Q & A of our Solar Farm Webinar

We recently held our 'Insights on Setting Up a Solar Farm' webinar and received a large volume of questions during the Q&A section. Below we have answered these questions:

1) what sort of tracking system did you use? NextTracker?

A: We used a company called S-Rack. We have had a relationship with several in the company for 10 years, this gave us confidence in the product.

2) How do you control (e.g. SCADA) and secure the operations of the facility?

A: In this installation the operation of the inverter is autonomous with the control algorithm based around the solar irradiation levels and the network conditions. Remote access to monitor and make adjustments can be made over an EtherNet TCPIP connection. It is also possible that the inverter, or inverters, can be full integrated over this same Ethernet connection into a customer, or networks, SCADA system.

3) Any plans for this site to  be fitted with BESS and interface with the Marlborough Lines?

A: At this stage there are no plans to integrate BESS. However should that become a future requirement the PE inverter is DC Bus ready and we can simply connect a battery source, via a DC/DC converter, to the inverter so we are future proofed.

4) Panels are potential Tilting, but no rotate?

A: On this site the panels are only configured with a single axis tilt control system. It simply comes down to an analysis of  cost versus payback, and increased system complexity and maintenance. Believe it or not in some cases it is actually more economic to increase your DC to AC ratio with more panels to solve this issue.

5) Hi, we built the 1MW floating array in Auckland.  Did you find plant/grid electrical integration costs to be high?

A: All these integration costs were built into the feasibility study and considered during that time of project evaluation.

6) Hi Guys – THanks for setting this session up.  Interested to know how the system was optimised?   How did you arrive at spacing/pitch?  Likewise, decision to go SAT vs Fixed?

A: Experience. With 14 solar farms scattered around the country, it was a matter of analysing all the data and relating it to other data, also in this is maths where you look at what the angle of the panel is and when it will overshadow the next row. Land price also needs to be taken into account.

7) What was the connection requirements from the local lines company? Also, was there any regulatory requirements to comply with for operation?

A: The connection with requirements with the lines company were discussed at a very early stage and we continued to engage with the lines company throughout the project. Their requirements were included in our modelling. On commissioning the protections in the inverter and MV switchgear were set up as per their request with a network representative present to confirm this was done. At this stage there isn't a specific AS/NZS standard for solar inverters connected to the MV network. AS/NZS 4777 is appropriate for low power, low voltage connected systems only.

8) do you have any data on the benfit of the tilt as opposed t0 a fixed 30 degree?

A: Yes, we do, we have sites throughout New Zealand tracking and fixed 25, 30 and 35 degrees and we have done enough modelling to correlate to most angles.

9) What type of modelling was done?

A: Extensive modelling was undertaken by a consulting engineer specialising  in power systems. Modelling is typically undertaken on either the PSCad or DigSilent platforms. This model was then reviewed by the network company.

10) Is the business case for array tracking systems quite strong or is the trade-off with array maintenance costs still unclear?

A: Please refer to question 4. Obviously this answer with change will every site but installing more panels is very cost effective and requires no maintenance.

11) Is the grass still growing under panels? How many years get the return for the investment?

A: Absolutely! Many sites will consider Agrivoltaics which is sharing the land for dual purpose - One part being traditional agricultural activities and the other solar generation. It makes sense and gets the maximum use of the land. With regards to ROI - this is different for every project and dependent on the "commercial model" that is used.

12) is the PE inverter AC or DC coupled? any consideration for battery storage in the future? if your inverter is DC coupled, would simplify the battery installation

A: The PE inverter is AC coupled at 11kV in this installation. Batteries can be connected, via a DC/DC converter, to the existing inverter so this makes for a very simple installation.

13) what was the project duration from start to energisation. what were the 3 biggest delays on the project.

A: 3 years which included the land purchase, biggest delays were land sub division, location(i.e. travelling to site), some equipment was missing and we needed this to be resent out.

14) In keeping the grid stable, what percentage of yield are you sacificing?

A: We are not allowed to disclose this information. But we seeing many specifications come through asking for 30% of the installed power capacity to be made available as KVAr for grid support e.g. 100MWac installation with 30MVAr reactive power.

15) How is the system availabilty?

A: We have 100% availability since commissioning in January 2021

16) What PR figures are you seeing?

A: We don’t have any Performance Ratio (PR) data at this stage as the plant has only been commissioned since January and we are still doing some fine tuning with axis control etc.

17) Can you please explain your earth grid requirements?

A: From an AC perspective - we chose to pile mount the inverter and MV skid. The piles were large galvanized steel I beams and we used one of these piles as a giant earth stake. From a DC perspective we opted for a floating system.

18) Hi, thanks for this. Why does the generation drop during the middle of the day?

A: The solar array has been positioned to achieve maximum generation at the shoulders of the day i.e. morning and afternoon

19) bifacial panels... reflecting on grey dark soil? what is the extra energy produced in this situation?

A: We can assure you there is significant advantage on installing bifacial panels - even with the reflection from normal soil. We cant disclose the amount of extra energy produced but it is significant.

20) Also does the power electronics inverter integrate with SCADA?

A: In single inverter applications like this the inverter can be connected to an external SCADA control system via Ethernet TCPIP. For multiple inverters we would install a Power Plant Controller. This would be the interface between the SCADA and all the inverters as typically the SCADA wants to see information from the entire site perspective as well as individual inverter details.

21) shading issues ?

A: We have no trees around the site and the rest comes down to good PV array design. Please see our case study video on YouTube https://www.youtube.com/watch?v=J6GzePYKXls&t=4s

22) Have you found any lines companies are better to work with than others around largescale solar within their network?

A: Not in particular. The lines companies want, and need, to understand the impact of a large solar installation on their network. We have found engaging with the network at a very early stage and ensuring that that are satisfied with your modelling and protections is a very critical part of the process.

23) how much more will the tracking device bring compared to fixed panels ? lifespan of the tracking device expected ?

A: We have had tracking equipment which is still running for over 8 years. One of our trackers recently needed a motor and gearbox replaced, other than that, if they are set up correctly the lifespan will be extended till the full life of the equipment, 30 years.

24) Before you picked the site, what sort of investigation / prep work did you do to choose your solar site at Malbourough. Do you put weather stations to monitor solar yield etc?

A: Weather stations are used and we also completed a geo tech report and pile testing. Being all in-house made things easier.

25) I missed the early discussions, so apologies if this was already discussed / clarified. Is Kea's generation capacity built to align with your retail book?

A: There is a portion of our energy that we sell to our own retail customers but this latest project is more to sell our energy to the spot market.

26) how much do you sell a kWh to the lines company ?

A: The sell price for the energy generated is determined by the NZ electricity spot price market.

27) How does the inverter peform under fault conditions and what protection is in place

A: There are varying levels of fault protection embedded within the inverter. Many basic protections, such as under or over voltage, under or over frequency, are achieved in the inverter firmware. The inverter has anti-islanding protection as well. Within the inverter we have software protections, all the major low voltage components are protected with fuses and circuit breakers, the overall low voltage side of the inverter is protected with a system circuit breaker. Then on the medium voltage side the inverter comes with transformer protections and a medium voltage circuit breaker as well. From a network perspective the medium voltage circuit breaker can also be tripped remotely by the network if required.

28) what 11kv voltage range did the untility company stipulate ?

A: Every network has their own requirements around voltage tolerances, for each specific site. In this installation we have employed the inverter to target a constant output voltage to the network and in parallel support the grid with KVAR 

29) Any thoughts on ongoing panel cleaning?

A: It is very much a wait and see approach, there are some automated cleaning products on the market, if you are considering a site we can manage the R and M. You would monitor the power and see if the loss is greater then the degradation of the panels.

30) What forms of Storage are preactical to use with such a system so that it can be used by sites so they can use what they want with the energy produced.  They may want to elemionates Peaks on the supplies they take or use it to run plants when production is ideal but ancillary equipment is running or even run plants when blackouts occur?

A: Battery storage is a really practical solution for this type of application. The PE solar inverter has the ability to connect BESS already built into it. It is always good to have some discussion around actual configuration and requirements as there are a number of different battery technologies available. It is also very important for us to understand your DC/DC ratio requirements.

31) what level of network modelling had to be done?

A: A lot of network modelling was undertaken prior to the project sign off to proceed. This modelling had to simulate a variety of network conditions and solar farm performance

32) Does Power Electronics supply Solar Panels as well as the inverters

A: Power Electronics supply the inverter only.

33) do you recieve carbon credits for this solar farm?

A: There was an article recently on Kea Energy on this topic. We sell renewable energy certificates to BOC to make green hydrogen.