Putting solar technology into the hybrid mix
Wendy Laursen reminds us that there are solar-collecting sails on the horizon but it may be some time before they make their way into the emissions reduction plans of most shipowners.
“I’ve got no doubt that in 50 years time you’ll look out at the horizon and all bulkers and tankers will have wings.” It is a vision for the future that Dr Robert Dane, CEO of Solar Sailor in Australia, is confident will give shipowners fuel savings of 20% to 40%. When they have finished looking at the options that currently offer savings of between 2% and 5%, harnessing solar and wind energy from rigid sails will offer that quantum leap, he says.
Dane has developed a design for a bulk carrier retrofit and is currently in negotiations with a shipowner for the Aus$7million installation of two 800m2 sails on a vessel that voyages between Australia and China. Payback time is expected to be two years.
The system has already been installed on passenger ferries in Australia and Hong Kong. It does not change the propulsion system of the vessel. Rather harnessing wind energy reduces the demand on the propulsion engine and the solar energy covers the hotel load with the added advantage of providing zero emissions in port.
The sails would be stowed in void spaces in the wing ballast tanks of the bulk carrier. They take about an hour to raise but can be lowered and secured within three minutes if required in stormy conditions. Strength, stability, cargo handling and bridge visibility all need to be taken into consideration with the design, but the challenges disappear with newbuilding designs, says Dane.
It is available light, not heat, which is required for the photovoltaic cells on the sails which are automatically positioned to maximise both wind and solar energy. The sails also automatically feather in adverse wind conditions, although manual operation is also possible if desired. The wings are engineered to handle 40 knot winds with a 300% safety margin when upright which equates to speeds of about 56 knots.
“They can trim and point to the wind much better than a kite sail,” says Dane. “Kites are good for going down wind so if you are going from Australia to Venezuela with the Roaring Forties, that would be fine, but as soon as you start going across the wind, or if the wind is variable or the voyage is short, then sailing is the way to go.”
In his vision for the future, Dane sees the sails as an important part of the adoption of fuel cells for propulsion because a ship can then generate its own hydrogen by the hydrolysis of water using clean, renewable energy from the sails. However, he admits that the current financial climate is slowing down adoption of both technologies.
David Surplus, managing director of B9 Energy O&M, has designed a 100% renewable energy-powered 3,000dwt sailing cargo ship – presented at The Motorship’s last Gas Fuelled Ships conference - and not included solar power in the mix. “Solar only has the potential of providing power to drive a proportion of the ship’s auxiliary load,” says Surplus. “The percentage contribution to total energy demand of a conventional ship design would at best be measured in single figures. We are trying to avoid the use of fossil fuel altogether and are expecting 60% thrust from wind, in the North Sea wind regime, and 40% from a bio-methane powered spark ignition engine or molten carbonate fuel cell.
“I suspect there is a degree of tokenism with solar which fits in with the mind-set that a 10% saving in fuel is a worthy target. The world needs to reduce carbon emissions by 80% by 2050 and the reductions need to be sooner rather than later in that timeline. We simply won’t make it if we aim for 10% cuts.”
Return on investment was a major sticking point for the shipowners that asked James Wolfe, naval architect and electrical engineer at The Glosten Associates in the US, to evaluate the feasibility of installing solar panels on the deck of their LNG carrier. Wolfe found that solar panels were more expensive than other readily available energy saving measures such as waste heat recovery so, unless reduced emissions were required in port or the company wished to demonstrate environmental leadership, solar panels did not make financial sense. “There aren’t any mass produced solar panels for the marine industry so that increases the price considerably,” he says.
Wolfe admits the situation is likely to change in the future. Thin film and solar laminates show promise but currently they can’t match the efficiency or cost of the silicon wafer type solar panels most commonly used today. Also, a move from centralised inverters to having inverters on each panel will improve efficiency as currently any shading on one panel, adversely affects the efficiency of the whole array. Energy storage techniques are rapidly evolving and there are several promising technologies that could be applied to marine vessels.
Solar panels need to be cleaned to maintain optimum power production so relatively high maintenance costs must be considered, says Wolfe. The cost and availability of replacement inverters must also be factored in. They have the highest failure rate of any parts of the system.
The proposed installation on an LNG carrier would have been ground-breaking for the industry. “In general, you can’t have any equipment in hazardous zones on ships unless it is necessary for the operation of the vessel so an argument would have needed to be made to the regulatory agencies,” says Wolfe, who approached major classification societies and found that none currently have published rules in place for solar installations. This uncertainty in the regulatory environment and the relatively small number of marine solar installations on classed vessels are significant hurdles for vessel owners and designers.
The Glosten study showed that the return on investment was unfavourable and the owner decided not to pursue a solar panel installation at this time. Wolfe believes that fuel prices (or emissions penalties and taxes) will need to increase significantly and the technology needs further development before it is widely adopted on cargo vessels. “Panel efficiency needs to double and prices need to drop by at least a half,” he says.
Shipping company, Nippon Yusen Kaisha (NYK Line) chose environmental leadership with the installation of solar panels on the car carrier Auriga Leader in 2008. The project involved partners Kawasaki Heavy Industries, the Monohakobi Technology Institute and ClassNK. Initial tests showed that providing a stable power supply from the panels was difficult because even a slight change in the weather has a significant influence on the amount of power generated. It was also found that attempting to make the solar power system bigger to gain more output could result in problems with regard to stable operations.
However, enhancement of the system into a hybrid arrangement with 100kW Gigacell batteries developed by Kawasaki Heavy Industries has stabilised the system and NYK now reports satisfaction. The system has generated 43MW per year on average with a maximum generated power of 43.6kW compared to the rated output of 40kW.
The solar cells have proved their ability to withstand rough seas including shocks, vibration and salt spray. NYK has also obtained useful guidelines for seafarers on the safety and operation of the system including how to avoid electric shocks and how to clean and maintain the solar cells.
NYK hopes that solar will become competitive as a CO2 reduction technology by 2030 or earlier, but the company sees the development of high capacity, low cost rechargeable batteries for maritime use as essential. NYK has designed the concept ship NYK Super Eco Ship 2030, an 8,000TEU containership with project partners MTI (NYK’s subsidiary technology institute), Elomatic (a marine consulting company in Finland), and Garroni Progetti (a ship designer in Italy).
Super Eco Ship 2030 will make progressive use of new technologies including LNG-based fuel cells, solar cells and wind power, all of which the company claims will lead to a reduction in CO2 of 69% per container carried. Tanker and bulker designs are also being developed that could reduce emissions by 30% to 50%.
Mitsui OSK Lines (MOL) of Japan has designed a hybrid car carrier equipped with solar panels and batteries. The vessel, expected to be delivered from Mitsubishi Heavy Industries (MHI) in June this year, is the result of a cooperative study by MHI, Sanyo Electric Group and MOL. The power generated by the solar panels while the ship is underway will be stored and used to hotel the ship while berthed. The batteries are located in the bottom of the vessel to act as fixed ballast and therefore do not affect the number of vehicles carried.
Other designs incorporating solar power are being developed including IHI Marine United’s eFuture 13000C container ship, Wallenius Wilhelmsen Logistics’ car carrier Orcelle, Sauter Carbon Offset Design’s Black Magic tanker and a range of passenger and cargo vessels from Eco Marine Power. The Aquarius Marine Renewable Energy system being developed by Eco Marine Power involves rigid, telescoping sails that feature solar panels. On large ships, up to 20 rigid sails could be installed, says director, Greg Atkinson. The Aquarius control system is being developed in partnership with Kei Systems of Osaka.
There is one vessel already sailing solely on solar energy and Imtech Marine has contributed as technology partner. Planet Solar has 500m2 of solar panels and a large lithium battery. An inverter is needed to convert the DC of photo voltaic cells to AC so the 50 or 60Hz electric grid can transfer the electrical energy around the ship. These energy conversions reduce the efficiency of the whole chain, says Martijn Berkhoff, Imtech consultant electrical systems. With a DC grid in a diesel-electric propulsion system, less energy conversions are needed and there is no need for bulky transformers so Imtech is developing an appropriate ‘plug-and-play’ DC grid. Even if shipowners decide solar is too expensive today, they can install panels later and with no extra effort connect them to the DC grid. “The sun is an inexhaustible energy source, so why not use it,” says Berkhoff.
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