Renewable, Hydrogen-Based Energy For Isolated Communities Worldwide

by Glenn Rambach, Desert Research Institute (left) and David Haberman, President, DCH Technology, Inc.

The U.S. Department of Energy (DOE) has identified isolated communities as a viable site option for demonstrating the practicality of integrated, renewable, hydrogen-based, utility power systems. DOE has a mandate to pursue this goal as part of the Hydrogen Futures Act of 1996. The [U.S.] State of Alaska is a candidate for such integrated demonstration projects because of its exceptional vulnerability to fossil fuel price fluctuations and its environmental and energy infrastructure logistical challenges.

These DOE-led initiatives are directly pertinent to meeting the energy needs of isolated communities worldwide by providing hydrogen energy system designs that can autonomously power isolated communities with uninterruptible renewable energy. Other candidate customers for such renewable power are military posts, remote mines, and remote autonomous devices.

The technological building blocks of a renewable hydrogen energy system have now reached a state of maturity that permits responsible planning. The implementation of such systems do not require scientific breakthroughs but are engineering, fiscal, and public policy challenges. The demonstration of integrated hydrogen energy systems in recent years in the United States has resulted in a systems engineering data base that can form the foundation of the next generation of energy system developments internationally.

There are two key benefits that would result from the implementation of a prototypical, uninterruptible renewable energy system demonstration:

  1. A generic design optimization algorithm that matches an arbitrary renewable energy source profile with an arbitrary community load profile with the right amount, and type of storage (this can be generalized for any energy storage process and medium); and
  2. A generic control system optimization algorithm that provides electricity to the customer at the lowest cost, based on temporally varying source and load conditions.

Various system elements are discussed below.

Primary Power Production

The primary power production installation must be “overbuilt” in peak capacity to permit simultaneous load following and stored energy production. The principal criteria that define the primary, renewable power source, require:

  1. the source to be intermittent;
  2. the average source power to be adequate enough to technically and economically justify installation of an autonomous system; and
  3. the maximum credible quiescent period to be within a range that permits the use of a realistic, economically viable energy storage system.

Wind Turbines–This is the most mature renewable technology that permits small-scale, and incremental installation. The current and expected capital and installation costs for wind turbines make them the most attractive choice for most potential sites. Quiescent periods may last for days to weeks. Wind turbines rated for arctic use are currently available commercially.

Solar Photovoltaic–A maturing renewable technology whose capital costs are several times higher than wind turbines. However, such costs are expected to fall to a competitive range in five to 10 years. Under certain conditions of regional power value and resource, solar PV can be the technology of choice. Quiescent periods would generally follow a diurnal cycle.

Micro-Hydroelectric–Under the conditions where an adequate flowing water resource is available, where it is intermittent (regularly spaced rain or monsoon episodes), and where topography, or other constraints prohibit the use of pumped—or other reservoir—hydroelectric storage, micro-hydroelectric power production with the type of energy storage systems considered here can be appropriate.

Low-Dynamic-Pressure (q) Water Turbines–Given the conditions in the section above, and intermittent, low-gradient river flows, submerged water turbines with the type of energy storage systems considered here can be appropriate.

Energy Storage

Energy storage capacity, to first order should be sized for the maximum credible period of quiescence for the primary power production system, and for the average load. There are several different possible energy storage technologies, with varying degrees of maturity, cost, and scaleability, they are: hydrogen-fuel cell, hydrogen-ICE gen, halogen fuel cell, Zn-Air fuel cell, Zn-FeCN fuel cell, flywheel, compressed air, pumped hydro, and battery.

This discussion will be confined to hydrogen-based energy storage methods. As such, all hydrogen energy storage possess three basic elements: (1) a primary power-to-hydrogen conversion system (hydrogen production), (2) a hydrogen storage system (storage), and (3) a hydrogen-to-electricity conversion system (electricity production).

Hydrogen Production Via Electrolyis

Potassium hydroxide (KOH) electrolyzers are commercially available in two basic configurations: low-pressure unipolar and intermediate-pressure bipolar. Both types are attractive methods of hydrogen production for remote power systems. Under certain conditions, the bipolar system may provide hydrogen elevated pressure, potentially up to the storage pressure, reducing or removing the requirement for a compressor. The current capital cost for KOH electrolysis systems is high, but the potential for economy of scale improvements is promising.

Solid polymer electrolysis is an emerging, solid-state method of hydrogen production that should have capital costs that evolve similar to PEM fuel cells. As the costs decline, this will be an attractive method of hydrogen production because of its simple, solid-state configuration and its ability to provide hydrogen at intermediate pressures.

Storage

The scale of the hydrogen storage system in remote, renewable power systems is directly proportional to the maximum credible quiescent period of the renewable resource and the average load. It is this property that makes flowing electrochemical storage methods more attractive than batteries in remote applications of renewable energy with long periods of stored energy conversion. In these systems, the power conversion and energy storage hardware are separate, requiring only the size of the storage hardware (generally least costly) to fit the quiescent power production conditions. Intermediate-pressure, 100 to 500 psi, gas vessels are a good choice for most small community power systems. The expected costs and required system volumes are reasonable. Where space is premium, or where the storage system is also supplying hydrogen for transportation applications, high pressure, 500 to 3,000 psi, or low-pressure hydride systems may be required.

Electricity Production

Hydrogen-ICE-Generator Set–An electrical generator driven by an internal combustion, reciprocating engine (ICE), with a high compression ratio and lean operation* can provide electricity production with efficiencies similar to a fuel cell. The production system would have to have an efficient turn-down ratio that matches well with the temporal load profile. The key advantage to a hydrogen-ICE genset is the very low near-term capital cost relative to the current cost of fuel cells. This leaves a cost “window of opportunity” while fuel cell costs decline. The primary environmental concern would be the small NOx emission from nitrogen fixation. However, it is unlikely that this type of power system would be used in a NOx nonattainment area.

Hydrogen Fuel Cell

Phosphoric Acid Fuel Cell–Currently available in 200-kW units integrated with a natural gas reformer. The reformer is not necessary for remote hydrogen stored energy applications. The PAFC operating temperature in excess of 150°C in a 200-kW unit permits cogeneration of utility heat, but also requires long start up times. Long start up times mean that the PAFC would have to “idle” even while stored electricity is not necessary.

Proton Exchange Membrane Fuel Cell–Currently 205-kW units have been integrated into buses for use with neat hydrogen. A hydrogen PEMFC could operate with short (several seconds) start up and shut down times. The primary issue for including a PEMFC in a remote, stationary power application is the capital cost.

Regenerative Fuel Cell–Solid polymer regenerative fuel cells are electrochemical devices that perform electrolysis electrochemistry when current is applied to its electrodes, and perform electricity production when hydrogen and air are applied to its electrodes. Current cost are high and system sizes are small, but if RFCs can be manufactured at a lower combined cost than electrolyzers and conventional fuel cells, then this would be the preferred technology.

Siting

A large fraction of the world’s population has yet to benefit from the use of utility electricity. These power systems can be a fully sustainable electrical resource in numerous isolated locations in the world where the following conditions are met:

The regions of the world where these requirements are met include remote Alaskan, Canadian, Russian, and other communities, insular islands, remote military installations, remote mines, and remote autonomous devices.

*Suggested and developed by Lawrence Livermore National Laboratory, et al.

©1997. All Rights Reserved. A Publication of the National Hydrogen Association.
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