As per a recent survey, India is
second among the countries in terms of growing electrical demand. To
meet this ever increasing electrical demand in an economically feasible and
environmentally friendly way, Renewable Energy and Energy Conservation are the
best options. In this regard, the Indian government is planning at a fast pace
and the result is schemes and programs like Jawahar Lal Nehru National Solar
Mission (JNNSM) and many more. Many states in the country have implemented solar
schemes such as roof top net metering arrangements and so on.
The current scenario in India is
that the roof top solar PV system along with major solar PV plants is coming up
at a rapid pace. A good population is keen to know and eager to install a roof
top solar PV module. Here are some of the vital basics needed as a priori to
install a roof top solar PV system for the residential sector in India.
What should be the ideal capacity of my solar PV system? (a FAQ)
I hope, the following paragraphs
will answer most of your queries.
First and foremost thing is to
know the key elements of any solar PV system. Any solar PV system, I am talking
of stand-alone solar PV system, consists of the below given equipments.
1. Solar PV module,
3. Battery,
4. Inverter,
5. Miscellaneous items such as supporting frame,
wires, switches, change-over etc.
Of the above listed electrical equipments and elements each has its own rated capacity, and to get a proper matching between them is very important. Prior to working out the optimum capacity of the solar PV system, one has to determine the right electrical loads which can be connected to make this solar PV system viable with a low pay back period. The steps in planning for a solar PV system are:
Step 1: Determination of proper electrical load
Make a list of
electrical appliances that you are planning to run from the solar PV system.
Prior to this one has to find out how much power each piece of equipment draws
for its operation. The electrical power needed by the
equipment is given on its name plate from where one can note down and prepare a
list. The electrical wattage of some of the commonly used appliances is:
Sr no
|
Equipment
|
Electrical load (in Watts)
|
1
|
Microwave oven
|
1200- 2000 W
|
2
|
Electric Geyser
|
2000-3000 W
|
3
|
Washing Machine
|
300-500 W
|
4
|
Electric Iron
|
600-800 W
|
5
|
Water pump (domestic, 1-phase)
|
375-750 W
|
6
|
Ceiling fan
|
80 W
|
7
|
PC
|
100-150 W
|
8
|
Color TV
|
150 W
|
9
|
Tubelight (including choke)
|
45 W
|
10
|
Freezer
|
150-250 W
|
11
|
Room Cooler
|
150-250 W
|
12
|
AC
|
1000-2000 W
|
The electrical load given above is for reference only.
Actual rating may be obtained from the equipment name plate or manufacturers
specification only, as the rating or electrical load of any equipment may vary
according to its capacity, features, etc.
Step 2:
Optimize your electrical load
As per the given list one can
very well judge that appliances such as microwave ovens, geysers, AC, hotplates
etc are equipments capable of drawing heavy current and hence power. To run
these equipments or appliances on solar you have to go for a much higher values
of installed solar capacity, which is going to increase the capital cost and
the pay-back period (period necessary to get back the investment). So it is advised not to connect or run these equipments on solar PV system.
(If you an inverter technology based refrigerator or AC, then the possibility of running them on solar PV system is there.)
In fact equipments such as Tubelight, CFL, fan, room cooler, TV, laptop etc, and in some emergency situations, electric iron, should be connected and run on solar PV system.
(If you an inverter technology based refrigerator or AC, then the possibility of running them on solar PV system is there.)
In fact equipments such as Tubelight, CFL, fan, room cooler, TV, laptop etc, and in some emergency situations, electric iron, should be connected and run on solar PV system.
To separate the equipments
requiring heavy power, moderate and low power one has to re-wire the
distribution system or separate the circuits from the distribution mains (MCB).
One can use a change-over switch also.
Step 3: Battery size
Appropriate battery size is the
key element in making your PV system a success. The life of a PV module is
around 25 years as claimed by the manufacturer, whereas the expected battery
life is 3 to 5 years. Also the battery cost is significant. As one goes for a
higher Ampere-hour (Ah; the rating of battery is given in Ah) battery, its cost
increases.
For example; recently I have installed a 400 W solar PV system costing around 52 thousand INR in Bhopal, India, the battery of 150 Ah capacity, with 5 years warranty, alone was of 14 thousand INR.
For example; recently I have installed a 400 W solar PV system costing around 52 thousand INR in Bhopal, India, the battery of 150 Ah capacity, with 5 years warranty, alone was of 14 thousand INR.
So the summary is:
Battery is a vital element of
your solar PV system whose life is less as compared to other equipments of the
system and is comparatively costlier. The equipments which you have selected to
get connected to the solar PV system, if works mostly during day time, is the optimum
load as per the solar PV system design. This in turn will permit you to have a
battery with lower Ah capacity which in turn will reduce the overall system
cost.
If your load is ‘switched off’ mostly
during the day time, then you have to keep a large battery to store the whole energy
produced by the PV module during the day. Thus, to optimize your electrical
requirements you have to look into your usage pattern and the criticality of
your application.
For a ready reference, the
back-up time for a particular capacity battery is given below
Load
|
Inverter capacity
|
Battery capacity/ Back-up time
|
|||||
100 Ah
|
150 Ah
|
200 Ah
|
|||||
Full Load
|
Half Load
|
Full Load
|
Half Load
|
Full Load
|
Half Load
|
||
2 TL + 2 F+
1 PC+ 3 CFL
|
650 VA
|
1 hr.
|
2 Hr, 40 m
|
1 Hr, 50 m
|
4 Hr, 20 m
|
2 Hr, 40 m
|
6 Hr, 10 m
|
2 TL + 4 F+ 1 PC+ 3 CFL
|
850 VA
|
40 m
|
1 Hr, 50 m
|
1 Hr, 10 m
|
3 Hr
|
1 Hr, 50 m
|
4 hr, 20 m
|
TL and F stands for Tube-light and fan respectively.
The charge controller is an equipment
that controls the charging of the battery and thus helps in improving the
battery health and life. The capacity of charge controller is in ampere. The charging current ( CC ) of a battery is
given in manufacturer’s specification, but for ready reference the CC of a 100 Ah battery is 10 A, 150 Ah battery is 15 A and so on. So for a
150 Ah battery a charge controller of 20 or 30 A is sufficient.
Step 4: Inverter size
Inverter is the equipment which
converts the DC voltage of the battery into AC 230 V, so that your normal AC
appliances can be connected to the solar PV system.
Selecting a proper inverter size is very important. Use only the inverter which provides a pure sine wave otherwise your equipments are going to suffer. The output capacity of inverter is given in Volt-Ampere (VA), whereas the appliances are rated in watts. We know that VA multiplied by power factor is watts. So you have to know the power factor of commonly used electrical gadgets for a precise calculation. For simplicity you can assume that the power factor is 0.8, which is the value for most commonly used inductive household equipments.
Selecting a proper inverter size is very important. Use only the inverter which provides a pure sine wave otherwise your equipments are going to suffer. The output capacity of inverter is given in Volt-Ampere (VA), whereas the appliances are rated in watts. We know that VA multiplied by power factor is watts. So you have to know the power factor of commonly used electrical gadgets for a precise calculation. For simplicity you can assume that the power factor is 0.8, which is the value for most commonly used inductive household equipments.
So a 850 VA inverter is of 850 x
0.8 = 680 W only. So the total electrical loads which can be connected to a 850
VA inverter can be about 600 W. This does not mean that for better utilization
of resources one has to keep an inverter of higher capacity. The answer is:
The efficiency of an inverter is
about 80% to 90% i.e. 10% to 20% of the energy given to an inverter is consumed
by the inverter itself. So higher the inverter capacity higher the losses. Also
a higher capacity inverter is useless unless the battery is also appropriately
sized.
For a better understanding, have
a look into my roof top solar PV system (photo below).
I have installed a 400 W solar PV
module (4 panels of 100 W each, make Topsun) along with a 40 A charge
controller. The battery used is of Luminous make, 150 Ah, 5 year warranty and
the inverter is of 850 VA sine wave of Su-Kam make.
The whole system is working quite satisfactorily since May 2015. On this system I have used a 150 W room cooler and one 80 W fan the whole day during the summer with occasional load of a 150 W color TV. I have tried to operate a 375 W water pump and a 600 W automatic iron also. Both the equipments worked nicely, but one at a time. The motor during starting draws a higher current (which is natural for motors), thanks to the in-built feature of the inverter which permits a 300% plus over-current for a few ms to cater such loads.
Recently I have connected the entire Light & Fan load of 2 bedrooms and a hall. The total connected load on the solar inverter system is now 850 W (4 x 40 tubelights, 4 x 80 W ceiling fan, 1 x 150 TV, 2 x 150 room cooler) but the maximum load at a time is restricted to 400 W.
The whole system is working quite satisfactorily since May 2015. On this system I have used a 150 W room cooler and one 80 W fan the whole day during the summer with occasional load of a 150 W color TV. I have tried to operate a 375 W water pump and a 600 W automatic iron also. Both the equipments worked nicely, but one at a time. The motor during starting draws a higher current (which is natural for motors), thanks to the in-built feature of the inverter which permits a 300% plus over-current for a few ms to cater such loads.
Recently I have connected the entire Light & Fan load of 2 bedrooms and a hall. The total connected load on the solar inverter system is now 850 W (4 x 40 tubelights, 4 x 80 W ceiling fan, 1 x 150 TV, 2 x 150 room cooler) but the maximum load at a time is restricted to 400 W.
