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MEDSolar Training Course
Module 3
Power Plant Design
Herminio Martínez-García
Department of Electronics Engineering
Barcelona College of Industrial Engineering (EUETIB)
Technical University of Catalonia - BarcelonaTech (UPC)
The objectives to be met in the sizing of a photovoltaic system are:
• Operate efficiently at the lowest possible cost.
• Be able to meet the expected demand for electricity
consumption.
• Match, as far as possible, the PV system to the consumption
characteristic.
• Setting the nominal voltage of the photovoltaic system.
• Proper sizing of photovoltaic module (in Wp).
• Dimensioning suitable battery (in Ah).
• Ensure proper connections and protections of the
installation.
• Proper implementation and ensure appropriate
maintenance measures.
Introduction (I)
Introduction (II)
DC Grid
(normally
lighting)
Batteries
(they accumulate the energy to
be used at times of low or no
sunshine )
AC Grid
(used to supply
different
appliances)
PV
Modules
or Panels
Inverter
(it converts the
direct current DC
into alternating
current AC)
Regulator
(it controls the
charge of
batteries, and
converters the
DC voltage from
PV modules into
another DC
voltage)
Solar collection
area (m2)
Storage capacity
(Ah)
Total losses of the
installation
Inst. amortization
& profitability
Energy demand or
electricity
consumption
(Wh/day)
Available solar
radiation energy
(MJ/m2)
Total monthly and
annual solar
production
Efficiency of PV
solar panels
Input Data Output Data
Other Data of InterestVoltages of interest
(in panels and
installation)
Introduction (III)
Dimensioning of
DC/DC controller
(A)
Dimensioning of
the DC/AC
inverter (W)
Sections of Wiring
Consumption of Electrical Equipment and Supplies (I)
When the size of a PV facility is carried out, it’s necessary to check the
consumption of all electrical, electronic and electrical appliances to be
connected to the aforementioned PV facility.
This consumption is usually stated on the nameplate of the
equipment or manufacturer’s catalog.
If you do not have these real data, approximate tables should be used.
Due to the high involved consumption, in PV facilities, it is not
recommended to use electric heating equipment such as electric
ovens, microwave, radiators, hot water washers, dryers, electric
water heaters, etc.
They may be substituted for thermal applications, that have better energy
efficiency.
In addition, we recommend using energy-efficient appliances, since
consumption, size and investment of the PV facility is reduced.
Consumption of Electrical Equipment and Supplies (II)
Information Labeling About Energy Efficiency (I)
Energy Efficiency Label. Old Labeling
Moderate or medium
energy consumption
High energy
consumption
High energy
efficiency
More efficient
Less efficient
Between 110% and 125%
Higher than 125%
Between 100% and 110%
Between 90% and 100%
Between 75% and 90%
Between 55% and 75%
Between 42% and 55%
Between 30% and 42%
Energy consumption higher than 30% of the average
Information Labeling About Energy Efficiency (II)
Examples of Energy Efficiency Label. For refrigerators and freezers.
An improved method for sizing a solar photovoltaic installation process consists
of:
• Determination of the nominal operating voltage for the system.
• Estimation of demand or overall power consumption of the facility (in
Ah/day).
• Loss assessment of photovoltaic solar installation.
• Choosing the optimum inclination of the photovoltaic panels.
• Calculation of daily total solar radiation received by month for that
angle.
• Panel model selection and determination of the electrical parameters
(nominal power, voltage, efficiency, etc.) provided.
• Calculation of the total number of modules in parallel and in series.
• Calculation of the total capacity of the storage batteries.
• Sizing regulator (DC/DC converter).
• Sizing the inverter (DC/AC converter).
• Sizing of wiring required for installation.
• Summary table of values over the 12 months.
Improved Design Guide in the Sizing of PV Systems
Application Example (I)
Autonomous PV Systems with DC and AC Loads.
Regulator
(voltage regulation subsystem)
DC Consumption
AC Consumption
Batteries
(accumulation subsystem)
Inverter
(DC into AC
conversion subsystem)
PV Modules or Panels
(generation subsystem)
Mountain house, near the Lleida Pyrenees (Spain), where conventional
electricity available is expensive by distance.
Installation consisting of:
• PV panels.
• DC/DC regulator.
• DC/AC converter.
• Storage batteries.
In the design study, we will explain the need of including a generator or a
wind turbine support.
Application Example (II)
• Determination of the nominal operating voltage for the system.
• Estimation of demand or overall power consumption of the facility (in
Ah/day).
• Loss assessment of photovoltaic solar installation.
• Choosing the optimum inclination of the photovoltaic panels.
• Calculation of daily total solar radiation received by month for that
angle.
• Panel model selection and determination of the electrical parameters
(nominal power, voltage, efficiency, etc.) provided.
• Calculation of the total number of modules in parallel and in series.
• Calculation of the total capacity of the storage batteries.
• Sizing regulator (DC/DC converter).
• Sizing the inverter (DC/AC converter).
• Sizing of wiring required for installation.
• Summary table of values over the 12 months.
Improved Design Guide in the Sizing of PV Systems
Nominal Operating Voltage.
• As it is a domestic house, we can choose nominal voltages equal
to 12 V, 24 V, 48 V or 120 V.
• We can select 24 V, in order to obtain lower section for the
wiring that connect PV panels and DC-DC regulator.
In general, it is recommended:
• 12 V: For power lower than 1.5 kW.
• 24 V: For powers between 1.5 kW and 5 kW.
• 48 V or 120 V: For power higher than 5 kW.
• > 120 V: For high power plants.
As in our design example, the consumption is near 1.5 kW (see following
consume tables), we can select a 24-V nominal voltage, in order to
minimize wiring current.
Important: Having a higher voltage, makes that wiring that connect
PV panels and regulator may have smaller section.
Determination of the Nominal Operating Voltage for the System
• Determination of the nominal operating voltage for the system.
• Estimation of demand or overall power consumption of the facility
(in Ah/day).
• Loss assessment of photovoltaic solar installation.
• Choosing the optimum inclination of the photovoltaic panels.
• Calculation of daily total solar radiation received by month for that
angle.
• Panel model selection and determination of the electrical parameters
(nominal power, voltage, efficiency, etc.) provided.
• Calculation of the total number of modules in parallel and in series.
• Calculation of the total capacity of the storage batteries.
• Sizing regulator (DC/DC converter).
• Sizing the inverter (DC/AC converter).
• Sizing of wiring required for installation.
• Summary table of values over the 12 months.
Improved Design Guide in the Sizing of PV Systems
DC Energy Consumption of the Facility (in Wh/day).
Energy Consumption of DC Equipments
Equipment, Device or
Electrical Appliance
Power
(W)
Nº
of Units
Functioning
(h/day)
Consumption
(Wh/day)
Spotlights in the
Dining Room20 1 3 60
Spotlights in the
Kitchen11 1 2 22
Spotlights in the
Bathroom11 1 1 11
Spotlights in the
Bedroom11 × 3 = 33 3 2 66
Refrigerator 60 1 12 720
TOTAL 135 879
Estimating the Demand of Electricity for the Facilities (I)
AC Energy Consumption of the Facilities (in Wh/day).
Total Energy Consumption, Etotal, of the Facility (Wh/day).
Energy Consumption of AC Equipments
Equipment, Device or Electrical
Appliance
Power
(W)
Nº
of Units
Functioning (h/day) Consumption
(Wh/day)
TV 50 1 4 200
Small
Appliances
200 1 2 400
Washing Machine 500 1 4 h @ week 285.7
TOTAL 750 885.7
879 / 885.7 /
1764.7 /
total DC AC
total
E E E Wh day Wh day
E Wh day
Estimating the Demand of Electricity for the Facilities (II)
Total Net Energy Consumption Required by the Facility, Ctotal
(Ah/day).
Connection Energy Losses, Closs (Ah/day). As a first approximation,
one may choose a value between 10% and 20%, depending on the desire
safety margin. Taking 10% in our case:
Total Energy Consumption Needed or Required, Creq (Ah/day).
1764.7 /73.53 /
24
total
total
nom
E Wh dayC Ah day
V V
107.353 /
100loss totalC C Ah day
73.53 / 7.35 / 80.88 /
req total loss
req
C C C
C Ah day Ah day Ah day
Estimating the Demand of Electricity for the Facilities (III)
• Determination of the nominal operating voltage for the system.
• Estimation of demand or overall power consumption of the facility (in
Ah/day).
• Loss assessment of photovoltaic solar installation.
• Choosing the optimum inclination of the photovoltaic panels.
• Calculation of daily total solar radiation received by month for that
angle.
• Panel model selection and determination of the electrical parameters
(nominal power, voltage, efficiency, etc.) provided.
• Calculation of the total number of modules in parallel and in series.
• Calculation of the total capacity of the storage batteries.
• Sizing regulator (DC/DC converter).
• Sizing the inverter (DC/AC converter).
• Sizing of wiring required for installation.
• Summary table of values over the 12 months.
Improved Design Guide in the Sizing of PV Systems
We can carry out an estimation of total losses of the facility, KT, thanks
to:
Being:
,
1 1 A aut
T B C R X
D max
K DK K K K K
P
Loss Estimation of the Photovoltaic Solar Facility (I)
Daily losses due to battery self-discharge,given at 20 C.
Losses due to battery efficiency.
Losses due to the inverter (DC/AC converter) efficiency (if any).
Losses due to the regulator (or
A
B
C
R
K
K
K
K
,
DC/DC converter) efficiency.
Other not considered losses (Joule efect, due to voltage drops, etc.).
Days of autonomy of the installation.
Maximum deep of discarge (DoD) (in %).
X
aut
D max
K
D
P
KA: It usually comes in the datasheets provided by the battery
manufacturer. Its default value is 0.5%. However, very common values
of 0.6% and 0.7% are also very common. The range is between 0.1% and
2%.
KB: This loss is due to the battery energy dissipated as heat due to the
chemical processes in its charge and discharge cycles. It usually has a
value of 5%, but can be chosen a value of 10% for old batteries,
strong discharges or low temperatures. The margin ranges is between
0.0% and 20%.
KC: The default value typically ranges between 5% (DC/AC converter’s
efficiency of 95%) and 20% (efficiency of 80%). The margin ranges is
between 0.0% and 40%.
KR: It usually depends on the technology used, but, if it is not known, the
default value is chosen 10% (DC/DC converter’s efficiency of 90%).
KX: A default value of 10% is chosen. The margin range is between 0.0%
and 20%.
Loss Estimation of the Photovoltaic Solar Facility (II)
Estimation of the total losses of the facility, KT:
,
1 1 A aut
T B C R X
D max
K DK K K K K
P
Loss Coefficient or Loss Parameter Practical Range
KA 0.001 – 0.020 (0.1% – 2%)
KB 0.00 – 0.20 (0.0% – 20%)
KC 0.00 – 0.40 (0.0% – 40%)
KR 0.00 – 0.40 (0.0% – 40%)
KX 0.00 – 0,20 (0,0% – 20%)
PD,max 0.10 – 0.80 (10% – 80%)
Daut 3 – 20 days
Loss Estimation of the Photovoltaic Solar Facility (III)
Daut: It is the number of consecutive days, in the absence of sunlight, that
the storage system is able to meet consumption without exceeding the
maximum depth of discharge of batteries.
It depends, among other factors, on the type of facility, climatic or
weather conditions, etc.
As a general rule, the MINIMUM autonomy of PV systems with
storage is 3 days.
Loss Estimation of the Photovoltaic Solar Facility (IV)
The number of autonomy days in the system depends on its use and
application:
• Areas with regular Sun: 3 days.
• Non-critical systems (Mediterranean climate, etc.): Between
2 and 5 days.
• Systems with irregular Sun: 5 to 7 days.
• Critical systems (professional systems): 5 to 10 days.
• Critical areas, with little sunshine: 15 days.
Loss Estimation of the Photovoltaic Solar Facility (V)
Necessary days of autonomy for critical and non-critical PV systems
operation vs. minimum available peak sun hours.
Loss Estimation of the Photovoltaic Solar Facility (VI)
(PSH)
A linear approximation to the data in previous Fig. yields the following
equations for estimating necessary storage days, based on minimum
average peak sun hours over the year, PSH:
… providing that PSH>1 h.
However, we can find tables showing (for instance, according to the
Spanish provinces) the days of autonomy.
These values are, in some cases, oversized.
1.9 18.3 for critical applications.
0.48 4.58 for non-critical applications.
aut
aut
D PSH
D PSH
Loss Estimation of the Photovoltaic Solar Facility (VII)
Depth of discharge (DOD) of a battery is defined as the percentage of
its capacity that has been “removed” from it, compared to full-charge
capacity.
PD,max is the maximum DOD allowed before disconnecting the regulator
to prevent from possible problems and to lengthen its lifetime.
It depends, among other factors, on the type or battery technology:
• Nickel-cadmium batteries (Ni + Cd): 1%.
• Lead batteries (or lead-acid) (Pb): 40%.
• Lead-calcium batteries (Pb + Ca): 50%.
• Lead-antimony batteries (Pb + Sb): 70%.
You should avoid, if possible, very deep discharge (greater than 60%
or 70%).
In any case, the maximum recommended for PD,max is 80%.
Loss Estimation of the Photovoltaic Solar Facility (VIII)
PD,max is the maximum discharge allowed to the battery before
disconnecting the regulator to protect it.
The maximum depths of discharge that are usually considered for a
daily cycle (maximum daily DOD) are around 15-20%.
In the case of seasonal cycle, which is the maximum number of days
that a battery can be discharged without receiving enough solar
radiation on the modules, is around 4-15 days, and a depth of discharge
of approximately 70%.
Loss Estimation of the Photovoltaic Solar Facility (IX)
Estimation of the total losses of the facility, KT:
,
1 1 A aut
T B C R X
D max
K DK K K K K
P
Loss Coefficient or Loss Parameter Practical Range
KA 0.001 – 0.020 (0.1% – 2%)
KB 0.00 – 0.20 (0.0% – 20%)
KC 0.00 – 0.40 (0.0% – 40%)
KR 0.00 – 0.40 (0.0% – 40%)
KX 0.00 – 0,20 (0,0% – 20%)
PD,max 0.10 – 0.80 (10% – 80%)
Daut 3 – 20 days
Loss Estimation of the Photovoltaic Solar Facility (X)
Total Energy Consumption Needed or Required Considering the
losses, C’req (Ah/day). In the case at hand:
73.53 / 7.35 / 80.88 /
80.88 /' 147.44 /
0.549
req
req
req
T
C Ah day Ah day Ah day
C Ah dayC Ah day
K
,
1 1 A aut
T B C R X
D max
K DK K K K K
P
0.005 12 days
1 0.05 0.15 0.10 0.10 1 0.5490.7
TK
Loss Estimation of the Photovoltaic Solar Facility (XI)
• Determination of the nominal operating voltage for the system.
• Estimation of demand or overall power consumption of the facility (in
Ah/day).
• Loss assessment of photovoltaic solar installation.
• Choosing the optimum inclination of the photovoltaic panels.
• Calculation of daily total solar radiation received by month for that
angle.
• Panel model selection and determination of the electrical parameters
(nominal power, voltage, efficiency, etc.) provided.
• Calculation of the total number of modules in parallel and in series.
• Calculation of the total capacity of the storage batteries.
• Sizing regulator (DC/DC converter).
• Sizing the inverter (DC/AC converter).
• Sizing of wiring required for installation.
• Summary table of values over the 12 months.
Improved Design Guide in the Sizing of PV Systems
Selection of the Angle of Inclination of the PV Panels.
• We can choose to set an “empirical” inclination that guarantees
plenty of sunlight on photovoltaic panels; for example, 60º.
Other alternatives are to perform any of the methods developed.
The best known are:
• ‘Critical month criterion’. It attempts to optimize the
consumption/radiation ratio in each month, and keep the data
of the worst month.
• ‘Annual maximum energy harvesting criterion’. It aims to
optimize the consumption/radiation relationship, not in the
critical month, but over a year, taking into account the annual
average global solar radiation.
Choosing the Optimum Inclination of the Photovoltaic Panels
Inclination or tilt angle of a PV module:
Solar radiation
Inclination
(tilt angle)
PV
module
Horizontal ground
Determination of the Suitable Tilt Angle for Photovoltaic Panels (I)
Some guidelines recommend an inclination equal to the
latitude, obtaining a value of annual average global solar
radiation slightly higher.
However, it is advisable to increase this inclination 10º, since
the distribution of solar contributions in the worst months
(winter) is better.
Determination of the Suitable Tilt Angle for Photovoltaic Panels (II)
sunlight in
winter
sunlight in
summer
Moreover, the inclination is calculated taking into account the period of
use of the facility. It is recommended that:
• 10º higher than the latitude to use facilities throughout the year
(e.g., for solar collectors in domestic hot water, DHW).
• 5º below the latitude to use facilities in summertime (e.g.,
outdoor pools or season hotels).
• 15º – 20º higher than the latitude to facilities for exclusive use
in winter season (e.g., ski resorts).
Minor differences in slope do not significantly influence the total annual
energy, but can determine a higher or lower average global solar
radiation in the winter months.
Determination of the Suitable Tilt Angle for Photovoltaic Panels (III)
In this case, the calculation of the optimum inclination of the receiving
surface will be such that the energy consumption/radiation ratio is
optimized for every month.
The procedure is as follows:
• Firstly, we must have an array with the values of global solar
radiation received for each month (usually measured in
kWh/m2), and for different inclinations.
• Secondly, from previous table, daily average
consumption/global solar radiation ratio is determined; i.e.,
the daily average consumption for each month, will be divided
by the values of each cell of previous table.
Optimum PV Panel Tilt Angle According to Critical Month Criterion (I)
For instance, for a particular place, we can have the following global
solar radiation received for each month and for different inclinations:
Optimum PV Panel Tilt Angle According to Critical Month Criterion (II)
Month
If we supposed a daily average consumption Lmd=3000 Wh/day, we have
this new table:
Optimum PV Panel Tilt Angle According to Critical Month Criterion (III)
Month
Then, we have to do the following two calculations:
• Step 1: For each tilt angle, the maximum ratio will be taken
up, thereby obtaining the critical month (for each given tilt
angle).
• Step 2: From all previous maximum values, we chose the
minimum of them, so that solar energy harvesting in the
critical month is maximized…
• … That is, it is chosen the optimum inclination for the worst
month, so that the tilt angle for the worst month is optimized.
Optimum PV Panel Tilt Angle According to Critical Month Criterion (IV)
Therefore, it is example, the optimum tilt angle for the PV modules
should be 40º.
Optimum PV Panel Tilt Angle According to Critical Month Criterion (V)
Month
Optimum Inclination According to Annual Maximum Energy Harvesting Criterion (I)
In this case, the aim is to determine the optimal inclination of the
receiving surface so that the consumption/radiation ratio is optimized,
not for critical month, but over a year.
We will proceed very similarly to the previous case, except that we take
into account only the overall annual average radiation (the average of the
twelve monthly values) for each inclination, and consumption, which in
this case is the annual average consumption.
Continuing with data from the previous example, the source table in this
case is similar to the following:
Annual
Average
The consumption/radiation ratio will be:
Finally, the optimum value will be the minimum:
The optimal tilt angle (inclination) will be, using this criterion, 10º.
Optimum Inclination According to Annual Maximum Energy Harvesting Criterion (II)
Annual
Average
Annual
Average
• Determination of the nominal operating voltage for the system.
• Estimation of demand or overall power consumption of the facility (in
Ah/day).
• Loss assessment of photovoltaic solar installation.
• Choosing the optimum inclination of the photovoltaic panels.
• Calculation of daily total solar radiation received by month for
that angle.
• Panel model selection and determination of the electrical parameters
(nominal power, voltage, efficiency, etc.) provided.
• Calculation of the total number of modules in parallel and in series.
• Calculation of the total capacity of the storage batteries.
• Sizing regulator (DC/DC converter).
• Sizing the inverter (DC/AC converter).
• Sizing of wiring required for installation.
• Summary table of values over the 12 months.
Improved Design Guide in the Sizing of PV Systems
Determination of Monthly Solar Radiation for the Inclination
Obtained.
• As in the case studied for solar thermal systems (CENSOLAR
tables).
• Tables using solar radiation as a function of inclination.
• http://re.jrc.ec.europa.eu/pvgis/
Anyway, differences between these methods in order to obtain solar
radiation should be minimal.
Sources for Determination of Solar Radiation on a Geographic Point
Irradiance and Solar Radiation
The irradiance is the instantaneous power of solar radiation received per
unit area, expressed in the corresponding SI unit (W/m2).
The irradiation or solar radiation (H) is the energy incident per unit area
in a given time.
The irradiation H corresponds to the integration of the irradiance in a
given period:
If the second one is considered constant, we have:
The units most commonly used for irradiation H are the kWh/m2 or
MJ/m2.
Over one day, as shown in tables, H is expressed in kWh/m2/day, or
MJ/m2/day.
H Irradiance t
1
0
t
H Irradiance dt
Orientation: South
Units: KJ/m2/day
Place: Lleida (Spain)
Latitude: 41º 41
Calculation of Solar Radiation Monthly Available (Method A)
In the particular case considered here, and using book tables [Tobajas-
2008], for an inclination of 60º, we have the following solar radiation
values:
http://re.jrc.ec.europa.eu/pvgis/
Calculation of Solar Radiation Monthly Available (Method B) (I)
Calculation of Solar Radiation Monthly Available (Method B) (II)
Calculation of Solar Radiation Monthly Available (Method B) (III)
Calculation of Solar Radiation Monthly Available (Method B) (IV)
Calculation of Solar Radiation Monthly Available (Method B) (V)
Correction of the Incident Solar Energy on Solar Panels (I)
The resulting value of E may be corrected to take account of
the actual orientation of the panels.
If the deviation in orientation of the panels is less than 20°,
it is not necessary to make any corrections.
If the deviation is greater than 20º (but always less than
70º), the power available by the PV modules must be
reduced in value that can be estimated, approximately, with
the following expression:
0.3Orientation Losses 0.71 0.29 cos 0.95
It is the inclination angle of the PV modules (in º).
It is the deviation of the orientation of the PV panel
relative to the South direction (in º).
South
Direction
Correction of the Incident Solar Energy on Solar Panels (II)
It is the inclination angle of the PV modules (in º).
It is the deviation of the orientation of the PV panel
relative to the South direction (in º).
0.3Orientation Losses 0.71 0.29 cos 0.95
For example, if the PV panels’ inclination is α=51º, and the
deviation of the orientation of the panels, relative to the
South, is β=30º, then we have:
It is the inclination angle of the PV modules (in º).
It is the deviation of the orientation of the PV panel
relative to the South direction (in º).
Correction of the Incident Solar Energy on Solar Panels (III)
0.3
0.3
Orientation Losses 0.71 0.29 cos 0.95
0.71 0.29 cos 0.95 30 51
0.71 0.29 0.04724 0.6973
• Determination of the nominal operating voltage for the system.
• Estimation of demand or overall power consumption of the facility (in
Ah/day).
• Loss assessment of photovoltaic solar installation.
• Choosing the optimum inclination of the photovoltaic panels.
• Calculation of daily total solar radiation received by month for that
angle.
• Panel model selection and determination of the electrical
parameters (nominal power, voltage, efficiency, etc.) provided.
• Calculation of the total number of modules in parallel and in series.
• Calculation of the total capacity of the storage batteries.
• Sizing regulator (DC/DC converter).
• Sizing the inverter (DC/AC converter).
• Sizing of wiring required for installation.
• Summary table of values over the 12 months.
Improved Design Guide in the Sizing of PV Systems
Selection of the PV Module. For instance, the commercial model
ATERSA’s A-150M.
Selection of the PV Module for the Application (I)
Nominal Power (W)
Maximum Power Point Current (Imp)
Maximum Power Point Voltage (Vmp)
Short-Circuit Current (Isc)
Open-Circuit Voltage (Voc)
Energy Provided by the Group of Photovoltaic Modules (PV
Generator). The energy (in Ah/día) provided by the array of
photovoltaic modules, Emod, is given by:
Being:
( )mod mod mpE I PSH
Energy provided by the PV module (in / ).
Efficiency of the PV module. It can be chosen a typical valuen between 85% and 95%.
Current at the module's MPP (in ).
Peak solar hou( rs)
mod
mód
mp
E
I
P
Ah día
A
SH
(in ) for an inclination of the PV module.h
Selection of the PV Module for the Application (II)
The parameter ηmod represents an overall loss factor that provides
reduction in the energy provided by such factors as:
• Dirt of the photovoltaic module and opacity of the glass.
• Reflection losses at times of very oblique incidence.
• Effect losses wiring.
• Etc.
For photovoltaic panels ...
• For monocrystalline and polycrystalline Si, ηmod can be caught
between 90% and 95%.
• For amorphous Si, between 65% and 85%.
Selection of the PV Module for the Application (III)
The ‘peak solar hour’ or ‘peak sun hour’ (PSH) is a parameter that
measures the “effective” or “net” solar radiation, and is defined as the
time in hours of a hypothetical constant irradiance of 1000 W/m2.
The PSH of a locality is the number of hours that should have an
irradiance of 1000 W/m2 to meet the real daily energy incident in
that locality.
For example, a radiation energy or equal to 3500 Wh/day equals an
irradiance of 1000 W for 3.5 h; so that PSH=3.5.
The Peak Solar Hour (PSH) for Obtaining the Provided Energy (I)
If a graph is shown of incident radiation on the earth’s surface, it appears
that levels vary throughout the day.
Graphically, the PSH is interpreted as a function of constant value that
delimits the same area as aforementioned distribution.
1000 W/m2
The Peak Solar Hour (PSH) for Obtaining the Provided Energy (II)
Peak Solar Hours
Irra
dia
nc
e
Day hours
1 PSH is equal to 3.6 MJ/m2 or, what is the same, 1 kWh/m2, as shown
in the following conversion:
After obtaining the value of the PSH, we can calculate how much daily
power theoretically we can get from the PV panels multiplying the power
by the PSH, although different correction factors must also be
considered.
Moreover, we must also have into account that, depending on the angle
of the PV panels, the amount of PSH we will vary.
We can get better performance depending on it.
2 2
1000 3600 1 /1 1 3.6
1 1
W s J s MJPSH h
h Wm m
The Peak Solar Hour (PSH) for Obtaining the Provided Energy (III)
From the solar radiation, H (expressed in kJ/m2/day), we have the
equivalent PSH, at a certain inclination α, which can be obtained as:
2/( ) ( ) 0.0239 0.0116
kJ mPSH H
day
2
2
2 2
/( )
/ 1( ) ( )
3600 3600
kJ mH
daykJ m PSHPSH H
day kJ m kJ m
2
2
2 2
/( )
/ 1( ) ( )
1000 1000
W mH
dayW m PSHPSH H
day W m W m
The Peak Solar Hour (PSH) for Obtaining the Provided Energy (IV)
In the present example, the monthly PSH can be obtained from the daily
solar radiation as:
/day
The Peak Solar Hour (PSH) for Obtaining the Provided Energy (V)
Orientation: South
Units: Kj/m2/day
Place: Lleida (Spain)
Latitude: 41º 41
Month Jan. Feb. Mar. Apr. May. Jun. Jul. Aug. Sep. Oct. Nov. Dec. Avg.
H(0º)
kJ/m2
6.078 12.168 15.592 19.226 21.954 24.262 24.638 21.340 16.740 11.980 6.302 4.006
H(60º)
kJ/m2
11.148 20.092 19.136 18.106 17.258 17.496 18.406 18.694 18.516 17.234 10.652 8.314
HSP(60º)
(h/day)3,097 5,581 5,316 5,029 4,794 4,860 5,113 5,193 5,143 4,787 2,959 2,309 4,515
• Determination of the nominal operating voltage for the system.
• Estimation of demand or overall power consumption of the facility (in
Ah/day).
• Loss assessment of photovoltaic solar installation.
• Choosing the optimum inclination of the photovoltaic panels.
• Calculation of daily total solar radiation received by month for that
angle.
• Panel model selection and determination of the electrical parameters
(nominal power, voltage, efficiency, etc.) provided.
• Calculation of the total number of modules in parallel and in
series.
• Calculation of the total capacity of the storage batteries.
• Sizing regulator (DC/DC converter).
• Sizing the inverter (DC/AC converter).
• Sizing of wiring required for installation.
• Summary table of values over the 12 months.
Improved Design Guide in the Sizing of PV Systems
Possible Interconnections of Photovoltaic Modules
If the total set voltage exceeds 75 VDC, notice that it could be dangerous
for people.
Parallel connection.
Series connection. Mixed connection.
Number of Photovoltaic Modules in Parallel, nPP. The required
number of panels in parallel will be the ratio between the energy
consumption required to meet the needs Creq (in Ah/day), divided by the
energy (also in Ah/day) from the photovoltaic panel set, Emod:
Being:
' '
( )
req req
PP
mod mod mp avg
C Cn
E I PSH
Nº of PV panels connected in parallel to meet energy needs.
Total energy consumption required to cover energy needs (in / ).
Energy provided by a single PV module (in / ).
Eff
'
PP
req
mod
mod
A
n
C h day
AE h día
iciency of the PV module. It can be select a value between 85% and 95%.
Current at the MPP of the PV module (in ).
Annual average PSH (in ) for the inclination angle o( ) f the PV module.
mp
avg
I
P
A
S hH
Determining the Number of Photovoltaic Modules in Parallel (I)
Taking the average value of PSH, PSHavg, and not the monthly value, and
considering a photovoltaic panel ηmod=90%, the required number of
panels in parallel will be:
With that, we need 9 panels in parallel.
When the number of rows in parallel is not an integer, it is
recommended to round up, except in those cases where the result
approximates closely to the nearest integer number.
' 147.44 /8.25 modules
( ) 0.9 4.40 4.515 /
8.25 modules 9 modules
req
PP
mód mp avg
PP PP
C Ah dayn
I PSH A h day
n n
Determining the Number of Photovoltaic Modules in Parallel (II)
Number of Photovoltaic Modules in Series, nPS. The required number
of panels connected in series will depend on system nominal voltage,
Vnom, and the PV module MPP (maximum power-point) voltage, Vmp:
Being:
nom
PS
mp
Vn
V
Nº of panels connected in series to meet the nominal voltage of the system.
Nominal voltage of the system (in ).
MPP voltage provided by a single PV module (in ).
PS
nom
mp
n
V
V
V
V
Determining the Number of Photovoltaic Modules in Series (I)
The number of modules in series is calculated based on the nominal
system voltage, Vnom, and the voltage at the maximum power point
(MPP), Vmp, of the selected PV module:
Thus, following with the example, we need a single panel in series.
240.71 panels 1 panel
34
nom
PS PS
mp
V Vn n
V V
Determining the Number of Photovoltaic Modules in Series (II)
Total number of PV modules, ntotal. It will be the product of the number
of panels in parallel, nPP, by the number of panels in series, nPS:
In our case:
Therefore, the connectivity scheme of the photovoltaic modules required
for the facility is designed as shown:
9 1 9 panelstotal PP PSn n n
total PP PSn n n
Determining the Total Number of Photovoltaic Modules of the Facility
To the DC-
DC
regulator
PV module
block 1
PV module
block 2
PV module
block 3
PV module
block 9
+
–
• Determination of the nominal operating voltage for the system.
• Estimation of demand or overall power consumption of the facility (in
Ah/day).
• Loss assessment of photovoltaic solar installation.
• Choosing the optimum inclination of the photovoltaic panels.
• Calculation of daily total solar radiation received by month for that
angle.
• Panel model selection and determination of the electrical parameters
(nominal power, voltage, efficiency, etc.) provided.
• Calculation of the total number of modules in parallel and in series.
• Calculation of the total capacity of the storage batteries.
• Sizing regulator (DC/DC converter).
• Sizing the inverter (DC/AC converter).
• Sizing of wiring required for installation.
• Summary table of values over the 12 months.
Improved Design Guide in the Sizing of PV Systems
Nominal Capacity and Discharge Rate of a Battery (I)
The battery capacity is the amount of electricity that can supply
(measured in Ah), and it is given under a discharge rate.
Therefore, a battery capacity is determined based on the duration of
discharge, and this value is provided by the manufacturer for a duration
of 10 h (C10). This value is often called ‘nominal capacity’.
However, according to some public European Institutions, the ‘nominal
capacity’ is the amount of charge that can be drawn from a battery in 20
h, measured at a temperature of 20 °C, until the voltage between its
terminals reaches 1.8 V/battery cell.
According to these public European Institutions, for other rates can be
used the following empirical relationships:
• C100/C20 ≈ 1.25.
• C40/C20 ≈ 1.14.
• C20/C10 ≈ 1.17.
The parameters that define the capacity of a battery are:
• Discharge time (h).
• Discharge current (A).
• Operating temperature (°C).
• Final voltage (V).
The ‘charge rate’ (or ‘discharge rate’) is the ratio Cn/I (measured in
hours).
For example, a battery with Cn=300 Ah, that provides a discharge current
of 5 A, has a discharge rate of 60 h ...,
whereas if it provides 10 A, the discharge rate is 30 h.
Therefore:
disc discC t I
Nominal Capacity and Discharge Rate of a Battery (II)
However, previous equation is completely ideal:
In the practice, we have the named Peukert equation or relation
(originally introduced by the German W. Peukert in 1897 for lead-acid
batteries, and defines one of the most important parameters to evaluate
the performance of a battery):
… where the parameter ‘k’ is the named Peukert constant or
coefficient, that depends on the battery type used.
Typically, it can be selected k=1.2, but it is important to know the
manufacturing technology of the battery.
disc discC t I
k
disc discC t I
disc k
disc
Ct
I
The larger the parameter ‘k’ and current, we
get further away from the ideal value tdisc.
Nominal Capacity and Discharge Rate of a Battery (III)
For instance:
• k = 1.05 – 1.15 for VRSLAB AGM batteries.
• k = 1,10 – 1.25 for gel batteries.
• k = 1.20 – 1.60 for flooded batteries.
AGM (VRLA): In AGM (Absorbed Glass Mat) batteries, the electrolyte
is contained in the absorbent fiberglass between the plates. This
technology based on regulated valve, has low maintenance because it
requires no water refill.
Gel (VRLA): In gel batteries (technology dryfit), the electrolyte is
contained in a gel suspension between the plates. This valve regulated
technology is low maintenance because it requires filling of water.
Liquid electrolyte or lead open: Lead-acid batteries have elements with
liquid electrolyte, and they are available in flat and tubular plate with a
wide variety of plate sizes.
Nominal Capacity and Discharge Rate of a Battery (IV)
Autonomous PV facilities are usually provided with an autonomy
between 5 and 15 days, approximately.
Therefore, in PV applications, the battery capacity is defined by its
ability to deliver a given charge in 20 h, 100 h, or 120 h, at 25 °C,
called C20, C100, and C120, respectively.
The more intense the discharge of a battery, less energy is able to
provide.
Fortunately, in PV systems, no aggressive discharges are required, but
rather progressive.
Thus, batteries are often used to discharge in 100 h (C100).
In addition, capacities are usually specified with discharge times of 100
h, because the autonomy of 5 or more days, the discharge would occur,
for example, in 24 h/day × 5 days = 120 h.
Thus, by default, 100 h is then chosen (C100).
Nominal Capacity and Discharge Rate of a Battery (V)
Notice that the capacity of a battery depends also on the temperature,
apart from the discharge rate.
The battery capacity decreases due to the temperature, especially
for T<20 °C.
The reference temperature to give the battery capacity is usually 25 ºC.
Thus, if the temperature is different, it should be corrected.
An approach to the correction factor in order to obtain a discharge
capacity for a temperature different to 25 °C is given by the following
table:
Temperature (in ºC) –20 –10 0 +10 +20 +25 +30 +40
Correction factor for a
discharge rate of 120 h0.58 0.72 0.83 0.91 0.98 1.00 1.02 1.05
Nominal Capacity and Discharge Rate of a Battery (VI)
1160
T
Tk
If the average operation
temperature is below 20 ºC, it
is recommended to correct
calculated nominal capacity,
by dividing its value by a
factor kT:
Nominal Capacity and Discharge Rate of a Battery (VII)
Temperature (in ºC) –20 –10 0 +10 +20 +25 +30 +40
Correction factor for a
discharge rate of 120 h0.58 0.72 0.83 0.91 0.98 1.00 1.02 1.05
% Capacity
Temperature (ºC)
Dependency of the capacity vs. temperature
Calculating the Total Capacity of Storage Batteries. It is determined
by the needs of the system, taking into account the days of autonomy,
according to:
Where:
,
'100
req aut
alm
D max
C DC
P
,
Nominal capacity of the accumulation system (in ).
Total energy consumption required to cover energy needs (in / ).
Days of autonomy for the PV system.
Maximum depth of disc
'
h
alm
req
aut
D max
Ah
Ah a
D
P
d y
C
C
arge (in %).
Calculation of the Required Accumulation System (I)
Nº of Batteries in Series, nBS. It is determined as a function of the
nominal voltage of the system, and the nominal voltage provided by a
single battery.
Nº de Batteries in parallel, nBP. It is determined as a function of the
total capacity of the accumulation system, and the nominal capacity
provided by a single battery:
Where:,
nom
BS
bat nom
Vn
V
,
Nº of batteries connected in series to obtain the nominal voltage of the system.
Nominal voltage of the installation (in ).
Nominal voltage of a single battery (in ).
Nº of batter
BS
nom
bat nom
BP
V
V
n
V
V
n
,
ies connected in parallel to provide the required consumption.
Nominal capacity of the accumulation system (in ).
Nominal capacity of a single battery (in ).
alm
bat nom
hC
C
A
Ah
,
alm
BP
bat nom
Cn
C
Calculation of the Required Accumulation System (II)
In the case that we have, for a DOD of 70%, we have:
Thus, we need an accumulation system with a 24-V nominal voltage, and
a total capacity around 2500 Ah (approximately).
Choosing a battery model with enough capacity, as the model 2 YS 31P
from the manufacturer Surrette/Rolls, with 2430 Ah @ 20 h, and a
nominal voltage of 2 V, we will need 1 single battery in parallel, and 12
batteries in series:
,
' 147.44 / 12100 2527.54
0.7
req aut
alm
D max
C D Ah day daysC Ah
P
,
2412 battery
2
nom
BS
bat nom
V Vn
V V
,
2527.541.04 1 battery
2430
alm
BP BP
bat nom
C Ahn n
C Ah
Calculation of the Required Accumulation System (III)
Calculation of the Required Accumulation System (IV)
To the
DC-DC
regulador
(24 V)
Battery 1
(2 V)
+
–
Battery 2
(2 V)
Battery 12
(2 V)
Battery subsystem connectivity scheme required for the designed PV
facility, consisting of 12 batteries, each of 2 V.
Calculation of the Required Accumulation System (V)
When the voltage across the battery is the same as that of a basic cell,
typically from 2 V, the battery is often called ‘element’.
When the accumulation subsystem is formed by a set of elements, these
must be connected in series and/or parallel to obtain the voltage and/or
the storage capacity required.
Batteries that are not single ‘elements’, often have a typical voltage of 12
V across its terminals, and are known as ‘monoblock’ or simply
‘batteries’.
In a similar way that elements, type ‘monoblock’ batteries must be
connected in series and/or parallel in order to obtain the voltage and/or
storage capacity required.
Calculation of the Required Accumulation System (VI)
The most recommended kind of batteries for this type of PV systems is
lead-acid stationary, with cells of 2 V each.
They are arranged in series to complete the typical voltages of 12 V, 24
V, 48 V or more, which will be adequate in each case and application.
In addition, they will be associated in parallel to obtain the total required
capacity.
These batteries can stay charged longer periods of time, and they
withstand deep discharges sporadically.
Calculation of the Required Accumulation System (VII)
Calculation of the Required Accumulation System (VIII)
• Determination of the nominal operating voltage for the system.
• Estimation of demand or overall power consumption of the facility (in
Ah/day).
• Loss assessment of photovoltaic solar installation.
• Choosing the optimum inclination of the photovoltaic panels.
• Calculation of daily total solar radiation received by month for that
angle.
• Panel model selection and determination of the electrical parameters
(nominal power, voltage, efficiency, etc.) provided.
• Calculation of the total number of modules in parallel and in series.
• Calculation of the total capacity of the storage batteries.
• Sizing regulator (DC/DC converter).
• Sizing the inverter (DC/AC converter).
• Sizing of wiring required for installation.
• Summary table of values over the 12 months.
Improved Design Guide in the Sizing of PV Systems
The regulator controls the charging of the storage subsystem (batteries)
from the PV array, and its discharge to the load.
The performance characteristics that define a regulator or DC/DC
converter are:
• The nominal DC output voltage (in V).
• The nominal input current from the generator (in A).
• The nominal output current to the load (in A).
• The efficiency at nominal power (in %).
Sizing of the Required DC-DC Regulator (I)
Sizing of the DC-DC Regulator. The regulator is determined by the
maximum current supplied by PV solar panels.
The maximum current delivered by the array of PV modules is the
controller input (considering a security increase of 20% –safety
coefficient of 1.2–):
Being:
1.2G PP mpI n I
Current at the MPP provided by a PV module (in ).
Efficiency of the PV module. It can be selected a typical value between 85% and 95%.
Maximum power provided by the PV module (in ).
Vo
mp
mod
mp
mp
I
P
V
A
W
ltage at the MPP provided by the PV module (in ).
Maximum current provided by the PV array (in ).
Nº of PV modules connected in parallel to cover the facility's needs.
G
PP
V
AI
n
mod mp
mp
mp
PI
V
Sizing of the Required DC-DC Regulator (II)
It should be taken into account the total load current from the known
powers:
Where:
If there are no efficiency data for the inverter, an acceptable estimation is
85%.
Total load power (in ).
Total DC-load power (in ).
Total AC-load power (in ).
Nominal DC voltage of the system (in ).
Total load current (in ).
Efficency of the inverter or
total
DC
AC
nom
L
inv
P
P
P
V
W
W
W
V
AI
DC/AC converter (in %).
DC AC
L
nom inv nom
P PI
V V
total DC ACP P P
Sizing of the Required DC-DC Regulator (III)
From these two currents, the maximum of both will be that the regulator
must support:
Sizing of the Required DC-DC Regulator (IV)
,reg G LI max I I
DC Energy Consumption of the Facility (in Wh/day).
Energy Consumption of DC Equipments
Equipment, Device or
Electrical Appliance
Power
(W)
Nº
of Units
Functioning
(h/day)
Consumption
(Wh/day)
Spotlights in the
Dining Room20 1 3 60
Spotlights in the
Kitchen11 1 2 22
Spotlights in the
Bathroom11 1 1 11
Spotlights in the
Bedroom11 × 3 = 33 3 2 66
Refrigerator 60 1 12 720
TOTAL 135 879
Sizing of the Required DC-DC Regulator (V)
AC Energy Consumption of the Facilities (in Wh/day).
Total Energy Consumption, Etotal, of the Facility (Wh/day).
Energy Consumption of AC Equipments
Equipment, Device or Electrical
Appliance
Power
(W)
Nº
of Units
Functioning (h/day) Consumption
(Wh/day)
TV 50 1 4 200
Small
Appliances
200 1 2 400
Washing Machine 500 1 4 h @ week 285.7
TOTAL 750 885.7
879 / 885.7 /
1764.7 /
total DC AC
total
E E E Wh day Wh day
E Wh day
Sizing of the Required DC-DC Regulator (VI)
In our example, these values give:
Or we must select a regulator that can support 47.52 A at its input
terminals and 42.39 A at its output.
If necessary, we can add different regulators, connected in groups of PV
panels (all of the same model).
1.2 1.2 9 4.40 / 47.52G PP mpI n I panels A panel A
135 7505.63 36.76 42.39
24 0.85 24
DC AC
L
nom inv nom
P P W WI A A A
V V V V
, 47.52 , 42.39 47.52reg G LI max I I max A A A
Sizing of the Required DC-DC Regulator (VII)
• Determination of the nominal operating voltage for the system.
• Estimation of demand or overall power consumption of the facility (in
Ah/day).
• Loss assessment of photovoltaic solar installation.
• Choosing the optimum inclination of the photovoltaic panels.
• Calculation of daily total solar radiation received by month for that
angle.
• Panel model selection and determination of the electrical parameters
(nominal power, voltage, efficiency, etc.) provided.
• Calculation of the total number of modules in parallel and in series.
• Calculation of the total capacity of the storage batteries.
• Sizing regulator (DC/DC converter).
• Sizing the inverter (DC/AC converter).
• Sizing of wiring required for installation.
• Summary table of values over the 12 months.
Improved Design Guide in the Sizing of PV Systems
Performance characteristics that define an inverter or DC/AC converter
are:
• Output waveform (sinusoidal, rectangular, trapezoidal, etc.).
• Nominal power (in kW).
• Nominal DC input voltage (in V).
• Nominal AC output voltage (in V).
• The operating frequency (in Hz).
• Efficiency at nominal power (in %).
The input voltage to the inverter is NOT always constant; thus it should
be able to convert different DC voltages within a certain range (about
15%).
The nominal power should be slightly higher than the maximum power
demanded by the output load.
If it is much higher than the demanded by the load, the converter
efficiency will drop significantly.
Sizing of the Required DC-AC Inverter (I)
In general, we can use the following expression for the sizing of the
inverter:
Where:
If there is no efficiency data, an acceptable estimated value is 85%.
AC
inv
inv
PP
Power required for the DC/AC converter (in ).
Total power consumed by the AC loads (in ).
Efficiency of the inverter (en %).
inv
AC
inv
W
P W
P
Sizing of the Required DC-AC Inverter (II)
Critical efficiency
region
Optimal efficiency
region
Sizing of the Required DC-AC Inverter (III)
The nominal power should be
slightly higher than the maximum
power demanded by the output load.
If it is much higher than the
demanded by the load, the converter
efficiency will drop significantly.
Sizing of the Required DC-AC Inverter (IV)
Sizing of the Required DC-AC Inverter (V)
Sizing of the Required DC-AC Inverter (VI)
In our example case, we have:
Thus, we need an inverter of 1 kW, approximately.
750882.35
0.85
AC
inv
inv
P WP W
Sizing of the Required DC-AC Inverter (VII)
• Determination of the nominal operating voltage for the system.
• Estimation of demand or overall power consumption of the facility (in
Ah/day).
• Loss assessment of photovoltaic solar installation.
• Choosing the optimum inclination of the photovoltaic panels.
• Calculation of daily total solar radiation received by month for that
angle.
• Panel model selection and determination of the electrical parameters
(nominal power, voltage, efficiency, etc.) provided.
• Calculation of the total number of modules in parallel and in series.
• Calculation of the total capacity of the storage batteries.
• Sizing regulator (DC/DC converter).
• Sizing the inverter (DC/AC converter).
• Sizing of wiring required for installation.
• Summary table of values over the 12 months.
Improved Design Guide in the Sizing of PV Systems
An improper sized wiring of the electrical circuit leads:
• A voltage drop excessive across the wiring. It will increase the losses
in the system.
• A temperature increase in the wiring. It will cause a fire hazard, and a
deterioration of insulating materials that will involve a risk of short
circuits.
In PV facilities, two different wiring must take into account:
• Wiring for DC circuitry. Because we usually have low voltages,
currents by wiring are greater than in 230 V-AC circuits. Thus, these
cables are typically thick, especially for 12-V installations.
• Wiring for AC circuitry. Although we have high voltages (230 V), the
currents through the wiring is lower than in the DC section. In addition,
it could be added cos(φ) for reactive loads (motors, pumps, etc.).
Sizing Wiring Required for the Photovoltaic Facility (I)
Conditions that the wiring sizing must meet:
• Maximum voltage drop. Limited by national regulations.
• Heating of the conductor at the maximum allowable current.
The maximum admissible temp. will be: T=70 °C for
thermoplastic insulation, and T=90 °C for thermosets.
• Short circuit current. This current should not exceed the
maximum allowable temp.
In a general case, the conductor section that simultaneously meets the
three conditions above must be installed in the calculated line.
However, in a PV facility, the 3rd condition is not applicable because the
PV panels self-limiting its maximum current value to ISC.
In addition, ISC is the maximum permissible current value to meet the 2nd
condition.
Sizing Wiring Required for the Photovoltaic Facility (II)
The resistance of an power line, Rlin, and its section, S, may be obtained
by following expressions:
Where:
2 1 2lin
U L LR
I S S
2
Total electrical resistance ("round trip") of the lines (in ).
Total voltage drop of the line (in ).
Current flowing through the line (in ).
Resistivity of the electrical material (in
lin
V
A
m
R
U
m
I
2
2
/ ).
Conductivity of the electrical material (in /( )).
Wiring lenght (only "one way") (in ).
Wiring section (in ).
L
m
m m
m
S
m
mm
2LI
SU
Sizing Wiring Required for the Photovoltaic Facility (III)
The resistivity of Cu and Al, at 20 °C, are, respectively:
• ρCu=0.0168 Ω·mm²/m ~ 0.0175 Ω·mm²/m.
• ρAl=0.0265 Ω·mm²/m.
And the conductivity of Cu and Al, also at 20 ° C, are respectively:
• σCu=59.5 m/Ω·mm² ~ 55.6 m/Ω·mm².
• σAl=37.7 m/Ω·mm².
It is recommended that the currents obtained for calculating
sections is increased by 20% ~ 25% to ensure that both the wiring
and protection elements operate below the 80% capacity.
It is necessary to specify outside cables, resistant to degradation by
sunlight.
Consider the option of conduit cables.
Consider possible correction terms due to Tª effect, if cables are
exposed to T>30 °C.
Sizing Wiring Required for the Photovoltaic Facility (IV)
Admissible voltage drop in typical conductors for general facilities.
In domestic uses (housing), in general, the voltage drop should be below
3%.
Circuit % of voltage drop admissible
Panels – Regulator 3% – 5%
Regulator – Batteries 0.5% – 1%
Regulator – Inverter 0.5% – 1%
Batteries – Inverter 0.5% – 1%
Regulator – DC Loads 3%
Inverter – AC Loads
(according to some European
regulations)
3% (housing)
5% (industries)
Sizing Wiring Required for the Photovoltaic Facility (V)
Maximum Currents Allowable According to the Section for Bipolar
Cables with Cu Conductors Insulated with Rubber or PVC. As an
approximate orientation, we have:
Sizing Wiring Required for the Photovoltaic Facility (VI)
Nominal Section
(mm2)
Current
(A)
Nominal Section
(mm2)
Current
(A)
0.75 8 10 44
1.0 10.5 16 59
1.5 13 25 78
2.5 18 35 97
4.0 25 50 115
6.0 32 70 140
The maximum current provided by the PV panel at the input terminals of
the regulator will be (considering a security increasing of 20%):
Being:
1.2G PP mpI n I
Current at the MPP provided by the PV panel (in ).
Efficiency of the PV panel. It can be chosen a typical value between 85% & 95%.
Maximum power provided by the PV panel (in ).
Voltage
mp
mód
mp
mp
A
W
I
P
V
at the MPP provided by the PV panel (in V).
Current provided by the PV generator set (in ).
Nº of panels connected in parallel to meet the energy needs.
G
PPn
AI
mód mp
mp
mp
PI
V
Sizing Wiring Required for the Photovoltaic Facility (VII)
Autonomous PV Systems with DC and AC Loads.
Imód-reg
IL,DC
Ireg-inv IL,AC
Ireg-bat
ΔUmód-reg
ΔUL,DC
ΔUL,AC
ΔUreg-bat
ΔUreg-inv
Smód-reg
Sreg-bat
SL,AC
SL,DC
Sreg-inv
Sizing Wiring Required for the Photovoltaic Facility (VIII)
Regulator
(voltage regulation
subsystem)
DC Consumption
AC Consumption
Batteries
(accumulation subsystem)
PV Modules or Panels
(generation subsystem)
Inverter
(DC into AC
conversion subsystem)
In our case, we have the following currents, considering a security factor
of 20%, in order to avoid of arriving to the maximum current capability
and subsequent wiring heating:
1.2 1.2 9 4.40 / 47.52mod reg G PP mpI I n I panels A panel A
, 1.2 5.63 6.75L DCI A
1.2 36.76 44.12reg invI A A
,
7501.2 1.2 3.26 3.91
230L AC
WI A A
V
47.52reg bat mod reg GI I I A
Sizing Wiring Required for the Photovoltaic Facility (IX)
Wiring length that exists and permitted voltage drops in the different
existing sections between the elements of the PV system:
ΔU=5%
ΔU=3%
ΔU=3%
ΔU=0.5%
ΔU=0.5%
L=8 m
L=20 m
L=1 m
L=1 m
L=35 m
Sizing Wiring Required for the Photovoltaic Facility (X)
Regulator
(voltage regulation
subsystem)
DC Consumption
Batteries
(accumulation subsystem)
PV Modules or Panels
(generation subsystem)
Inverter
(DC into AC
conversion subsystem)
AC Consumption
In our case:
Normalized Europe sections used for the wiring of the electrical facilities
are:
Circuit Vnom
(DC o AC)
(V)
ΔV
(%)
U
(V)
Length L
(m)
Current I
(A)
Obtained
Section
(mm2)
Normalized
Section
(mm2)
Panel – Regulator 24 V 5% 1.2 V 8 47.52 A 11.40 mm2 16 mm2
Regulator – Battery 24 V 0.5% 0.12 V 1 47.52 A 14.24 mm2 16 mm2
Battery/Regulator –
Inverter
24 V 0.5% 0.12 V 1 44.12 A 13.23 mm2 16 mm2
DC Grid 24 V 3% 0.72 V 20 6.75 A 6.74 mm2 10 mm2
AC Grid 230 V 3% 6.9 V 35 3.91 A 0.713 mm2 1.5 mm2
2 · ²2 0.0359
55.6 / · ²
LI LI mm LIS
U m mm U m U
Sizing Wiring Required for the Photovoltaic Facility (XI)
1,5 mm2 – 2,5 mm2 – 4 mm2 – 6 mm2 – 10 mm2 – 16 mm2 – 25
mm2 – 35 mm2 – 50 mm2 – 70 mm2 – 95 mm2 – 120 mm2 – 150
mm2 – 185 mm2 – 240 mm2 – 300 mm2
Sizing Wiring Required for the Photovoltaic Facility (XII)
Wiring sections obtained by previous general equation corresponds to a temp =
27 °C (300 K).
To ensure that this section is valid even if the wiring temp, at full load and at
steady state, was the maximum allowable under these conditions, the value
initially obtained by the mentioned calculations should be increased according to
the following table:
Isolation
Type
Maximum
Allowable
Temperature
Section
Increasing
Thermoplastic
Thermostable
For DC circuits, color code to be used is:
• Red. Para el positive (+) pole.
• Black. For the negative (–) pole.
And for AC circuits, the color code to be used is:
• Black, brown or gray. For the phase conductors (L).
• Blue. For the neutral conductor of the installation (N).
• Bicolor (yellow and green). For the ground conductor of the
electrical facility (GND).
Sizing Wiring Required for the Photovoltaic Facility (XIII)
• Determination of the nominal operating voltage for the system.
• Estimation of demand or overall power consumption of the facility (in
Ah/day).
• Loss assessment of photovoltaic solar installation.
• Choosing the optimum inclination of the photovoltaic panels.
• Calculation of daily total solar radiation received by month for that
angle.
• Panel model selection and determination of the electrical parameters
(nominal power, voltage, efficiency, etc.) provided.
• Calculation of the total number of modules in parallel and in series.
• Calculation of the total capacity of the storage batteries.
• Sizing regulator (DC/DC converter).
• Sizing the inverter (DC/AC converter).
• Sizing of wiring required for installation.
• Summary table of values over the 12 months.
Improved Design Guide in the Sizing of PV Systems
Resume Table of the Photovoltaic Facility Designed
Jan. Feb. Mar. Apr. May. Jun. Jul. Aug. Sep. Oct. Nov. Dec.
DC Voltage (V) 24 24 24 24 24 24 24 24 24 24 24 24
Consumption (Wh/day) 1764.7 1764.7 1764.7 1764.7 1764.7 1764.7 1764.7 1764.7 1764.7 1764.7 1764.7 1764.7
Consumption without losses
(Ah/day)73.53 73.53 73.53 73.53 73.53 73.53 73.53 73.53 73.53 73.53 73.53 73.53
Consumption with losses
(Ah/day)147.44 147.44 147.44 147.44 147.44 147.44 147.44 147.44 147.44 147.44 147.44 147.44
Rad. H(60º) (kJ/m2/day) 11,148 20,092 19,136 18,106 17,258 17,496 18,406 18,694 18,516 17,234 10,652 8,314
PSH (for 60º) 3.097 5.581 5.316 5.029 4.794 4.860 5.113 5.193 5.143 4.787 2.959 2.309
Ah/module·day 12.26 22.10 21.05 19.91 18.98 19.25 20.25 20.56 20.37 18.96 11.72 9.14
Nº required mod., nPP 12.03 6.67 7.00 7.41 7.77 7.66 7.28 7.17 7.24 7.78 12.58 16.13
Nº installed modules
(nPP·nPS)9·1 9·1 9·1 9·1 9·1 9·1 9·1 9·1 9·1 9·1 9·1 9·1
Ah provided 110.38 198.91 189.46 179.23 170.86 173.21 182.23 185.08 183.30 170.61 105.46 82.29
Deficit or surplus (Ah) -37.06 51.47 42.02 31.79 23.42 25.77 34.79 37.64 35.86 23.17 -41.98 -65.15
Autonomy days, Daut 12 12 12 12 12 12 12 12 12 12 12 12
PD,máx 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7
Battery Capacity, Calm
(Ah)2527.5 2527.5 2527.5 2527.5 2527.5 2527.5 2527.5 2527.5 2527.5 2527.5 2527.5 2527.5
MEDSolar Training Course
Module 3
Power Plant Design
Thank You for Your Attention!
Herminio Martínez-García
Department of Electronics Engineering
Barcelona College of Industrial Engineering (EUETIB)
Technical University of Catalonia - BarcelonaTech (UPC)