Source: Z4 ENERGY SYSTEMS, LLC submitted to
WIND POWERED WATER PUMPING INCORPORATING COMPRESSED AIR ENERGY STORAGE
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
TERMINATED
Funding Source
Reporting Frequency
Annual
Accession No.
0222876
Grant No.
2010-33610-21820
Project No.
WYOK-2010-02113
Proposal No.
2010-02113
Multistate No.
(N/A)
Program Code
8.4
Project Start Date
Sep 1, 2010
Project End Date
Aug 31, 2013
Grant Year
2010
Project Director
Luke, K.
Recipient Organization
Z4 ENERGY SYSTEMS, LLC
25 DIZZY HORSE ROAD
BUFORD,WY 82052
Performing Department
(N/A)
Non Technical Summary
Z4 Energy System, LLC's Compressed Air Water Pumping (CAWP) system is a new water pumping product that uses compressed air produced by wind power to operate a water pump, and stores compressed air for pumping during times with no wind. CAWP will be employed in areas where municipal water systems and grid provided electricity to operate water pumps are not available or practical. CAWP will provide a solution for water problems experienced by livestock growers that raise animals in remote pastures, organic/natural livestock producers, off-grid homeowners and recreational landowners, off-grid commercial and government facilities and municipal waste pond operators, wildlife habitat conservators, humanitarian and water relief organizations, and international users with similar requirements and site conditions. Water is a basic requirement for virtually all agricultural, industrial, urban, and recreational activities, as well as the sustained health of the natural environment. In the last 100 years the global population has tripled and the global water demand increased by a factor of six. Worldwide, a billion people do not have access to clean, sanitary water. In the U.S., the agriculture industry is the largest consumer of fresh water resources and includes 856,143 livestock operations that consume more than 1 billion gallons of water per day. During Phase II, a prototype system will be fabricated and tested under controlled, laboratory conditions to verify that operating efficiency meets computer model predictions. A prototype will then be field tested for 12 months to confirm actual performance to laboratory test results. Field trials are expected to show that CAWP features enable 21 key benefits: CAES - (1) water pumping during times of no wind, (2) no batteries required, (3) energy storage method is maintenance free and (4) is not temperature dependent. On-demand water pumping - (5) no need for oversized water tank, (5) eliminates water tank overflow, (7) reduces water evaporation losses, (8) eliminates mud and ice buildup around stock tanks, (9) pond or stream water can be pumped away from riparian areas and (10) eliminates need for water holding tank for domestic use. Wind-powered air compressor powers the system - (11) excess air aerates stock tank to delay wintertime freeze-over, (12) water can be available in remote pastures longer during winter to improve pasture utilization and (13) better pasture utilization reduces cost of feed. Water pump powered by compressed air - (14) pump can pump dry without damage and (15) pumping sludge will not damage the pump. Low cost air hose transfers energy for pumping and energy storage - (16) air compressor tower can be sited in the best wind resource area and (17) air compressor tower can be centrally sited with low-cost air hose used to run multiple wells. 100% wind powered - (18) no recurring fuel costs, (19) sustainable energy, (20) benign impact on the environment and (21) eligible for renewable energy rebates, tax incentives and cost sharing programs.
Animal Health Component
100%
Research Effort Categories
Basic
(N/A)
Applied
100%
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
4020210202030%
4025310202070%
Goals / Objectives
Z4 Energy Systems LLC (Z4) will design, fabricate and test a prototype wind-powered water pumping system incorporating compressed air energy storage which will include a wind-powered air compressor, compact high-pressure air storage, and a float-regulated air-powered submersible water pump, based on Phase I feasibility study results. Extensive laboratory testing and one year field trials will be conducted to verify performance projections. Design goals to be met include: (1) wind-powered air compressor with drive train efficiency of at least 90%, (2) end-to-end Compressed Air Water Pumping (CAWP) system bench prototype with a thermodynamic efficiency of at least 10% and an average flow rate of at least 3.5 gallons per minute for a simulated static water level of 200', and (3) Compressed Air Energy Storage (CAES) system able to pump and maintain a 24-hour supply of water (at least 1000 gallons of pumped water). Bench testing under controlled laboratory conditions will confirm operating goals are met, prior to field testing. A field-deployable prototype will be fabricated and installed, and operate for a 12 month field trial. The prototype will be extensively instrumented to monitor and document atmospheric conditions as well as water pumping performance.
Project Methods
Phase II will commence with software modeling of the wind-powered air compressor. Optimizing the prototype design via software modeling will eliminate the time and expense required to physically test multiple variations of the air compressor under varied wind conditions. The design that results from modeling will then be fabricated, incorporating off-the-shelf and custom-built components. A series of laboratory tests will be performed on an end-to-end bench prototype of CAWP. Each stage of the system will be fully instrumented during lab testing to monitor compressed air properties and determine system performance. Modifications from lab testing results will be incorporated before assembling the bench prototype components into a field prototype. Custom components will be fabricated for the field prototype including: (1) nacelle equipped with cooling vents to house the wind-powered air compressor, (2) connection plate between the air compressor and tower including a rotary air union, and (3) support rack/safety enclosure for the compressed air energy storage system. Off-the-shelf components that will be assembled into the prototype include air compressor and pressure booster, water pump, pressure vessels, air tubing and connectors. At least 12 months of field testing of the CAWP prototype will be performed. Field testing will verify performance predictions from Phase I analyses and Phase II laboratory testing. By performing the field test over an entire year, performance will be determined over a wide range a conditions and CAWP technical advantages will be quantified. A successful field test will prove the efficacy of CAWP to be a reliable water pumping system at remote sites and promote Phase III commercialization. Meteorological conditions and system performance will be monitored during field testing. Instrumentation includes: anemometer, wind vane, sensors to measure air temperature, relative humidity and barometric pressure; air flow, pressure and temperature sensors; water flow, pressure and temperature sensors; shaft encoder, vibration sensors, data acquisition electronics and time-lapse camera. Performance goals to meet are: water flow rates average at least 3.5 gallons per minute for a static ground water level of 200' and a fully-charged CAES system provides 24-hour water storage (at least 1000 gallons of pumped water) when the wind-powered air compressor is not producing (due to a no-wind condition).

Progress 09/01/10 to 08/31/13

Outputs
Target Audience: The target audience is consumers who require on-demand, off-grid water pumping. A focus group of ten individuals representing ranching operators, land developers, building contractors, off-grid communities, water conservation associations, Engineers Without Borders, agricultural wind power system manufacturers, commercial wind farm developers, and rural water (and wastewater) advisory agencies participated in comprehensive discussions about their specific needs for wind-powered compressed air water pumping with energy storage. Outreach activities designed to inform members of the target audience include presentations to the Laramie Rivers Conservation District, American Wind Energy Association, the University of Wyoming, Carbon County Higher Education Center in Rawlins Wyoming, CRDF Global, and commercial entities representing livestock growers, commercial hunting guides and religious sects that avoid modern technologies. Changes/Problems: A 12 month No-Cost Extension was requested and granted for the project because a pre-fabrication end-to-end engineering analysis indicated that braking, equipment lubrication methods, rotor torque and speed matching, tower-top equipment platform yawing and field test safety precautions required modifications. The brake system was modified to include a fail-safe mechanism that can be manually initialized to secure the rotor in extreme winds. A transmission was included to ensure sufficient lubrication during startup and low winds and to match rotor speed and torque. The tower-top equipment platform was modified for downwind operation thereby eliminating tail and furling mechanisms. A self-contained, closed-loop simulated well was designed and fabricated in order to eliminate the connection between the prototype and ground water. Structural testing was added to the research to verify system response to extreme wind loads and to validate brake performance. Field testing protocol was altered to include multiple, focused tests to verify wind turbine compressor, compressed air energy storage and water pumping performance independently as well as end-to-end system operation. What opportunities for training and professional development has the project provided? Nothing Reported How have the results been disseminated to communities of interest? Nothing Reported What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Water is a critical global priority, especially for agricultural operations. In the US, $8 billion is spent annually to combat fresh water shortages and US agriculture is by far the largest consumer of fresh water. Livestock watering alone requires over a billion gallons of water per day, and specific challenges arise when providing livestock water at remote, off-grid locations. Extending grid power costs on the order of $25,000/mile and the electric utility often requires a minimum power purchase agreement before considering a power line extension. Fuel-powered generators can be used to pump water at these remote, off-grid sites; however they have high long-term fuel and maintenance costs and contribute to the global problem of carbon emissions. Renewable energy based systems are an ideal match for remote water pumping applications as evidenced by the long, successful history of the traditional windmill and the more recent adoption of solar powered water pumping systems. Solar systems generally work well but have substantial initial equipment costs and lack the ability to effectively store energy since batteries are intolerant to freezing. The traditional ranch windmill (virtually unchanged for 150 years) is an excellent application of renewable energy for remote water pumping. However, a large stock tank (with high evaporation) is required to ensure water availability with a variable wind resource. Further, during periods with continuous or high winds the windmill can over produce, leading to tank overflow and water waste. With increasing concern for diminishing fresh water resources, any waste of water is no longer acceptable. To address these problems, Z4 Energy Systems, LLC developed Compressed Air Water Pumping (CAWP), a wind powered water pumping system with Compressed Air Energy Storage (CAES) for remote, off-grid applications. A wind turbine rotor directly drives an air compressor to supply a down-well pneumatic water pump. CAES is environmentally benign, freezing-tolerant and allows demand controlled water pumping that mitigates the variability of wind and improves water conservation over conventional methods. Phase I of this USDA SBIR project proved technical and economic feasibility by: determining livestock water requirements and US water well characteristics, thermodynamic modeling to determine system specifications to meet these requirements and analyzing initial and lifetime costs compared to alternatives. Phase II included complete system design, specification, mathematical modeling and full-sized prototype fabrication. Laboratory, structural and field testing were performed to verify CAWP performance. CAWP performance met or exceeded all Phase II Technical Objectives and Phase I predictions and field testing confirmed it is capable of satisfying the requirements of remote livestock watering. Testing confirmed CAWP: (1) can have double the efficiency of the traditional mechanical windmill; (2) has the ability to service 95% of water wells nationally; (3) produces between 1000 - 6000 gallons of water per day depending on water depth and average wind speed; and (4) compressed air provides reliable, low cost energy storage for up to 5 days water pumping, mitigating the variability of wind. Field test results also showed an opportunity for expansion in applications where high water flow rates are required such as an irrigation system or a network of water pumps servicing multiple well locations using efficient, low-cost air line to connect each well to a central wind turbine compressor optimally sited to take advantage of wind exposure. This SBIR project proves that a small-scale compressed air energy storage system can be coupled with a pneumatic water pump to supply well water using 100% wind power. Compressed air from one or more storage tanks operate the water pump whenever water is required (on-demand) with a float or control valve. Wind-powered CAES ensures that fresh water is available with or without blowing wind. Markets for this product include: livestock and wildlife feeding operations in remote areas; off-grid residences and communities; isolated commercial, government and research facilities; backcountry campgrounds and recreational areas; disaster relief and humanitarian operations. Applications beyond water pumping include: pneumatic tool operation for construction and emergency services; lake and pond aeration to provide oxygenation and delay freezing; and aeration and circulation in wastewater ponds. Design goals: (1) Wind-powered air compressor with drive train efficiency of at least 90%. Prospective methods of coupling the wind turbine to the air compressor were modeled and analyzed in FAST (the National Renewable Energy Laboratory’s general purpose wind turbine modeling software). Taking into account efficiency and ease of fabrication, the optimum method of coupling the wind turbine rotor to the air compressor is through a simple, fixed ratio transmission with a clutch to allow the air compressor to come on-line after wind turbine rotor start-up. The belt drive used in the Phase II prototype simplified fabrication and installation and provided more than 90% power transmission efficiency. In production, a gear drive could be used to reduce system footprint, improve reliability and provide similar power transfer performance. (2) End-to-end Compressed Air Water Pumping (CAWP) system bench prototype with a thermodynamic efficiency of at least 10% and an average flow rate of at least 3.5 gallons per minute for a simulated static water level of 200' Laboratory and field testing determined the end-to-end power conversion efficiency of CAWP varies between 7 - 22% and water pumping capabilities also exceeded Phase II goals. For a 200 ft well water depth (representing 85% of wells nationally), the daily water production is greater than 1000 gal for average wind speeds greater than 16 mph, assuming 5 hours of wind turbine compressor operation per day. For an average wind speed of 24 mph, the water production is more than 6000 gal per day. Performance improves if wind is available more than 5 hours per day or with shallower well water depths. The air operated water pump, used in this prototype, services well water depths up to 340 ft or, 95% of wells nationally based on USGS data. (3) Compressed Air Energy Storage (CAES) system able to pump and maintain a 24-hour supply of water (at least 1000 gallons of pumped water). Pumping using CAES determined how CAWP performs during extended periods without wind. The field test prototype included a 250 gal air storage tank with a maximum storage pressure of 250 PSI. This 250 gal tank, pressurized at 200 PSI, supplied enough air to pump more than 1000 gal of water for well water depths less than 55 ft. For a well water depth of 200 ft, the air storage provided 250 gal of pumped water. Further, it took less than 40 min to completely charge the air storage tank from empty to 200 PSI in an average wind speed of 18 mph, potentially providing more than 1000 gal of water from each full air tank. These results highlight the expandability of CAWP with: (1) more air storage capacity, (2) a water pump capable of higher output (with greater air demand) or (3) a network of water pumps servicing multiple well locations using efficient, low-cost air line to connect each well to a central wind turbine compressor.

Publications


    Progress 09/01/11 to 08/31/12

    Outputs
    OUTPUTS: Using previously developed mathematical models, a complete engineering review was performed that identified several areas of the design in need of additional research and redesign in order to produce a viable product at the end of Phase II. Consequently, additional research, modeling and analysis were performed. The redesigned components include: (1) brake and a fail-safe mechanism to secure the rotor in extreme winds; (2) speed increasing belt drive and clutch to ensure sufficient compressor lubrication during start-up and to match torque and rotor speed; (3) tower-top mounting plate to facilitate a downwind design and eliminate the furling mechanism; and (4) a self-contained apparatus and method to perform testing that avoids contact with ground water. The components library was updated with new components' data sheets, features-and-benefits comparison and detailed analysis. Additions to the library include: a screw-jack fail-safe brake actuator system, sheaves and belts for belt-drive, rotary union, yaw bearing, air surge tank and condensate drain assembly, tanks and pumps for simulated well, food-safe lubricant and sensors. Mathematical models were updated to reflect the new design and a complete engineering review was performed on the new design. Laboratory test protocols and the scheme for data acquisition and sensors were updated to reflect the design changes. Schematic diagrams, 3 dimensional drawings, fabrication drawings and parts lists were prepared, and prototype components were purchased and received. The University of Wyoming Machine shop fabricated, modified and assembled tower-top components, and component tests and modifications for field testing are underway. Project information was disseminated to the University of Wyoming College of Engineering and Wyoming Business Council Agribusiness Director through one-on-one discussions. PARTICIPANTS: Kevin Luke (PI/PD), Steven Turner, Mike Maloy and Georgia Gayle, Z4 Energy Systems, LLC staff, worked on the project during the reporting period. Luke directed technical development, prepared reports, set up test site, programmed data collection instrumentation, analyzed results and liaised with consultants. Turner directed and set up the test site, installed test instrumentation and reviewed technical progress. Maloy developed mathematical models, and created drawings, schematics, parts list, and test plan. Gayle coordinated labor and equipment resources, documented and recorded project activities, and purchased and received components. Project consultants, Scott Morton, University of Wyoming College of Engineering (UW) Research Scientist, and Dr. Robert Erikson, UW Shop Manager, advised on design and prototype development progress. Morton collaborated on lab test plan development, schematic development and model analysis. Erikson collaborated on tower-top equipment modifications and directed prototype fabrication by the UW Machine Shop. Bridget Schabron, UW Staff Engineer, advised on instrumentation configuration and programming. TARGET AUDIENCES: The target audience is consumers who require on-demand, off-grid water pumping. This includes livestock producers in remote areas, wildlife habitat operators, remote recreational property owners, individuals who practice a sustainable lifestyle, inhabitants of underdeveloped countries, and regions suffering from natural or man-made disasters without reliable energy to supply water when needed. Outreach activities designed to inform members of the target audience include presentations to the Laramie Rivers Conservation District, American Wind Energy Association, the University of Wyoming, Carbon County Higher Education Center in Rawlins Wyoming, CRDF Global, and commercial entities representing livestock growers, commercial hunting guides and religious sects that avoid modern technologies. PROJECT MODIFICATIONS: A 12 month No-Cost Extension was requested and granted for the project because a pre-fabrication end-to-end engineering analysis indicated that braking, equipment lubrication methods, rotor torque and speed matching, tower-top equipment platform yawing and field test safety precautions required modifications. The brake system was modified to include a fail-safe mechanism that can be manually initialized to secure the rotor in extreme winds. A transmission was included to ensure sufficient lubrication during startup and low winds and to match rotor speed and torque. The tower-top equipment platform was modified for downwind operation thereby eliminating tail and furling mechanisms. A self-contained, closed-loop simulated well was designed in order to eliminate the connection between the prototype and ground water.

    Impacts
    Following the complete engineering review, several components were selected based on mathematical models and designed to meet project specifications. Mathematical models for the brake and fail safe mechanism showed it provides 4700 foot pounds force of torque to stop the wind turbine rotor spinning at 1000 revolutions per minute in 80 miles per hour wind. Speed increasing belt drive and clutch was shown to operate the air compressor between the manufacturer's specified range of 400 and 900 revolutions per minute to ensure proper lubrication and avoid overheating. Solid models and finite element analysis of the tower top mounting plate showed it supports system components and applied wind loads during operating and extreme winds up to 80 miles per hour. Solid models and drawings were used by the University of Wyoming Machine Shop to perform fabrication. Commercially available components were purchased and the machine shop performed modifications and assembly. The component library was updated and a complete system schematic was created using final component selections. Tower-top assembly prototype was fabricated and assembled for laboratory testing. Field test protocol was modified to avoid direct contact with ground water. In order to meet this objective, a self-contained, circulating water loop was designed for field testing. Field test expanded to determine if oil contamination occurs in test water.

    Publications

    • No publications reported this period


    Progress 09/01/10 to 08/31/11

    Outputs
    OUTPUTS: A library of components for Compressed Air Water Pumping was compiled, including: air compressors, gear boxes, air-powered water pumps, air and water tubing, and a range of attachments, adapters, and connectors. The library includes detailed specifications of each component and is accompanied by a features-and-benefits comparison with detailed analysis. Individual specifications were converted to common units so direct comparisons could be made between prospective components. A mathematical model was developed. The model calculates air delivery, air storage and water pumping performance as well as energy efficiency. The overall mathematical model is a combination of several models that describe the physics of each sub-system including: wind turbine rotor, drive train, air compressor, tubing, air storage, and air-powered water pump. The National Renewable Energy Laboratory's Fatigue, Aerodynamics, Structures and Turbulence (FAST) general purpose wind turbine modeling software was used to optimize performance of the Wind Turbine Compressor by simulating performance in operating and extreme wind conditions. Laboratory test protocol was developed. Sensors and data acquisition equipment were selected and a custom laboratory test bench was designed. The test bench includes a variable speed motor to simulate wind turbine rotor performance and a dynamometer to monitor drive train input and output power curves. Pressure, temperature and flow sensors will monitor air compressor output. Field-test site analysis was performed, and equipment layout was planned and mapped. Project information was disseminated to commercial entities, government bodies and the public in several ways. PowerPoint presentations were prepared and presented, product data sheets were distributed, and presentations were made at national and regional exhibitions accompanied by one-on-one discussions with attendees. PARTICIPANTS: Individuals who worked on the project include Kevin Luke (PI/PD), Steven Turner, Ed Riter and Georgia Gayle. Luke directed project activities, evaluated technical progress, compared Phase II activities with Phase I outcomes, guided the development of mathematical models, and reviewed test protocols. Turner researched and developed test site plan; reviewed prototype equipment selection; guided the selection and development of test equipment and instrumentation, data collection methods and analysis. Riter created mathematical models, optimized rotor performance with air compressors, collected and analyzed a library of component and test equipment specifications, designed bench test equipment and method, specified prototype components, vetted and liaised with equipment suppliers. Gayle coordinated and tracked work schedules, and documented and recorded project activities. Two Partner Organizations, QED Environmental Systems and Compression Leasing Services, Inc. (CLS) are commercial firms that manufacture equipment in the compressed air industry that are participating in product development. QED manufactures compressed air-powered down-well water pumps, and they consulted on pump-side equipment design and selection. QED will provide in-kind pumping equipment during testing. CLS manufactures air compressors and storage tanks, and consulted on the selection of air compressors and storage tanks, and methods of drying stored air. CLS will supply the air compression equipment. Two collaborators with the University of Wyoming College of Engineering, Scott Morton, Research Scientist and Dr. Rob Erikson consulted on the project. Morton guided development of mathematical models, collaborated on high-pressure air storage and suggested optional designs for a custom test bench. Erikson analyzed test bench designs for manufacturability and mechanical compatibility with other components such as hub and attachment points. TARGET AUDIENCES: The target audience is consumers who require on-demand, off-grid water pumping. This includes livestock producers in remote areas, wildlife habitat operators, remote recreational property owners, individuals who practice a sustainable lifestyle, inhabitants of underdeveloped countries, and regions suffering from natural or man-made disasters without reliable energy to supply water when needed. Outreach activities designed to inform members of the target audience include presentations to the Laramie Rivers Conservation District, American Wind Energy Association, the University of Wyoming, Carbon County Higher Education Center in Rawlins Wyoming, CRDF Global, and commercial entities representing livestock growers, commercial hunting guides and religious sects that avoid modern technologies. Discussions were conducted with Dr. Tony Hoch, Laramie Rivers Conservation District Director/Water Quality Specialist relating to practical utilization in Wyoming's prairie regions and the impact on water conservation and ranching economics. After successful demonstration, he will sponsor applications for federal and state incentives that financially benefit end-users. Product data sheets were distributed at the American Wind Energy Association Small and Community Wind Conference in Portland, OR in December 2010, and discussions were conducted with potential strategic partners and end users. Dr. Jon Benson, CEO of Wyoming Technology Business Center facilitated presentations to University of Wyoming faculty, staff and students, and Wyoming Governor Matt Mead. Z4 sponsored an entry and information booth at the Carbon County Higher Education Center "Celebration of Wind" in Rawlins Wyoming in May 2010 where product information was provided to commercial and residential attendees. Rohit Shukla, LARTA Institute, initiated Z4's participation at "The 2011 Renewable Energy Conference: Supporting Sustainable Development for Iraq" in Baghdad, Iraq May 2 - 4, 2011. This conference was put on by the U.S. Department of State and organized by CRDF Global. The event was attended by Iraqi government officials, researchers and scientists; U.S. DOS officials and renewable energy professionals. Kevin Luke, PI/PD prepared a PowerPoint presentation and networked with conference attendees. Online CRIS project reports generated numerous inquiries by individuals and business entities. Among the most notable were a Texas-based hunting camp operator wishing to solve the problem of water delivery to wildlife (and livestock), and a representative searching for acceptable energy storage methods to fit Amish lifestyles. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

    Impacts
    The component library enabled side-by-side comparison of equipment from different manufacturers, and selection of the most suitable off-the-shelf components considering durability, performance and cost. The end-to-end mathematical model resulted in optimization of system specifications, selection of off-the-shelf components and requirements for purpose-built elements. The mathematical model allows design modifications to be quickly evaluated to select the most promising system for initial testing, and in-depth analysis of the potential impact from varying operating conditions. Using FAST simulations, variable speed rotor and air compressor power curves were matched to maximize compressed air delivery for each wind condition. The mathematical models further enable comparison of theoretical predictions with laboratory and field test results. Models will be refined as required based on laboratory test results. Modeling to date revealed a viable alternative to storing air at very-high pressure (in excess of 3000 PSI). It showed that while storing air at a lower pressure of 200 PSI increases the footprint, it reduces air storage system complexity and potentially reduces manufacturing cost. The lower pressure storage system will be evaluated further during laboratory testing. The laboratory test protocol provides a method for evaluating components in a controlled environment prior to field testing. The field test site map facilitates efficient installation, access and test data collection. Development of the Compressed Air Water Pumping system to date has progressed as indicated by the Phase I Feasibility Study results, and no significant problems have been encountered that warrant major deviations or workarounds. Investigation into the Compressed Air Energy Storage feature indicates the possibility of a much less complex and safer system than originally envisioned, which could result in substantial savings in the cost of producing the commercial end-product.

    Publications

    • No publications reported this period