PEM FUEL CELL SYSTEMS

Rapid developments in proton-exchange membrane (PEM) fuel cell technology suggest that small-scale fuel cell systems may soon make inroads in both automotive and residential power conversion applications. PEM fuel cell systems offer clean and efficient production of electricity, and the capital costs of these systems are expected to decline rapidly as production expands. The deregulation of regional electric utilities is enabling new regimes of distributed power generation, to which fuel cell systems are ideally suited. Also, fuel cell systems are presently the focus of intense research efforts among industrial, academic, and government organizations, but this work is primarily concentrated on technical hurdles to fuel cell commercialization. Also needed are research efforts that examine the theoretical cost and benefit relationships, and environmental impacts of fuel cell systems as used in different settings. This includes innovative ways of introducing fuel cell systems into transportation and stationary power system markets, and novel policies to make fuel cell systems attractive at the early stages of commercialization.

This project is modeling and analyzing the economics of small-scale (5-250 kW) PEM fuel cell systems used for distributed electricity generation, and assessing the full fuel-cycle emissions of greenhouse gases and criteria pollutants from different fuel and end-use technology combinations, using a MATLAB/Simulink-based building electrical load and fuel cell response model. This model, known as CETEEM, includes an assessment of fuel cell system performance in terms of overall system efficiency, modeled as a function of the percentage of peak load that the fuel cell meets during any model hour in a simulation run, as well as the cost of electricity produced and approximate in-basin and out-of-basin emssions of criteria pollutants and greenhouse gases.

We have thus far used CETEEM to conduct two investigations:

• a comparison of the costs of producing electricity from stationary PEM fuel cells and fuel cell vehicles (FCVs) used for distributed power generation; and
• an analysis of hydrogen energy stations (or "H2-E Stations") that co-produce electricity and pure hydrogen using the same natural gas reformer; electricity with a building-integrated stationary fuel cell, and hydrogen to refuel FCVs as an "offshoot" using available reformer capacity.

The findings from both of these analyses suggest that there are interesting synergies between stationary and mobile applications of PEM fuel cell technology, and that both the use of FCVs to generate power and the concept of the "H2-E Station" appear to be worthy of continued study and analysis. Some details of the findings from these studies can be found below, and full details can be found in the reports in the publications section of this website.

Furthermore, there are many interesting and novel applications of fuel cell technology that we are exploring now and that can be further explored, such as the "H2-E Stations" that we are investigating that co-produce electricity and hydrogen to refuel FCVs using a common fuel reformer. Finally, in addition to PEM fuel cells, there are several other fuel cell types of interest to DG, and a host of other technologies such as microturbines, photovoltaics, wind turbines, other reciprocating engines, battery and other storage systems and peak power devices, etc. We plan to methodically expand CETEEM to include these additional technologies in the coming years.

In addressing these questions, we are integrating advances in fuel cell system performance modeling, geographic research methods, and technology price and performance forecasting (Lipman and Sperling, 1997; Duke and Kammen, 1999), to analyze the potential costs and benefits of the operation of small PEM fuel cell systems, and to propose, test, and evaluate state and federal policy options to potentially support this distributed clean energy resource. The study is also considering uncertainties and sensitivities of key input variables, opportunities for policy action to encourage fuel cell system proliferation, and examining the potential impacts on utilities and consumers of candidate policies to facilitate fuel cell system deployment.

Sample Results from Stationary PEM FC vs. PEM FCV Used for DG

While the costs of producing power from stationary and motor vehicle systems are rather different in terms of the costs involved - for stationary systems much of the cost is capital cost while for FCVs much of the cost is for periodically refurbishing the vehicle's fuel cell stack - the economics of producing power from these systems can be comparable, and potentially competitive with grid power in the future, if the systems are operated with similar overall efficiencies. However, results are highly sensitive to the compounding effects of variations in key input variables, as shown in the figures below. Where FCVs are used to produce power to meet very low load levels, such as at individual residences (e.g. and operate at very high turndown ratios), their efficiencies suffer and they become much less economically attractive at producing power. This suggests that net-metering policies may be critical to improving the economics of FCVs used to produce power in this way.

FCVs Used as DG vs. Stationary PEM Fuel Cells at Medium CA Office Building Setting	FCVs Used as DG vs. Stationary PEM Fuel Cells at CA Residential Setting
Note: LF = load following; NM = net metering.

Sample Results from Hydrogen Energy Station Economic Analysis

One interesting option for developing hydrogen-refueling infrastructure for early FCVs is the concept of the "hydrogen energy station" (or 'H2E-Station'). These H2E-Stations would be either dedicated refueling facilities, or a key component of the energy production, use, and management portion of a commercial or industrial facility. The energy station component would consist of a natural gas reformer or other hydrogen generating appliance, a stationary fuel cell integrated into the building with the potential capability for combined heat and power (CHP) production, and a hydrogen compression, storage, and dispensing facility.

In essence, H2E-Stations would seek to capture synergies between producing hydrogen for a stationary fuel cell electricity generator that provides part or all of the power for the local building load (as well as the capability to supply excess electricity to the grid), and refueling FCVs with additional high-purity hydrogen that is produced through the same hydrogen-generation system. In principle, many different H2E-Station concepts and designs are possible, including:

• "service station" type designs that are primarily intended to produce hydrogen for FCV refueling;
• "office building" based designs that primarily provide electricity and waste heat to the building but also include a small off-shoot for FCV refueling; and
• "distributed generation" facilities that are primarily intended to supply excess electricity to the power grid, but that also include some provision for FCV refueling.

In addition, FCVs parked near the H2E-Station for any sizable length of time could in principle supply electricity to the building or grid, since they would have access to a fuel supply (as in the above example).

Our analysis of the economics of several potential H2E-Station designs shows that for the California setting examined, H2E-Stations appear to be potentially attractive ways of supplying small numbers of FCVs with hydrogen (download full report from link below). In general, H2E-Stations tend to be more attractive economically than dedicated hydrogen refueling stations, especially for low numbers of vehicles supported per day, but the economics depend importantly on several variables including natural gas and electricity prices, captial equipment costs, the hydrogen sales price, and fuel cell maintenance and stack refurbishment costs.

The first figure, below, shows that for all of the service station cases examined the H2E-Station designs are more attractive economically than dedicated hydrogen refueling stations. None of the dedicated or H2E-Stations are economically profitable with so few vehicles supported, but the H2E-Stations offer a lower-cost pathway to ultimately supporting greater numbers of vehicles profitably.

Estimated Annual Costs of H2E-Stations with 25 and 40 kW Fuel Cell and 5-15 FCVs Refueled per Day, Compared with Costs of Dedicated H2 Stations (H2 price of $10/GJ)

Note: FL = future low cost case; FH future high cost case; MT = medium term case; SS = service station; X_Y = Fuel Cell Size in kW_# of FCVs per Day refueled.

The second figure shows the the results for a 250-kW fuel cell H2E-Station at an office building setting, along with approximate 10% ROI targets for each case (based on the installed capital costs of each fuel cell/reformer/H2 storage and dispensing system). Note that even with the medium-term case it appears that the ROI target could be met or exceeded with a range of H2 sales prices. It would seem that in the energy market conditions that prevail in certain parts of California such as the South Coast, fuel cells with the assumed capital and operating costs can be cost-effective, and H2E-Stations based on these relatively large fuel cells at office buildings could prove to be attractive. This result shows that much of the economic benefit of H2E-Stations may be their ability to displace relatively costly (at least in California) purchases of grid power, thereby effectively cross-subsidizing hydrogen sales in early FCV market development scenarios.

Finally, the third figure shows that a 10% simple ROI target can be met with the service station type of H2E-Station, but only with relatively high hydrogen sales prices of about $20 per GJ and only with about 50 or more vehicles per day refueled. At lower hydrogen sales prices of $10-15/GJ, the economics of this type of station do not look attractive, even with significant numbers of vehicles refueled. However, with lower natural gas prices than the $6/GJ assumed in this "future high cost case," this picture would change somewhat, with hydrogen sales prices of $15/GJ potentially becoming profitable for large numbers of vehicles per day supported.

Estimated Savings from Office Building (OB) H2E-Stations with 250-kW Fuel Cell and 10 FCVs/Days Refueled for 264 Days/Year, with Medium-Term (MT), Future-Low (FL), and Future- High (FH) Cost Cases, and Approximate 10% ROI Targets

Estimated Profit/Loss from H2E-Service Station with 40 kW Fuel Cell, 5 to 75 FCVs Refueled per Day, and Future High Costs (w/approx. 10% ROI target)