GB2286717A

GB2286717A - Power management apparatus comprises an electrolyzer combined with reconverter such as a fuel cell for producing electricity

Info

Publication number: GB2286717A
Application number: GB9502977A
Authority: GB
Inventors: Donald James Highgate; Marcus Newborough; Robin Graham Murison Crockett
Original assignee: SEEBOARD PLC; Cranfield University; Northern Electric PLC
Current assignee: SEEBOARD PLC; Cranfield University; Northern Electric PLC
Priority date: 1994-02-22
Filing date: 1995-02-16
Publication date: 1995-08-23
Anticipated expiration: 2015-02-16
Also published as: GB2286717B; GB9403592D0; GB9502977D0

Abstract

Power management apparatus comprises: a converter of electrical input, eg. an electrolyzer, to produce one or more storable chemical compounds eg. hydrogen and/or oxygen; means for storing the or each compound; a reconverter of the or each produced and/or stored compound, to produce electricity eg. a fuel cell of solid electrolyte type and optionally also heat, and means for controlling the level of reconversion. Such apparatus can store the output of the converter and the consequent ability to decouple power input and power output. Power supplies can thus be managed as required, with high efficiency. <IMAGE>

Description

POWER MANAGEMENT Field of the Invention This invention relates to apparatus that can be used to manage power resources.

Backaround of the Invention Large-scale power systems comprise one or more power stations, optionally also sub-stations, that convert fuel into power, and a grid of, say, electric cables or gas pipes. One example of apparatus that converts fuel into power comprises combined heat-power (CHP) systems. There are two primary problems with such systems. The first problem is that the heat output, which may be 60-70% of the total energy produced, must be used immediately if it is not to be wasted. The second, related problem is that combustion is difficult to manage, in the sense that power output cannot be decoupled from fuel input.

Summarv of the Invention The present invention is based on the discovery that combined electrolyser/reconversion systems can be used for the management of electricity supplies. In its broadest aspect, the present invention provides apparatus comprising: a converter of electrical input, to produce one or more storable chemical compounds; means for storing the or each compound; a reconverter of the or each produced and/or stored compound, to produce electricity and possibly associated heat; and means for controlling the level of reconversion.

Essential characteristics of the present invention are the ability to store the output of the converter and the consequent ability to decouple power input and power output. Power supplies can thus be managed as required, with high efficiency. In addition to its use in association with a conventional large scale power system comprising an electricity grid and possibly an associated gas pipe grid, the present invention can be particularly helpful in the operation and management of CHP systems.

Brief Description of the Drawina The accompanying drawing is a schematic diagram of a combined electrolysis/reconversion system that embodies the present invention.

Description of the Invention The present invention is based on studies showing that the utilisation of combined electrolyser/reconversion systems is technically feasible at a variety of points within the electricity supply system. Essentially two modes of operation exist.

Firstly, there is "electricity in, electricity out" operation. This would be used solely for the management of electricity supplies (e.g. load levelling and security of supply). An efficiency can be achieved, within this mode of operation, of 51-59%.

Secondly, there is "electricity in, electricity-andhydrogen/oxygen out" operation. By providing clean gas(es) for combustion or fuel-synthesis purposes in addition to electricity supply management, "total fuel" schemes driven solely by electricity are feasible. The combustion efficiency via electricity-to-gas conversion is c.88%, indicating the advantage of this mode of operation.

Combined electrolyser/reconversion (ER) systems, therefore, offer two commercial possibilities: load management and an "all options" energy supply based solely upon the existing electricity system. This latter option affords electricity suppliers the opportunity of meeting all the energy needs of communities, an option previously available only to the gas industry via CHP.

As indicated, the output of the converter, e.g. an electrolysis unit, may be a gas such as hydrogen and/or oxygen. For storage, the apparatus may include means for converting the gas to a liquid, e.g. methanol. The reconverter preferably comprises a fuel cell. The converter and/or reconverter may each operate on the basis of a solid polymer electrolyte. The advantage of such electrolytes is that they avoid the need to circulate a liquid electrolyte, i.e. there is no circulating lye. In the absence of a circulating liquid phase, there is no dissolved gas, so that starting or stopping an electrical input starts or stops gas production, and vice versa. Such electrolytes have low power requirement, operate below 1000C, and are environmentally-friendly, i.e. CO2-free.

ER systems are the preferred means of storing energy in association with an electricity system, particularly because the storage system can be sized independently of the electrolyser and reconversion systems and thus the requirements for energy storage can be optimised and/or modified at will. No other system offers this degree of controllability and flexibility.

Although the preferred reconversion device would be a fuel cell (particularly a device employing a solid polymer electrolyte), when the resulting system can be described as an EFC system, it is technically possible to reconvert some or all of the stored products using a conventional heat engine driving a conventional electric generator. Such a route is not at this time as efficient in producing output electricity as an EFC device but developments in heat engine technology, enabling the combustion of oxygen and hydrogen, or the use of the heat engine as a part of a CHP system, could significantly improve the overall energy efficiency of the heat engine reconversion route.

ER systems can provide energy density of up to 39.7 kWh/kg, 639 kWh/m3 (gaseous hydrogen at 20"C, 20 MPa (198 atm)). They are not restricted to "electricity in, electricity out", and involve negligible storage losses (gaseous products). They can provide hydrogen (and oxygen) directly, clean gaseous fuel for "mains" gas supply and/or synthesis of liquid hydrocarbon fuels. They can thus provide a local supply where there is no mains supply of natural gas.

Further, ER systems can provide combustion efficiency of c. 88% (assuming power conversion losses of c. 3%).

They are flexible, since conversion and storage elements are separate. Thus, elements can be changed separately in case of altered mode of operation. Extra storage can simply be provided by more tanks. They are thus an excellent demand-side management tool.

EFC systems offer, in addition to the above, "electricity in, electricity out" efficiency of 51-59% (assuming power conversion losses of 5%), and scaleindependent efficiencies. They can be located anywhere in a T & D network. Electricity supply/demand management in accordance with this invention offers improved utilisation of primary generation plant, reduced requirement to operate specific peak-load plant, improved efficiency, reduced fuel requirements, and reduced pollutant emissions.

Reduced peak-loads can be met by the T & D system.

There may be reduced line ratings, reduced requirement to uprate existing lines, and reduced investment in new generation plant.

Advantages of the present invention for the electricity industry, consequent on the use of an electrolyser/fuel cell, are that it can: (1) provide CO2-free electricity at point of use, and in general provided that the input electricity is originally derived from nuclear or other non fossil fuel sources; (2) provide a means of distributed energy storage, and hence load management within the electricity distribution system; (3) operate at low temperatures and achieve good end use electricity-generation efficiencies; and (4) provide an environmentally-clean high-value fuel (e.g. hydrogen or methanol) for combustion if desired.

Similar advantage can be derived by applying this technology to the management of the electrical component of any CHP system irrespective of its primary fuel type and scale because, as mentioned above, both the electrolyser and fuel cell components are largely scale-independent, both in respect of their operating efficiencies and the unit costs of the basic equipment.

Claims

1. Power management apparatus comprising: a converter of electrical input, to produce one or more storable chemical compounds; means for storing the or each compound; a reconverter of the or each produced and/or stored compound, to produce electricity and optionally also heat; and means for controlling the level of reconversion.

2. Apparatus according to claim 1, wherein the converter is an electrolyser.

3. Apparatus according to claim 1 or claim 2, wherein the reconverter is a heat engine.

4. Apparatus according to any preceding claim, wherein the reconverter comprises a fuel cell.

5. Apparatus according to any of claims 2 to 4, wherein the converter and/or the reconverter comprises a solid polymer electrolyte.

6. Apparatus according to any preceding claim, which additionally comprises a rectifier for an AC electrical input.

7. Apparatus according to any preceding claim, which additionally comprises an inverter for an AC electrical output.

8. Apparatus according to any preceding claim, wherein the converter produces gas.

9. Apparatus according to claim 8, wherein the gas comprises hydrogen and/or oxygen.

10. Apparatus according to claim 8 or claim 9, which includes means for converting the gas to liquid, for storage.

11. Apparatus according to claim 1, substantially as illustrated in the accompanying drawing.