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Solar photovoltaic (PV) technology has become well-established for addressing both greenhouse gas emission reductions and regional air pollution. Rapid developments within the solar PV sector are still facing various technical barriers, economic impediments, and institutional barriers. The technical system innovations and their uses in society co-evolve with the engagement of multi-actors between scientific communities, users, investors, policymakers, and other stakeholders. Therefore, a holistic and interdisciplinary approach is called to analyze the complexities and solve the issues. 

This doctoral thesis takes a social science perspective in conjunction with technical considerations. China is a major producer and market for solar PV. But it is still not clear that how economically competitive solar PV electricity is, compared with the traditional coal-fired power generation without subsidies. Compared with China, the energy transition in Sweden has been progressively proceeding, which enables it to build a low-carbon economy with the lowest share of fossil fuels in the primary energy supply. An interesting part is to explore how solar PV applications, along with smart city transformation, change the electricity market logic with the emerging of new actors. Further, it is vital to assess the potential availability of solar applications for policymaking and grid accommodation. 

In this thesis, economic feasibility, grid party capability, and investment values in the market of China are modeled, calculated, and analyzed. The geographical and technical potential of solar PV applications is explored in Sweden. Also, based on a Service-Dominant logic perspective, the new players and their roles in the transformation of smart cities are explored, using the Swedish electricity market as an example. The results of the grid parity analysis show that distributed solar PV projects have reached a tipping point of cost-effectiveness, when solar PV can be guaranteed to be competitive with conventional power sources in the context of a subsidy-free in China. This also implies a gradual replacement of currently operating coal power plants. The investment return examination shows that profitability levels vary from city to city, taking into account local resource endowments and local economic conditions. By highlighting the flexibility issues associated with integrating a higher percentage of solar power, key performance indicators are presented to assess the performance of current individual technology components and combined system modules. Zooming out to the macro level, we show the theoretical explanation of how the Swedish electricity market is being changed by renewable energies and the emergence of new actors. 

Solar photovoltaic energy, driven mostly by the residential and commercial market segments, has been growing a lot in recent years in Sweden. In response to the commitment towards sustainability goals, this paper explores the potential of roof-mounted solar photovoltaic projects. This paper focuses on: roof area estimation, potential installed capacity, and potential electricity generation, at the single municipal scale and at the national scale. The following categories of different building types have been investigated: residential buildings, industrial buildings, buildings of social function, buildings of business function, buildings of economic/agricultural function, buildings of complementary function, and buildings of other unknown functions. The analysis starts from Västerås, a typical Swedish municipality and ranking seventh among the largest cities in Sweden. An estimate of 5.74 km2 available roof area potential is calculated, by considering factors such as building purposes, roof orientations, shadows and obstacles. The total potential installed capacity is calculated, assuming the installation of commercial photovoltaic modules, and design parameters for flat roofs such as inter-row distances and tilt angles. With the inputs of meteorological parameters and geographical information, the potential yearly electricity generation is calculated. The results reveal 727, 848, and 956 MWp potential installed capacity and 626, 720, and 801 GWh annual electricity production for Västerås on pitched roofs and flat roofs with three scenarios, respectively. The extrapolation of the methodology to the entire of Sweden yields a total of 504 km2 usable roof area and 65, 75, and 84 GWp installed capacity. Finally, we reveal a new understanding of usable roof area distribution and of potential installed capacity of roof-mounted solar photovoltaic systems, which can largely help evaluate subsidy scale and solar energy policy formulation in Sweden. 

This paper analyzes if solar photovoltaic technology is economically feasible enough to compete with coal-fired power in Chinese cities in the subsidy-free context. Considering this, this paper further investigates how profitable investing in solar PV projects is. This paper firstly analyzes to what degree local coal-fired power plants can be replaced by distributed solar power in 344 prefectural-level cities in China. Levelized Cost of Electricity of solar PV power and the local desulfurized coal benchmark price are used for simplified cost crossover math to identify the replacement risk of local coal-fired power plants. Four risk-levels and their corresponding cities are identified, i.e. deemed no cost-risk, potentially at cost-risk, at cost-risk, and substantially at cost-risk. As a whole, 85.17% of current coal-fired power plants from the investigated cities are under cost-risk. Levelized Profit of Electricity, Net Present Value, Internal Rate of Return, and Discounted Payback Period are calculated for each city, and grouped using K-means algorithm. The cities are clustered into four groups, i.e. high return, medium return, moderate return, and low return. The results show that 65.99% of all the cities could achieve a moderate or higher financial return. The cost-risk and investment profit results are mapped for a better understanding of the regional variation in China.

In recent years, China has become not just a large producer but a major market for solar photovoltaics (PV), increasing interest in solar electricity prices in China. The cost of solar PV electricity generation is affected by many local factors, making it a challenge to understand whether China has reached the threshold at which a grid-connected solar PV system supplies electricity to the end user at the same price as grid-supplied power or the price of desulfurized coal electricity, or even lower. Here, we analyse the net costs and net profits associated with building and operating a distributed solar PV project over its lifetime, taking into consideration total project investments, electricity outputs and trading prices in 344 prefecture-level Chinese cities. We reveal that all of these cities can achieve—without subsidies—solar PV electricity prices lower than grid-supplied prices, and around 22% of the cities’ solar generation electricity prices can compete with desulfurized coal benchmark electricity prices.

This study addresses the emergence of new actors and their roles in the transformation of smart cities. By building on a Service-Dominant logic perspective, the study capture how smart city transformation is closely related to a smart market transformation. While prior conceptualizations of markets have followed a linear supply-demand structure, the new market conceptualization can be described as a service ecosystem. The study empirically follows the increased use of renewable energy, such as photovoltaic (PV) systems and their related services, as they are incorporated into smart cities. The results reveal that the overall interaction level among the involved actors increases as the energy market changes from a linear to a networked logic. This transition impacts the market's information quality and, subsequently, the actors’ level of required knowledge. The study shows that even if the prevailing actors become more informed, information needs to be ‘translated’ into ‘knowledge-in-context’ to become a valuable resource. Thus, the resulting service ecosystem demands a complementary actor that requires the role of a knowledge broker to function. The paper describes the mechanisms behind this smart city transformation and clarifies the broker functions.

The increasing penetration of variable energy sources not only enables the power system to become greener and more cost-effective, but also brings more uncertainty to the energy balance equation. This new transition introduces a new challenge to manage the multi-energy system flexibility. Efforts have been made to assess the impact of such a large-scale integration.This study presents the results of identifying and selecting the key performance indicators (KPIs) that ca nbe used to assess the flexibility of the combined system modules for the evaluation of the entire multi-energy systems. The potential KPIs are initially collected via as ystematic literature review. Afterwards, a questionnaire is created with the aim to carry out a survey and identify the essential metrics to assess the system of interest. A statistical analysis is conducted using the respondents feedback. The results reveal the different importance of the KPIs among selected categories. In total, a list of 16 KPIs through four categories are recommended

Thermal energy storage (TES) can effectively recover thermal energy from low-temperature waste heat and it has now been received increasing attentions in practical engineering applications. Nevertheless, the relatively low thermal conductivity of engineering available phase change materials (PCMs) greatly limits the energy efficiency of TES applications. To enhance the phase change process, open-cell metal foam with a porosity of 0.94 and pore density of 15 PPI (pore per inch) was employed to be inserted either in heat transfer fluid (HTF) or in phase change material (PCM). A two-dimensional axis-symmetric problem was numerically solved and was validated through comparing temperature history at selected points. Results demonstrated that the involvement of open-cell metal foam can effectively enhance the phase change heat transfer, greatly reducing the full melting time. By comparing the four cases (without metal foam, inserting metal foam into HTF, PCM and both domains), the case that both HTF and PCM domains were embedded with porous media can provide the best heat transfer enhancement, from which practical applications with thermal engineering may benefit.

The increasing penetration level of renewable energy requires more flexibility measures to be implemented in future energy systems. Integrating an energy consumer’s local energy supplies connects multiple energy networks (i.e., the electrical grid, the district heating network, and gas network) in a decentralized way. Such integration enhances the flexibility of energy systems. In this work, a Swedish office building is investigated as a case study. Different components, including heat pump, electrical heater, battery and hot water storage tank are integrated into the electricity and heat supply system of the building. Special focus is placed on the flexibility that the studied building can provide to the electrical grid (i.e., the building modulates the electricity consumption in response to the grid operator’s requirements). The flexibility is described by two metrics including the flexibility hours and the flexibility energy. Optimization of the component capacities and the operation profiles is carried out by using Mixed Integer Linear Programming (MILP). The results show that the system fully relies on electricity for the heat demand when not considering the flexibility requirements of the electrical grid. This suggests that district heating is economically unfavorable compared with using electricity for the heat demand in the studied case. However, when flexibility requirements are added, the system turns to the district heating network for part of the heat demand. The system provides great flexibility to the electrical grid through such integration. The flexibility hours can be over 5200 h in a year, and the flexibility energy reaches more than 15.7 MWh (36% of the yearly electricity consumption). The yearly operation cost of the system slightly increases from 62,273 to 65,178 SEK when the flexibility hours increase from 304 to 5209 h. The results revealed that flexibility can be provided from the district heating network to the electrical grid via the building.