Where to go in Cook Islands
To where in Cook Islands?While the only way to succeed is to minimise the amount of energy required for storing energy by deploying far more PV power than is needed to cover the needs ("overgeneration"), this has its own set of issues. Inset-Rarotonga, the biggest and most populated of the Cook Islands. Cook Islands are 15 far apart, partly populated and partly uninhabited islands 3,000-4,000 km north-east of New Zealand, subdivided into north and south groups (see below).
There is an island quarantine area of 1. but the islands themselves are only 236 square kilometres: The United Nations reports that the Cook Islands had a total of 17,389 inhabitants in 2017 and, according to the World Bank, in 2016 the total face value of gross domestic product was 311 million US dollars, equivalent to a per capita GNP of around 17,900 US dollars.
It is denominated in New Zealand dollars (the Cook Islands are self-governing, but the Cook Islanders are New Zealand citizens). Most of the production of the Cook Islands is from 6.5 MW diesels (photo below). A non-specified amount of photovoltaic has also been installed, with the biggest individual deployment being the 0. 96 MW facility at Rarotonga Airfield.
The yearly power consuption was 30. However, due to the costs of importing fuel, the prices of power are higher than in Denmark or South Australia. To cut fuel use, the Cook Islands launched "net metering" in 2009 to boost the PV on the roof. The Cook Islands have conceived a sum of $41. 85 million in financing, only $7. 14 million of which was raised by the Cook Islands according to the 2017 Pacific Energy Update.
Fig. 2, from the above interlinked document, shows details: Chart 2: Financing for the Cook Islands 100% Renewable Energy Programme. However, while there are a number of ongoing research programs in the project phase, there is some uncertainty in the world' s publications about exactly how many of these programs exist and on which islands they are located.
So in this article I consider the 15 different Cook Islands as one unit. So the first thing to ask is, how good is the Cook Islands' sunbase? In spite of their favourable latitudes, which lie between 10 and 20 degree Celsius southwards, the Cook Islands get 1,500 - 2,000 mm of precipitation per year, and according to Weatherspark the whole year round Aitatuke is covered in clouds just outside Rarotonga.
And, according to weather and climate, Rarotonga itself will receive an intersection of only 177 hrs of Sunshine a month or about 5. 8 hrs a days (Figure 3). In addition, Sunny Portal supplies power for the two photovoltaic systems currently in use on Rarotonga.
First is the UPS (University of the South Pacific) arrays, 3 km due eastwards of the much bigger airfield arrays to be next mooted. The total power output is 11. In the case of an east-west alliance, the panel is tilted approximately 20° northwards ((Figure 4).
Chart 5 shows the UPS Solars power since early 2013. While the system was completed at the end of October 2012, it does not appear to be operating at full load until mid-2014. However, for the three full operating years from 2015 to 2017, it only reached a capacitance ratio of 11.5%.
Fig. 7 shows the Rarotonga plant's output since early 2015. In the first two full years of operations (2015 and 2016), it ran at a capacitance of only 13.5%. In April 2017, however, production declined sharply, and in the 14-month period since then the production rate has dropped to 3.8%.
Fig. 7: Production from Rarotonga 961 airport. A 5 W photovoltaic system (the system is also called "Te Mana O Te Ra" - the force of the sun). With these two samples we can see that the Cook Islands do not have surplus sourcing.
Capacitance factor of 11.5% and 13. The 5% are only slightly better than the British photovoltaic capacitance factor, and fierce fluctuations in day-to-day production, as shown in Figure 8, do not give rise to trust either. Also the fact that sometimes for no apparent reasons the production of electricity drops to zero, as was the case at Rarotonga International Rarotonga between 18 April and 24 May 2017 and at the USP factory on 8, 9 and 10 May this year:
Fig. 8: Rarotonga 961 International Airports day-to-day production of electricity from sunlight. Built-in 5 W photovoltaic system, November 2016. However, on the assumption that these are indigenous malfunctions, do the Cook Islands have a reasonable prospect of substituting 100% photovoltaic production for the production of fossil fuels? In assessing Rarotonga's generating power output I used the Rarotonga sun exposure information collected by the South Pacific Wind and Solars Monitoring Project and used a 17.5% capacitance ratio consistent with the results for the degree of latitude retrospectively given in my estimate of overall PV loads and actually reached by the Rarotonga airfield arrays in 2015.
Horizonal radiations are a prop for generating electricity from the sun, so I have translated them into 30GWh of the Cook Islands' total energy use. Then, I extrapolated a Rarotonga month-by-month capacity graph (Chart 4) from this survey, adapted it to the 30 GWh of the yearly production and calculate the gap between production and supply.
Results are shown in Fig. 9: Fig. 9: Monthly PV yield, supply, excess amount of PV ("storage") and deficiencies ("release") estimates of sunlight horizontally. There is not much variation in year on year use, but between the April/May low and the November/December high there is a two-fold variation in PV production. This results in a photovoltaic shortfall between February and August and a photovoltaic excess for the remainder of the year, and these shortfalls and excess stocks determine the need for reservoirs to compensate for seasonality in demand-based production.
How many MW of PV are needed to produce 30 gigawatt-hours of Cook Islands per year at a power output of 17.5% without taking into account the need for compensation? A 1 GW at a 17.5% capacitance generates 1 * 8,760 * 0.175 = 1,533 GWh/year, so we need 30/1533 = 0.2 GW or about 20MW for 30 GWh/year.
Concerning the cost of sun:: An offer made in 2016 for 1,364 MW of photovoltaic power on four different Cook Islands amounted to USD 2,870 per kW sold kW. By 2015, Mpower was the winning tenderer for 5 MW photovoltaics on the near Samoa at $US 2,121/kW.
I' ve taken $2,000/kWh for the 20 MW of PV power needed to meet the Cook Islands' needs, which is a $40 million investment. For the Raratonga airfield arrays, the 5. 6Mw H lithium-ion accumulator system is rated at $A4. The 3,237 megawatt hour of lithium-ion batteries needed to compensate for the Cook Islands' sun's peak season would come at around $1.7 billion at this rate.
A 60% overproduction would mean the reduction of very large quantities of overproduction. Probably there would not be enough memory to cope with a longer period of insolation, e.g. a whole month without it. To keep the mains frequencies within tolerable limits, if this is possible at all, it would probably be necessary to add costly power factor correction systems, e.g. King Island, Tasmania.
100 percent renewed production can be more costly and less dependable than the diesels it will replace. Those who plan 100% clean energy on isolated islands do well to recognise that the results of "test cases" such as King Island and Gorona del Viento show that the replacement of more than 60% of current fuel production with intermittently clean energy is not a feasible target.