Power ships: a real solution to South Africa’s short-term energy needs

April 20th, 2015, Published in Articles: EE Publishers, Articles: Energize

 

A set of cost-effective privately owned and operated floating power stations, moored at a number of South African harbours, would provide much needed electricity to the country and would remove the need for most of the loadshedding currently being experienced. These floating power stations are known as power ships (Fig. 1).

 

Rauf Bey 3

Fig. 1: A power ship at sea.

 

Having recently returned from a site visit to an operating power ship which is moored in Beirut, Lebanon (Fig. 2), I am convinced that this solution is exactly what South Africa needs right now.

A power ship is a fully self-contained power station built on an ocean-going ship. Each power ship contains its own generation, electrical control, and substation components. The ship also includes its own maintenance workshop and engineering capabilities. The onboard substation, which can be connected to the national grid without lengthy delays or complicated engineering, can be configured to meet the specific requirements of the host country’s electricity grid at the point of power injection.

Four 500 MW power ships, moored at different harbours around the country, would supply the grid with an additional 2000 MW – equivalent to stage two loadshedding which has been frequently imposed by Eskom in recent times.

Power ship operators supply electrical power as independent power producers (IPPs) working under contract to supply a certain amount of electricity to the national grid. This contract is usually known as a power purchase agreement (PPA). Tap changers on the power transformers in the power ship’s substation allow the substation to supply the correct high voltage to match the grid infrastructure.

Power ships are designed to supply base load power 24-hours a day, seven days a week. Each ship manages its own electrical supply by means of its own on-board electrical control system. The sophisticated control rooms in these power ships are as advanced as any control room one would expect to find in a modern land-based power station.

The electricity is generated by a number of high power alternators in the hull of the power ship, driven by reciprocating engines which can run on natural gas or heavy fuel oil. Since most harbours already have storage facilities for heavy fuel oil, all that would be required is for a fuel line to be run from the storage tanks to the ship. Each ship also has its own fuel storage tanks onboard which act as a buffer to prevent power interruption should the onshore storage tanks run low. In addition to the fuel line, high voltage powerlines will be required to evacuate the electricity from the ship’s on-board substation to the electricity grid.

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Fig. 2: Power ship “Fatmagul Sultan” moored at Beirut.

 

The fact that these power ships operate on heavy fuel oil is another advantage. Heavy fuel oil is significantly cheaper than the diesel fuel which is currently used to power South Africa’s aging open cycle gas turbines (OCGTs). Furthermore, the engines in the power ships are designed to operate on that fuel – unlike the OCGTs which had to be modified to run on diesel fuel instead of gas. Also, power ship engines are designed to operate continuously at full load delivering base load power – unlike the OCGTs which were designed to operate for short periods of time to provide the additional power required during peak demand. OCGTs are often referred to as “peakers” for this reason.

 

Fig. 3: On-board substation and high-voltage powerlines for electricity evacuation.

Fuel oils

To fully appreciate the advantage of running an alternator’s engine on heavy fuel oil instead of diesel fuel, it is necessary to understand the difference between the different grades of fuel oil.

Table 1 lists the four primary types of oil in order of cost, with the most expensive first [1]:

Table 1: The four basic oil types [1].
Oil type Examples Details
Very light oils / light distillates Jet fuel, petrol, paraffin, light virgin naphtha, heavy virgin naphtha, petroleum ether, petroleum spirit, and petroleum naphtha. These oils tend to be highly volatile and can evaporate within a few days.
Light oils / middle distillates Most grade 1 and grade 2 fuel oils, diesel fuel oils, most domestic fuels, and light crude marine gas oils. These oils are moderately volatile, less evaporative and moderately toxic.
Medium oils Most of the crude oil on the market these days falls into this particular category Volatility makes for messier and more complex “clean ups” and increased toxicity levels.
Heavy fuel oils These are crude oils, Grades 3, 4, 5 and 6 fuel oils (bunker oil) as well as intermediate and heavy marine fuels. With these oils there is very slow and little evaporation and therefore toxicity is highly increased

 

Table 2 lists the fuel oils by grade number, in order of cost, with the most expensive grade first [2].

 

Table 2: Table of fuel oils [2].
Table of fuel oils
Name Alias Also known as Type Sulphur content Viscosity
No.1 fuel oil No. 1 distillate No. 1 diesel oil Distillate 0.001%
No.2 fuel oil No. 2 distillate No. 2 diesel oil Distillate 0.1%
No.3 fuel oil No. 3 distillate No. 3 diesel oil Distillate 1,0% 180 Cs
No.4 fuel oil No. 4 distillate No. 4 residual fuel oil Distillate/Residual 1,0% 380 Cs
No.5 fuel oil No. 5 residual fuel oil Heavy fuel oil Residual <3,5% 180 Cs
No.6 fuel oil No. 6 residual fuel oil Heavy fuel oil Residual <3,5% 380 Cs

 

As can be seen in Table 2, heavy fuel oil (No. 6 fuel oil) is significantly less expensive to buy than diesel fuel (No. 2 fuel oil). Since the engines used in the generation of electricity in a power ship use heavy fuel oil they are cheaper to run. In addition to this, the engines are new, built to new specifications and with new modern materials. For this reason, the engines can be expected to be more efficient than the older modified gas engines in Eskom’s fleet of  OCGTs. This means that the engines which drive the alternators in a power ship can be expected to use less fuel for the same power output. Calculations show that fuels savings as high as 30% can be achieved. These cost savings are significant considering that Eskom is reportedly spending between R1-billion and R2-billion per month on diesel fuel to run its OCGTs.

Standards and classification of fuel oils

Two indexes are used to describe the ignition quality of residual fuel oil: Calculated Carbon Aromaticity Index (CCAI) and Calculated Ignition Index (CII). CCAI is often calculated for marine fuels with their maximum viscosity rating, as set by the ISO 8217 standard (Table 3), because marine engines are designed to use different viscosities of fuel. The unit of viscosity used is the Centistoke (Cs) and the fuels most frequently quoted are listed below in order of cost, with the most expensive first [2]:

Table 3: Classification of fuel oil according to the ISO 8217 standard [2].
Name of oil type Description
ULSMGO Ultra low sulphur marine gas oil (0,0015% maximum in the US and 0,001% maximum in the EU
LSMGO Low-sulphur (<0,1%) marine gas oil
MGO Marine gas oil
MDO Marine diesel oil
LS 180 Low-sulphur (<1,0%) intermediate fuel oil with a maximum viscosity of 180 Cs
LS 380 Low-sulphur (<1,0%) intermediate fuel oil with a maximum viscosity of 380 Cs
IFO 180 Intermediate fuel oil with a maximum viscosity of 180 Cs (<3,5% sulphur)
IFO 380 Intermediate fuel oil with a maximum viscosity of 380 Cs (<3,5% sulphur)

 

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Fig. 4: Fuel pipes supplying the power ship with heavy fuel oil.

 

In addition to the efficiency of the newer type of engine running on cheaper fuel, the power ships also capture the heat generated by the engines in operation which is converted into superheated steam and is used to drive a steam turbine which also generates electricity. This adds to the total efficiency of the power ship by about 6%.

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Fig. 5: A power ship’s generation room with engines in the centre, alternators and exhaust on the left and ventilation on the right (Karadeniz).

 

Fig. 5 shows one of two on-board generation rooms in a power ship. The ship is configured with two generation rooms, one at each end of the power ship, with the control rooms and substation in the middle. This configuration provides the flexibility of operating either of the two generator rooms or both depending on requirements. The output of the two generation rooms is independently controlled and sent to the substation separately. The high voltage electricity from the substation can be evacuated to two different points on land or be bus-tied to supply a single point.

Electricity supply

In order to keep the power ship autonomous from the country to which it supplying electricity, all of its own electrical needs are supplied by the ship itself. The on-board alternators generate 11 kV which is sent to the control room in the middle of the ship. The control room routes some of this electrical supply to step-down transformers where 400 V is provided for the ship’s own systems such as lighting, refrigeration, communications, computers, etc.

The bulk of the electricity however, is sent to the sub-station which is located on the top of the power ship for conversion via power transformers to the high voltage as required by the host country. This high voltage power, typically 132 or 150 kV is evacuated from the power ship’s sub-station and synchronised via high-voltage power lines into the country’s electrical grid system.

Advantages of shoreline generation

One advantage a power ship offers is being able to meet the demand of a coastal city or industrial facility. When power from the power ship is supplied into the local network it will meet the demand of, or part of, a coastal city or large industrial facility. This reduces the demand on the national network, leaving power available to meet the rest of the country’s demand.

Another advantage, particularly where multiple power ships are deployed at a number of different ports, is the reduction of the power losses associated with long powerline runs from centralised generation at inland power stations to coastal cities and industrial facilities. It has been estimated that such losses could be as high as 6% in South Africa. This reduction in energy loss results in higher efficiencies with attendant financial savings.

Water desalination

Every power ship requires water. Since the power ship is floating in seawater, water is drawn up and desalinated as part of the power ship’s systems. This water is used in various applications in the ship such as cooling, washing, cooking, etc.

Another potential benefit is the supply of desalinated water into the immediate area where the ship is moored for use by the local community.

International use of power ships

Power ships are in use in many places around the world. The particular company whose power ship I visited in Beirut, and upon which this article is based, Karadeniz Powerships, has a number of power ships in various international locations. The company was also recently awarded a contract to supply power ships to Ghana which is desperately short of generation capacity.

 

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Fig. 6: Starboard side of the power ship showing exhausts and water intake pipes.

 

The South African context

In the South African context, four 500 MW ships, moored at four different locations so as not to take up too much space in any one harbour, would provide 2000 MW at about 30% less per MW than what Eskom’s OCGTs cost. Not only would the electricity be cheaper, but because these power ships are designed to supply base load, security of supply can be guaranteed. Eskom’s existing fleet of OCGTs would then be able to operate as they were designed to – as peakers – and return to their peaking duties.

Timing

Land-based power stations have to be built onto purchased land which needs to be properly cleared and prepared for this specific use. A power ship, however, is built onto an existing hull. Hulls of various sizes and types (called “classes”) are sought and purchased by the power ship company for specific power ship sizes and types. The two main classes are ships (Fig. 1) and barges (Fig. 2). Ships can be propelled by their own power to the port of destination. Barges have to be towed to their destination as they have no motive power of their own. In some cases a barge type of power ship is required as a result of the depth of water in a specific location where the power ship is to be moored. Barges require shallower water than a ship which has a deeper draft. This is the case with the power ships in Beirut.

Power ships are built to standard designs which are adapted to suit the requirements of the host nation. This standardisation reduces manufacturing time significantly. The Karadeniz company, for example, recently purchased a 300 x 52 x 42 m hull (Fig. 7) which will become a 500 MW power ship within about eight months. It is impossible to build a 500 MW power station from scratch on land within that time.

 

Hull for 500 MW power ship

Fig. 7: Hull for 500 MW power ship.

If the company was to receive an order for a power ship for which it had no hull, it would have to start the process by finding a suitable hull for the type and size of power ship it needs to build to fill its client’s order. In this case, the delay between date of order and date of commissioning could extend to 18 months.

What the host nation would usually provide

A power ship needs very little infrastructure from the host nation. However the following will be essential:

  • High-voltage powerlines up to the ship’s substation
  • A flexible fuel line from on-shore storage tanks to supply heavy fuel oil to the ship

A temporary solution

Power ships are not a permanent solution and are not meant to be. A set of power ships would only be required until permanent power stations are completed. The immediate advantage of these power ships is that the host country could expect to suffer far fewer power disconnections with all of the advantages associated with a stable electrical supply.

Conclusion

South Africa’s electricity generation capacity shortfall can only be solved by additional generation capacity. Although additional power stations are under construction there is a lengthy gap of time between the present shortage and the commissioning of all units of these new power stations. In the meantime, the economy suffers from the reduction of productivity and increased costs resulting from power interruptions caused by equipment failure (so-called unplanned maintenance) and loadshedding.

Access to cost-effective temporary base-load generation of a significant magnitude will help to solve the problem by supplying the power to meet the load which is often being shed at present. In South Africa that load is frequently about 2000 MW. Power ships offer a quick, tried and trusted solution which can be supplied in months instead of years, with no capital outlay on the part of the government or power utility.

Power ships are another source in the total energy mix, together with coal-fired power stations, nuclear power stations, and renewable power sources such as wind, hydro and solar. A power ship is simply another IPP, offering a short- to medium-term (three to ten years) supply of electricity.

For this reason, it should be seen that power ships offer a real solution for temporary power generation when the country needs it most.

References

[1] “A Detailed Guide on the Many Different Types of Crude Oil”, http://oilprice.com/Energy/Crude-Oil/A-Detailed-Guide-On-The-Many-Different-Types-Of-Crude-Oil.html

[2] “Fuel oil”, http://en.wikipedia.org/wiki/Fuel_oil

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