Introduction to on-board Energy ManagementBy Bruce Schwab – OceanPlanet Energy

Bruce Schwab Energy Systems

Preview...● Understanding energy – the basics

● The usual energy sources on board

● Typical energy storage, monitoring, & maintenence

● Fossil fuel vs. Renewable

● Solar-wind-hydrogenerator options

● How much energy do you need?

● Coming up with a plan

Understanding electricity...or, Watts Up?A bit of terminology...

We say “Volts” and “Amps”, however, electrical energy is best expressed in Watts.

Here's how I like to think of it...

Amps = current, or rate of energy flow

Volts = power of the current, or “pressure” (voltage is also known as “potential”)

Important fact: Volts x Amps = Watts

So...what are Amp Hours?

● Amps over time = Amp hours (Ah's)● 100 amps x 1hr = 100Ah's● 10 amps x 10hrs, also = 100Ah's● 5 amps x 24hrs = 120Ah's● 10 amps x 24hrs = 240Ah's● And so on...

Why do I care about Volts and Watts?

● 100 amps @ 12V = 1200 watts, or 1.2kW (this is an expression of energy flow/power)

● 100Ah's @ 12v = 1200Wh, or 1.2kWh

(this is an expression of energy/power over time)

● 100 amps @ 24V = 2400W, or 2.4kW

● 100Ah's @ 24V = 2400Wh, or 2.4kWh

● Twice the voltage = twice the power, at the same amps!

So why then do we use wimpy 12V?

● Good question! Most larger boats are now 24V

● Some still use 12V for instrumentation or LED lighting

● A separate battery can used for the 12V loads

● High voltage is dangerous, can jump across gaps (arc), etc.

AC vs. DC – what's the difference?

● DC = Direct Current...energy flows from higher voltage “source” to load with lower voltage. Positive & negative conductors form a circuit for energy flow from source to load.

● AC = Alternating Current...one or more conductors provide energy with reversing (alternating) polarity (pos-neg, pos-neg...) 50hz (Europe) or 60hz (USA). hz = cycles per second. Usually much higher voltage than DC.

AC vs. DC, continued....● Low-voltage DC is used on boats, usually 12V or

24V. Requires larger cables/fuses/etc. however is usually safer than high-voltage AC.

● 120/240V (USA) or 230V (Europe) AC used where high loads would require too much current (amps) to run with low-voltage DC. Think – air conditioning, water heaters, etc.

What goes out, must be put back in...where will it come from?

The usual suspect: fossil fuel (diesel/gas):● By engine alternator● AC genset, through AC/DC charger● DC genset, straight to batteries (rare)● Fuel cell (rare)

Energy sources, continued...

Renewable energy sources (not fuel):● Solar power – must have sun

● Windgen – must have wind

● Hydrogenerator – must be moving

● For renewables to work best, we need a way to store energy when they are available, for later use – thus we have batteries.

● More on this later...

How much energy do you have?

Having a voltmeter and an ammeter does NOT really show you how much energy you have.

A battery monitor measures/tracks the current flowing in and out of the battery, and calculates how much energy

you have left in the “tank”.

A battery monitor is a good thing● Tells you your SOC - Stage Of Charge

● TTG - Time To Go (before you run out)

● The net current in or out of the batteries

● System voltage (same as a voltmeter)

● And lots more...for instance some monitors also can show your tank levels, individual energy sources & loads, etc.

Stuff to know about batteries...

● Flooded, Gel, AGM, are all Pb (lead-acid) batteries. The Gel & AGM are “sealed” to prevent water loss in normal use.

● Pb batteries are about 15% inefficient. That is, for every 100Ah's you put in, you get about 85Ah's back out.

● For proper care, Pb batteries require somewhat complicated charging regimes.

● Some say, with good reason: “Most batteries don't die...they are killed” (by improper charging!)

● Typically only about 50% of the battery capacity is considered “useable”, in order to reach rated cycle life

Comparing battery types...

● Flooded Pb: Best value, long lasting, however require maintenance (adding water, equalization, etc.)

● Sealed Gel: Long life, good for low-moderate loads. More expensive than flooded.

● Sealed AGM: Good life (if properly charged!), usually better than Gel for high loads and faster charging (not always). Also more expensive than flooded.

● Lithium (Lithium Iron Phosphate): Safe, great in every way, however the most expensive by far and require professional installation.

Battery charging terminology● Bulk charging – filling the battery in the middle of

it's capacity - from 50% SOC to about 80-85% SOC

● Absorption – holding the battery voltage at a moderately high level for a few hours to full top off the battery

● Float – the “storage” or maintenance voltage level that the charger should taper off to

Charging Pb batteriesNote that the charging voltage level changes over time, with a period of high voltage (absorption) after the intial

“fill-up” (bulk). Then the voltage is lowered to “float”.

Notes for proper Pb battery charging with an engine alternator

● Engine alternator should have an external “smart” alternator regulator

● Regulators for alternators (and other charging sources) should have battery temperature sensing

● Bigger is usually better when it comes to alternator charging...saves fuel and the alternator lasts longer.

The Pb charging “Catch-22”

● Pb batteries require periodic charging of several hours at “absorption” voltage to be fully charged. This charging is at low current.

● Such low-charging charging is wasteful of fuel, is not good for diesel engines (running at low load), and it is tiresome to listen to the engine for so long. Especially to your anchorage neighbors!

More battery bad news...● Typically Pb batteries should be discharged not more

than about 50% of their “rated” capacity, if they are to deliver their expected cycle life (number of times discharge)

● The CAR (Charge Acceptance Rate) of Pb batts is “fast” only up to about 15-20% left to charge. After that the CAR drops off and it takes a long time (several hours) to fully recharge the battery.

● So, using the engine (fuel) to charge is great for the “bulk”, and not so good for the “absorption” stage.

Which brings us to...Fossil fuel vs. Renewables

● Of course if you're motoring all the time then you'll be charged up anyhow

● However, if not motoring all day then the batteries could use a long slow charge from something else...like solar panels, or windgen, hydrogenerator, etc.

● Solar or wind power is a Pb battery's best friend for maintenance & longevity

Solar panels come in several forms

● Traditional “hard” glass panels (sharp corners, heavy!)

● Thinner semi-flexible panels with metal backing and non-skid surface (a bit lighter, good for walking on)

● Lightweight high-power semi-flexible that can be sewed to canvas, etc. (popular now for dodgers, biminis, etc.)

● Lightweight flexible or roll-up panels made from “amorphous” silicone cells (very low power, not much use on boats)

Flexible/sewable mounting examples...

Zippers are sewed to the edges of the panel...

Or Velcro only, no zipper...

5 x Solbian SP100

Aurinco or new Solara (better than the old Solara) are better for mounting in trafficked area:

A hydro-what?

● That's right, a hydrogenerator:

Hydrogenerator pros/consThe good:

● High output when moving, up to 500W

● Easily lifted out of the water for less wear and drag after batteries fully charged

● Much less weight than a generator

● No fuel needed while sailing

The bad:

● Expensive (although less than a generator)

● Useless when moored (except for starting conversations)

Then there's wind...

● The good: Free energy when there's wind

● Combined with solar can be a good combo

● The bad: Noise (varies), sometimes not as much power as anticipated, can be dangerous

Let's back up...so how much energy (and energy storage) do you need, anyway?

● Need to know your 12hr or 24hr loads in watts or Ah's

● Method #1 (the easy way): Using your battery monitor, start from 100% SOC, and run the boat without charging for 12hrs or 24hrs (if you can). The monitor will show how much you used, in Ah's.

● Method #2 (more work): Estimate your loads by listing all your devices (lights, fridge, autopilot, pumps, inverter/AC, etc. etc.), the current draw of each one, and the amount of time each one is on per day. Note: I have an excel calculator for doing this...

I think I need 150Ah/day. Now what?

● How long do you want to go without charging?

● If 24hrs, then you need to put back in about 172Ah's (remember batteries are about 15% inefficient!) in order to make it another day. Also, your batteries need to have at least 150Ah “useable” capacity to last until recharging.

● If 12hrs (charge twice per day), then you'll need at least 75Ah's of useable battery capacity, and put in about 86Ah per charge.

Can I go all solar or renewable?

Well, given our 150Ah example it IS possible, however you would require about 500 watts of solar panels. And sunny days. Here is that 500W of solar again...

A little of both (fuel & renewable) is most realistic...

● You motor or charge 2hrs/day (2 x hr) and sail the rest.

● The engine alternator charges at 60A, for one hour (60Ah's) each time.

● Total charging from fuel: 120Ah

● 172Ah (150Ah x 1.15 inefficiency) – 120Ah = 52Ah

● You have a deficit of 52Ah, which would require about 150W of solar (in good sun). A more reasonable figure than 500W, and less expensive

● Or, just motor all day.

A reminder about watts & voltage...

● The previous example (150Ah/day) was assuming a 12V system. In watt hours (Wh's), that would be 1.8kWh/day (150Ah x 12V = 1800W)

● If a 24V system, 150Ah would be twice the Wh's, at 3.6kWh/day (150Ah x 24V = 3600W)

● So would need twice the solar power in watts to cover your 24hr loads.

Long trip, don't want to run the engine?

● Let's say that you had enough solar to cover your loads while moored (fridge, lights, etc.). However when sailing the autopilot load doubles your total load in Ah's. Moored: 100Ah/day, sailing 200Ah/day

● Your 300W of solar usually covers you when anchored in a nice sunny spot, however falls short while sailing. Now what?

● For short trips, you'd just run the engine more.

● For a longer trip, add a windgen or hydrogenerator

So, what's your plan?

● Find out how much energy you need, by measuring or calculation

● Decide how long/often you want to run the engine(s)

● If you don't have a battery monitor, get one

● Size your battery bank to cover your loads between charging sessions

● Reduce your loads with LED lighting, improved DC refridgeration, etc.

● Add as much renewable as you can fit (and afford)

Get help.

● After you figure all this out...or even before you do...

Remember there are folks who do this stuff all the time, and they can help you. Especially when it comes to safe installations that meet ABYC recommendations, etc. There are very

good reasons for the rules and specs that exist, to prevent shock, injury, or worse.

Go Sailing

Thanks!

OceanPlanet Energy

Bruce Schwab Energy Systems

72 Front St. Suite 15

Bath, ME 04530

207-370-9112

Www.bruceschwab.com