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This article looks at the growth of solar energy generation in Australia, its benefits and challenges posed to grid operators due to the inability of traditional energy infrastructure to accommodate increased capacity from distributed resources.

The article provides recommendations to address challenges stemming increased grid-DER integration.

This article first appeared in Smart Energy International Issue 3-2019.
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According to the Australian Energy Market Operator the average daily peak generation of rooftop photovoltaic (PV) increased 25% from 3110MW to 3878MW between Q4 2017 and Q4 2018.

The increase in solar PV generation is attributed to a record amount of installed rooftop solar capacity over 2018, which made up 74% of total solar generation in Q4 2018.

The Clean Energy Regulator estimated that 1.6GW of solar capacity was installed across Australia over 2018, with more than 1GW of this capacity expected in the National Electricity Market, the system connecting electricity transmission grids of the eastern and southern Australia states and territories to create a cross-state wholesale electricity market.

Regulation

The speed and magnitude of our solar PV uptake is expected to continue skyrocketing following increased focus to expand portfolios of renewables by utility companies and an increase in both private and public funding in addition to the adoption of favourable policies by regulators as part of efforts to address climate change.

In Victoria and New South Wales (NSW), political parties offered rooftop solar rebate and battery storage subsidies.

Recently, the NSW Labour Opposition promised to deliver the biggest renewables rollout of 7GW of renewable energy.

Network challenges

However, the growth of the country’s renewable energy portfolio is expected to pose challenges for grid operators, as the current electricity infrastructure was not designed with the intention for electricity to move in two directions.

While it is not impossible for electricity to flow backwards, it is tricky to manage the grid on a technological level, especially when there is a lot of distributed electricity feeding back into the grid in the same area. Transformers may become saturated due to increased voltage from exportation. So what challenges do networks face when the local part of the grid is full?

Maintaining grid stability

Networks will face new technical and operational challenges in managing the future grid. The two main technical issues caused by large amounts of solar being fed back into the grid include: Voltage spikes on low voltage lines could damage network and consumer equipment and result in networks needing to temporarily shut down solar inverters to restore voltage to normal limits. Presently, because of limited visibility of data, there is little ability for low voltage networks to manage distributed energy resource (DER) export and the constraints in their networks that lead to high levels of DER causing them to breach technical obligations, such as voltage limits.

Thermal overloading of substation transformers or fault currents caused by net reverse (upstream) flows.

South Australia Power Networks (SAPN) conducted a pilot project in Salisbury which included integrating consumer onsite energy storage and solar generation to address voltage spikes and overloading of substation tranformers.

The study revealed that for customers installing solar systems of 5kW or more, even with batteries, energy exports are still typically significantly exceeding imports as most customers’ batteries are fully charged by about midday.

SAPN projects that zone substation reverse flows will be emerging across South Australia by 2020, and by 2050, distributed solar load flows on high voltage feeders could potentially exceed asset ratings at times of minimum demand.

Network impacts will arise first in the low voltage network, where the effect of increasing penetration of solar and other DER is to increase the dynamic range of power flows between peak demand and peak export and the rate with which the system can swing from one end of this range to the other.

Hence, investments such as changes to network configurations or equipment become necessary to maintain grid stability and reduce risks. But, who should pay for these investments?

According to the country’s standard for electrical and general safety installation for inverter energy systems, AS/NSZ 4777, most networks will allow system sizes as per the below:

1 Single phase connection (most homes): Up to 5kW

2. Three-phase connection (some homes and many businesses): Up to 30kW

Another important implication of size limitations is solar feed-in tariff eligibility. ‘First in best dressed’ access policy applies – so once certain (very localised) saturation levels are reached, new customer connections within the same area may not be allowed to export into the grid due to technical network constraints. New solar customers will naturally expect to be able to get connected to the grid and take advantage of feed-in tariffs to the same extent as their neighbours. But this is not always possible and it is raising questions of ‘solar equity’. Questions like ‘Why should my neighbours be able to export up to 5kW but I am restricted to 0kW because I connected after them?’ and ‘Do they pay more than me for this privilege’? The governing National Electricity Rule 6.1.4 states that ‘a distribution NSP must not charge a distribution network user, distribution use of system charges for the export of electricity generated by the user into the distribution network’. This leads to significant constraints as it bans export charging.

Legitimate questions are being raised about the local access regime and whether it remains fit for purpose. The reality is, the ‘first in best dressed’ approach needs assessment and innovative approaches considered – for example, sharing of export capacity among all customers, with energy potentially tradeable or auctioned.

Customers applying to install solar should always contact their local distributor to check network capacity before they make the decision to invest; and solar companies with an interest in their business should be advising them to do so.

Curtailment

Curtailment or the restriction of a customer’s generation capacity because of weakness in the grid in an area is a growing issue in Germany and China. It becomes essential to protect wholeofsystem security, safety and power reliability. In Germany, grid operators are being forced to dramatically increase operating costs to stabilise a centralised grid that was never built for fragmented renewable production. While in China the government has been trying to adjust the timing of construction and has set up an early warning system forcing regions suffering from excess capacity growth to slow down the pace of new approvals.

Considering these international scenarios, curtailment could become an issue in Australia, particularly as DER uptake accelerates as solar and battery subsidy policies take full effect.

In Australia, the Australian Energy Market Operator (AEMO) manages curtailment in large-scale generation in the National Electricity Market. While you would think new solar customers in Australia would prefer occasional curtailment to blanket export restrictions, distribution businesses do not have capacity to curtail at the local level. This poses the question of how curtailment in small-scale generation will be managed in future in order to ensure power system security and fairness for customers.

Promises versus challenges

It is essential that Australia establishes an effective mechanism to properly integrate solar and storage into the grid so customer exports aren’t restricted and they are able to get full benefit from their DER.

Energy Networks Australia has developed the Energy Network Transformation Roadmap to facilitate the development of a pathway forward for network businesses to accommodate distributed energy throughout their networks.

Energy Networks Australia is soon to launch DER connection guidelines, which will provide technical guidance for standardising rooftop solar connections for all Australian network businesses.

At a political and government level, policies and programmes must consider network and whole-of-system challenges. If they don’t, not only will customer expectations not be met, the system simply won’t cope. The solar boom could go bust. SEI

About the author: Monishka Narayan is a programme coordinator at Energy Networks Australia. Previously, worked with Charles Darwin University as a Research fellow developing organic, hybrid and perovskite solar cells.