Evaluating instruments stimulating sustainability transitions: promoting biomass boilers in Germany and the UK

Germany’s Market Incentive Program (MAP) and the UK’s Domestic Renewable Heat Incentive (RHI) are economic instruments promoting the uptake of small-scale renewable heat, yet to date, a technology-specific evaluation comparing their impact on the uptake of biomass boilers in existing residential dwellings is lacking. The comparison yielded insights into the relative advantages and disadvantages of Germany’s upfront subsidies, and the UK’s tariff payments for renewable heat generated. A review of academic and grey literature as well as semi-structured expert interviews were used to evaluate the instruments according to a combined theory-based and sustainability transition evaluation framework. The Domestic RHI faced challenges limiting scheme overpayments and responding quickly to issues, due to an inflexible instrument design which required timeconsuming parliamentary approval for scheme modifications. Both instruments struggled to balance flexibility and stability, with historic variations in financial support-levels negatively impacting their predictability. The MAP was significantly more stringent regarding emission and efficiency standards than the Domestic RHI, while the amount of financial support provided by the Domestic RHI was more than three times higher than the MAP for a reference 25kW pellet boiler installed in 2019 generating 20,000kWh annually. Nonetheless, uptake under the Domestic RHI was seven to ten times lower than the MAP. A consideration of contextual factors revealed that the UK faces challenges promoting biomass boiler uptake due to its low endogenous biomass supply, immature biomass boiler market, and negative perceptions regarding biomass boilers, illustrating the importance of contextual factors on the success of implemented policies.