Feasibility Study for the University of Massachusetts Lowell
Carport Photovoltaic System
by
A.R.K.D. Engineering
Samir Ahmad
Andres Reinero
Pooja Kapadia
VamshiKrishna Domudala
1
Table of Contents
1. Executive Summary............................................................................................................3
2. Background Information
1. Site Overview.........................................................................................................4
2. Project Rationale....................................................................................................6
3. Project Budget…....................................................................................................6
4. Utility Service.........................................................................................................6
5. Permitting and Community Concerns....................................................................7
3. Technical Analysis
1. Modules..................................................................................................................7
2. Inverters..................................................................................................................8
3. Carport Racking......................................................................................................9
4. Other Hardware......................................................................................................9
5. System Design......................................................................................................10
6. System Results......................................................................................................13
4. Financial Analysis
1. System Costs.........................................................................................................15
2. Incentives..............................................................................................................17
3. Simple Payback.....................................................................................................17
4. Net Present Value..................................................................................................17
5. Recommendation..............................................................................................................19
6. Appendix I – Data Sheets
7. Appendix II – System Drawings
8. Appendix III – NEC Calculations
9. Appendix IV – Sources
2
I. Executive Summary
We were asked by The University of Massachusetts Lowell (UML) to study the
feasibility of a commercial scale carport photovoltaic (PV) system located over the North
Campus Athletic Fields parking lot (hereafter, the 'Site'). This study looks at a proposed 761.6
kW carport system which will cover approximately 49% of the total Site area. Overall this would
be a good location for a PV system, with the main roadblock being securing the capital and
financing.
The report is split into three main sections, background in section II, technical analysis in
section III, and financial analysis in section IV. The background will review the Site
characteristics, and background information relevant to the Site owner. The technical analysis
will review the materials used, system design and layout, a one-line drawing, and other technical
details of the system design. The financial section will review the estimated costs and returns of
the designed system using simple payback, and net present value approaches. The financial
analysis will include three scenarios with varying assumptions from conservative to optimistic.
This report will reflect a best estimate on a probable design and financial return of a
commercially sized PV system located at the Site, however should this project move forward, it
is likely that the technical and financial options reviewed here will change. This report does not
guarantee its results and should only be used as a general guide by UML officials.
3
II. Background
1. Site Overview
The Site, outlined in yellow below, is located at the north end of the UML North Campus
at coordinates – 42.66° N 71.32° W at an elevation 24.23 m (79.5 ft) above sea level [1]. The
street address of the entrance to the lot is at 35 Sparks St., Lowell MA. The Site is oriented 10
degrees west of south (the bottom of the image is due south). The Site contains 257 parking
spaces distributed over 7382.5 m2 (79464.9 ft2)
Fig. 1
(Google Earth)
The gray shaded area indicates the approximate PV coverage, and the shaded blue area
indicates objects that will create significant shading. Shaded in green is the location of the
equipment pad. Directly south of the Site is a large playing field so the arrays will have excellent
southern exposure. The Site also has a 1 degree slope running east to west so that the eastern
4
edge of the Site is about 1.524 m (5 ft) lower than the western edge. The support structure can
compensate for this slope so that the arrays are level. The shaded blue obstruction to the east of
the Site are elevated bleachers and a press box. The bleachers rise approximately 5.18 m (17 ft)
above the ground, the press box sits on top of the bleachers increasing the height in the middle of
the structure by 2.98 m (9.79 ft). Both the bleachers and the top of the press box are bordered by
fencing bringing the maximum height of the bleachers to 6.50 m (21.33 ft) and the press box to
9.08 m (29.79 ft). This obstruction will only be an issue in the early mornings during the winter,
and even less so during the autumn and spring.
In the center of the Site is a lighting tower for the parking lot which will need to be
removed in order to construct the proposed system. This lighting can be replace by installing
lighting (such as LEDs) on the underside of the carport structure. There are no obstructions from
trees or other vegetation and no other site preparation is necessary, excluding digging trenches
for conduit and post holes for the carport structure.
According to our PVSyst model average ambient temperature ranges from -2.91 °C in
January to 22.72 °C in July. The table below lists the average monthly global horizontal
irradiation at the Site.
January
February
March
April
May
June
Global Horizontal
(kWh/m2)
59.2
76.0
115.8
142.6
176.4
184.1
July
August
September
October
November
December
5
Global Horizontal
(kWh/m2)
185.8
166.1
127.7
93.9
56.2
47.4
2. Project Rationale
UML is interested in this project for several reasons. First, the school hopes to generate
income and lower its electric bill. Second, they hope to increase the visibility of their renewable
energy efforts, and third, they hope that students in the solar energy engineering program can use
the installation for educational purposes. Keeping in perspective the universities objective for
30% carbon reduction by 2050 which was shared to us by the UML sustainability and the
parking department thus it is imperative the university go solar! The university has a large fleet
for buses and vans which operate between campuses and consume a considerable amount of
gasoline. The university intends to buy a large fleet of EV vehicles in the future and to test this
concept they have already started talks for starting a beta test for this concept. In order to supply
the electricity needed to charge these vehicles the university would prefer using the sustainable
electricity they are producing at their parking lot. Quantifying the energy used by cars and
resulting savings by not buying gasoline is premature to determine at this stage.
3. Project Budget
As a large university UML has a sizable endowment and can raise significant amounts
through capital campaigns. In addition, being a large successful public university means
financing should not be difficult to obtain, therefore we will not adhere to a limited project
budget.
4. Utility Service
National Grid is the utility that services the UML campus. The grid interconnection point
for the UML North Campus is located near the Pinanski Energy Center, just south of the main
reactor building. This location is quite far away from the Site and would require approximately
6
600 m (1968.5 ft) of high voltage wire. To mitigate this cost we will assume a grid interconnect
substation located next to the Site.
5. Permitting & Community Concerns
The permitting process in Massachusetts involves going through several step. First the
project must go to the zoning committee to ensure the project is within the property boundaries
and does not violate the specified land use. Second the project must be reviewed by a
conservation or environmental committee to ensure habitats and/or endangered species are
unharmed. Next, the project goes to the municipal permitting agency who will ensure the project
meets safety requirements and local ordinances. Finally the project goes to the utility company,
in this case National Grid, so that they can confirm that the project will not disrupt their service.
Since the location identified for our carport project is near a residential area, there is a
chance that residents will raise concerns, such as the project is an eye-sore which will cause
property values will go down, the system will create sound that will cause disturbances, or
possible hazardous materials can cause problems for healthy living. However most concerns are
due to a lack of education on PV systems which could be rectified at community meetings.
III. Technical Analysis
1. Modules
PV modules are the source of power production in the system which converts sunlight
into electricity. PV modules are comprised of a series of PV cells which are wired together,
standard modules typically contain 60 or 72 cells per module. PV module are one of the main
expenses for a PV system so care must be taken in balancing cost and performance. The modules
7
used for this study are from the Yingli Solar YGE 60 Cell Series. We used the YL260P-29b
modules which are polycrystalline and rated at 260 W. The table below gives a brief overview of
the technical specification for the module, for the complete data sheet see Appendix I.
Open Circuit Voltage (VOC)
Short Circuit Current (ISC)
Max. Power Point Voltage (Vmpp)
Max. Power Point Current (Impp)
Module Efficiency (η)
Module Length
Module Width
37.7 V
9.09 A
30.3 V
8.59 A
16.0 %
1.64 m
0.99 m
Yingli modules were used since they are one of the largest and least expensive PV
manufacturers allowing us to lower our costs and maintain reasonable performance.
2. Inverters
After the PV modules, the inverters are the next most critical piece of a system design.
An inverter converts the direct current output of a PV module into alternating current that is
required to connect to the electric grid. Because the inverter connects the power production to the
power distribution grid it is critical for proper functioning of the PV system, so a higher price for
quality products is acceptable. We will be using string inverters from SMA Solar Technology
AG. SMA is one of the leaders in solar inverter technology. Our design will utilize the SMA
Sunny Tripower 15000TL-US and the SMA Sunny Tripower 25000TL inverters rated at 15 kW
and 25 kW respectively. Both inverters are transformerless which greatly reduces their size and
weight, and operate at 1000 V so care must be taken to ensure the safety of pedestrians. Both
inverters also have dual maximum power point tracking inputs to ensure optimal power
production. Since PV module power output is rated at unrealistically ideal conditions, it is
standard to slightly undersize the inverter for a module to inverter power ratio of 1.2 to 1.3. This
8
allows for smaller, less expensive inverters without sacrificing power production. See Appendix I
for detailed data sheets.
3. Carport Racking
The carport racking is what distinguishes this system from standard rooftop or ground
mount systems. Parking lots create large areas of essentially wasted space, but by covering a lot
with PV one can generate electricity (money) and shade the cars underneath. Additionally, many
parking lots, like those around big box stores, have little to no obstructions on the southern
horizon making them ideal locations to increase PV penetration. Our design will utilize the
Single and Double Beam Over Carport structures from Carport Structures Corporation. The
Beam Over design uses evenly spaced central T-shaped supports which are posted several feet
into the ground. Mounting beams run perpendicular across the top of the T supports. Arrays can
be tilted from 0 – 10 degrees and can have up to 10 feet of overhang at each end of the array. The
Single Beam Over is 20 feet wide which can accommodate 6 modules in landscape orientation,
and as the name implies can cover a single row of parking spaces. The Double Beam Over is 40
feet wide which can accommodate 12 modules in landscape orientation, which can cover a
double row of parking spaces. For details see Appendix I.
4. Other Hardware
In addition to main pieces of the system listed above, various other components are
required. Combiner boxes take electricity from multiple conductors and merge them into a few or
a single conductor. This is required since inverters and grid connections will have only a limited
number of physical connection points. Our design will utilize Bentek Solar Integrated
Disconnect Combiners for use in Ungrounded Systems. In this case 'ungrounded' indicates that
the negative side of the PV source circuit is not connected to ground, not that the entire system is
9
ungrounded. This setup is required for use with transformerless inverters. In addition to the
combiner boxes, other hardware required are AC disconnects and fuses, a data acquisition and
monitoring system, wiring, conduit, and grid connection hardware.
5. System Design
With the modules and carport structure selected and a our desired area coverage at the
Site, a quick to-scale sketch was done in AutoCAD to determine the system size and placement.
Our initial estimate was a 575.64 kW system comprised of 2214 modules arranged in five arrays,
four double rows of parking and one single row of parking, however due to space constraints and
string - inverter matching this was reduced to a 561.6 kW system comprised of 2160 modules in
a similar five array layout (see Fig. 2 below).
Fig. 2
10
As shown in Figure 2 the black lines indicate the existing parking layout. The blue boxes
indicate the extent of the PV system, and the blue dots indicate where the T support beams will
be located. The orange square indicates the location of the current lighting tower that will need to
be removed. Array #1 will use the Single - Beam Over structure and is comprised of 6 x 36
modules in landscape orientation. Array #2 will use the Double - Beam Over structure (as will
Arrays #3 - #5) and is comprised of 12 x 36 modules in landscape. Arrays #3 - #5 are comprised
of 12 x 42 modules in landscape.
Constructing a project at a site which is used very frequently by the general public
especially students at the university is a challenge and the time of the year has to be carefully
chosen. This itself can be a challenge. Maximum effort has to be made for minimum demolition
work. However trenching for wires and the removal of the lighting posts will be necessary to
accommodate the carport structure. The location of the new light post will be decided with
approval of the property owner.
After using PVSyst to develop the system design, we settled on the following string and
inverter layout: Array #1 will be split in to strings of 18 modules (three columns of six) with four
strings running to a 15000TL-US inverter with two strings per MPPT input, for a total of three
inverters. Array #2 will also be split into strings of 18 modules (one row of 18) with four strings
running to a 15000TL-US inverter with two strings per MPPT input, for a total of six inverters.
Arrays #3 - #5 will be split into strings of 21 modules (one row of 21) with six strings running to
a 25000TL inverter with three strings per MPPT input, for a total of four inverters.
We decided to use a string inverter based configuration instead of a central based
configuration because string inverters provides several important advantages. There is less
impact due to shading compared to central inverters, more MPPT inputs for every string will
11
give higher yields, operating and maintenance costs are reduced due to the ability to pinpoint
individual malfunctioning modules from the whole field, and string inverters can avoid some
trenching which is advantageous when working in an urban environment. A graphical depiction
of the string and inverter layout can be found in Appendix II.
The DC:AC ratio for Arrays #1 and #2 is 1.25, and the ratio for Arrays #3 - #5 is 1.31
both are within standard design limits. Based on a shading analysis of the the array spacing we
decided on a 3 degree tilt, with the low end of the array elevated about 2.74 m (9 ft) above the
ground at the western end of the array. The eastern end of the array will have a higher elevation
above the ground to compensate for the slope of the Site. The low tilt angle will minimize the
arrays from shading each other during the winter. This system design was entered into PVSyst
and the results are reviewed in the next section.
We made several assumptions in PVSyst in order to model the energy production. We
assumed a monthly soiling loss of 2% to account for dust and snow, especially since the arrays
have a low tilt angle so soiling will be slower to wash off. We assumed 1.5% AC wiring losses
(at STC) for wiring between the inverters and the grid connection. We will also need to transform
the power to connect to the grid and we assumed 0.98% losses (at STC). For the summer months
we set the Site albedo to 0.1 for the asphalt, and during the winter and early spring we set the
albedo to 0.55 to account for more reflective snow.
12
6. System Results
To recap, the following table shows the basic system design.
Parameter
System size (KW)
Modules
Modules per string
Inverter
Racking
Azimuth
Tilt
Total number of strings
Number Transformer
Grid interconnection voltage
Total Busbars
Value
561.6
2160 x Yingli 260 Watt
Variable (21 and 18 strings/inverter)
21 SMA Tripower (15KW and 25KW)
Carport Racking (double and single overhang)
10 Deg
3 Deg
108 Strings (two types)
Grounding transformer, Step up transformer
13.8 KVA
6
We obtained the following results after running the our proposed design through PVSyst.
Our system produced 696.5 MWh of electricity in the first year, with a performance ratio of
84.3%, and a specific production of 1240 kWh/kWp/year. The most significant loss, is of course,
the efficiency of the module, which for the Yingli YG206P-29b module is 16%. An other
significant loss is the IAM loss due to air mass, which is unavoidable, but it is important to
13
remember how important atmospheric conditions are for PV system production. We assume a
year-round 2% soiling loss due to snow and dust which is important to consider given the very
low tilt angle of the system.
We spent a considerable amount of time assessing the shading of the site when analyzing
the system. Since the location of the arrays is fixed above the parking area our arrays had to be
very closely spaced, thus the low 3 deg tilt angle. In addition to array self shading, the nearby
bleacher seating and press box provided significant shading during winter mornings. To try and
compensate for the sources of shade, various string layouts were reviewed. However, despite
significant differences in string layout, the system production was largely unaffected. A 3D
rendering of the proposed system was drawn using Google Sketch Up and is shown below to
give an idea of what the system might look like.
14
IV.Financial Analysis
Financial analysis of the system has been carried out over a period of 25 years, assumed
productive life of the system, including installation cost, incentives and financing. It can be
assumed that the installed system cost will not exceed $3/Wp.
1. System Costs
Photovoltaic modules cost the most of all the PV system components. The power rating
of the selected Yingli module is 260 Wp at STC. The average module cost is $0.73/W hence the
modules for 561.6kW PV system will cost $409,968.00. Selected panel is 16% efficient and it
has a linear power warranty of 25 years.
Inverter is usually the single point of failure in a PV system; hence it needs to be selected
carefully. SMA string inverters, 12 25000TL and 9 15000TL-US, have been selected for DC to
15
AC power conversion. Considering cost inverters to be approximately $0.16 per watt of rated
power, total cost of all the inverters is $69,600.00.
Michigan based, Carport Structures Corporation custom designs the carport structure for
each specific parking lot. The typical cost is $0.85/W, which has been divided into materials’
cost, engineering and design cost and installation cost. Other installation costs including but not
limited to the interconnection fee, electrical equipment are considered with reference to a study
conducted by NREL on PV System Prices in the United States [2] and class lectures. These
figures are given in the following table.
Hard Costs
Soft Costs
Module
Inverter
Electrical
Installation Materials
Extra
Installation
Engineering
Permitting and
Commissioning
Installer Overhead
Installer Profit
Supply chain costs
Tax
Interconnection fee
0.73 $/W
0.16 $/W
0.64 $/W
0.1275 $/W
0.2 $/W
0.2125 $/W
0.425 $/W
$409968
$69600
$359424
$71604
$112320
$119340
$238680
20.86%
3.54%
18.29%
3.64%
5.71%
6.07%
12.14%
0.15 $/W
$84240
4.29%
0.08 $/W
0.08 $/W
0.49 $/W
0.235 $/W
4.5 $/kW-ac up
to $ 7500
$44928
$44928
$275184
$131976
2.29%
2.29%
14.00%
6.71%
$7500
0.38%
$1969692
100%
Total
Component Costs
16
2. Incentives
The proposed carport system is eligible for Federal Renewable Energy 30% Investment
Tax Credit (ITC). The system is also eligible for Solar Renewable Energy Certificates (SRECs),
a very valuable income that will balance out the installation cost of the system. Under the Solar
Carve-Out II program, systems are differentiated by generation unit type and are assigned a
particular SREC Factor. The proposed PV carport system would receive 1 SREC for every MWh
it generates.
Market Sector
A
Generation Unit Type
SREC
Factor
1
Generation Units witha capacity of <= 25 kW DC
Solar Canopy Generation Units
Emergency Power Generation Units
Community Shared Solar Generation Units
Low or Moderate Income Houseing Generation Units
Assignment of the proposed Generation Unit to a particular market sector [2]
1.
2.
3.
4.
5.
3.Simple Payback
Payback period predicts the economic value of the system. It is the number of years the
system will take to pay for itself. The simple payback period without considering the SREC
income is around 21 years and assuming the energy cost to be $0.09 per kWh. This figure
conveniently reduces to around 5 years considering the SREC value as $300/MWh for the year
2014 [1].
4.Net Present Value
Net present worth is the value of money brought forward to their worth in the present day. For
the evaluation of Net Present Value of the 561.6 kW PV carport system has been done for three
different scenarios. Following fixed inputs are used in the NPV model:
17
Fixed Inputs
Degradation rate
Value
0.50%
Maintenance cost
$11,232
Estimated property tax
Total annual cost per
space
Total annual cost
Increase in property tax
3133.344
Increased asset value
Inverter replacement cost
Replacement period
Income tax rate
384
98688
10%
32477.583
0.25 $/W
15 years
Comments
The selected module has efficiency 16% and a
linear warranty of 25 years.
$20/kW - found to be in the range of 15-20 $/kW
[3] [4]
$31.75 per $1000 - property tax rate of MA found
on the Assessor page of lowellma.gov [5]
Estimate found in a case study regarding parking
tax [6]
Total annual cost per space*total spaces (257)
Estimated property tax/increased asset value
Hard cost of the system is taken into consideration
to calculate increase in the asset value
Found in a case study [7]
Considered the value which was already in the
35% model
Fixed input Values for NPV evaluation
To generate the three NPV scenarios (conservative, likely, and optimistic), SREC value,
per unit energy cost and market discount rate has been changed. SREC value fluctuates every
month. It is evident from the above table that it plays a major role in reducing PV system cost
compared to cost figures obtained without considering SREC. For the conservative scenario,
181.5 $/MWh has been used because it is the least value that SREC has assumed since it was
launched [8]. The highest value assumed by SREC is 500 $/MWh but this value gives an over
optimistic evaluation, therefore, a reasonable value of 300 $/MWh has been taken for the
optimistic NPV evaluation. Different values of market discount rate, which is the rate at which
money can be borrowed, and the inflation rate, rate at which monetary value of the system
changes each year, have been considered in different scenarios.
18
Conservative
Likely
Optimistic
181.5
274
300
1
2.0
2.0
Inflation rate (%)
1.00
1.5
2.00
SPB w/o SREC (Years)
20.8
20.8
20.8
SPB with SREC (Years)
7.1
5.4
5.0
NPV w/o SREC ($)
-$520,780.85
-$401,477.60
-$332,187.01
NPV with SREC ($)
$644,097.01
$1,267,025.52
$1,494,641.23
LCOE w/o SREC
$0.12
$0.12
$0.12
LCOE with SREC
$0.04
-$0.01
-$0.02
Value of SREC
($/MWh)
Market discount rate
(%)
V. Recommendation
Based on our work we believe that this project is technologically feasible, and with
Massachusetts' SREC program financially feasible, if UML can raise the capital to do the project.
The project will be a visible symbol of the University's commitment to renewable energy and
would proved excellent educational value on top of it financial and environmental benefits. If
UML decides to go ahead with they project, it would be better to start sooner rather than later
since the financial payoff requires the SRECs which is subject to market and political volitility.
19
Appendix I
Data Sheets
PV Module
YL260P-29b Module
20
Inverters
Sunny Tripower 15000TL-US
21
Sunny Tripower 25000TL
22
Carport Structure
Beam Over - Single
23
Beam Over - Double
24
Appendix II
Design Drawings
DC One Line Diagram
AC One Line Diagram
NEC Calculations:
690.7 Maximum System Voltage = Number of modules per string * maximum module voltage
dT = Temp. difference between ASHARE cold temp and STC temp = -18-25 = -43 deg C
dT * TVoc = Voltage increase because of temp below STC = -43 * (-0.32/100) * 37.7 = 5.19 Volts
Maximum module voltage = Voc + dT * TVoc = 37.7 + 5.19 = 42.89 Volts
Maximum system voltage = 18 * 42.89 = 772.02 Volts
= 21 * 42.89 = 900.69 Volts
As per the NEC code standards the calculated value falls below the limit which is 1000 volts.
690.8 Circuit sizing and current:
690.8(A) Maximum DC circuit current is to be calculated for two different configurations
Configuration 1: # of strings = 4
PV source circuit current Imax(a) = Isc * 1.25 = 9.09 * 1.25 = 11.36 Amps
PV output DC circuit current Imax(b) = I max(a) * # of strings in parallel = 11.36 * 4 = 45.44
Amps
Configuration 2: For # of strings = 6
PV source circuit current Imax(a) = Isc * 1.25 = 9.09 * 1.25 = 11.36 Amps
PV output DC circuit current Imax(b) = I max(a) * # of strings in parallel = 11.36 * 6 = 68.16
Amps
690.8(B) Conductor ampicity calculations:
To find current carrying capacity of a conductor, NEC code has two articles 690.8(B)(1) or (2)
Method 1:
Configuration 1:
PV Source circuit current = Imax(a) * 1.25 = 14.2 Amps
27
PV DC circuit = Imax(b) * 1.25 = 56.8 Amps
From table 310.15(B)(17), at 90 deg C temperature size of conductor is selected as 18 AWG for
PV source circuit current carrying conductor.
PV DC circuit current carrying conductor 6 AWG size is selected, from table 310.15(B)(16).
Configuration 2:
PV Source circuit current = Imax(a) * 1.25 = 14.2 Amps
PV DC circuit = Imax(b) * 1.25 = 85.2 Amps
Similarly for configuration 2, 18 AWG for PV Source circuit conductor, 4 AWG for PV DC
circuit conductor is selected from tables 310.15(B)(17) & (16).
Method 2:
Configuration 1:
PV Source circuit current = (Imax(a) * 1.25)/temp. correction factor = 14.2/0.65 = 17.48Amps
PV DC circuit = (Imax(b) * 1.25) /temp. correction factor = 56.8/0.65 = 69.91 Amps
From table 310.15(B)(17), at 90 deg C temperature size of conductor is selected as 18 AWG for
PV source circuit current carrying conductor.
PV DC circuit current carrying conductor 6 AWG size is selected, from table 310.15(B)(16).
Configuration 2:
PV Source circuit current = (Imax(a) * 1.25)/temp. correction factor = 14.2/0.65 = 17.48Amps
PV DC circuit = (Imax(b) * 1.25) /temp. correction factor = 85.2/0.65 = 104.86 Amps
Similarly for configuration 2, 18 AWG for PV Source circuit conductor, 3 AWG for PV DC
circuit conductor is selected from tables 310.15(B)(17) & (16).
28
690.9 Over current protection:
Configuration 1:
PV Source circuit current = Isc * 1.56 = 9.09 * 1.56 = 14.18 Amps
PV output DC circuit = Isc * 1.56 * # of strings on parallel = 14.18 * 4 = 56.72 Amps
From article 240.6(A), over current protection devices must be selected from standard ratings.
For the PV source circuit and output DC circuit 15 Amps, 60 Amps OCPD’s are to be selected.
Configuration 2:
PV Source circuit current = Isc * 1.56 = 9.09 * 1.56 = 14.18 Amps
PV output DC circuit = Isc * 1.56 * # of strings on parallel = 14.18 * 6 = 85.08 Amps
Similarly, for configuration 2 15 Amps, 90 Amps OCPD’s are to be selected
Table 8: Voltage Drop Calculations:
Voltage drop =
Length = 50 ft – PV source circuit to combiner box
Resistance = 5.08 ohm/Linear foot
I = 11.36 Amps
V.D = 5.77 which is 0.75 % of maximum voltage
Similarly for 6,4,3 AWG voltage drop calculations are 1.16, 0.73, 0.58 volts which are less than
2% and are within NEC code limits.
29
Appendix IV
Sources
[1] http://www.nrel.gov/docs/fy12osti/53347.pdf
[2] http://www.dsireusa.org/incentives/incentive.cfm?Incentive_Code=MA136F&re=1&ee=1
[3] http://www.nrel.gov/docs/fy14osti/60599.pdf
[4] https://financere.nrel.gov/finance/content/cost-utility-scale-solar-one-quick-way-compareprojects
[5] http://www.lowellma.gov/Assessor/Pages/default.aspx
[6] http://www.vtpi.org/parking_tax.pdf
[7] https://financere.nrel.gov/finance/content/cost-utility-scale-solar-one-quick-way-compareprojects
[8] http://www.srectrade.com/srec_markets/massachusetts
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