Post on 07-Jul-2018
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SYDNEY 5 KW PV SYSTEM
Q1. COMPONENT SELECTION
a.
Product List
b. i. Reasons for Choice
Panels
Poly-crystalline technology is most researched type in industry, and if roof space is not short (as in
this instance), then it proves more cost-effective than mono.
Trina is rated Tier-1 manufacturer, globally ranked no. 1 panel supplier. This should assure the client
of yield performance (provided she is ready to pay premium price).
250 W is exact factor of 5 kW, resulting in a whole number of 20 (i.e. 5000 / 250 = 20). Using another
module wattage (e.g. 265 W), would not provide a whole number and some power would be lost as
we round down on quantity of modules.
Panel dimensions of 1650 mm x 992 mm mean that 20 such panels easily fit into the shade-free zone
(see layout diagram provided later).
Inverter
Fronius is a well-reputed Austrian manufacturer, and this should help the client get some peace of
mind on long-term reliability/warranty of the product.
It is assumed that client has 1-phase grid supply and she does not require a system larger than 5 kW,
so a single-phase inverter is chosen.
The chosen inverter is single-MPPT, which is fine in this case because all panels on the client’s roof
will have the same direction and tilt.
5 kW inverter rating will match the quantity of panels installed (Fronius IG 60 has max output 5000
WAC and is available in Australia). There is no compulsion to undersize (e.g. 4 kW), as it will not offer
noticeable price savings, so clipping losses and inverter over-heating are best avoided in the long
term.
The inverter has HF transformer, which provides galvanic isolation between DC and AC sides, as well
as keeping the device efficient, light-weight. Drawback is high-frequency noise.
Mounting
360Rack is Australian-made, so the company’s local presence would mean lower costs and quicker
stock availability, as well as any follow-up warranty claims.
L-foot bracket mounts are suitable for tiled roof and can sit flush.
Module thickness range of 31 –50 mm means the chosen Trina panels are compatible (35 mm).
Item design incorporates latest Australian standards (AS-5033, AS-1170).
Anodized stainless steel material and galvanized screws render this product electrochemically similar
to aluminium frames of solar modules.
Item Brand Model Qty Type
Panel Trina TSM-PC05A (250W) 20 Polycrystalline
Inverter Fronius IG 60 HV (5 kW) 1 Separated
Mounting 360Rack Tile-roof kit as needed Mid/end clamps, earth plates, rails,
tile hooks
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b. ii. Inverter-Array Matching
Site Data
Panels Data (Trina Solar Honey 250 W polycrystalline TSM-250-PC05A)
Property at STC Symbol Value
Max power PMP 250 W
Open-circuit voltage V OC 34.8 VMax power voltage V MP 30.3 V
Short-circuit current ISC 8.79 A
Max power current IMP 8.27 A
Max fuse rating IREV 15 A
Temperature coefficient of power ϒ MP -0.41 % / K
Temperature coefficient of voltage αOC -0.32 % / K
Temperature coefficient of current βSC 0.053 % / K
NOTE: Temperature coefficient of power is given in % above, and so can be approximated straight away as
temperature coefficient for VMP without further conversion.
Inverter Data (Fronius 5 kW IG 60 HV)
Property Symbol Value
Min start-up voltage V in-min 170 V
Min MPP voltage V MPP-min 150 V
Max MPP voltage V MPP-max 400 V
No. of MPPT inputs / DC inputs - 1 / 5
Max DC input current Iin-max 35.8 A
Max DC input power Pin-DC 5,380 W
Max AC output current Iout-max 21.7 A
Voltage Matching
Step 1: Minimum string length by VMP
Sub-step Calculation Result
Adjust module V MP to max temperature V MP x {1 – [ϒ MP x (T max – T STC )]} 30.3 x {1 – [0.0041 x (70 – 25)]} = 24.71 V
Factor in voltage drop V MP-75oC x (1 – VD) 24.71 x (1 – 0.03) = 23.96 V
Add inverter min voltage margin V in-min x 1.1 170 x 1.1 = 187 V
Round up after division 187 / 23.96 = 7.80 Min 8 modules per string
Parameter Symbol Value
STC temperature T STC 25 oC
Voltage drop (max assumed for sizing) VD 3 %Inverter min voltage safety margin - 1.10
Inverter max voltage safety margin - 0.95
Min cell temperature T min 0 oC
Max cell temperature T max 70 oC
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Step 2: Maximum string length by VMP
NOTE: The method used here will be by VMP and not VOC because there is no compulsion to have longer strings
(i.e. urban regulations in NSW prohibit 1-phase supply from having a larger solar array than 5 kW and client is
not pressed for roof space). Thus, and it would be advantageous to size shorter strings that always operate in
the MPP range. Using MPPmax of inverter also means the calculation will automatically be below V in-max of
inverter.
Sub-step Calculation Result
Adjust module V MP to min temperature V MP x {1 + [ϒ MP x (T STC – T min)]} 30.3 x {1 + [0.0041 x (25 – 0)]} = 33.41 V
Reduce inverter max voltage margin V MPP-max x 0.95 400 x 0.95 = 380 V
Round down after division 380 / 33.41 = 11.37 Max 11 modules per string
Current Matching
Step 3: Maximum no. of string inputs to inverter
Sub-step Calculation Result
Adjust module ISC to max temperature ISC x {1 + [βSC x (T max – T STC )]} 8.79 x {1 + [0.00053 x (70 – 25)]} = 8.99 A
Compare to Iin-max and round down 35.8 / 8.99 = 3.98 3 string inputs
Power Matching
Step 4: Total no. of modules
Sub-step Calculation Result
Compare max input to module W (STC) Pin-DC / PMP 5380 / 250 = 21.52
Limitation by regulation Nominal power max 5 kW 20 modules in system
Array Configuration
Step 5: Module combinations
No. of modules per string = 8 – 11
No. of modules in array = 20 Max no. of strings = 3; for simple symmetry, I shall use 2 strings (as 20 divides evenly into 2 not 3)
From above, various configurations can be attempted as below.
String 1 String 2 Total modules Satisfy V, I, P matching?
8 12 20 No
9 11 20 Yes
10 10 20 Yes
While any of the last 2 combinations is fine, for simplicity and balance, a 10 + 10 combination would be preferred.
Array Classification
Step 6: Maximum system voltage
10 modules per string means maximum PV system voltage (under cold conditions):
V max-array = 10 x V OC x {1 + [αOC x (T STC – T min)]} = 10 x 34.8 x {1 + [0.0032 x (25 – 0)]} = 375.84 = 376 V
This is less than 600 V, classed as LV by Clause 3.1 of AS-5033: 2014 for unrestricted domestic installations.
c.
System Expansion
Not applicable to Sydney home scenario.
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Q2. DESIGN DETAILS
a. Roof vs Ground Mounting
Not applicable to Sydney home scenario.
b. BOS Equipment Specifications
Item Discussion Standards and Calculations Sizing Result
IP rating All enclosures should ideally be rated to IP-66
as recommended by CEC, even though AS-
5033 requires only IP-55. All enclosures,
conduits and inverter should be UV-resistant.
CEC installer guidelines
AS-5033 Clause 4.3.3.1
IP-66 (proof to dust and powerful water jets)
rating for DC isolator/combiner boxes (at string-
ends) and inverter
String
protection
Each string fed into separate DC input of
inverter but internal isolation not specified, so
we presume that inputs share single-MPPT in
parallel.
By AS-5033 Clause 3.3.4, not required because
(n – 1) x ISC = (2 – 1) x 8.79 = 8.79 < IREVERSE = 15 A Not required
String
disconnection
Supplied by module manufacturer, marked
“no-load break” and only accessible with tool .
AS-5033 Clause 4.4.1.3 Plug-and-socket, non-load-breaking
1 per panel
Voltage rating ≥ string maximum (376 V)
Current rating ≥ CCC string cable (see below)
String cable No downstream protection, inverter back-
feed current 0, so string cable to carry short-
circuit from other strings (total 2 strings in
system).
To avoid inductive loops, two cores of DC (-ve
& +ve) will run together in series; modules areplaced in row along entire roof length. VD of
3% is permissible along each string (fed
directly to inverter, no separate array cable).
AS-5033 Clause 4.3.6
CCC ≥ In + (1.25 x ISC-mod ) x (n – 1)
= 0 + (1.25 x 8.79) x (2 – 1) = 10.99 A
Longest DC core length (worst case scenario) to
inverter near switchboard is 18 m (roof) + 6 m(height) + 8 m (house) = 32 m, so
CSA ≥ (2 x LDC x IMP x ρCu) / (VD x V MP-string)
= (2 x 32 x 8.27 x 0.0183) / (0.03 x 10 x 30.3)
= 1.07 mm2
CCC ≥ 11 A & CSA ≥ 1.07 mm2 so 1.5 mm2 cable
is sufficient (can carry 21 A as seen from
standard cable tables)
Voltage rating ≥ string maximum (376 V)
Stranded copper cable
Inductive loops to be minimized by running both
cores (-ve & +ve) together PVF-1 (UV-rated) compliant or housed in UV-
resistant conduit through external run to
inverter
Sub/array
protection
Each string fed into inverter directly, so no
sub-array exists; also no external energy
source (battery bank or generator).
AS-5033 Clause 3.3.5.3 Sub-array/array does not exist as such because
each string is fed into inverter directly
Additional protections at sub-array/array level
are not applicable
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DC
disconnection
switches or
isolators
No line-of-sight from PCE to array and
separation > 3 m, so required on each end of
both strings (as there is no common array
cable). Labeled for simultaneous operation to
fully isolate array. Functional earthing not
specified by panel manufacturer, and inverter
is separated.
AS-5033 Clause 4.4.1.3
AS-5033 Clause 4.4.1.4
AS-5033 Clause 4.4.1.5
AS-5033 Appendix B
No overcurrent protection, so switch rating
1.25 x ISC-mod = 1.25 x 8.79 = 11 A
Equipotential earthing, so per pole rating
0.5 x V max-array = 0.5 x 376 = 188 V
2-pole DC isolator in 1-pole configuration
2 isolators per string (both ends, so total 4)
Readily available, load-breaking
Voltage rating ≥ 188 V per pole e.g. 200 V
Current rating ≥ 11 A per pole e.g. 15 A
Combiner 2 string cables (2-core each) kept separate
from each other up to inverter, but joined to
4-core DC cable at combiner box for ease ofinstallation.
Rating of 4-core DC cable will be same as string
cable specified above Combiner box to house DC switch of each string
2 x 2-core string cables joined to 1 x 4-core
common cable up to inverter
AC cable Inverter installed next to switchboard
(southern side, shaded from direct sun) so
connecting cable length taken as 3 m. Max 1%
VR. Power factor is assumed at 0.95.
AS-4777.1
CEC installer guidelines
CCC ≥ max inverter output current Iout-max = 21.7 A
CSA ≥ (2 x L AC x Iout-max x ρCu x cosφ/ (VR x VAC)
= (2 x 3 x 21.7 x 0.0183 x 0.95) / (0.01 x 230)
= 0.98 mm2
Stranded copper cable
PVF-1 compliant or laid in UV-resistant conduit
Voltage rating ≥ mains supply 230 Vrms so 400 V
CCC ≥ 21.7 A & CSA ≥ 0.98 mm2 means 2.5 mm2,
2-core cable CSA is sufficient (can carry 28 A as
seen from standard cable tables)
AC CB /
disconnector
Inverter in line of sight, so AC breaker to be
installed inside switchboard.
Rating > max inverter Iout-max = 21.7 A
Rating < CCC of AC cable = 28 A
Voltage rating > 230 V
Load-breaking circuit breaker
Lockable in off position
Rated 25 A, 400 V
c.
Earthing Requirements Module manufacturer does not require functional earthing, and inverter is separated so per pole voltage rating of DC disconnection switch (isolator) is 0.5
of array maximum voltage.
Only protective earthing is required. This is achieved by equipotential bonding between exposed conductive parts of array (e.g. PV frames, mounting rails)
using piercing washers (WEEB) to connect the system to earthing cable.
It is advisable that lightning protection rod be incorporated into earthing system. According to AS-3000, minimum cable size for earthing would then be 16
mm2. AS-5033 Clause 3.4.3 also mandates earth fault alarm to be visual or audible. This is generally implemented by inverter.
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d. Site Plan
Site shading zone was drawn on graph paper (to scale), and scan is attached below.
Steps to calculate shading given below:
Effect of Tree-A only is significant (remaining 2 trees do not affect roof)
Tree 10 m high, but roof 6 m high (at lowest edge) so 10 – 6 = 4 m (i.e. height of obstruction)
For each hour of day given in shade table, hypotenuse is constructed to scale on graph paper from
given perpendiculars for 1 m tall object (e.g. E & S), and multiplying length by 4
For example, Tree-A is west of roof, so its shadow would be longest when sun is low in western sky
(late afternoon). At 4 pm, shade table for 1 m object in Sydney gives 5 E, 3.7 S. Thus shadow angle is
tan-1 (3.7/5) = 36.5o south of east and shadow length over roof = 4 x √ (52 + 3.72) = 24.88 m
Site layout was sketched in MS Visio software, and is pasted below. Module layout rules are:
Edge zone 0.2 m from all sides, inter-module spacing 0.02 m
Roof length 18 m, subtract edge zones 18 – (2 x 0.2) = 17.6
Module width 0.992 m, add spacing 0.992 + 0.02 = 1.012 m
Max no. of modules in bottom row = 17.6 / 1.012 = 17.39 (subject to shading)
Shading from trees (8 am to 4 pm) checked by shading table using graph paper. Largest shading zone
experienced from Tree-A late afternoon (4 pm), making lower diagonal half of roof unusable
20 modules including 0.02 inter-spacing (1.67 m x 1.012 m) can be fit in shade-free region in 2 rows
of 14 + 6; however, electrically strings are wired as 10 + 10 as sized previously
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Site Layout: TOP VIEW
Combiner box
Inverter
AC CB inside switch board
Earth pit
Lightning rod
Earthing cable 1-core, 16 mm2, connects
PV array & lightning rod to s take
String DC isolator
String A has 10 modules
(outlined in black)
String B has 10 modules
(outlined in blue)
Module junction box
(back of each panel)
DC string cable 2-core, 1.5 mm2
DC string cable 4-core, 1.5 mm2 (strings still
separate but common cable for ease of install)
AC cable 2-core, 2.5 mm2
Shade zone of trees
(8 am to 4 pm)
C
Azimuth 20o
E of N
Intermodular spacing
0.02 m
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Site Layout: SIDE VIEW
e. Electrical Schematic
System schematic was drawn in MS Visio, and is given below. Note that as discussed previously by AS-5033
standards, DC string isolators are provided on each side (inverter and rooftop) as inter-distance > 3 m.
However, for inverter output, only one AC CB is provided in main-switchboard because inverter is within
line-of-sight (installed next to it).
Lightning rod
Earth pit Earth cable 1-core, 16 mm2,
connects PV array, enclosures
and lightning rod to ground stake
AC CB inside
switch board
Inverter
AC cable, 2-core,
2.5 mm2
DC string cable 4-core, 1.5 mm2
(strings still separate but common
cable for ease of install)
String DC isolator
(1 per string)
PV module
PV junction box
(1 per module)
Mounting rails ( > 5 cm
gap of module from roof)
m
20o
2
1 2
1 10
10
A
N
Mainsfuse
Netmeter
MEN
House loads
Mainsswitch
Solar CB25 A, 400 V
Main switchboard Inverter Fronius IG 60 HV (5 kWac)
DC isolators, 2-pole15 A, 200 V
Array Trina TSM-PC05A (250 Wdc x 20)
(inverterside)
(rooftopside)
DC isolators, 2-pole15 A, 200 V
10 PV modulesx 2 strings
AC cable, 2-core,2.5 mm2, 3 m
DC cable, 4-core,1.5 mm2, 14 m
String cable, 2-core,1.5 mm2, 18 m
MPPT 1
MPPT 2
Equipotential earthing
rid
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Q3. SYSTEM PERFORMANCE
a. Operating Assumptions
i. Shadows have been sketched to scale from 8 am to 4 pm, and panels placed in shade-free area. In reality
however, sunlight is present outside of these hours as well, especially during summer and so some
degree of shading in weak light hours can occur. In addition, shading table provides an average, whereas
shadows are longer in winter than summer. Over time, trees also tend to grow. Due to these reasons,
1% shading loss is still assumed despite placing panels in shade-free zone.
ii. It is assumed that system owner is conscious of metropolitan pollution and will regularly wash panels,
so dirt factor of 3% is assumed (as for sites with frequent rain).
iii. Panel-bearing roof of house is at azimuth of 20o east of north and 20o tilt.
iv. Average ambient at site is 23oC.
b.
Loss Calculations
Type Discussion / Calculation Result
SYSTEM LOSSES
Tolerance Panel specs state manufacturing tolerance 0/+3 so no de-rating in worst case f MM = 100%
Dirt Modules are tilted, and owner washes them regularly as discussed in operating
assumptions above
f dirt = 97%
Inverter Max efficiency rating specified by manufacturer is 94.3% ηinv = 94.3%
Temperature Average ambient at site is 23oC; panel specifications state NOCT = 44oC (when
ambient is 20oC),
so average cell temperature is 44 + (23 – 20) = 47oC
and de-rating is (T avg – T STC ) x ϒ MP = (47 – 25) x 0.41% = 9.02%
Note: Practical factors such as metal roof thermal properties, panel-roof gap
due to mounting etc. can mean temperature rise is even higher
f temp = 91%
Volt Drop On DC side, cable has been sized slightly better than that required for 3%
voltage drop. So a maximum of 3% is taken for average operating conditions.
Similar argument is true for AC side, where sizing was done for max 1% drop.
Total cable drop factor for power derating is 0.97 x 0.99 = 0.9603
Note: Actual drop calculations can also be performed on chosen sizes and
lengths using VD coefficient from cable tables, and adjusting VMP for average
cell temperature.
f VD = 96%
IRRADIATION LOSSES
Shading Shade-free zone but some factor considered as discussed in operating
assumptions above
Hshade = 99%
Tilt &
Orientation
Site azimuth 20o east of north with 20o tilt, whereas optimum orientation is true
north (0o) with latitude tilt (~30o). Horizontal irradiation data of design task
adjusted by tilt/orientation factors of CEC tables for Sydney (see below).
Annual irradiation comparison is:
Site PSH / Optimum PSH = 1870.8 / 1936.5 = 96.6 %
Htilt = 97%
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Total system yield is now calculated as follows:
1. Array rating 5 kW
2. Annual irradiation = Site tilted global irradiation x Hshade = 1870.8 x 99% = 1852.1 kWh/m2/year
3. System efficiency = f MM x f dirt x ηinv x f temp x f VD = 100% x 97% x 94.3% x 91% x 96% = 79.9%
4. Expected average yearly yield = 5 x 1852.1 x 79.9% = 7,399 kWh/year
c. GHG Avoidance
In NSW, each kWh of PV energy offsets 1.06 kgCO2 according to design data given. So GHG emissions
avoided per year due to this system are:
7,399 x 1.06 = 7,842.9 kgCO2/year = 7.84 ton-CO2/year
Q4. ITEMS AND CONCERNS LIST
a. Components List
Equipment
Inverter: Fronius IG HV 60
Panels: Trina TSM-PC05A (250 W) x 20
Mounting: 360Rack sub-items
i. Anodized aluminium rails (2080 mm per 4 panels) with integrated cable clamps and
earthing lugs
ii. End-clamps (2 per long-edge of last panel on either side of strings) with T-bolts and nuts
iii. Mid-clamps with earthing washers (2 per long-edge between panels)
iv. Rail joiners with earthing washers
v. Tile mount brackets (hooks) and galvanized 17-10x40 roof screws, fixed on to truss, batten
or rafter under colorbond roof
GHI
kWh/m2 /d
Days GHI
kWh/m2 /mo
Site factor
N 20o , tilt 20o
Site TGI
kWh/m2 /mo
Optimal
N 0o , tilt 30o
Optimal Irr.
kWh/m2 /mo
Formula A B A x B C A x B x C D A x B x D
Jan 6.5 31 201.5 100% 201.5 96% 193.4
Feb 5.7 28 159.6 105% 167.6 104% 166.0
Mar 4.7 31 145.7 113% 164.6 117% 170.5
Apr 3.6 30 108.0 124% 133.9 134% 144.7May 2.7 31 83.7 137% 114.7 155% 129.7
Jun 2.4 30 72.0 142% 102.2 163% 117.4
Jul 2.6 31 80.6 141% 113.6 160% 129.0
Aug 3.4 31 105.4 130% 137.0 143% 150.7
Sep 4.6 30 138.0 117% 161.5 124% 171.1
Oct 5.6 31 173.6 107% 185.8 108% 187.5
Nov 6.2 30 186.0 101% 187.9 99% 184.1
Dec 6.6 31 204.6 98% 200.5 94% 192.3
Annual Total 1658.7 1870.8 1936.5
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Cabling
i. 1.5 mm2 2-core, DC-type for string connection to DC isolator (normally provided by
manufacturer between modules)
ii. 1.5 mm2 4-core, DC-type for joining with 2 panel strings while keeping them independent
iii. 2.5 mm2 2-core, AC-type to connect inverter with switchboard
iv. 16 mm2 1-core, earthing between lightning rod, panel assembly and earth stake
Switchgear
i.
DC isolators x 4 (15 A, 200 V, 2-pole, load-breaking) one on either end of each of DC string
cables (i.e. on roof and near inverter)
ii. AC isolator (25 A, 400 V, load-breaking)
Tools
Impact driver with 10 mm magnetic hex bit, to tighten roofing screws
13 mm ratchet spanner, to tighten mount M8 lock nuts (min. torque 15 Nm)
Cordless angle grinder with ceramic disc to cut groove into tile for bracket to sit flush
Measuring tape and chalk, for initial layout markings
Bubble meter (to check horizontal level of mounting)
Winch, to assist in lifting panels to roof
Safety harness tied to rope and anchor on roof
Ladder
Cordon to secure area on ground against passer-bys
Accessories
Signage:
i. “Solar DC Cables” for cable conduits
ii. “Hazardous DC Voltage” for string isolator/combiner box
iii. “PV Array DC Isolator” for string DC disconnection switch
iv.
“Shutdown Procedure” next to inverter
v. “Warning Dual Supply” inside switchboard, indicating solar and grid sources
vi. “Solar Array on Roof” next to switchboard
Mounting plates and brackets for inverter
Cable ties and tags
Conduits: UV-rated (PVF-1) for carrying DC cable from roof array to inverter, and from inverter to
switchboard
Dektite rubber flashing to seal vertical penetrations made in roof for DC cable conduit if required,
for pathway to inverter
Lightning rod
b. Safety Concerns
Risk assessment form must be completed on arrival at worksite
Panels can act as wind sail and push person off balance
Panel edge can cause bruise or cut if handled carelessly
Harness to be used on roof for safety at height, and area below to be cordoned off to protect
passerbys against falling objects
Safety gear to be worn includes helmet, gloves, rubber shoes, sunglasses for protection against
bright light, mechanical injury or DC shock
Installation not to be undertaken in rainy or windy conditions, to prevent injury from instability orDC shock
Hat and sunscreen to be worn for protection against dehydration, with regular water and rest
breaks taken
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Q5. APPROXIMATE COSTING
The following costing is approximate, based on prevalent market conditions (as of March, 2016). Currency used in
Australian Dollar, and values are assumed to include GST.
Item Discussion ResultPanels Trina are at higher end of market, and would cost ~ $ 0.89 /W
So 5,000 W x 0.97 = $ 4,450
$ 4,450
Inverter Fronius 5 kW inverter would be approx. $ 2,000 $ 2,000
Balance of System Cabling, mounting kit, breakers, isolators, signage is expected to
cost around $ 800
$ 800
Installation Installers would charge around $ 80 per panel as a metric for
total system cost
So 20 panels x $ 80 = $ 1,600
$ 1,600
Height Access Difficulty fee charged by installers on double-storey houses $ 150
Net Metering To be done by L2 electrician by purchase of net meter from grid
owner; market rate including service charges is ~ $ 500
$ 500
Total $ 9,500
Note that this is the upfront system price BEFORE application of STC point-of-sale discounts (also known as
PV rebates).
Q6. ECONOMIC BENEFITS
a.
RECOne STC (small-scale technology certificate) is issued for each MWh of clean energy that a system shall
produce over 15 years, based on the average performance determined per kW of installed capacity, and
the available Peak Sun Hours (PSH) in a given area. For Ms Architect, post-code NSW 2000 is used (Sydney).
It can be seen from REC Registry website, that this post-code falls in sunlight Zone 3, and awards 103 STC
to 5 kW PV system.
Spot market price (March 2016) of STC is very high, at $ 39.85 (indicating there are more buyers than sellers,
hence a deficit of new systems being installed).
Thus Ms Architect would receive rebates of $ 39.85 x 103 = $ 4,104 on her upfront cost.
b.
Grid Savings
Energy yield (from Question 3) = 7,399 kWh/year
Self-consumption savings = 70% x 7,399 kWh/year x $ 0.22/kWh = $ 1,139
Export income (from feed-in) = 30% x 7,399 kWh/year x $ 0.06/kWh = $ 133
Expected yearly benefit $ 1,139 + $ 133 = $ 1,272