Solar System

An important requirement of electric power distribution systems is the need for automatic operation. In particular, the rapid and reliable transfer of the system from one power source to another during certain system events is important to achieving the reliability goals for such systems and the facility serves. However, the design of such an automatic transfer system is all–too-often considered “less important” than many other aspects of the overall power system design.

Nowadays, electrical power supply is one of the important elements in human being needs. The most of the human activities is dependent on electrical power supply. In other words, without electrical power supply, almost the whole of activities is become postponed or worse cancelled. For usage of daily routine, voltage supplied is within 240V ac. The need for power supply is paramount for the growth of a country, access to electricity as the basic form of energy supply to the masses is vital for the development of a nation’s economy. The strategic role and policy of generation electricity in the development of an economy has always been appreciated by most developed nations, with the likes of France, Germany, and Italy. All these mentioned countries are well and truly developed countries that sustain the supply of energy to it environment for the purpose if industrial development. 

The power sector provides a platform for economic development; electricity has brought about development in all area of productions and services. Electricity has become indispensable to socio-economic and industrial development of any nation. Using uninterrupted power supply in an automated mode, we always have a substitute arrangement as backup to take place of main power supply in case of power-cut in an emergency case, where the power cut cannot be avoided.

Rated Capacity at STC (Wp)	Isc	Imp	Voc	Vmp	Length (mm)	Width (mm)	Weight (kg)
50Wp	3.04	2.8	21.77	17.89	608	666	4.6
100Wp	6.11	5.57	21.84	17.99	1152	666	8
200Wp	8.1	7.48	32.65	26.74	1486	982	15.5
250Wp	8.71	8.18	37.55	30.58	1639	982	17.45
300Wp	8.74	8.05	45.1	37.28	1956	992	27

WORKING

Solar System Works

The solar panel converts sunlight into direct current (“DC”) electricity. This DC electricity is used to charge a battery through a charge controller. The inverter converts that "DC" power from the solar panel or battery into alternating current or "AC" power. AC power output from inverter can be used to operate light, fan, TV, computer etc. It is also possible to operate DC loads like DC lights, DC pump, computer, mobile charger, etc. directly from the solar panel or battery.

Movement of Sun across the sky

On 21st June the Sun reaches highest position in the northern hemisphere sky and on the 21st December the Sun position is lowest in the sky. In the summer season the days are long and the Sun is high in the sky. The days during summer are longer than the days during the winter season.

Seasonal variation of solar radiation due to earth’s movement

Tilt Angles

Solar modules should be installed so that as much radiation as possible is collected. Ideally the solar modules should be tilted at an angle to the horizontal (β°) as shown, facing true south (if installed in the northern hemisphere such that there is 90 degrees between the sun (at solar noon) and the solar module. To have a module face directly towards the sun at all times would require a solar tracking frame to be installed. This can be expensive, so it is not common practice for most PV applications.

To have a module face directly towards the sun at all times would require a solar tracking frame to be installed. This can be expensive, so it is not common practice for most PV applications.

Modules mounted on a fixed structure should be tilted up from the horizontal. The correct tilt angle varies with the times of year the system is used, and the latitude of the site.

The tilt should be within 10 degrees of the listed angle. For example, a system used throughout the year at a latitude of 25° can have a tilt angle of 15° to 35° without a noticeable decrease in annual performance.

Peak Sun Hour

In solar PV system design practice, the average daily solar insolation in units of kWh/m²/day is referred to as "peak sun hours". Since the peak solar radiation is 1kW/m², the number of peak sun hours is numerically identical to the average daily solar insolation. For example, a location that receives 5kWh/m² per day can be said to have received 5hours of sun per day at 1kW/m². This helps to calculate energy generation from a PV power plant as PV modules are rated at an input rating of 1kW/m².

Operations of a PV Module

A typical silicon solar cell produce only about 0.5 volt. A solar module is basic building block of any solar system where multiple cells are connected in series. Usually 36 solar cells are connected together to give a voltage of about 17V, which is enough to charge 12V battery. Similarly, a 72 cells module produces about 34V, which can be used to charge a 24V battery.

Cells are connected in series to make a PV module

In many applications the power available from one module is inadequate for the load. Individual modules can be connected in series, parallel, or both to increase either output voltage or current. This also increases the output power. When a number of modules are connected in series, it is called a PV string. Voltage of a string is addition of voltages of individual module. If 10 modules of 34V are connected to make one string, voltage of the string will be 340V.

When modules or PV strings are connected in parallel, the current increases. For example, three modules which produce 34V and 5A, connected in parallel, will produce 34V and 15A. If three PV strings of 340V are connected in parallel, will produce 340V and 15A.

The collective of multiple strings connected in parallel for greater power is called PV Array.

PV Module I-V Characteristics

I-V curve represents a ‘snap-shot’ of all the potential combinations of current and voltage possible from a module under specified environmental conditions. Every solar cell has a characteristic I-V curve, where I_SC and V_OC are quoted to help characterize a cell.

Short Circuit Current (I_sc):

A photovoltaic module will produce its maximum current when there is essentially no resistance in the circuit. This would be a short circuit between its positive and negative terminals. This maximum current is called the short circuit current (I_sc). When the module is shorted, the voltage in the circuit is zero.

Open Circuit Voltage (V_oc):

The maximum voltage in a PV module is produced when there is a break in the circuit. This is called the open circuit voltage (V_oc). Under this condition the resistance is infinitely high and there is no current, since the circuit is incomplete.

Maximum Power (P_max):

The power available from a photovoltaic module at any point along the curve is expressed in watts (W). Watts are calculated by multiplying the voltage times the current (W = VA). At the short circuit current point, the power output is zero, since the voltage is zero. At the open circuit voltage point, the power output is also zero, since the current is zero. There is a point on the “knee” of the curve where the maximum power output is located. Maximum power (P_max) is the product of current at maximum power times the voltage at maximum power.

Current at Maximum Power (I_mp):

The current that results in maximum power under given conditions of light and temperature, used as the “rated” current of a device. This value occurs at the “knee” of the I-V curve.

Voltage at Maximum Power (V_mp):

The voltage that results in maximum power under given conditions of light and temperature, used as the “rated” current of a device and to determine how many cells or modules are needed to match a load voltage requirement. This value occurs at the “knee” of the I-V curve.

Module Energy Output

For a specific load, PV module output depends on the following factors:

·         Irradiance or light intensity

·         Temperature

Solar irradiance directly affects the module energy output. If light falling on a solar module increases twice, it will produce twice as much current. The open circuit voltage does not change dramatically with irradiance; however it increases slightly with higher irradiance. This is why modules should be completely unshaded during operation. A shadow across a module can almost stop electricity production.

Module temperature affects the output voltage inversely. Higher module temperatures will reduce the voltage by 0.04V/°C to 0.1V/°C, for every one degree centigrade rise in temperature.

This is why the modules should be installed in such way that there is enough air circulation in the back of each module, so that its temperature does not rise and reducing its output. An air space of 4 – 6 inches is usually required to provide proper ventilation.

Standard Test Conditions (STC):

The specifications in manufacturers’ data sheets are all determined using standard test conditions (STC) which are considered as below:

·         Cell Temperature 25°C

·         Irradiance of 1000 W/m²

·         Air Mass of 1.5

A summary of typical losses is provided in the following table. Estimated loss for a solar microgrid system depends on system design, component selection and site operating temperature and normally total loss is around 30%.

Cause of loss	*Estimated Loss (%)	De-rating Factor
Temperature	10%	0.90
Dirt	3%	0.97
Manufacturer’s Tolerance	3%	0.97
Shading	2%	0.95
Orientation	0%	1.00
Tilt Angle	1%	0.99
Voltage Drop	2%	0.98
Inverter	5%	0.95
Loss due to irradiance level	3%	0.97
Distribution & transmission	2%	0.98
Total de-rating factor (multiplying all de-rating factors)		0.70

Pros & Cons

pros:

Ø        Power supply can be controlled from four different sources

Ø        I f any problem occurred in one source than other source can be used

Cons:

Ø        It is very difficult to install and maintain the kit

Ø        Cost of equipment is very high

Applications

Power supply can be controlled in:

Ø        Industries

Ø        Hospitals

Ø        Schools

Ø        Multiplexes

Ø        Banks etc