The Friday Australian has an article announcing a $610 million loan from the federal government’s Northern Australia Infrastructure Facility to facilitate the construction of a combined solar/pumped hydro scheme in north Queensland – “Power of gold to help run energy”.
Apparently the NAIF is “investing in this project because of the importance of affordable and reliable power in developing the north”. One might ask why the government is not doing something about the problems further south. The coming summer will see a repeat of high prices and the grid on the edge of collapse.
The scheme involves using an abandoned gold mining operation in the middle of nowhere to develop a pumped hydro scheme. There are 2 mine pits separated by sufficient height, and of sufficient capacity, to operate a 250 MW hydro station for 8 hours and generate 2,000 MWh.
The power to pump the water will come from a 320 MW solar array adjacent to the mine pits.
Using the numbers spruiked by the proponents the solar farm will produce 928,000 MWh per year. The hydro pumping/generating cycle has an efficiency of 80% so each 2,000 MWh generated needs 2,500 MWh of pumping power to get the required water into the upper storage.
Dividing the solar output by the pumping power gives a possible 371 cycles per year, just over 1 per day, so the hydro output is 742,000 MWh per year. When this is “annualized” by dividing by 8,760 hours per year the “equivalent” rated capacity becomes 85 MW.
A continuous generator rated at 250 MW will produce 2,190,000 MWh per year so the capacity factor of the hydro scheme is 34% which is just above what a wind farm can manage.
The site is at 18 degrees south latitude so is in a good spot for solar compared to southerly climes. There will be times of the year when the sun is directly overhead and even in the south as we get into the summer solstice for the southern hemisphere. On the down side, the tropics are liable to be clouded over for quite a bit of the time and this will curtail solar production.
In previous posts I have analysed solar farms on a daily basis to show the seasonal decline and the chaotic nature when the sky gets cloudy. I cannot find a weather station with the data needed except for Cairns which is some distance away and frankly the analysis is a bit tedious.
If the hydro station can run for 8 hours at full capacity it is reasonable to expect that the refilling would take at least as long – probably longer as the pump efficiency will likely be less than the generator efficiency. Either way, the refilling must take about as long as the sun shines enough to generate solar power so it would seem the scheme is limited to one cycle of generating per day and this must be in the dark hours because generating needs to be finished before the sun rises.
The project is being sold with the usual hyperbole about “storing and dispatching electricity at full design capacity for 8 hours” and “being available on demand” as well as “lowering prices and increasing electricity network security and stability” but I wonder if reality will agree with theory here.
When the numbers are done we have a situation where there is a scheme with a “rated capacity” of 570 MW, (320 of solar and 250 of hydro), that ends up the equivalent of a reliable generator rated at 85 MW. If the 570 MW is “annualized” then the overall capacity factor of the scheme is a paltry 15%. Also, it can only produce electricity for 8 hours every day so I wonder where “the north” will get the other 16 hours’ worth.
The question to ask is, is this a good use of $610 million of taxpayers’ dollars? Yes, I know it is a “loan” but as they say “if you owe the bank a million dollars and you can’t pay the bank has a problem”.
Interestingly the proponents have some production and revenue figures on their website for 3 quarters, (Dec 2017, Mar 2018 and June 2018), for the 50 MW solar array that is already in operation and the average revenue per MWh is $146 so it is unlikely that lower prices will result.