Technical study · Technical Advisory & Assurance

Grid Connection Strategy for a 50 MW Solar Farm

Comparing a 33 kV connection, a 132 kV line and a co-located battery for a 50 MW solar farm on curtailment, loss factors, system strength and 25-year value, and where the connection process slips.

Solar farm spread across a valley

What the client needed

A developer had a 50 MWac solar farm site in regional Queensland, with two connection routes on the table and an early preference for the cheaper one. Network constraints, curtailment and system strength requirements were all unknowns.

The question they needed answered: Which connection option gives the best project value, and how do we get through the connection process without losing a year?

  • 11% to 3%curtailment, 33 kV connection alone versus with a co-located battery
  • +$10.7Mproject value of the battery option against the cheapest connection
  • $16Mextra capex of the 132 kV line, not recovered

What we did

  • Compared three options: a 33 kV connection to a nearby zone substation, a 22 km 132 kV line to a transmission substation, and the 33 kV option with a co-located 25 MW / 100 MWh battery.
  • Estimated curtailment, marginal loss factors and connection capex for each, then modelled 25-year project value.
  • Assessed system strength obligations and the role of grid-forming inverters.
  • Mapped the connection process and where its schedule risk sits.

What we found

The 33 kV connection loses about 11% of output to network constraints, at a time when midday prices are already low.

The 132 kV line cuts curtailment, but its extra $16 million of capex isn't recovered over the project life.

A co-located battery absorbs energy that would otherwise be curtailed and sells it into the evening peak. With grid-forming inverters it also helps meet system strength requirements.

Most of the battery's value depends on evening price spreads. If they fall 30%, which is plausible as more batteries join the NEM, its advantage drops to roughly zero.

Schedule risk sits in power system modelling and negotiating the generator performance standard. Accurate plant models early are the best protection for the timeline.

Bar chart of net present value for three connection options relative to the 33 kV option
Connection option value relative to the 33 kV connection: the 132 kV line loses value, the 33 kV option with a battery adds it.

What we recommended

  • Proceed with the 33 kV connection, with connection rights, performance standards and system strength studies covering a future 25 MW / 100 MWh battery.
  • Build the battery once its revenue is underpinned by a tolling agreement or offtake, not on merchant assumptions alone.
  • Lock in the inverter vendor and plant models before the connection application, so power system modelling is done once.
  • Engage the network service provider early on system strength and performance standards.

Key assumptions

Solar capacity factor 28% (DC/AC ratio 1.3), energy and certificate value $65/MWh. Battery evening spread around $110/MWh at 330 cycles a year, plus FCAS. 25-year life, 7% discount rate. Curtailment and MLF indicative for a constrained regional network.

Related work

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