GB2469494A

GB2469494A - Solar panel for water heating and purification

Info

Publication number: GB2469494A
Application number: GB0906511A
Authority: GB
Inventors: David Osborne
Original assignee: CELSIUS SOLAR Ltd
Current assignee: CELSIUS SOLAR Ltd
Priority date: 2009-04-16
Filing date: 2009-04-16
Publication date: 2010-10-20
Also published as: GB0906511D0

Abstract

A solar panel 1 comprising of annular heat exchanger 6 is made of a thin high conducting metal tubing which is attached to a water tank 14 and act as a source of heating and partially purifying water in rural developing countries. The solar panel is made of metal tray with clear plastic lid containing annular heat exchanger and is connected to a water tank which heats the water in the sunlight. The heat exchanger as a portable unit is detached out of the solar panel and placed onto a stone cooking stove to attain rolling boil to partially purify water, whilst standard cooking occurs without utilising any additional energy resources. The solar panel and heat exchanger is aimed to be used by rural communities in developing countries.

Description

SOLAR PANEL FOR WATER HEATING & PURIFICATION

BACKGROUND:

14 The majority of people in rural areas in developing countries e.g. Kenyan, India etc. rely almost exclusively on biomass-wood, charcoal 16 and organic waste for cooking and heating, given that over 50-75 17 percent of the population has no access to grid electricity or other forms 18 of modern commercial energy. Ironically, renewable energies such as 19 wind and solar power remain under-utilized despite being abundantly available. In addition, they have no access to running water, and water 21 is manually obtained or transported from wells, ponds or rivers.

22 Wood fuel is an important source of fuel energy in developing countries 23 e.g. Kenya, constituting about 75% of the total energy consumedi. The 24 rural population relies almost entirely on fuel wood which has become increasingly difficult to obtain. The availability of agricultural residues for 26 use as fuel and the possibility of using briquettes for cooking were 27 established. In rural communities majority of households have a 3- 28 stone cooking stove in which they burn fuel wood or agricultural 29 residues e.g. cow dung, maize cobs and stalks, sugarcane residues etc. In general, 1 5-35% of a household's income is spent on fuel 31 though this does not take into account the time spent gathering fuel.

32 Worse, is that these populations depend exclusively on fossil fuels for 33 cooking and heating in simple devices that produce large amounts of 34 indoor and local air pollution linked to between four and five percent of the global disease burden.

36 Indeed, fuel wood supplies are fast dwindling in these countries and 37 poor families are compelled to spend more time and money to procure 38 it. On the other hand, the high cost of imported high tech solar panels 39 has prevented many households from utilizing solar power.

41 Solar heating water and purifying systems have been developed and 42 are described below in detail: 44 Solar heating water systems have been developed and are described belowindetail: 46 Solar water heating systems as disclosed by W02007053859 and 47 US6014968 describes heat exchanger which primarily consists of a 48 heat absorbing pipe or pipes which are connected to a water tank and 49 utilize solar energy for energy supply. US6014968 discloses a heat exchanger comprising of a number of heat absorbing pipes which are 51 surrounded by water cooling return pipes and is aimed at industrial 52 applications. W02007053859 is aimed at low cost users and is 53 inexpensive and discloses solar water-heater which includes a water 54 storage tank connected to heat absorbing pipe and an outlet which is connected to hose pipe for supplying heated water to a user.

56 US61 19682 discloses solar energy powered thermo siphon-circulated 57 water heater and storage device comprising of a flat, tilted solar 58 radiation absorber panel and an insulated hot fluid storage tank and 59 connecting pipes, but also enclosed is an electric immersion heater. A solar energy powered water heater and storage device. In essence it 61 provides a low-profile, flat-plate solar energy collector holding a fluid 62 which is heated and circulated to an integrated, insulated hot fluid 63 storage tank, the hot fluid in turn heats line pressure water passing 64 through an extended length, heat-exchange piping circuit incorporated within said tank, in conjunction with a supplementary, electric water- 66 heating means.

67 CN1 837711 discloses split type solar water heater comprising of heat 68 collector formed by glass vacuum tubes, a water tank, inlet and outlet 69 heat collector tubes, a closed electromagnetic valves and a computer control plate for controlling the system.

71 W09531 677 describes a heat exchanger for vacuum systems, 72 especially for use as a flat solar absorber or a wall or roof panel, with 73 an envelope for the heat exchange medium sealed and core which has 74 narrow flutes, grooves or channels on the heat-exchanger surface.

US4261 333 describes a solar heating panel apparatus which has a 76 supporting base with a plurality of elongated heat exchanger members 77 mounted to the base. Each heat exchanger is operatively connected to 78 one end of an adjacent heat exchanger to provide a continuous path 79 through the heat exchangers from a fluid input to a fluid output. Each heat exchanger has a hollow centre core having a passageway running 81 spirally around the centre core and uses the centre core as one wall of 82 the spiralling passageway.

83 US41 59708 discloses a solar energy collector and heat exchanger for 84 use in a solar energy system that provides space heating and preheating of water for a building or residence. It is aimed at improved 86 solar energy collector and heat exchanger of the type which comprises 87 a radiation collecting surface enclosed within a housing surface which 88 absorbs the solar energy of the sun and transfers it to a portable 89 storage medium. An improved solar energy collector and heat exchanger includes baffles in the housing that define a first serpentine 91 channel beneath the surface and a second serpentine channel above 92 the surface. Air inlet and air outlet parts in the housing communicate 93 with both the first and the second channels. A fluid system having an 94 inlet and an outlet is provided. A fluid system includes an array of interconnected tubes mounted on the solar absorption surface.

96 CN1294284 discloses a photoelectric and passive photo thermal 97 appliance for greenhouse. Its solar battery is connected with 98 accumulator or inverse transformer of electric network to provide 99 electric energy to the electric appliances. The solar heat collector is linked with air purifier and heat exchanger for regulating air quality and 101 indoor temp. A cold water tube passes through heat exchanger for 102 providing hot water.

103 FR 2787868 discloses a solar collector which consists of a supporting 104 housing with a translucent cover, containing a heat exchanger made from a hollow ribbed panel with water circulating via ribs. The ribbed 106 panel which can have flat surface is sealed by adhesive or welding in 107 the housing, leaving a gap between it and the translucent cover.

108 FR 2699991 discloses a panel which consists of a series of tubes made 109 from two layers of plastic joined together by welded seams to form a series of linked tubes which both receive the heat and store the heated 111 water. The tubes are enclosed inside housing with a base, an inner 112 layer of a thermal insulation material, and a transparent covering panel.

113 During use the panel is mounted with its cold water inlet at the bottom 114 and its warm water outlet at the top.

WO 2009005453 discloses a method for producing clean water and 116 electricity, in which water that is to be cleaned is caused to undergo 117 membrane distillation by means of one or several units comprising a 118 solar cell panel that is impermeable to water, a membrane through 119 which water in the gaseous phase can only pass, and a sheet where water is led and condensed. The solar cell panel with electrically active 121 layers facing away from the membrane, and is located such that it is 122 illuminated by sunlight.

123 CN200986328 and CN1O1 0551 25 describe a method for purifying 124 drinking water by employing solar energy using radiation heat from the sun to heat the water to evaporate into steam and then liquefied into 126 water.

127 FR 2899575 discloses a water purifying device which comprises of a 128 container with black external walls, where the water is purified by 129 distillation using solar energy. The container is enclosed in a wide glass to form an air vacuum envelope.

131 WO 2007080751 discloses a water purifying apparatus which 132 comprises of a tank for reserving water, a circulation device, an ozone 133 generator for generating ozone, and a solar cell panel. Similarly, water 134 purification in conjunction with sunlight is attained by air filtration -JP 2004283679, filter -JP 10043519, ceramic filter -WO 02100780, 136 distillation -US20031 50704, ozone generator -CN 1436739 and jetting 137 boiling water -JP 9299265. Whilst, JP 2001300585 has a simple self- 138 purification system.

This invention is aimed at a cheap simple system to provide 141 households with means to heat and partially purify water utilizing solar 142 energy. The simple system is easy to maintain, cheap and affordable to 143 poor households in developing countries. Unlike above described prior 144 art, this system not only heats water by solar energy but also provides means of partially purifying water whilst using bare minimum existing 146 utilities. In essence, it provides an inexpensive, easy to adapt system 147 which heats and partially purifies water as a dual function.

Summary of In vent/on

148 Key embodiment of invention is a simple solar panel system consisting 149 of; solar tray which is blackened from inside, 151 heat exchanger made of high conducting metal, 152 clear plastic lid, 153 which utilises solar energy via sunlight during daytime and utilises clean 154 or unclean water from a well, river and pond to: heat the water to 60-100°C to be used for cooking and bathing, 156 partially purify water by rolling boil to be used for drinking and cooking; 158 Another embodiment of the invention is a simple solar panel system 159 consisting of; solar tray which is blackened from inside, 161 heat exchanger made of high conducting metal, 162 clear plastic lid, 163 which utilises solar energy via sunlight during daytime and utilises clean 164 or unclean water from a well, river and pond to: heat the water to 60-100°C to be used for cooking and bathing, 166 partially purify water by rolling boil to be used for drinking and cooking; 167 In absence of the sunlight, portable heat exchanger part can be 168 detached from the solar panel and it can be coupled or placed on to the 169 local heating source for cooking to: heat the water to 60-100°C to be used for cooking and bathing, 171 partially purify water by rolling boil to be used for drinking and cooking 172 and is aimed at developing countries, where there is no electricity or 173 running water, and water comes from well, pond or river.

A solar panel tray is made of a metal e.g. aluminium, iron, brass etc. or 176 plastic e.g. polycarbonate, polyester, polyacrylic etc. 178 The solar panel tray inner sides and bottom layer are blackened by a 179 paint or black anodising etc. such that it acts as a black body 181 The solar panel can be of any shape, e.g. square, rectangular, circular, 182 oblong etc., however, it is easier and cheaper to construct square and 183 rectangular shapes.

A solar panel lid or top layer is made of a clear plastic e.g. typically 186 polycarbonate for being cheap and tough and has functionality to allow 187 sunlight to be transmitted through it.

189 The solar panel tray can have an area of 0.025m2 to 3m2 and a height of 0.01 m to 0.5m. Preferably, solar panel of size of an area of 0.56m2 191 and height of 0.05m 193 The solar panel tray has an opening for an insertion of the heat 194 exchanger, preferably a latch type of opening which is closed or locked after the insertion of the heat exchanger into the solar panel tray.

197 Another embodiment of the invention is the heat exchanger which is 198 made of a high conducting metal forming an annular shape, preferably 199 made of the copper tubing.

201 The heat exchanger can be of various shapes e.g. circular, annular, 202 square, rectangular, oblong with central void.

204 The heat exchanger of annular shape is made of tubing of size 5mm to 205 20mm diameter, preferably 10mm in diameter.

207 The heat exchanger of annular shape has the outer annular size of 208 O.25m to 1 m preferably, 0.46m diameter and inner annular size of 0.1 m 209 to 0.3m, preferably 0.175m.

211 The heat exchanger has water capacity of 0.01 litres to 20 litres or 212 more, preferably 1-3 litres.

214 The heat exchanger is held together by clamps, made of high 215 conducting metal e.g. copper to maintain high energy absorbance 216 characteristics.

218 The heat exchanger has a handle to transport it around by hand.

220 Another embodiment of the invention is a solar panel connected to the 221 water tank of 5 to 100 litres or more capacity made of cheap material 222 e.g. plastic or metal.

224 The water tank has a solar panel outlet which is connected to a float 225 made of light density materia' e.g. polystyrene by a trap 227 Another embodiment of the invention is for the solar panel to heat water 228 to 60-100°C within 0.1 to 10 hours, preferably 0.5 to 4 hours at sunlight 229 temperatures of 10 to 50°C, preferably 25 to 45°C 231 Another embodiment of the invention is for the heat exchanger of 0.1 to 232 10 litre capacity, preferably 1 -3 litre capacity when used in conjunction 233 with rural stove e.g. 3 stone cooking stove to heat the water to 60 to 234 100°C, within 0.1 to 60 minutes or more, preferably in <6 minutes 236 Another embodiment of the invention is for the heat exchanger of 0.1 to 237 10 litre capacity, preferably 1 -3 litre capacity when used in conjunction 238 with rural stove e.g. 3 stone cooking stove to heat the water to 60- 239 100°C and partially purify the water in 60-1 00°C by rolling boil, 240 preferably in <6 minutes 242 The rural cooking stove e.g. 3 stone cooking stone uses wood or 243 agricultural residues e.g. cow dung, maize cobs and stalks, sugarcane 244 residues etc. to generate the fire and heat.

DESCRIPTION

Detailed Description:

245 Figure 1: Top view of solar panel 246 Figure 2: Top view of solar panel 247 Figure 3: Side view of solar panel with method of placing heat 248 exchange 249 Figure 4: Side view of solar panel with heat exchange in place 250 Figure 5: Top view of make up of heat exchanger 251 Figure 6: Schematic of solar water heating system 252 Figure 7: Side view of water tank 253 Figure 8: Schematic of water partial purification 256 Figures 1 & 2 show top view of the solar panel comprising of a tray (1) 257 which can be made of a metal (e.g. aluminium) or plastic materials e.g. 258 dependent on cost (aluminium, iron, brass, polyproplene, 259 polycarbonate, polyester, polyacrylic etc.). The top layer (2) of the solar 260 panel is made of a clear plastic e.g. typically polycarbonate for being 261 cheap and tough. The clear plastic layer allows the sunlight to be 262 transmitted through it. The inner sides (4) and bottom layer (3) of the 263 solar tray are blackened by paint or black anodising etc. such that it 264 acts as a black body. The solar panel can be of varying shapes i.e. 265 square, rectangular, circular etc., however, it is easier and cheaper to 266 construct it from square and rectangular shapes. Also, the size of tray 267 can varying, e.g. area of O.25m2 to 3m2 and height of 0.02m to 0.2m.

268 Typically, the solar panel of area of O.56m2 and height of 0.05m is easy 269 to move around and is used in conjunction with the heat exchanger for 270 partial water purification and heating of water. Figure 3 shows that the 271 bottom layer (3) of the solar panel which has a latch type opening (5), 272 that can be lowered down enabling for the heat exchanger (6) to be 273 inserted and or assembled into the solar panel tray. Figure 4 shows 274 that once the latch has been closed by a locking mechanism (7) and 275 top sunlight transmitting clear plastic sheet (2) is at placed at the top 276 end and the heat exchanger (6) is inserted into solar panel tray, 277 constituting a fully assembled solar panel.

279 Figure 5 shows top view of the heat exchanger, which is made of a 280 metal e.g. copper tubing of 5mm to 20mm, preferably 8mm in diameter.

281 The inlet (8) and outlet (9) tubes are spiralled in parallel to form an 282 annular shape (1 0) with a void in the centre (11). The annular shape 283 tubes are held in shape by clamps (1 2). Typically, the outer annular 284 size is 0.25m to 1 m, preferably 0.46m in diameter and inner annular 285 size is 0.1 m to 0.3m in diameter, preferably 0.1 75m. These sizes can 286 vary depending on individual needs. For example, the outer size is 287 O.46m in diameter and inner size of 0.175m in diameter and has a 288 capacity of 3 litres.

290 The clamp around the inlet and the outlet is extended to the handle (13) 291 by which the heat exchanger is inserted or taken out of the solar panel.

292 The clamps are made of copper or high conducting metal as the part of 293 heat exchanger to exhibit high energy absorbance properties such as to 294 maximise the conversation of the sunlight energy into the heat energy.

295 The handle part which stays in the solar panel can also be made of 296 copper or high conducting metal. The inlet (cold end) and outlet (hot 297 end) are separated by air or insulating material which enables the 298 handle not to get very hot. The part of handle which stays outside the 299 panel can be made of insulating materials. However, to make parts 300 cheaper it is easier for the handle to be made from one type of material 301 e.g. copper.

303 Figure 6 shows a schematic diagram of the water heating system. The 304 solar panel (1) is connected to the water tank (14) via an inlet (8) and 305 an outlet (9) of the heat exchanger (6). Both inlet and outlet connect to 306 the water tank which is made of a plastic or any cheap metal. The inlet 307 is connected to the tank at a level slightly above the base of the tank, 308 i.e. above 5mm such that the sedimentation in the water tank is not 309 passed into an inlet stream. The outlet is connected to a float (1 5) of 310 the tank. The tank is filled with water to a level (16) by removing the lid 311 (18) and adding the water from well, pond, river or even rain water. If 312 the water is dirty, murky etc., then it should be allow the particulates to 313 settle down and form sediment, henceforth the inlet is kept above 5 mm 314 so that the sediment particulates do not enter the inlet stream. The tank 315 is cleaned regularly to remove the sediment particulates. The sunlight is 316 transmitted (17) by a clear plastic and its energy is trapped in the solar 317 panel as a green house effect and is absorbed by the heat exchanger 318 made of a high conducting metal and result in heating of water in the 319 copper tubes. The blackening of the inside of solar tray results in 320 maximising the heat transfer of sunlight energy by acting as a black 321 body. As a result, the water at ambient temperature is heated to 40- 322 80°C, preferably to 50-65°C. This is dictated by the outside temperature 323 which varies from 22-50°C in most of the developing countries e.g. 324 Kenya, India etc. Figure 7 shows the water tank float mechanism. The 325 outlet pipe (9) is attached to the polystyrene (water inert low density 326 material) float (1 7) by a strap or a clamp (1 8). This enables the hot 327 water always to be discharged at the top level of the water tank. The 328 water tank can be of 50 to 100 litres capacity or less or more. The water 329 can be heated to 50-65°C within 0.5-4 hours and is dependent upon on 330 the amount of water in the tank, outside temperature and the size of 331 solar panel and the heat exchanger. The system is usually placed in a 332 horizontal position with the sunlight vertically transmitted onto the solar 333 panel for maximum absorbance. However, the panel can be tilted at an 334 angle of < 60 degree, to maximise the entrapment of the sunlight. The 335 height at which the water tank is placed can be adjusted to aid 336 flowability.

338 In absence of the sunlight (i.e. night time and cloudy conditions) the 339 heat exchanger (6) is removed from the solar panel and is placed on a 340 typical three stone cooking stove (21) used in rural developing 341 countries. The annular design of the heat exchanger allows the outer 342 part (1 0) of the heat exchanger sitting on stones or enclosure of the 343 cooking stove and the cooking pot (23) is sited or placed in the void 344 part (11) of the heat exchanger. In essence, the cooking carries on as 345 usual, and simultaneously the fire (22) generated by wood or biomass 346 fuel heats the water in the heat exchanger. The rate of flow of water is 347 controlled which determines the temperature of the heated water 348 attained. The water from the tank flows from the inlet 8 into the 349 exchanger and after being heated by the fire of the three stone cooking 350 stove in parallel to cooking flows out from the outlet 9 which can be 351 collected in a container and can be used for various purposes e.g. 352 bathing (after dilution with cold water), cooking and drinking. For a heat 353 exchanger of O.45m diameter outer annulus and 0.17mm diameter 354 inner void and the tubing of 8mm diameter has a capacity of 3 litres.

355 When there is 1 kg of wood or bio fuel burning in the stove, and the 356 water is added at 0.5kg/mm flow rate to the inlet at 20°C, the water after 357 6 minutes coming out of the outlet is between 85-1 00°C. Water at this 358 temperature has gone through rolling boil for 3 minutes and is sufficient 359 enough to be classified as partially purified and drinkable. When 360 steaming is observed from the water coming out of the outlet, it is an 361 indication of attainment of>85°C water temperature.

363 The flow rate of the heat exchanger is controlled by a simple valve (24) 364 which can be from 0.01 litres to 3 litres/mm, preferably 0.5 litres/mm, for 365 the water coming out of the outlet to reach boiling temperature. The 366 water temperature is also dependent on the status/condition of the fire, 367 in addition to the flow rate of the water to attain rolling boil i.e. > 1 368 minute and leads to partial purification of the water.

370 General advice seems to be to bring the water to a rolling boil and keep 371 it boiling for at least one minute. At higher altitudes, water boils at a 372 lower temperature and a longer period such as 3 minutes is required.

373 When water is heated for long enough to inactivate or kill micro- 374 organisms that normally live in water at room temperature. Near sea 375 level, a vigorous rolling boil for at least one minute is sufficient. At high 376 altitudes (greater than two kilometres or 5000 feet) three minutes is 377 recommended. For water obtained from ponds and rivers there are 378 micro-organisms and particulates present. Allowing this water to stand 379 in the tank for few hours will remove majority of particulates as 380 sediment, and the rolling boil will kill micro-organisms. It will partially 381 purify water and in rural developing countries it will provide means of 382 partially purified water for drinking and cooking with simple means of 383 using their existing amenities as 3 stone cooking stove without using 384 electricity or battery etc. and no added cost of fuel.

386 Water purification is the process of removing undesirable chemical and 387 biological contaminants from raw water. The goal is to produce water fit 388 for a specific purpose. Most water is purified for human consumption 389 (drinking water) but water purification may also be designed for a 390 variety of other purposes, including to meet the requirements of 391 medical, pharmacology, chemical and industrial applications. In general 392 the methods used include physical process such as filtration and 393 sedimentation, biological processes such as slow sand filters or 394 activated sludge, chemical process such as flocculation and 395 chlorination and the use of electromagnetic radiation such as ultraviolet 396 light.

398 The purification process of water may reduce the concentration of 399 particulate matter including suspended particles, parasites, bacteria, 400 algae, viruses, fungi; and a range of dissolved and particulate material 401 derived from the minerals that water may have made contacted after 402 falling as rain.

404 The standards for drinking water quality are typically set by 405 Governments or by international standards. These standards will 406 typically set minimum and maximum concentrations of contaminants for 407 the use that is to be made of the water.

408 It is not possible to tell whether water is of an appropriate quality by 409 visual examination. Simple procedures such as boiling or the use of a 410 household activated carbon filter are not sufficient for treating all the 411 possible contaminants that may be present in water from an unknown 412 source. Even natural spring water -considered safe for all practical 413 purposes in the 1800s-must now be tested before determining what 414 kind of treatment, if any, is needed. Chemical analysis, while 415 expensive, is the only way to obtain the information necessary for 416 deciding on the appropriate method of purification.

418 Henceforth, some filtration as sedimentation and rolling boil of water 419 from well, pond or river in rural communities in developing countries 420 provide a cheap way of obtaining partially purified water with no 421 additional cost except paying for solar panel containing heat exchanger 422 and a plastic tank. Currently, the cost of solar panel + tank is 423 approximately �30, which can be reduce to <30% when the product is 424 mass produced and will be affordable to majority of rural communities 425 in developing countries who encounter serious problem in obtaining 426 drinkable and heated water

428 Example 1:

430 Water heating by solar panel 431 Panel size: O.75m2 x 75mm height, made of aluminium tray coated by 432 black paint, with polycarbonate lid 433 Heat exchanger made of copper tubing of 8mm diameter, outer core = 434 0.46m, inner core=0.17m 436 Outside temperature 3OoC 437 Water heated to 65°C in 30 minutes 439 Outside temperature 45°C 440 Water temperature heated 65°C in 30 minutes

442 Example 2:

444 Heat exchanger made of copper tubing of 8mm diameter, outer core = 445 0.46m, inner core = 0.17m. Capacity 3 litres 447 3 stone cooking stove, fuel = 1 kg of wood 449 Flow rate: 1 litre/mm 450 Water heated to 85°C in attained in 3 minutes at the outlet 452 Flow rate 0.5: litre/mm 453 Water heated to 95°C in attained in 3 minutes at the outlet

455 Example 3:

457 Heat exchanger made of copper tubing of 8mm diameter, outer core = 458 0.35m, inner core = O.15m. Capacity 2 litres 460 3 stone cooking stove, fuel = 1 kg of wood 462 Flow rate: 1 litre/mm 463 Water heated to 85°C in attained in 2 minutes at the outlet 465 Flow rate 0.5: litre/mm 466 Water heated to 95°C in attained in 2 minutes at the outlet 468 1. Ref: Biomass and Bioenergy, Volume 8, Issue 6, 1995, Pages 445-469 451