raytaylor:In some winters, lake levels get quite low so it makes sense to hold back as much of that water as possible.
During the day, solar can be used to run the grid, more water is left in the lakes. Over a month or two that can make a big difference to lake levels, and delays the possibility of needing more dams to be built as no matter where you try and build a dam in NZ now its getting less and less possible with the iwi, Fish&Game etc opposition.
However there may be less opposition to pumped hydro where two lakes are used, excess electricity during the day is used to pump water up hill, then in the evening it is run back down.
To see that happen we would have to increase solar installations quite a bit.A pumped hydro company will typically buy electricity when its cheap, and then sell it back for a higher price later (evening) so it could make sense with mass solar installations when our daytime solar, wind and geothermal production exceeds consumption at which point we can store it in pumped hydro for the evenings.
In germany they are making a huge success with solar - they have some of the highest rates of solar production in the world per capita, but even all of germany has less clear sky hours than invercargil (one of our worst areas)
Just because something is possible from a purely technical perspective, doesn't mean that it is a good idea from an economic perspective as well.
Let's compare say 100MW of fossil fuel or Geothermal generation to a solar and pumped storage system. The fossil fuel and Geothermal generation can run at their rated output 24/7, all year round, and in any weather conditions. Solar panels only output around 10-15% of their rated output on cloudy days, and they only work during the daytime. So you would need to build at least 2000MW of solar, just to get the same daily power production as the 100MW of Geothermal or fossil fuel generation. And since winter peak demand is at around 8pm, you still have to build the pumped storage. And when there is a shortage of hydro water, wholesale prices are never cheap. Right now, prices are around $150 per MW with lots of coal and gas generation in use. Adding efficiency losses, CAPEX and OPEX costs, the pumped storage would need to sell power for at least $250 per MW.
Meanwhile, the original version of the proposed Project Aqua hydro scheme would have broken even at an average selling price for its power at $35 per MW. And it was abandoned when extra RMA costs pushed the break even price closer to $50 per MW. Coal generation has a break even cost around $75 / MW.
And when the hydro dams are overflowing or close to it. The dam owners will happily sell their electricity for virtually nothing on the wholesale market. As any money is better than otherwise letting that water flow to waste.
Since fossil fuel generation can be run at any time, Owners of fossil fuel generation can sign futures contracts or supply agreements, well in advance of the agreed time of supply, with certainty of profit. And if the hydro generators start selling power really cheaply, the fossil fuel generation owner makes an even bigger profit. As they can shutdown their generators, and resell power that they have purchased from the hydro generators.
So there is no scenario where solar and pumped storage can undercut the current generators on price.
Even in Samoa, they have some massive solar farms next to the airport. Meaning they sometimes generate enough power during the day to have 100% renewable generation. Except that they found out the hard way. That they still need to keep the diesel generators running to provide spinning reserves. They tried turning the diesel generators off once. Then the sun went behind a cloud, the drop in output caused a blackout, as the hydro generators have nowhere near enough capacity to run the whole load, even for a very short time. It took them 3 hours to get the power back on again. (not helped that it happened on a Sunday)
Samoa is now in the middle of a program to build lots of hydro generation. And that is despite their climate and load profiles being far better suited to solar than NZ, and the only practical fossil fuel generation they have is diesel. Which is far more expensive to run compared to fossil fuel generation in NZ. Yet they have a goal to have 100% renewable generation. And the way things are going in NZ, Samoa will be far more likely to successfully reach 100% than NZ. Despite Samoa previously getting well over 50% of their generation from diesel, only around 10 years ago.
As for Germany, They are still well under 50% renewable generation on a yearly basis. Despite all of their solar, and their ability to export any excess generation to other European countries. Their figures are even worse when compared to NZ and Samoa. As German households use lots of Natural gas for heating and hot water. While NZ mostly uses electricity for heating and hot water. And not many households in Samoa even have piped hot water, while a heater in Samoa is about as much use as an ash tray on a motorbike.
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