Frequently Asked Question and Answers (Solar FAQ)
Q. What is a Solar Panel?
Q. What material is a Solar Panel made of?
Q. What is efficiency of Solar Panel?
Q. What is typical efficiency of Solar Panels?
Q. What is the expected life of Solar Panels?
Q. What is the difference between mono-crystalline and poly-crystalline?
Q. Can I connect my DC appliances directly to Solar Panel?
Q. Can I connect my Battery directly to the Solar Panel?
Q. What is better AC or DC?
Q. What is a Charge Controller?
Q. What is a VRLA Battery?
Q. Why do you need an Inverter?
Q. Why is the Solar System so expensive?
Q. What is a Grid Tied Inverter?
Q. Can a Grid Tied System work in Pakistan?
Q. What is a Hybrid Inverter?
Q. What is the Solar Payback Time in Pakistan?
Q. What is the Capacity of a Battery?
Q. What is the life time of a typical Battery?
Q. What is the Depth of Discharge of a Battery?
Q. What is the function of a Charge Controller?
Q. What is MMPT?
Q. What is a Solar Panel?
A. A Solar Panel is a device that converts solar energy into electrical energy.
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Q. What material is a Solar Panel made of?
A. A Solar Panel is composed of cells which are usually made of Silicon but there are new materials that are always being experimented with.
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Q. What is efficiency of Solar Panel?
A. Efficiency of Solar Panel is a measure of how much of available solar energy is converted into electrical energy e.g. a 15% efficient Solar Panel of 1 m2 area would convert 1000 W/m2 of available solar energy into 150 W of electrical energy.
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Q. What is typical efficiency of Solar Panels?
A. Most Solar Panels available in the market have efficiency of 15%-20% but researchers have achieved as high as 40% efficiency in lab environment.
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Q. What is the expected life of Solar Panels?
A. Solar Panels typically have an expected life of 25 years.
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Q. What is the difference between mono-crystalline and poly-crystalline?
A. The difference between them is in how Silicon is packed in the cells. Mono-crystalline cells have a more ordered structure than poly-crystalline cells and require a more intensive fabrication process. Mono-crystalline panels are usually a bit more expensive than poly-crystalline panels.
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Q. Can I connect my DC appliances directly to Solar Panel?
A. Although it is not recommended but you can connect a 12 Volt Solar Panel directly to a 12 Volt load such as a fan or bulb. But the wattage of the panel must be higher than wattage of the load.
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Q. Can I connect my Battery directly to the Solar Panel?
A. Although it is not recommended but you can connect a 12 Volt Solar Panel (open circuit voltage of around 17 Volt) to a 12 Volt Battery. A better way is to use a Charge Controller between the two to prevent the Battery from being overcharged or being completely discharged.
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Q. What is better AC or DC?
A. Both have their pros and cons. AC voltages are higher and result in lower Ohmic losses. DC appliances usually consume lesser energy and this results in lower system cost.
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Q. What is a Charge Controller?
A. A Charge Controller is a device that connects your Solar Panel to your Battery and Load. It protects Battery from being overcharged or undercharged. It also protects the Battery when a very high wattage load is connected to it.
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Q. What is a VRLA Battery?
A. VRLA stands for Valve Regulated Lead Acid Battery. It is also known as Maintenance Free or Sealed Battery. There are two main types of VRLA Batteries, Gel Type or AGM.
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Q. Why do you need an Inverter?
A. Most appliances in a typical home operate at AC voltages (220 V or 110 V) whereas the energy produced by the Solar Panel is DC (12 V, 24 V, 36 V...). The Inverter converts DC voltages to AC voltages so that AC appliances can operate.
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Q. Why is the Solar System so expensive?
A. A Solar System is usually composed of four components: Solar Panels, Charge Controller, Batteries and Inverter. The two most costly components are the Solar Panels and Batteries. The price for Solar Panels has come down a lot in the past five years and it is expected that it will continue to do so in future. But Batteries continue to be quite expensive and need to be replaced every 2-4 years (unlike Solar Panels which have an expected life of 25 years).
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Q. What is a Grid Tied Inverter?
A. A Grid Tied Inverter connects your Solar System to the Grid. It transfers energy produced by the Solar System to the Grid during the day and receives energy from the Grid during the evening and night. It is a very economical system since it does not require any Batteries.
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Q. Can a Grid Tied System work in Pakistan?
A. No a Grid Tied System cannot work in Pakistan since this system requires the Grid to be ON 24 hours. In case of a power breakdown as happens quite frequently in Pakistan a Grid Tied Inverter would be turned off. A better solution for Pakistan is a Hybird Inverter.
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Q. What is a Hybrid Inverter?
A. A Hybrid Inverter takes energy from both the Solar Panels and the Grid to charge the Batteries. It can be considered to be similar to a conventional UPS but with added capability of solar charging.
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Q. What is the Solar Payback Time in Pakistan?
A. The Solar Payback Time for systems without storage is about 4 years. For systems with storage the Payback Time is about 6-8 years.
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Q. What is the Capacity of a Battery?
A. The Capacity of a Battery is usually given in Ampere Hours (Ah). A 100 Ah Battery can supply 5 Amperes for 20 hours or 10 Amperes for 10 hours or any other combination. The Energy Storage Capacity of a Battery is sometimes expressed in Watt Hours (Whr) which can be obtained by multiplying Ah of a Battery with its Output Voltage, typically 12 Volts.
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Q. What is the life time of a typical Battery?
A. The life time of a typical Battery may vary from 300 to 1500 charge-discharge cycles. If a Battery is charged and then discharged once each day then the age may vary from about 1 to 5 years. The exact life time of a Battery depends upon the Depth of Discharge.
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Q. What is the Depth of Discharge of a Battery?
A. Depth of Discharge (DoD) of a Battery is the percentage of Capacity that is used in each cycle e.g. if for a 100 Ah Battery only 30 Ah is consumed in each cycle then the DoD is 30%. Lower the DoD, longer is the life time of a Battery. If in the above example all of the 100 Ah is consumed in each cycle the life of a Battery will be pretty short (around 300 cycles).
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Q. What is the function of a Charge Controller?
A. A Charge Controller protects a Battery from being over charged and under charged. This ensures that the Battery has a long life. In addition Charge Controllers also operate the Solar Panel at their Maximum Power Point. This is called Maximum Power Point Tracking (MMPT).
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Q. What is MMPT?
A. Output power of a Solar Panel is the product of output voltage and output current. Ideally the Solar Panel must be operated in a region where the current and voltage are maximum. But this is not possible because at max voltage, current is min and at max current, voltage is min. So a Solar Panel is operated in a region where current and voltage are not at their max but the product of voltage and current is max. This is called Maximum Power Point Tracking (MMPT).
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