The power of Lithium
One of the important decisions we had to make for Wildling, was the design of our on-board power systems. The traditional way to power a cruising sailboat at sea is to install a large house battery bank, typically comprised of 500 – 1000 Amp hours of lead acid batteries that will power all the ship’s systems. Many systems such as refrigeration, radios, instruments, autopilot, lights, pumps and winches are powered directly from the batteries, usually at 12 volts DC. Other systems such as the battery charger, water heater, air conditioning, microwave, and miscellaneous appliances need AC power which can be provided by running a diesel generator or via an inverter which converts DC power from the batteries to AC power.
There are some really important choices here and making the wrong ones can lead to a lot of extra weight, cost and complexity. Before I go into the details, let me start by laying out the objectives for an ideal electrical system.
The power systems on a cruising catamaran need to be:
- Simple – we want to avoid complicated troubleshooting and repairs at sea if something goes wrong
- Flexible – we need to be able take advantage of shore power at the marina, yet be autonomous at sea and at anchor
- Reliable – the system needs to just work, and keep working for extend periods of cruising through many, many charge/discharge cycles
- Lightweight – batteries are very heavy, so are generators. The combined weight of the two systems on our last boat was over 600 kg 1,300 lbs! We want to keep this to a minimum
Thanks to the electric car industry, Lithium-Ion battery technology has now matured to a point where traditional lead acid batteries (including Gel and AGM type batteries) no longer have any place on-board a cruising catamaran.
LEAD ACID BATTERIES
Lead acid batteries are no longer a good solution for powering a catamaran. They are heavy, they take up a lot of space, they can’t be discharged below 50%, they have a limited lifespan of 4-6 years, and they are slow to recharge. The slow recharging time (10+hours) is one of the biggest problems, because you either need a lot of solar or wind generation to recharge them (not always available) or you have to run the engines for long periods of time (expensive). Many folks install diesel generators in order to keep their lead-acid battery banks topped up, which makes a bad situation worse.
The contrast with lithium is enormous. Lithium batteries weigh less than half of lead-acid and take up half the space. They can discharge down to 80%, last 10+ years, and here’s the best part, they can be recharged as quickly as you can throw current at them. So if you have 400 amps of alternators, you can recharge a 500 amp hour battery bank in 1 hour!
WILDLING IS GREEN!
Because of the rapid recharging ability of lithiums, we were able to design our power systems on Wildling to meet all of our needs without a generator. We will have 700 Watts of solar panels, a 600 Watt hydro-generator and 5,000 watts of alternators on the two engines. This gives us a lot of flexibility to run the systems we need and take full advantage of our green energy power systems to recharge the batteries, so no available sunlight or hydro-power is wasted. When needed we can run the engines for limited periods to top up the batteries. And by removing the need for a generator and using the lighter lithium batteries we save 480 kg (1,056 lbs)!!! And since less weight means we can sail more in lighter winds, we will run the engines less and save even more!
Over the past few years, many of the ocean racing sailboats have been testing out hydro-generators. They have been refined to a point now, where they are quite reliable.
A word of caution about these generators! There are two versions, a cruising version and a racing version. The cruising version operates in a speed range of 5 to 10 knots and the propeller will strip out if it’s driven at higher speeds. The racing version works at 8 knots to well over 15 knots. We are installing the racing version on Wildling.
There are very few technology choices on a boat that have as many positive benefits as lithium batteries. If you are buying a new boat or your house batteries need to be replaced, then go with lithium!