The PhotoVoltaic (PV) power system uses solar panels to harvest energy from the sunlight. The PV panel is a packaged assembly of solar cells. A PhotoVoltaic power system typically includes an array of solar panels, Maximum Peak Power Tracking (MPPT) controller, inverter system and batteries. For efficient use of the PV power system, it is necessary to select suitable solar panel and battery. Here describes some tips to select the panel and battery for the PV power systems.
Solar Panel parameters
The Solar panel uses photons of sunlight to generate electric current through the Photovoltaic effect. Most of the solar panels use wafer like crystalline silicon cells or thin film cells. Crystalline Silicon is widely used as the semiconductor in solar cells. Electrical connections in the solar panel are made in series/parallel to get desired output voltage and current. Electrical characteristics of solar panel includes nominal power PMax measured in Watts (W), open circuit voltage (Voc), short circuit current(Isc) measured in amperes etc.
Peak power output of the solar panel is represented in Kw. Nominal voltage of the solar panel refers to the battery voltage that the panel is best suited to charge. The actual output from the panel depends on the amount of sunlight falling on the panel, load characters, temperature etc. Most of the light spectrum cannot be used to generate electricity. So the efficiency of most solar panel is limited. Open circuit voltage of the panel is the maximum voltage that the panel can produce when not connected to a load. Open circuit voltage can be measured with a volt meter directly on the panel’s terminals.
Load Power consumption
The power efficiency of the PV power system depends on the selection of suitable solar panel and battery. It is better to calculate the total power consumption of the load that is to be used with the inverter. The load rating of individual appliance is represented in terms of Watts or VA (Volt Ampere). For example a 20W CFL consumes 0 watts power in 1 hour. Before selecting the battery, inverter and solar panel, it is better to add all the power ratings of the loads together.
For example if you wish to connect Four 20 Watts CFL, One 60W TV and One 40W Fan, then the total power consumption of the load is 20+20+20+20+60+40 = 180Watts. This is the minimum power rating of the Inverter system. But consider the power loss also. So it is better to use a higher rated inverter, say 300 VA or 500 VA to run 180W load.
Solar panels power efficiency
To calculate the power efficiency, it is necessary to calculate the power consumption in hours also. This can be done by multiplying the total load in watts by the time required. So if you want to run 180 W load for 5 hours, then 180W X 5h = 900Wh(Watts Hour). So a 300 Watts inverter is necessary for the purpose.
Battery efficiency and selection
The battery capacity is also important. The battery should have sufficient charging capacity to store 900 Wh energy to run the load and not the 180 watts of the load. Battery capacity is usually represented in Ah (Ampere hour). For example a 40 Ah battery can run 1 ampere load for 40 hours.
If a 12 volt 40 Ah Lead Acid or Tubular battery is used, then the energy storage capacity of the battery is 12 x 40 = 480 Wh. So if the load requires 900 Wh energy, then a 12 volt 80 Ah battery can hold 960 Wh energy which is the minimum rating. Consider the power loss also. Then it is better to use a 100 Ah 12 volt battery so that it can give 1200 Wh efficiency.
Solar panel selection
Before selecting the Solar panel, it is necessary to calculate the energy efficiency of the battery. For example, if you want to use a 60 W fan for 10 hours, then total energy requirement is 600 Wh. Using this example, add the wattage of all the appliances and multiply by the hours of use to get the energy efficiency of the power system. If the load rating is 180 watts as the example cited is running for 5 hours, then the energy consumption is 180W x 5 h = 900 Wh.
Solar panel can give current only for 5-6 hours per day. More over only 70-80 percent efficiency can be expected from the panel. That is a 100 Watts (Wp) solar panel can give only 80 watts maximum power for 6 hours. This gives the energy of 5 h x 100 x 0.7 = 420 Wh. 0.7 is the minimum power loss in the system. So to get sufficient energy for the 900 Wh, it is necessary to use a 300 Wp solar panel so that it can give 1050 Wh energy to store in 12 volt 100 Ah battery.