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With increasing power tariffs, power cuts and decreasing solar panel prices, there is a lot of interest in people to adopt solar technologies. Solar electricity is one possible way to electrify houses when the power supply is erratic. To convert, store and use the energy in the sunrays as electricity a solar electric system is utilised. Here solar energy is converted to electrical energy by solar panel made up of transducers called solar cell. These panels are placed on the top of houses for the purpose of obtaining maximum solar energy. This received energy is temporarily stored in a battery via a charge controller and is finally made available for use through the inverter. This paper describes briefly the components that make up a solar system, how to calculate the required power output and the cost implications.
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Intern ational Journ al of Scientific & Engineering Research, Volume 6, Issue 11, November-2015 453
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An economical solar PV system for home
use: explained
Nathan David
Department of Electronic Engineering, University of Nigeria.
Corresponding author
Nathan David
Email: nathan.david@unn.edu.ng
Abstract: With increasing power tariffs, power cuts and decreasing solar panel prices, there is a lot of interest in people to adopt
solar technologies. Solar electricity is one possible way to electrify houses when the power supply is erratic. To convert, store and
use the energy in the sunrays as electricity a solar electric system is utilised. Here solar energy is converted to electrical energy by
solar panel made up of transducers called solar cell. These panels are placed on the top of houses for the purpose of obtaining
maximum solar energy. This received energy is temporarily stored in a battery via a charge controller and is finally made available
for use through the inverter. This paper describes briefly the components that make up a solar system, how to calculate the required
power output and the cost implications.
Keywords: Solar photovoltaic, charge controller, battery, inverter
1 INTRODUCTION
Two urgent energy issues in Nigeria today are rural
electrification and development of renewable energy
sources. Solar electricity is an appealing solution
since there is no need for fuel and little need for
maintenance. Electricity is produced in the daytime
while it is consumed mainly after dark with the use
of battery storage.
The sun is the source of virtually all energy on earth.
It provides energy for the photosynthesis, is the
engine for all wind and rain, and warms up the
atmosphere. Indirectly we harvest the energy from
the sun when we use fossil fuels, firewood,
hydroelectricity, wind energy, and even when we eat
our food. By using solar cells we can convert the
solar energy directly to electric energy, so-called
solar electricity.
Solar energy is generated by harnessing power from
the sun. It is a renewable source of energy. Recurring
cost is low since the facility for harnessing power
from the sun has little or no moveable parts that may
require periodical servicing [1].
There is an increased dependency on electricity for
various domestic and commercial purposes and the
seemingly declining capacity of power utilities, in
Nigeria, makes it necessary for an additional backup
power source. So, there is a global need to increase
energy conservation and the use of renewable energy
resources [2].
A survey was carried for a period of five months
from February to July 2015 to determine the number
of hours of power supply per day to a particular
region, University of Nigeria, in Nsukka, Nigeria as
shown in Figure 1. A similar graph illustrated in
figure 2 shows the amount of power received
between 8:00 - 17:00 hours, (sunshine period for the
region). From the graph it could be clearly seen that
there is indeed a dire need to support the grid supply
with an alternative source of energy.
Figure 1 Power supply from February to July 2015
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Figure 2: Power Supply between 8:00 – 17:00hrs, from February to July 2015
With the evident erratic power supply, the necessity
for an alternative power supply arises. When the
electricity supply is running properly via the ‘grid,
your home/office would use this power. However,
in the event of blackout or load shedding on the grid,
the system would switch to "off-grid mode" drawing
power stored in your battery bank to power your
home AND using your solar panels to recharge your
battery bank.
To be able to harvest, store and use the energy in the
sunrays, there is need for a set of electrical devices
combined into a solar electric system or a Solar
Photovoltaic (PV) system. This system has 4 basic
entities as illustrated in figure 3:
PV Solar Panel Size (which will depend on total
electricity that is needed)
2.1 CHARGE CONTROLLER
Battery size (will depend on the total electricity that
needs to be stored)
Inverter Size (total electricity load or wattage that
needs to be handled).
Figure 3: 4 basic components that make up a Solar PV system
2.0 PHOTOVOLTAIC SOLAR PANELS
There are number of different types of solar panels,
from an ever increasing range of manufacturers.
Each manufacturer claims that they are best for one
reason or another; with different sales people all
giving different information.
There are differences between the various types of
panels that are worth mentioning. However in the
end, it is the total overall power that makes the
biggest difference. A 2.4KW system would generate
a very similar amount of electricity whether the
panels being used are poly, mono, a thin film or
hybrid. The ‘panel efficiency’ quoted by
manufacturers has very little bearing on the annual
generation, it just affects how much roof space is
needed for the same powered system [3].
Solar panels are classified according to their rated
power output in Watts. This rating is the amount of
power the solar panel would be expected to produce
at standard testing conditions (STC) of sunlight
intensity 1000W/metre2 at 25°Centigrade [4]
Photovoltaic solar panels can be wired in series or in
parallel to increase voltage or current respectively.
The rated terminal voltage of a solar panel is usually
between 17-22 volts (for 12V) and between 34V-44V
(For 24V) but through the use of a solar regulator,
this voltage is reduced to around 13 or 14 volts as
required for safe battery charging.
Higher wattage panels are presented as 24V or even
36V Solar panels, i.e. 250W, 300W etc.
Solar panels output is affected by the cell operating
temperature. The output of a solar panel can be
expected to vary by 0.3% for every 1 degrees
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variation in temperature. As the temperature
increases, the output decreases.
The cost of solar panels has greatly reduced in recent
years. The cost of a solar panel is determined in part
by the size (in Watts), the physical size, the brand,
quality of materials, the durability / longevity (or
warranty period) and any certifications the solar
panel might have.
2.2 CHARGE CONTROLLER
The Charge Controller or Voltage Regulator is
basically the same thing just a different name. This
essential piece of your solar system controls the
Charge put into your battery, stops overcharging and
prevents the solar panel pulling power from the
battery at night. There are two main types of charge
controllers.
Pulse Width Modulation (PWM) is the most effective
means to achieve constant voltage battery charging
by switching the solar system controller’s power
devices. When in PWM regulation, the current from
the solar array tapers according to the battery’s
condition and recharging needs [5].
The PWM controller is in essence a switch that
connects a solar array to a battery. The result is that
the voltage of the array will be pulled down to near
that of the battery.
The Maximum Power Point Tracking (MPPT)
controller is more sophisticated (and more
expensive): it will adjust its input voltage to harvest
the maximum power from the solar array and then
transform this power to supply the varying voltage
requirement, of the battery plus load. Thus, it
essentially decouples the array and battery voltages
so that there can be, for example, a 12 volt battery on
one side of the MPPT charge controller and a large
number of cells wired in series to produce 36 volts on
the other [6].
2.3 BATTERY
A battery bank stores electricity produced by a solar
electric system. There are many types of batteries
available, and each type is designed for specific
applications. Lead-acid batteries have been used for
residential solar electric systems for many years and
are still the best choice for this application because of
their low maintenance requirements and cost. These
batteries are specially designed for stationary solar
electric systems. The size of battery storage required
is also dependent on the number of cloudy days the
system must operate using energy stored in the
battery.
2.3.1 BATTERY TIPS
1. The largest cost, over the life of the system, is the
batteries. The lifetime cost, including
maintenance, of your batteries is dependent on
your initial purchase price, how well you adhere
to a maintenance schedule, and the replacement
interval for the batteries you select.
2. The energy storage capacity of a battery is
measured in watt-hours, which is the amp-hour
rating times the voltage. For example, a 12-volt,
100-amp-hour battery has a storage capacity of
1,200 watt-hours, which is the same as a 600-amp-
hour, 2-volt battery.
3. Follow manufacturer recommendations for
voltage set points. Make sure that your charger or
charge controller will supply the correct voltage.
4. Place batteries in a well-ventilated, temperature-
moderated area because batteries give off gases
that could accumulate to form an explosive
mixture. Batteries should be kept in an
uncluttered, dry area of a shed or garage or
placed in a vented box with a strong lock for easy
but safe access.
5. Always refer to the battery manufacturer’s
recommendations for use and maintenance.
Battery Charging Current and Battery Charging Time
formula
Here is the formula of Charging Time of a Lead acid
battery.
Charging Time of battery = Battery Ah / Charging
Current
T = Ah / A
Example, Suppose for 100 Ah battery,
First of all, we will calculate charging current for 100
Ah batteries. As we know that charging current
should be 10% of the Ah rating of battery.
So charging current for 100Ah Battery = 100 x
(10/100) = 10A. But due to losses, we can take 11-12A
for charging purpose. Suppose we take 12A for
charging purpose, then charging time for 100Ah
battery = 100 / 12 = 8 Hrs. (this is an ideal case
scenario) [7].
2.4 INVERTER (POWER INVERTER)
A power inverter is an electronic device that converts
Direct Current (DC) from sources (like batteries or
solar panels) to Alternating Current (AC) [8].
The input voltage, output voltage and frequency, and
overall power handling depend on the design of the
specific device or circuitry. The inverter does not
produce any power; the power is provided by the
DC source.
3.0 HOW INVERTERS WORK
DC power is steady and continuous, with an
electrical charge that flows in only one direction. A
power inverter uses electronic circuits to cause the
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DC power flow to change directions, making it
alternate like AC power. These oscillations are rough
and tend to create a square waveform rather than a
rounded one, so filters are required to smooth out the
wave, allowing it to be used by more electronic
devices [9].
AC is thus the form of electricity that powers
appliances in homes or offices. The inverter makes
use of electronic components like transistors, battery
bank and all other necessary connections,
particularly on the utility side. Inverters also provide
over voltage protection to connected load.
Figure 4: An inverter system
Both the inverter and the charger work together to
provide you with backup power when the regular
utility power goes off by doing the following:
It charges the batteries by converting AC into DC
when power supply is available.
It converts the energy stored (DC) in the battery to
AC energy that powers your appliances when there
is power outage as illustrated in figure 4.
Inverters can be seen as a form of UPS that can
provide backup power to run your appliances when
there is a power outage. However, the duration of
the backup supply is dependent on the rating of the
inverter and capacity of battery storage connected. In
other words the higher the capacity of both the
inverter and the battery storage the longer the
duration of the backup supply. Compared to
generators, inverters are noiseless and do not pollute
the environment.
3.1 CALCULATING YOUR SOLAR POWER
REQUIREMENTS
There are three main things to consider in order to
create a Solar system.
How much energy can your battery store? Battery
capacity is measured in Amp Hours (e.g. 100Ah).
You need to convert this to Watt Hours by
multiplying the Ah figure by the battery voltage (e.g.
12V). For a 100Ah, 12V battery the Watt Hours figure
is 100Ah x 12V = 1200 WH. This means the battery
could supply 1200W for 1 hour, 600W for 2 hours
and so on. The more energy you take, the faster the
battery discharges. However you are never really
able to take all the power from a battery as once the
voltage drops below your equipment’s requirements
it will no longer be able to power it.
How much energy will your appliance(s) use over a
period of time? The power consumption of
appliances is generally given in Watts (e.g. an LED
TV is around 60W this information can be found on
the data sticker that most electrical items have). To
calculate the energy you will use over time, just
multiply the power consumption by the hours of
intended use. The 60W TV in this example, on for 2
hours, will take 60 x 2 = 120WH from the battery.
Repeat this for all the appliances you wish to use,
and then add the results to establish total
consumption.
How much energy can a Solar panel generate over a
period of time? The final part to sizing your solar
system is the solar panels. The power generation
rating of a Solar panel is also given in Watts (e.g. our
part number STP010, is a 10W solar panel). In
Theory, to calculate the energy it can supply to the
battery, you multiply Watts (of the solar panel) by
the hours exposed to sunshine. Therefore if we
consider on average, 6 hours of sunshine daily a
200w panel will provide 1200W worth of energy back
into your battery. Using the above calculation takes
into consideration any losses in the system from the
regulator, cables and battery you may be using.
How much Watts Solar Panel We need for our Home
Electrical appliances?
We can find it by very easy and simple example and
explanation. Suppose we want to power up 5 lights
of 20 Watts and we need to use these 5 lights for 7
hours every day plus a TV of 60 Watts for 4 hours.
Plights = 20 x 5 = 100W. Than we multiply 100Watts
with 7 hours. Plights Daily = 100 x 7 = 700Wh.
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PTV = 60W. Than we multiply 60Watts with 5 hours.
PTV Daily = 60 x 4 = 240Wh.
PTotal = (700 + 240)W = 940Wh
We are going to use 1100Wh daily. Let us say we are
going to have complete sunshine 6 hours each day.
Now we divide 1100W with 6 hours, so we will get
hourly power charge that we need
So here will be hour power charge that we need i.e.
watts of solar panel that we want for our electrical
appliances.
PHourly = 940 / 6 = 156W.
So we could use a 200W solar panel.
4.1 COST OF THE SIMPLE SYSTEM
There is no valued reaction to the question how
much it would cost to own a power system
substitute, unless the capacity of load/appliance the
system will carry is ascertained.
From the above we have identified the various
components required to set up our simple solar
energy system for a home. We have assumed that a
1KVA system would be sufficient for simple home
use, bearing in mind the cost of the system. Table 1 is
the breakdown of the various cost involved (cost is in
Naira, approximately $1=N220).
Table 1: Cost implications for a simple solar PV system.
component size cost (N)
1solar panel 200W, 5. 4A, 40V 35,000
2charge controlle r (PWM) 20A 6,000
3Battery 100AH, 12V 26,000
4Inverter IKVA 24,000
5Accessories 5,000
TOTAL 96, 000
4.0 INSTALLATION
Figure 5: pictorial depiction of the complete solar PV system
Once all the components are available, setting up the
system is the final phase as shown in figure 5. The
panel is mounted on the roof so as to enable it get
maximum sunlight. It is then connected to the charge
controller. Since a 200W panel is expected to generate
40V DC, on connecting to the charge controller, this
is stepped down to 12V that is connected to the
battery terminals. It should be noted however, that
the corresponding current depends on the amount of
sunlight, which could be about 5A on a hot day,
(depending on the panel specifications). Since the
charge controller under consideration is rated 20A,
we are well within the range. If the number of panels
and batteries is increased, this would amount to the
batteries charging faster, and a longer period of
electricity.
5.0 CONCLUSION
As have been clearly outlined and enumerated, solar
energy could be greatly utilised to generate
electricity that would power a house. The system
could be used to power the entire house, from your
electric fans to lights, as long as the power
consumption is monitored. If the system is required
for even longer periods of time, the size of the
inverter, panels and batteries should be increased.
This of course would increase the cost of the overall
system, but the benefits are significant.
It is good practice to consider the combination of
renewable energy source like solar panels as this will
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save you the costs of paying the hefty electricity bills
that come from charging the inverter batteries among
other things. These solar panels charge the batteries
during the day when sunlight is available.
REFERENCES
1. David N., Nzewi O.N., Onuora K.C., Abioye A. O.,
ALTERNATE POWER SOURCE: WIND TURBINE,
JECER Volume1 ~ Issue1 (2013) pp: 01-09,
http://www.questjournals.org/jecer/papers/vol1-
issue1/A110109.pdf
2. David N., Abioye A.O., Solar Power System: A Viable
Renewable Energy Source For Nigeria, JECER
Volume1 ~ Issue1 (2013) pp: 10-19,
http://www.questjournals.org/jecer/papers/vol1-
issue1/B111019.pdf
3. http://www.c-changes.com/types-of-solar-panel
4. http://www.solarpanel.co.za/solar-power-
calculator.html
5. http://www.morningstarcorp.com/wp-
content/uploads/2014/02/8.-Why-PWM1.pdf
6.http://www.victronenergy.com/blog/2014/07/21/w
hich-solar-charge-controller-pwm-or-mppt/
7.http://www.electricaltechnology.org/2013/03/easych
argingtimeformulafor.Html
8. The Authoritative Dic tionary of IEEE Standards
Terms, Seventh Edition, IEEE Press, 2000,ISBN 0-7381-
2601-2, page 588
9. http://www.wisegeek.com/what-is-a-power-
inverter.htm
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... Usually, the PV system will be installed the panels at a maximum capacity that can fit on the rooftop [10]. An example of a complete PV system in a single line diagram shown in Figure 14. ...
... There are number of different types of solar panels, from an ever increasing range of manufacturers. Each manufacturer claims that they are best for one reason or another; with different sales people all giving different information [3]. Knowledge of the characteristic of a PV panel is a prerequisite for designing and dimensioning a PV power supply. ...
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Solar Power System: A Viable Renewable Energy Source For Nigeria/www.questjournals.org/jecer/papers/vol1- issue1/B111019.pdf 3. http://www.c-changes.com/types-of-solar-panel 4
  • N David
  • A O Abioye
David N., Abioye A.O., Solar Power System: A Viable Renewable Energy Source For Nigeria, JECER Volume1 ~ Issue1 (2013) pp: 10-19, http://www.questjournals.org/jecer/papers/vol1- issue1/B111019.pdf 3. http://www.c-changes.com/types-of-solar-panel 4. http://www.solarpanel.co.za/solar-powercalculator.html 5. http://www.morningstarcorp.com/wp- content/uploads/2014/02/8.-Why-PWM1.pdf 6.http://www.victronenergy.com/blog/2014/07/21/w hich-solar-charge-controller-pwm-or-mppt/