The DC generator and electric motors used on the 18m proa were selected for their high efficiency. In normal operating range both exceed 90% efficiency.
Lithium batteries achieve a cycle efficiency around 95% when pulled at 2 hour rate. That compares with 80% for new lead/acid when pulled at much lower 4 hour rate. The linked chart compares lithium and lead/acid under high discharge/charge rates:
Also there does not appear to be any significant degradation in performance with lithium over time either - my oldest lithium battery is 7 years old and still delivers rated energy.
The advantage of electric transmission is particularly apparent for a proa. Typically sail drives are not intended to feather in both directions. The electric motors are light enough to be easily deployed and lifted clear of water when not required so no drag when sailing.
On 20/03/2015, at 3:24 AM, "taladorwood@yahoo.com.au [harryproa]" <harryproa@yahoogroups.com.au> wrote:
If diesel is used to generate electricity it is generally 60% efficient so it has 40% losses for production and then 15% resistance losses. That means in the end diesel directly powering the the prop is 70% efficient and if it goes through a generator it is 45% efficient.Similarly if the electricity is coming from solar, there is a 40% loss going through the batteries, and another 15 percent loss going to the prop. Ideally the motor should be driven directly from the solar panels and then it becomes more efficient, but that requires 30KW worth of solar panels.
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Posted by: Rick Willoughby <rickwill@bigpond.net.au>
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