Emissions reduction data for grid-connected photovoltaic power systems

This study measured the pollutant emission reduction potential of 29 photovoltaic (PV) systems installed on residential and commercial building rooftops across the US from 1993 through 1997. The US Environmental Protection Agency (EPA) and 21 electric power companies sponsored the project. This article presents results of analyses of each PV system’s ability to offset electric utility power plant emissions of sulfur dioxide (SO₂), nitrogen oxides (NO_x), and carbon dioxide (CO₂). Each PV system’s performance was monitored and compared with hour-by-hour operating characteristics of the participating electric utilities in order to determine pollution offsets. The monthly mean and standard deviation offset are given for each pollutant, along with the coefficient of variation.     

Distributed grid-connected photovoltaic power system emission offset assessment: statistical test of simulated- and measured-based data

This study assesses the pollutant emission offset potential of distributed grid-connected photovoltaic (PV) power systems. Computer-simulated performance results were utilized for 214 PV systems located across the US. The PV systems’ monthly electrical energy outputs were based on a performance calculator called PVWATTS. Offset emissions of sulfur dioxide (SO₂), carbon dioxide (CO₂), and nitrogen oxides (NO_x) were determined from PV system outputs and average utility emissions data from each state. For validation, the simulated monthly results were statistically compared with measurement-based data (both production and corresponding emissions data) from 29 PV systems installed at different sites across the US.

While the data shows high (geographic) variability, the substantial number of measurements allows reliable statistical analysis. The methods are found to give consistent results in spite of the necessity to employ some even quite crude input approximations—such as the use of statewide rather than specific emissions data for the systems. No significant differences between simulated and measured monthly means for any of the pollutants were noted on the basis of individual monthly analyses, though the results for NO_x suggest the possible existence of some difference in that case. A more detailed statistical modeling using all monthly data in one combined analysis (allowing improved variability estimation) confirms these conclusions. Even the shorter confidence intervals for expected offsets obtained through the combined analysis show no significant differences between simulated and measured methods for SO₂ and CO₂. The differences for NO_x are statistically significant but consistent—suggesting useful prediction by the simulations via a constant correction factor. As expected, significant differences between months are evident for both simulated and measured offsets.     

Optimal sizing of grid-connected photovoltaic energy system in Saudi Arabia

Resource optimization is a major factor in the assessment of the effectiveness of renewable energy systems. Various methods have been utilized by different researchers in planning and sizing the grid-connected PV systems. This paper analyzes the optimal photovoltaic (PV) array and inverter sizes for a grid-connected PV system. Unmet load, excess electricity, fraction of renewable electricity, net present cost (NPC) and carbon dioxide (CO₂) emissions percentage are considered in order to obtain optimal sizing of the grid-connected PV system. An optimum result, with unmet load and excess electricity of 0%, for serving electricity in Makkah, Saudi Arabia is achieved with the PV inverter size ratio of R = 1 with minimized CO₂ emissions. However, inverter size can be downsized to 68% of the PV nominal power to reduce the inverter cost, and hence decrease the total NPC of the system.     

Transmission network-based energy and environmental assessment of plug-in hybrid electric vehicles

The introduction of plug-in hybrid electric vehicles (PHEVs) is expected to have a significant impact on regional power systems and pollutant emissions. This paper analyzes the effects of various penetrations of PHEVs on the marginal fuel dispatch of coal, natural gas and oil, and on pollutant emissions of CO₂, NO_x, SO₂ in the New York Metropolitan Area for two battery charging scenarios in a typical summer and winter day. A model of the AC transmission network of the Northeast Power Coordinating Council (NPCC) region with 693 generators is used to realistically incorporate network constraints into an economic dispatch model. A data-based transportation model of approximately 1 million commuters in NYMA is used to determine battery charging pattern. Results show that for all penetrations of PHEVs network-constrained economic dispatch of generation is significantly more realistic than unconstrained cases. Coal, natural gas and oil units are on the margin in the winter, and only natural gas and oil units are on the margin in the summer. Hourly changes in emissions from transportation and power production are dominated by vehicular activity with significant overall emissions reductions for CO₂ and NO_x, and a slight increase for SO₂. Nighttime regulated charging produces less overall emissions than unregulated charging from when vehicles arrive home for the summer and vice versa for the winter. As PHEVs are poised to link the power and transportation sectors, data-based models combining network constraints and economic dispatch have been shown to improve understanding and facilitate control of this link.     

The technical,geographical, and economic feasibility for solar energy to supply the energy needs of the US

So far, solar energy has been viewed as only a minor contributor in the energy mixture of the US due to cost and intermittency constraints. However, recent drastic cost reductions in the production of photovoltaics (PV) pave the way for enabling this technology to become cost competitive with fossil fuel energy generation. We show that with the right incentives, cost competitiveness with grid prices in the US (e.g., 6–10 US¢/kWh) can be attained by 2020. The intermittency problem is solved by integrating PV with compressed air energy storage (CAES) and by extending the thermal storage capability in concentrated solar power (CSP). We used hourly load data for the entire US and 45-year solar irradiation data from the southwest region of the US, to simulate the CAES storage requirements, under worst weather conditions. Based on expected improvements of established, commercially available PV, CSP, and CAES technologies, we show that solar energy has the technical, geographical, and economic potential to supply 69% of the total electricity needs and 35% of the total (electricity and fuel) energy needs of the US by 2050. When we extend our scenario to 2100, solar energy supplies over 90%, and together with other renewables, 100% of the total US energy demand with a corresponding 92% reduction in energy-related carbon dioxide emissions compared to the 2005 levels.     

Review of research on autonomous wind farms and solar parks and their feasibility for commercial loads in hot regions

In the wake of rising cost of oil and fears of its exhaustion coupled with increased pollution, the governments world-wide are deliberating and making huge strides to promote renewable energy sources such as solar–photovoltaic (solar–PV) and wind energy. Integration of diesel systems with hybrid wind–PV systems is pursued widely to reduce dependence on fossil-fuel produced energy and to reduce the release of carbon gases that cause global climate change. Literature indicates that commercial/residential buildings in the Kingdom of Saudi Arabia (KSA) consume an estimated 10–40% of the total electric energy generated. The study reviews research work carried out world-wide on wind farms and solar parks. The work also analyzes wind speed and solar radiation data of East-Coast (Dhahran), KSA, to assess the technical and economic potential of wind farm and solar PV park (hybrid wind–PV–diesel power systems) to meet the load requirements of a typical commercial building (with annual electrical energy demand of 620,000 kWh). The monthly average wind speeds range from 3.3 to 5.6 m/s. The monthly average daily solar global radiation ranges from 3.61 to 7.96 kWh/m². The hybrid systems simulated consist of different combinations of 100 kW wind machines, PV panels, supplemented by diesel generators. NREL (and HOMER Energy's) HOMER software has been used to perform the techno-economic study. The simulation results indicate that for a hybrid system comprising of 100 kW wind capacity (37 m hub-height) and 40 kW of PV capacity together with 175 kW diesel system, the renewable energy fraction (with 0% annual capacity shortage) is 36% (24% wind + 12% PV). The cost of generating energy (COE, $/kWh) from this hybrid wind–PV–diesel system has been found to be 0.154 $/kWh (assuming diesel fuel price of 0.1$/L). The study exhibits that for a given hybrid configuration, the number of operational hours of diesel generators decreases with increase in wind farm and PV capacity. Attention has also been focused on wind/PV penetration, un-met load, excess electricity generation, percentage fuel savings and reduction in carbon emissions (relative to diesel-only situation) of different hybrid systems, cost break-down of wind–PV–diesel systems, COE of different hybrid systems, etc.     

Short-term predictability of photovoltaic production over Italy

Photovoltaic (PV) power production increased drastically in Europe throughout the last years. Since about the 6% of electricity in Italy comes from PV, an accurate and reliable forecasting of production would be needed for an efficient management of the power grid. We investigate the possibility to forecast daily PV electricity production up to ten days without using on-site measurements of meteorological variables. Our study uses a PV production dataset of 65 Italian sites and it is divided in two parts: first, an assessment of the predictability of meteorological variables using weather forecasts; second, an analysis of predicting solar power production through data-driven modelling. We calibrate Support Vector Machine (SVM) models using available observations and then we apply the same models on the weather forecasts variables to predict daily PV power production. As expected, cloud cover variability strongly affects solar power production, we observe that while during summer the forecast error is under the 10% (slightly lower in south Italy), during winter it is abundantly above the 20%.     

Economic impact of integrating photovoltaics with conventionalelectric utility operation

The parameters which impact the value of photovoltaics (PV) to the electric utility is examined. High, medium, and low-load days in winter (January) and summer (July) are studied. The daily peak load is varied from 5838 MW to 9712 MW. These six days are studied for reference (no PV), high, medium, low, and intermittent-PV output cases. Results from these 30 case studies are summarized. In order to study the impact of operating PV systems on the electric utility production cost (fuel and variable operation and maintenance), the load profile of a southeastern utility and the PV output data from solar test facilities in Virginia and North Carolina are used. The performance analysis shows that, while the total production (fuel and variable O&M) cost savings are higher for higher solar days, the increase is not proportional to the amount of PV energy output. It is shown that the high solar day never produced the highest per-unit PV energy value. The highest per-unit PV energy values for both winter and summer days are found to be for the low solar days     

Solar space heating and cooling for Spanish housing: Potential energy savings and emissions reduction

An experimental solar energy facility was designed to meet as much of the heating demand in a typical Spanish dwelling as possible. With a view to using the facility during the summer and preventing overheating-induced deterioration of the solar collectors in that season of the year, an absorption chiller was fitted to the system to produce solar-powered air conditioning. The facility operated in solar space heating mode in the winter of 2008–2009 and in cooling mode during the summer of 2008. The design was based on a new type of flat plate vacuum solar collectors that delivered higher efficiency than conventional panels. This type of collectors can reach temperatures of up to 110 °C in the summer and up to 70 °C on the coldest winter days. The solar facility comprised a 48-m² (with a net area of 42 m²) solar collector field, a 25-kW plate heat exchanger, a 1500-l storage tank, a 4.5-kW (Rotartica) air-cooled absorption chiller and several fan coils. The facility was tested by using it to heat and cool an 80-m² laboratory located in Madrid. As the average area of Spanish homes is 80 m², the findings were generally applicable to national housing. The solar facility was observed to be able to meet 65.3% of the space heating demand. For air conditioning, the system covered 46% of the demand, but with high indoor temperatures. In other words, the collector field was found to be able to air condition only half of the home (40 m²). Lastly, the savings in CO₂ emissions afforded by the use of this facility compared to conventional air conditioning were calculated, along with its amortisation period. These results have been extrapolated calculating the potential energy savings and emissions reduction for all the Spanish households.     

Design of direct solar PV driven air conditioner

Solar air conditioning system directly driven by stand-alone solar PV is studied. The air conditioning system will suffer from loss of power if the solar PV power generation is not high enough. It requires a proper system design to match the power consumption of air conditioning system with a proper PV size. Six solar air conditioners with different sizes of PV panel and air conditioners were built and tested outdoors to experimentally investigate the running probabilities of air conditioning at various solar irradiations. It is shown that the instantaneous operation probability (OPB) and the runtime fraction (R_F) of the air conditioner are mainly affected by the design parameter r_pL (ratio of maximum PV power to load power). The measured OPB is found to be greater than 0.98 at instantaneous solar irradiation I_T > 600 W m⁻² if r_pL > 1.71. R_F approaches 1.0 (the air conditioner is run in 100% with solar power) at daily-total solar radiation higher than 13 MJ m⁻² day⁻¹, if r_pL > 3.     

Hydrogen production from solar energy powered supercritical cycle using carbon dioxide

A hydrogen production method is proposed, which utilizes solar energy powered thermodynamic cycle using supercritical carbon dioxide (CO₂) as working fluid for the combined production of hydrogen and thermal energy. The proposed system consists of evacuated solar collectors, power generating turbine, water electrolysis, heat recovery system, and feed pump. In the present study, an experimental prototype has been designed and constructed. The performance of the cycle is tested experimentally under different weather conditions. CO₂ is efficiently converted into supercritical state in the collector, the CO₂ temperature reaches about 190 °C in summer days, and even in winter days it can reach about 80 °C. Such a high-temperature realizes the combined production of electricity and thermal energy. Different from the electrochemical hydrogen production via solar battery-based water splitting on hand, which requires the use of solar batteries with high energy requirements, the generated electricity in the supercritical cycle can be directly used to produce hydrogen gas from water. The amount of hydrogen gas produced by using the electricity generated in the supercritical cycle is about 1035 g per day using an evacuated solar collector of 100.0 m² for per family house in summer conditions, and it is about 568.0 g even in winter days. Additionally, the estimated heat recovery efficiency is about 0.62. Such a high efficiency is sufficient to illustrate the cycle performance.     

Assessment of high penetration of solar photovoltaics in Wisconsin

This paper provides an assessment of the large-scale implementation of distributed solar photovoltaics in Wisconsin with regard to its interaction with the utility grid, economics of varying levels of high penetration, and displaced emissions. These assessment factors are quantified using simulations with measured hourly solar radiation and weather data from the National Solar Radiation Database as primary inputs. Hourly utility load data for each electric utility in Wisconsin for a complete year were used in combination with the simulated PV output to quantify the impacts of high penetration of distributed PV on the aggregate Wisconsin electric utility load.     

Study of solar energy powered transcritical cycle using supercritical carbon dioxide

In this paper, the performance of solar energy powered transcritical cycle using supercritical carbon dioxide for a combined electricity and heat generation, is studied experimentally. The experimental set‐up consists of evacuated solar collectors, pressure relief valve, heat exchangers and CO₂ feed pump. The pressure relief valve is used to simulate operation of a turbine and to complete the thermodynamic cycle. A complete effort was carried out to investigate the cycle performances not only in summer, but also in winter conditions. The results show that a reasonable thermodynamic efficiency can be obtained and COP for the overall outputs from the cycle is measured at 0.548 and 0.406, respectively, on a typical summer and winter day. The study shows the potential of the application of the solar energy powered cycle as a green power/heat generation system. Copyright © 2006 John Wiley & Sons, Ltd.     

Life cycle assessment study of solar PV systems: An example of a 2.7 kWp distributed solar PV system in Singapore

In life cycle assessment (LCA) of solar PV systems, energy pay back time (EPBT) is the commonly used indicator to justify its primary energy use. However, EPBT is a function of competing energy sources with which electricity from solar PV is compared, and amount of electricity generated from the solar PV system which varies with local irradiation and ambient conditions. Therefore, it is more appropriate to use site-specific EPBT for major decision-making in power generation planning. LCA and life cycle cost analysis are performed for a distributed 2.7 kW_p grid-connected mono-crystalline solar PV system operating in Singapore. This paper presents various EPBT analyses of the solar PV system with reference to a fuel oil-fired steam turbine and their greenhouse gas (GHG) emissions and costs are also compared. The study reveals that GHG emission from electricity generation from the solar PV system is less than one-fourth that from an oil-fired steam turbine plant and one-half that from a gas-fired combined cycle plant. However, the cost of electricity is about five to seven times higher than that from the oil or gas fired power plant. The environmental uncertainties of the solar PV system are also critically reviewed and presented.     

Hydrogen production by water electrolysis and off-grid solar PV

This work concerns a methodology for PV-H₂ hybrid system design that consider the weather data and the electrical variables of the subsystems to perform energy balances and to assess the systems in terms of the capacity and operation of the components, and the resulting costs.Two configurations (with and without batteries) and two locations (Madrid and Fisciano) were studied to find the best trade-off between the efficiency and sizes of the subsystems. Directly connected systems operate at intersection points between the PV output and electrolyzer (EL) input curves for different solar irradiance levels, while the battery assisted systems reduce the sizes of EL at the expense of higher energy loss and additional cost of batteries (B). It was found how is not convenient to operate the EL at fixed rate, resulting in high PV and B sizes, as well as power unbalances in winter and summer. Solutions are to run the EL at a minimal load at night and change the intensity of daytime operations to achieve null cumulative energy each season.The H₂ supplied by these systems has the merit of being sustainable (renewable) and autonomous (avoiding power constraints in off-grid locations), and the costs are around 6–7 €/kg_H2.     

Off-grid solar-hydrogen generation by passive electrolysis

A novel embodiment of a polymer electrolyte membrane (PEM) electrolyser is presented as a means for producing hydrogen off-grid by the efficient absorption of the time-varying power output of a solar photovoltaic (PV) panel or array. The balance-of-plant power load was minimised using passive design principles to ensure efficient operation under cloudy, sunset and wintry conditions. Heat generated during the electrolysis process is stored when appropriate to significantly enhance the efficiency of hydrogen production after a period of darkness. A prototype field trial demonstrated the electrolyser's ability to track closely the highly variable output of the PV year-round under a wide range of operating conditions. Hydrogen yields for various geographical locations were estimated to vary from 25 to 65 kg p.a. for a 1.6 kW electrolyser with fixed-tilt PV panels depending on local levels of solar insolation. This could be increased to over 100 kg p.a. by employing a PV panel of greater capacity and a battery for absorbing the peak generation and then discharging it overnight to the electrolyser.     

Photovoltaic (PV) electricity: Comparative analyses of CO2 abatement at different fuel mix scales in the US

Photovoltaic electricity has the potential to mitigate CO₂ emissions from the grid. A methodology to more accurately evaluate CO₂ abatement by PV electricity is developed. We develop a capacity factor based dispatching model to evaluate marginal abatement in the load zones of ERCOT and CAISO, and compare it to the abatement using national, regional and state average resource profiles. The average cases over-estimated and under-estimated CO₂ abatement in ERCOT and CAISO, respectively. Marginal abatement was lower by 17% than the average cases in ERCOT, due to the predominant displacement of the low carbon natural gas plants at the margin. In CASIO, marginal abatement was higher (1.3–2.4 times) than that of the average cases due to the displacement of highly inefficient gas plants at the margin. We demonstrate that actual CO₂ abatement of PV electricity is dependent on both peak load resources and capacity of installations. Subsequently, we develop a CO₂ indicator that can be used as a guideline for selecting PV installation sites to derive maximum abatement. Installing photovoltaics in regional areas of MRO, SPP and RFC was determined to be most beneficial. The results of this study can guide energy planning and CO₂ mitigation policy-making using photovoltaics in the future.     

A solar and wind driven energy system for hydrogen and urea production with CO2 capturing

A novel solar PV and wind energy based system is proposed in this study for capturing carbon dioxide as well as producing hydrogen, urea and power. Both Aspen Plus and EES software packages are employed for analyses and simulations. The present system is designed in a way that PEM electrolyzer is powered by the wind turbines for hydrogen production, which is further converted into ammonia and then synthesizes urea by capturing CO₂ and additional power is supplied to the community. The solar PV is employed to power the cryogenic air separation unit and the additional power is used for the industrial purpose. In the proposed system, ammonia does not only capture CO₂ but also synthesizes urea for fertilizer industry. The amount of electrical power produced by the system is 2.14 MW. The designed system produces 518.4 kmol/d of hydrogen and synthesizes 86.4 kmol/d of urea. Furthermore, several parametric studies are employed to investigate the system performance.     

Technico-economic analysis of off grid solar PV/Fuel cell energy system for residential community in desert region

A technico-economic analysis based on integrated modeling, simulation, and optimization approach is used in this study to design an off grid hybrid solar PV/Fuel Cell power system. The main objective is to optimize the design and develop dispatch control strategies of the standalone hybrid renewable power system to meet the desired electric load of a residential community located in a desert region. The effects of temperature and dust accumulation on the solar PV panels on the design and performance of the hybrid power system in a desert region is investigated. The goal of the proposed off-grid hybrid renewable energy system is to increase the penetration of renewable energy in the energy mix, reduce the greenhouse gas emissions from fossil fuel combustion, and lower the cost of energy from the power systems. Simulation, modeling, optimization and dispatch control strategies were used in this study to determine the performance and the cost of the proposed hybrid renewable power system. The simulation results show that the distributed power generation using solar PV and Fuel Cell energy systems integrated with an electrolyzer for hydrogen production and using cycle charging dispatch control strategy (the fuel cell will operate to meet the AC primary load and the surplus of electrical power is used to run the electrolyzer) offers the best performance. The hybrid power system was designed to meet the energy demand of 4500 kWh/day of the residential community (150 houses). The total power production from the distributed hybrid energy system was 52% from the solar PV, and 48% from the fuel cell. From the total electricity generated from the photovoltaic hydrogen fuel cell hybrid system, 80.70% is used to meet all the AC load of the residential community with negligible unmet AC primary load (0.08%), 14.08% is the input DC power for the electrolyzer for hydrogen production, 3.30% are the losses in the DC/AC inverter, and 1.84% is the excess power (dumped energy). The proposed off-grid hybrid renewable power system has 40.2% renewable fraction, is economically viable with a levelized cost of energy of 145 $/MWh and is environmentally friendly (zero carbon dioxide emissions during the electricity generation from the solar PV and Fuel Cell hybrid power system).     

Temporal CO2 emissions associated with electricity generation: Case study of Singapore

Studying temporal patterns in emissions associated with electricity generation is increasingly important. On the supply side, there is interest in integrating renewable energy sources (solar, wind), which are known to vary daily and hourly. On the demand side, the concept of demand response is driving a need to better understand the impact of peak versus off-peak loading, with the objective of maximizing efficiency. In this study, we examine the case of electric power generation in Singapore, and aim to assess the half-hourly variation in associated average carbon dioxide emissions. Given the country’s serious push for clean energy solutions and a possibility of adopting carbon trading in the future, we feel the need to address the currently existing gap in research on daily CO₂ emissions patterns. By associating representative electricity generation data with the characterized fleet of power plants, half-hourly emissions are found to range between 415 and 455 kg CO₂ per MW h. Marginal emission factors show a fluctuating daily pattern between 390 and 800 kg CO₂/MW h. Policy makers able to work with real generation data can use this approach to understand the carbon footprint of short-term supply and demand interventions.