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Smarter power

Apr 18, 2017 Technology

Cruising boats wanting 240VAC power on board typically opt for large diesel generators. But there is another lighter, cleaner, quieter and much more efficient way, writes Norman Holtzhausen. Photos supplied.

The power requirements of microwave ovens, TVs, washing machines and air conditioners can be significant. And traditionally, an owner installs a dedicated genset capable of providing sufficient power
to handle the highest possible load. This is when several appliances are used simultaneously.

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A peak load capacity solution raises several issues. The main one is that a relatively large genset is needed to cope with the short periods of highest demand. At other times, when only a few appliances are in use and power requirements are more modest, the genset is idle or running at sub-optimal capacity.

Gensets are usually large, heavy and noisy, and less than efficient in converting fuel energy to electricity.

THE BATTERY ALTERNATIVE
A different approach to on board 240VAC is using lithium-ion batteries. With its high-energy density, a lithium-ion unit weighs about a third of its lead-acid equivalent. Even better, it can be cycled rapidly, delivering large amounts of power quickly and then recharged rapidly. It also has a much longer lifespan, with up to 5,000 or more charge cycles compared to as little as 500 for a conventional battery.

The battery 240VAC option sees the installation of sufficient battery capacity to cope with whatever the peak power load is, calculated according to the vessel’s mix of appliances and likely usage pattern. Effectively, the batteries provide full capacity and the boat runs entirely off the battery bank, coupled with smart controller technology to convert DC power into mains voltage.

With peak load calculations completed and the appropriate battery size selected, the opposite side of the equation is ensuring sufficient charging capacity is in place to make sure the capacity is available when needed.

And this is where the savings occur. Although peak load’s only required for a few hours each day, the batteries can be recharged at various times over the remaining lower-usage part of the day. So the battery bank is sized based on the peak load, while recharging can be sized based on the time available outside of the peak load period.

This effectively separates the charging duty cycle from the house duty cycle, allowing longer periods of efficient charging to be implemented. Recharging is typically provided by a small but energy-efficient variable speed genverter. It may be supplemented by solar panels, wind generator, engine-driven generation or even shore power when in a marina.

Consider this example:

Say a cruising yacht has a peak load of around 10kW, powering lights, fridges, a washing machine, microwave oven, air conditioner and TV. But these appliances are only likely to be used – at the same time – at night when a meal is being prepared. Peak load lasts for an hour or two a day.

A suitable battery bank would provide the required 10kW of power for this period, and most likely also provide less output (for the fridge and, say, the air conditioner) for the reminder of the night (silent time).

A 4kW genverter would completely recharge the battery bank in just over six hours. It can be run during the day when noise is less of an issue, making for a silent vessel at night for a good sleep. Of course, supplemental sources like solar panels can further reduce recharging time and fuel.

A hybrid approach is also possible, with a mix of battery and generation. In this configuration, the batteries and genset are used together to provide peak capacity, with the batteries only used during periods of low demand.

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In the example above, 7kW of battery power and 3kW of genset would together provide the required 10kW total. This option reduces the up-front cost of the lithium-ion batteries, and achieves the same weight and fuel-saving efficiencies. On the other hand, though, it means the genset may have to run during undesirable periods, such as in a crowded anchorage.

Dutch company Whisper Power is a market leader in the lithium battery/genset solution, with a range of appropriate products such as genverters, AC Powercubes and DC Powercubes. It’s Pacific outlet – Whisper Power Pacific – is based in Auckland, and has been working with Napier-based Dickey Boats to install a Whisper Power system.

Dickey Boats is the first Australasian builder to adopt Whisper Power’s ‘new school’ one-stop-shop approach. The system is for a long-range cruising vessel, to be based in Europe.

The Dickey hull is easily-driven and the owners wanted a similarly efficient power system to minimise diesel consumption. In addition, the technology would meet tight environmental restrictions and cater to a range of voltages available in European marinas. The owners wanted to be self-contained while
maximising energy efficiency and reducing their carbon footprint.

THE SYSTEM
A 24VDC lithium storage bank is the heart of the system, together with a battery management system to optimise the charging characteristics for each individual cell.

On the house side, AC PowerCube units are set in a redundant array ensuring no single point of failure. Each PowerCube provides 7kW of 230V mains power, and can be paralleled for a capacity of 14kW or more. These switched-mode inverter units are light and energy-efficient and waste little energy in the
form of heat.

On the charging side is an 8kVA genverter – a programmable RPM three-cylinder diesel with a permanent-magnet alternator. It has a 94 percent efficiency rating. Power is fed into the Whisper Power DC PowerCubes.

A 230VAC genset is typically used to power battery chargers, requiring two sets of voltage conversions (with associated energy losses), along with underutilised/ mismatched capacity much of the time. The genverter delivers power from every drop of diesel used to either the house or storage systems.

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DC powercubes can take power from multiple sources (90V to 265V, 45Hz to 65Hz frequencies, from
solar or wind generator or any form of shore power) and efficiently transform the power into optimal charging capacity for the lithium-ion batteries. The PowerCube controls the genset and reduces its output or even shuts it down when the batteries are fully charged.

All the Whisper Power units are networked, with a touch screen providing a visual display and full control of the entire system. A NMEA2000 interface is also available for communicating with other smart devices, and shore power transformers as well as an engine-driven AC generator form part of the mix.

Whisper Power Pacific’s John McGettigan says the space, weight and fuel consumption savings of the entire system make it a compelling option for a discerning owner. The lightweight, efficient genverter alone represents a savings of 160kg over a conventional synchronous genset.

Running a smaller engine at peak efficiency means that less diesel is required (per kilowatt produced) than a larger genset. Because a larger unit is rated for peak load, it runs sub-optimally at other times. Smaller engines are quieter and generate fewer emissions.

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Lithium-ion batteries aren’t cheap, so this system requires a considerably higher up-front investment that a conventional large generator with lead-acid batteries. But the fuel savings over the life of the system should pay for itself.

In highly-regulated environments like Europe, the reduced emissions from such a system may be essential for a vessel to meet emission standards. Vessels which don’t meet the standards may be barred from certain waterways.

Battery storage for homes
Lines company Vector recently announced that a battery storage system had been implemented in
the Auckland suburb of Glen Innes, a first for the Asia-Pacific region. Installed in October, it represents a new approach to power distribution.

Traditional power grids face the same issue as cruising boats – peak power capacity is only required for a few hours each day, with the lines carrying far lower loads the rest of the time.

Because everyone wants power the moment the switch is flicked, power companies plan their power lines to cope with the periods of highest demand. This is hugely expensive and inefficient. Most of the time, large, intrusive transmission lines and pylons are only carrying a fraction of their capacity.

Facing a multi-million dollar upgrade to its infrastructure to support a new subdivision, Vector instead installed a bank of lithium-ion batteries at the Glen Innes substation. This installation has enough power to supply 450 homes for nearly two-and-a-half-hours.

It comes on stream during the peak period. At times of reduced load the spare capacity in the lines is used to recharge the batteries.

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