Better price signals are expected to deliver improved decisions on generation investment and see grid-scale batteries used efficiently – instead of just for avoiding transmission costs. Those benefits could be worth another $350m.
"Under the current TPM, customers are investing in alternatives - such as batteries - to avoid paying the peak charge, which wastes resources and shifts the cost of operating and maintaining the grid to others," Stevenson-Wallace said.
"This avoidance is likely to increase if the TPM is not amended, as more grid investments are made to support the shift to a low emissions economy – and batteries and distributed generation become more affordable."
The industry has been debating improvements to transmission pricing for a decade. Some changes have already been made, freeing up generation in the South Island and removing transmission subsidies from small, regional power stations unless those plants actually provided a network benefit.
But the main issues – charging all of the $145m annual cost of the high-voltage link across Cook Strait to South Island generators, and smearing the costs of major transmission projects across all consumers whether they benefited or not – remain unresolved.
The EA says the country needs more renewable generation, yet potential South Island generation projects are being disadvantaged by an effective 'tax' increasing their costs by about 10 per cent.
Leaving firms and households in most of the South Island and parts of the North Island paying for – but getting little benefit from - more than $2b that was invested in the past decade upgrading the power link across Cook Strait, the lines around the Wairakei geothermal fields, the lines from Whakamaru into Auckland, is also adding further risk.
The authority noted that increased spending signaled by Transpower means it can't leave those historic project costs being carried by consumers across the country.
"For example, with a benefit-based charge, Christchurch consumers could expect to pay most of the $283m cost of the planned new switching station and new transmission line into Islington.
"If the seven major grid investments were to be grand-parented, the same consumers would also continue to pay nine per cent of the cost of investments that benefited mainly North Island consumers, such as the $876m North Island Grid Upgrade."
The scheme proposed today is little changed from that proposed in 2016, when the authority had also proposed a cap on the annual impact the change could have on households.
But the benefits and costs are generally smaller, as falling interest costs mean transmission charges will be much lower – about $848m in 2022 when the change could take effect – down from about $950m today and less than had been projected in 2016.
The authority has also trimmed the post-2004 major projects that will be captured by the benefits-based charge from 10 to seven, and the value remaining after depreciation for those projects has also fallen further since then.
Where Auckland power distributor Vector, a vocal opponent of the change, had in 2016 faced a potential increase in its transmission costs of $59m, today's proposal would see those costs rise in 2022 by $7m.
Similarly, Meridian Energy, which had been expected to benefit by $57m, gets about a $29m cut under the latest proposal. The Tiwai Point aluminium smelter, which was expecting a $20m benefit, will likely be $11m better off than would otherwise be the case in 2022.
Among lines companies, Wellington Electricity and New Plymouth-based Powerco may get the biggest savings at $7.6m and $5.1m respectively. Christchurch-based Orion and Dunedin-based Aurora Energy face the biggest increases at $7.7m and $3.6m respectively.
The authority is receiving submissions on its proposals until October 1. It is aiming to make a final decision early next year.
