It has many applications in the developing world where electricity supply networks are either unavailable or unreliable. Solar-powered submersible pump systems have been successfully used in both village and commercial projects for decades. They provide clean and renewable source of drinking water, solar electricity (secondary use), solar heating (district heating/hot water) and solar desalination (seawater).
Solar-powered well pumps
Solar-powered well pumps are increasingly popular in developing countries because they run off solar power so there is no need for batteries or power cords. These solar-powered wells can be placed anywhere that gets enough sunlight to charge the solar panel.
In solar-powered water pumping, solar panels charge a battery(ies), which in turn power the submersible pumps or rotate the turbine for water displacement. This saves on fuel and operating costs compared to solar-powered well pumps. The solar array can provide electricity for other uses such as lighting after dark, powering refrigerators or televisions, charging batteries, etc. Essentially the solar array is used both day and night. An inverter may be needed if household appliances are run from solar electricity during daylight hours (generally cloudy days).
Solar-powered borehole pump systems
Solar-powered borehole pump systems have many of the same components as solar water pumping except that they circulate groundwater rather than surface water – typically used in developing countries with access to remote water supplies. Many solar-powered borehole pump systems can be used in solar water pumping applications as well.
Solar-powered pumps for agricultural uses
Solar-powered pumps for agricultural uses are designed to pump low and medium heads of water (moderate lift) for irrigation purposes. These solar-powered systems are cost-effective, environmentally friendly, and electricity-free sources of energy with no running costs once installed. Systems that include solar-powered submersible pumps or solar-powered centrifugal pumps deliver pressurized irrigation water directly to the root zone of crops by solar power from solar panels. Pressurized irrigation is used around plants close to the ground surface level where the minimum amount of sunlight is available during daytime or cloudy days in rural areas due to high-rise buildings, trees, etc., where solar panels are not visible.
Solar-powered solar energy systems used for irrigation purposes are particularly beneficial where high-quality water is required for agricultural use. Irrigation pump solar power technology is particularly useful in remote, rural, and urban areas, with solar-powered batteries or solar generators which provide up to 24 hours of uninterrupted solar-powered water pumping on cloudy days as well as throughout the night; an especially important benefit in areas without reliable access to electricity (off-grid).
Solar heating systems & Solar water pumping
Solar heating systems use solar thermal collectors, storage, and distribution equipment to deliver hot water or space heating from solar energy. A solar collector directs sunlight into a centrally located heat exchanger that is connected to conventional radiators/water-based solar heater panels or a similar form of a localized heating system such as radiant flooring or solar air heating.
In solar water pumping using solar thermal technology, a solar hot water collector is positioned on the roof, and the solar-heated water is distributed via a network of insulated pipes to domestic hot-water storage tanks inside individual buildings or in solar district heating installations (see solar ground source heat pumps). A related system called “concentrated solar power” uses a large field of mirrors pointed at a central solar energy tower to generate high temperatures for industrial processes that require extremely high temperatures. These systems are highly variable depending on location and seasons, and they are used mainly in areas where there is an abundant supply of sunlight throughout most of the year such as in deserts.
Rainwater harvesting system & Solar Water Pumping
A rainwater harvesting system usually has three main elements: collection, storage and use. The solar-powered water pump is primarily used to move rainwater from an underground collection system or natural sources such as rivers, lakes, or reservoirs into a storage tank for later use in irrigation, toilets, or other uses. This prevents the rainwater from becoming contaminated by pollutants that may be present on roof surfaces; rainwater collected directly off roofs is not recommended for drinking purposes because it can become contaminated by chemicals coming from rooftops and gutters. Rainwater harvesting systems are also known as “catchment” systems, especially in Australia where they are widely used for urban water supplies. A solar power system may be used to assist in moving the harvested water into storage tanks.
Solar-powered pumps most commonly used in solar pumping applications include solar pumps in solar water pumping solar energy systems and solar-powered solar heaters.
Solar thermal collectors and solar water pumping
Solar heating systems, also known as solar thermal collectors or solar thermal collectors, are commonly used for domestic hot-water supply under passive solar building design incorporating a cold roof or “solar attic.” A network of insulated pipes is connected to the solar panels which collect heat from sunlight and transfer the heat to water during the summer months. Solar air heating is very effective in colder climates where temperatures drop below the freezing point during the winter months. In these installations, an air collector heats up by absorbing heat from ambient air using a glazed panel that is exposed to direct sunlight.
A solar district heating system provides centralized climate control in multi-dwelling buildings (apartments, nursing homes, schools, hospitals), district parks and gardens (e.g., solar greenhouses), solar power plants as well as industrial processes such as solar thermal energy in solar power generation. Solar multi-family housing is particularly beneficial because solar heat can be used to provide space heating for a large number of buildings at once. The systems are highly variable depending on location and seasons, and they are used mainly in areas where there is an abundant supply of sunlight throughout most of the year such as in deserts.
A solar water pumping system uses PV panels or solar thermal collectors to collect and transfer solar energy to the water source from which it will be pumped out. This process requires a pump that runs off-grid electricity or solar-powered batteries attached to the solar energy system. If solar and battery power are used to pump water, solar-powered batteries need to be charged during daylight hours so that they can recharge at night.
Solar solar-powered water pumping systems are widely used in remote areas with fresh groundwater or rainwater as their primary sources of drinking water supply. As a standalone solar collector, solar pumps can be used to move groundwater from boreholes equipped with solar-powered downhole pumps (submersible) into storage tanks or elevated reservoirs. Standalone solar pumping systems are also commonly used in combination with solar thermal collectors for domestic hot-water supply under passive solar building design incorporating a cold roof (“solar attic”). The usage of both types of installations is optimized by locating them on the same solar collector array.
A solar thermal energy system (STS) is a solar heating installation that utilizes solar-thermal technology to provide space and water heating, ventilation, and hot water supply for residential and commercial buildings. A solar thermal system comprises solar collectors, heat transfer fluids, a solar distribution network, solar storage tanks, and an optional backup heater or boiler. In a combined solar/conventional heating system the circulation of heated solar air or water permits the use of solar collectors with much greater temperature differences than in a standalone solar-only installation. Solar thermal collectors are typically mounted on the rooftops of buildings just like traditional roofing materials such as tiles or shingles. However, they can also be mounted in walls facing areas where heat accumulation would make solar thermal systems advantageous for space heating purposes.
Solar thermal energy systems can be categorized into solar air collectors and solar water/fluid collectors: solar air collectors heat up fresh or ambient air that is then used by the building to heat its spaces via a network of ducts (forced convection solar system) whereas solar water/fluid collectors directly heat water or tap fluids which are then used for indoor hot-water supply, ventilation and space heating (passive solar system).
In a solar thermal installation, two types of solar thermal collectors can be distinguished based on their medium of heat transfer: the evacuated tube collector in which vacuum insulation tubes are used as absorbers and fluidized bed collector in which porous media such as sand or gravel particles are heated by solar radiation and undergo convection.
Solar thermal energy systems may be integrated with gas, pellet, or wood-fired boilers to cover peak heat periods in cold winters (i.e. solar-boiler system) where solar heating alone is not sufficient for covering the entire space heating demand. A solar/conventional solar/heat pump hybrid solar system combines solar collectors with a conventional heat pump water heater that employs the low-temperature output of a solar collector for preheating incoming hot water before passing it on to an auxiliary electric resistance heater which raises its temperature level to required delivery standards due to its higher efficiency at higher temperatures than solar panels can achieve under natural insolation conditions. This type of system provides additional savings compared to a solar water heating system alone.
Solar Domestic Hot-water generation & Solar Water Pumping
Solar energy systems can be employed for solar domestic hot-water generation (SDHW) or solar space heating either to satisfy all of the solar demand in a building or as an additional solar resource at times when solar insolation conditions are suitable and electricity is expensive. In most cases, solar thermal collectors are installed on roofs above living spaces where they can collect solar radiation coming from above. However solar thermal collectors can also be mounted in walls that face towards areas where heat accumulation could make solar thermal systems advantageous for space heating purposes.
Hybrid solar/natural circulation SDHW systems employ the use of a natural convection circuit to circulate domestic hot water between storage tanks at different temperatures (warm tank and cold tank). Thermal solar energy systems can also be used for solar pool heating in order to reduce the solar fraction (i.e. solar collector area relative to swimming pool surface) by employing a solar thermal collector with a relatively small absorber and large solar collector circulation tank.
Solar thermal collectors are made of heat-resistant low emissivity glass or plastic sheets covered by vacuum insulation that prevents the solar radiation from being absorbed by the material inside, keeping it at high temperatures even when partly covered by snow outside (snow covering losses are less than 5%). The vacuum insulation also prevents air from entering into the tubes and causing overheating that could damage them. Vacuum insulation allows more solar radiation to enter into evacuated tube collectors which allows their total efficiency to be increased by maintaining solar tube temperature above 55C compared to conventional solar water heating collectors that reach solar efficiencies of around 0.75-0.85 when solar insolation is at its peak in summer; which decreases with decreasing solar insolation, reaching as low as 0.35 in winter.
Solar radiative solar collector tubes are filled with either air or a working fluid (i.e. closed circuit solar collectors) such as antifreeze solutions (glycol/water mixtures), water, organic liquids, and even oil that absorbs solar radiation more efficiently than water does. The insulation around the solar collector tubes prevents heat dissipation from the hot side to the cool side of the absorber. Heat transfer between these two sides is carried out by convection to a solar collector heat transfer fluid (water, air, or working fluid) that transfers solar thermal energy collected by the solar collectors to either a storage tank for domestic hot water supply (preheated solar water heating systems) or directly to buildings that use solar thermal energy for space heating purposes.
Solar thermal collectors require specific orientation so as to face the sun’s path during summer and maximize solar insolation. The best orientation of solar collectors is based on existing geographical conditions such as latitude, height above ground level, building structure obstructions, and roof inclination angle which can be optimized using computer-aided models for each case. However solar direct gain windows can be installed at any suitable orientation (i.e. not necessarily facing south) where solar thermal collectors are not available on the roof (i.e. solar energy can be used as solar radiation passing through windows).
Due to their higher operating temperatures solar water heater collectors have been called solar hot-water generation (SDHW) solar water heaters or solar space heating when located in a building’s walls facing areas of potential solar thermal accumulation (thermal mass). Solar collector efficiency is expressed as the quantity of solar thermal energy transferred from solar collectors to domestic hot-water at its outlet per hour, day, or year and also as part of a solar fraction that gives an idea about the amount of surface area dedicated for sun capture relative to total pool surface area. Passive, semi-passive, and types of solar thermal solar collectors are described below.
Solar active solar water heater collector (PV/T, solar pool heating) systems use solar energy for solar steam generation and are therefore solar-heated domestic hot water (DHW) solar water heaters. In the way, they work these types of solar thermal energy systems may be compared to large conventional gas or electric boilers that also produce high temperatures by passing a fluid through a boiler heat exchanger with an additional step: solar-powered pumps circulate the working fluid inside either evacuated tubes or pipes made of metal. Solar heating can be continuous as in swimming pools where solar collectors transfer heat collected during summer to storage tanks and then supply it as needed while maintaining a temperature above 55C throughout the year, or solar solar solar storage solar water solar systems can be cyclic with solar heating taking place only when solar insolation is higher than a pre-set threshold value (i.e. winter season). Solar heat transfer fluid circulation and flow rate are adjusted to maintain high temperatures in winter or low temperatures in summer respectively.
Solar energy for thermal generation is supplied by solar power through the use of silicon photo-voltaic cells installed on collector roofs or walls that convert sunlight into electricity (see also: solar power ) sometimes augmented with wind turbine technology (see also: wind power plant ).
Solar pool heating applications include swimming pools, fish-rearing ponds, hot tubs commercial and industrial buildings’ process water supply as solar water heaters and space heating systems.
Solar thermal energy conversion (i.e. from sunlight into thermal energy) is a physical process that takes place in three steps:
1. Solar radiation passes through the transparent cover and vacuum glass of a closed evacuated tensile structure or pipe made of metal;
2. The fluid absorbs the incoming radiation, heats up, expands its volume, and fills the voids between molecules with vapor bubbles thus increasing its specific volume;
3. Collection assembly components (evacuated tubes/pipes, pressure vessel, or an attached hot water storage tank) are heated by this “hotter” liquid because it has less specific volume than the solar radiation absorbing initially cold fluid.
Solar water heaters attached to swimming pools
Solar water heaters attached to swimming pools are called active and use either evacuated tube collectors or flat plate (i.e. type of) collectors. Flat-plate collectors consist of a metal absorber plate painted black on the top surface, polished on the bottom side with transparent cover glass to allow sunlight to reach the bottom absorber as well as a vacuum insulation envelope that creates a leak-free tight vapor barrier between inner and outer layers of this sandwich structure. Evacuated-tube or pipe collectors work in similar ways except that there is no inner layer; instead, the pressure inside pipes is slightly above the outside atmospheric pressure so that solar radiation heated fluid can freely circulate through pipes.
Solar funnel collectors or Archimedean screws are commonly used for small-scale applications such as residential swimming pools in Mediterranean countries (see also: passive water heating ).
Solar collector array mounting systems may be fixed or movable, with a single axis being the most often utilized option to adjust southern exposure according to seasonal changes in the sun’s apparent path at different times of the year. Solar hot water storage tanks vary in shapes and sizes depending on their application: large volume capacities are required by industrial plants to store heat; medium volumes are suitable for space heating systems; low volumes are usually designed into commercial buildings’ central air conditioning systems solar solar solar solar solar solar solar solar solar solar solar solar solar water heaters.
Solar thermal-powered systems are used with conventional air-conditioning for cooling during summer because they are able to directly supply the space heating system too. This approach is called “dual-use” and involves simultaneous or sequential use of a single energy storage/circulation medium in both heating and cooling seasons. When using evacuated tube collectors, dual-use means that the same vacuum insulation layer is also used to insulate hot water pipes against outside cold temperatures thus avoiding the need for installing another costly layer of protection against freezing. Energy losses due to heat conduction through solid materials can be avoided by isolating vacuum glass from metal absorber plates (or from each other) with vacuum-insulating adhesive (like RTV or similar products).
Solar water heaters are used in conventional centralized fossil fuel-powered systems to preheat hot domestic water and swimming pool water. A special device called a “desuperheater” is installed outside the building on its roof; it uses an additional collector next to the usual hot water storage tank and exchanges heat between them when this is needed. Desuperheating economizers may not be able to achieve 100% thermal efficiency for two reasons: they have larger heat loss rates than absorption chillers, because of higher thermal conductivity of air that must first be warmed up before being heated by collectors; also, solar solar solar solar solar solar solar solar solar solar solar solar solar water collectors usually operate at lower temperatures than absorption chillers, typically 100 °C to 130 °C (212 °F to 266 °F), therefore requiring less heat exchange.
Solar water heaters can be used independently of the conventional systems mentioned above for space heating and cooling applications. This approach is called “off-grid” because there is no connection to the main public utility grid – a system that represents approximately 20% of US households as well as a number of housing developments in other countries. These off-grid systems make it possible to provide almost all necessary thermal energy by using only renewable but non-dispatchable power sources: sunshine and wind. Systems for solar solar solar solar solar solar solar solar solar solar solar solar solar water heating can be used also by camps, settlements, and other isolated areas where installation of conventional power lines is expensive or not feasible at all. For such applications either photovoltaic panels (for direct conversion of sunlight into electricity) or small renewable-power plants using microturbines as well as generators running on biofuels (like biodiesel ) are most often used.
Solar thermal collectors are passively heated; there are no mechanical moving parts involved in their operation: they use only the energy of solar radiation to collect heat from the sun and transfer it to the fluid inside collection tubing without pump assistance. Consequently, these systems have been called “passive” solar solar solar solar solar solar solar solar solar solar solar solar solar water heaters, but they lose much of their performance in cold climates unless backed up with auxiliary heating devices like gas or wood stoves. (see also bottom of this page for additional information on “active” systems).
Solar thermal energy is considered a renewable form of energy because it can be harnessed without consuming the stored human power plant fuel that is non-replenished by natural processes and continually being depleted. However, if fossil fuels are used to manufacture collectors and the same approach is followed as with conventional electric-powered pumps, then indeed all environmental costs associated with such extraction will not be avoided: climate change caused by fossil carbon dioxide emissions remains a serious problem.
A more environmentally friendly solar water heating system is one that uses direct solar radiation and does not use fossil fuels to manufacture collectors, heat storage tanks, or other related equipment. This concept is called “solar thermal energy”, and when it comes to residential applications it is being used as an alternative for conventional electric-powered systems in conjunction with passive solar house designs.