Hotels are one of the classic applications for small-scale CHP units. One such installation at a hotel in the Harz National Park in Germany won a project of the year award – for its high operational efficiency, high utilization factor and net carbon emissions reduction. Wilhelm Meinhold writes.

A 140 kWe cogeneration unit installed last year at the Maritim Berghotel, Braunlage, was named the CHP unit of the year in Germany (BHKW des Jahres 2009) by the German cogeneration association B.KWK and the magazine: Energie & Management last December. The investor is the Essen-based favis GmbH, which operates the CHP unit as a contractor for the Maritim hotel.

The judging comprised representatives of Comco Leasing GmbH, public utilities provider Stadtwerke Schwäbisch Hall, cogeneration scheme operator BTB Berlin and the B.KWK itself.

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The 140 kWe unit installed at the hotel in Braunlage, Germany operates at an overall efficiency of 91%

The CHP schemes being considered ranged from a small, 34 kWe project to a much larger, 7.4 MW scheme, were fuelled by natural gas, biogas and diesel, and employed a range of technologies – gas engines, diesel engines, turbines and trigeneration. To make a choice, the judges considered creativity, the on-site integration of generated energy, environmental aspects, profitability, project energy ratios, and replication potential.

After discussion, the experts agreed upon the Sokratherm ‘GG 140 S’ CHP unit installed in the Maritim Berghotel. The scheme scored particularly well due to the nearly full on-site consumption of the electricity produced, the exemplary quality of the contracting concept, and the expected potential for replication of the project when looking at the modernization of existing or construction at new cogeneration sites.

The unit’s carbon dioxide emissions of 230 g/kWh are said to be 37% below those of modern gas-fired power plant without heat use, achieved with a 35% electrical efficiency and a total fuel efficiency of 91%.

The 309 bed hotel attracts its guests with a quiet location on a hill, in the heart of the mountainous Harz national park in the north of the country. The location, at over 700 m height, is a cold spot, which makes the overall energy bill of the first-class hotel, with its indoor and outdoor swimming pools, a spa area, sauna and solarium, quite substantial.


The cogeneration unit installed and operated by favis takes advantage of the long winters in the Harz, since they provide for a good utilization ratio for the unit. The compact GG 140 CHP unit was selected by limited tender and is equipped with a MAN gas engine.

Due to the altitude, the unit’s electrical power output is reduced to 130 kWe and its thermal energy output to 201 kWth. The total efficiency however, is the same outstanding 91% as the efficiency measured at the nominal power data (140 kW electric, 216 kW thermal energy, 392 kW gas consumption) which applies at heights up to 100 m above sea level.

With the reduced power data, and the hourly load curves known from the gas supplier, favis engineers calculated a utilization rate of at least 6000 operating hours per year. With this utilization, the CHP unit will cover around 40% of the site’s heat demand. The remaining heat load is supplied by the existing gas boiler.

Under a framework agreement signed with the Maritim Hotel Group in 2005, favis had already been providing heat in the hotel before the new CHP unit was installed. The agreement also includes consulting at electricity procurement and the optimization of energy technology for the 44 Maritim hotels in Germany.

The electricity produced by the CHP unit is mainly consumed in the hotel and could therefore be priced with the hotel’s purchase cost of imported electricity. Only small amounts of surplus electricity are fed into the mains and paid by the stock price defined by the EEX (European Energy Exchange).


Before the new installation, the previous CHP unit had reached the end of its lifetime after 80,000 operating hours at the hotel. The decision to install a new CHP unit was backed up by Germany’s revised law to promote cogeneration (KWK-Gesetz) which became effective on 1 January 2009. With this law, CHP units installed in the years 2009 to 2016 receive the cogeneration bonus (KWK-Bonus) for the full amount of electricity generated by the unit – including the electricity consumed on site.

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The Maritim Hotel is located at over 700 m above sea level – the long winter season means that the CHP units is used for around 6000 hours per year

In the case of the Braunlage CHP scheme, the bonus is 5.11 €cent/kWh for the first 50 kW, and 2.1 €cent/kWh for the remaining 80 kW of electric power. This bonus is paid for six years, or 30,000 operating hours maximum. In this way, the net investment of around €140,000 will have reached a full payback after five years. At the same time, the hotel can reduce its energy costs by roughly 10% due to the longer-term contracting agreement for 15 years.

The Maritim group has 44 hotels in Germany and further hotels in Spain, Turkey, Egypt and China. The group is currently working with favis GmbH to decide at which of its sites CHP units can be modernized or replaced with new equipment. The hotel group management sees a high priority in the optimization of its energy supply, and has already equipped another hotel with a Sokratherm GG 50 unit. It also bolsters the ‘energy in gastronomy’ campaign initiated by the German gastronomy association DeHoGa, which is supported by the federal Umweltbundesamt and endorses the installation of cogeneration units.


Earlier this year, Sokratherm received the largest order in over 30 years of company history. Three cogeneration units of 200, 400 and 600 kW electrical output and a combined 1500 kW thermal power, are to be installed in the district office Minden, the Kampa Hall Minden and a nearby hospital in Bad Oeynhausen, in North Rhine-Westphalia, Germany.

A special feature of this project is the combination of classic fossil-fuelled cogeneration and renewable alternatives in the fuel supply – the district of Minden-Luebbecke refines biogas created in its compost works to natural gas quality, and feeds it into the local gas network. The CHP units use this refined biogas to generate heat and power with a total efficiency of up to 90%. With the legal framework for CHP improved in 2009, the project is a particularly reasonable investment from an economic and environmental view.

Wilhelm Meinhold is the marketing manager at Sokratherm, Germany. Email:

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