This review explores the relationship between urban energy planning and smart city evolution, addressing three primary questions: How has research on smart cities and urban energy planning evolved in the past thirty years? What promises and hurdles do smart city initiatives introduce to urban energy planning? And why do some smart city projects surpass energy efficiency and emission reduction targets while others fall short? Based on a bibliometric analysis of 9320 papers published between January 1992 and May 2023, five dimensions were identified by researchers trying to address these three questions: (1) energy use at the building scale, (2) urban design and planning integration, (3) transportation and mobility, (4) grid modernization and smart grids, and (5) policy and regulatory frameworks. A comprehensive review of 193 papers discovered that previous research prioritized technological advancements in the first four dimensions. However, there was a notable gap in adequately addressing the inherent policy and regulatory challenges. This gap often led to smart city endeavors underperforming relative to their intended objectives. Overcoming the gap requires a better understanding of broader issues such as environmental impacts, social justice, resilience, safety and security, and the affordability of such initiatives.

Efficient solar and wind energy to electricity conversion technologies are the best alternatives to reduce the use of fossil fuels and to evolve towards a green and decarbonized world. As the conventional photovoltaic systems use only the 600–1100 nm wavelength range of the solar radiation spectrum for electricity production, hybrid systems taking advantage of the overall solar radiation spectrum are gaining increasing interest. Moreover, such hybrid systems can produce, in an integrated and combined way, electricity, heating, cooling, and syngas through thermochemical processes. They have thus the huge potential for use in residential applications. The present work proposes a novel combined and integrated system for residential applications including wind turbines and a solar dish collector for renewables energy harvesting, an organic Rankine cycle for power production, an absorption chiller for cold production, and a methanation plant for CH₄ production from captured CO₂. This study deals with the energy, exergy, economic, and exergoenvironmental analyses of the proposed hybrid combined system, to assess its performance, viability, and environmental impact when operating in Tehran. Additionally, it gives a clear picture of how the production pattern of each useful product depends on the patterns of the collection of available renewable energies. Results show that the rate of methane production of this hybrid system changes from 42 up to 140 Nm³/month, due to CO₂ consumption from 44 to 144 Nm³/month during a year. Moreover, the energy and exergy efficiencies of this hybrid system vary from 24.7% and 23% to 9.1% and 8%, respectively. The simple payback period of this hybrid system is 15.6 and the payback period of the system is 21.4 years.

This research aims to analyze the relationship between environmental justice and urban green space connectivity in Tehran, Iran. The evaluation of green space connectivity in this study is conducted through two distinct cost layers: one aimed at enhancing existing connections and another focused on establishing new green spaces. Key factors influencing connectivity, extracted from the relevant literature, were identified to facilitate this analysis. Employing graph theory and least-cost analysis, the results determined critical resistance factors, current connectivity and cost status, the varying degrees to which different districts benefit from green space ecosystem services, and the most effective routes for establishing green corridors. Research findings highlight significant disparities in access to these services, particularly in the underserved central districts of Tehran. Moreover, spatial analysis reveals a higher potential for enhancing east–west ecosystem service corridors due to the higher density of green hubs and lower costs in this orientation, while north–south connectivity faces more challenges. By exploring land use/land cover, and physical and socio-economic factors affecting urban green space connectivity, this study provides urban and environmental planners with a novel methodology and comprehensive insights for effective decision making, resource allocation, and land use planning.