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  Mar 8, 2021   

Basic Electrical Terminologies in Solar Energy Systems – Current, Voltage, Power, and Energy

electrical terminologies

Electricity has been the most important part of our day-to-day life. Electricity is generated by either conventional or non-conventional sources. Currently, the generation of electricity from renewable energy such as solar energy is one of the primary goals of the Government of India. 

We cannot even imagine a few hours without electricity. But do you know some basic terms for determining the electrical quantities? 

We have heard of basic terms such as “energy”, “efficiency”, “power consumed”, “high voltage/low voltage”, “current” etc. Here, in this article, we have described basic electrical quantities and their units that are generally used while designing solar energy systems.

Some basic electrical energy terms are:

  1. Charge
  2. Current
  3. Voltage
  4. Power – AC/DC
  5. Energy
  6. Efficiency

Charge:  Charge is the capability of particles (atoms, ions, and molecules) to attract and repel each other when placed in an electric field. Charges are of three types positive charge (proton) negative charge (electron) and neutral (neutron). These particles experience a force when placed in an electromagnetic field.  When similar charges (of the same polarity) are placed near each other it experiences a repulsive force, whereas when dissimilar charges are placed close to each other it attracts.

     Unit – Charge is measured in Coulombs

     1 Proton = 1.602X10-19 Coulombs

     1 Electron= -1.602X10-19 Coulombs

Current:  Current is defined as the flow of charges per unit time. Current flows only when voltage is present in the cell, when voltage is zero current also becomes zero. The symbol for current is “I” and it is measured in Ampere (A).  

Current(I) = Charge (Q) / Time (T)

How does the current flow?

Electric current flows only through a closed path or a closed medium. To supply a current medium with a low resistance path and good conductivity is required. Metal wire such as copper and aluminum wire is used for the passage of current. 

The electric current depends directly on the cross-sectional area of the conductor, potential difference, electron density, and inversely on the resistance (i.e., as resistance decreases electric current flow increases).

Measuring Instrument: An Ammeter is used to measure current.                                        

Types of Electric Current 

  • Alternating Current (AC) – Alternating current is a sinusoidal current (positive and negative waves) with generally 50 or 60 Hz frequency (cycles per seconds). We get AC supply in industrial and commercial buildings which is further supplied to various appliances.

Some appliances work on AC supply while some work on DC supply, appliances working on DC supply consist of an inverter which helps in converting AC to DC supply.

  • Direct Current (DC) – Direct current is a unidirectional waveform with zero frequency. It is mostly used as primary energy in industries for low power and electronic applications like batteries, aircraft, applications, etc.

Do you Know: Solar panel produces DC power which is further converted into AC power using an inverter and supplied to various AC loads.

Most of the electronic appliances require DC power for their working, so we can directly connect the DC output of the solar panel to our loads without the requirement of the inverter.

Voltage:  Voltage is defined as the potential difference between two-point charges, it is measure in Volts(V). In simple terms, voltage is the pressure applied in the wire that helps in the movement of charges leading to the generation of electric current. Voltage is the cause and current is the effect i.e., the current is directly proportional to the amount of voltage applied.

There are different voltage ranges depending on the application. In India, we require in general 1.5V for small batteries and 12V for car batteries, 230V at home, and high voltage of 11000V (1.1KV) in industries.

Measuring Instrument: A voltmeter is used to measure the voltage.

Current, voltage and resistance are interdependent

Voltage (V) = Current (I) * Resistance (R)

Power: Power is the amount of work done or the amount of energy used in a given time period.  Power is measured in Watts or Joule per second or Horsepower (HP).  

1HP = 746 Watt

Power depends on the amount of voltage and current of the particular appliance. 

Power (P) = Voltage(V) * Current(I)

Measuring Instrument: Wattmeter is used to measure the power dissipated in the circuit. 

We have different power ratings for different applications, for example, a bulb with 50W will provide more brightness as compared to the 30W bulb, i.e., the amount of work done by 50W is more. Power cannot be stored, we can only store energy.

Power is classified into two types:

  1. DC Power: Unidirectional flow of current, is termed as DC power. Most of the electrical appliances such as fans, TV, refrigerator require DC supply i.e., it consumes DC power.
  1. AC Power: In this current flows sinusoidally i.e., it flows in both positive and negative directions, hence it is termed as AC power. It switches from positive to negative flow.

It is divided further as follows:

  • Active Power(P) – The used power is defined as real or active or true power and measured in Watts(W) or MegaWatts (MW) or KiloWatts (KW). It is responsible for running electrical loads. Most of the electrical loads like a lamp, motors, heaters are rated in KW or Watts.

   Real Power(P) = Voltage(V) * Current(I) * CosΘ
Where Θ – Angle between voltage and current

  • Reactive Power(Q) – Reactive power is the dissipated power from the inductive and capacitive load, this power oscillates between the load and source.
    When the voltage and current are out-off phases reactive power is produced, it is measured in VAR (Volt-Ampere Reactive)
    Reactive power is not directly used power, but it ensures voltage stability for active power generation to do useful work.

Reactive Power(Q) = V x I SinΘ

  • Apparent Power(S) – Summation of active and reactive power is known as apparent power, it is measured as KVA (Kilo Volt-Ampere) or VA (Volt-Ampere). 
    In an AC circuit, when the circuit is purely resistive then apparent power is the same as real power.
    Rating of power generation and transmission equipment such as generators and transformers are rated in KVA or VA.

Apparent Power(S) = IRMS*VRMS

Energy: Energy is the total amount of work done for a specified duration. It is measured in Watt-hours or Joule. 

Energy (Joule) = Power (Watt) * Time (Second)

Measuring Instrument: An Energy meter is used to calculate the amount of energy consumed.

FAQ: People often get confused between energy and power reading, The electrical loads used in day-to-day life have power ratings specified on their nameplate. The power rating of the appliance is multiplied with the average daily hour usage to know the energy consumed.

Electrical bills that we get are calculated based on the energy consumed. 1 unit of electricity is equal to 1KWh or 1000Wh of energy. 

Electricity/Energy Billing (KWh or KVAh?)

Kilowatt-hour (KWh) is used to define the electric energy consumed per unit for the domestic tariff.

Kilo Volt Ampere hour (KVAh) is used to define the per unit energy consumed for the industrial and commercial tariffs. Industrial loads consist of inductive loads, these loads require reactive power for their functioning in addition to the active power. KVAh based billings are preferred by the utilities as it takes into account both reactive and active power. 

Energy Units: Energy can be defined in the following units.

1.      1 Joule = 1 Watt * 1 second

2.      1 KWh = 1 KW * 1 hour

Energy Conversion (Relation between KW, Joule, Watt)

1.  1KW = 1000 Watt

2.  1Wh = 3600 Ws (Joule)

3.  1KWh = 1000 Watt-hour

                      = 1000 * 3600 (Watt-seconds)

                      = 3600000 Joule

                      = 3.6 x106 J

                      = 3.6 KJ

4.  1Kilo J = 1000 J

Let us understand the conversion based on an example.

For example, consider a bulb with a 7-Watt rating, and used for say 10 hours per day.

Here, Power= 7 Watt, Time = 10 hours then

Energy (Watt/Hour) = Power (Watt) * Time (Hour)

                                  = 7 Watt * 10 hour

                                  = 70 Watt- hour

How we can convert Watt-hour(W-h) into Kilo-Watt hour (KWh)

   We know, 1KWh = 1000 Watt – hour             

        70 Watt-hour = 70/1000

                                              = 0.07 KWh  

How we can convert KWh into Joule

           We know, 1KWh = 3,600,000 J

   Hence, 0.07 KWh = 0.07 * 3,600,000

                                          = 252000 J

                                              = 252 KJ (1 KJ = 1000 J)

Do you know: Well, we are aware of the fact that installing solar panels can help us to reduce our electricity bills by up to 95%. 

But do you know how much energy a solar panel can produce? 

The energy production depends on the panel selection, location, and climatic conditions. But, in general, a 1KW solar plant is capable of producing on an average 4 to 5 KWh electricity on a daily basis and approximately 1600 to 1800 KWh per year.

The size of solar panels depends on the individual power requirement, the number of appliances, space area, etc. Generally, for residential areas, a solar power plant of 1KW to 10 KW capacity proves to be a good choice.

Efficiency: Efficiency, in general, is defined as the ratio of output to input. The efficiency of the load defines the system to do the work. 

When the output power is equal to the input power then the system is said to be 100% efficient which is an ideal case. Often systems suffer from losses due to which system efficiency gets reduced.

The efficiency of electrical loads is calculated as follows:

                      Efficiency = Output Power/Input Power

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