Modern boats are very dependent on electricity. For this reason almost 4 years ago when Yuka and I started envisioning our life on Oroboro, one of our main goals was establishing a very balanced battery-powered electrical system. So we wrote down our power needs and then we doubled it:
- Anchor light: 1.0 amps
- Anchor windlass 300 amps
- Refrigerator: 7 amps
- Etc etc…
We needed to calculate our exact power requirements in order to size all systems correctly. Then we started to design the electrical system and its components. We had everything installed after market, by MultiMarine in Cape Town, choosing top of the line products.
There are two different type of batteries for a boat:
- Engine batteries
- House batteries
Engine batteries are used solely for cranking up the engine. They are designed to deliver quick bursts of energy (such as starting engines), and they should never be discharged. They can be any type of heavy duty cranking battery rated for your specific engines.
House batteries on the other hand, have less instant energy, but greater long-term energy delivery. They can survive a number of discharge and so need to be deep-cycle batteries. The question is, which is the best deep-cycle battery for marine application, a wet-cell, gel-cell, AGM (Absorbed Glass Mat) or Lithium Iron Phosphate? The answer is Lithium Iron Phosphate.
Unfortunately Robertson and Caine did not offer lithium iron phosphate batteries (LiFePO 4 battery) as an option. Lead acid was the standard option, and AGM the only upgrade.
So we went with the AGM LifeLine Deep Cycle 210 Ahr:
We thought that we could upgrade to LiFePO 4 in the future when the AGM batteries will die.
We have 3 house batteries of 210 Ahr each for a total of 630 amp hours. But because you can’t discharge AGM batteries more than 30/40 percent if you want them to last, we actually have only 180 amp hours at our disposal.
If we had the equivalent amp hours in Lithium Iron Phosphate batteries, we could actually use all the 630 amp hours because these batteries can be safely 100% discharged without degrading them or shortening their life spam.
We are not sure how long these AGM batteries will last, probably 5 years or so, if we never discharge them more than 30% like we are doing now.
And we hope than in 5 years time the price of Lithium batteries will be significantly lower than now. To give you an idea of the cost, a LifeLine AGM 210 Amp hours battery costs around USD750.00 whereas a ReLion LIfePO4 200 Amp hours battery costs around USD2,500.00.
How do we recharge the batteries? Mainly from our 3 rigid solar panels, that provide us with nominal 960 watts during a sunny day.
We deliberately decided not to have a genset, because it’s heavy, expensive, loud, takes a lot of room, needs maintenance and simply because burning fossil fuel to produce energy is neither environmentally friendly or efficient.
When in Cape Town, we had a stainless steel structure built for for us by a company called FormaTube. They are real artists!
With our array of 3 rigid SunPower E20 solar panels (320 watts each) on the stainless steel structure over the davits, and the 4 flexible SunBeam panels (100 watts each) on the rooftop, we produce more electricity than we can use: 960 watts + 400 = 1.330 watts!
The rigid solar panels are controlled by Victron Blue Solar MPPT 75/15. The flexible solar panels are controlled by 2 Victron BlueSolar PWM LIght 12/24V-20A.
When we go to bed at night, our batteries are usually 95% full. When we wake up in the morning the batteries are 86% full.
Another way to recharge batteries is by the engine alternator when we are motoring along. On our Yanmar engine we have the standard Valeo 125 amps alternator:
To recharge the batteries faster, we have installed a Sterling Alternator to Battery Charger on both engines:
This device is pretty clever: The system puts a “load” on the alternator to pull the alternator voltage down. This fools the alternator into thinking that there is a major drain on the system and as such, the standard regulator works at full current to charge the battery bank at a much higher voltage than the base system voltage.
So the time needed to fully charge the batteries is cut in half. During a rainy day, if our solar is not able to fully charge the batteries, we can run the engine and quickly recharge the batteries.
To transform that 12 volts DC electricity provided by the batteries into the 220 volts AC that you need to run electric appliances, we use an Inverter. This is a 3000 watts Victron MultiPlus inverter, which is the very best in the industry:
Our water heater for example, is connected directly to the inverter. In this way, usually around noon when our batteries are almost full, we can switch on the water heater for 20 minutes in order to be able to have a hot shower at night. The water heater has an high energy demand of approx 1,400 watts, so it’s paramount to have a large inverter like the one we have.
The inverter also works as artery charger when we connect to on shore power when we’re in a marina. By using a shore power cable we can take the 220 volts from the marina to power our boat and at the same time keep our batteries fully charged.
To monitor how much electricity is produced and consumed on board by the boat systems and appliances, we use the Victron Venus GX:
The Venus GX is the communication-centre of our installation. It talks to all components in our system (Inverter, MPPT controllers etc.) and makes sure they are working in harmony. We can monitor live data, and change settings using our smartphone via an open-source app:
As a secondary battery monitor system, we use the Victron BMV 712 Smart Battery Monitor. Its essential function is to calculate ampere hours consumed and the state of charge of a battery.
Think of it as our battery “fuel gauge”. You can also connect it to an app on your smartphone via BlueTooth.
In these 2 years that we have lived on board, we have never been in “energy saving mode”. Electricity is just an afterthought, thanks to our well balanced battery-powered electrical system.
When we are at anchor, the vast majority of boats around us need to run their genset in the evening to recharge their batteries, whereas when we go to bed our batteries are usually 95% full.
And having a pleasure of a hot shower at night, even in the tropics, it’s priceless!