Law (EEG) The efficiency of the combined Bio Heat and Power Unit is more than double the efficiency of even the most modern technology of large power plants. The use of local, re-growing raw materials will not only make a sustainable contribution to the reduction of climate-threatening CO2 emissions, but also to the political independence from fossil fuel suppliers and the avoidance of transportation risks.

Operator Bucher Solar heating system.
Operator Bucher; Vegetable Oil CHP, Solar heating system. Photos: Frederik Arnold

The environmentally friendly and also economically feasible system replaces old oil heating system. Bucher’s decentralised bio-power plant shows that already today innovative technologies are available in the market. The state-of-the-art heat storage unit and control technology allow the efficient integration of a solar thermal system. That this concept can not only be implemented in new buildings but also in existing buildings is proven by the installation in the house dating to the year 1968. The essential components are the vegetable oil CHP and the approx. 30 square metres of a solar collectors, which both feed heat into a heat storage unit of 1 000 litres. A combined control system monitors the different components according to energy supply and/or demand.

Schematic presentation of energy supply with solar energy and bio-energy.

[Wording of schematic presentation: Motor 22 kW/th, Generator 11 kWel, Vegetable oil CHP, Solar primary, Solar secondary, 1000 l Heat storage unit, potable water circulation, potable water charge pump, Heating circuit 1 House, Heating circuit 2, Indoor pool hall and water, potable water] Schematic presentation of energy supply with solar energy and bio-energy. Graphics: Martin Bucher

Earning money and taking the strain off the environment when heating

The Mini-CHP of 11 kW and the solar heating system fully replace a 55kW oil-fired boiler and use only renewable energy sources. In addition, the motor of the CHP runs a power generator. It was not only the goal to reduce the CO2 emissions but also to lower the operating costs of the building, including the indoor swimming pool and hall. Since the installation of the CHP, Martin Bucher is no longer concerned about oil, gas or electricity prices; the environmentally friendly power from the CHP is fed into the grid of the Electricity supplier EnBW and is remunerated with 19,3 Cent per kW hour for 20 years. This additional income lowers the operating costs in comparison to the old oil heating system by approximately 80 %. "The advantages of this mini cogeneration unit are not only the economic factors but particularly the pricelessly good feeling that we can now also morally afford to have a swimming pool in our own home. We always felt guilty when the large tank truck parked in front of our house with the heating oil to fill up the 16 000 litre underground tank,” the graduated engineer emphasises. Bucher’s cogeneration unit is no bigger than a conventional heating boiler and fits into any basement. The often irritating smell of oil is gone. The use of pure vegetable oil annually saves the environment approximately 26 tons CO2 and other ecologically harmful substances such as sulphur hydrides.

Looking into the CHP with motor and electricity generator. The Stuttgart Lord Mayor Dr. Schuster fuels the power station with salad oil. Heat storage unit.
From left to right: Looking into the CHP with motor and electricity generator, the Stuttgart Lord Mayor Dr. Schuster fuels the power station with salad oil, Heat storage unit. Photos: Frederik Arnold

High efficiency, minimal emissions, low costs

Coupling electricity and heat leads to more efficient utilisation of energy than the separate generation of electricity and heat: conventional heating boilers use the thermal energy in combustibles very well, but waste the entire electricity potential contained in the energy carrier. Power plants, on the other hand, utilise only the electricity potential and emit the entire available heat potential to the environment through their cooling towers. It is only the cogeneration that allows the optimised utilisation of both energy forms. Cogenerationplants require less fuel and have a significantly lower ecological impact through reduced emissions. Small decentralised cogeneration plants (MEHG) have an efficiency of over 90 %. Modern coal or oil-fired power plants only transform 35 - 42 % of the energy contained in energy carriers into utilisable energy, nuclear power plants achieve 58 % - and cars only transform 25 % of primary energy into motion. Furthermore, small decentralised CHP protect against large-scale blackouts and have far lower line losses and network utilisation costs because electricity is produced where it is used. A remarkable 50 % of conventional electricity costs are attributable to grid utilisation and distribution costs.

Power-Trio: CHP, solar system and heat storage unit

The Mini-CHP, as most electricity/heat cogeneration plants, has an extremely high degree of efficiency of over 90 %. The generation of electricity is thermally controlled (monovalent): the conventional 4-cylinder Diesel engine, converted to run on vegetable oils, only performs if heat is required. At only 1 500 revolutions per minute it generates 11 kWel and has an additional heat output of 22 kWth. The mechanical output is converted to electricity in a water-cooled generator that feeds power into the grid. The thermal output is stored, through a plate heat exchanger (comparable to a car radiator), in a heat storage unit (buffer storage unit). The entire unit of motor and generator is contained in a sound-proof housing. A soot particle filter, as well as an oxidation catalyst, are coupled to the motor to avoid annoyance through bad smells.

Customary flat solar thermal collectors with a surface area of just below 30 square metres capture solar energy and also feed it into the heat storage unit via a heat exchanger. The heat storage unit is fitted with a special device to store the hot water, by convection (heat transport through moving matter), at the top and the cold water at the bottom. This is particularly important to optimise the solar output but also to allow the longest possible operating times of the CHP. Frequent start-up and shut-down of the CHP would lead to unnecessary emissions, higher wear and tear and increased consumption. The storage unit has ten in- and outflows on different levels. This allows the water of different producers and consumers to be pre-sorted and stored according to required temperatures without prior mixing.

Modern control unit

The “brain” of the overall concept is a freely programmable control unit. It differentiates between summer and winter operation and regulates the correct flow temperature for the respective heating systems on the basis of heating characteristic lines and according to the outside temperature. The control mechanism does not only regulate the solar system and the hot water demand, but also the pool pump (e.g. when to operate with night electricity, but also when to utilise additional solar energy during a summer day when large solar radiation is available and the storage unit issaturated . The data of all operating parameters as well as the 16 different temperature sensors are continuously monitored for later evaluation and optimisation.

Fully operated with renewable energies: residential house in Stuttgart. Indoor swimming pool and hall.
Fully operated with renewable energies: residential house in Stuttgart, indoor swimming pool and hall. Photos: Victor Brigola

Climatically neutral and safe energy from vegetable oil

Currently Martin Bucher fuels the CHP motor with salad oil from cold-pressed canola. This biologicaloil is stored in the original heating oil tank and is supplied to the CHP by a gear pump. Instead of canola, soya oil, sunflower oil or other vegetable oils could be used. To allow canola oil to have virtually the same properties as Diesel or heating oil, it is pre-heated to approx. 60 ºC before being injected into the motor. As a renewable raw material canola plants absorb while growing exactly the same amount of CO2 as is released during their combustion. Thus, this form of energy is CO2-neutral. Canola oil falls under Hazard Class 0 and is thus absolutely non-hazardous for the groundwater. It can be stored “everywhere”. In the event of fuel spillage, the environment is not poisoned. The high flash point (for vegetable oils approx. 300 ºC, for Diesel approx. 80 ºC) makes this fuel extremely explosion-proof. It can be transported and stored in unlimited quantities.

Farmers as energy producers

The currently tilled fields in Germany with a harvest cycle of 4 years, which is typical for canola, could replace 30 % of the entire Diesel consumption in Germany, claims Martin Bucher. Local farmers are highly dependent on subsidies. Through the direct sale of self-produced vegetable oil they achieve an additional income. Besides utilising the oil as fuel, the farmers can also benefit from the green plant as fodder and the so-called “press cake” from oil production for animal feeding.

Solar power specialist as fuel station operator

A logical and consistent step for Bucher is the fuelling of all vehicles of his household with the same canola oil used for the CHP. The graduated engineer emphasises that many Diesel vehicles can easily be converted to vegetable oil operation. Full or partial fuelling with conventional Diesel is nevertheless possible. A compact fuelling station with counter, as mounted on Bucher’s garage wall, can be accommodated almost everywhere.

Bio fuelling station owner Bucher. Ground-mounted photovoltaic plant by Martin Bucher in Pocking.
Bio fuelling station owner Bucher. Ground-mounted photovoltaic plant by Martin Bucher in Pocking. Photos: Frederik Arnold.

Dipl.-Ing. Martin Bucher (Process engineering) is amongst the most experienced project developers in the field of photovoltaics. As "Father" of the ground mounted photovoltaic power plants he has significantly contributed to the development and success of the largest "PV Parcs". He repeatedly held the world record for the largest photovoltaic power plant, e.g. the 10 MW PV parc in Pocking. Through his work and his private commitment the 39-year-old father of two children wishes to show future generations real possibilities to the solution of environmental problems.

Material and photos: Martin Bucher. Solarserver Editor: Rolf Hug


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