Cost of energy with Marine Gensets

The efficiency of the electrical systems on most boats is open to improvement.

The most in-efficient, and a big enery burner, is the marine genset.

If the genset was 100 percent efficient at converting diesel fuel into electrical power we would use around 80 g of diesel/kWh. However, a small diesel engine is lucky to attain a peak efficiency of even 30 percent. Combined with other losses through the alternator the actual fuel conversion to electrical energy is more like 350 g of diesel/kWh.

One of the in-efficiency reasons is that the alternator output is directly related to speed. Most alternators don’t reach their rated output until up to 4,000-plus rpm. Typically, they have a 2:1 pulley ratio with the engine, which means the engine must run at 2,000-plus rpm. No one wants to run this fast when battery charging at anchor. 

Charge Acceptance Rate

However, the charge acceptance rate of lead acid and gel batteries that is also a big culprit.

As non-Lithium batteries rise in charge level, the Charge Acceptance Rate declines causing the  alternator output to fall (kilowatt decreases), and the fuel consumption per kW soars.

This means the charging process of lead acid chemistry is increasingly inefficient.

In absolute terms of converting diesel fuel into electrical power, we start around 10 percent efficiency and end at 2 percent efficiency. The losses in charging and discharging conventional lead-acid batteries are about 15 percent in each direction, so in terms of producing the electrical power that gets to our appliances via the batteries we are now down to an absolute efficiency of between 7 and 1.4 percent! Most AC generators have to be run at a fixed speed in order to maintain the correct output frequency. AC generators have to be sized to handle the peak load they will encounter. This is typically at least four times the average running load, and frequently much higher.

However, there is often no load on a generator. Air conditioners may cycle to off because the room has cooled to the temperature set point. The net result is that AC generators on boats spend most of their time operating at between 0 percent load and 25 percent load.

If the generator is being used to power a battery charger which is charging non-Lithium batteries, the total additional losses through the charger and batteries can easily be another 40 percent, bringing us down to an absolute efficiency of between 8.5 and 2.4 percent — not dissimilar to using the boat’s engine for battery charging at anchor.

Marine Genset Alternative

An Integrel system will replace a generator of up to about 10kVA. The Integrel generator itself is fitted directly on to the propulsion engine occupies very little space and weighs only 15kg. The storage batteries that it uses are normally fitted into the same space as the stand alone generator it replaces; a 10kWh Lithium Battery Pack measures  928 x 555 x 210mm and weighs 113kg. 

Demonstration (short version | 4min)

the Integrel generator is like an alternator on steroids. Permanent magnets embedded in the rotor improve the internal magnetic coupling, delivering exceptionally high power and efficiency.

Nigel Calder is the author of hundreds of magazine articles and eight books, include of one of the best-sellers, the ‘Boatowners Mechanical and Electrical Manuall’.

Lithium Batteries

The answer in improving efficiency starts with the batteries: switch to Lithium Batteries.
Lithium batteries have the ability to soak up astonishing amounts of power.

We supply 48V Lithium batteries modules of 9.6kWh each expandable to 80kWh.

For smaller yachts, we supply 12V 125Ah up to 700Ahr and 24V up to 350Ahr.

The next step is a DC generator that can charge at 24 or 48V very efficiently. 

Integrel High Capacity 8kW Generator

One might be tempted to see this simply as a large second alternator bolted to the side of a yacht’s main propulsion engine. However, the Integrel System exploits the large gap between the propeller "power demand curve" and the optimum "power output curve" of an engine. It draws that spare power intelligently to charge Lithium batteries, without effecting propulsion performance. 

The amount of fuel used for propulsion actually goes down when Integrel is drawing power. Of course, overall fuel consumption rises, but because of the battery charging, the percentage of fuel used in propulsion is less. 

The system can cope with going ‘open circuit’ so that Integrel can instantly stop drawing power from the alternator. This allows maximum propulsion power when manoeuvring at idle speed or towards maximum rpm.

A typical installation can generate 3.5kW of additional power at idle out of gear and 8kW or more when underway at normal cruising speed. That energy is directed to 48V banks of high capacity Lithium batteries which then supply onboard 240V and 12V power demand via inverters and converters. 

The system drives a 5in display providing control and precise information about energy generation and consumption. Operation is completely automatic and requires no attention from the owner.

An early success has been the installation of an Integrel system on a new Discovery Yachts Southerly 480, launched this year and owned by Distant Shores TV adventurers, Paul and Sheryl Shard. Distant Shores III will spend much of her time in remote locations globally with paying guests aboard. Despite needing to service high domestic power demands, the Southerly has no generator, a testament to the Shard’s confidence in the new system. The anticipated fuel savings and ability to draw AC power for extended times silently will no doubt be an added benefit in some of the enviable locations they visit. This system has sealed lead batteries and not the higher capacity Lithium batteries.

If you add up installation and lifetime costs, the investment favourably compares against an equivalent generator installation. The benefit of potential propulsion engine longevity through its more efficient utilisation should follow. However, it is the space saving and the convenience of automatically available, SILENT, AC power that is compelling. 

It remains the case that for longer-range passage-making in particular we are going to be burning fossil fuel for a while to come. If we cannot eliminate that altogether, then the next best idea to sustainable energy is to make that fuel work much harder.

Here is a video by the Shard's on board Distant Shores III with the Integrel system and sealed lead acid batteries

The standard Integrel system consists of:

  • 8kW engine mounted Integrel generator
  • Engine mounting kit
  • Integrel system controller
  • 48v battery sensor
  • Integrel 600W 48v to 12/24/36v battery to battery charger
  • 5” touch screen user interface
  • 48v 9.6kWh advanced Safiery Lithium Battery Module, expandable to 80kWr
  • Wiring loom and fuses
  • 3kW 48v inverter/charger

The retail price in Australia excluding installation is around AUD $18,000 without the 9.6kWh Lithium and Inverter/Charger. Add $9,000 for each additional 9.6kWh of Lithium capacity and $1,600 for 3kW inverter/charger.. 

We have available engine mount kits (approved by the engine manufacturer) for these engines:

  • Volvo D2
  • Yanmar 4JH

The Integrel System comes from Triskel Marine in UK. Here is the team after winning the 2018 DAME Award for best product at the METS Show.


If you would like a Quote, complete the Configure Form.