One of the biggest obstacles to economic profitability of solar water heating systems is the investment cost. Retrofitting existing domestic hot water heaters when a new solar hot water system is installed can reduce both the installation and material costs. In this study, retrofitting existing water heaters for solar water heating systems in Swedish single-family houses was theoretically investigated using the TRNSYS software. Four simulation models using forced circulation flow with different system configurations and control strategies were simulated and analysed in the study. A comparison with a standard solar thermal system was also presented based on the annual solar fraction. The simulation results indicate that the retrofitting configuration achieving the highest annual performance consists of a system where the existing tank is used as storage for the solar heat and a smaller tank with a heater is added in series to make sure that the required outlet temperature can be met. An external heat exchanger is used between the collector circuit and the existing tank. For this retrofitted system an annual solar fraction of 50.5% was achieved. A conventional solar thermal system using a standard solar tank achieves a comparable performance for the same total storage volume, collector area and reference conditions.

In order to make cities more resilient, our urban environment should not only consume energy, it should also become energy producing. Flat roofs are highly suitable for the placement of PV systems to produce renewable energy, but the assessment of its exact energy potential is not straightforward. Important configurations parameters of PV systems are the inclination and row distance, both leading to mutual shading. This study examined the technical and economic consequences of mutual shading of PV systems. In the first part, a comparison is performed between an unshaded module and a shaded module with different row distances and inclinations; in the second part, the energy output as well as payback times of a PV system on a flat roof were simulated. A significant decrease in energy production was seen due to mutual shading, while the configuration to achieve the maximum energy output was at an inclination of 0° and a row distance of 0 metres. Payback calculations showed that, when electricity prices rise in the future, more options concerning inclination and row distance became feasible

Many agricultural technology interventions that aim to improve farmers’ livelihoods focus on households as the unit of analysis and ignore gender roles that entail different benefits and costs for different household members. Agricultural projects have shown limited success where gender roles and relations were ignored and thus more gender sensitive research is needed in agricultural technology development to ensure social acceptance. In this study, we address this need by investigating the importance of gender roles and relations in the case of solar fruit drying in Mozambique. We apply a variety of gender sensitive participatory methods that enable farmers to actively take part in the technology development process. First results indicate that the costs and benefits of solar fruit drying are not shared equally between genders. Women have much less time available for using the solar fruit dryer. The data also indicate that certain steps in the solar fruit drying process are clearly gender divided. We finally discuss potential mechanisms that can be applied in agricultural technology projects that can create awareness of the risk to reproduce traditional gender roles and unequal relations in the development process of new agricultural technologies.