PV is best suited for remote site applications that have small to moderate power requirements, or small power consuming applications even where the grid is in existence. A few power companies are also promoting limited grid-connected PV systems, but the large market for this technology is for stand-alone (off-grid) applications. Some common PV applications are as follows:
Water Pumping. Pumping water is one of the most competitive arenas for PV power since it is simple, reliable, and requires almost no maintenance. Agricultural watering needs are usually greatest during sunnier periods when more water can be pumped with a solar system. PV-powered pumping systems are excellent for small to medium scale pumping needs (e.g., livestock tanks) and rarely exceed applications requiring more than a 2 hp motor.
There are thousands of agricultural PV water pumping systems in the field today throughout Texas. PV pumping systems’ main advantages are that no fuel is required and little maintenance is needed. A PV-powered water pumping system is similar to any other pumping system, only the power source is solar energy; PV pumping systems have, as a minimum, a PV array, a motor, and a pump.
PV water pumping arrays are fixed mounted or sometimes placed on passive trackers (which use no motors) to increase pumping time and volume. AC and dc motors with centrifugal or displacement pumps are used with PV pumping systems.
The most inexpensive PV pumpers cost less than $1,500, while the large systems can run over $20,000. Most PV water pumpers rarely exceed 2 hp in size. Well installed quality PV water pumping systems can provide over 20 years of reliable and continuous service.
Gate Openers. Commercially available PV-powered electric gate openers use wireless remote controls that start a motorized actuator that releases a gate latch, opens the gate, and closes the gate behind the vehicle. Gates are designed to stop if resistance is met as a safety mechanism. Units are available that can be used on gates up to 16 ft wide and weighing up to 250 lb.
Batteries are charged by small PV modules of only a few watts. Digital keypads are available to allow access with an entry code for persons without a transmitter. Solar-powered gate-opening assemblies with a PV module and transmitter sell for about $700.
Electric Fences. P-power can be used to electrify fences for livestock and animals. Commercially available packaged units have maintenance free 6 or 12-V sealed gel cell batteries (never need to add water) for day and night operation. T
hese units deliver safe (non-burning) power spikes (shocks) typically in the 8,000 to 12,000 V range. Commercial units are UL (Underwriters Laboratories) rated and can effectively electrify about 25 to 30 miles of fencing. Commercially packaged units are available from about $150 to $300, depending on voltage and other features.
Water Tank Deicers. For the north plains of Texas in the winter, PV power can be used to melt ice
for livestock tanks, which frees a rancher from going out to the tank with an ax to break the surface ice so the cows can drink the water. The PV module provides power to a small compressor on the tank bottom that generates air bubbles underwater, which rise to the surface of the tank.
This movement of the water with the air bubbles melts the tank’s surface ice. Commercially available units are recommended for tanks 10 ft in diameter or greater, and can also be used with ponds.
Performance is best for tanks that are sheltered, bermed, or insulated. Installation is not recommended for small, unsheltered tanks in extremely cold and windy sites. Approximate cost for a complete ownerinstalled system, including a PV module, compressor, and mounting pole, is about $450.
Commercial Lighting. PV-powered lighting systems are reliable and a low-cost alternative widely used throughout the United States. Security, billboard sign, area, and outdoor lighting are all viable applications for PV.
It’s often cheaper to put in a PV lighting system as opposed to installing a grid lighting system that requires a new transformer, trenching across parking lots, etc. Most stand-alone PV lighting systems operate at 12 or 24 V dc.
Efficient fluorescent or sodium lamps are recommended for their high efficiency of lumens per watt. Batteries are required for PV lighting systems.
Deep cycle batteries specifically designed for PV applications should be used for energy storage for lighting systems. Batteries should be located in protective enclosures, and manufacturer’s installation and maintenance instructions should be followed.
Batteries should be regulated with a quality charge controller. Lighting system prices vary depending on the size; average systems cost from $600 to $1,500.
Residential Power. Over 500,000 homes worldwide use PV power as their only source of electricity. In Texas, a residence located more than a mile from the electric grid can install a PV system more inexpensively than extending the electric grid. A
Texas residence opting to go solar requires about a 2 kW PV array to meet its energy needs, at a cost of about $15,000. The first rule with PV is always energy efficiency. A PV system can provide enough power for an energy-efficient refrigerator, lights, television, stereo, and other common household appliances.
Evaporative Cooling. PV-powered packaged evaporative cooling units are commercially available and take advantage of the natural relation that when maximum cooling is required is when maximum solar energy is available. These units are most appropriate for comfort cooling in the dry climate of West Texas where performance is best. Direct evaporative coolers save 70% of the energy over refrigerated units.
Battery storage is obviously required if cooler operation is desired at night. Array size would vary with the power requirements of the cooler motor. A linear current booster (LCB) is useful between the PV modules and the cooler’s dc motor if the cooler is coupled directly to the PV array. Packaged PV evaporative cooling systems for residences generally run from $500 to $1,500, depending on size.
Telecommunications. This was one of the early important markets for PV technologies, and continues to be an important market. Isolated mountaintops and other rural areas are ideal for stand-alone PV systems where maintenance and power accessibility make PV the ideal technology. These are often large systems, sometimes placed in hybrid applications with propane or other type of generators.