GB2539700A

GB2539700A - Renewable energy system

Info

Publication number: GB2539700A
Application number: GB1511217.0A
Authority: GB
Inventors: Hyde Kris; Cooley Graham
Original assignee: Itm Power (trading) Ltd
Current assignee: Itm Power (trading) Ltd
Priority date: 2015-06-25
Filing date: 2015-06-25
Publication date: 2016-12-28
Also published as: GB201511217D0

Abstract

A system for converting marine renewable energy into hydrogen comprises an electrolyser powered by a source of marine renewable energy, such as an offshore wind turbine, wave generator or tidal generator. Hydrogen from the electrolyser is fed into a buffer tank, which is located underwater. Hydrogen is then fed into a gas compressor from the buffer tank. The electrolyser may comprise proton exchange membrane (PEM) technology or alkaline polymer electrolyte membrane (APEM) technology. The buffer tank may be located at an underwater depth such that the water pressure acting on the tank equals the inlet pressure of the compressor. The volume of the buffer vessel may be varied by means of an elastic material or a piston. A second system may use hydrogen from the compressor to produce alternative compounds, such as liquid hydrocarbon (e.g. diesel), methane, ammonia or urea. There may be transport means for distributing compressed hydrogen to an end user.

Description

RENEWABLE ENERGY SYSTEM

Field of the Invention

This invention is in the field of the storage and transport of renewable energy using electrolysers.

Background of the Invention

The marine environment is a rich source of renewable energy. These include, but are not limited to wave generation, tidal generation and offshore wind farms. The rollout of this technology is hampered by factors such as the cost of sub-sea cables to export the energy to land and the strong electricity grid connection that is required to move the energy from the coast to the point of demand. Therefore, projects do not become realised if located too far from shore, or a coastal town with a high voltage (HV) connection.

One way in which energy can be exported is by using electrolysers to convert the renewable energy into hydrogen. Such a system typically comprises an electrolysis module, a buffer tank, a compressor and a high-pressure tank. The pressurised hydrogen can then be transported by pipe or road vehicle, or converted into another form of energy, such as methane (by reacting with 002), ammonia (by reacting with nitrogen), urea (by reacting ammonia with CO2), or liquid fuels such as diesel (by reacting with 002).

The buffer tank that is adapted to receive the hydrogen generated from the electrolyser is typically a pressure vessel that is several cubic metres in volume and made of austenitic steel, leading to high costs. This is necessary because the hydrogen contained within the buffer tank is at higher than ambient pressure.

Conventionally, the buffer tank supplies a gas compressor. Generally, compressors can only operate over a small range of input pressures. Therefore, the buffer tank is required to allow the compressor to operate for a reasonable period, before shutting off. In practice, this may be a range of approximately 20%. Thus, the buffer tank cycles between, say, 8 and 10 bar, which results in 80% of its contents being unused.

There is still a high energy demand associated with pressurising and transporting the hydrogen that may be produced at the marine source, and there exists a need for reducing this energy demand. This has obvious environmental benefits.

Summary of the Invention

This invention is based on the realisation that by locating an electrolyser, buffer tank and compressor at sea, next to a source of renewable energy, pressurised hydrogen can be generated and transported to an end-user using a reduced energy requirement.

According to a first aspect the present invention, a system for converting marine renewable energy into hydrogen, comprises an electrolyser powered by a source of marine renewable energy, and a buffer tank connected to a gas compressor, wherein the electrolyser is adapted to generate hydrogen which is fed into the buffer tank, and wherein the buffer tank is adapted to feed the hydrogen into the gas compressor, and wherein the buffer tank is located underwater, in use.

According to a second aspect of the present invention, a method of transferring energy generated from a marine renewable source to an end user, comprises transferring the energy in the form of hydrogen, wherein the hydrogen is generated from an electrolyser powered by the marine renewable energy source, and wherein the hydrogen passes through a buffer tank and a gas compressor, wherein the buffer tank is located underwater such that the pressure differential across the external walls of the buffer tank is minimised. Description of the preferred embodiments As used herein, the electrolyser can be any suitable electrolyser that generates hydrogen. Preferably, the electrolyser comprises a proton exchange membrane (PEM). In some embodiments, the electrolyser is based on liquid alkaline technology. In some embodiments, the electrolyser is based on alkaline polymer electrolyte membrane (APEM) technology.

As used herein, "marine renewable energy" means any renewable energy source that is derived from or is associated with a marine environment. 30 Examples of marine renewable energy sources are sources derived from wave generation, tidal generation or wind farms located offshore.

As used herein, a "buffer vessel" is a vessel adapted to receive hydrogen that is generated from an electrolyser. In the present invention, the buffer vessel is located, in use, underwater. Typically, the buffer vessel is located under the sea, at a specified depth below sea level. By locating the buffer vessel below sea level, there is sufficient pressure acting on the outside of the buffer vessel, such that it aims to equalise the pressure acting on the inside walls of the buffer vessel (acting outwards) caused by the high-pressure hydrogen fed into the buffer vessel (generated from the electrolyser). This pressure on the external surface of the tank is approximately 1 bar per 10 m of depth below sea level. With knowledge of these parameters, an underwater depth can be selected for the location of the pressure vessel dependent on the external pressure required to equalise the internal pressure of the hydrogen.

The aim of equalising the pressure differential across the wall of the pressure vessel means that the wall of the buffer tank can have a reduced thickness, or that is can be made from a material that is not required to be able to withstand high pressure differentials. In some embodiments, therefore, the external walls of the pressure vessel are made from low-strength materials or thin sections of high strength materials.

In some preferred embodiments, the buffer vessel has a variable internal volume. The potential advantage of this is that a particular internal pressure can be maintained irrespective of the volume of hydrogen contained therein. This may be achieved by way of an elastic 'bladder' or a piston. The bladder design in particular could be made for a substantially lower price than a high-pressure steel pressure vessel.

In the present invention, the buffer tank feeds a gas compressor. By allowing the buffer tank to change its volume, the buffer tank pressure is decoupled from the volume of hydrogen it contains. This allows the input to the compressor to remain at a constant pressure (which can be determined by the tank depth). Therefore, the entire buffer tank may be emptied on a single compressor 'on' period. For the same tank volume as a traditional rigid tank, this can result in reduced compressor cycling (leading to longer lifetimes) or if the number of compressor on/off cycles are maintained, the tank volume can be reduced by -80%, leading to a capital cost saving.

The pipe required to transport high-pressure hydrogen created by a renewable generator to land is cheaper than the cost of a cable to transport the electrical energy over the same distance. For a given amount of renewable energy generation, this leads to either a reduction in the cost of the project, or for the same cost, allows the project to operate at a greater distance from land.

If converted to hydrogen, once the energy comes ashore, there is no longer a requirement to locate near the project near a HV substation. Instead, the hydrogen may be simply loaded to a tube-trailer and transported by road, or converted immediately into other forms of energy (methane, ammonia, urea or diesel), which may be used locally or shipped / piped to where required.

In a preferred embodiment of the present invention an electrolyser is coupled to a marine renewable electricity source, converting to hydrogen and then storing the hydrogen in a submerged expandable buffer tank. This supplies the compressor with constant pressure hydrogen into its inlet. The high-pressure hydrogen is then taken ashore where it is fed into a tube trailer and transported by road to its end-use.

Claims

CLAIMS1. A system for converting marine renewable energy into hydrogen, comprising an electrolyser powered by a source of marine renewable energy, and a buffer vessel connected to a gas compressor, wherein the electrolyser is adapted to generate hydrogen which is fed into the buffer tank, and wherein the buffer tank is adapted to feed the hydrogen into the gas compressor, and wherein the buffer tank is located underwater, in use.
2. A system according to claim 1, where the renewable source is an offshore wind turbine.
3. A system according to claim 1, where the renewable source is a wave generator.
4. A system according to claim 1, where the renewable source is a tidal generator.
5. A system according to any preceding claim, wherein the electrolyser comprises of proton exchange membrane (REM) technology.
6. A system according to claim 5, where the electrolyser is based on proton liquid alkaline technology.
7. A system according to claim 5, where the electrolyser is based on alkaline polymer electrolyte membrane (APEM) technology.
8. A system according to any preceding claim, wherein the buffer tank is located, in use, at an underwater depth such that the water pressure acting on the buffer tank is approximately equal to the inlet pressure of the compressor.
9. A system according to any preceding claim, wherein the volume of the buffer vessel can be varied.
10. A system according to claim 9, wherein the buffer vessel comprises an elastic material, and the elastic material is the means for varying the volume of the buffer vessel.
11. A system according to claim 9, wherein the buffer vessel comprises a rigid material.
12. A system according to claim 9 or claim 10, wherein the buffer vessel comprises a piston, and the piston is the means for varying the volume of the buffer vessel.
13. A system according to any preceding claim, additionally comprising transport means for distributing compressed hydrogen from the compressor to an end user.
14. A system according to claim 13, wherein the transport network comprises road or rail vehicles.
15. A system according to claim 13, wherein the transport network comprises a pipeline.
16. A system according to any preceding claim, wherein compressed hydrogen from the compressor is fed to a second system adapted to convert the hydrogen into alternative compounds, before being distributed to end users.
17. A system according to claim 6, wherein the alternative compound is a liquid hydrocarbon.
18. A system according to claim 17, wherein the liquid hydrocarbon is diesel.
19. A system according to claim 16, wherein the alternative compound is methane, ammonia or urea.
20. A method of transferring energy generated from a marine renewable source to an end user, comprising transferring the energy in the form of hydrogen, wherein the hydrogen is generated from an electrolyser powered by the marine renewable energy source, and wherein the hydrogen passes through a buffer tank and a gas compressor, wherein the buffer tank is located underwater such that the pressure differential across the external walls of the buffer tank is minimised.
21. A method according to claim 20, using a system according to any one of claims 1 to 19. 25