Electrical transmission or interconnection systems – Plural load circuit systems – Plural sources of supply
Reexamination Certificate
2000-07-10
2002-09-17
Jackson, Stephen W. (Department: 2836)
Electrical transmission or interconnection systems
Plural load circuit systems
Plural sources of supply
C307S044000, C307S064000, C700S295000
Reexamination Certificate
active
06452289
ABSTRACT:
FIELD OF INVENTION
The present invention relates to an economical power supply topology, which provides 100 percent of the required power to residential, commercial or industrial consumers, and that, further, protects consumers from power surges, dips, and outages; and, more particularly, to a on-site, grid-linked distributed electricity generation power supply topology that draws power for normal operation from fuel cells and/or other alternative energy sources, relying, on power from a public utility grid, which is coupled to an inverter through the direct current bus rather than in parallel with the inverter, to meet abnormal or anomalous peak power demand.
BACKGROUND OF THE INVENTION
Foreseeable energy shortages from conventional electrical power sources and global concerns about the environment have sparked greater interest in alternative energy sources. These alternative sources include fuel cells, which produce electrical power by electrochemical reactions, and other means that produce power from wind or wave action, photovoltaic (solar) cells, micro-turbines et cetera. Unlike fossil fuels, renewable energy sources, such as wind power, wave power and solar power, are inexhaustible and environmentally friendly. However, power generated by wind, waves or the sun is highly dependent on weather and meteorological conditions; thus, subject to interruption. Fuel cells are relatively clean and efficient; however, they are limited to a design load and have a relatively slow response time. Thus, fuel cells cannot respond immediately to sharp increases in demand. Batteries, which have an immediate response time, store rather than produce energy hence are only good until the battery has drained. Moreover, battery cost is directly proportional to the stored energy needed. In the existing application, batteries are used to provide peak power, and a fuel cell is used to provide the continuous power, as well as to keep the battery charged.
Two methods exist for providing distributed power, which is defined as modular electrical generation or storage at or very close to the point of use, to consumers from alternative energy sources, such as fuel cells, batteries, wind turbines, etc. The first means is by grid independent architecture, which implies that distributed power delivered comes completely from the output power of an inverter, which converts energy from at least one fuel cell, battery, and/or other alternative power source into alternating current. Inherent in grid independent architecture is a need for sufficient distributed power to supply maximum, or peak, current demand. Hence, to be effective, the sum of the power capabilities of all of the connected energy sources, including fuel cells, batteries or other alternative energy sources must be designed to provide peak power on a worst-case basis, even though peak power demand may only occur, if at all, a few times a year and, even then, relatively briefly. Also, energy generating sources must be sized for the maximum continuous load the system would ever deliver—an expensive proposition considering the low frequency of such an occurrence. Typically, what is done is to size only the battery energy conversion equipment for this high power case, which works for very short periods of time at high load, within the limits of battery energy storage. Consequently, grid independent architecture suffers from over design and is inherently less economical and less cost efficient than the second means, which is to say grid parallel architecture. Grid independent architecture, further, cannot satisfy demand in excess of the demand for which it was designed. So, abnormal or anomalous demands that exceed the design peak demand may overtax a grid independent architecture.
The alternative to grid independent architecture is grid parallel architecture. Grid parallel architecture delivers distributed power from a fuel cell, battery or other alternative energy source as well as power from a public utility grid. The redundancy of the two power sources, which are parallel systems, provides the ability for the power supply to deliver a constant level of power at its output. This is most beneficial when the source of power is unpredictable, such as solar. In the case of solar, it is a rare event when the load power matches available power. In this case, if the distributed power source cannot provide sufficient power to meet demand, power from the utility grid makes up the difference. Hence, alternative energy sources do not have to be designed for a worst case scenario. Furthermore, the utility grid provides redundancy and peak capability to the alternative energy source. Hence, there is a cost saving in not providing redundant fuel cell, battery, and/or other alternative energy source, which would only operate during abnormal or peak demand.
Another advantage of a grid parallel topology is that utility grid absorbs surplus power generated by the distributed power source, which surplus power is available to help meet peak demands elsewhere on the public utility's network.
However, the consequence of grid parallel topology is a requirement for inter-connection between the inverter of the distributed power source and the utility grid. A recent study by the National Renewable Energy Laboratory entitled “Making Connections: Case Studies of Interconnection Barriers and their Impact of Distributed Power Projects”, which is incorporated herein by reference, highlighted the technical, business-practice and regulatory barriers to the interconnection of an alternative energy source distributed power source and a public utility grid. Technical barriers to interconnection include, without limitation, personnel safety, power quality, operation of the local distribution system, and compatibility with the utility grid and grid operation. Business-practice barriers include, without limitation, lengthy contractual and procedural requirements, application fees, insurance requirements, and operational requirements, all of which consume time and increase the cost of installing a distributed power alternative energy source. Finally, regulatory barriers include, without limitation, absolute prohibition, disincentives in the form of discounted energy from the public utility, special fees and tariffs, and environmental permitting. There are no national, or federally mandated, standards for the application process; hence, each public utility may have unique fees, rules, approval processes, and specifications for permitting power generation into a utility grid, potentially requiring multiple applications to a myriad of public utilities. Additionally, as provided above, some public utilities do not compensate or unfairly under-compensate consumers for surplus power supplied into the utility grid.
Therefore, a need exists for a distributed power-generating source that benefits from many of the advantages offered by both a grid independent and a grid parallel topology. Such a solution should reduce the cost and delay associated with regulatory, contractual and procedural requirements while simultaneously providing power more reliably, by virtue of the ability to draw power from the grid, and more efficiently and more cost effectively, by sizing the alternative energy source for only normal demand. In addition it is desirable for the owner of the distributed generator to have a feeling of independence from the utility grid.
In this setting, it would be desirable to provide a grid-linked power supply (“GLPS”), comprising a distributed power source comprising fuel cells, and/or other alternative energy sources, that is intermediate to grid independent and grid parallel architectures. Indeed, it would be particularly desirable to provide a GLPS, wherein the alternative energy source provides continuous demand load, relying on clean, efficient, and economical fuel cells, and/or other alternative energy sources for normal power demands and, further, on a public utility grid for peak, abnormal or anomalous power requirements. Furthermore, it would be desirable to provide a GLPS t
Holmansky Evgeny N.
Lansberry Geoffrey B.
Dike, Bronstein, Roberts & Cushman Intellectual Property Group
Hartnell, III George W.
Jackson Stephen W.
Neuner George W.
Rios Roberto J.
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