Solar Water Heating Part 1&2

Solar Water Heating-Part 1 Solar water heating or solar hot water is water heated by the use of solar energy. Solar heating systems are generally composed of solar thermal collectors, a fluid system to move the heat from the collector to its point of usage. The system may use electricity for pumping the fluid, and have a reservoir or tank for heat storage and subsequent use. The systems may be used to heat water for a wide variety of uses, including home, business and industrial uses. Heating swimming pools, underfloor heating or energy input for space heating or cooling are more specific examples. In many climates, a solar hot water system can provide up to 85% of domestic hot water energy.[1] This can include domestic non-electric concentrating solar thermal systems. In many northern European countries, combined hot water and space heating systems (solar combisystems) are used to provide 15 to 25% of home heating energy. Residential solar thermal installations can be subdivided into two kinds of systems: passive (sometimes called "compact") and active (sometimes called "pumped") systems. Both typically include an auxiliary energy source (electric heating element or connection to a gas or fuel oil central heating system) that is activated when the water in the tank falls below a minimum temperature setting such as 50°C. Hence, hot water is always available. The combination of solar water heating and using the back-up heat from a: wood stove chimney to heat water or heat source; can enable a hot water system to work all year round in cooler climates, without the supplemental heat requirement of a solar water heating system being met with fossil fuels or electricity. In order to heat water using solar energy, a collector is fastened to the roof of a building, or on a wall facing the sun. In some cases, the collector may be free-standing. The working fluid is either pumped (active system) or driven by natural convection (passive system) through it. The water from the collector can reach very high temperatures in good sunshine, or if the pump fails. Designs should allow for relief of pressure and excess heat through a heat dump. Economics, energy, environment, and system costs The typical 50 gallon electric water heater uses 11.1 barrels of oil a year, wich translates into the same amount oil used by a typical 4 door sedan driven by the average consumer. Electric utility companies often provide electricity by burning and releasing energy from fuels such as oil, coal and nuclear energy. An electrical home hot water heater sits on an electrical grid and may be driving the use of unclean fuels on the other end of the grid. Solar water heating systems can significantly reduce such electricity consumption. In sunny, warm locations, where freeze protection is not necessary, a batch type solar water heater can be extremely cost effective. In higher latitudes, there are often additional design requirements for cold weather, which add to system complexity. This has the effect of increasing the initial cost (but not the life-cycle cost) of a solar water heating system, to a level much higher than a comparable hot water heater of the conventional type. When calculating the total cost to own and operate, a proper analysis will consider that solar energy is free, thus greatly reducing the operating costs, whereas other energy sources, such as gas and electricity, can be quite expensive over time. Thus, when the initial costs of a solar system are properly financed and compared with energy costs, then in many cases the total monthly cost of solar heat can be less than other more conventional types of hot water heaters (and also in conjunction with an existing hot water heater). At higher latitudes, solar heaters may be less effective due to lower solar energy, possibly requiring dual-heating systems. In addition, federal and local incentives can be significant. As an example, a 56 ft.2 solar water heater can cost US $7,500- but that initial cost is reduced to just $3,300 in the US State of Oregon due to federal and state incentives. The system will save approximately US $230 per year, with a payback of 14 years. Lower payback periods are possible based on maximizing sun exposure.[16] As energy prices rise, payback periods decrease. In cooler locations, solar heating used to be less efficient. Usable amounts of domestic hot water were only available in the summer months, on cloudless days, between April and October. During the winter and on cloudy days, the output was poor. Independent surveys have shown that modern systems do not suffer these limitations.[17] There are cases of households in cool climates getting all of their domestic hot water year round from solar alone.[18] Systems have been shown to efficiently work as far north as Whitehorse, Yukon (latitude of 60 B 43' N ).[19] The collector could be made of a simple glass topped insulated box with a flat solar absorber made of sheet metal attached to copper pipes and painted black, or a set of metal tubes surrounded by an evacuated (near vacuum) glass cylinder. In some cases, before the solar energy is absorbed, a parabolic mirror is used to concentrate sunlight on the tube. A simple water heating system would pump cold water out to a collector to be heated, the heated water flows back to a collection tank. This type of collector can provide enough hot water for an entire family. Heat is stored in a hot water tank. The volume of this tank will be larger with solar heating systems in order to allow for bad weather, and because the optimum final temperature for the absorber is lower than a typical immersion or combustion heater. The working fluid for the absorber may be the hot water from the tank, but more commonly (at least in active systems) is a separate loop of fluid containing anti-freeze and a corrosion inhibitor which delivers heat to the tank through a heat exchanger (commonly a coil of copper tubing within the tank). Another lower-maintenance concept is the 'drain-back': no anti-freeze is required; instead all the piping is sloped to cause water to drain back to the tank. The tank is not pressurized and is open to atmospheric pressure. As soon as the pump shuts off, flow reverses and the pipes empty by the time when freezing could occur. When a solar water heating and hot-water central heating system are used in conjunction, solar heat will either be concentrated in a pre-heating tank that feeds into the tank heated by the central heating, or the solar heat exchanger will be lower in the tank than the hotter one. However, the main need for central heating is at night when there is no sunlight and in winter when solar gain is lower. Therefore, solar water heating for washing and bathing is often a better application than central heating because supply and demand are better matched. The water from the collector can reach very high temperatures in good sunshine, or if the pump fails. Designs should allow for relief of pressure and excess heat through a heat dump. The typical 50 gallon electric water heater uses 11.1 barrels of oil a year, which translates into the same amount oil used by a typical 4 door sedan driven by the average consumer. Electric utility companies often provide electricity by burning and releasing energy from fuels such as oil, coal and nuclear energy. An electrical home hot water heater sits on an electrical grid and may be driving the use of unclean fuels on the other end of the grid. Solar water heating systems can significantly reduce such electricity consumption. In sunny, warm locations, where freeze protection is not necessary, a batch type solar water heater can be extremely cost effective. In higher latitudes, there are often additional design requirements for cold weather, which add to system complexity. This has the effect of increasing the initial cost (but not the life-cycle cost/ [/scotty comments: The Addition of a Solar Power Water Heater to your electric or gas Water Heater Should Prolong the Life since it won't get used as much!!!) of a solar water heating system, to a level much higher than a comparable hot water heater of the conventional type. When calculating the total cost to own and operate, a proper analysis will consider that solar energy is free, thus greatly reducing the operating costs, whereas other energy sources, such as gas and electricity, can be quite expensive over time. Thus, when the initial costs of a solar system are properly financed and compared with energy costs, then in many cases the total monthly cost of solar heat can be less than other more conventional types of hot water heaters (and also in conjunction with an existing hot water heater). . Part 2 Will Post Saturday Part 2, Sat 11/7/2009 Part 2 The installation costs in the UK used to be prohibitive, on average about £9,000. This is reduced in more recent years to £3,000, with payback period reduced, with the rise in the gas price, to 12 years [20]. As energy prices rise, payback periods shorten accordingly. According to ANRE (a Flemish energy agency, subsidised by the Flemish or Belgian government,[21] a complete, commercial (active) solar water heating system composed of a solar collector (3-4 m²; this is large enough for 4 people), pipes and tank (again large enough for 4 people) costs around 4000 euro. The installation by a recognised worker costs another 800 euro.[22] Electrabel's home magazine Eandismagazine stated in 2008 that a complete system (including 4m2 of solar collectors and a supply barrel of 200-240 liters) to cost 4500 euro. [23] The system would then pay back itself in 11 years , when the returns are weighed off against a regular electric boiler. Calculation was as follows: a saving of 1875 kWh (which is 50% of the energy requirements in domestic hot water production) x 0.10 euro/kWh = 187, 5 euros. This multiplied by 11.6 years made 2175 euros (or the cost of the system with deducted regional tax benefits). Solar leasing is now available in Spain for solar water heating systems from Pretasol [24] with a typical system costing around 59 euros and rising to 99 euros per month for a system that would provide sufficient hot water for a typical family home of six persons. The payback period would be five years. In Australia, the cost for an average solar water heating system fully installed is between $1,800 and $2,800. This is after tax rebates (there is a federal rebate,[25] some state rebates and Renewable Energy Certificates[26]). According to the Department of Environment and Water Resources[27], the yearly electricity savings are between $300 and $700. This brings the payback period to under 2 years in the best case and under 10 years in the worst case. Easy Being Green has a program available where consumers can acquire a system for free (with government rebates) excluding the cost of installation. [edit] Types This classification is in need of attention from an expert on the subject. WikiProject Technology or the Technology Portal may be able to help recruit one. (September 2009) A monobloc solar heater in Cirque de Mafate, La Réunion There are two main categories of solar water heating systems, active systems which require a pump and passive systems which rely on convection or heatpipes. In addition, there are a number of other system characteristics that distinguish different designs: The type of collector used (see below) The location of the collector - roof mount, ground mount, wall mount[28] The location of the storage tank in relation to the collector The method of heat transfer - open-loop or closed-loop (via heat exchanger) Photovoltaic thermal hybrid solar collectors can be designed to produce both hot water and electricity. [edit] Passive systems A passive system also known as a compact system or monobloc has a tank for the heated water and a solar collector mounted on the same chassis. Typically these systems will function by natural convection (thermosiphon) or heatpipes to transfer the heat energy from the collector to the tank. It is usually based on the architectural design in order to heat up any building. [29] A integrated collector storage system A special type of passive system is the Integrated Collector Storage (ICS or Batch Heater) where the tank acts as both storage and solar collector. Batch heaters are basically thin rectilinear tanks with glass in front of it generally in or on house wall or roof. They are seldom pressurised and usually depend on gravity flow to deliver their water. They are simple, efficient and less costly than intense plate and tube collectors but only suitable in moderate climates with good sunshine. [30][31] A step up from the ICS is the Convection Heat Storage Unit. These are plate type intense collectors with built-in insulated tanks. The unit uses convection (movement of hot water upward) to move the water from heater to tank. Neither pumps or electricity are used. It is more efficient than an ICS as the intense collector heats a small(er) amount of water that is constantly rising to the tank. It can be used in areas with less sunshine than the ICS. A passive open loop system A thermosiphon solar hybrid system Direct ('open loop') passive systems, if made of metals are not suitable for cold climates. At night the remaining water can freeze and damage the panels, and the storage tank is exposed to the outdoor temperatures that will cause excessive heat losses on cold days. Some passive systems have a primary circuit. The primary circuit includes the collectors and the external part of the tank. Instead of water, a non-toxic antifreeze is used. When this liquid is heated up, it flows to the external part of the tank and transfers the heat to the water placed inside. ('closed loop'). Open loop (direct) systems have the disadvantage that during the night-time, where the temperature of the solar panel starts to drop below that of the water tank, the system starts working in reverse heating the water in the panel and cooling the water inside the tank. This problem is least noticeable in closed loop system using a heat exchanger as only the water in the heat exchanger and not the whole tank is affected by it. Zhuhai Tianke Energy Saving Equipment Manufacture Co., Ltd. managed to solve this problem using a patented design in their solar water heating systems heat exchanger which forces the flow of the water in the heat exchangers inlet pipe in an upward flow, thus restricting cold water flowing down to the panel.The force of the flow is made through a driver inside the heat exchanger (jacket). The jacket and the driver part is made of the same heat conducting material therefore sharing the same temperature on same levels of the heat exchanger. A passive system can save up to 4.5 tonnes annually of greenhouse gas emissions. In order to achieve the aims of the Kyoto Protocol, several countries are offering subsidies to the end user. Some systems can work for up to 25 years with minimum maintenance. These kinds of systems can be redeemed in six years, and achieve a positive balance of energy (energy they save minus energy used to build them) of 1.5 years. Most part of the year, when the electric heating element is not working, these systems do not use any external source for power (as water flows due to thermosiphon principle). Flat solar thermal collectors are usually used, but passive systems using vacuum tube collectors are available on the market. These generally give a higher heat yield per square meter in colder climates but cost more than flat plate collector systems. [edit] Active systems Schematic of an passive solar heating system Schematic of an active solar heating system Active solar hot water systems employ a pump to circulate the water or heat transfer fluid and a controller to turn the pump on and off depending on the temperature of the tank and collectors. Active systems are usually significantly more efficient that passive systems but are more complex, more expensive, more difficult to install and rely on electricity to run the pump and controller. During active heating, solar energy is stored, collected, and distributed in buildings, providing hot water or space heating. When sunlight falls on a building's collector, it is transformed into heat and conveyed into a carrier fluid. It is then pumped into a conversion, later into a storage, and finally into the distribution system. [32] Newer electronic controllers permit a wide range of functionality such as measurement of the energy produced; more sophisticated safety functions; thermostatic and time-clock control of auxiliary heat, hot water circulation loops, or others; display or transfer of error messages or alarms; remote display panels; and remote or local datalogging. The most commonly used solar collector is the insulated glazed flat panel. Less expensive panels, like polypropylene panels (for swimming pools) or higher-performing ones like evacuated tube collectors, are sometimes used. [edit] Differential controller operated system Schematic of an active solar heating system with a differential controller The direct active system, has one or more solar energy collectors installed on the roof and a storage tank somewhere below, usually in a garage or utility room. A pump circulates the water from the tank up to the collector and back again. This is called a direct (or open loop) system because the sun's heat is transferred directly to the potable water circulating through the collector tubing and storage tank; no anti-freeze solution or heat exchanger is involved. This system has a differential controller that senses temperature differences between water leaving the solar collector and the coldest water in the storage tank. When the water in the collector is about 15-20°F warmer than the water in the tank, the pump is turned on by the controller. When the temperature difference drops to about 3-5°F, the pump is turned off. In this way, the water always gains heat from the collector when the pump operates. A flush-type freeze protection valve installed near the collector provides freeze protection. Whenever temperatures approach freezing, the valve opens to let warm water flow through the collector. The collector should also allow for manual draining by closing the isolation valves (located above the storage tank) and opening the drain valves. Automatic recirculation is another means of freeze protection. When the water in the collector reaches a temperature near freezing, the controller turns the pump on for a few minutes to warm the collector with water from the tank. Photovoltaic operated system The photovoltaic system , differs from other direct active systems in that the energy to power the pump is provided by a photovoltaic (PV) panel. The PV panel converts sunlight into electricity, which in turn drives the direct current (dc) pump. In this way, water flows through the collector only when the sun is shining. The DC-pump and PV panel must be suitably matched to ensure proper performance. The pump starts when there is sufficient solar radiation available to heat the solar collector. It shuts off later in the day when the available solar energy diminishes. As in the previous systems, a thermally operated valve provides freeze protection. The main advantage of this system is that hot water is always available during a power outage. The pump is operated by the sun and is completely independent from the FPL utility. [edit] Active System Operational Carbon Footprint The source of electricity in an active system determines the extent to which a system contributes to atmospheric carbon during operation. The type of active solar thermal systems[33] which use mains electricity to pump the fluid through the panels are called low carbon solar because the pumping negates the carbon savings of the solar by about 20%, according to data in a report called "Side by side testing of eight solar water heatings" by DTI UK. However, zero-carbon active solar thermal systems typically use a 5-20W PV panel which faces in the same direction as the main solar heating panel and a small, low power diaphragm pump or centrifugal pump to circulate the water. This represents a zero operational carbon footprint and is becoming an important design goal for innovative solar thermal systems. [edit] Types of thermal collector It has been suggested that this article or section be merged into Solar thermal collector. (Discuss) There are three main kinds of solar thermal collectors in common use. In order of increasing cost they are: Formed Plastic Collectors, Flat Collectors, and Evacuated Tube Collectors. The efficiency of the system is directly related to heat losses from the collector surface (efficiency being defined as the proportion of heating energy that can be usefully obtained from insulation). Heat losses are predominantly governed by the thermal gradient between the temperature of the collector surface and the ambient temperature. Efficiency decreases when either the ambient temperature falls or as the collector temperature increases. This decrease in efficiency can be mitigated by increasing the insulation of the unit by sealing the unit in glass e.g. flat collectors or providing a vacuum seal e.g. evacuated tube collector. The choice of collector is determined by the heating requirements and environmental conditions in which it is employed.[34][35][36] [37][38] [edit] Formed plastic collector Formed plastic collectors (such as polypropylene, EPDM or PET plastics) consist of tubes or formed panels through which water is circulated and heated by the sun's radiation. These are often used for extending the swimming season in swimming pools. In some countries, heating an open-air swimming pool with non-renewable energy sources is not allowed, and then these inexpensive systems offer a good solution. This panel is not suitable for year-round uses like providing hot water for home use, primarily due to its lack of insulation which reduces its effectiveness greatly when the ambient air temperature is lower than the temperature of the fluid being heated. [edit] Flat plate collector A flat plate collector A flat plate collector consists of a thin absorber sheet (of thermally stable polymers, aluminum, steel or copper, to which a black or selective coating is applied) backed by a grid or coil of fluid tubing and placed in an insulated casing with a glass or polycarbonate cover. Fluid is circulated, using either mains or solar electricity, through the tubing to remove the heat from the absorber and to transport it to an insulated water tank, sometimes directly or otherwise to a heat exchanger or to some other device for using the heated fluid. Some fabricants have a completely flooded absorber consisting of 2 sheets of metal stamped to produce a circulation zone. Because the heat exchange area is greater they may be marginally more efficient than traditional absorbers.[39] As an alternative to metal collectors, new polymer flat plate collectors are now being produced in Europe. These may be wholly polymer, or they may be metal plates behind which are freeze-tolerant water channels made of silicone rubber instead of metal. Polymers, being flexible and therefore freeze-tolerant, are able to contain plain water instead of antifreeze, so that in some cases they are able to plumb directly into existing water tanks instead of needing the tank to be replaced with one using heat exchangers. By dispensing with a heat exchanger in these flat plate panel, temperatures need not be quite so high for the circulation system to be switched on, so such direct circulation panels, whether polymer or otherwise, can be somewhat more efficient, particularly at low light levels. As with evacuated tubes, most flat plate collectors have a life expectancy of over 25 years. [edit] Evacuated tube collector Evacuated (or vacuum) tubes panel. Evacuated tube collectors are made of a series of modular tubes, mounted in parallel, whose number can be added to or reduced as hot water delivery needs change. This type of collector consists of rows of parallel transparent glass tubes, each of which contains an absorber tube (in place of the absorber plate to which metal tubes are attached in a flat-plate collector). In some cases, the tubes are covered with a special light-modulating coating. In an evacuated tube collector, sunlight passing through an outer glass tube heats the absorber tube contained within it. The absorber can either consist of copper (glass-metal) or specially-coated glass tubing (glass-glass). The glass-metal evacuated tubes are typically sealed at the manifold end, and the absorber is actually sealed in the vacuum, thus the fact that the absorber and heat pipe are dissimilar metals creates no corrosion problems. Some systems use foam insulation in the manifold. Soda-lime glass is used in the higher quality evacuated tubes manufacture. Later technology evacuated tube systems use the glass coated absorber. The glass is a boron silicate material and the aluminum absorber and copper heat pipe are slid down inside the open top end of the tube. In lower quality systems moisture can enter the manifold around the sheet metal casing is eventually absorbed by the glass fibre insulation and then finds its way down into the tubes. This leads to corrosion at the absorber/heat pipe interface area, also freeze ruptures of the tube itself if the tube fills sufficiently with water. Two types of tube collectors are distinguished by their heat transfer method: the simplest pumps a heat transfer fluid (water or antifreeze) through a U-shaped copper tube placed in each of the glass collector tubes. The second type uses a sealed heat pipe that contains a liquid that vapourises as it is heated. The vapour rises to a heat-transfer bulb that is positioned outside the collector tube in a pipe through which a second heat transfer liquid (the water or antifreeze) is pumped. For both types, the heated liquid then circulates through a heat exchanger and gives off its heat to water that is stored in a storage tank (which itself may be kept warm partially by sunlight). Evacuated tube collectors heat to higher temperatures, with some models providing considerably more solar yield per square metre than flat panels. However, they are more expensive than flat panels, but generally of a less cost to repair in the event of damage. Evacuated heat tubes perform better than flat plate collectors in cold climates because they only rely on the light they receive and not the outside temperature.[40] The high stagnation temperatures can cause antifreeze to break down, so careful consideration must be used if selecting this type of system in temperate climates.Tubes come in different levels of quality so the different kinds have to be examined as well. High quality units can efficiently absorb diffuse solar radiation present in cloudy conditions and are unaffected by wind. They also have the same performance in similar light conditions summer and winter.[41] For a given absorber area, evacuated tubes can maintain their efficiency over a wide range of ambient temperatures and heating requirements. The absorber area only occupied about 50% of the collector panel on early designs, however this has changed as the technology has advanced to maximize the absorption area. In extremely hot climates, flat-plate collectors will generally be a more cost-effective solution than evacuated tubes. When employed in arrays of 20 to 30 or more, the efficient but costly evacuated tube collectors have net benefit in winter and also give real advantage in the summer months. They are well suited to extremely cold ambient temperatures and work well in situations of consistently low-light. [edit] Solar thermal cooling Main article: Solar thermal cooling Solar thermal cooling can be achieved via absorption refrigeration cycles, desiccant cycles and solar-mechanical processes.[42] The absorption cycle solar cooling system works like a refrigerator in that it uses hot water to compress a gas that, once expanded, will absorb energy, which cools the air. The main problem currently is that the absorber machine works with liquid at 90 °C, a fairly high temperature to be reached with pumped solar panels with no auxiliary power supply.[citation needed] The same active solar thermal installation can be used for producing hot water for the whole year. The auxiliary electric heater is for thermal energy storage in the nighttime, while the solar energy collection is used in the daytime as well as dry cooling. [43] Part 3 Will post soon