Singapore is a city-state with high economic activity, high energy consumption and high population density (8,000 people per km2).2). Only about 10% of Singapore’s energy needs could be met by local solar energy. There is no wind or hydropower potential, and offshore solar energy options are limited by adjacent territorial waters and the need to maintain shipping lanes.
Currently, Singapore is dependent on imported fossil fuels. In the future, Singapore could source large amounts of solar energy from nearby countries including Indonesia, Malaysia, Thailand and Australia. This solar energy could be transmitted to Singapore via submarine HVDC cables. Wind energy could also be possible are imported from Vietnam.
Submarine HVDC cables are expensive and require complex negotiations with neighboring countries. Therefore, it is desirable that cables operate at maximum capacity most of the time.
This requires the deployment of substantial storage at the generating end of the cable. Storage absorbs excess solar energy during the day, which can then be sent to Singapore at night. Excellent locations for pumped hydroelectric power storage (PHES). are widely available in Southeast Asiaas well as batteries.
PHES is much cheaper than batteries for energy storage ($/GWh) for overnight and extended periods, and provides more than 90% of the current global energy storage for the electricity industry. However, batteries are cheaper in terms of storage capacity ($/GW). A hybrid PHES+ battery solution is usually superior to either solution because it benefits from the lower cost of battery storage power and the very low cost of PHES energy storage.
Solar cable options
Transmission of several GW of solar energy to Singapore from nearby Indonesian islands via submarine cable are proposed. This cable requires significant battery storage to increase the cable’s capacity factor. Alternative options are listed in Table 1.
| Table 1 | Solar park location | Cable length (km) | Sea depth max (m) | PHES quality | Indicative solar capacity factor |
| ZonCable | Australia | 4000 | 1800 | Marginal | 22% |
| Sumatra | Indonesia | 400 | < 100 | Excellent | 15% |
| Sarawak | Malaysia | 1100 | < 100 | Excellent | 15% |
The Sumatra and Sarawak (a Malaysian state on Borneo) options include cables that are quite similar to existing cables. However, ZonCable from Australia is ambitious, both in length and depth. SunCable has better access to sunlight, although resistance losses in HVDC cables reduce this advantage.
Good PHES is not available for SunCable in Australia. Sumatra has excellent PHES capabilities in the west of the island, within 400 km of Singapore, in the size range of 50-5000 GWh. For perspective, 5000 GWh corresponds to the effective storage in 100 million electric vehicle batteries. About three such systems would provide enough storage capacity to support a prosperous, fully electrified and carbon-free Indonesia.
Sarawak has a world-class PHES potential that could operate between two existing reservoirs, Bakun and Murum, with a potential storage capacity of 4,000 GWh. This far exceeds the needs of a completely carbon-free Singapore Malaysia. The water transport between the two reservoirs would consist of a 12 km long aqueduct and a 3 km long pressure tunnel, with a drop of 300 meters. The two reservoirs could house more than 100 GW of floating solar energy.
Solar energy
For a solar energy system in Sarawak or Sumatra, with a solar capacity factor (CF) of 15%, approximately 7 GW of solar capacity is required to deliver 1 GW continuously (24/7) via cable to Singapore: 8760 GWh (almost 9 TWh ) per year.
After taking into account a PV system performance ratio of 80% and 1 GW of solar energy continuously flowing through the cable during the day, a storage capacity of 4.6 GW is required to cover the solar panel output of a 7 GW PV system to absorb when the sun shines. .
Tracking solar energy can be used to achieve a greater daily energy yield per unit of peak solar energy. Another option is to overbuild the solar park (for example 10 GW instead of 7 GW). The low wholesale price of solar panels makes this option economically feasible.
Energy storage
An energy storage of at least 16 GWh is required to supply 1 GW to the cable during the night. However, significant additional storage is required to withstand cloudy periods of several days.
Class AA and AAA PHES systems are available in both Sumatra (50-5000 GWh) and Sarawak (Bakun-Murum, 4000 GWh) at a capital cost of approximately $5 billion for 3 GW of storage capacity plus 150 GWh of energy storage (ANU PHES Cost Model updated to 2024 prices). This is far below the cost of equivalent batteries.
The marginal capital cost of additional PHES energy storage in Sumatra is approximately $6 million per GWh, which is extremely cheap compared to batteries. This low cost is due to the fact that increasing energy storage simply means removing more rock from the bottom of the reservoirs to make the reservoir walls a few meters higher. More battery storage, on the other hand, entails the use of more electrochemicals. In Sarawak, the marginal cost is essentially zero due to the sheer size of the existing Bakun-Murum system.
It is therefore beneficial to build sufficient storage on Sumatra or Sarawak to ensure that the cable to Singapore runs almost continuously at full load. SunCable, on the other hand, has to rely on batteries.
10 GW solar energy on Sumatra
Consider a high-density solar farm of 10 GW and a capacity factor of 15% (Table 2), located in Sumatra, somewhere along the 360 km transmission cable route shown in red in the figure. The cable reaches prime PHES locations in Sumatra and the route crosses existing high-power north-south transmission lines, which would be a good location for the solar park.
The cable continuously (24/7) transports 1 GW of solar energy to Singapore (9 TWh per year). Excess solar energy (4 TWh per year) is supplied to Sumatra’s transmission system. Sharing system output between Singapore and Indonesia is strongly preferred due to cost savings on both sides.
The solar park will cost approximately $10 billion, according to Australia Gene costs model. It is linked to a Class AAA3 GW, 150 GWh, PHES system. Singapore and Indonesia will share energy storage equally and will be allocated PHES generation capacity of 1 and 2 GW respectively. Indonesia provides land in exchange for its share of solar energy, energy storage, storage energy and local economic activity.
The total system cost is approximately US$15 billion, excluding transmission to Singapore. Assuming an economic life of the system of 30 years and a real (inflation-free) discount rate of 5%, this corresponds to 80 US$/MWh.
The combined costs of solar energy generation and storage are commercially interesting, especially if they include a carbon price. Many variations can be explored to optimize such a system.
| Table 2 | Singapore | Indonesia | System |
| Solar energy (GW) | 10 | ||
| Energy supply (TWh per year) | 9 | 4 | 13 |
| PHES pump power (GW) | 3 | ||
| PHES generation capacity (GW) | 1 | 2 | 3 |
| PHES energy storage (GWh) | 75 | 75 | 150 |
| Solar Cost (US$B) Gene costs | 10 | ||
| PHES fees (US$B) | 5 | ||
| Solar park area (km2) | 70 | ||
| PHES flooded area (km2) | 10 | ||
| Local content | Low | High |
Authors: Prof. Ricardo Rüther (UFSC), Prof. Andrew Blakers/ANU
Andrew.blakers@anu.edu.au
rruther@gmail.com
ISESthe International Solar Energy Association is a UN accredited member NGO founded in 1954 working towards a world with 100% renewable energy for all, used efficiently and wisely.
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