Cost of energy with Marine Gensets
The efficiency of the electrical systems on most boats is open to improvement.
The most in-efficient 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, it is the charge acceptance rate of lead acid and gel batteries that is the biggest 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 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.
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. These are just around the corner in release...
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