Sizing of a Photovoltaic System in the City of Quevedo for
Residential Use
Dimensionamiento de un Sistema Fotovoltaico en la Ciudad de Quevedo para
Uso Residencial
Ricardo Chu Zheng
Master, Universidad Técnica Estatal de
Quevedo, Quevedo, Ecuador,
ricardo.chu2017@uteq.edu.ec
https://orcid.org/0000-0003-2108-4306
Jorge Merino Peña
Master, Universidad Técnica Estatal de
Quevedo, Quevedo, Ecuador,
jorge.merino2016@uteq.edu.ec
https://orcid.org/0000-0002-9014-7000
Yadyra Ortiz Gonzalez
Master, Universidad Técnica Estatal de
Quevedo, Quevedo, Ecuador,
yortizg@uteq.edu.ec
https://orcid.org/0000-0002-2824-0132
Diego Peña Banegas
Master, Universidad Técnica Estatal de
Quevedo, Quevedo, Ecuador,
dpena@uteq.edu.ec
https://orcid.org/0000-0001-8696-7463
ricardo.chu2017@uteq.edu.ec
http://centrosuragraria.com/index.php/revista, Published by: Edwards Deming Institute,
Quito - Ecuador, October - December vol. 1. Num. 11 2021, This work is licensed under
a Creative Commons License, Attribution-NonCommercial-ShareAlike 4.0 International.
https://creativecommons.org/licenses/by-nc-sa/4.0/deed.es
Received July 05, 2021
Approved: September 24, 2021
Abstract
The sizing of a small photovoltaic system of a
residence in the city of Quevedo is presented, with
the objective of analyzing solar photovoltaic
installations as a measure to promote the use of
distributed generation in homes and the reduction
of costs to be paid for electricity consumption. The
load profile of the residence is made through
personal estimates and the global horizontal solar
irradiation and temperature data are obtained from
NASA's Surface meteorology and Solar Energy
(SSE) weather database. They will then be entered
into the HOMER Pro software for the respective
simulations with different types of photovoltaic
systems.
Keywords: sizing, photovoltaic system,
generation, renewable, grid-connected.
Chu Zheng, et. al
October - December vol. 1. Num. 10 2021
Resumen
Se presenta el dimensionamiento de un pequeño sistema fotovoltaico de una residencia en la ciudad de
Quevedo, con el objetivo de analizar las instalaciones solares fotovoltaicas como una medida para
fomentar el uso de la generación distribuida en los hogares y la reducción de los costos a pagar por el
consumo eléctrico. El perfil de carga de la residencia es realizado a través de estimaciones personales
y los datos de irradiación solar horizontal global y de temperatura se obtienen a partir de la base
meteorológica Surface meteorology and Solar Energy (SSE) de la NASA. Posteriormente serán
introducidos en el software HOMER Pro para las respectivas simulaciones con diferentes tipos de
sistemas fotovoltaicos.
Palabras clave: dimensionamiento, sistema fotovoltaico, generación, renovables, conectado a red.
Introduction
The increase in the use of renewable energies has become remarkable due to the awareness of
optimizing resources and reducing environmental pollution, this causes the need to generate
new projects that contribute to the improvement of this type of systems Salamero et al. (2009)
indicates that a photovoltaic generation system is proposed in which the advantages and
disadvantages of an isolated system with respect to a system interconnected to the grid will be
analyzed and compared. In addition, the economic analysis of both systems will be presented,
which will allow deciding which of them is adequate for the sizing of the system for a residence.
For Farfán et al. (2015) there are 3 types of PV systems that can be implemented:
Off-grid or isolated system
The greatest development of this energy source is undoubtedly in rural areas (electrification of
houses, farms and hamlets) or in isolated locations where electricity supply is often impossible
by other means. (Solar Energy Aragon)
Figure 1. Basic diagram of an off-grid photovoltaic system.
On-grid or grid-connected system
A grid-connected photovoltaic system can be defined as a photovoltaic generation system that
works in parallel with the utility grid, i.e., the outputs of both generation systems are connected
to each other, so that the first one acts as if it were another generator of the utility, injecting
electricity into its distribution network.
58
Figure 2. Diagram of on-grid photovoltaic system.
This is why for Cossoli et al. (2014) in general terms, grid-connected distributed PV generators
can bring significant benefits to distribution systems, as well as from the location of these
within the grid.
Hybrid, grid-connected system with batteries
In this case Cáceres et al., (2014) indicates that hybrid systems generate power in the same way
as a common grid-connected system, but use special hybrid inverters and batteries to store
energy for later use. This ability to store energy allows most hybrid systems to also function as
a backup power source during a blackout, similar to a UPS system.
Figure 1. Hybrid photovoltaic system diagram
Traditionally, the term hybrid refers to two generation sources such as wind and solar, but in
the solar world the term "hybrid" refers to a combination of energy storage and solar power
that is also connected to the grid. (Farhat et al., 2015, p. 480)
Components of a photovoltaic system
Solar panels: convert solar radiation into direct current. The higher the radiation, the more
energy the solar panels will produce at the same power.
Charge regulator: it acts by cutting and regulating the energy flow between the panels and the
battery, depending on the battery's state of charge. In order for it to work properly, its power
Chu Zheng, et. al
October - December vol. 1. Num. 10 2021
must be sized correctly and the right type must be chosen to obtain the best performance from
the panels. Charge regulators can be of 2 types:
PWM regulators: it is more economical and recommended for small low-cost solar systems. It
can only be used if the nominal voltage of the solar panels and batteries is the same, for
example, with 12V solar panels and 12V batteries.
MPPT regulator: they are much more efficient as they adjust the incoming panel voltage to that
required by the battery according to its charging stage, so they can extract about 30% more
energy than a PWM. The only requirement is a nominal voltage in panels higher than the
working voltage in batteries and they are the only possible option when using panels with a
non-standard voltage. (Auto Solar, 2020)
Off-grid inverters: isolated inverters need to be connected to batteries and are responsible for
converting the direct current that can be extracted from them to alternating current suitable for
normal household consumption. Seraphim et al. (2014) states that generally, they can be of:
12V, 24V or 48V and it is important that they generate a pure sine wave so as not to have
breakdowns in the electrical devices that are connected. It is common to integrate the charge
regulator within the inverter itself and also the functionality of a battery charger from an
external source. This is very useful because in isolated installations it is common to have a
gasoline generator or diesel generators that can cover emergency consumption in low
production conditions. p. 1482
Microinverters vs. central inverters: the great advantage of a microinverter over a central
inverter is that the system is not affected by shadows. That is, if one panel is affected by a
shadow the other panels continue working at 100%. If one panel is damaged all the other panels
continue to work. The maximum power is going to be obtained from each of the panels. This
is how Firman et al. (2014) indicates that with a centralized inverter, the total power generation
of the system can decline drastically if a single panel stops producing power due to a failure or
shadow.
Batteries or accumulators: they are responsible for storing the energy that is captured and not
used during sunlight hours. In this way, this energy is available at night or at times of lower
production. They account for almost half of the budget in an off-grid solar system and therefore
it is very important that they are adjusted to the needs. (Auto Solar, 2020)
There are small and economical batteries for more discreet uses and large accumulators for
greater needs. Similarly, there are also different types of technologies such as lead acid
batteries, AGM batteries, GEL batteries, lithium battery stationary batteries. (Recalde et al.,
2015 p. 100) "Batteries are grouped to obtain the working voltage required by the inverter and
their capacity must also be in line with the power of the inverter and the use to be given to the
system". It must also be ensured that the charge regulator is prepared to work at the voltage of
the battery bank to operate...
60
Materials and methods
The study area of the photovoltaic sizing project is located in the city of Quevedo, parish of 7
de octubre, on D Street, between third and fourth streets. Its geographical coordinates are: -
1.041667, -79.473333.
For the simulation of the photovoltaic system, the load profile of the residence of the kW
consumed per hour, during the 365 days of the year, is required. For this purpose, 8760 data
were obtained and used by HOMER Pro to simulate and find the optimal components.
Global horizontal solar irradiance and temperature data were obtained from NASA's Surface
meteorology and Solar Energy (SSE) database and are presented in Table 1and ¡Error! No se
encuentra el origen de la referencia..
Table 1 . Global average global horizontal solar irradiance of the study area.
Month
Daily irradiance (kWh/m2/day)
January
4.21
February
4.38
March
4.76
April
4.64
May
4.18
June
3.78
July
3.81
August
4.21
September
4.32
October
3.97
November
4.21
December
4.09
Result
For the present project, it was decided to carry out two simulations, which will later be
compared in order to select the most feasible project:
1. A stand-alone system with generator set
2. A networked system
3. Isolated system with generator set
The components of the isolated system are shown in Table 2
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October - December vol. 1. Num. 10 2021
Table 2 . Components for the isolated system
Component
Features
Photovoltaic panel
Renogy RNG 235P
$230 / unit
Power: 235 W
Voc: 37.08 V
Isc: 8.34 A
Type: polycrystalline silicon
Battery
Trojan SAGM 12 205
$290 / unit
Voltage: 12 V
Capacity: 205Ah @ 20Hr
Material: Polypropylene
Type: VRLA, maintenance-free
Shelf life: +8 years
Inverter
Studer Xtender XTS 1200-24
1365 / unit
Nominal battery voltage: 24V
Input voltage range: 19 - 34V
Continuous power at 25C: 800 / 650VA
Maximum yield: 93%.
Pure sinusoidal output voltage: 230Vac / optional
120Vac
Gasoline generator
PTK GG 1/18220
$290 / unit
Power: 3.3 kW, 6.5 HP
Engine: 196 cc 4-stroke gasoline
Tank: 15 liters
Continuous operation: up to 10 hours
62
The isolated system design has two generators: the photovoltaic panels with an energy
production of 4034 kWh/year and the gasoline generator of 713 kWh/year, representing 85%
and 15% respectively. Figure shows that the gasoline generator is mostly used during the
months of May, June, July and August, when electricity consumption is much higher due to
the use of heating and/or cooling appliances, and therefore the backup generator has to be used.
Figure 4. Average monthly electricity production by type of isolated system generation
The solar array consists of 14 panels with a total installed capacity of 3.31 kW, generating an
average of 11.1 kWh/day or 4034 kWh/year.
The gasoline generator will have consumed a total of 277 L of gasoline during its 25 years of
useful life, works an average of 753 hours per year, has a useful life of 19.9 years and an
efficiency of 28.5%, i.e. it only uses that percentage of the fuel energy to transform it into
electricity.
Figure 5. Monthly state of charge of Trojan SAGM 12 205 batteries.
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October - December vol. 1. Num. 10 2021
The battery bank is composed of two batteries in series and three in parallel working at a total
voltage of 24 V and with a nominal capacity of 12.6 kWh. The system has a total autonomy of
29.3 hours, at a cost of $0.138 per kWh stored and a projected lifetime of 7.53 years. Figure
shows the simulation of the monthly state of charge of the battery system, where the charge
and discharge limits of the controller were set between 20 - 100%.
Table 3. Cost of installation, operation and maintenance and salvage value of the system
during its useful life as an isolated system3
Components
Capital ($)
Total
GenGasolinePTK3.3
$957.00
$3,133.52
Renogy235RNG-235P-60
$3,236.92
$4,635.48
Studer Xtender XTS 1200-24
$2,730.00
$4,506.05
Trojan SAGM 12 205
$1,740.00
$3,257.99
System
$8,663.92
$15,533.05
Networked system
The components of the networked design are shown in Table 4.
Table 4 . Components for the grid-tie system
Component
Features
Photovoltaic panel
Renogy RNG 235P
Power: 235 W
Voc: 37.08 V
Isc: 8.34 A
Type: polycrystalline silicon
Inverter
Schneider Conext SW4024
Nominal battery voltage: 24V
Input voltage range: 20 - 34V
Power: 3400 W
64
Maximum yield: 92%.
Pure sinusoidal output voltage: 120/240 Vac
The photovoltaic solar panels generate 4013 kWh per year and the grid delivers 2045
kWh/year, representing 66.2% and 33.8% of energy production respectively.
The residence is connected directly to the electricity provider's grid and to the photovoltaic
system. The grid will be delivering energy to the house, and at the moment there is enough
solar radiation on the photovoltaic panels, the inverter goes to work and delivers energy to the
grid, thus reducing the costs in the electric bill since the meters will have the function of
measuring the flow of power in and out. In the event that more energy is generated than is
consumed, the excess electrical energy will be considered as a credit that will be deducted from
the electricity consumption of the following month.
The solar array consists of 14 panels with a total installed capacity of 3.29 kW, generating an
average of 11 kWh/day or 4013 kWh/year.
Figure 6. a) Energy purchased and b) energy sold from the grid in the grid-on system.
Figure shows the energy bought and sold by the user in the electric grid. It can be seen that no
energy is purchased during the 8 to 18 hours because there is solar radiation and therefore it is
generating energy that can be sold or used by the user.
Table 5. Cost of installation, operation and maintenance and salvage value of the system
during its grid-tie system lifetime5
Components
Capital ($)
Total
Web
$0.00
$165.35
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October - December vol. 1. Num. 10 2021
Renogy 235RNG-235P-60
$3,220.00
$4,611.25
Schneider Conext SW4024
$1,600.00
$2,482.00
System
$4,820.00
$7,258.60
Comparison of results
Table 6presents a summary of the results obtained by simulating in HOMER Pro and a
comparison of these two systems.
Table 6 . Comparative results of the isolated system and the grid-connected system of the
project.
CHARACTERISTICS
ISOLATED
SYSTEM
NETWORKED SYSTEM
Components
- 14 RNG 235P
panels
- 6 Trojan SAGM
12 205 batteries
- 2 Studer Xtender
XTS 1200-24
inverters
- 1 generator PTK
GG 1/18220
- 14 RNG 235P panels
- 1 Schneider Conext SW4024 inverter
Net Present Value (NPV)
$15,533.05
$7,258.60
Energy produced
Panels: 4034
kWh/year
Generator: 713
kWh/year
Total: 4747
kWh/year
Panels: 4034 kWh/year
Network: 2045 kWh/year
Total: 6058 kWh/year
Advantages
- It is independent of
the power grid, it
- Much cheaper because fewer
components are required
66
consumes what the
system generates.
- Ideal for areas with
no access to the
power grid
- A back-up
generator can
supply the missing
demand
- No batteries required
- When the panels do not produce, the
electricity supplier supplies the
demand
Disadvantages
- The cost of the
system is high due
to the batteries.
- Battery leakage
poses high risk to
people and the
environment
- Requires a
ventilated space for
the battery bank
- Excess energy
produced is wasted
- Grid-dependent, do not operate
during power outages
- With no backup generators, you will
have no power during an outage.
Final decision
The grid-connected system is the most suitable for this project. The residence is located in the
city and has access to the electric grid, the addition of a grid-connected PV system will help
decrease consumption and therefore decrease electric bill costs.
Single-line connection diagram
Once the grid-connected system has been selected as the final design for the residence, we
proceed to represent the single-line connection diagram in Figure 2of the elements that
compose it.
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October - December vol. 1. Num. 10 2021
Figure 2 . One-line diagram of grid-connected photovoltaic installation of the residence.
Shadow simulation
The shading simulation performed with the SketchUp Pro software took into account the hours
from 7:00 am to 6:00 pm. In Figure 3, it can be seen that the photovoltaic panels are not affected
by the shadows of the panels themselves and that their spacing is adequate.
Figure 3 . Simulation of shadows of the 3D model between 7h00 and 18h00 in SketchUp Pro
software.
68
In the design of the isolated system, AGM type VRLA batteries were used for energy storage.
Due to the boom of new energy storage systems, it is convenient to perform the economic and
technical analysis of these technologies in distributed generation systems such as:
The inertial battery also known as flywheel or flying disk, which store kinetic energy of
rotation.
• Supercapacitors
• Thermal storage
• Other types of electric batteries (flow battery, metal-air, lithium-ion, etc.)
For the sake of simplicity, the study was limited to two types of photovoltaic systems. The
analysis of a hybrid system, similar to the grid-connected one, but with batteries, could be
useful in specific applications.
Conclusions
The choice of a grid-connected photovoltaic system or a stand-alone system will depend on
several factors such as economic profitability, the user's needs or the geographical location of
the project. Isolated systems are usually expensive, bulky and not very environmentally
friendly. Whereas a grid-connected system in most residential homes because they are covered
in case the system produces less or more with respect to their different energy needs.
For the design of this project, it was concluded that a grid-connected system was ideal, since
its costs are reduced by half with respect to an isolated system, it is located in an urban area
with access to the electrical grid, and it reduces the cost of electricity bills. The location of the
photovoltaic panels is of vital importance, since their performance is proportional to the amount
of solar radiation to which they are exposed, this performance will be affected by the shadows
that may be caused by objects and structures near the project area. Through a simulation of
shadows in SketchUp Pro, it was possible to analyze that the performance would decrease if
placed at a low height, so it was decided to use in an elevated structure in the form of a roof.
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