A Flywheel Energy Storage and Conversion System for Solar Photovoltaic Applications

A low-drag, low-power magnetic bearing and a permanent magnet brushless d-c motor-generator have been developed for a satellite flywheel. These will be combined with a terrestrial flywheel and control electronics to make up a flywheel energy storage and conversion system for use in a stand-alone solar photovoltaic residence. Technical and economic performance analyses indicate that, contrary to general thought, a flywheel system will be competitive if not superior to more conventional systems utilizing either present-day or advanced batteries. This derives from the ability of the flywheel to perform the functions of d-c to a-c inversion and optimal impedance matching between the PV arrays and the load in addition to providing energy storage. The motor-generator design will also be discussed. This paper describes the structural topology, performance data, design parameters, and test measurements of the magnetic bearing and motor-generator as well as a description of the flywheel and control electronics to be used. A preliminary discussion of the economic aspects is also included.

Mississippi County Community College Solar Photovoltaic Total Energy Project

Mississippi County Community College at Blytheville, Arkansas, will derive its total electrical and thermal energy demand from an actively cooled photovoltaic energy system being developed under the management of TEAM, Inc. of Springfield, Virginia. The facility has a design peak electrical requirement for 240 kw to be supplied by a 26-sun concentrating collector field that fully tracks E-W. A 2.4 megawatt-hour electrical energy storage system under consideration is an iron redox system using FeCl2 electrolyte and pressure-molded carbon/PVC electrodes. The power conditioning system will include a 300-kw solid-state inverter to furnish 480-v, three-phase, 60-Hz ac to the College, and appropriate switching to acquire utility company power in emergencies. Process control includes the capability to gather vital signs on the collectors, thermal loop, electrical storage and building demands, and to provide closed-loop tracking and all control signals for energy efficient operation of the total system.

Textile Drying Using Solar Process Steam

This paper describes a solar energy collector system for providing process heat to a textile drying process in a WestPoint Pepperell mill in Fairfax, Alabama. The solar collector system uses 24 single axis tracking parabolic trough concentrating collectors to heat water in a high temperature water loop. The high temperature water fuels a steam generator to provide process steam. The process that was solarized is a textile drying process using cylindrical can dryers. The dryers are utilized in the slashing operation, a textile process where yarn is treated with sizing in preparation for weaving.

Solar Rankine Engines: Examples and Projected Costs

Solar heat can be converted into shaft power by use of the Organic Rankine Cycle Engine (ORCE). The efficiency of the ORCE to convert the solar heat to shaft power varies from 7 or 8 percent for an ORCE heated by low temperature flat plate collectors at 200 F, to near 15 percent when heated by intermediate temperature collectors (300 F), and up to 25 percent with high temperature concentrating collectors (600 F). Barber-Nichols designed, built, and tested its first solar heated ORCE in 1973, which produced three tons of air conditioning. Since that time, the three-ton unit has reached its fourth iteration on the development path to production; a 77-ton water chiller was installed at LASL; two ORCE drives for 100-ton water chillers were delivered to Honeywell; seven 25-ton water Chillers were delivered to DOE demonstration sites; and a 25-hp ORCE for irrigation pumping was installed in Willard, N.M. Photographs, design details, and the measured performance of these units are presented herein as examples. The cost of solar power systems using an ORCE is also presented which shows that for the current $150 to $200/m2 cost of cencentrating collectors, the system cost would be in excess of $2500/kw peak. The ORCE is approximately 25 percent of this cost or $600/kw. Consequently, while reductions in the cost and improvements in the performance of the ORCE can and should be made in the development process, the cost competitiveness of a solar power system is largely dependent on developing low cost concentrating collectors which can be sold for 1/2 to 1/3 of today’s price.

Hawaiian Sugarcane Energy Plantations

Hawaiian sugarcane plantations are presently in the business of producing food sugar and are nearly energy self-sufficient through use of residual fiber for fuel. They could be converted to “energy plantations” by converting sugar to ethanol by fermentation. Energy and economic analyses of this alternative energy source are presented.

On Air Conditioning With Photovoltaics

A simple solar photovoltaic power system comprised of photovoltaic modules and a vapor-compression air conditioner is described and its performance characteristics are analyzed. The mathematical model expresses the system’s cooling capacity as a function of insolation, ambient air temperature, and indoor air temperature. The economics of photovoltaic power systems are generally optimum when the power supply matches exactly the load demand, thus eliminating the need for on-site energy storage or backup power. Correlations between predicted cooling capacities and air conditioning loads are presented as one measure of the economics of air conditioning with photovoltaics.

Power Characteristics of a Continuous Crystallization Latent Heat Recovery System

A system for low quality heat storage through the latent heat of salt hydrates has been devised which gives only a slowly varying power output. This utilizes continuous generation and sedimentation of crystals. Heat transfer is accomplished by buoyant kerosene drops rising through a salt solution with concentration and size of suspended crystals controlled primarily by kerosene flow rate. The system has been investigated for sodium sulfate, sodium thiosulfate, and sodium acetate at working temperatures of 33, 48, 58 C, respectively. The sodium acetate system showed most promise and was studied quantitatively in a pilot unit.

Initial Investigations of a Shallow-Layer Algal Production System

A system for the intensive cultivation of the marine diatom Phaeodactylum tricornutum is described and evaluated. Unique features of the system include: (a) the incorporation of solar heat collection device which transmits only photosynthetically active radiation (PAR) to the growing culture; (b) the formulation of a new seawater enrichment medium that promotes physiological responses not previously observed in culture; and (c) the use of a foam fractionation device which separates microalgae, from the culture media, adds CO2-enriched air, and/or simultaneously recirculates the growing culture in shallow layers through an interconnecting series of hemicylindrical channels. The outdoor system demonstrated that very high ash-free dry weight yields of Phaeodactylum tricornutum are produced, a result of high photosynthetic efficiency. Actual yield over an eight-day period was equivalent to 39.57 ash-free dry tons/acre-year. Observed photosynthetic efficiency, based on photosynthetically active radiation incident upon the external surface of the system, is 13.1 percent, nearly three times the limit previously considered economically practical. The data indicate that greater yields may be expected using this system at locations receiveing higher insolation. A conservative projection is that 80 ash-free dry tons/acre-year will be realized in land regions receiveing 3 × 1010 Btu/acre-year total solar radiation. It is concluded that this system clearly warrants further investigation to determine its capacity to produce large and economical quantities of algal biomass for use as potential petroleum-fuel substitutes. The development of a comprehensive and systematic bio-engineering program is recommended to upgrade and evaluate the system to its full potential.

Review of Liquid Piston Pumps and Their Operation With Solar Energy

Liquid Piston Pumps are considered to be systems involving the up and down oscillations of a fluid column contained in a vessel which is enclosed at the top. At the bottom a suitable arrangement of check valves converts the oscillatory motion to a pumping action. The oscillations may be generated by cyclic heating, inertia forces, or combinations of the two. Existing designs of LPP’s are reviewed. Experimental results, and a theoretical analysis, are given for a straight tube L.P.P. The design of a Solar LPP is presented, which appears to be a practical and simple means of converting heat energy from a solar panel to potential energy of a water reservoir.

An Overview of Photovoltaic Power Systems

The United States is supporting a very aggressive research and development program in the field of photovoltaics. The goals of this program are to reduce the cost of solar cell arrays to a capital cost of 50¢/peak watt by the year 1986. The long-term goals are to achieve 10 to 30¢/peak watt by 1990 or 2000. The photovoltaic community is optimistic that the 1986 goals will be met with the use of silicon solar cells. The longer term goal may require the development of new thin film photovoltaic devices. As the price of solar cell arrays continues to decrease; the number of applications that are economically justified increases. The present production rates of photovoltaic arrays are close to 1 MW of production per year. The maximum expected efficiencies of 20 to 25 percent have already been achieved. Thus, cost reduction must come about through producing cells per unit area more cheaply. A separate alternative for producing low cost electricity from solar cells is to concentrate sunlight onto the cell, thus reducing the area of the cell per unit electrical output. Concentration systems also make available the option of using multiple cells to increase the overall conversion of sunlight to electricity. One two-cell concentration system has already demonstrated 28.5 percent efficiency.