PV and SHW faqs
Q: what is photovoltaics (solar electricity) or “PV”?
A: What do we mean by photovoltaics? The word itself helps to explain how photovoltaic (PV) or solar electric technologies work. First used in about 1890, the word has two parts: photo, a stem derived from the Greek phos, which means light, and volt, a measurement unit named for Alessandro Volta (1745-1827), a pioneer in the study of electricity. So, photovoltaics could literally be translated as light-electricity. And that’s just what photovoltaic materials and devices do; they convert light energy to electricity.
Q: How can we get electricity from the sun?
A: When certain semiconducting materials, such as certain kinds of silicon, are exposed to sunlight, they release small amounts of electricity. This process is known as the photoelectric effect. The photoelectric effect refers to the emission, or ejection, of electrons from the surface of a metal in response to light. It is the basic physical process in which a solar electric or photovoltaic (PV) cell converts sunlight to electricity.
Sunlight is made up of photons, or particles of solar energy. Photons contain various amounts of energy, corresponding to the different wavelengths of the solar spectrum. When photons strike a PV cell, they may be reflected or absorbed, or they may pass right through. Only the absorbed photons generate electricity. When this happens, the energy of the photon is transferred to an electron in an atom of the PV cell (which is actually a semiconductor).
With its newfound energy, the electron escapes from its normal position in an atom of the semiconductor material and becomes part of the current in an electrical circuit. By leaving its position, the electron causes a hole to form. Special electrical properties of the PV cell—a built-in electric field—provide the voltage needed to drive the current through an external load (such as a light bulb).
Q: What are the components of a photovoltaic (PV) system?
A: A PV system is made up of different components. These include PV modules (groups of PV cells), which are commonly called PV panels; one or more batteries; a charge regulator or controller for a stand-alone system; an inverter for a utility-grid-connected system and when alternating current (ac) rather than direct current (dc) is required; wiring; and mounting hardware or a framework.
Q: How long do photovoltaic (PV) systems last?
A: A PV system that is designed, installed, and maintained well will operate for more than 20 years. The basic PV module (interconnected, enclosed panel of PV cells) has no moving parts and can last more than 30 years. The best way to ensure and extend the life and effectiveness of your PV system is by having it installed and maintained properly. Experience has shown that most problems occur because of poor system installation.
Q: What’s the difference between PV and other solar energy technologies?
A: There are four main types of solar energy technologies:
- Photovoltaic (PV) systems, which convert sunlight directly to electricity by means of PV cells made of semiconductor materials.
- Concentrating solar power (CSP) systems, which concentrate the sun’s energy using reflective devices such as troughs or mirror panels to produce heat that is then used to generate electricity.
- Solar water heating systems, which contain a solar collector that faces the sun and either heats water directly or heats a “working fluid” that, in turn, is used to heat water.
- Transpired solar collectors, or “solar walls,” which use solar energy to preheat ventilation air for a building.
Q: Can I use photovoltaics (PV) to power my home?
A: PV can be used to power your entire home’s electrical systems, including lights, cooling systems, and appliances. PV systems today can be blended easily into both traditional and nontraditional homes. The most common practice is to mount modules onto a south-facing roof or wall. For an additional aesthetic appeal, some modules resemble traditional roof shingles.
Q: Can I use photovoltaics (PV) to power my business?
A: PV systems can be blended into virtually every conceivable structure for commercial buildings. You will find PV being used outdoors for security lighting as well as in structures that serve as covers for parking lots and bus shelters, generating power at the same time.
Q: How do I know if I have enough sunlight for PV?
A: A photovoltaic (PV) system needs unobstructed access to the sun’s rays for most or all of the day. Shading on the system can significantly reduce energy output. Climate is not really a concern, because PV systems are relatively unaffected by severe weather. In fact, some PV modules actually work better in colder weather. Most PV modules are angled to catch the sun’s rays.
Q: How big a solar energy system do I need?
A: The size of solar system you need depends on several factors such as how much electricity or hot water or space heat you use, how, the size of your roof, and how much you’re willing to invest. Also, do you want the system to supply your complete energy usage or to supplant a portion of your higher cost energy usage? You can contact a system designer/installer to determine what type of system would suit your needs.
Q: Why should I purchase a PV system?
A: People decide to buy solar energy systems for a variety of reasons. For example, some individuals buy solar products to preserve the earth’s finite fossil-fuel resources and to reduce air pollution. Others would rather spend their money on an energy-producing improvement to their property than send their money to a utility. Some people like the security of reducing the amount of electricity they buy from their utility, because it makes them less vulnerable to future increases in the price of electricity.
If it’s designed correctly, a solar system might be able to provide power during a utility power outage, thereby adding power reliability to your home. Finally, some individuals live in areas where the cost of extending power lines to their home is more expensive than buying a solar energy system.
Q: How is a solar electric system designed, installed, and maintained?
A: You could install a photovoltaic (PV) or solar electric system yourself, but to avoid complications or injury, you will probably want to hire a reputable professional contractor with experience in installing solar systems. PV systems have few moving parts, so they require little maintenance. The components are designed to meet strict dependability and durability standards so they can stand up to the elements. However, they are fairly sophisticated electric systems, so installation usually requires the knowledge and experience of a licensed electrical equipment contractor.
Q: Where can I find someone who designs, installs, and maintains photovoltaic (PV) systems?
Q: How much does a solar energy system cost, and how much will I save on utility bills?
Unfortunately, there is no single or simple answer. But a solar rebate and other incentives can reduce the cost of a PV system. This cost depends on a number of factors, such as whether it is a stand-alone system or is integrated into the building design, the size of the system, and the particular system manufacturer, retailer, and installer. For solar water heaters and space heaters, you also have to consider the price of the fuel used to back up the system. In most cases, you would have to add the cost of natural gas or electricity to get a more accurate estimate of how much you can expect to pay for a solar energy system.
It is also difficult to say how much you will save with a solar energy system, because savings depend on how much you pay your utility for electricity or natural gas, and how much your utility will pay you for any excess power that you generate with your solar system. You can ask your solar system provider how much your new system will produce on an annual basis and compare that number to your annual electricity or hot water demand to get an idea of how much you will save.
Q: What is net metering? Is net metering available where I live and work?
A: Net metering is a policy that allows homeowners to receive the full retail value for the electricity that their solar energy system produces. The term net metering refers to the method of accounting for the photovoltaic (PV) system’s electricity production. Net metering allows homeowners with PV systems to use any excess electricity they produce to offset their electric bill. As the homeowner’s PV system produces electricity, the kilowatts are first used for any electric appliances in the home. If the PV system produces more electricity than the homeowner needs, the extra kilowatts are fed into the utility grid.
No.1 What is Solar Water Heater?
Ans. A Solar Water Heater is a device which provides hot water for bathing, washing, cleaning, etc. using solar energy. It is generally installed at the terrace or where sunlight is available and heats water during day time which is stored in an insulated storage tank for use when required including mornings.
No. 2 How does it work?
Ans. A Solar Water Heater comprises of an array of solar collectors to collect solar energy and an insulated tank to store hot water. Both are connected to each other. During the day time, water in solar collectors gets heated which is either pumped or flown automatically on thermosyphon principle to the storage tank. Hot water then stored in the tank can be used for various applications.
No. 3 What are different types of Solar Water Heaters?
Ans. Two types of Solar Water Heaters are available; one based on flat plate collectors and the other based on evacuated tube collectors. Flat plate collector (FPC) based systems are of metallic type and have longer life as compared to Evacuated tube collector (ETC) based system because ETCs are made of glass which are of fragile in nature.
Both these systems are available with and without heat exchanger. They can also work with and without pump. Systems without pump are known as thermosyphon systems and those with pump are known as forced circulation systems.
No. 4 Which type of SWH is suitable for different places/Category of users?
Ans. ETC based systems are cheaper than FPC based system. They perform better in colder regions and avoid freezing problem during sub-zero temperature. FPC based systems also perform well with anti-freeze solution at subzero temperature but their cost increases. In other regions, both perform equally well.
Systems working on thermosyphon principle are simple and relatively inexpensive. They are suitable for domestic and small institutional applications, provided water quality is good and it doesn’t have large chlorine contents. Forced circulation systems are generally preferred in industries or large establishments.
At places where water is hard and have larger chlorine content, if FPC based system is being installed, it must be with heat exchanger as it will avoid scale deposition in copper tubes of solar collectors which can block the flow of water as well reduce its thermal performance. ETC based systems will not block the flow of water but its performance may go down due to deposition of salt contents on inner surface of glass tubes, which could be cleaned easily once in a year or so.
No. 5 What is the approximate cost of solar water heater?
Ans. Cost of solar water heater depends on size and type of system installed.
Smallest size of a system is 100 liter per day, which means that it can deliver 100 litres of hot water in a day at 60 C. A 100 liter capacity system is sufficient for a family of 3-4 members and it may cost Ksh 75,000 to Ksh 85,000 depending on the type of system.
The system cost does not include the cost of cold water tank, & its stand which is required if overhead tank is not installed in a house/ building. Cost of hot water insulated pipe line also, may be extra if number of bathrooms is more than one. Additional cost towards all these components may increase by 5 to 10%.
The cost, however, does not increase linearly with increase in capacity; rather it comes down proportionately as we go for higher capacity system.
No. 6 Is there any subsidy available from Government?
No. 7 Why should I go for a Solar Water Heater? What do I save from it?
Ans. A 100 litre per day capacity system suitable for 3-4 people can save up to 1500 units of electricity in a year depending on the amount of hot water used. It can also save around 140 litres of diesel in an establishment using oil fired boiler besides reducing greenhouse gas emissions in the atmosphere. Higher capacity systems will save higher amount of electricity/fuel oil besides reducing higher amount of GHG emissions.
Electricity is expensive and is not available due to power cuts in many areas when required for heating water. Solar Water Heater, since it stores hot water in an insulated tank, provides water all the time when required. Fuel oil is also expensive and creates pollution. Storing the fuel oil for long term use in commercial establishments is another problem.
The table below gives approximate likely electricity and money savings for a typical 100 liters per day system located in different parts of the country.
|Northern Region||Eastern Region||Southern Region*||Western Region*|
|Expected no. of days of use of hot water per year||200 days||200 days||300 days||250 days|
|Expected yearly electricity saving on full use of solar hot water (units of electricity)||1000||1000||1500||1250|
|Monetary savings at different prices of electricity, ksh/year|
Q.No.8 What happens on cloudy/rainy day? Do I still get hot water?
Ans. On cloudy days also, if it is for a day or two, you still get warm water as water gets heated due to diffused radiation available in the atmosphere. The system, however connected to an electric back-up provided in the storage tank of the system which is switched on when water is not sufficiently hot. So, you get hot water all the time even on rainy days.
Q.No.9 How do I decide about the size/capacity of the system to be installed?
Ans. For a house with one bathroom and 3 to 4 members, 100 liter per day capacity system should be sufficient. For more numbers of bathrooms, the capacity will increase accordingly due to pipe losses & more number of family members. Generally the capacity is decided based on hot water required in mornings for bathing. If the usage is in evening & at other times also, the capacity is decided accordingly. Some useful thumb rules for estimating the hot water requirement are given below:
|Application||Typical Requirement of Hot Water at 60OC.|
|Household bathing using buckets||10-20 liters per person per bath.|
|Household bathing using shower with a mixing tap||20-30 liters for 10-15 minute bath|
|Shaving, while a tap runs||7-10 liters|
|Household bathing in bathtub (one filling)||50-75 liters|
|Wash basin with a mixing tap (hand wash, brushing of teeth, etc.)||3-5 liters per person per day.|
|Kitchen washing||2-3 liters per person per day.|
|Dishwasher||40-50 liters per wash cycle|
|Clothes washing machine||40-50 liters per cycle|
Q.No.10 How do I assure that a good quality system is installed at my house?
Ans. The Ministry has laid down some minimum technical requirements for installation of solar water heating systems in the field. These have been made mandatory for manufacturers and suppliers and are available on erc website: www.erc.co.ke These requirements are have been prepared in such a way that even a lay man can also check them and ensure that those are being adhered to by the manufacturers/suppliers. In case any manufacturer/supplier is found not sticking to these requirements, he may be blacklisted if informed to the Ministry.
Q.No.11 Are there any maintenance requirements?
Domestic solar water heating system do not need significant maintenance requirements. Occasional leakages in the plumbing could be easily repaired by common plumbers. In case quality of water is hard, scale deposition in the collectors may result over the years. This may require de-scaling with acids for which it is best to contact the suppliers. Broken glass may also have to be replaced by the suppliers. If outside exposed surfaces are painted, the paint may have to be redone every 2-3 years to prevent corrosion of the surfaces.
Q.No.12 Any trouble shooting guide for solar water heating systems?
Ans. Some of the troubleshooting steps are mentioned below:
|Problem faced||Probable cause and remedies|
|No water in tap||– No cold water supply
– Wall at the outlet of system closed
– Air lock in the pipes
|Water not heated at all, although cold water flow is normal||– Consumption of hot water may be too high; Check use points and use pattern
– Collector may be shaded
– No flow of water through the collector as it might be choked due to scaling; Get it checked from the manufacturer
|Water not hot enough or sufficient quantity of hot water is not available||– Cloudy weather
– Consumption too high
– Frequent on-off of hot water tap
– Collector dirty
– Vapour lock in the collector which can be removed by allowing it to cool & draining the system
– Partial choking of the collector
|Little quantity of boiling hot water is received||– Vapour locking in the collector
– Pinched inlet/outlet pipes