Load-following Strategy Research Articles

Influence of climatic conditions and control logic on NOx and CO emissions of a micro-cogeneration unit serving an Italian residential building

The increasing diffusion of micro-cogeneration systems is raising the need for studying their environmental impact in order to assess their sustainability. The adoption of the systems for the combined production of heat and power may provide a significant reduction of global impact in terms of carbon dioxide emissions with respect to the separate production of electricity and heat. However, a comprehensive environmental evaluation of this technology should take into account as well the impact due to the presence of plants spread over the territory that could increase the local pollution, in particular due to nitrogen oxides and carbon monoxide, and thus could worsen the local air quality.In this paper the nitrogen oxides and carbon monoxide emissions of a residential building-integrated micro-cogeneration system were evaluated; a 6.0 kWel natural gas fuelled internal combustion engine-based micro-cogeneration unit was coupled with a multi-family house compliant with the transmittance values suggested by the Italian Law. The analyses were carried out by using the whole building simulation software TRNSYS upon varying the city where the building is located (four Italian cities representative of different climatic regions were considered) as well as the control logic of cogeneration device (electric and thermal load-following strategies). The simulated performance of the proposed system was compared with those of a conventional system composed of a natural gas-fired boiler (for thermal energy production) and a power plant mix connected to the central electric grid (for electricity production) in order to assess the suitability of the cogeneration-based system in reducing the local emissions.

Load-following mode control of a standalone renewable/fuel cell hybrid power source

A hybrid power source (HPS), fed by renewable energy sources (RESs) and fuel cell (FC) sources, with an energy storage device (ESS) to be suitable for distributed generation (DG) applications, is proposed herein. The RESs could be a combination of photovoltaic (PV) panels and wind turbines (WT) based on common DC-bus, which are used as the primary DC source. The FC operates as a backup, feeding only the insufficiency power from the RESs based on the load-following strategy. The battery/ultracapacitor hybrid ESS operates as an auxiliary source for supplying the power deficit based on dynamic power balance strategy (the transient power – mainly via the ultracapacitors stack, and the steady-state power – mainly via the FC and batteries stack). If the FC stack is designed and operates based on average load-following strategy, then the ESS will operate in charge-sustaining mode during a load cycle. This feature permits to optimize the batteries stack capacity and extend its life time as well. The ultracapacitors stack can be designed considering the peaks of RESs power on DC-bus and the imposed window for its state-of-charge (SOC). This FC/RES/ESS HPS is ideal to be used for standalone plug-in charge station (PCS) or as DG system grid connected. In the last case, which is not analyzed here, the energy management unit (EMU) that communicates with smart grid will establish the moments to match the HPS power demand with grid supply availability, stabilizing the grid. Using load and RES power profiles that have a higher dynamic than in reality, the HPS operation is shown based on an analytical analysis and the appropriate Matlab/Simulink® simulations.

Multi-objective optimization design and operation strategy analysis of BCHP system based on life cycle assessment

The promising energetic and environmental benefits of building cooling heating and power (BCHP) system are greatly dependent upon its design and operation strategy. In this paper, the energy and emission flows and different operation strategies of a BCHP system driven by gas engine are analyzed. Life cycle assessment (LCA) is employed to assess and compare the whole life energy saving potentials and pollutant emission reductions of BCHP system with the traditional energy system. Furthermore, energy consumption and three pollutant-related impacts, global warming, acid precipitation and respiratory effects, are selected as objective functions to optimize the gas engine capacity of BCHP system in different operation strategies. A numerical case of BCHP system for a commercial office building in Beijing, China is applied to obtain the optimum BCHP alternative in terms of the comprehensive energy and environment performance. The uncertainty of different evaluation criteria weights is also analyzed to show their influences on the optimal design and operation strategy. The results show that a reasonably sized BCHP system with an electric load-following strategy has the best performance under a wide interval of criteria weights, when the energetic and environmental benefits of producing excess electricity for nearby users are not considered.

Load-Following Strategies for Evolution of Solid Oxide Fuel Cells Into Model Citizens of the Grid

Proper converter design can allow solid oxide fuel cells operated as distributed generators to mutually benefit both the load and the electric utility during steady-state conditions, but dynamic load variations still present challenges. Unlike standard synchronous generators, fuel cells lack rotating inertia and their output power ramp rate is limited by design. Two strategies are herein investigated to mitigate the impact of a large load perturbation on the electric utility grid: 1) external use of ultracapacitor electrical storage connected through a DC-DC converter and 2) internal reduction of steady-state fuel utilization in the fuel cell to enable faster response to output power perturbations. Both strategies successfully eliminate the impact of a load perturbation on the utility grid. The external ultracapacitor strategy requires more capital investment while the internal fuel utilization strategy requires higher fuel use. This success implies that there is substantial flexibility for designing load-following fuel cell systems that are model citizens.

Trigeneration in food retail: An energetic, economic and environmental evaluation for a supermarket application

This paper presents results on the evaluation of energy utilisation efficiency and economic and environmental performance of a micro-gas turbine (MGT) based trigeneration system for supermarket applications. A spreadsheet energy model has been developed for the analysis of trigeneration systems and a 2800 m 2 sales area supermarket was selected for the feasibility study. Historical energy demand data were used for the analysis, which considered factors such as the fraction of the heat output used to drive the absorption chillers, the chiller COP and the difference between electricity and gas prices. The results showed that energy and environmental benefits can be obtained from the application of trigeneration systems to supermarkets compared to conventional systems. The payback period of natural gas driven trigeneration systems and greenhouse gas emissions savings will depend on the relative gas and electricity prices and the COP of the vapour compression and absorption systems. It was also shown that operation at full electrical output gives a better performance than a heat load-following strategy due to the reduction of the electrical generation efficiency of the MGT unit at part load conditions.

Effects of ambient conditions on fuel cell vehicle performance

Ambient conditions have considerable impact on the performance of fuel cell hybrid vehicles. Here, the vehicle fuel consumption, the air compressor power demand, the water management system and the heat loads of a fuel cell hybrid sport utility vehicle (SUV) were studied. The simulation results show that the vehicle fuel consumption increases with 10% when the altitude increases from 0 m up to 3000 m to 4.1 L gasoline equivalents/100 km over the New European Drive Cycle (NEDC). The increase is 19% on the more power demanding highway US06 cycle. The air compressor is the major contributor to this fuel consumption increase. Its load-following strategy makes its power demand increase with increasing altitude. Almost 40% of the net power output of the fuel cell system is consumed by the air compressor at the altitude of 3000 m with this load-following strategy and is thus more apparent in the high-power US06 cycle. Changes in ambient air temperature and relative humidity effect on the fuel cell system performance in terms of the water management rather in vehicle fuel consumption. Ambient air temperature and relative humidity have some impact on the vehicle performance mostly seen in the heat and water management of the fuel cell system. While the heat loads of the fuel cell system components vary significantly with increasing ambient temperature, the relative humidity did not have a great impact on the water balance. Overall, dimensioning the compressor and other system components to meet the fuel cell system requirements at the minimum and maximum expected ambient temperatures, in this case 5 and 40 °C, and high altitude, while simultaneously choosing a correct control strategy are important parameters for efficient vehicle power train management.