This will be technical blog entry created by a Captain/mechanic, not by Admiral, so may not be interesting for everybody. I will add some pictures to this entry later.
I believe that a sailboat energy management consists of three basic components:
- Production or purchase of energy
- Storage of that energy
- Usage of that energy
The aim is to keep consumption below production/purchase and to have enough storage to bridge time gaps between production and consumption.
We wanted to make Heron as self sufficient as possible covering our own needs for electricity and water - two reasons why many yachts go to marinas to resuply with water and electricity.
We never lived under illusion to have fully energy self sufficient boat - that is almost impossible. We still rely on fosil fules for main diesel engine, for dinghy outboard and for cooking gas. We want to have enough capacity of diesel, gasoline and propane to be able to venture to remote places without fuel stations, but that is a topic for some other time.
Today we look at electrical system.
Main aim is to keep consumption as low as possible.
Major loads are: refrigeration, producing water, navigation (including radar, autopilot chart-plotter, AIS and other electronics), computers, lights, power tools and there is more.
Lights: We have replaced standard light bulbs with LEDs, including anchor light and sailing navigation lights. This reduced out total needs of Ah for ligths drastically and having a ligth is no longer a problem.
Making water: We use one of the most efficient water-makers available on the market and can we produce 54 l of fresh water in one hour using only 216 Wh according to manufacturer brochure. Reality is very close to this numbers.
Last remaining hog and biggest of them all is refrigeration.
The boat came with a strange refrigeration system:
It is a combination of 12V and 220V "megafrost" system with holding plate in each fridge (we have two fridges) designed to run only when the main engine is running or when shore power is available. An excellent system for charter use. Two hours per day is all what is needed to have beer always cold. Run it longer and you have frozen beer.
It works like this: A dedicated 80A alternator (in addition to main 80A alternator) supplies 12V to inverter/control unit, which runs very powerful compressor on 220V (more then 500W - 10 times as much as normal domestic fridge in Europe), plus supporting pumps running on 12V. The fridge is sea water cooled, which is great in the tropics as it does not heat up the boat. This works fine in charter use as most clients motor out of the marina and return into marina under motor. Two hours per day under engine and beer is cold. To me it was not OK as I do not want to run the engine every day - and specially not for two hours, so a powerful alternate generation was needed to feed the fridge with energy.
We decided for solar power and we have two large (240W peak power each) solar pannels controlled by an MPPT controller.
The solars are mounted on a stern arch/radar mount/dinghy davit. The stainless steel arch is a work of art and was done by an excellent welder in marina Portorož, Slovenia: Janez Ovčak. I reccommend this guy. Very nice and professional work. He and his father needed the whole week to finish it, but is is worth.
The solar pannels are from Slovene manufacturer Bisol.
They are not marine solar panels, but they offer best power per area and they work great. I wired them into series, to get more V and less A, so my cables can be smaller and power loss is smaller too. My advice: calculate power looses and voltage drops carefully. You do not want to loose most of the power on heating the cables and possibly make a fire on a boat.
I am using TriStar MPPT controller from Morningstar to convert 60V into whatever the batteries need at the moment.
The MPPT controller a 4 stage charger/solar controller and is essential is you want to use high power solar pannels to their maximum capabilities. MPPT stands for maximum power point tracking and boosts the energy produced by solars - in essence it is an DC to DC converter with a lot of smart SW to maximize solar energy and preserve the batteries at the same time.
The system works great in Mediteranian summer in Adriatic, Greece, Italy and Spain. In 3 months we never needed to run the engine just to produce electricity and we keep frozen stuff in the freezer and produce all the water we need.
About Electricity storage: We stil have a relatively small battery bank which came with the boat 220Ah for "house" and 55Ah for engine. Some cruisers with 1000 Ah would laugh at this, but my trick is in usage - I use energy when there is plenty and not much during the night. I make water on a sunny day from solar energy directly. I cool the holding plates of both fridges while the sun is high and they keep the fridges cold during the night without using electricity.
On a normal day at anchor the batteries are fully charged before 10 in the morning as my night drain is so low.
We only use few LED lights during the night and some for water pump. Other stuff is turned off: Computers run from their own batteries, we do not make water during the night, navigation is off and fridge is using accumulation from its own holding plates.
This means I can start recharging small appliances (computers, cameras, phones, ... already at 10 in the morning and I am not even draining my main battery bank at all, as production is bigger than usage. We can also start producing water at this time or have a laundry day (we have a camping 220V washing machine we run from inverter). At about 11 I can turn on the fridge.
The fridge is a major hog with 40 A of draw at 12V, which is more then we can produce at any time, but the solars are producing 20 to 30 A between 11 and 15 hours, so I drain the batteries while the fridge compressor is running, but that energy is replenished with solar panels when the compressor is not running.
We have spare energy for power tools, mixer, vaccum cleaner (yes we have a vacuum cleaner, there is a lot of dust on the boat and boat is full of tiny little corners hard to reach with a broom).
This means: While at anchor we do not need to run an engine to produce water or electricity and we do not need a large battery bank as the biggest consumers (fridge and watermaker) can be run when energy is available. If we run into rainy, foggy, cloudy days our production is a lot less, so we would need to run the engine to produce electricity. But we went cruising to avoid rain and fog in the frst place, so we would probably move out of fog and rain and follow the sun anyway.
While underway (passage) our energy consumption is different: less watermaking, less laundry, less power tools and other things which can wait until we are at anchor, but a lot of power consumption by autopilot, radar and other instruments. Major difference is, that we use a lot of energy during the night.
Autopilot - we cruise under autopilot 99% of the time and we only hand steer in the harbors or when I want to squeeze a few degrees more to windward. Our powerful Raymarine with linear drive does use a lot of power, but this is unavoidable.
Radar: We use radar most of the time and definitely at night. We have a new generation broadband radar, which uses very little power, but produces excellent target identification on close range.
Chart plotter and instruments: At night one runs the screen in night mode to preserve night vision, so it uses much less electricity. AIS is not that energy hungry and it is on all the time. Running lights in sailing mode (on top of the mast) are LED as well, so they are not a concern.
We finish the night with batteries in a very good condition - at about 12,5 V, but it takes solars a little longer to fully charge them again. So we start the fridge later.
So far we did not need to run the engine to produce electricity. But we needed to run it when there was no wind.
And if we run the engine anyway to propel the boat we freeze the fridge very cold, make a lot of water and sometimes wash laundry while underway.
We have no experience with shorter days in fall and with rainy cloudy days. We will see. In worst case (no energy from solar at all) would mean we need to run engine one to two hours per day. We will see.