Small Residential Stand Alone Roof-top Solar PV System:

A Case Study

By: Manoj Nair,M-Tech. (H.E.E.)

Why Renewable ?

Demand for electricity in India is increasing day by day, doubles every 7 years.

Gap between demand and supply, Limitations of Large scale Mega Power Plants; • Financial issues, • Govt. clearances, • Gestation period; 5 years to 10 years • Environmental issues, • Limited availability; to exhaust in near future etc. Significant T & D losses; excess of 30%

Why Solar PV?

• Free and Abundant sunlight; average 5 hours, and 300 days per years.

• Long Life of PV panels; 25 years

• Pollution free and Minimum Maintenance,• Fast response and reliable,• Modular units, easy scope for future expansion,• Inherent short circuit protection,• No T & D losses for small Roof Top PV plants• Low Gestation periods

Potential of Roof top Solar PV System

As per census 2011, India has 140 million houses with proper Roof Tops.

Roof Top Solar PV Systems (RTPV) is best suited for urban areas where the houses are crowded and dense.

Roof top stand alone PV systems can be installed with in a few days (2-3 days)

• Stand alone PV system is directly connected to the load through an inverter of appropriate capacity,

• Excess energy is stored in a battery of user defined capacity for use in emergency period,

• In a grid tied system, excess energy produced is returned to the grid if net metering facility is available in the area.

Key Elements of Stand alone Roof top Solar PV System

• Solar PV panels,

• Charge controller,

• Battery,• Inverter,• Cables,• Switches etc.

Role of Charge Controller

• A Charge controller protects the battery from overcharging, moderates the charging at the end of the charging cycle,

• It indicates the charging status of the battery such as undercharge, overcharge, or deep discharge through indicators.

• IGBT or MOSFET technology is used now a days which reduces the idle current of the charge controller

Role of Battery & Inverter

• Battery is used to store the excess energy produced. • The cost of a battery is significant, hence there use should be kept

at an optimal value.• Inverter is used to convert the DC output of the battery/solar PV

panel into AC of 230 V, 50 Hz.• Care should be taken while selecting the inverter. An inverter with

sine wave output should be adopted as a sinusoidal AC supply will increase the efficiency and life of your electrical appliances.

• Wires of appropriate size should be selected to avoid un-necessary voltage drop and power loss as wires of lesser cross section will have higher resistance, increasing the voltage drop and losses.

Check whether your house is suitable for the solar PV system?

• It is very important to assess the amount of sunlight available at the location where a solar PV system is being installed.

• To collect maximum sunlight the ideal orientation of a solar panel is towards south. However a 45-degree east or west of south can also work.

• The system should be placed in such a place so that there is no obstruction of trees or adjoining building.

• Roof should be of RCC to bear the weight of the solar PV system.

Sizing a roof top solar PV system

• It is very important to size your solar system properly. • Sizing will depend on the load requirements in your

setup. Solar system is good for operating low wattage appliances like lights, fans, TV, etc.

• It is not advisable to operate High wattage appliances like Air Conditioners, Microwave Ovens and Water Heaters on a solar PV system (in fact solar water heaters and solar air conditioners are available separately).

• The connected load of your setup will help you determine the size of system that you need and that in turn will drive the cost of the system.

Primary Designing of a Roof top Solar PV system

• Collection of Information/Data; wattage of electrical appliances, duty cycle, load profile, monthly electricity consumption & bill, cost of panels, battery, inverter etc.

• Load Selection; load to be placed on solar PV system should be selected

• Sizing solar array,• Deciding battery capacity,• Selection of Charge controller,• Deciding of Inverter capacity,• Structure,• Wiring

Load / Energy Calculation

Load of Equipment in Watts x No. of working hours per Day gives the Watt Hours Per Day (WHPD)To calculate the Ampere Hours Per Day (AHPD)

AHPD = WHPD/(Av. Power Factor of the load x System Voltage)

Average Power Factor of the load to be connected to the solar PV system is taken as 0.8 lagging in this study.

Capacity of Solar PV Panel

• The Solar PV Panel will supply to your electrical load through the inverter as well as will charge your battery.

• If the electrical load on the panel is more it will provide less current to the battery, thus battery charging will be slow.

• So simultaneous calculation is necessary.• The max. current of a 100 W PV panel is 5.8 A, considering

that a single panel is giving a current of 5 A, the calculations were carried out.

• If you are running an electrical load of 200 W on the solar system i.e. using the output of 2 panels, only 2 panel outputs i.e. 10 A will be available for battery charging.

Charging Current of Battery

Charging Current

200 Ah 20 A

165 Ah 16 A

150 Ah 15 A

135 Ah 13.5 A

100 Ah 10 A

400 W, stand alone solar PV system: Case study

Introduction of the premises

• The premises which is considered for case study is a 3 BHK Duplex house located near Minal Residency, Bhopal.

• The total connected load is 7.7 kW and the details are given in next slide.

• Only Light and fan loads and other small loads as T.V., kitchen chimney, aquarium, water filter are considered as the load which is to be shifted on solar system.

• The system capacity is so selected that the energy produced by solar system can be directly utilized at the max., i.e. battery storage should be min.

• Occasionally electric iron and water pump of ½ h.p. is also used.

Connected Electrical Load of the Premises• Total connected load of the premises is 7.7 kW

Light Load (8 x 40 W, T/L & 4 x 10 W, CFL ) 360 WFan Load (6 x 70 W Fan & 2 x 220 W cooler) 860 WT.V. (CRT type) 150 WElectric Water Geyser 2000 WMicrowave Oven 2200 W Water Pump 375 WElectric Iron 600 WKitchen Chimney 190 W Mixer/ Juicer 600 W Fridge 110 WWashing Machine 450 W Acquarium 120 W

Loads to be put on solar..• So the average connected electrical load of any middle class

residential house comes between 5 to 8 kW.• It is never advised to take the full electrical load on solar PV

system; as it will-• Increase the initial investment,• Payback period will be too long.• In this case electrical loads such as water geyser, water pump,

microwave oven, washing machine etc are still grid connected.• In this case electrical loads such as T/L, fans, coolers, kitchen

chimney, water purifier, etc of 1680 W are put on solar system.

Solar PV panels

Solar PV Panel

Solar PV panelsMake: Topsun,

Gandhinagar, Gujarat.Cap: 100 Wp, x 4 nos.Warranty: 25 years (conditions apply) * Output of solar panel

reduces by 2.5 to 3.5% during the first year, then after a min. reduction of 0.7% per year [3]

Nameplate details of PV panel

• Max Output = 100 Wp per panel,

• Max voltage = 18 V,• Max current = 5.8 A

End Terminals

• End Terminal Box,• Connecting leads,• (parallel connections

so that output is 18 V and current 5.8 x 4 A)

Rear view of the panel

Supporting Structure

• MS Iron angle of appropriate size painted with ‘Al’ paint.

Solar Charge Controller

Solar Charge Controller• Make: RXL,• Cap: 40 A, 12 V,• Warranty: 1 year,

Solar Battery

• Tall tubular Lead-Acid battery

• Make: Luminous,• Cap: 150 Ah, 12 V,• Warranty: 5 years

Inverter

• 850 VA, 50 Hz, Sine-wave Inverter

• Make: Su-Kam

Change Over Switch

• Simple Switch used as Change Over Switch

• Make: Anchor * This simple switch is a

key element responsible for the scheduling

Technical Details of the Solar PV System

System capacity: PV panel = 100 W x 4 Nos, Charge Controller ; 40 A Battery; 150 Ah, 12 V, Tubular Lead-Acid, Inverter; 850 VA, sine wave PVC insulated stranded ‘Cu’ wires of 4/2.5 sq.mm

Cost of installing the Solar PV system

Sr. No Component Cost (INR)

1 Solar PV panel, 4 x 100 W, Topsun Make 20,000.00

2 Charge controller, 40 A, 12 V, RXL Make 1,300.00

3 Battery, 150 Ah, 12 V, 5 yr warranty, Luminous Make 14,500.00

4 Inverter, 850 VA, 220 V, 50 Hz, sine wave, Su-Kam Make 5,500.00

5 ‘Cu’ stranded wires 4/2.5 sq.mm and switches 3,000.00

6 M.S. angle painted frame 2,000.00

7 Installation & Transportation Charges 2,000.00

8 Misc. Cement, sand, metal etc 7,00.00

8 Total 49,000.00

Scheduled Load on Solar System

• Of the total connected load, equipments of 1680 W, with diversity factor of 4, are connected manually to the solar PV/ Battery system.

• Three schedules were followed till date:• 5.30 AM to 6.30 PM (May to July 2015)• 5.30 AM to 5.00 PM (Aug to Sep 2015)• 10.00 PM to 5.00 PM (Nov 2015) * The above schedule are purely tailor made depending on the

seasonal variation and individual use which anybody can do.

Ref

1. Govt. of India, Ministry of Railways, “Handbook on installation and Maintenance of Solar Panel”, RDSO, Gwalior.

2. Shanmugawalli K.R., & Veedamuthu R, “Viability of Solar Rooftop PV Systems in Group Housing”, Current Science, Vol. 108, No.6, March 2015.

3. Tata Power Solar, “Warranty Document”.4. Su-Kam, “Solar Batteries”

Any ?????

Thank You,Have a Nice Day