Essential Components to Set Up An Off-grid, Captive Solar Power Plant- Energy Alternatives India

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While setting up a solar plant, a few components seem to be essential:

i. Solar modules

A module is a group of cells connected electrically and packaged into a frame (more commonly known as a solar panel), which can then be grouped into larger solar arrays.

There are two types of solar modules:

Crystalline silicon

Monocrystalline
Polycrystalline

Thin-film

ii. Mounting structures

Solar panels mounting: Solar panels are mounted on iron fixtures so that it can withstand wind and weight of panels. The direction of panel is south facing for maximum power tracking. The tilt angle of panels will be 25° from horizontal. This angle is called axis tracking angle. You can set 40° degree tracking angle in the month of December and 10° degree in the month of June. In the month of September & March it will be 25° degree.

iii. Charge controllers

There are basically two types of charge controllers existing today in terms of functionality:

PWM charge controllers: These kinds of charge controller operate by sending out pulses of charge which helps in uniform distribution of the charges on the plates of battery. These are modulating the pulse widths and slopes of the voltage and current levels and also their rate of change. They operate in three phases:

Bulk phase: During the Bulk phase of the charge cycle, the voltage gradually rises to the Bulk level (usually 14.4 to 14.6 volts) while the batteries draw maximum current. When Bulk level voltage is reached the absorption stage begins.

Absorption phase: During this phase the voltage is maintained at bulk voltage level for specified times (usually an hour) while the current gradually tapers off as the batteries charge up.

Float phase: After the absorption time passes the voltage is lowered to float level (usually 13.4 to 13.7 volts) and the batteries draw a small maintenance current until the next cycle.

Relationship between the Current and the Voltage during the 3 Phases of the Charge Cycle

Source: http://www.solardropshipping.com/charge_controller.php

MPPT charge controllers: They constantly track and maintain the optimum voltage and current to charge the battery. They match the output of the solar panels to the battery voltage to insure maximum charge (amps).

For example: even though your solar panel is rated at 100 watts, you won't get the full 100 watts unless the battery is at optimum voltage.

If the batteries are low at say 12.4 volts, then your 100 watt solar panel rated at 6 amps at 16.5 volts (6 amps times 16.5 volts = 100 watts) will only charge at 6 amps times 12.4 volts or just 75 watts. You just lost 25% of your capacity!

The MPPT controller compensates for the lower battery voltage by delivering closer to 8 amps into the 12.4 volt battery maintaining the full power of the 100 watt solar panel! 100 watts = 12.4 volts times 8 amps.

Comparison of PWM and MPPT charge controllers:

Parameters	PWM	MPPT
Capacity	a)Available only up to 60 Amps only b)Can take only certain input voltages :12V,24V,48V c)Limits solar panel output voltage	a) Available up to 80 Amps b) Can take a varying range of input voltages and hence, reduces losses in transmission and provides flexibility in solar module configuration.
Cost	Inexpensive;	Almost thrice that of PWM
Efficiency	60-80%(approx. 68%)	Increases charging efficiency to up to 30% Peak efficiency:99%
Physical Size		Larger in size Ex:- Xantrex XW Solar Charge Controller368 × 146 × 138 mm
Flexibility for system growth	Low; Input voltage should be equal to battery nominal voltage	High; Arrays having higher output voltage than battery nominal voltage can be used
Warranty and life	Low	Much higher than PWM
Operating Power consumption	4.5W	2.5 W
With ‘Edge of Cloud’ effect
Without

iv. Batteries

Batteries chemically store electrical energy in renewable energy systems. They come in several voltages, but the most common varieties are 6 Volt and 12 Volt.

The following types of batteries are commonly used in PV systems:

Lead-acid batteries

Liquid vetted or flooded
Sealed (VRLA – Valve Regulated Lead Acid)

Gel Cell
Absorbed Glass Mat (AGM)

Alkaline batteries

Nickle-cadmium
Nickle-iron

Lead-acid Batteries: in the United States, the battery most commonly used for residential scale PV application is the lead-acid battery. This chapter primarily discusses the lead-acid battery system, since these batteries are rechargeable, widely available, relatively inexpensive and available in a variety of sizes and options. They are also commonly used, easily maintained, and reasonably long lived.

Flooded lead-acid batteries are the most cost-effective variety. They require maintenance that involves monitoring voltage, adding water, and occasional. Additionally, FLA batteries vent hydrogen under heavy charging so they must be stored in a ventilated enclosure. Because of the maintenance issues of FLAs, some people prefer sealed batteries, which don’t require maintenance. Since they are sealed, they do not require watering, nor do they typically vent any gasses. AGM batteries cost more and are more sensitive to overcharging than FLAs. Gel Cell batteries are similar to AGMs in that they are also sealed and therefore do not require maintenance, but tend to be the most expensive of the three types. The useful life of all battery types is measured in rather than units of time. is directly related to number of charge cycles possible: the deeper you drain batteries each time you use them, the fewer charge cycles you will get from them. Sealed batteries tend not to last as long as flooded batteries. Well-maintained FLAs can last as long as ten years, with sealed batteries lasting closer to five years. Other factors to keep in mind are that some of these batteries weigh over 200 pounds and, depending upon capacity, can cost anywhere from $20 to $1200 each. So, given the maintenance issues, weight and expense, consider your energy storage needs very carefully.

Types of Batteries:

Parameters	Flooded	Sealed
		AGM	Gel
Cost	Cost-effectiveness, least cost per amp hour	Nearly three times the cost of flooded batteries	2-3 times the cost of flooded batteries
Maintenance	Require maintenance	No/negligible maintenance required
Size and placement	Need ventilation; Mostly need to be kept outdoors which hinders working at ambient temperature	Sealed batteries conform to situations with space constraints that require you to store your batteries in unusual orientations or where venting is not possible
Transportation	classed under “hazardous materials” rules, which restrict shipping options	increased ease of transportation
Life	Longest life	less than a 2% self-discharge rate during transport and storage
Life	3-7 years Industrial(Traction):20 years Industrial(Stationary):20 years	10 years	8 years
% of electrical power lost as heat	15-20%	4%	10-16%

http://www.vonwentzel.net/Battery/01.Type/index.html

Alkaline Batteries

Alkaline batteries, such as nickel-cadmium and nickel-iron batteries, also have positive and negative plates in an electrolyte. These plates are made of nickel and cadmium or nickel and iron and the electrolyte is potassium hydroxide. Each cell has a nominal voltage of 1.2 volts and charge termination point is 1.65-1.8 volts per cell. These batteries are often expensive and may have voltage window compatibility issues with certain inverters and charge controls. An advantage is that they are not affected by temperatures as other types of batteries. For this reason, alkaline batteries are usually only recommended for commercial and industrial applications in locations where extremely cold temperatures (-50^oF or less) are anticipated.

In residential PV systems, typically liquid lead-acid batteries are the wisest choice. They usually constitute a significant part of the total system cost. The majority of PV systems and components are designed to use lead-acid batteries.

v. Inverters:

An inverter is used in the system where AC power output is needed. There are basically three types of inverters on the basis of the output that they give:

Parameter\Type	Square Wave Power Inverter	Modified Sine Wave Power Inverters	True Sine Wave Power Inverters
Cost	Least Expensive	Most popular and economical type of power inverter	Most expensive and best quality; Twice the price of modified sine wave power inverters of same capacity, generally.
Output quality	The square wave it produces is inefficient and is hard on many types of equipment.	It produces an AC waveform somewhere between a square wave and a pure sine wave. (Some instruments like motors consume more than 30% their normal consumption and also make a buzzing sound.)	It produces an AC waveform somewhere between a square wave and a pure sine wave
Capacity	500 watts or less. Appropriate for small resistive heating loads, some small appliances and incandescent lights.		They have high surge capabilities and can start many types of motors easily.
Usability	Not suitable for captive systems; cabin systems or mobile applications	This style of inverter is more appropriate for operating a wide variety of loads, including motors, lights, standard electronic equipments like TV and stereos. However, some electronic devices may pick up inverter noise.	They are the most common inverters today in residential application. It will run practically any type of AC equipment. For grid tied applications one may use a sine wave inverter
Merits		Very economical and reliable	Most appliances run more efficiently and use less power with a True Sine Wave inverter as opposed to a Modified Sine Wave power inverter.

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