Renewable energy – it’s a buzzword we hear more and more. Electrification is a trend toward having all power-consuming devices run directly from electricity because it is clean to use. But is it really environmentally friendly? Electric heatpumps for heating and electric cars for driving, seem to make sense, but only if the electricity is produced from a renewable source of power (ie wind, solar, tidal, etc). An electric car only worsens your carbon footprint if the power to charge it comes from burning gas, oil and coal many miles away. For millennia, sailboats have used renewable energy as primary means of propulsion – sails harness the wind. But unlike centuries ago, we have recently added the convenience of auxiliary propulsion because we don’t want to wait for the wind.
He is the best sailor who can steer within fewest points of the wind, and exact a motive power out of the greatest obstacles.Henry David Thoreau
We’re coming up on one year since we purchased our 1996 Pacific Seacraft 40, Fayaway, scheming and planning ever since, for our next great escape. We’re spending oodles of boat bucks to upgrade and renew, and it’s a monumental effort of planning to accomplish a complete overhaul within an 18 month period, at a rate only as fast as cash-flow allows. More about that topic later. But for now let’s go back to the powerful topic at hand: Electrification.
Unless you’re hard-core, your cruising sailboat will have an auxiliary engine. Having already decided to install a more reliable auxiliary, I studied available options for converting to electric propulsion and we came to the conclusion that it’s not ready for us. For extensive independent cruising we need optimal energy-density storage, which diesel oil offers. Sorry readers, as much as I’d love to claim that our home is entirely powered by renewable sources of energy, we’re just not hard-core.
Energy density comparison: Imagine being 300 nautical miles offshore from your destination, a storm is coming and there’s no wind. You want to keep moving. For only 36 hours of mid-speed motoring (approximately 150 nautical miles in calm seas), you’d need more than $20,000 worth of batteries! Contrast this with 100 gallons of diesel fuel, capable of more than 800 nautical miles at a higher speed. And even if we could afford $20k worth of batteries, we’d also need to give up valuable storage space, and probably purchase an additional diesel generator for when the sun doesn’t shine. So as I write this post a new efficient Diesel engine is being installed by competent folks under a warm roof at Johanson Boatworks in Rockland, Maine.
But everything else is electric… sort of. First let’s look at Fayaway’s electrical load summary, and then how we’re storing and making the electricity.
Other assumptions: I didn’t include the anchor windlass because it’s so infrequently used without the motor running, which negates power consumption. We’ll only run the watermaker every two or three days, and typically time it (and the water heater) for peak-sunshine hours. Space heating is the other diesel consumer, and it also runs infrequently and very efficiently.
We use an amply-sized Victron 3,000 watt inverter for A/C loads, appropriately fused and wired with massive 4/0 cables. Our 2.5 gallon electric water heater, oven and TV are used infrequently and so are discounted in the average daily battery load. Yes, I know these items are big power hogs, and there will be those days, but we can compensate by temporarily reducing other loads, and/or not fully recharging until the next day. Reducing consumption is also key toward not using more power than we can produce (read further below).
At the bottom of the DC loads estimate (first spreadsheet above) is the calculated required battery capacity – the bottom line. For contrast I’ve included the requirement for two common battery types: AGM (Absorbent Glass Matt, or essentially, lead-acid) and LiFePo4 (Lithium Iron Phosphate). AGM used to be THE ultimate marine battery; not any more! Note how due to the reduced allowable depth of discharge %, AGM requires at least 40% more capacity than LiFePo4 to provide the same amount of storage! I rounded down the conservatively calculated estimate of five batteries, and only installed four 100 amp-hour (Ah) LiFePo batteries. We can always add more later if deemed necessary, but based on our live-aboard experience it should be enough.
Depth of charge - Or depth of discharge. The amount of useable battery capacity (how for can you charge and discharge it?) without reducing its life expectancy. Those with AGM batteries will also notice that it is nearly impossible to fully charge as they approach 100%. In essence, a 100 Ah-rated AGM battery has a useable capacity of 60 Ah, and that’s pushing it, as many folks will say less than 50%. So that’s why I said, “at least”.
Sailboat Guru Nigel Calder suggests that 30% “useable capacity” is a more appropriate number because even a good AGM battery takes longer to fully charge, and that it isn’t realistic to attempt charging above 80%. He believes that rated capacity should be 3-4 times the storage need!
Despite the high initial cost, I can’t say enough good things about our new lithium batteries. We first used them last summer with only a temporary 100 watt solar panel, and were not disappointed. They weigh only 31 pounds, can be drawn completely down to zero charge, and then recharge again very quickly. Voltage remains level throughout their cycle. Why is voltage level so important?
Electricity 101: AGM batteries typically drop voltage as their charge level drops. So a fully-charged battery at 13.5 volts will usually drop to 12.5 volts (and lower) as charge level drops. Most electrical devices, especially motors, are designed for optimal efficiency at a certain voltage and amperage. Watts (power) = amps (flow) x volts (force). Wiring inside motors is sized for minimum resistance (highest efficiency) at a given voltage. If you force more amperage through it, the added “friction” produces unwanted heat, which is essentially wasted energy (not used for pumping or steering). For example, an autopilot uses 10 amps at 13.5 volts for 135 watts. To keep wattage (steering) active as the batteries deplete and voltage drops, the amperage must increase. So that same pilot with only 12.5 volts available must now run at 10.8 amps. Higher amperage is required which makes more heat in the connecting wires and motor. Hence you’re wasting your precious battery power, and using it up more quickly.
Contrarily, LiFePo4 batteries’ voltage remains nearly constant throughout the charge level. Ask a chemist to explain why that is, but for now you can assume that because voltage remains high, power is used more efficiently, and will last longer. Furthermore, because motors run cooler, there is an increase in life-expectancy. What could be more more compelling toward choosing to use lithium batteries!?
How do we recharge our awesome batteries? For now, we have one primary and two backup sources (when not plugged into a dock):
- Primary: Two 325 watt photovoltaic (solar) panels. These are high-voltage, mono-crystalline, low-cost, Italian-made, high-efficiency, household-duty panels. We used smaller panels from the same manufacturer on the prior Fayaway, and they held up very well, despite being often thoroughly sprayed with corrosive seawater. (Don’t let someone tell you that over-priced “marine-duty” panels are necessary on a boat.) Each of our panels is wired independently to its own MPPT (maximum power point tracking) solar charge controller for redundancy and shade-tolerance. On a clear sunny day we hope for up to 370 amp-hours for an ideal day.
- Backup: Balmar 170 amp alternator with external regulator to further optimize charge efficiency when running the engine. Lithium batteries can charge incredibly fast. So fast that they’ll overload any sub-par alternator if not properly regulated. To reduce engine run-time, it’s best to install the largest possible alternator, as the batteries can take as much as you can give them. A smaller flexible 100 watt solar panel provides a secondary backup.
Side note: Nigel Calder recommends a “3-hour rule” for conservatively determining solar PV panel output. According to his rule, our panels are assumed to produce an average of 3x 325w x 2 / 12v = 162 Ah. If you’re paying attention, that’s less than half of my earlier ideal estimate! To appease pundits, I’ll acquiesce to arrive somewhere in the middle or around 275Ah, based on my experience and how this system is designed. Later I’ll try to remember to post some actual numbers.
As an aside, remember me saying earlier that we used “massive” 4/0 cables to the inverter? Similar to the benefits of keeping the voltage high, reducing resistance in the wire has similar efficiency benefits. Larger wire = less resistance = less heat = more power going to the autopilot.
In the spirit of full-disclosure, we haven’t quite yet eliminated using other fossil fuels either – propane (for the grill) and our little 8hp outboard engine. While the electric cooktop is on order we’ll keep using gas for that too. Partial electrification. But we have been looking at an electric outboard for shorter dingy trips: electricpaddle.com.
More to come in a future post: More Design Details Of Fayaway’s (mostly) LiFePo4 System. If you can stomach the initial battery cost, I’ll show how this simple system will pay for itself!
I read friends’ blogs, already out there pushing past the present pandemic deterrence. Kelly and I envy their impatience, but feel the price we’re paying (another cold winter) is worth waiting for: a more comfortable boat and a more welcoming world.
Kelly and I owe a plug to our perhaps inadvertent sponsor: Mestek, Inc. We owe much gratitude to their leadership team and colleagues for their friendship and support of our daring (their term) liveaboard dream. Mestek embraces forward-thinking with regards to allowing a more sustainable energy future.