Frequently Asked Questions?

Sun Wize

The following information helps answer the most frequently asked general questions about -

What are Photovoltaics?

Photovoltaics are solar cells that produce electricity directly from sunlight. They are usually made of silicon-the same material that makes up the common beach sand. The cells are wafer-think circles or rectangles, about three to four inches across.

Solar cells operate according to what is called the photovoltaic effect, ("photo"-light, "voltaic"-electricity). In the photovoltaic effect, "bullets" of sunlight-photons-striking the surface of semi-conductor material such as silicon, liberate electrons from the material's atoms. Certain chemicals added to the material's atoms. Certain chemicals added to the material's composition help establish a path for the freed electrons. This creates an electrical current. Through the photovoltaic effect, a typical four-inch silicon solar cell produces about one watt of direct current electricity.

How are photovoltaic cells made?

In the most common cell production process, very pure silicon is reduced to its molten form. Through a painstaking and time-consuming process, the silicon is re-formed into a solid, single-crystal cylinder called an ingot. Extremely thin slices cut from the ingot are chemically treated to form photovoltaic cells-sometimes referred to as solar batteries. Wires attached to the negative and positive surfaces of the cell complete the electrical circuit. Direct current electricity flows through the circuit when the cell is exposed to light.

Silicon photovoltaic cells convert sunlight directly to electricity.

For efficiency and practicality, multiple cells are wired together in a series/parallel fashion and placed in a glass-covered housing called a module. The modules themselves can then be wired together into arrays.

PV arrays can produce as much direct current electricity as desired through the addition of more modules.

Can PV modules power regular appliances?

Photovoltaic modules and arrays produce direct current (DC) electricity. Because most appliances and equipment are designed to be powered by alternating current (AC), PV-produced electricity must be converted. This is accomplished by an inverter.

Most of these solid state devices convert DC current to an AC current compatible with that sent over utility grids. As a result, PV installations may be interconnected with a utility grid, sending power onto the grid whenever there is an excess, and drawing electricity from the utility when sunlight is not available. Most inverters have a fail-safe relay that disconnects the PV system from the utility grid whenever the grid fails, ensuring the safety of utility repair personnel.

Why are PV cells so expensive and how can the cost be reduced?

Material and manufacturing costs are the two major factors that influence the price of photovoltaic cells. Even though silicon is the second most abundant material on earth, the silicon used for PV cells must be very pure; refining high-grade silicon to remove most of its impurities is an expensive process. In addition, the manufacture of PV cells at present is labor and capital intensive, although methods of automation have been undertaken.

How quickly Photovoltaics become cost-effective depends on whether research resolves these material and production problems.

More efficient cells also will help to lower the costs somewhat. The limit of efficiency for silicon PV cells is estimated to be about 30 percent. As they currently are manufactured, most PV cells operate at about 12 percent efficiency. When the cells and systems can be made to operate at higher efficiency levels, the cost of a system may be lower because fewer cells will be needed to generate the desired amount of electricity.

What are the current uses of Photovoltaics?

Many remote uses of Photovoltaics are cost-effective and practical now. Photovoltaics are generating power for both on-and off-shore traffic control systems, crop irrigations systems, bridge corrosion inhibitors and radio relay stations. They are also providing electricity to remote cabins, villages, medical centers and other isolated sites where the cost of Photovoltaics is less than the expense of extending cables from utility power grids or producing diesel-generated electricity.

What future applications of Photovoltaics are anticipated?

When system costs are reduced, several options will be feasible. Residences, such may have their south-facing roofs covered with photovoltaic modules, either as an integral part of the roof structure or mounted on supports designed for that purpose.

Such residential PV systems will probably be connected to the utility grid as well as the home. In that way, excess power would be sent onto the grid for credit during sunny periods, and power would be drawn from the utility at night and on cloudy days.

In another option, clusters of homes and businesses may jointly own or share a common photovoltaic array located at a central site. Such centralized installations also could be owned and operated by a utility company. Because maintenance needs are generally low for photovoltaic systems, on-site crews and auxiliary equipment could be kept to a minimum, cutting utility operating costs.

What is a solar water heater?

A solar water heater uses the sun's energy rather than electricity or gas to heat water, thus reducing your monthly utility bill. When installed properly, solar water heaters are more economical over the life of the system than heating water with electricity, dedicated heat pumps, heat recovery units or propane

The direct circulation system circulates potable water from the water storage tank through one or more collectors and back into the tank. The solar collector is the main component of the solar system. It is usually a box with insulation and a black absorber plate that collects solar radiation and heats the water.

In integral collector storage systems, the solar water storage system is built into the collector. The potable water in the collector unit is heated by the sun and delivered by city or well water pressure to an auxiliary tank (which contains non-solar back-up heating) or directly to the point of use.

A thermo siphon solar water heating system has a tank mounted above the collector (normally on the roof) to provide a natural gravity flow of water. Hot water rises through piping in the collector, which is mounted below the tank; heavier cold water sinks to the lowest point in the system (the collector), displacing the lighter hot water which rises to the tank.

How does a direct circulation solar system work?

As sunshine strikes the collector, the water inside it is heated. During periods of insufficient sunshine or high hot water demand, a backup electrical element in the storage tank heats the water. The check valve prevents heat loss when the circulating pump is off or with the flow of water mounted over the collectors.

What size solar system do I need?

For a family of four, 2500x1500x2500mm of collector and a total tank storage of 125 ltrs. are typical. It must be noted that thermo siphon systems will include two tanks, the solar system tank as well as the auxiliary tank.

Add on Solar systems electrically-assisted can also be procured ,electrically-assisted system that uses a 2 K.W or 3 K.W electrical loads retrofitted. which can be useful for the non sunny days or increased demand for hot water supply.

How much do I save?

Your monthly savings will depend on the amount of hot water you use, storage tank size and type and price of fuel used for backup water heating . For a family of four, the typical hot water usage is 100-litres per day, thus using 1530-kilowatt-hours per year to heat the water electrically, or Rs.7420/-(considering 300days for usage) per year worth of electricity at Rs.4.85/- per kilowatt hour.

A solar water heater should save between 50% and 85% of the hot water portion of the monthly utility bill, or Rs.7500/- to Rs.8500/- per year for a family of four.

A solar water heater can save even more if you turn off the backup and rely solely on the sun for your hot water. During summer months, when hot water demands are lower and the sun shines longer, most solar owners turn off the backup element circuit breaker, or switch. As electricity and other fuel prices go up, solar savings will increase accordingly.

Do I have to change my habits to use a solar water heater?

No. Solar water heaters could always be installed with a backup heating system in the storage tank to ensure that hot water is available at all times. However, to maximize solar utilization and your savings, you should attempt to use the most hot water in the late morning and early afternoon when the solar system is operating at its peak due to the available sunshine. Also, your solar system will be more effective if your use of hot water is spread more evenly over the week . For example, if you use hot water for laundry, instead of washing seven loads of clothes in a single day, wash one load each day. This will reduce the amount of backup energy required for your solar system.

How do I finance a solar water heating system?

The best way to finance a solar energy system is to include it as part of your home mortgage. In long-term loans of 20 years or more, the monthly solar savings will normally be greater than the monthly mortgage payments for the solar system.

If you are buying an existing home with a new mortgage, you may be able to include a new solar water heater in the mortgage. Check with your local lending office. Also, many lending institutions such as Nationalized banks offer short-term loans for solar systems, based upon the applicant's personal credit rating.

What kind of a solar collector should I buy?

A basic flat-plate collector consists of a metal/thermo-plastic enclosure, an absorber plate and flow tubes, insulation, and a glass/Myler sheet covering. Flat-plate collectors can be 2 to 4 feet wide, 5 to 12 feet long, and 4 inches thick. The absorber takes in the sun's energy, which is then transferred in to the water flowing through the collector panel. all flat-plate collectors generally have insulation behind the absorber plate to reduce the heat loss and a glass cover/myler sheet on the front, facing the sun. Some edge insulation inside the enclosure box is also supplied.

What is the proper orientation of the solar collector?

Collectors should be mounted on an un-shaded area of a south-facing roof. They can face up to 45 degrees east or west of south without a significant decrease in performance. Collectors mounted in this manner are more aesthetically pleasing. However, for flat or very low-sloping roofs, collectors should be tilted at an angle (to the horizontal) that is approximately equal in degrees to the local latitude. Since the sun is lower on the horizon during the winter months, tilting the collector at an angle up to 15 degrees greater than latitude will increase winter performance, which is desirable in most cases.

How do I protect my solar system?

Flush-type prevention valves are being used. These valves open when the water temperature in side the tank approaches to the the 80 degree centigrade level. Water pressure forces water from the storage tank through the collectors and out through the valve. The valve closes when the water leaving the valve reaches 750 C.

Another method of protection is achieved by water re-circulation. Consistent use of solar collector at high temperatures may acquire scaling due to oxidation of hard water components such as magnesium, sodium etc., depending on the level of water hardness from the bore well. When the scaling components are high, temperature through solar collectors might drop. The undue scaling can be cleaned with a pump to circulate high pressure clean water or adding dilute HCL through the collectors. A second level of protection in this system, is provided by drain valves that manually drain the collector. Manual protection alone may be adequate for conscientious homeowners in areas where hard water are frequent.

What's more, because there are no moving parts, there's little to break down. These systems last a long, long time.

Are solar water heating systems reliable?

Properly designed and installed systems with glass-covered/myler sheet collectors should perform well for more than 8 to 10 years . Controllers, like other electronic devices, may require servicing during the life of the system, and hot water tank may have to be replaced after 10 years. Since conventional water heaters have the same expected lifetime, water tank replacement costs are not regarded as unique to solar energy systems.

Normal maintenance consists of checking pipe insulation, roof penetrations and collector mounting, and tank flushing . The latter is also recommended for conventional water heating systems, as is periodic replacement of the water heater sacrificial anode rod.

What other ways are there to save on water heating bills?

Besides simply using less hot water, and timing solar-heated water use to peak when the solar exposure is at its peak, the following strategies are suggested:

  1. Wash clothes in cold or warm rather than hot water.
  2. Wrap extra insulation around the tank and insulate a few feet of the hot water line near the tank.
  3. Install an automatic timer so that the heating element comes on only during certain hours of the day. This may be cost effective if hot water is needed only for a few hours per day.

Finally, in a one-tank solar system, it's a good idea to have the back-up element controlled by a timer or manual on/off switch to keep it from coming on during the day. This strategy allows the solar system to produce all the hot water without the back-up heater being activated.