Grid-connect PV Design Project

8/19/2019 Grid-connect PV Design Project

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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.


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


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


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


8/12

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


9/12

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%


10/12

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


12/12

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

Documents

Grid-connect PV Design Project