NREL/TP-442-7227 • UC Category: 1210 • DE95000247

Village Power Hybrid Systems Development in the United States

L. Flowers, J. Green, M. Bergey, A. Lilley, L. Mott Prepared for European Wind Energy Conference October 10-14, 1994 Thessaloniki, Greece

National Renewable Energy Laboratory 1617 Cole Boulevard Golden, Colorado 80401-3393 A national laboratory of the U.S. Department of Energy Managed by Midwest Research Institute for the U.S. Department of Energy under contract No. DE-AC36-83CH10093

Prepared under Task No. WE517210

November 1994

NOTICE

This report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof.

VILLAGE POWER HYBRID SYSTEMS DEVELOPMENT IN THE UNITED STATES

L. Flowers and J. Green, National Renewable Energy Laboratory, USAM. Bergey, Bergey Windpower Company, USAA. Lilley, Westinghouse Electric Corporation, USAL. Mott, Northern Power Systems, USA

INTRODUCTION

The energy demand in developing countries is growing at arate seven times that of the OECD countries, even thoughthere are still 2 billion people living in developing countrieswithout electricity; most of these people live in remotevillages, far from the established grid. Line extension isgenerally uneconomical; and diesel g6nsets are expensiveto operate and maintain, and have proven to not beenvironmentally and economically sustainable for remoteapplications. Renewable energy technologies offer aneconomical and environmentally sustainable solution forbringing power- and its educational, economic development.health, and quality of life benefits- to remote villages.

Many developing countries have social and economicdevelopment programs aimed at stemming the massivemigration from the rural communities to the overcrowded,environmentally problematic, unemployment-bound urbancenters. It has been estimated that $1 invested in ruralcommunities potentially offsets $6 required to providesupport services and mitigate impacts on an urban setting.

To address the issue of providing social, educational,health, and economic benefits to the rural communities ofthe developing world, a number of government and non­government agencies are sponsoring pilot programs toinstall and evaluate renewable energy systems asalternatives to line extension, diesels, kerosene, andbatteries. These programs are underway in Mexico, Brazil,Indonesia , Bolivia, Guatemala, Mauritania, the Caribbean.the Philippines , and India. These programs are aimed atgenerating the experience and pertormance data requiredto develop large loan requests to the financial communityfor multiple village-power applications. Several of theseloan requests are on the order of $100 million. An officialof the World Bank's Environmentally SustainableDevelopment Department recently stated that the WorldBank and multilateral institutions should strive to incorporaterenewable energy options into ongoing and pendingprojects in the developing world.

The use of renewables in remote international villages hasyielded mixed results over the last 20 years. However,recently, photovoltaics, small wind turbines, and micro­hydro systems have gained increasing recognition asreliable, cost-effective alternatives to grid extension anddiesel gensets for Village-electricity applications. At thesame time, hybrid systems based on combinations ofPV/wind/batteries/diesel gensets have proven reliable andeconomic for remote international telecommunicationsmarkets. With the growing emphasis on environmentallyand economically sustainable development of internationalrural communities, the U.S. hybrid industry is respondingwith the development and demonstration of hybrid systems

and architectures that will directly compete withconventional alternatives for Village electrification. Assistingthe US industry in this development, the NationalRenewable Energy Laboratory (NREL) has embarked on aprogram of collaborative technology development andtechnical assistance in the area of hybrid systems forvillage power.

Following a brief review of village-power hybrid systemsapplication and design issues, this paper will present thepresent industry development activities of three U.S.suppliers and the National Renewable Energy Laboratory.

APPLICATION ISSUES

Off-grid applications in developing countries typically fallinto three broad categories that differ in level of energydemand and system configuration: (1) individual home ordwelling power systems for lighting and small appliances :(2) dedicated productive use or rural community facilitiesapplications such as communications. commercialenterprises, health clinics, and water pumping; and(3) general-purpose electrification of rural communities.The systems options for these applications fit into two basicconfigurations: (1) distributed stand-alone systems that areeach dedicated to physically localized load use, and(2) centralized generation systems with a local "minigrid"that distributes power to a number of physically separatedloads.

The mini-grid category represents multipurpose electricalpower service to communities with populations of severalhundred to several thousand (perhaps 50 to 500households or more). with overall energy demand rangingfrom several tens to several hundred kWh per day.Depending on the physical layout of the community andload density, the appropriate technical options can rangefrom the distributed individual stand-alone systems tocentralized wind hybrid system generation with a localdistribution network, to an appropriate mix of the two that istailored to the local needs and load distribution of thecommunity. The higher overall energy demands for thecentralized community power system options discussedhere will typically require the use of multiple windgenerators of 5-50 kW capacity.

The appropriate technical options for off-grid power needsdepends on the available energy resources; the end-useenergy requirements and anticipated demand for power,and social, economic, and cultural factors that impact thepracticality. acceptance, and sustainability of the variouspossible technical approaches. There will always be trade­offs between achieving optimum technical performance in

any given system and providing a practical solution formeeting an energy need that is both acceptable andsustainable under local conditions and constraints. Thereare three practical guidelines to follow when consideringappropriate technical options: (1) ensuring a good matchbetween the available energy resources, the end-useneeds, and the end-user culture; (2) reducing energyrequirements where possible through conservation andefficiency measures; and (3) designing and implementingsystems and support services with long-term sustainabilityin mind.

DESIGN ISSUES

The design of a village power system begins with adefinition of the current, anticipated, and long-term electricalloads. The loads definition process should include averagepower levels, start-up surge power levels, and a diurnaldistribution, which is usually based on hourly averages. Ifthe village currently has a diesel generator, this definition isbest accomplished using manual or automatic loadmonitoring. If no power generation exists, then an analysismust be performed to calculate the anticipated loads andtheir time profile. This analysis is usually based onassumptions of specific appliance use (e.g., homes willhave four 10-W fluorescent lights operating 4 hours perday, etc.). Projections on future load growth are alsomade, and systems are typically sized for anticipated needstwo ~o ten years after commissioning. System capacityrequirements are normally expressed in terms of energy(kWh/day) and peak power (kW).

The next step, and often the most challenging, is to definethe resources (the wind and solar resources). As a firstcut, the 1980 U.S. Department of Energy "World WindEnergy Resource Map" provides reasonable estimates ofyearly average wind speeds. (However, it should be notedthat wind resources can be very site-specific). The windresource information available from local meteorologicalsources in developing countries is notoriously inaccurate,usually underestimating available resources by a widemargin. The problem is that wind data are often taken fromsheltered urban or airport sites. Higher quality data areavailable from military, upper air, and maritime sources, butcollecting and processing these data can be timeconsuming and expensive. For large-scale projects, eitherin size or scope, site resource monitoring is prudent, even ifonly for a few months to verify the resource. On verysmall, single-system projects, site monitoring may not bejustified economically.

From the loads information and wind/solar resourceestimates, the designer can explore various component­sizing options. In almost all situations, the system includesa battery bank for short-term energy storage, an inverter tosupply the AC power, and a system controller, switchgear,and back-up diesel generator to cover the loads duringperiods of low wind. From a hardware perspective, windturbines have a cost advantage over PV and often anadvantage over diesel systems; so, wind is often chosen asthe dominant supply option when an adequate windresource is available.

Least-cost (life-cycle) design is normally the major goal, butother customer-driven factors like the renewable energycontribution ratio, environmental benefits, maintainability/support, and initial capital costs can significantly influencethe process. Design tools are limited and are largely

proprietary. Least-cost designs arrive at relative energycontributions of 50%-75% from renewables and theremainder from the diesel genset, depending on a numberof local economic and site-specific resource factors.Currently, system integration is not a prescriptive science,yet a number of firms have gained wide experience invillage system design. U.S. industry can now install com­plete systems that provide a quality of service and reliabilitylevels approaching grid-based utility service.

INDUSTRY DEVELOPMENT ACTIVITIES

While the market for hybrid village power systems is still inits infancy, several companies in the United States haveinvested in system and market development activities thatwill generate the experience and equipment that arenecessary to open this potentially large remote electricitymarket. The current systems offered by these companieshave resulted from their experience in the relatedtelecommunications and small, stand-alone wind andphotovoltaic remote applications in international markets.Each of the three hybrid systems suppliers discussed in thispaper have selected system designs based on what theybelieve will meet the multiple needs of the internationalvillage marketplace.

BERGEY WINDPOWER COMPANY (BWC)

Bergey Windpower Company is a manufacturer of smallwind turbines in the size range of 0.85-10 kW. BWeturbines utilize passive controls, fiberglass blades, direct­drive permanent magnet alternators, and integratedstructures to provide for mechanical simplicity that results inhigh reliability turbines and low maintenance costs.Approximately 1400 BWe turbines have been installed inmore than 60 countries. These systems are primarily usedfor rural electrification, water supply, and remotetelecommunications. In addition to supplying wind turbineand balance-of-system equipment, BWC also serves as asystem integrator, installer, trainer, and after-sales servicecontractor.

Bwe is pursuing village power systems in the size rangefrom 1.5 to 80 kW. Village power systems utilizing BWCwind turbines have been installed in twelve countries,including India, Indonesia, Australia, Russia, and Mexico.Pilot installations are underway in the Philippines, Uruguay,and Brazil. These systems typically include one to tenturbines, a DC bus, batteries, a bidirectionalinverter/charger, a back-up diesel generator, and on smallersystems, photovoltaics. The wind turbines and PV arraysare connected to the DC bus through separate, non­communicating voltage regulators. Battery banks aretypically configured for 120, 220, or 240 VDe and are sizedat 18-48 hours of load support. Static inverters usuallyinclude a reverse-mode battery charging capability andhave a sinusoidal output waveform. Most systems operateautomatically with the back-up generator start and othercontrol functions being activated based upon battery bankvoltage. On an annual basis the typical system derives 60­90 % of its energy from renewables and the balance fromthe back-up source.

Several of the village power systems are instrumented tomonitor system performance; the system in Xcalac, Mexico,was heavily instrumented to evaluate system and

subsystem performance. Tho Xcalac system was installedin August, 1992, and is comprised of six 10-kW turbines, an11.2-kW PV array, a 400-kWh battery, and a 40-kVAinverter. It is monitored by a 40·channel data acquisitionsystem which telemeters the data records to the Instituto deInvestigaciones Electricas (liE) in Cuernavaca, Mexico.The analysis of the data from this site has provided usefulinsights into the design and operation of DC bus-basedvillage power systems, including subsystem interactions.

From a development perspective, BWC is working on bothadvanced equipment and new applications to improve itsproducts and expand its markets. BWC, under contract toNREL, is developing a 15-kW IGBT high-frequency link, full­digital-control inverter to provide high reliability at low costfor its stand-alone AC systems. Also, BWC is developing,collaboratively with NREL, wind-electric ice-making systemsfor fishing and agriculture-based villages.

INTEGRATED POWER CORPORATION (IPC)

Integrated Power Corporation, a subsidiary ofWestinghouse Electric Corporation, has installed PV/windhybrid systems in Mexico and Indonesia. Theseinstallations have successfully demonstrated the applicationof pv/wind-based hybrid systems for rural villageelectrification. The following is a brief description of IPC'sexisting and imminent hybrid village projects.

Mexico experience: IPC, in collaboration with Compania deLuz y Fuerza Del Centro (CLYF), and Pronasol (theMexican rural-development fund) installed two hybridsystems in the villages of Santa Maria Magdelena and SanAntonio de Aquas Benditas, Mexico. The system that wasinstalled in Maria Magdelena (54 homes) in 1991 has anominal capacity of 45-kWh/d and is composed of 4.3-kWPV, 5-kW wind generator, 18.4-kVA diesel genset, a132 kWh battery bank, and a 7-kVA, single-phase inverter.The system that was installed in Aquas Benditas(100 homes) in 1992 has a nominal capacity of 125 kWh/d;and is comprised of 12.4-kW PV, two 10-kW wind turbines,a 50 kVA genset, a 250 kWh battery bank, and two 7.5 kVAinverters operating in parallel. The system serves100 homes.

The systems were designed to support both residential andcommercial loads, and to accommodate load growth.Typical loads include household lights, radios, televisions,commercial refrigerators, and grain mills. Each systemprovides 24-hour available, utility-grade, 120-VAC power;IPC's Alliance inverter was specially designed for villagepower applications. Local labor was used for thefoundation construction and wind turbine and PVarrayerection at both sites. The system at Maria Magdelenautilized a modular, factory-built system that was trucked tothe site. The system at Aquas Benditas was site built usinglocal contractors and equipment.

Both systems have proven extremely reliable, having beenoperated unattended, with virtually 100 % availability sinceinstallation. Anemometers were recently installed at thesites so that the system performance data can be analyzed.The analysis will be done collaboratively among IPC, NREL,and the appropriate Mexican agencies.

Indonesia experience : IPC has installed two identicalsystems in 1993 to supply electricity to Julingan andTanglad, two villages of 200 homes each, on Nusa Penida

Island, near Bali, Indonesia. Each system has a ratedcapacity of 100 kWh/d and is comprised of 9.5-kW PV, one10-kW wind turbine, a 10-kVA diesel genset; a 2000-Ahbattery bank, a 7.7-kVA sine-wave inverter, and amicroprocessor controller. An interesting design feature ofthis installation is the use of two parallel hybrid systems ona single distribution system, thereby demonstrating thefeasibility of building up local mini-grids by adding modularhybrid power plants as load demand grows.

Another important feature of this installation is the use ofremote monitoring and control capability that utilizes adirect link to a low earth-orbit satellite, VITASAT. TheVITASAT link permits uploading and downloading systemstatus and performance data. as well as permitting remotediagnostics and control. This first-of-its-kind application of asatellite for remote village electricity monitoring and controlwas a collaborative effort between IPC and the Volunteersin Technical Assistance (VITA).

Currently the systems are operating at about 50 % of theirdesign capacity, thereby providing the potential of doublingthe load with no loss in reliability or system efficiency.Nearly 90% of the current electrical energy is supplied byrenewable sources. Load growth, primarily through newhook-ups by PLN, the national utility, is anticipated.

Currently, IPC is taking its next major step incommercialization of PV/wind hybrid systems by initiating aproject to electrify up to 70 villages in the eastern islands ofIndonesia. The project will combine the lessons learned todate with a volume-manufactured, standardized system.The next generation system will embody the followingimprovements: AC-bus, factory assembly and test,transportability, and simplified installation. The AC-busdesign allows the diesel to be operated in parallel with theinverter (as compared to the DC-bus design that requiresthe diesel energy to be stored in the batteries and theninverted to AC). This architecture improves systemefficiency by avoiding the diesel rectification, battery run­around losses, and inversion. This system design canmeet higher peak loads (both the diesel and the invertercan combine to meet peaks). Additionally, the inverter willbe bidirectional and operate as a battery charger, storingexcess diesel energy during low to intermediate villageloads. The systems will be factory assembled and self­contained to minimize the expense and problems of site­built structures. The systems can be transported in a 5-tontruck and installed in 2 days.

Phase 1 of the project will be completed in 1995 and willinclude the electrification of up to 10 villages; the systemshave the following specifications: 110/120/220/240 VAC,SO/50 Hz, single phase; 25-kW nominal peak power; 50­100-kWh/d energy output; 7.5-kW PV; 10-kW WTG; 25-kVAdiesel genset; 525-Ah battery bank; 7.5-kVA, single-phase,bi-directional inverter. Following the successful completionof this initial phase, IPC, in collaboration with thegovernment of Indonesia and technical assistance fromNREL, will embark on the replication phase that will includeinstallation of systems to service an additional 50 villages.

NEW WORLD POWER CORPORATION (NWPC).

New World Power Corporation is utilizing its experience inwind, solar, and hybrid power systems, primarily in remotetelecommunications and small isolated power applications,to develop the balance of systems components required toreliably integrate renewables into remote mini-grids. NWPC

is in its second year of a 5- year program to develop andcommercialize a renewable-based, packaged hybrid-powersystem. NWPC is currently focusing its productdevelopment and initial marketing toward harsh, farnorthern climates , and in the Latin America/Caribbeanregion.

The core of the prepackaged system is an electronicallycontrolled, renewable energy-based, diesel/battery cyclecharging unit. The novelty of this system is the use of arotary converter, which replaces the need for large-scalepower electronic inverters. The combination of an ACalternator and a DC motor/generator inverts the battery­stored and generated DC electricity to AC. The potentialbenefits in reliability, serviceability, and economics of rotarytechnology (which has been used for emergency hospitalsfor years) are the drivers for NWPC to develop larger scaleversions for remote village . mini-grid applications. Thisdevelopment is being cost-shared with Sandia NationalLaboratory andNREL.

The prepackaged system consists of a diesel engine clutch ­coupled to a synchronous alternator, which is in turn shaft­coupled to a DC regenerative-drive unit. The DC drive islinked to the battery bank. This architecture allows the loadto be supplied either from the diesel or from the batterybank (via the same synchronous alternator). The PLCmaster-controller monitors the power flows, andautomat ically makes judgements from preprogrammed data,or for remote commands, allowing for efficient operation ofthe power sources. Addit ional controls are included in thepackage for AC-output and DC-input supervision/protection,and PV and wind turbine generator control. The system ishoused in a prefabricated shelter.

The rotary converter can be readily reconf igured toaccommodate a variety of village-power electricspecifications, including 50/60 Hz, 120/208/240/480 AC,single or three phases. The rotary package has two basicconfigurations, with or without an integral engine. In mostcases, the integral engine will be the preferred configurationas a complete power system . However, in those cases thatdo not require an engine/genset, the rotary package can beprovided without it, and the PV and/or wind generator(s) willbe interconnected and controlled by the package. Anotherfeature of the package is the ability to operate multiplepackages in parallel, to accommodate load growth.Interconnection of the rotary packages is simpler than thecurrent diesel-genset parallel operation controlrequirements, not requiring the use of a synchroscope-typecontroller.

The rotary package can be configured to adapt to a numberof different architectures, depending on the renewableresources, the load, and relative economics of thegenerating sources. Typical generating architectures thatthe rotary package could accommodate include stand-alonePV, PV/ellgine, PV/wind, PV/wind-engine, and wind/engine.This last arch itecture is particularly interesting since theNWPC package can integrate AC and DC wind turbinesinto the village grid. In large village applications, the windturbines will most likely use induction generators; NWPC'sdesign provides a stable AC grid without the engineoperating (reactive power can be supplied by the engine orthe battery bank). NWPC believes this feature is asignificant advantage of this architecture.

NWPC's first stage of commercialization focused onsystems in the 50-100 kW range. Currently, they are

expanding their scope to larger systems in the severalhundred kW to multi-megawatt range, using the sameprinciples. These large systems typically do not includebatteries . The larger systems employ synchronousalternators/condensers and fast acting "dump loads" forpower and frequency control. With this architecture, loadscan be met solely by each power source subsystem or witha combination of any or all of them. The key to gridstability is the synchronous alternator acting as the primarypower supplier in all the generation modes, resulting in ACpower that is free of harmonic content, supplies reactivepower, and absorbs large impulse loads.NWPC has installed its system in southern California forSouthern California Edison Company . Additional systemsare currently being installed in Alaska, Argentina, and inPara, Brazil.

HYBRID SYSTEM R&D AT NREL

The U.S. DOE has designated NREL as its lead laboratoryfor wind technology research and development, includingwind-hybrid systems . The objective of the hybrid systemR&D activities at NREL is to collaborate with the windindustry in the development of technology, analysis tools,and applications analys is for wind-based hybrid systems inoff-grid applications . The major activit ies for 1995 aredescribed below.

Development & Beta-Testing of the Wind/HybridPerformance Model, "HYBRID2 ".

In 1993, NREL made an assessment of the available toolsfrom the United States and Europe for predicting the long­term performance of hybrid-power systems. The conclusionwas that there was no single tool capable of modeling thefull range of hybrid-power technologies being considered forvillage power in the 1990s and beyond. The existing toolsespecially lacked flexibility in system configuration anddispatch of components. As a result, NREL developed aspecification of a model for making comparisons ofcompeting technology and systems options on a "levelplaying field."

Development of this tool, called HYBRID2, by NREL andthe University of Massachusetts (UMass) is now underway .It builds on the wind/diesel model, HYBRID1, developedpreviously by UMass with DOE funding, and expands thatmodel to accommodate the wider array of technolog ies andsystem architectures now being considered for hybridvillage-power systems . In order to accommodate a varietyof potential analysts , UMass will incorporate the analyticalsoftware into a user-fr iendly format, using Microsoft VisualBasic. An initial version of HYBRID2 will be completed latein 1994 and beta-tested early in 1995, both internally andby a group of users outside the lab including private andpublic analysts. The executable version of the code shouldbe available in mid-1995 .

Construction & Operation of NREL's Hybrid Power TestFacility.

Because of the need to gather performance data fromoperating hybrid-power systems, NREL will develop in1995 a Hybrid-Power Test Facility at the National WindTechnology Center in Golden, Colorado. This facility will

test state-of-the-art packaged hybrid power systemsdeveloped by the U.S. industry. The facility will include avillage load simulator, at least two wind turbines, aphotovoltaic array, and a data acquisition system.Repeatable testing will be possible with energy sourcesimulators capable of imitating either wind turbines or PVarrays, either AC or DC connected.

Develop Predictive Tools for Small Wind TurbinePerformance.

Predicting the performance of small wind turbines iscomplicated by the fact they typically operate at variable­speed and are used in a variety of applications. The threemost common applications are battery-charging (as in ahybrid system configuration), wind/electric (directconnection to an induction motor), and grid-connectedthrough an inverter. Each application imposes a differentelectrical load on the wind turbine which impacts theperformance of the generator and rotor. As a result, theperformance of small wind turbines have been observed tovary significantly depending on the application.

In 1995, NREL will assemble existing models of windturbine rotor and generator performance into a unified toolfor the prediction of small wind turbine performance undervarious electric loads. Dynamometer testing of one or moregenerators will be conducted . This data, along with fielddata on turbine performance, will be used to verify theoverall performance model. This model will subsequentlybe used to develop guidelines for alternator design and formotor selection (in wind/electric applications).

Parametric Experimental Study of Wind/DieselConfigurations.

In 1994, the U.S. DOE initiated a 5-year, cost-sharedresearch collaboration with the U.S. Department ofAgriculture (USDA) to investigate a range of wind/dieselsystem configurations. The goal of this collaboration was todevelop systems powered entirely from renewable sources(e.g., wind, solar, and vegetable oils) that would be reliableand cost competitive. The experimental study will focus onperformance and stability for various system configurationsand will identify necessary controls. This study will beperformed in a wind/diesel test facility at the USDAresearch laboratory at Bushland, Texas.

Field Performance Data.

In order to improve systems' field performance andeconomics, it is essential that data from power systemsoperating in field applications be acquired and analyzed.To accomplish this, NREL has a two-pronged program:system monitoring protocol and equipment development.and field data acquisition. NREL will develop and test aportable data acquisition system suitable for commissioningand long-term monitoring of hybrid-power systems inremote locations. This will include demonstrating thecapability to down-load data sets by phone or by satellitelink. Additionally, NREL will engage in a program withindustry and in-country institutions to equip existing andnewly installed hybrid systems with data acquisition systemin order to develop a data bank on system performanceunder the variety of conditions that exist in the field. It is

anticipated that field performance data will be collected andanalyzed from hybrid systems in Mexico, Brazil. andIndonesia. While some of the collected data may beindustry sensitive (and will be treated accordingly), there willbe valuable general information gleaned from suchmonitoring that can lead to technology improvements andapplications developments.

Renewables for Sustainable Village Power (RSVP)Initiative.

The development of a field performance data bank is anelement in NREL's new initiative to address the manyissues associated with deploying renewable energy systemsin villages in an economically sustainable manner. Inaddition to supporting technology development appropriatefor village-scale systems, RSVP will offer technicalassistance to U.S. companies and in-country institutionswhich are interested in evaluating and deployingrenewables. Technical assistance includes training, boththrough workshops and an on-site visiting professionalprogram, resource assessment, preliminary analysis ofalternatives, program/project development, andperformance monitoring and evaluation. It is anticipatedthat RSVP will become a clearing house for experience,technology development, and analysis for both U.S.companies and international institutions involved in villagepower.

CONCLUSIONS

The developing world will experience rapid growth in theapplication of electricity to meet community economic andsocial needs over the next decade. Because renewableresources are abundant (and varied) around the world,renewable hybrid-energy systems offer reliable,economically competitive. and environmentally friendlypower for many currently non-electrified villages throughoutthe developing world. It will be important that emerginghybrid technologies and system architectures be designedsuch that they consider the communities ' needs, includingloads, system reliability, ability to pay, economicdevelopment opportunities/limitations, and social needs.Although there are many places in the developing worldwhere the current hybrid systems are economicallycompetitive today, it is also important to makeimprovements in the systems and technologies so that theymay be competitive in a larger set of rural situations. TheU.S. industry. with assistance from NREL, is on the way todemonstrating the economic and environmentalsustainability of alternate hybrid-system configurations andcontrol strategies.