GB2460548A - Storage heater comprising an electrical capacitor - Google Patents

Abstract

A storage heater for domestic use, where the means of energy storage is in the form of electrical charge on a large capacitor, such as a double-layer or ultra capacitor 'Cu', rather than as stored heat. Preferably, a controller is configured to control the storage of electrical energy in the capacitor and the output of heat from the heater. The controller may be arranged to control the storage of energy from an energy supply dependent on the time of day; a precision digital timer may be provided so as to allow accurate control. Preferably, the energy supply comprises a low rate tariff mains power supply or renewable energy derived from local micro generation such as wind, solar, tidal or wind turbine generation. The storage heater may also include an indicator to provide information relating to the capacity remaining in one or more storage capacitors. Furthermore, the stored electrical energy may be released as an electrical output to power external devices and appliances, such as refrigerators, freezers and televisions. In use, the storage heater is designed to enable greater control over the storage and usage of energy, and may help to optimise the use of renewable energy resources.

Description

1 Storage Heater 3 The present invention relates to a storage heater for 4 controlling the transfer of energy into and out of the storage heater so as to improve the storage of energy.

6 In particular, the present invention relates to a storage 7 heater which utilises ultracapacitors to store energy.

9 Storage heaters are often used as a source of heat in domestic and office applications. These may comprise a 11 set of high thermal capacity bricks in an insulated 12 container, which are heated by mains supplied electrical 13 power often taken at off-peak periods where the tariffs 14 can be substantially cheaper. Other heat storage mediums such as the latent heat of the liquefaction and freezing 16 of salts or waxes are also sometimes utilised. The heat 17 contained therein can then be released over a period by 18 means of an adjustable vent until the bricks or other 19 mediums cool down. Both methods tend to be heavy and bulky, and leak' heat due to poor thermal insulation 21 when it is not required, so that after a fairly short 22 period the heat stored is lost. However, with the recent 23 development of the various forms of renewable energy such 1 as wind, tidal, wave and solar, which tend to be 2 generated at unpredictable times, it is becoming 3 desirable for some sort of improved storage heater to be 4 available to store such energy efficiently from the time it is generated until the time it is required. One 6 alternative possibility is the use of large batteries to 7 store the energy in electrochemical form, but such 8 batteries can be expensive and have a limited number of 9 charging cycles before some form of deterioration occurs to the battery.

12 It is therefore an object of at least one aspect of the 13 present invention to provide an improved storage heater 14 that obviates and mitigates one or more of the

disadvantages and limitations of the prior art.

17 According to a first aspect of the present invention, 18 there is provided a storage heater, the storage heater 19 comprising: a storage means adapted to store energy received 21 from a supply; 22 a heating means adapted to controllably output 23 energy from the storage means in the form of heat; and 24 a control means; wherein the storage means comprises one or more 26 ultracapacitors and the control means is configured so as 27 to control the storage of energy in the storage means and 28 the output of heat from the heating means.

Preferably, the control means is configured so as to 31 control the storage of energy from the supply dependent 32 on the time of day. A precision digital timer may be 33 provided so as to allow accurate control.

2 Preferably, the storage heater is configured to receive 3 energy from a renewable energy source and the control 4 means configured so as to control the storage of energy from the renewable energy source dependent on whether the 6 renewable energy source is generating energy.

8 The energy from the renewable energy source may be 9 received from a mains supply. Alternatively, the energy from the renewable energy source may be generated by 11 local micro-generation.

13 Preferably, the control means is configured so as to 14 control a rate of charge of the one or more ultracapacitors in the storage means dependent on the 16 nature of the energy generated by local micro-generation.

18 Alternatively, the control means is adapted to receive 19 one or more signals relating to the nature of the energy received from the mains supply and control a rate of 21 charge of the one or more ultracapacitors dependent on 22 the nature of the energy received from the mains supply.

24 This signal or signals may originate from a mains supply provider and be indicative of when energy in the mains 26 supply is being generated by a renewable source, or 27 alternatively when the energy in the mains supply is 28 being charged at a lower tariff.

Preferably, the storage means comprises a charging 31 circuit comprising a high frequency converter.

1 Preferably, the high frequency converter is configured so 2 as to draw a unity power factor load from the supply.

4 Optionally, the heating means comprises a further high frequency converter configured to output a fixed voltage 6 to a resistive heater load.

8 Preferably, the control means is configured so as to 9 control the rate of output of heat from the heating means.

12 Preferably, the storage heater further comprises a 13 temperature sensor configured to provide an indication of 14 ambient temperature to the control means, and the control means adapted to control the rate of output of heat 16 dependent on said ambient temperature.

18 Preferably, the control means comprises a precision 19 digital timer so as to allow the control means to accurately control the output of heat dependent on the 21 time of day.

23 Optionally, the storage heater further comprises an 24 indicator means configured so as to provide an indication relating to the capacity remaining in the one or more 26 ultracapacitors.

28 Optionally, the storage heater further comprises an 29 electrical energy output means adapted to output energy from the ultracapacitors in the form of electricity.

32 This electrical output can then be used to power 33 appliances such as fridges, freezers, televisions etc. 1 from stored energy that may have specifically originated 2 from renewable energy sources, or simply in the event of 3 the corresponding mains supply being interrupted.

The present invention will now be described by way of 6 example only and with reference to the accompanying 7 figures in which...

9 Figure 1 illustrates in schematic form a charging circuit for a storage heater in accordance with an 11 aspect of the present invention; and 13 Figure 2 illustrates in schematic form an output 14 converter for a storage heater in accordance with an aspect of the present invention.

17 What is proposed is a new form of storage heater where 18 the energy is stored in such ultra-capacitors either at 19 low rate tariffs or when the energy is being generated from one or other renewable sources, or both. Such energy 21 may come either from the mains supply or from local 22 micro-generation at the premises by any of the 23 aforementioned means. The energy stored may then be used 24 for domestic or office heating or hot water at exactly such a time as the user wishes.

27 Recently, developments have taken place in these so- 28 called double-layer or ultra-capacitors', which have led 29 to devices having huge capacitance of the order of many farads in very small bulk and weight, and which may be 31 charged and discharged at almost unlimited rates and for 32 an almost unlimited number of cycles. These also have low 33 leakage currents so that energy can be stored for long 1 periods with minimum leakage until it is required. For 2 example, current designs have a specific energy of 3 280Watt-iours per Kilogram, but new nano-technology 4 developments are promising even larger capacities. Thus a heater able to store 8 Kilowatt-hours could weigh in the 6 order of 30Kilograms or less.

8 One aspect of the charging circuit (see for example 9 Figure 1) is that the rate of charge may be chosen to suit the energy being generated, which makes it suitable 11 for small micro-generation capacities. The charging of 12 the heaters may optionally be controlled by radio data 13 from the power companies at suitable times when the power 14 is being generated. It can charge faster than the usual thermal storage or slower if desired. It is a known fact 16 that the stability of power grid systems is compromised 17 by the introduction of the relatively unpredictable power 18 generation from renewable sources, and the new ability 19 given by this method of storage to the power generating companies to control the load on the grid by charging at 21 different times and rates will help to stabilise it.

23 Another aspect of the use of ultra-capacitors as a 24 storage medium is the ability to take power out of the storage heaters at different rates as the heating demands 26 change. Unlike thermal storage which has limited control 27 over the discharge rate using dampers in the heater, the 28 energy stored can be taken out at a high rate to warm a 29 room quickly then cut back, for example by using a temperature sensor, to a low rate once the room has 31 warmed adequately. Should the weather be warmer than 32 expected, most of the energy in the ultra-capacitors can 33 be stored until the next cool period.

2 The heater can be controlled by a precision digital timer 3 to output heat at exactly the required times. A capacity 4 gauge is easily implemented for such capacitive storage as the energy left in the capacitor is directly 6 proportional to the square of the voltage remaining in 7 the capacitors, something difficult to obtain with 8 thermal storage. Again, unlike the thermal storage 9 method, the capacitive energy can be used right down to zero, whereas the low-grade heat left in the thermal 11 storage medium is basically useless and is in effect 12 wasted. The heater may also be used directly should the 13 energy store be depleted.

One further optional application of the heater is that 16 the energy stored may conveniently be used to supply 17 other applications within the home for example in the 18 event of mains failure, by adding a DC-AC converter 19 module to a suitable outlet from the unit. This could keep freezers, refrigerators, televisions etc. powered 21 for long periods until the supply can be restored.

23 The ultra-capacitors Cu look like a short circuit load 24 due to their very low impedance, so it is necessary to charge them using a current source. One implementation of 26 the charging circuit is shown in Figure 1. This comprises 27 an input filter Fl to reduce any radio frequency 28 interference, a mains rectifier circuit B1, and a flyback 29 converter circuit that charges the ultra-capacitor bank Cu at a controlled current. The current may be pre-set to 31 a fixed value or chosen depending on information sent 32 from the Power Company or the capacity of the micro- 33 generation source. A precision digital timer allows the 1 input converter to be automatically enabled at certain 2 times, for example to take advantage of low tariffs, or 3 it may be over-ridden as required. An optional radio 4 receiver module allows the converter to be controlled both in current demand and to switch on during periods of 6 low grid demand or high grid generation capacity from 7 renewable sources.

9 The current into the flyback converter is constrained to have a waveform close to that of the mains line waveform 11 so that a near unity power factor load is drawn by the 12 charging circuit and low harmonic current content is 13 taken from the line. An efficient switching device Ti 14 such as an Integrated Gate-controlled Bipolar Transistor (IGBT), Power mosfet or bipolar transistor is controlled 16 to switch on and off at high frequency as the current in 17 the converter input is measured in resistor Ri and 18 compared with a scaled down version of the rectified line 19 waveform appearing at the voltage divider Rvi and Rv2.

Such power factor correction circuits are well known to 21 those skilled in the art. An inductor Ls and capacitors 22 Cs and Cf in the DC line feeding the converter circuit 23 smooth out the high frequency chopped current waveform 24 and remove most of the harmonics so that these do not affect the supply line.

27 The flyback transformer Tx has its windings phased in 28 such a way as to allow energy stored in the transformer 29 core and airgap when the transistor Ti is on, to flow to the connected ultra-capacitor bank when Ti is switched 31 off, via rectifier diode Di. The peak current in Ti may 32 be measured by a resistor in the low side of Ti to limit 33 peak current through the device. Also when Ti switches 1 off, the energy stored in the leakage inductance of the 2 primary winding of transformer Tx is returned to the 3 supply via the network comprising Csnub, Dsnubl, Dsnub2 4 and Lsnub for maximum efficiency.

6 The ultra-capacitor bank Cu is charged until it reaches a 7 maximum voltage value depending on the voltage rating of 8 the capacitors, then the charging is stopped. This is 9 measured by means of feedback via resistor Rfb. Once Cu is fully charged, the energy stored can be left there 11 until it is required to be used. It may be extracted at 12 any desired time by a second high frequency output 13 converter circuit, also utilising a suitable IGBT, Mosfet 14 or bipolar switch T2. In this case the energy must be withdrawn from Cu over a wide range of voltages from the 16 fully charged state down to zero, but supplied to a fixed 17 or adjustable room heater resistance. Since using an 18 adjustable resistance which might require wearing 19 contacts is not desirable, a fixed resistance can be used by ensuring the converter can both boost and buck the 21 voltage from Cu to suit the resistance value chosen.

22 Another option for the heater resistance is the use of 23 Positive Temperature Coefficient resistors (PTC5), where 24 a fan is speed-controlled to blow at variable rates, thus varying the power output. This can give a very compact if 26 more expensive design.

28 A suitable circuit to supply a fixed resistance heater is 29 shown in Figure 2. T2 is switched on until the current through it reaches a pre-set value measured by resistor 31 Ri2 and set by the output power level required. This 32 current comprises the current through inductor L2 and 33 through DC blocking capacitor Cl. L3 limits the current 1 through Cl and also stores energy. D2 blocks the flow of 2 current through Cl back from the output side when 12 3 turns on. Once this current is reached, 12 is switched 4 off, and the energy stored n L2 is constrained to flow through capacitor Cl in the opposite direction and 6 through D2 to the resistance load. The energy stored in 7 L3 is also fed through D2 to the heater load. Capacitor 8 Cs2 smoothes the chopped voltage appearing across the 9 heater resistance. L2 and L3 may be combined into a single wound component. The voltage across Cs2 is 11 measured via feedback resistor Rfb2 to calculate the 12 output power being delivered via the heater and the value 13 fed back to control the peak current allowed to flow in 14 12 before it is switched off. In this way the energy delivered to the heater is independent of the voltage 16 charge level on Cu, until of course Cu is fully 17 discharged. Such buck-boost converter circuits are well 18 known to those skilled in the art. The efficiency of this 19 second converter circuit does not have to be particularly high as any heat generated simply adds to that of the 21 heater.

23 At high power settings, a fan may be optionally be used 24 to blow the heat out of the heater element and spread it more effectively throughout the surroundings, or it may 26 be used without the fan simply as a convector heater at 27 low powers for low noise. A thermostat, thermistor or 28 other suitable temperature sensor fitted to the unit 29 controls the amount of heat output to the surroundings by reducing the voltage supplied to the heater as the room 31 reaches its desired temperature. This gives true 32 proportional control at an exact temperature; there is no 33 hysteresis such as is often found in other 1 thermostatically controlled devices. It also has 2 background' and frost-stat' settings so that the heater

3 both keeps the background at a cooler but still

4 acceptable level and can also be programmed to always come on in the event of the temperature falling to close 6 to freezing, thus protecting water pipes and houseplants 7 etc. A second precision digital timer fitted to the unit 8 allows the user to have the output come on at exactly the 9 desired temperature at exactly the desired time.

11 Where the option to have a secondary output to supply 12 other devices in the event of a power cut is required, 13 the voltage on Cu is made available via a fused socket to 14 a separate add-on module containing a separate but identical buck-boost converter to that shown in Fig. 2.

16 This would supply a regulated 300Vdc at its output, 17 allowing a third (DC to 50Hz AC) converter, also in the 18 module, to be supplied from this voltage and in turn to 19 supply outside appliances with a 23OVac 50Hz supply.

21 The energy capacity remaining in Cu will be shown by 22 calculating the square of the voltage on Cu. This may be 23 done by an analogue or digital multiplier circuit and the 24 resulting voltage digitised and shown as either a bar graph or digital number reading actual Kilowatt-hours or 26 a percentage of full capacity. Other multiplication 27 methods can be used, including a simple microcomputer 28 program. Along with the capacity remaining, the two 29 digital timers for charging and outputting power will have their times and other data shown on a low powered 31 LCD screen. These can be set by the user using a simple 32 microcomputer program accessing the time generated by a 33 Real-Time Clock (RTC) generator, and stored in non- 1 volatile memory in the microcomputer or separate memory.

2 The RTC will be kept at its correct time even in the 3 event of mains failure either by keeping a small amount 4 of charge in Cu as a supply, or a small battery back up.

The keyboard access to set this and any other of the 6 various user parameters which it may be desirable to set 7 will preferentially use an inexpensive capacitance touch 8 sensing method. The various methods of generating such a 9 program are well known to those skilled in the art.

11 Further modifications and improvements may be added 12 without departing from the scope of the invention herein 13 described.

Claims (9)

1. Claims: 1. An improved storage heater for domestic use where the means of energy storage is in the form of electrical charge on a large capacitor such as an ultra capacitor.
2. 2. An improved storage heater as described in claim 1 where the energy stored in the capacitor is supplied from a mains supply controlled both in time and level in order to minimise energy cost to the user.
3. 3. An improved storage heater as described in claim 1 where the current supplied by the mains supply is constrained to be taken at close to unity power factor.

   4. An improved storage heater as described in claim 1 where the energy stored may also be derived from local micro-generation means such as wind, solar, tidal or water-turbine generation.
4. 4. An improved storage heater as described in claim 1 where the energy stored in the capacitor may be released on demand in the form of heat
5. 5. An improved storage heater as described in claim 1 where the amount of heat released is manually or automatically controlled to suit the exact requirements of the user.
6. 6. An improved storage heater as described in claim 1 where the energy stored may also be remotely controlled by the entity supplying the energy in response to the energy available from renewable sources.
7. 7. An improved storage heater as described in claim 1 where the user is provided with an indication of the amount of stored energy available.
8. 8. An improved storage heater as described in claim 1 where the output of heat may be taken directly from the mains supply when the energy storage is depleted.
9. 9. An improved storage heater as described in claim 1 where the energy stored may optionally be released in the form of mains voltage to power external devices.