Impact of high PV penetration on distribution transformer insulation life

The reliable operation of distribution systems is critically dependent on detailed understanding of load impacts on distribution transformer insulation systems. This paper estimates the impact of rooftop photovoltaic (PV) generation on a typical 200-kVA, 22/0.415-kV distribution transformer life under different operating conditions. This transformer supplies a suburban area with a high penetration of roof top photovoltaic systems. The transformer loads and the phase distribution of the PV systems are significantly unbalanced. Oil and hot-spot temperature and remnant life of distribution transformer under different PV and balance scenarios are calculated. It is shown that PV can significantly extend the transformer life.

Evaluating the effects of high penetrations of roof-top wind Turbines on secondary distribution circuits

Incentives for using wind power and the increasing price of energy might generate in a relatively short time a scenario where low voltage customers opt to install roof-top wind turbines. This paper focuses on evaluating the effects of such situation in terms of energy consumption, loss reduction, reverse power flow and voltage profiles. Various commercially-available roof-top wind turbines are installed in two secondary distribution circuits considering real-life wind speed data and seasonal load demand. Results are presented and discussed. © 2006 IEEE.

Voltage balance improvement in urban low voltage distribution networks

This project is a step forward in developing effective methods to mitigate voltage unbalance in urban residential networks. The method is proposed to reduce energy losses and improve quality of service in strongly unbalanced low-voltage networks. The method is based on phase swapping as well as optimal placement and sizing of Distribution Static Synchronous Compensator (D-STATCOM) using a Particle Swarm Optimisation method.

Multi-agent systems for modeling high penetration photovoltaic system impacts in distribution networks

This paper reviews the use of multi-agent systems to model the impacts of high levels of photovoltaic (PV) system penetration in distribution networks and presents some preliminary data obtained from the Perth Solar City high penetration PV trial. The Perth Solar City trial consists of a low voltage distribution feeder supplying 75 customers where 29 consumers have roof top photovoltaic systems. Data is collected from smart meters at each consumer premises, from data loggers at the transformer low voltage (LV) side and from a nearby distribution network SCADA measurement point on the high voltage side (HV) side of the transformer. The data will be used to progressively develop MAS models.

Initial insights on the biodiversity potential of biosolar roofs: A London Olympic Park green roof case study

Cities dominated by impervious artificial surfaces can experience myriad negative environmental impacts. Restoration of green infrastructure has been identified as a mechanism for increasing urban resilience, enabling cities to transition towards sustainable futures in the face of climate-driven change. Building rooftops represent a viable space for integrating new green infrastructure into high density urban areas. Urban rooftops also provide prime locations for photovoltaic (PV) systems. There is increasing recognition that these two technologies can be combined to deliver reciprocal benefits in terms of energy efficiency and biodiversity targets. Scarcity of scientific evaluation of the interaction between PVs and green roofs means that the potential benefits are currently poorly understood. This study documents evidence from a biodiversity monitoring study of a substantial biosolar roof installed in the Queen Elizabeth Olympic Park. Vegetation and invertebrate communities were sampled and habitat structure measured in relation to habitat niches on the roof, including PV panels. Ninety-two plant species were recorded on the roof and variation in vegetation structure associated with proximity to PV panels was identified. Almost 50% of target invertebrate species collected were designated of conservation importance. Arthropod distribution varied in relation to habitat niches on the roof. The overall aim of the MPC green roof design was to create a mosaic of habitats to enhance biodiversity, and the results of the study suggest that PV panels can contribute to niche diversity on a green roof. Further detailed study is required to fully characterise the effects of PV panel density on biodiversity.

Potential of making - Over to sustainable buildings in the Kingdom of Bahrain

Two unique large buildings in the Kingdom of Bahrain were selected for make-over to sustainable buildings. These are the Almoayyed Tower (the first sky scraper) and the Bahrain International Circuit, BIC (The best world Formula 1 Circuit). The amount of electricity extracted from using renewable energy resource (solar and wind), integrated to the buildings-has been studied thoroughly. For the first building, the total solar electricity from the PV installed at the roof and the 4 vertical facades was found 3 017 500 kWh annually (3 million kWh), i.e. daily energy of 8219 kWh (enough to Supply electricity for 171 houses, each is rated as 2 kW house-in Europe the standard is 1.2 kW). This means that the annual solar electricity produced will be nearly 3 million kWh. This correspond to annual CO, reduction of 3000 t (assuming each kWh of energy from natural gas lead to emission of 1 kg of CO2). For the second building (BIC) the solar electricity from PV panels installed at the roof top, fixed at tilt angle of 26 degrees facing south, will provide annual solar electricity of is 2.8 x 10(6) kWh. The solar electricity from PV panels installed on the windows (12,000 m(2)) will be 45.3 x 10(6) kWh. This means that the total annual electrical power from PV panels (windows and roofs) will be nearly 12 MW (32 kW per day). The CO2 reduction will be 48,000 t. Under the carbon trading or CDM scheme the revenue (or the reward) would be (sic)480,000 million annually (the reward is (sic)10 per tonnes of CO2). The BIC circuit can have diversified electricity supply, i.e. from solar radiation (PV), from solar heat (CSP) and from wind (wind turbines), assuring its sustainability as well as reducing the CO2 emission.

Optimized operations of Distributed Renewable Energy Sources in Smart Grid

The renewable energy sources (RES) will play a vital role in the future power needs in view of the increasing demand of electrical energy and depletion of fossil fuel with its environmental impact. The main constraints of renewable energy (RE) generation are high capital investment, fluctuation in generation and requirement of vast land area. Distributed RE generation on roof top of buildings will overcome these issues to some extent. Any system will be feasible only if it is economically viable and reliable. Economic viability depends on the availability of RE and requirement of energy in specific locations. This work is directed to examine the economic viability of the system at desired location and demand.

Voltage unbalance reduction in low voltage feeders by dynamic switching of residential customers among three phases

Low voltage distribution feeders with large numbers of single phase residential loads experience severe current unbalance that often causes voltage unbalance problems. The addition of intermittent generation and new loads in the form of roof top photovoltaic generation and electric vehicles makes these problems even more acute. In this paper, an intelligent dynamic residential load transfer scheme is proposed. Residential loads can be transferred from one phase to another phase to minimize the voltage unbalance along the feeder. Each house is supplied through a static transfer switch with three-phase input and single-phase output connection. The main controller, installed at the transformer will observe the power consumption in each load and determine which house(s) should be transferred from one phase to another in order to keep the voltage unbalance in the feeder at a minimum. The efficacy of the proposed load transfer scheme is verified through MATLAB and PSCAD/EMTDC simulations.

Mathematical modelling and experimental validation of solar assisted heat pump system

Singapore is located at the equator, with abundant supply of solar radiation, relatively high ambient temperature and relative humidity throughout the year. The meteorological conditions of Singapore are favourable for efficient operation of solar energy based systems. Solar assisted heat pump systems are built on the roof-top of National University of Singapore’s Faculty of Engineering. The objectives of this study include the design and performance evaluation of a solar assisted heat-pump system for water desalination, water heating and drying of clothes. Using MATLAB programming language, a 2-dimensional simulation model has been developed to conduct parametric studies on the system. The system shows good prospect to be implemented in both industrial and residential applications and would give new opportunities in replacing conventional energy sources with green renewable energy.

Studies in biogas technology. Part IV. A novel biogas plant incorporating a solar water-heater and solar still

A reduction in the heat losses from the top of the gas holder of a biogas plant has been achieved by the simple device of a transparent cover. The heat losses thus prevented have been deployed to heat a water pond formed on the roof of the gas holder. This solar-heated water is mixed with the organic input for ‘ hot-charging ’ of the biogas plant. A thermal analysis of such a solar water-heater ‘ piggy-backing ’ on the gas holder of a biogas plant has been carried out.To test whether the advantages indicated by the thermal analysis can be realised in practice, a biogas plant of the ASTRA design was modified to incorporate a roof-top solar water-heater. The operation of such a modified plant, even under ‘ worst case ’ onditions, shows a significant improvement in the gas yield compared to the unmodified plant. Hence, the innovation reported here may lead to drastic reductions in the sizes and therefore costs of biogas plants. By making the transparent cover assume a tent-shape, the roof-top solar heater can serve the additional function of a solar still to yield distilled water. The biogas plant-cum-solar water-heater-cum-solar still described here is an example of a spatially integrated hybrid device which is extremely cost-effective.

Estudo de espécie nativa da restinga para plantio em telhados de construção de interesse social.

O alto crescimento populacional tem desencadeado uma elevada ocupação das áreas urbanas com a expansão de edificações e estradas causando alterações no meio ambiente com a consequente minimização das áreas verdes e da infiltração de água no solo. Estes fenômenos acarretam problemas como enxurradas, inundações, aumento da temperatura local e diminuição da biodiversidade com inúmeros efeitos adversos, tanto econômicos quanto ambientais e sociais. Uma das alternativas para minimizar estes problemas é a construção de telhados verdes, que tem como uma das principais funções retardar o escoamento devido ao aumento da infiltração e retenção da água das chuvas atenuando o efeito avassalador das enchentes e das zonas de calor, principalmente em climas muito quentes, além de colaborar para recuperação de ecossistemas, através do replantio de mudas. Este projeto faz parte de um conjunto de ações integradas de cidadania e inclusão social na região hidrográfica da baixada de Jacarepaguá, especificamente envolvendo a Comunidade da Vila Cascatinha, em Vargem Grande, a fim de gerar subsídios para políticas públicas em áreas de assentamentos informais, integrado ao projeto HIDROCIDADES (CNPq, FAPERJ, FINEP), que visa a conservação da água em meios urbanos e periurbanos associado à cidadania, inclusão social e melhoria da qualidade de vida nas grandes cidades. Este trabalho utiliza uma tecnologia adaptada dos telhados verdes para edificação popular (telhado de fibrocimento) muito comum no Brasil, com o objetivo de verificar uma espécie com potencial de geração de renda (visando o social) de ecossistema regionais como restinga, em edificação; analisar o crescimento e biomassa da espécie de restinga cultivada em telhados; e avaliar qualidades das mídias em função do plantio em análise de armazenamento (retenção) de água no solo. A partir da metodologia empregada na implantação dos telhados verdes em habitações populares, os resultados obtidos são desenvolvimento da espécie Ipomoea pes caprae Brasiliensis, em três tipos de mídias de crescimento e também eficiência dessas mídias no escoamento superficial. Observou-se retenção de 69,24L de água para o bagaço de cana de açúcar e 64,7L para a fibra de coco. E foi observado também um retardo da ocorrência do pico de até 14 minutos no telhado vegetado em relação ao telhado controle (convencional).

Effect of building integrated photovoltaics on microclimate of urban canopy layer

Building integrated photovoltaics (BIPV) has potential of becoming the mainstream of renewable energy in the urban environment. BIPV has significant influence on the thermal performance of building envelope and changes radiation energy balance by adding or replacing conventional building elements in urban areas. PTEBU model was developed to evaluate the effect of photovoltaic (PV) system on the microclimate of urban canopy layer. PTEBU model consists of four sub-models: PV thermal model, PV electrical performance model, building energy consumption model, and urban canyon energy budget model. PTEBU model is forced with temperature, wind speed, and solar radiation above the roof level and incorporates detailed data of PV system and urban canyon in Tianjin, China. The simulation results show that PV roof and PV façade with ventilated air gap significantly change the building surface temperature and sensible heat flux density, but the air temperature of urban canyon with PV module varies little compared with the urban canyon of no PV. The PV module also changes the magnitude and pattern of diurnal variation of the storage heat flux and the net radiation for the urban canyon with PV increase slightly. The increase in the PV conversion efficiency not only improves the PV power output, but also reduces the urban canyon air temperature. © 2006.

Planning Urban Food Production into Today's Cities

If cities are to become more sustainable and resilient to change it is likely that they will have to engage with food at increasingly localised levels, in order to reduce their dependancy on global systems. With 87 percent of developed regions estimated to be living in cities by 2050 it can be assumed that the majority of this localised production will occur in and around cities.
As part of a 12 month engagement, Queen’s University Belfast designed and implemented an elevated aquaponic food system spanning the top floor and exterior roof space of a disused mill in Manchester, England. The experimental aquaponic system was developed to explore the possibilities and difficulties associated with containing fish tanks, filtration units, vertical growing systems and roof top growing systems within and upon existing buildings, including the structural considerations needed when undertaking such transformations. Although capable of producing 4000 crops at any one time, the elevated aquaponic system utilised space within the existing building, which could otherwise be used as lettable area, and also located some crop growth within the building where light levels are reduced.
The following paper takes the research collected from the elevated aquaponic system and extrapolates the findings across a whole city. The resulting research enables the agricultural productive capacity of todays cities to be determined and a frame work of implementation to be developed for city wide food production. The research focuses specifically on facade and roof based systems, thus elevating the need to utilise lettable area within cities in addition to locating crops where light levels are highest.

Caracterização do potencial eólico urbano: o caso de Lisboa

Trabalho Final de Mestrado para obtenção do grau de Mestre em Engenharia Civil na Área de Especialização em Edificações

Referencing of street-level flows measured during the DAPPLE 2004 campaign

Street-level mean flow and turbulence govern the dispersion of gases away from their sources in urban areas. A suitable reference measurement in the driving flow above the urban canopy is needed to both understand and model complex street-level flow for pollutant dispersion or emergency response purposes. In vegetation canopies, a reference at mean canopy height is often used, but it is unclear whether this is suitable for urban canopies. This paper presents an evaluation of the quality of reference measurements at both roof-top (height = H) and at height z = 9H = 190 m, and their ability to explain mean and turbulent variations of street-level flow. Fast response wind data were measured at street canyon and reference sites during the six-week long DAPPLE project field campaign in spring 2004, in central London, UK, and an averaging time of 10 min was used to distinguish recirculation-type mean flow patterns from turbulence. Flow distortion at each reference site was assessed by considering turbulence intensity and streamline deflection. Then each reference was used as the dependent variable in the model of Dobre et al. (2005) which decomposes street-level flow into channelling and recirculating components. The high reference explained more of the variability of the mean flow. Coupling of turbulent kinetic energy was also stronger between street-level and the high reference flow rather than the roof-top. This coupling was weaker when overnight flow was stratified, and turbulence was suppressed at the high reference site. However, such events were rare (<1% of data) over the six-week long period. The potential usefulness of a centralised, high reference site in London was thus demonstrated with application to emergency response and air quality modelling.