Key Points on Design of Commercial Scale Distributed Photovoltaic System Produced by: Rodd Zhang and Carl Patrick. Presenter: Rodd Zhang

Transcription

1 Key Points on Design of Commercial Scale Distributed Photovoltaic System Produced by: Rodd Zhang and Carl Patrick Presenter: Rodd Zhang

2 Disclaimer This Presentation will aim to provide recommendations and limitations to the design of a commercial scale Distributed photovoltaic system. Micro Inverter systems are not covered in this presentation. If there is any conflict within the system design presented here, the Australian Standards will always prevail.

3 Solar Australia At Solar Australia, we focus on providing the highest quality products and services, introducing the latest solar & energy storage products to the Australia market whilst providing professional advice and service to our valued clients. Solar Australia believes in providing local support to our customers, which is why we employ local staff and local installers. This enables us to respond quickly and professionally to after-sales support requests. We demonstrate our commitment by staffing a team of dedicated service technicians. At Solar Australia, we strive to be the first choice in renewable and storage solutions for the home and business. To do this, we commit to delivering excellent customer service, from initial enquiry right through to after-sales support.

4 Commercial Scale System Larger size (30kW to 200kW) More parts (module, inverter and BOS) Higher Vdc and AC fault currents (PID, string fuse, cascading circuit protection) Grid protection and power quality (Utility interaction) 15mins or 30mins interval Monitoring with specific data quality requirement. LGC involved, Tender involved, Performance Guarantee involved. More detailed grid connection applications

5 Agenda 1. Size the System 2. Site Inspection 3. Product Selection 4. DC Design 5. AC Design 6. Power Quality

6 Past Electricity Bill Size the System Pros: 1. Easy to obtain 2. Convenient to analyse and estimate 3. Quick response to the customer

7 Past Electricity Bill Size the System Cons: 1. There is a different time of use contract between the retailer and the utility (use the correct section!) 2. High possible error margin due to variations in clients load profiles

8 Size the System

9 Size the System Load Profile Before and After 40kW Solar kw 40 Proposed Solar Load Data After Solar Load Data Before Solar :00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00

10 Size the System Request 30 minute or 60 minute interval data from the retailer/utility 1. It can be like pulling teeth 2. Sometimes you won t get what you need It can be a different resolution. You will need extra work on the data. Some software tools need an hourly rate but you may receive 30 minute rate from energy retailer/utility. It can be a matrix spreadsheet. No units It can be a mixture of kw and kvar You may only receive the current (I) data. What about the voltage?

11 Size the System Oversize the PV system 1. STC (standard test condition) operating performance is unlikely to be achieved in the field. Our analysis has shown it is normally 77% of the system performance on the inverter output, comparing to the rated PV power 2. PV module price is going down and it is often more cost effective to oversize the DC array power as this squares the traditional bell curve of PV generation by operating the PV inverter(s) at its rated power more frequently 3. Use the best available roof space 4. BUT!...

12 Size the System 5. An oversized Inverter extends the full power operating period during the daytime - You may void the warranty. (Not all inverters are designed to perform this way) - Inverter input/output power may be reduced. You could have much less AC power - Inverter life may shortened 6. More Strings - String fuses are important! (first and second faults are difficult to predict) 7. CEC Design Guidelines - The Inverter nominal AC power output cannot be less than 75% of the array peak power and it shall not be outside the inverter manufacture s maximum allowance array size specifications

13 Size the System Source: Fronius SYMO series Grid Connected Inverter Datasheet ( )

14 Size the System

15 Size the System

16 Size the System 0.75 x PV array size = Minimum Inverter size or 1.33 x Inverter size = Maximum PV size NOT 1.25!! Source: Fronius SYMO series Grid Connected Inverter Datasheet,

17 Site Inspection 1. Roof Type - Different roof types may require different racking systems. (corrugated, kliplok, trimdek, spandek, decromastic etc.) - Screw line distance determines the orientation and racking foot spacing and needs to confirm with the product wind loading certificate : upwind (UW) and downwind (DW) minimum distance requirements - Structural Engineers certification may be required to ensure a safe and compliant PV installation Source: Select Metal Roofing Pty Ltd Roofing Profiles,

18 Site Inspection 2. Shading - Shading is more complicated than the public realise - Bypass diodes are primarily used to protect the module from hotspots. It is not designed to improve your system performance - Shading in commercial scale systems may result in Multiple Maximum Power (MMP) points and confuse the inverter MPPT, thus significantly dropping the output power - More Information:

19 Source: P Bulanyi and R Zhang, Shading Analysis and Improvement for Distributed Residential Grid- Connected Photovoltaic's Systems, Solar2014, 27/09/2016 Site Inspection

20 Source: P Bulanyi and R Zhang, Shading Analysis and Improvement for Distributed Residential Grid- Connected Photovoltaic's Systems, Solar2014, 27/09/2016

21 LOW CURRENT/NO CURRENT NO VOLTAGE!! Source: K.B.D. Esmeijer, PV performance during low irradiance and rainy weather condition 27/09/2016

22 DC Design 2. Choose panel and Decide No. of Panels per string Panel with higher reverse current rating will be compatible with more parallel strings without string fuse protection. String OPERATING voltage close to 400Vdc single phase and 600Vdc three phase will result in the most optimal inverter efficiency. (230V 2, 400 2). This means that the string Voc is optimal at 500Vdc single phase and 800Vdc three phase. 1500V string voltage will be the future but cell material, module back contact, junction box, PV cabling PID all have to be improved. Cabling identification. (new AS ) Segregation of Circuits. Segregation insulation barriers shall be no less than IP4X (new AS )

23 DC Design 2. String Layout Think about how installers can wire the strings when placing your panels on NearMaps or CAD Smart string layouts can significantly benefit installers and save on installation costs If shading cannot be avoided, group the potential shaded modules on one string. This can minimise the shading effect on the whole system Mark your strings on the roof layout (important!) Portrait or Landscape? (pros & cons)

24 DC Design 3. Tilt Angles and Array Orientation Commercial roofs are not like residential roofs. Residential roofs are normally pitched at degrees for flush mounting but commercial roofs are often low pitch <10 degrees. Tilt angle at latitude? This may not be necessary for a commercial system. Maximise self-consumption is the key to deciding the orientation and tilt angle. (lower tilt angle, better performance in summer) 0 degree tilt is not recommended. Dual orientation strings on the same MPP tracker? Think carefully about voltage mismatch.

25 AC Design 1. BOS Selection Cable: Voltage Rise Calculation Vs Current Carrying Capacity ( ) Circuit breaker: fault current discrimination and CB cascading, up stream to down stream Circuit breaker is used to protect the cable at all times. Undersized circuit breakers can cause nuisance tripping in the switch board when the inverter delivers full power. An oversized circuit breaker may cause a fire hazard. Site inspection: you may need to upgrade the switchboard or supply an additional load centre if the existing switch board is full.

26 AC Design 2. Grid Protection Device (secondary protection) New AS/NZS make it mandatory for a system over 30KVA. Protection must be installed as close to the main switch (grid supply) of the installation as practicable. You can build your own! Can be difficult if the utility specifically requires the GPD to be located in the MSB, where your solar is connected to one of the DB s.

27 3. Utility Application AC Design A well prepared application can significantly reduce the waiting period You may be asked to supply your own LV level fuse discrimination curve Temporary site shutdown may be required

28 Source: Clean Energy Council Scoping Study for National Standards for Grid Connection of Mid-Scale Embedded Generation ( )

29 Source: Clean Energy Council Scoping Study for National Standards for Grid Connection of Mid-Scale Embedded Generation ( )

30 Source: Clean Energy Council Scoping Study for National Standards for Grid Connection of Mid-Scale Embedded Generation ( )

31 Power Factor and Power Quality Power factor adjustment has already been put into new AS and it will be the direction for future grid development. AAAAAA ppppp 1. Power Factor equals = and is usually expressed as leading or AAAAAAAA ppppp lagging power factor. (Negative power factor Lagging power factor) 2. For solar inverters, it was treated as a source by some major inverter manufactures, this means lagging power factor is supplying reactive power to the load. But new AS4777 clause 4.2 has specified the definition and treated it as a load. Lagging power factor: inverter sinks reactive power from the grid and act as an inductive load. Leading power factor: inverter source reactive power to the grid and act as a capacitive load.

32 Source: GSES Pty Ltd, Power Factor and Grid- Connected Photovoltaics, 27/09/ es.com.au/wpcontent/uploads /2016/03/GSES_ powerfactor pdf

33 Reference 1. Clean Energy Council and Energeia, Scoping Study for National Standards for Grid Connection of Mid-Scale Embedded Generation, , file:///c:/users/roddzhang/downloads/gridconnection-scoping-study-workshop-presentation%20(1).pdf 2. Fronius SYMO series Grid Connected Inverter Datasheet, Select Metal Roofing Pty Ltd, Roofing Profile, P Bulanyi and R Zhang, Shading Analysis and Improvement for Distributed Residential Grid- Connected Photovoltaic's Systems, Solar2014, 27/09/ K.B.D. Esmeijer, PV performance during low irradiance and rainy weather condition, 27/09/ GSES Pty Ltd, Power Factor and Grid-Connected Photovoltaics G Olson, Impact of leading power factor loads on synchronous alternators,