Electricity Generation using Solar Energy

Abstract

Exploiting freely-available solar energy from rooftop photovoltaic solar panels is a promising tool to meet the day-to-day operational energy requirements in a residential and/or commercial building complex. The article provides a broad overview of rooftop solar system. An attempt is made to keep write up simple, which could be understood by even a layperson. It highlights the main advantages of using rooftop solar system and briefly covers the principal components of the solar power installation. The concept of ‘net metering’ is also touched upon briefly. Finally, two examples are included to provide an insight in the working of a typical rooftop solar system, including the capital cost requirement, monthly energy output and the payback estimate. While one example calculates the solar panel requirements and the capital costs for a typical bungalow, the other example illustrates solar power requirements for common electrical lighting and hot water needs of the tenements of five building complex consisting of 143 flats.

Introduction: Why Solar?

While a majority of the world’s current electricity supply is generated from fossil fuels such as coal, oil and natural gas, these traditional energy sources face a number of challenges including rising prices, security concerns over dependence on imports from a limited number of countries which have significant fossil fuel reserves, and growing environmental concerns over the climate change risks associated with power generation using fossil fuels. With a view to mitigate these challenges facing traditional energy sources, governments, businesses and consumers are increasingly supporting the development of alternative Renewable Energy (RE) sources and new technologies for electricity generation.

RE sources such as solar, biomass, geothermal, hydroelectric and wind power generation have emerged as potential alternatives which address some of these concerns. As opposed to fossil fuels, which draw on finite natural resources that may eventually become too expensive to retrieve, renewable energy sources are generally unlimited as far as their availability is concerned.

Solar power generation has emerged as one of the most rapidly growing renewable energy sources of electricity all over the world, including India

Solar Power: Main Advantages

Solar power generation has several advantages over the other forms of electricity generation. There are few concerns as well, which are discussed later.

We are highlighting the major advantages of solar power below:

• Ample availability of Solar Power

Earth receives equivalent of one unit of electricity per square meter of earth’s surface – land and water alike!

Surface area of earth is about 510.1 trillion m ² – which means every hour 510.1 trillion units of electricity can be produced.

Considering about 6 hours of bright sunshine per day for only 200 days in a year, the total generation will be 510.1 x 6 x 200 = 612,120 trillion units annually!

As against this, it is reported that global electricity generation in the entire year 2020, was 26907 trillion units (TWh) ( see Figure 1). This means ample free resource in the form of solar power is available for utilization.

Figure 1. Global electricity generation (1990-2020) ¹ Photovoltaic (PV) panels are commonly used for tapping the solar power. PV panels use only visible light to produce electricity. The radiation received from sun on earth consists of visible light rays as well as infra-red and ultra-violet rays. The solar PV panels utilise only visible light to produce electricity.

2. Reduction in Electricity bill and Maintenance Cost

Solar energy generation using PV cells and their combinations is currently the only available method of energy generation which does not have moving parts. All other major sources of power generation such as hydro, thermal, nuclear, and wind need moving parts. Hence, the maintenance of solar power generation units is the lowest. In fact, major maintenance activity in solar power generation units is just periodic cleaning of dust that settles on the solar PV panels.

The capital cost for setting up of thermal power plant is substantially high and there is a recurring cost of raw material like coal/oil etc. In contrast, the capital cost of setting up rooftop solar power units is comparatively very small and he raw material of solar energy is easily available – free of cost! Further, solar power generation requires negligible manpower, while a number of engineers, operators and other workers are needed for running of thermal power plant. All these factors result in significantly lower cost of solar power generation.

As the use of solar power increases, there will be further reduction in the power cost, resulting in reduced electricity bills to the consumers. Thus, the use of solar power is a win-win situation for all stakeholders – consumers, governments, and the climate!

3. Long Life

Solar PV modules have long working life – guaranteed generation till 25 years! However, it may be noted that the generating capacity of every panel tends to reduce due to several internal and external factors. In the 25 ^th year of operation, it is estimated to be of the order of 80% of its original generating capacity

4. Clean Power

Solar power is environmentally-friendly, as it reduces the use of fossil fuels.

It is estimated that generation of 1 kW of solar power from PV system saves 49 fully grown hardwood trees!

Concerns about Solar Power

Now let us look into few concerns regarding solar PV installations.

Power Generation only during day time

Visible light is a must for a solar cell to generate electricity. Thus, during the evening and night hours no generation of electricity is possible from a solar installation. During this period the requirement of electricity needs be met with by an alternative source of electricity generation. Commonly available options are:

• Grid Supply
• Separate generating set (gas / diesel powered)
• Battery Bank (commonly seen in offices and banks to tackle abrupt power outages or in homes and commercial establishments in the form of so-called “Inverter".)

These are expensive options.

Shadow Effect

The solar modules are connected in series / parallel in order to ensure that the output voltage of the entire array at the output of the Grid Tie Inverter will be 220 V AC, 50 Hz(single phase) or 440V AC, 50 Hz(3-phase) to match corresponding grid voltage. However, in case of central inverter (one inverter for the entire installation, which is the most common arrangement), if the output current of even a single panel drops for any reason, such as bird droppings, dust accumulation, etc. the output current of the entire array drops causing significant drop in power output. Until such panels are identified and rectified, the output continues at reduced level.

Net Metering

In order to promote the use of renewable energy sources (solar / wind), many state electricity boards across India offer the facility of ‘Net Metering’. Under this option, the consumer can install Solar PV modules under agreed conditions on the rooftop / ground. The generation takes place only during the daytime. The solar energy, not consumed during this period, is sent to the central grid via ‘Solar Inverter’ and ‘Net Meter’ which replaces existing energy meter. The extra energy so “banked" with the grid during daytime is used by the consumer during the period when generation is not taking place.

To further promote the use of solar PV installations among the residential consumers, state electricity boards also offer subsidy for residential consumers only subject to compliance with specified conditions. The conditions applicable to the State of Maharashtra are available on the website of Maharashtra State Electricity Distribution Company Ltd. (MSEDCL) ²

Solar Panel Installation

Having discussed the main advantages and few concerns on solar energy, the following paragraphs briefly enumerates principal components of a solar installation. Typical solar panel installation diagram is shown in Fig 2 and a photo in Fig 3. The basic elements of solar PV modules include the following:

• Solar PV Modules
• Tie Inverter
• Mounting Structure
• DC and AC Cabling
• Earthing
• Lightning Arrester

Fig 2 Typical Solar PV Installation Block Diagram

Solar PV Modules

A solar panel (also described as solar module, photovoltaic (PV) module or photovoltaic (PV) panel) is a connected assembly of solar cells. The solar panel can be used as a component of a larger photovoltaic system to generate and supply solar power in commercial and residential applications. Each panel is rated by its DC output power under standard test conditions and typically ranges from 100 to 450 W. The solar cell efficiency of a Solar PV panel determines the area of a panel for the given output. For example, an 8% efficient 230-W panel will require twice the area of a 16% efficient 230-W panel. Because a single solar PV panel can produce only a limited amount of power, most installations contain multiple panels. The electrical connections are made either in series or in parallel or both to achieve desired output voltage and/or current capability.

Inverters

Solar inverter converts the DC power generated from Solar PV Panels to AC power to facilitate feeding into the grid. The inverter is the most complicated part of the PV system. It has to act as interface between the PV array and the grid. As the PV array output varies with the solar radiation, the inverter has to manage the same. The inverter has protection features to take care of the problems such as over-voltage, under-voltage, surge etc. The inverter is provided with the features for logging and display of parameters related to plant operation and faults etc. The inverter typically uses Maximum Power Point Tracker (MPPT) to maximize energy drawn from the array. The MPPT is microprocessor-based to minimize power losses. The output from the inverter is fed to the AC Distribution Board (ACDB).

The main functions carried out by the inverter are as follows:

• Converting the incoming DC received from PV modules into AC with suitable power quality. The inverter produces sinusoidal AC wave forms with low harmonic distortion.
• The inverter is programmed to act intelligently to draw power either from the grid or from Solar PV system, depending on load and availability of solar power. The inverter also has to act as a protective device of the system. It needs to trip if the voltage, current or frequency goes outside the acceptable ranges.

Mounting Structures

Solar photovoltaic power plant consists of solar photovoltaic panels connected in series and parallel giving a DC output based on incident solar radiation. Utilization of incident solar irradiation is at its highest when incident irradiation is perpendicular to the PV module. Hence, orientation and tilt of these panels are important design parameters, as well as shading from surrounding obstructions. Structures are typically made of GI / aluminium and are required to be sized to withstand loads such as own weight and wind loads and also comply with relevant standards specified by the Ministry of New and Renewable Energy (MNRE). The array frames are designed for simplicity and ease of installation at site. The structures are designed to survive adverse weather conditions with minimum maintenance.

DC and AC Cabling

The unique capability of wire harness of connecting parallel strings eliminates the use of array junction box. It provides a simpler and safer solution. Two-wire harnesses are used in each array-one for connecting all the positive terminals at one side and negative terminals at the other side. The multi-strand copper/aluminium cables will be used for interconnection of electrical components like PV modules, junction boxes, distribution boards and inverter. All the cabling will be carried out as per the applicable Indian standards. The size and length of the cable is so selected that there is minimum voltage drop and the effect of temperature is minimized. The size of cables is selected considering the short circuit current that can flow through the cables. Cables are housed inside PVC conduit pipe for un-armored cables and all cables with underground cabling.

Earthing and Lightning Arrestors

The earthing of all outdoor equipment and provision of associated earthing systems, electrodes and connections are as per latest IEEE and IS 3043 standards. Earth electrodes are provided throughout the plant areas along with the main earth grid. The number of earth electrodes is so selected as to maintain the total earth grid resistance at less than 1 ohm. The earth electrodes are provided in earth pits. The earth pit is of two types – treated with earth links and untreated. The main buried grid conductors are connected to all the earth electrodes to form a total earth grid. Galvanized Iron (GI) flats are used as per approved design.

Protection

Following protective measures are usually taken:

• DC side modules are connected to the DC Distribution Board (DCDB) for protection and to avoid any short circuit.
• AC side is connected to AC Distribution Board (ACDB) as a protection on AC side. Thus, every care is taken to protect the system and give it more service life.

As far as product warranty is concerned, MNRE requires the following:

• Module: Performance warranty for 25 years as per the module Manufacturer’s specification in the data sheet, and
• 60-months warranty of inverter from date of installation.

Fig 3. Installation of PV panels on rooftop

Typical Example

Two examples are included. One deals with the calculation of solar power requirements including cost for a typical bungalow and the other with a building complex consisting of 143 flats where only common electrical lighting and hot water requirements are to be met with the use of solar power.

Example 1

Typical example of the electricity requirement for an individual bungalow is discussed. The brief highlights are as given below

• The current annual electricity consumption of the bungalow is 3650 units and electricity bill is Rs. 32,266.
• The units generated by 1 kW solar panel system are 4.00 kWh. In this case, 3 units are recommended which will generate 12 kWh. Thus, the annual generation of solar power will be 12 x 365 = 4380 units.
• Assuming typical rate of turnkey installation of Rs 63,000/kW, the capital cost of the solar PV installation will be 63000 x 3 = Rs 1,89,000.
• Based on the above, thus the return period will be 70.29 months (5.86 years)

The detailed calculations are shown in the following tabular forms which cover (I) Average rate computation; (II) Recommendation and capital cost; and (III) Financial viability

Example 2

A typical complex has 5 buildings A, B, C, D E, which together have 143 flats. It was proposed that solar panels will be used for common lighting and hot water supply for all flats. Fig 4 shows typical layout of the buildings. Three tables are included which cover solar panel requirement for common electrical lighting (Table 1), solar panel requirement for hot water (Table 2) and space planning for these two requirements (Table 3).

Fig 4 Typical layout building plan ( in Example 2)

Table 1 Solar Photovoltaic Panel Requirement for common electrical lighting
1	Number of common Electrical Lamps of project	100	Nos
2	Number of common lamps proposed to be operated on solar PV panel system	100	Nos
3	Lamps Proposed – T5, 28W	28	W
4	Operating hours considered	13	hours
5	Energy consumed (in kilowatt hour)	36.4	kWh
6	Units generated by 1 kW solar panel system	4.00	kWh
7	PV panels system required,	36.4/4 = 9.1	kW
8	PV panels system proposed,	9.00	kW
9	Units generated by 9 kw system	36.00	kWh
10	Electricity generated by one panel	0.35	kW
11	Numbers of panel required	9/0.35 = 26	Nos
12	Size of one panel	1.00 m x 1.80 m	m²
13	Area of one panel	1.80	m²
14	Nos of panels in one kW system	2.86	Nos
15	Panel area required for 1 kW system (4 x 1.80 m2)	5.14	m²
16	Area required for 1 kW system including maintenance	6.69	m²
17	Area required 9 kw system	60.17	m²

Table 2: Solar Panel Requirement for Hot Water Generation
A	Solar panels for hot water	100	Nos
1	Total numbers of tenements	143	Nos
2	Capita assumed per tenement	5	Nos
3	Total capita	715	Nos
4	Hot water requirement as per norms of ECBC 2007	15	lcpd
5	Hot water required	10,725	lit
6	Nos of solar panels required @ 125 litres / panel	85.80	Nos
7	Nos of solar panels proposed	86.00	Nos
8	Area required for one panel including working place 2.00 x 1.50 m = 3.00 m² (Panel size = 2.00 x 1.00 = 2.00 m²)	3.00	m²
9	Area required	258.00	m²

Table 3: Space Planning of Solar Panels for Common lighting and Hot water
For Building A, B and C
		Area	Unit
1	Total terrace area available	1200	m²
2	Area available for Solar Panel  (75% is taken maximum area it may vary between 60 % to 75%)	75%
3	Area available in square meter (m²)	900	m²
4	Space required for solar PV panel for A, B & C	167.22	m²
5	Space required for Solar water heater
a	Building “A"	258.00	m²
b	Building “B"	189.00	m²
c	Building “C"	258.00	m²
	Space required Solar water heater	705.00	m²
	Total area required for mounting solar panels on Building A ,B & C	872.22	m²
	Balance roof top area on building. A, B and C	27.78	m²

References