Solar Energy : Photo Voltaic Basics [ Part1 ]

Introduction:

Here are some facts on solar power generation using photo voltaic cells and how to put it to practical use. Just the right amount of information you need when you set up your own or buy a solar powered system. I will keep it as simple as possible :)

Ohms Law:
This law helps us do our simple math. This is just for reference.
Voltage (E) = Current (I) * Resistance (R) 
Power (watts) = Voltage (E) * Current (I)


The main components in our system are:

• Solar Panel.
• Charge Controller.
• Battery 
• Inverter

Solar Panel:

A PV [Photo Voltaic] panel converts incident light into electrical DC voltage. The term " Photo Voltaic " comes from "Photon" for light particle and "Voltaic" for voltage. The panels are rated at their "Watts" . You might have hear people say 100 watt panel, 250 watt panel and so on. The output wattage of the solar panel remains the same across the voltages. For example a 100 watt panel produces 100 watts whether it is rated at 6V or 12V or 24V , the current [ Amp ] however varies.

eg:
6 V 100 Watt panel gives 16.7 Amps at 6 V [ 100/6=16.7 as per Ohms Law]
12 V 100 Watt panel gives 8.3 Amps at 12 V
24 V 100 Watt panel gives 4.2 Amps at 24 V
and so on......

Charge Controller:

A circuit that sits between the PV panel and the battery, the charge controller is a crucial component in the system. The efficiency of the system can largely depend on the type of charge controller used. It has the following functions:

• Ensures optimal charging of the battery using different charging patterns .
• Prevents over charging of the battery.
• Prevents discharge of battery below critical value.
• Conditions battery to ensure prolonged life.
• Visual information display on battery condition [ some models ]

There are different types of charge controllers the most popular being PWM [ Pulse Width Modulation ] and MPPT [ Maximum Power Point Tracking ]. MPPT is more efficient and costlier than PWM. We will go into the differences of the two in a later post.

Battery:

This is our storage tank where we store the DC energy produced by the PV panel. We see certain values written on a battery, say 12 V 100 Ah. Let us take a quick look at these values.

The "12V" indicates that the battery voltage is 12 V. The 100 Ah stands for the amount of storage. "Ah" stands for "Ampere Hour". This means that, if we draw 100 Amps from this battery it will last for 1 hour. If we draw say, 50 Amps from the battery it will last for 2 hours and so on.

Since most of the appliances and devices have a wattage rating lets calculate the batteries wattage output. A 12 V 100 Ah battery produces 1200 Watts for one hour [ 12x100 = 1200 ]. If we use a 120 watt appliance it will run for 10 hours [ 120x10=1200].

Direct Current [DC] Vs Alternating Current [AC]: 

When we plot a DC output it produces a straight line. The AC however produces a wave and this is called a Sine wave. The trick in converting DC to AC is to take the DC source and convert it into AC source as close as possible to the Sine wave. This process is done in the inverter.

Inverter:
The inverter converts and steps up the DC voltage into the rated AC mains voltage, based on your regions standard voltage specification. This is done by a process of pulsing the DC voltage and modifying the output wave as required. The three common types of inverters are Square Wave, Modified Sine Wave and Pure Sine Wave. The square wave inverter is the most economical inverter and the pure sine wave is the most expensive type of the three. If you plan to connect sensitive electronic equipment to your inverter a sine wave is highly recommended.

Note: Another term that you might comes across is the term "Offline" and "Online" . This is generally used in relation to the UPS [ Uninterrupted Power Supply ] connected to the AC mains. Both these charge the battery from the mains and maintain it at full charge. In  the case of the "offline" ups the battery power is used only when the main power goes down, while in the "online" ups, the output is always coming from the battery which is constantly topped up from the mains.

Connecting Components:

Solar Panel [DC]  >> Charge Controller [DC]  >> Battery [DC]  >> Inverter >> AC Out

The PV panel output is fed to the charge controller and the output from the charge controller goes to the battery. The battery output is taken by the inverter which converts the DC into usable AC mains voltage. Many of the modern day solar inverters have a built in charge controller, letting the PV panel output to be plugged directly to it.


This concludes part one.