Photovoltaic
“Parallel System”
for
Duke Farms
Group Members
Trecia Ashman
Paola Barry
Mukti Patel
Zarina Zayasortiz
Project Update
In this update the group will discuss all of
the new findings as well as planned
approaches for the spring semester of
2005. This semester, there will be a
greater overall focus on the electrical
layout design of the photovoltaic system
as well as the refining and finalizing of the
solar panel support.
Gantt Chart
Solar Energy Harvesting

For effective harvesting
of the sun’s rays the
angle that the sun hits
the panel must be close
to 90 degrees.

When the angle is not
90 degrees the incoming
power is reduced by a
factor of cos(beta)

Where beta is the is the
deviation from 90
degrees.
Solar Energy Harvesting (cont.)

The modules should be placed
in an unobstructed area.

If the modules are set up
behind one another, then the
distance from each other has to
be wide enough to prevent
shading.

As in the case with Duke
Farms, the modules will be
set up on a stand and placed
behind one another. The
proper distance (b) has to
be determined.
Control Configuration

To enable one axis tracking a good control
configuration was needed.

Options


One tracker for every five modules.
One tracker that will control all of the modules

Master/slave configuration
Master/Slave Configuration

The primary module
will have a tracker,
while the others
(secondary modules)
will mimic the motion
of the primary
module.

The motion will be
mimicked by using
small motors that will
position the modules.
PVWATTS Algorithm Description
Background:





Recommended by Department of Energy
Internet accessible
User sets location in US from station map
User sets PV system parameters or selects default values
Program performs hour-by-hour simulation


Monthly energy production (AC) in kilowatts
Energy value in dollars
PVWATTS - Background
System Parameters:
 Size (AC rating for Standard Reporting Conditions)
 PV array type (fixed or one/two-axis tracking)
 PV array tilt angle
 PV array azimuth angle
 System size can range from 0.5 to 1000 kW
 SRC stipulates certain meteorological conditions:
 PV array solar irradiance of 1000 W/m2
 Spectral irradiance conforming to American Society for
Testing and Material Standard E892
 PV cell temperature of 25ºC
 Electricity default cost is average 1999 residential electric rate
for state selected
Program Parameter - Tracking
Program Parameter – Tilt Angle

Angle from horizontal of the inclination of PV array


For one-axis tracking:




Tilt angle is angle from horizontal of the inclination of
tracker axis
Tilt angle not applicable for two-axis tracking
Default angle is equal to station’s latitude


0º = horizontal and 90º = vertical
Normally maximizes annual energy production
Increasing tilt angle favors energy production in winter
Decreasing tilt angle favors energy production in
summer
Program Parameter – Azimuth Angle


Angle clockwise from true north of direction that PV array faces
For one-axis tracking:



Azimuth angle not applicable for two-axis tracking
Default value is 180º (South-facing)



Azimuth angle is angle clockwise from true north of direction of axis of
rotation
Normally maximizes energy production
Increasing azimuth angle favors afternoon energy production
Decreasing azimuth angle favors morning energy production
Orientation
Azimuth Angle
(˚)
N
NE
E
SE
S
SW
W
NW
0 or 360
45
90
135
180
225
270
315
Set Program Parameters
 Users cannot change the following parameters:
 Installed nominal operating cell temperature of 45ºC
 Power degradation due to temperature of 0.5% per ºC
 Soiling losses of 3%
 Angle-of-Incidence (reflection) losses for glass PV
module cover
PVWATTS Calculations
Maximum Power of Array:
 Accounts for differences in solar radiation and dry bulb
temperature
 Wind speed on module temperature and changes in
inverter efficiency with power not accounted for (assumed
small)
Pmp 
E
 [1    (T  T0 )]
1000
Where:
Pmp = Maximum Power (Watts)
E = Plane-of-Array (POA) Irradiance (W/m2)
γ = Pmp Correction Factor for Temperature (-0.005 ˚C-1)
T = PV Module Temperature (˚C)
PVWATTS Calculations (con’t)
Monthly POA Irradiance (Edg):
 Sum of the direct beam, diffuse sky, and ground-reflected
radiation components
 Scaled based on ratios of monthly direct, diffuse, and global radiation
 Values for data grid cells denoted by subscript “dg” and for reference
stations “TMY”
Edg 
DN dg
DN TMY
 ETMYdn 
DFdg
DFTMY
 ETMYsky 
GH dg

ALBdg
GHTMY ALBTMY
Where:
DN = Monthly Direct Normal Radiation
DF = Monthly Diffuse Horizontal Radiation
GH = Monthly Global Horizontal Radiation
ALB = Monthly Albedo
ETMYdn= Monthly Direct Beam Component of POA
ETMYsky= Monthly Diffuse Sky Component of POA
ETMYrefl= Monthly Ground Reflected Component of POA
 ETMYrefl
PVWATTS Calculations (con’t)
Monthly AC Energy Production (ACdg):
Where: ACdg 
ETMY =
E dg
ETMY
 [1    (Tdg  TTMY )]  ACTMY
ETMYdn + ETMYsky + ETMYrefl
Tdg = Monthly Average Daily Maximum Dry Bulb Temperature for Data Grid
Cell
TTMY = Monthly Average Daily Maximum Dry Bulb Temperature for
Reference Site
ACTMY = Monthly AC Energy Production Calculated for Reference Site
*Calculations have overall accuracy of 10-12%
PVWATTS Verification

PVWATTS was developed by the National
Renewable Energy Laboratory in order to
calculate the electrical energy thaw would be
produced by a d grid connected photovoltaic
system.

The group cross checked the PVWATTS data with
other 30 year data from the Department of
Energy website in order to check the accuracy of
the program.

The team uncovered that the PVWATTS
generator was correct, since another source
validated its data.
PVWATTS Verification (cont.)



In order to verify the data on
PVWATTS, the group sampled
data from January 1963, for a
50kW system with one axis
tracking
The group found hourly data,
and totaled it for the month
and checked to see if it
matched with PVWATTS data
The total amount of AC power
for January 1st 1963 is
6099900 watts or 6099.9kWh.
The number that is generated
by PVWATTS for a 50 kW
system is 6110 kWh.
Year
"Month"
"Day"
"Hour"
"AC Power (W)"
1963
1
1
08:00
2439
1963
1
1
09:00
23962
Total for January
1st
1963
1
1
10:00
34774
283009 watts
1963
1
1
11:00
36458
1963
1
1
12:00
43528
1963
1
1
13:00
42011
1963
1
1
14:00
40908
1963
1
1
15:00
36621
1963
1
1
16:00
21657
1963
1
1
17:00
651
PVWATTS Verification (cont.)



The group also sampled
another data set from
February 1966.
It was found that the data
was also consistent.
The total amount of AC
power for February 2nd
1966 is 6704357 watts or
6704.357kWh. The
number generated by
PVWATTS for a 50kW
system in February is 6734
kWh.
Year
"Month"
"Day"
"Hour"
"AC Power (W)"
1966
2
27
07:00
212
1966
2
27
08:00
30701
1966
2
27
09:00
42787
1966
2
27
10:00
47515
1966
2
27
11:00
50939
Total for February 28th
1966
2
27
12:00
50080
382729 watts
1966
2
27
13:00
45641
1966
2
27
14:00
38079
1966
2
27
15:00
41025
1966
2
27
16:00
23701
1966
2
27
17:00
12049
Electrical Layout

The group needs to communicate to
Duke Farms their alternatives
System that provides electricity only
for Duke Farms:
1.
2.
No electricity is sold back to the grid.
All surplus to power grid.
Interconnection Protection

If surplus is connected back to the power grid it
is necessary

The function is three-fold:

Disconnects the generator when it is no longer
operating in parallel with the utility system.

Protects the utility system from damage caused by
connection of the generator, including the fault current
supplied from the generator for utility system faults
and transient over voltages.

Protects the generator from damage from the utility
system, especially through automatic re-closing.
Interconnection Protection (Cont.)

Interconnection protection varies
depending on the following factors:




System Size
Point of Interconnection to PSE&G
Type of Power Generated
Interconnection Transformer Configuration
Therefore the group needs to find what works
best for our system.
Typical Interconnection Systems
Maintenance Costs

This expense can be explored in
three ways:



Delegate work to current
employees
Hire part-time workers
Hire contractors
System Placement
Visuals
Life-Sized Models vs. Display:

Life- Size Model



Give the customer an idea of how one individual
module will look.
Not working model.
Small Display

Commercial visualization with the purpose to create
a better overall picture of the system and what kind
of space it would take up.
Original Solar Support

Several Problems:


Presence of a hole
where pipe met flat part
of support
Hole did not aid to the
design


Created more stresses
in the design
Presence of hole did not
allow for one-axis
tracking

Type of tracking group
decided on
Refined Solar Support
Figure 1 – Refined Design of Solar Support
Figure 2 – Close-up of Solar Support Joint
Further analysis is needed in order to determine how wind, rain, and snow
loading will affect this new design.
Total Capital Cost
A large portion of the total capital cost will
come from the structures themselves.
 This large amount of capital will probably
need to be borrowed so interest costs will
have to be taken into account.
 Operation and maintenance costs will also
be added to the total capital cost.

Payback Period

Factors that may cause the payback time
to change:



The price you pay for your system will vary
depending on local market conditions.
Another factor is that the energy generated by
your system depends on sunlight conditions at
your location.
Finally, the inclination of your solar module
array may be less than optimal.
Questions