FEASIBILITY OF A HYDROGEN-BASED RENEWABLE-ENERGY- POWERED RESIDENTIAL ELECTRICITY SYSTEM

Transcription

1 FEASIBILITY OF A HYDROGEN-BASED RENEWABLE-ENERGY- POWERED RESIDENTIAL ELECTRICITY SYSTEM Hajo Ribberink, Maria Mottillo, Libing Yang, Ian Beausoleil-Morrison, Alex Ferguson, Kamel Haddad CANMET Energy Technology Centre, Ottawa, Canada Type of Paper: Refereed ABSTRACT The feasibility of a renewable energy (RE) powered hydrogen (H 2 ) based electricity system for houses has been investigated as a possible way to reduce the export to the electricity grid of large amounts of excess power from renewable sources. The RE-H 2 system involves production of H 2 from excess PV power, seasonal storage of the H 2, and consumption of this H 2 during less sunny periods. This RE-H 2 concept has been modelled in the wholebuilding simulation program ESP-r using calibrated component models. The influence of main system parameters on the system performance is investigated and the results of applying a viable RE-H 2 system at different locations across Canada is discussed. Conclusions are presented on the performance of the RE-H 2 systems related to the reduction of greenhouse gas (GHG) emissions and energy use, as well as the technical and economic feasibility of the concept for residential buildings. INTRODUCTION The integration of photovoltaics (PV) within buildings to meet local electricity demands offers great potential for reducing the environmental impact of central electricity production and distribution. However, the inherent temporal mismatch between electrical production and consumption represents a significant obstacle in the long-term. With the present low fraction of nondispatchable power on most electricity distribution systems, it is technically feasible to use the grid to absorb excess power and to supply power during deficits of production. In the future, however, it is likely that some form of local storage will be required to reduce grid reliance. This paper examines the feasibility of a concept based upon the local production, storage, and conversion of hydrogen (H 2 ) that might address that need. A renewable electricity production system for the residential sector is presented (see Figure 1), consisting of PV modules, batteries for short-term storage, and a H 2 system for seasonal storage. Excess PV power production over the electric demand of the house is stored in the batteries or converted into H 2 in an electrolyzer. The H 2 is stored in pressurized containers, and reconverted to electricity when the electrical demand of the house exceeds the PV power production. H 2 is also used to displace electricity demand for cooking and clothes drying. The renewable hydrogen (RE-H 2 ) concept has been studied experimentally and examined through simulation by a number of researchers, like e.g. Voss et al. (1996), Ulleberg (1998), Santarelli and Macagno (2004), and Miland (2005). A more complete list of research in this area is provided by Beausoleil- Morrison et al. (2006). However, a number of researchers have highlighted the difficulty in studying the RE-H 2 concept due to a paucity of performance characteristic data for key system components (e.g. Bernier et al. 2005), uncertainty about the reference point for the H 2 s heating value (higher or lower heating value) in published data, and neglectance of the power consumption of ancillary devices such as pumps, controls and power conditioning in presented research results. To address this need, models that are of the appropriate resolution for use in building simulation have been developed for the key systems components. These models have been incorporated into the ESP-r building simulation program and experimental work has been conducted to calibrate model inputs (Beausoleil-Morrison et al. 2006). The focus of this paper is the use of the calibrated models to investigate the performance of the RE-H 2 system. First the RE-H 2 system is described, followed by the discussion of the simulation results for the RE- H 2 base case and for system variants with varying PV area, PV tilt angle, battery capacity, and weather data. Then a more viable system for Ottawa is presented and the applicability of this system at different locations in Canada is discussed. Conclusions are presented on the performance of the RE-H 2 systems related to the reduction of greenhouse gas (GHG) emissions and energy use, as well as the technical and 1

2 economic feasibility of the concept for residential buildings. 2

3 PV AC bus 100% bus battery air AC electrolyzer ON electrolyzer OFF PEMFC OFF battery SOC electrolyzer produces electrolyzer compressor compressed H 2 PEMFC PEMFC produces electricity PEMFC ON thermal output (to plant) clothes dryer and stove 0% Figure 1 RE-H 2 system topology (left) and system control strategy (right) Finally, ongoing work to investigate the RE-H 2 concept experimentally and through additional simulations is outlined. SYSTEM TOPOLOGY The RE-H 2 system that is studied in this paper is illustrated in Figure 1. The backbone of the system is a bus onto which flows the power produced by the PV modules and which supplies the house s power requirements through a -AC power inverter. A leadacid battery regulates the voltage of the bus while the - voltage converters allow power to flow from the -bus. The H 2 produced by the electrolyzer is compressed and stored in pressurized vessels. This compressed H 2 can either be drawn off to produce electricity in the PEMFC or can be combusted for cooking and clothes drying. The battery and H 2 path (i.e. the components appearing below the bus in Figure 1) are used, respectively, for short-term (up to a few days) and long-term storage. The battery has limited storage capacity but offers a high round-trip efficiency. Although the H 2 path has a much lower round-trip efficiency, it can store energy over weeks or months and can displace electricity demand for cooking and clothes drying. This storage scheme is accomplished with a system controller whose prime input signal is the battery s normalized state of charge (SOC). The controller logic is illustrated in the right-side of Figure 1. When the battery s SOC reaches the electrolyzer on setpoint (95%), excess PV production is diverted to the H 2 path. Excess PV power continues to flow to the electrolyzer until the battery is drained to the electrolyzer off setpoint (85%). When the battery is drained to the PEMFC on setpoint (20%) the controller actuates the fuel cell to supply the house s power requirements. The deficit in PV production continues to be met by the fuel cell until the point in time that the battery is charged to the PEMFC off setpoint (30%). COMPONENT MODELS Simulation models for all components of the RE- system (se Figure 1) have been developed and implemented in ESP-r. The inputs of the electrolyzer and PEMFC models have been calibrated using data from specific calibration experiments performed at Hydrogenics with a 5 kw air-cooled PEM electrolyzer and a 12 kw water-cooled PEMFC (Beausoleil-Morrision et al. 2006). The PV inputs were taken from Mottillo et al. (2006). Inputs for the other models (H 2 compressor, H 2 storage, H 2 stove, H 2 clothes dryer, power conditioning units (PCU) and battery storage) came from either manufacturor data or published data. SIMULATION RESULTS All component models of the RE-H 2 system were connected using ESP-r's plant network and electric network facilities to form the total system of Figure 1. Examples of the system s operation at a characteristic summer and winter day can be found in (Beausoleil- Morrison et al. 2006). Before the first set of annual simulations was run, values were determined for component parameters for a base case and for a set of different cases defined by variations of some of the main parameters. The 3

4 simulation parameters that were varied and the values assigned to these parameters are listed in Table 1. The capacities of the electrolyzer and of the PEMFC were set by the sizes of the units that were tested at Hydrogenics since validated performance characteristics were available for these capacities only. Table 1 Main characteristics of base case RE-H 2 system and parameter variation cases Parameter Unit Base Variations case PV size m , 75 PV tilt angle degrees 30 0, 45, 60 Battery capacity kwh 50 14, 29, 108 Electrolyzer capacity kw H 2 storage volume m H 2 storage pressure MPa 12 - PEMFC capacity kw Electricity demand Stove and dryer (H 2 ) Total (electr. + H 2 ) GJ/yr GJ/yr GJ/yr Climate data - Ottawa* 2004 * Ottawa is situated at 45 N and 75 W. Ottawa* 2003 The objective of the first round of simulations in the performance assessment was to gain insight into the general operation of the RE-H 2 system and the sensitivity of the values assigned to the main model parameters. A major point of interest regarding the general operation of the system is the balance between hydrogen production and consumption and the interaction between the system and the grid. The H 2 storage plays an important role in the system. In general, the storage will contain the most H 2 at the end of the summer, and the least at the end of the winter. However, when over a full year the H 2 production of the electrolyzer does not match the H 2 consumption of the PEMFC and the H 2 appliances, the system will show either a H 2 surplus (higher production) or a H 2 deficit (higher consumption). Figure 2 displays the pressure profiles of the H 2 storage over 5 years of operation for 3 different scenario s: A balanced H 2 production and consumption, a H 2 surplus and a H 2 deficit. Over the years, also the systems with an H 2 imbalance will reach an equilibrium annual pressure profile. In the system with the H 2 surplus, the operation of the electrolyzer will be restricted by the maximum storage pressure of the H 2, while the minimum allowed storage pressure will limit the H 2 consumption of the PEMFC and H 2 appliances in the system with an H 2 deficit. From Figure 2 it is clear that multi-year simulations are necessary to find the converged results for the annual operation of the RE-H 2 systems. pressure (MPa) Months production 10 kg more than consumption Equal production and consumption production 5 kg less than consumption Figure 2 H 2 storage pressure curves over a 5 year period for a storage with a maximum pressure of 12 MPa and a minimum pressure 0.5 MPa. Figure 3 presents the annually integrated electricity and H 2 flows for the base case (multi-year) simulation. The annual PV power production (a), electrolyzer electrical consumption (f) and H 2 production (A), PEMFC H 2 consumption (C) and electrical production (k), H 2 combustion by the appliances (D) and net grid interaction (t, negative represents a net import; positive represents a net export) are presented. Figure 3 also includes data on the ancillary power draws (l, m, n, s), losses from each of the power conditioning units (b, e, j, p), and energy flows into and out of the battery (g, h). Approximately 15% of the PV module s annual electricity production of 31 GJ coincides with the house s electrical loads, and as such passes directly along the bus and through the -AC inverter to supply the house s lights, appliances, and the RE-H 2 system s ancillaries. Roughly 55% of the PV s annual electrical output is diverted to the battery for short-term storage while 30% of the PV-produced energy follows the H 2 path. There is a net import of energy from the grid over the year (1.0 GJ). The H 2 balance shows less favourable results. The total H 2 production of 45 kg is not sufficient to meet the annual demand for cooking and clothes drying alone, while the 6 kg H 2 provided to the PEMFC covers only 15% of the demand. The total H 2 demand is 94 kg, resulting in a H 2 deficit of 49 kg. This clearly indicates that the PV modules are undersized for the house s electrical load, at least for the climate data utilized in the simulation. The H 2 compression has only a limited impact on the power consumption of the RE-H 2 system. For the base case simulation, the energy consumed by the compressor is less than 4% of the total electric energy consumption of the H 2 loop. 4

5 Solar Energy GJ (a) / GJ (b) Battery GJ (c) GJ (g) GJ (h) Bus GJ (d) GJ (i) / GJ (e) kg (B) / GJ (j) GJ (o) GJ (f) Deficit kg Demand kg (E) GJ (k) kg (A) Supply 6.14 kg (C) Electrolyzer Compressor Gas Cylinder PEMFC /AC GJ (p) Supply kg (D) GJ (l) GJ (m) Demand kg (F) GJ (n) GJ (q) Deficit kg Appliances GJ (r) GJ (s) GJ (t) AC Bus Non-HVAC loads Pumps Figure 3 The annually integrated electricity and H 2 flows for the base case RE-H 2 system. Table 2 Results for the parameter variation cases of the RE-H 2 system. RE-H 2 base case results are printed bold. PV Generation Electrolyzer Power in PEMFC Power Out Battery Charge Battery Discharge Grid House Electrical Loads Grid Interaction Production Consumption Deficit Case Name GJ GJ GJ GJ GJ GJ GJ kg kg kg PV 30 m PV 50 m PV 75 m Tilt Tilt Tilt Tilt Battery 14 kwh Battery 29 kwh Battery 50 kwh Battery 108 kwh Ottawa Ottawa Table 2 gives the results for the parameter variation cases for Ottawa as defined in Table 1. The PV-size is an important parameter in optimizing the energy flows through the RE-H 2 system. In general, an undersized PV system will negatively influence the H 2 balance in two ways. Not only will there be insufficient excess power available for H 2 production, but also a larger part of the electricity demand will have to be supplied by the PEMFC, which itself creates a greater H 2 demand. For the electric load profile considered for the base case simulation, the RE-H 2 system with a PV capacity of 30 m 2 showed a major H 2 deficit and a net grid import, while the system with a PV capacity of 75 m 2 had sufficient excess power for both H 2 production and export to the grid. The PV-tilt angle was varied between 0 and 60 degrees from the horizontal. The tilt angle has only a small influence on the PV s total energy output for the location investigated (Ottawa). The battery size does influence the operation of the RE-H 2 system negatively when it is too small. In that case, the RE-H 2 system has to rely heavily on the PEMFC to supply the requested power during cloudy periods and/or in the winter and will require considerable amounts of H 2 for this. 5

6 For Ottawa, the PV energy production varied only slightly for the different climate data (2003: 31.5 GJ; 2004: 30.9 GJ) resulting in a negligible difference in the operation of the RE-H 2 system. A viable RE-H 2 system for Ottawa The objective of the second round of simulations was to determine component sizes for a viable RE-H 2 system for Ottawa and investigate the applicability of this system for various locations across Canada. In the context of this study, the RE-H 2 system is considered viable if it is always able to supply the required H 2 (no H 2 deficit) and if there is a limited amount of net interaction with the grid over the year. In a series of simulations, the component sizes for PV, battery, and H 2 storage were varied to determine the minimum sizes that would still allow the desired operation of the system. These simulations were performed using actual weather data for Ottawa for 2004 and a tilt angle of 30. The capacities of the electrolyzer and of the PEMFC were not varied. Again they are set by the sizes of the units that were tested at Hydrogenics. Almost all of the systems evaluated in the first round of the simulations displayed a substantial hydrogen deficit, due to an undersized PV component. Increasing the size of the PV was therefore identified as one of the most important keys to make the RE-H 2 system viable. The PV area of the viable system was determined at 75 m 2. The PV has been slightly oversized (by about 15%) to ensure that sufficient PV-energy will also be available during a cloudy year. For the reference year (2004), the oversized PV results in a net export to the grid. The larger PV component allowed the viable system to have a smaller battery capacity (29 kwh). This battery capacity equals about 2 days of electricity consumption. A H 2 storage of 5 m 3 was chosen. With this storage size, approximately 60% of the H 2 storage capacity is used for seasonal storage (using Ottawa 2004 climate data). The remainder of the storage capacity is a margin for potential cloudy years. Figure 4 presents the annually integrated electricity and H 2 flows for the viable system for Ottawa. It should be stated clearly that the detemination of the component sizes for the viable system has not been a full optimization of the RE-H 2 system, but rather a sizing of the system components to the right ballpark figures. Application of the viable RE-H 2 system at various location across Canada Canada is a large country with clear variations in climate. A system that is viable for one location could be oversized or undersized for other locations. Additional simulations runs were made to apply the viable system for Ottawa at different locations from coast to coast in Canada (Halifax, Montréal, Ottawa, Calgary, Vancouver) using CWEC weather data. Table 3 displays the results of these cases. To facilitate the determination of trends in Table 3, the results for the different locations are listed in order of decreasing annual PV output. Table 3 shows that the results for the RE-H 2 system differ considerably over the range of locations. General trends that can be found for the RE-H 2 system are: A decreasing net grid interaction for decreasing PV generation; Solar Energy GJ (a) / GJ (b) Battery GJ (c) GJ (g) GJ (h) Bus GJ (d) GJ (i) / GJ (e) kg (B) / GJ (j) GJ (o) GJ (f) Deficit 0.00 kg Demand kg (E) GJ (k) kg (A) Supply kg (C) Electrolyzer Compressor Gas Cylinder PEMFC /AC GJ (p) Supply kg (D) GJ (l) GJ (m) Demand kg (F) GJ (n) GJ (q) Deficit 0.00 kg Appliances GJ (r) GJ (s) GJ (t) AC Bus Non-HVAC loads Pumps Grid 6

7 Figure 4 Annually integrated electricity and H 2 flows for a viable RE-H 2 system for Ottawa. 7

8 Table 3 Main characteristics of the application of the viable RE-H 2 system for Ottawa at various locations across Canada (CWEC weather data; Vancouver* results represent a viable system for Vancouver) Case Name PV Generation Grid Interaction Production Consumption Deficit Min./Max. Pressure (monthly averages) Pressure swing (m.avg.) Stored seasonally GJ GJ kg kg kg MPa MPa kg % Calgary / Ottawa / Montreal / Halifax / Vancouver / Vancouver* / Stored seasonally An increase in H 2 consumption with a decrease in PV power production; An increase in the amount of produced hydrogen that is stored seasonally for less sunny locations. The results for Halifax sometimes look to contradict the general trends described above. This is because Halifax has a relatively sunny winter and therefore needs less seasonal H 2 storage, especially compared to Vancouver, a location with a relatively cloudy winter. The component sizes that lead to a viable RE-H 2 system for the base case system in Ottawa do not necessarily lead to viable systems for the other locations. The system is oversized for Calgary and not big enough for Vancouver. It is clear that viable RE-H 2 systems are location-specific, due to the large differences in the annual amount of sunshine for the various locations across Canada and the way this amount is divided over the seasons. A viable RE-H 2 system for Vancouver, i.e. a system with no H 2 deficit, would need a PV area of around 100 m 2, a battery capacity of 50 kwh, and a H 2 storage volume of 7 m 3. The simulation results for this case are included as in Table 3 under Vancouver*. Long term operational behaviour of the H 2 storage A special multi-year simulation run was done for the viable RE-H 2 system using 15 years ( ) of actual weather data for Ottawa. The results of this simulation display how the system would have operated over this 15-year period and what influence a realistic sequence of more and less sunny years would have on the pressure in the hydrogen storage. Figure 5 presents the annual profile of the hydrogen storage pressure for the 15 years of the simulation. The annual pressure profiles for the 15 years of the simulation are quite similar, characterized by a full storage at the end of the summer and a minimum pressure at the end of the winter. The value of the minimum pressure varies due to differences in weather (i.e. sunshine) over the years. In general, the oversizing of the PV and the H 2 storage was sufficient to create ample margin for cloudier periods. In all 15 years the RE-H 2 system showed a H 2 deficit only once (in February 1997). This deficit could easily have been prevented by a small change in the RE-H 2 controller strategy giving priority to H 2 for cooking and clothes drying over power production by the PEMFC for storage pressures close to the minimum pressure. The fact that the PEMFC is temporarily not allowed to operate should not cause a problem as the grid is still available for backup. Average monthly pressure (MPa) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Figure 5 Annual pressure curves for the hydrogen storage of the viable RE-H 2 system for 15 years of actual weather data for Ottawa GHG performance of the RE-H 2 system The greenhouse gas performance of the viable RE-H 2 system for Ottawa was evaluated by assuming that in the absence of the system, all of the house s electric demands would be met by the power grid and that any energy savings resulting from the operation of the RE- H 2 system will result in the reduced use of the power grid s marginal fuel source. The marginal fuel source is defined as the fuel source that is the last to be dispatched by the electricity provider to meet the load 8

9 at a given time. Given this assumption, the GHG emissions of the marginal fuel source are displaced due to the energy saved by the RE-H 2 system. The GHG emission savings are found as a function of the amount of energy saved, the marginal fuel source and the GHG emission factor that corresponds to the marginal fuel source. The method employed to calculate the GHG emission savings of the RE- system in Ottawa uses a correlation between the price of electricity and the on-themargin fuel source. Power grid data were obtained from Ontario s Independent Electricity System Operator (IESO), specifically the corresponding cost of power and marginal fuel source on a 5-minute timestep for two distinct periods. The data were analyzed to obtain the percent probability of each fuel source setting the hourly Ontario Energy Price (HOEP) within ranges of $10/MWh. A weighted displaced emission factor for each HOEP price range was then determined. Thus, HOEP values for a given year, which are published by the IESO on their website, can be used to obtain the displaced weighted emission factor for every hour of the year. The hourly GHG emission savings are determined by multiplying the hourly displaced weighted emission factor and the energy savings for that hour. Annual GHG emission savings are then calculated taking the sum of the hourly GHG emission savings for every hour of the year. There are several limitations to this methodology that should be noted: (1) it is assumed that the percent probabilities determined by analysing the IESO data for the two distinct periods apply for the entire year and for the year being considered in this study; (2) there may be differences between the resource that sets the cost of power and the type of resource that is actually the marginal resource reflected in the real time dispatch instructions issued by the IESO. It should also be noted that imported power is not taken into account in this methodology. The annual GHG emission savings predicted for the viable RE-H 2 system for Ottawa using the methodology described above are 8.3 tonnes CO 2 e. Energy performance of the H 2 loop The round-trip efficiency for the electricity-to-electricity route of the H 2 path was calculated using the approach of Bernier et al. (2005). Power draws of ancillaries, inefficiencies in the electrolyzer and PEMFC, and PCU losses were taken into account (see flows e, j, l, m, s in Figure 4). The round-trip efficiency of the H 2 loop in the viable RE-H 2 system is 20.9%. Economic performance The annual cost savings of the viable RE-H 2 system for Ottawa are calculated by considering the cost savings due to the reduction of imported electrical energy from the grid and the cost savings due to exporting electrical energy to the grid. It is assumed that in the absence of the RE-H 2 system, all of the house s electric loads (including the electric demand of the clothes dryer and stove) are met by the power grid. Therefore, the annual cost savings S, in dollars, are calculated as: S ( Elimp, ref Elimp, RE H 2 ) pbuy + Elexp, RE H 2 psell = Where El imp,ref is the imported energy from the grid in the absence of the RE-H 2 system (MWh/yr), El imp,re- is the imported energy from the grid for the RE-H 2 system (MWh/yr), p buy is the cost of energy imported from the grid ($/MWh), p sell is the price paid by the utility ($/MWh) for the energy exported to the grid, and El exp,re- is the annual amount of energy that is exported to the grid by the RE-H 2 system (MWh/yr). The residential customer rate charged by Hydro- Ottawa, including transmission and delivery charges, is $87/MWh. This value is used for p buy. Given the context of this paper, a scenario in which export of large amounts of excess power from renewable sources becomes problematic for managing the electricity grid, a value of $0/MWh was used p sell. The annual cost savings for the viable RE-H 2 system in Ottawa are predicted to be $654. The capital cost of the RE-H 2 system must be below $13000 in order to obtain a simple payback period less than 20 years. The Ontario government has recently announced a new renewable energy incentive program that will offer $420/MWh for power generated from a solar photovoltaic energy source. This incentive represents a scenario in which excess PV power is valued quite differently than in the one on which this study is based. Under this different scenario, the design and operation of a RE-H 2 system could be drastically different. CONCLUSIONS This study successfully demonstrates the use of inhouse developed and/or calibrated component models (PV system, electrolyzer, compressed gas cylinder for hydrogen (H 2 ) storage, PEMFC, H 2 appliances, powerconditioning units and battery) within the wholebuilding simulation program ESP-r to investigate the feasibility of a hydrogen-based renewable energypowered system for grid-connected houses. The performance assessment study of the RE-H 2 system included an investigation of the general operation of the RE-H 2 system and the sensitivity of certain system parameters. The PV capacity, battery 9

10 capacity, and climate had a significant impact on the operation of the RE-H 2 system, while the tilt angle of the PV had little impact. Several system parameters were selected and modified to define a viable RE-H 2 system for Ottawa. The RE- H 2 system is considered viable if it is always able to supply the required hydrogen to the PEMFC and H 2 appliances and has only a limited amount of interaction with the grid (net import or net export). The viable RE- H 2 system for Ottawa requires a PV area of around 75 m 2 for a house with an average electricity demand. This is quite large and may not be feasible for averagesized homes. The system may therefore only be appropriate for houses with a smaller electricity demand or large houses with large roofs. The viable RE-H 2 system for Ottawa was applied at different locations across Canada. The results show that the local climate (the amount of sunshine and its division over the seasons) has a strong influence on the performance of the system. Component sizes required for viable systems vary substantially between locations. The RE-H 2 system can significantly reduce GHG emissions. Applied in Ottawa, the RE-H 2 system would displace 8.3 tonnes CO 2 e from on the margin fuel sources of grid electricity. The design, operation, and economic feasibility of a RE-H 2 system will strongly depend on the way on-site produced PV power is valued. The current paper describes only part of the results of the performance assessment study. Full results will be reported in a journal publication at a later date. FUTURE WORK The conclusions made in this study will be re-evaluated in future work. Specifically, experiments will be designed and conducted with a laboratory prototype of the RE-H 2 system at the University of Victoria. The objective of the future experimental work is to validate the existing component models and identify aspects that must be improved in order to predict the impact of transient behavior upon the system's long-term performance. Subsequent model enhancements will be made and additional simulations with the enhanced models will be carried out to optimize the system configuration and control. This activity will explore such questions as the minimum feasible operating time for the electrolyzer and whether the electrolyzer and PEMFC should be controlled based upon the battery's state of charge or other control signals. Moreover, a comparison will be made with a non-hydrogen PVbattery system. Also the possibility to use the thermal output of the electrolyzer and PEMFC system in the house will be investigated. These are critical steps in moving the RE-H 2 system concept towards application in a commercial context. ACKNOWLEDGMENT The authors would like to acknowledge the Ontario Energy Board and Independent Energy Electricity Operator for the market data used to derive the methodology used to assess GHG emission savings. The authors would also like to acknowledge the Government of Canada s Technology and Innovation fund for the resources to carry out this research. REFERENCES Beausoleil-Morrison I., Mottillo M., Ferguson A., Ribberink H., Yang L., and Haddad K. (2006), "The Simulation of a Renewable-Energy-Powered Hydrogen-Based Residential Electricity System", Proc. SimBuild 2006, Boston USA. Bernier E., Hamelin J., Agbossou, K., and Bose T.K. (2005), Electric round-trip efficiency of hydrogen and oxygen-based energy storage, Int. J. Hydrogen Energy, 30, Miland H. (2005), Operational Experience and Control Strategies for a Stand-Alone Power System based on Renewable Energy and Hydrogen, PhD dissertation, Norwegian University of Science and Technology, February Mottillo M., Beausoleil-Morrison I., Couture L. and Poissant Y. (2006), A Comparison and Validation of two Photovoltaic Models, Proceedings of the Canadian Solar Buildings Research Network Conference, Montréal, Canada. Santarelli M. and Macagno S. (2004), A Thermoeconomic Analysis of a PV-Hydrogen System Feeding the Energy Requests of a Residential Building in an Isolated Valley in the Alps, Energy Conversion and Management, 45, Ulleberg, O. (1998), Stand-Alone Power Systems for the Future: Optimal Design, Operation and Control of Solar-Hydrogen Energy Systems, Ph.D. Thesis, Norwegian University of Science and Technology, Trondheim, Norway. Voss K., Goetzberger A., Bopp G., Häberle A., Heinzel A. and Lehmberg H. (1996), The Self Sufficient Solar House in Freiburg-Results of Three Years of Operation, Solar Energy, 58,