THOUGHT LEADERSHIP

The art of solar grid connection

With 2020 and its renewable energy targets fast approaching, the race is on to deploy renewable energy developments in Australia.  Efficient and right-sized grid connection can get projects moving quickly and ensure future productivity.

In our previous article, Overcoming potential roadblocks when developing a solar farm, we outlined four possible hurdles to successfully delivering a utility-scale solar PV energy project.  One of these potential blockers is the grid connection.

Grid connection is about the system you’re connecting to as much as it is about the gear you’re connecting.  Understanding what lies beyond your plant boundary and the impact it can have on you and vice-versa can benefit the project as it comes to life, and make it a more valuable asset into the future.

Successful grid connection of solar plants is based on three rules.  Each of these rules isn’t necessarily specific to solar PV, but we think that solar PV is uniquely placed to adhere to them and consequently optimise the connection.

Rule 1: Don’t stray too far

The low visual impact and ubiquitous resource that solar PV utilises means there’s no need to hide your solar farm away or build it in a high-sun area (although some sun will be good).  Shorter lines between your site and the grid will save time and money.  The time is saved through shorter, less-complicated approvals.  The money is saved in design, construction and materials.  Pretty obvious.

This is a paradigm shift from previous renewables development though.  Wind developers, like their hydropower counterparts, have had to observe keenly the vagaries of climate, weather and geography to understand where viable sites might be.  These sites have often proven remote from the existing transmission system and so new lines or new upgrades to the transmission system have been required at great project expense.

Solar has an advantage in this regard and developers should capitalise on that advantage.  Spare capacity and land in the transmission and distribution networks can be used for solar farms without perhaps the need for the economies of scale that have driven the large wind farms and hydropower schemes of the past to stretch the megawatt capacity to support an expensive connection asset.

Rule 2: Don’t try to overdo it

Whether you build close to the grid or not, there’s no real advantage in over-burdening the grid with your generation.  The shared network is planned around efficient delivery of power to the customers.

Currently, customers are pretty well catered for in terms of generation sources, and so the likelihood is quite low of the shared network being augmented to allow greater power evacuation from a solar site with no cost to the solar developer.  This means that the grid constraints become a cap on the economic size of the solar farm.  These constraints are not just driven by the thermal rating of the lines but may also relate to voltage control or power quality.

The reality is that the more power you try to plug into the grid, the more you’ll have to pay to do so.  This is especially true if you push the limits.  So don’t – or if you think you can, or think you have to, then follow rule 3.

Rule 3: Do your bit

The Australian National Electricity Rules provide for a graded connection standard to be assessed based on the capacity of the plant being connected and the capacity of the grid to connect that plant.  The plant will be connected if it can meet automatic access standards or a negotiated level above the minimum standard.  The standards are generally assessed against the grid of today.

We know, however, that reductions in the level of synchronous generation may leave the grid weaker than it is now.  This weakening may impact the future capacity of the grid to support substandard generation connections.  This will mean that these generating systems that are substandard may be constrained or disconnected during weak system conditions.

This is a threat and an opportunity for new solar projects.  The threat is declining revenue as the grid weakens over time.  The opportunity is to not only avoid the revenue decline but potentially increase production opportunities or scalability of your asset.

This opportunity can be realised through two main avenues:

• Matching the capabilities of the solar farm to the needs of the local network: For example, if the network has customers nearby, it’s likely that those customers or the network equipment supplying them will be sensitive to swings in voltage profile.  A solar farm with good reactive capability and voltage controls could have higher capacity and/or a cheaper grid connection since the network operator won’t have to augment their plant.

• Providing transparency of performance capabilities: To gain advantage from these additional capabilities, they must be clearly defined and communicated.  This is most often done through clear documentation and the provision of accurate dynamic models.  Accurate dynamic models are already mandatory for plants over 30 MW in Australia.  They may well be good business practice for smaller installations too, depending on the impact the plant can have on the network.

The solar industry and the wider electricity supply industry in Australia are on an accelerated learning curve when it comes to utility-scale solar due to the rapid deployment of this technology.

Grid connection does not need to be a roadblock to the roll-out of solar farms , but it must be carefully considered not just as a hurdle but as a tool to ensure the plant continues to be able to inject to the grid as the grid changes.

If you would like to find out more about how Entura can help you overcome grid connection challenges when developing your solar farm, please contact Donald Vaughan on +61 3 6245 4279 or Ranjith Perera on +61 3 6245 4272.

About the authors

Donald Vaughan is Entura’s Technical Director, Power. He has more than 25 years of experience providing advice on regulatory and technical requirements for generators, substations and transmission systems. Donald specialises in the performance of power systems. His experience with generating units, governors and excitation systems provides a helpful perspective on how the physical electrical network behaves and how it can support the transition to a high renewables environment.

Ranjith Perera is a Specialist Power Systems Engineer at Entura.  He has over 22 years of experience in Australia and South-East Asia, working on customer and generation connections and broader power system analysis.  Ranjith has provided power system advice on a wide range of network augmentations, network planning and system stability in Australia and internationally. These studies included option analysis in transmission planning, constraint analysis, determination of reactive support (dynamic or static) in system stability / TOV and detail load modelling in voltage stability. Ranjith also developed voltage recovery guidelines to TNSP based on regulatory requirement and customer equipment tolerances.

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26 September, 2016