Energy Management Part 3 - Charging Sources Overview

Most sailing boats come with two standard charging sources for their batteries:

  • shore power charger
  • alternator

Our boat was no different, the Yanmar engine was equipped with a standard Hitachi 80 A alternator (see picture), and for charging in the marina two 40 A Cristec chargers connected in parallel to charge both starter and service batteries.

A classic "no frills" setup, that is.

The stock alternator was internally regulated and had no over temperature protection (as far as we could find out).

Well, we have to do better if we are planning to cruise offshore for prolonged times.

While a shore power charge is basically a no-brainer (however, we will get back to this topic later), the real challenge is to choose additional charging sources that provide sufficient power when offshore.


We already made the decision to install a LiFePO4 battery based system, so we have to factor in its capabilities (and challenges).

Our goal is to let the higher efficiency and charge acceptance rate of LiFePO4 batteries work in our favor by absorbing every little bit of energy our other charging sources can produce.

This influences our decisions for charging sources, for example it is easy for us to skip on wind generators - the main reason many cruisers choose them is that they constantly produce power. Lead acid batteries need a long time to recharge, so a permanent power supply from a wind generator complements this property.


By the way, Yachting World published a summary and poll among the ARC 2014 participants with a nice overview on the common solutions (most of them will be using lead acid batteries).

Stock Alternator (main engine)

Every boat comes with one equipped, but most standard alternator installations are pretty baseline. They are totally sufficient to recharge traditional lead acid batteries, but the designers actually rely on the diminishing charge acceptance rate of lead acid banks: An 80 A rated alternator will produce its top power for about 15 to 30 minutes before getting too hot. If the high output current is maintained for a prolonged time the alternator will eventually be destroyed by overheating.

Fortunately traditional batteries implicitly protect the alternator by increasing their internal resistance during charging. The alternator will only produce full power for a short time.


This is also the reason why most cruisers are not too happy with their lead acid batteries and alternator. This combination simply does not make proper use of engine operating time.



  • comes already installed at no extra cost or effort
  • charges battery whenever engine runs
  • "invisible" installation


  • standard models not suitable for charging LiFePO4 batteries
  • uses fuel to operate
  • not very efficient (considering Wh per l of fuel)

The main disadvantage for our purpose is that LiFePO4 batteries do not go well with a standard alternator. Due to their extremely low internal resistance they will effectively short the alternator. If it is not protected from thermal overload it will be destroyed after a short time of continuous operation.

We decided to get rid of our old alternator and use a high performance model instead...


High Performance Alternator with External Regulator

A better alternative is to install a high performance alternator. These devices are designed to deliver much higher output (about double the rated output of a baseline model), but more importantly they are more resilient to operation under high load.

They also run hot when overloaded, but they fare a lot better.

A high performance alternator should always be installed together with an external regulator and over temperature protection.



  • high output
  • charges battery whenever engine runs
  • "invisible" installation


  • alternator must fit engine (not trivial as we found out)
  • installation effort (typically requires replacing pulleys and belt)
  • expensive

After having some bad luck with a Balmar AT 165 we installed a Balmar 6 type alternator and a Balmar MC614 charge regulator.

Solar Panels

Today most cruisers make use of solar panels as supplemental charging source, it has practically become a standard within the community to use the sun as an unobtrusive energy source.


Advantages are

  • ubiquitous, silent operation - whenever the sun is shining
  • little maintenance and no moving parts
  • independent of cruising state (produces power at anchor and while cruising)


  • solar panels need substantial real estate on the boat - sometimes it is not easy to find suitable installation spaces
  • weather and time-of-day dependent
  • even partial shading of the panels cause substantial power reduction
  • expensive

We decided that we definitely want to have solar panels on our boat. Our Bimini is quite large, so we figured that fitting the panels on the Bimini was the most useful place to install them. That way we would not have to clutter the deck with panels or install heavy steel frames to carry comparatively small panels as many cruisers do.


After some research we settled for Solbian SP panels which are light, flexible, efficient and can be installed on a Bimini. We found that our Bimini could host

  • 2 Solbian SP 125 panels in the front section
  • 1 Solbian SP 75 panel in the middle and
  • 2 Solbian SP 50 panel in the aft section

providing a total 425 WP which will be divided in two asymmetrical "banks" for port and starbord side.

Hydro Generator

Hydro generators are basically propellers in the water driving an electric generator. They are quiet and produce a steady and reliable amount of power - but only if the boat is moving through water. This means that a hydro generator will be useless when moored or at anchor.

In addition to a decent solar panel bank they can be an excellent complement to the mix, possibly even making other charging sources unnecessary.



  • silent
  • independent of weather
  • comparatively high output


  • only produces power when moving
  • must likely be mounted/dismounted repeatedly
  • expensive
  • uses space at the stern
  • slows down the boat a bit (but not much)

A hydro generator would have been our personal first choice as an additional charging source for our offshore cruising energy balance. The reason is that our solar panels should provide enough power to sustain daily use when at anchor, but they will not suffice when cruising.

A hydro generator only provides power when moving, but if it does, it's plenty. There you go, a perfect match!

We would choose this option without hesitating when crossing the Pacific Ocean, but since we are currently only planning to sail the Atlantic, we should get by with recharging the batteries using the engine alternator.

Wind Generator

Chances are that if it has a wind generator it is a cruising boat. And in most cases the reverse is true as well. 

The common narrative seems to go somewhat like this: "There's always wind, even if the sun does not shine, so let's add this to the mix. In addition, we need constant charging current to get the batteries back to full."



  • comparatively cheap
  • independent of daytime
  • independent of cruising state (produces power at anchor and while cruising)


  • noisy
  • ugly
  • moving parts (subject to wear and tear, and also possibly dangerous to crew in heavier winds)
  • need to be shut down and protected in heavy winds
  • needs wind speeds > 15 knots to produce a significant of energy (inefficient in light wind situations)

We decided against using a wind generator. The main reasons are that they are bulky, loud and ugly. Moreover, they are only efficient in higher wind speeds - exactly what you would like to avoid when moored!

Finally, we don't need the charging profile they'd bring us. Sure, they provide power permanently but it's low power typically. It fits lead acid but LiFePO4s are excellent in sucking up every bit of charge you can throw at them, so no need for constant power trickle.

Fuel Cell

Fuel cell technology has reached a certain maturity, allowing cruisers to adopt this charging source as an alternative source for energy.



  • produces power regardless of cruising state
  • small and lightweight
  • "invisible" installation possible
  • does not produce toxic or dangerous exhaust gases


  • quite expensive solution
  • requires proprietary fuel (typically not available in most marine supply stores or gas stations)
  • comparatively low (but constant) power output
  • limited life time of the fuel cell
  • exhaust installation necessary

We seriously considered adding a Fuel Cell to our charging sources for covering the energy intensive phases of cruising offshore. However, we decided against using them, primarily because the fuel cannot be easily obtained.


Engine Generator (Gen Set)

In marine applications there are basically two variants: the bigger type is permanently installed in the boat and normally runs on the same fuel type as the main engine. They are quite efficient but bulky and expensive.

There are also portable generators which are typically powered by a small gasoline or LPG engine.



  • provides power when needed
  • invisible (if installed internally)


  • noisy
  • produce exhaust (and possibly dangerous gases)
  • engine maintenance required
  • fuel and oil required
  • expensive solution (internal)

Not our cup of tea.

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