The gains from electrifying the car fleet are much greater, but the widespread adoption of solar panels would not do much good, and in the longer term might actually increase emissions.
That is partly because the manufacture of photovoltaic (PV) panels results in substantial "embodied" emissions. If the electricity needed to prise silicon from its oxide and refine it to the requisite purity came from the Manapouri power scheme, say, that would be one thing. But if it comes from a coal-fired plant in China, it is a different story.
Not only that. The widespread adoption of solar PV panels in our suburbs would be likely to crowd out the development of wind farms with lower embodied emissions. Much lower. Concept puts the life-cycle emission factor of wind power at 6.5kg of CO2 per megawatt hour, or about an eighth of solar PV.
The widespread adoption of solar PV panels in our suburbs would be likely to crowd out the development of wind farms with lower embodied emissions. Much lower.
Widespread use of PV would also increase the seasonality of the electricity system.
Households' demand for power is greatest in the winter, when solar is least available. The most cost-effective way of dealing with seasonality is likely to be the construction of gas-fired "peaker" generating plants.
"Because New Zealand's hydro stations are limited in their ability to perform significantly more seasonal storage than they currently do, and because batteries are not cost-effective options for performing seasonal storage, this increase in the seasonal gap between demand and supply will increase the need for fossil-fuelled power stations, which run in winter to supplement solar PV," says Concept director Coates.
"This issue doesn't arise to the same extent with new geothermal or wind generation because their generation is much flatter through the years."
Concept's model of the electricity sector enables it to figure out how its response to these technology shifts would vary over time.
Households' demand for power is greatest in the winter, when solar is least available. The most cost-effective way of dealing with seasonality is likely to be the construction of gas-fired "peaker" generating plants.
We are starting from a situation of excess capacity and little or no investment in generation. Thermal power stations are the marginal generators that would initially meet any increase in demand from electric vehicles.
So an increased uptake of electric vehicles is likely to increase emissions until the generation market gets back into balance. Further out, increased demand from EVs would mean more investment in renewables, although the timing of that would depend on what happens to the Tiwai Point aluminium smelter.
We are starting from a situation of excess capacity and little or no investment in generation. Thermal power stations are the marginal generators that would initially meet any increase in demand from electric vehicles.
Conversely, in the near term (the next couple of years) more PV on rooftops is likely to displace generation from fossil fuels.
But in the medium term (from 2022 onwards) high PV uptake would displace wind and geothermal plants that would otherwise be built, the Concept report concludes, and in the long term (from 2033) increase fossil fuel generation by amplifying the seasonality of the system.
The scenarios Concept has modelled have uptake of solar PVs (4kW per household) rising steadily from essentially zero now to 60 per cent of households by 2040.
By 2040 they have 80 per cent of households owning an electric vehicle. As many households have more than one vehicle, that would represent about 35 per cent of the light vehicle fleet.
And they have 60 per cent of households having invested in 7kWh of battery storage to smooth intra-day fluctuations in electricity consumption.
All three represent a similar upfront investment: "A 4kW solar PV unit retails at around $12,000 to $14,000 and a 7kWh storage battery is expected to have a similar price. This is also roughly the price difference between an EV and its conventional equivalent."
But the impact on emissions varies widely. The report's authors expect an EV operating this year to reduce emissions by around 1.2 tonnes of CO2 a year and that this would rise to around 1.5 tonnes in the longer term as the renewables' share of generation rises.
By contrast, they expect a 4kW solar panel installed this year to deliver almost no net reduction in emissions as the avoided emissions from the electricity sector largely offset the embodied emissions from the manufacture of the panel.
Over time they expect the savings from electricity sector emissions to decline as solar PV panels increasingly crowd out wind farms. "As a result over the longer term we expect a solar PV panel installed in 2031 to increase emissions by around 0.6 tonnes a year." For batteries, they expect reductions of around 0.2 to 0.3 tonnes a year, by increasing demand for baseload as opposed to peaking plant, and that this would not change much over time.
Concept's analysis found that combining batteries with solar PV did not fundamentally alter the results for PV by itself. The hydro stations already act like a giant battery, providing considerable flexibility in offsetting intra-day swings in output from solar panels.
"Furthermore batteries are not well suited to shifting power across seasons, for which there would be a greater need with high PV uptake."
Read the full report here:
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