Contemporary combined heat and power (CHP) systems are often based on fossil fuels, such as natural gas or heating oil. Thereby, small-scale cogeneration systems are intended to replace or complement traditional heating equipment in residential buildings. In addition to space heating or domestic hot water supply, electricity is generated for the own consumption of the building or to be sold to the electric power grid.

The adaptation of CHP-systems to renewable energy sources, such as solid biomass applications is challenging, because of feedstock composition and heat integration. Nevertheless, in particular smallscale CHP technologies based on biomass gasification and solid oxide fuel cells (SOFCs) offer significant potentials, also regarding important co-benefits, such as security of energy supply as well as emission reductions in terms of greenhouse gases or air pollutants. Besides emission or air quality regulations, the development of CHP technologies for clean on-site small-scale power generation is also strongly incentivised by energy efficiency policies for residential appliances, such as e.g. Ecodesign and Energy Labelling in the European Union (EU). Furthermore, solid residual biomass as renewable local energy source is best suited for decentralised operations such as micro-grids, also to reduce long-haul fuel transports. By this means such distributed energy resource technology can become an essential part of a forward-looking strategy for net zero energy or even smart plus energy buildings.

In this context, this paper presents preliminary impact assessment results and most recent environmental considerations from the EU Horizon 2020 project "FlexiFuel-SOFC" (Grant Agreement no. 641229), which aims at the development of a novel CHP system, consisting of a fuel flexible smallscale fixed-bed updraft gasifier technology, a compact gas cleaning concept and an SOFC for electricity generation. Besides sole system efficiencies, in particular resource and emission aspects of solid fuel combustion and net electricity effects need to be considered. The latter means that vastly less emission intensive gasifier-fuel cell CHP technologies cause significant less fuel related emissions than traditional heating systems, an effect which is further strengthened by avoided emissions from more emission intensive traditional grid electricity generation. As promising result, operation "net" emissions of such on-site generation installations may be virtually zero or even negative. Additionally, this paper scopes central regulatory instruments for small-scale CHP systems in the EU to discuss ways to improve the framework for system deployment.

During recent years comprehensive work has been done on the development of small-scale solid biomass based combined heat and power generation technologies but still only few systems are available, their efficiencies are rather moderate, their fuel flexibility is restricted and their market penetration is poor. Against this background, the on-going Horizon 2020 project FlexiFuel-SOFC aims at the development of a new, highly efficient and fuel-flexible micro-scale biomass CHP technology for a capacity range of 25 to 150 kW (fuel power). The technology consists of an updraft gasifier, a gas cleaning system and a solid oxide fuel cell (SOFC). The new technology is developed with a main focus on (i) the further development of a small-scale fixed-bed updraft gasifier technology towards higher fuel flexibility and integration into the SOFC based CHP system, (ii) the development of a novel and compact gas cleaning unit and (iii) the further development of a SOFC system (stack efficiency of ~40 % with product gas from the updraft gasifier). A first testing plant has been designed, constructed and is presently taken into operation.