Metrological issues in energy measurement on biogas

The use of biogas as regenerative energy can be achieved more efficiently by injecting the treated biogas into natural gas grids since the localisation of the biogas CHP (combined heat and power) plant is made independent from the site of the biogas production. Thus, the utilisation of the heat generated in the CHP plant may be optimised. For that reason, the National and European regulations support injection into the natural gas grid. This paper deals with the general metrological issues concerning injection from the specific aspects of measurement technology. The issues discussed include the adjustment of biogas to the characteristics of natural gas (treatment to produce biomethane) and the measurement of biomethane calorific value. Measuring the calorific value of natural gas today is almost always based on the use of process gas chromatographs specifically designed for the analysis of typical natural gases. Natural gas chromatographs are only suitable under minted conditions for use with biomethane due to differences in the composition of natural gas and biomethane. This paper explains the specific issues and solutions for the measurement of the calorific value of biomethane and their implementation in current plants equipped with injection facilities.