The present invention relates to the use of renewable energy for providing a supply of steam. Particularly, but not exclusively, the invention relates to the supply of steam on a large scale using renewable energy that may provide only an interrupted supply of electricity.

Existing large-scale uninterrupted steam supplies are generally based on fossil fuelled boilers (mainly coal, natural gas, diesel, gasoil, heavy fuel oil) or nuclear powered boilers.

It is desirable to be able to provide a reliable high volume source of steam for use remote in industrial applications, such as for use in a mine. The use of renewable energy provides a useful source of energy for remote locations. However, renewable energy is typically intermittent in its supply. There is therefore a need to provide a system and method for supplying steam that is not dependent upon an uninterrupted power supply.

According to the invention there is provided a system and method as defined by the claims.

The invention has application in the provision of electricity and/or heating to one or more of: residential buildings, office buildings, complexes of residential buildings, complexes of office buildings, factories, and/or industrial estates. A preferred embodiment of the system may therefore comprise a multi-story building having a plurality of office rooms and/or a plurality of residential rooms. The plurality/pluralities of rooms each having heating means supplied with heat using the steam supplied by the system of the invention. The steam may be directly provided to each heating means. Alternatively, a heat exchanger may be used to heat a heating fluid that circulates through each heating means. In many cities in Europe and other parts of the world, the infrastructure is already in place for supplying heat to entire towns, or districts of larger cities, and so this invention can replace existing coal, oil, or gas boilers, so as to avoid harmful C02 emissions.

The invention has application in the provision of steam to a mine, preferably a salt mine, but other mineral mines also require a supply of steam. A preferred embodiment of the system may therefore comprise a mine supplied with steam supplied by the system of the invention. A supply of steam obtained using the invention can be used in a mineral mine to dry or wash minerals in a conventional manner. The invention can also provide the mine with electricity. In an example of a salt mine, the steam may be provided to an evaporator (in particular, a vacuum evaporator) for the evaporation of water from brine to produce salt in a conventional manner. The provision of steam using the invention can allow a supply of steam on demand independently of the supply of renewable power. The use of the invention in a mine can reduce reliance on fossil fuels

Throughout the following description and in the claims, the phrase "renewable energy generator" is intended to mean a generator that generates electricity from a renewable energy source, such as solar power or wind power.

For a better understanding of the invention, and to show how the same may be put into effect, reference is now made, by way of example only, to the accompanying drawings in which: Figure 1 shows a schematic representation of an embodiment of a system in accordance with the invention.

As can be seen in Figure 1 , an embodiment of a system in accordance with the invention comprises: a main source of water (and/or steam) 30; a renewable energy generator 10; and an induction heater 18. The renewable energy generator 10 is arranged to directly supply electricity to the induction heater 18. The renewable energy generator 10 may be any form of renewable energy generator, but typically will include solar panels 2 (e.g. photovoltaic cells) and/or wind power 4 (e.g. wind turbines). Typically, the renewable energy generator 10 is arranged to intermittently provide power in the range 10 MW to 100 MW, more preferably 50 MW to 100 MW. That is, it is preferable for the generator 10 (for example, a plurality of solar panels and/or wind turbines) to have a maximum output (MWp) in this range. The renewable energy generator 10 will provide high power at peak times, for example, powers in excess of 10 MW may be generated.

For example, suitable photovoltaic panels may collectively have an area of at least 100 acres, preferably 500 acres. Alternatively, tidal power may be used instead of, or in addition to, solar 2 and wind 4 power. Also considered are offshore wind turbines.

Typically, but not always, the electrical supply will be direct current and so it is preferable to provide an inverter 12 to convert the direct current into alternating current.

A transformer 14 may be provided if it is necessary to change the voltage of the supplied electricity. The transformer 14 receive current from the inverter 12. Preferably, a transformer is provided to convert the step up the voltage to, for example at least 1 1 kV minimum. Such a transformer will be designed to transmit a power in the range 1 1 kVA to 66 kVA, and preferably around 33 kVA.

Preferably, the induction heater 18 is powered only by the renewable energy generator 10. However, optionally, some other electrical energy storage (not shown) may be provided. Such electrical energy storage may be charged with the renewable energy generator 10.

The induction heater 18 comprises an induction coil 16 and a solid charge 20 (i.e. a solid mass). The induction coil 16 is arranged to receive power from the generator 10 to heat the solid charge 20. For example, the coil 16 may be coiled around the solid charge 20. As is known in the art of induction heaters, the solid charge 20 is formed of a material that will generate eddy currents in the presence of an alternating magnetic field, and the eddy currents in turn generate heat.

Whilst the renewable energy supply 10 can provide the necessary power to the induction heater 18 when power is available (e.g. during sufficient winds and/or during daylight hours), the supply will inevitably be intermittent and unpredictable.

Therefore, it is necessary to use a large solid charge 20 for retaining heat when there is no electricity supplied by the renewable means. Furthermore, the solid charge 20 is preferably encased in insulating material, such as refractory bricks.

For example, it is preferable that the solid charge 20 has a mass of at least 30,000 kg, most preferably 30,000 kg to 125,000 kg. Suitable materials for such a solid charge 20 include: steel, in particular martensitic or ferritic steel; and any ferrous metal or alloys thereof.

The solid charge 20 may therefore be manufactured by casting.

The solid charge 20 comprises one or more inlets 21 for receiving water and one or more outlets 22 for supplying steam.

One or more fluid flow channels 25 extend between the inlet(s) 21 and the outlet(s) 22. The flow channel(s) 25 preferably are formed with inwardly extending vanes to provide a large area of contact between the channel 25 and fluid therein. Optionally, the flow channel(s) 25 may extend through the solid charge 20 by a serpentine/labyrinthine path.

The inlets 21 may be supplied with water from a main source of water 20. Optionally, the water may be preheated to form steam or may be a mixture of steam and water.

The main source of water may be under pressure (for example, it may be stored at a greater height than the rest of the system). However, optionally, a pump may be provided to pump the water into the solid charge 20.

It is possible to use the steam leaving the outlets 22 of the solid charge 20 to supply industrial processes directly. However, it is preferred to recirculate this flow of steam back to the main source of water 30. A supply of steam may be provided for a user to use in a process 200 by using a heat exchanger 60. The heat exchanger 60 comprises a first path 65 and a second path 66 and is arranged for heat to pass from the first path 65 to the second path 66 by conduction therebetween as is known in the art. This can allow a more flexible delivery of steam to the end user.

The outlet of the solid charge 20 is connected to the main source of water 30 via the first path 65 to provide a main circuit 70 for recirculating steam and/or any water to the source of water 30. The main circuit 70 may circulate just steam/water (i.e. steam and/or water) although it is preferred to circulate a mix of water and glycol. A steam delivery system comprises a secondary source of water 140 in communication with the inlet 63 of the second path 66 and delivery means 1 10 for delivering steam from the outlet 64 of the second path 66 to a user. Since the user may require delivery of steam to the process 200 on an intermittent basis, a secondary circuit 80 is formed for recirculating steam and/or water not delivered to a user back to the secondary source of water 140.

Alternatively, the main source of water 30 may be used in place of the further, secondary source of water 140.

The secondary circuit 80 may comprises a pressure vessel 120 for storing steam, e.g. on a short-term basis. This can provide a volume from which users can draw upon.

The secondary circuit 80 may comprises a steam recovery unit 130.

From the description above, it can be seen that a constant flow of steam may be provided irrespective of the intermittent nature of the renewable energy source.

In some case, it may also be preferable to provide a stable source of electricity that is not dependent upon the renewable source. In which case, the main circuit 70 (and/or, optionally, the secondary circuit 80) also may preferably include a steam turbine generator 40, 50 for generating electricity. The steam turbine generator may comprise a turbine 40 that drives a generator 50 to rotate to thereby generate electricity. Embodiments of the invention may be used in a method comprising: providing a supply of electricity using a renewable energy generator 10; heating a solid charge 20 using an induction coil 16 powered by the renewable energy generator 10; providing a main source of water 30 to one or more inlets 21 in communication with one or more fluid flow channels 25 extending through the solid charge 20; and outputting steam from one or more outlets 22 in communication with the one or more fluid flow channels 25.

Preferably, the solid charge 20 is heated to temperatures of at least 600°C, and preferably up to 850°C when power is available. However, heating may be stopped if the solid charge 20 approaches its melting point. At which point, electricity may be stored in the electrical energy storage discussed above, or used to power other local systems. In such a method, it may be the case that the renewable energy generator 10 intermittently provides no power. In which case, the system may still supply power from the steam turbine generator 40, 50 with steam from the one or more outlets 22 and generate electricity with the steam turbine generator 40, 50.

Furthermore, the system preferably still delivers water to the inlet 21 of the solid charge 20 even when the renewable energy generator 10 is not generating electricity to power the induction coil 16. During that time, steam may be delivered on demand to a user via the second path 66 and delivery means 1 10.

The various components of the system may be controlled by an electronic controller (not shown), which is programmed with one or more operating modes. In a first operating mode, the controller commands the system to deliver water from the main source of water 30 to the inlet 21 of the solid charge 20 continuously and

independently of whether the renewable energy generator 10 is generating electricity and powering the induction coil 16. In a second operating mode, the controller commands the system to circulate water/steam continuously through the main circuit 70 independently of whether the renewable energy generator 10 is generating electricity and powering the induction heater 18. At the same time, the controller commands the system to circulate water/steam continuously through the secondary circuit 80 with steam being delivered on demand to a user via delivery means 1 10. Fluid lost from the secondary circuit 80 is replaced with fluid from the secondary water source 140 or main water source 30.