Boat Energy Balance

[FlyingScot]

Energy Balance:
Battery bank is one thing.
How you fill it is another.

If you forget about aircon, the next biggest use for most boats is refrigeration. Depending on location (tropics vs anywhere cool) one unit could pull over 100 amp hours per day (12v). Some have multiple ones. How cold do you like your beer/wine?

Once you get big enough the small loads become almost meaningless. Who cares how many amps your electric flush toilet draws (6 amps). It's not like you flush it for an hour a day. Lighting is LED or should be, this should be all of them. Or at least any you use for more than a few minutes at a time.

Make sure you understand a few simple things: (this is what we do)
How much you use overnight? (200 ah from a 450 ah house bank)
How much you use during the day? (300 ah)
How do you generate enough power for the two items above plus about 10% extra for losses? (1440wp solar, Our max single day harvest @ 12N = 8.2kwh)

Honestly, if we made twice as much power, I bet we would find a way to use it.

I've never heard anyone say they make too much power.

[Pegu Club]

For DOD capacity firefly batteries can be a good an alternative to lead acid, or standard AGM batteries, being firefly’s can do 80% DOD, this can allow for fewer batteries and less weight, because of the available amp hours. FWIW Maine sail did a write up on this, on his marine how to site I believe.

Fair winds,

[sailorboy1]

FWIW - 200ah a day usage with a 400ah battery doesn’t mean 50% soceach day. It means -100ah in morning, or 75% soc, and during the day you recharge that with solar while using another 100ah during the day to start the night with 100% soc

[jamhass]

As you work through all this, don't forget to look for was to reduce power consumption. Some areas that we've found especially effective are led lights, including nav lights, and a low power computer (computers are often one of the major power sucks, and one often ignored ) . Also, eliminating the need to run an inverter, for example to run a 110 v tv can help a lot.

[Pizzazz]

You will hear lots of opinions. The key is to understand that batteries are less important, how you generate electricity is more important. Technically, batteries should only cover you during the night when your consumption is very low and you sleep. Then it comes to charging sources:

- Most people charge with the engine alternator. For your size boat you can get a good 120A alternator - run the engine for two hours a day and you are set.

- Solar is great but ugly.

- A generator is a really good option as well. You need to balance your battery capacity with your generator size and solar size. Read about it.

Regarding consumption - I thought I knew something about power consumed until my son brought his PlayStation on board. That thing and the TV was drawing 22A for hours on end. Another sailor told me his family of five had 17 iDevices. Relative to that the autopilot and the fridge are just the icing on the cake.

SV Pizzazz

[Stu Jackson]

Originally Posted by Pizzazz

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- Most people charge with the engine alternator. For your size boat you can get a good 120A alternator - run the engine for two hours a day and you are set. >>>>>>>>>>>>>>>>>>>>>
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Would it be possible to only have to run your engine for one hour only every three days with the same loads which with good management can be reduced from 100 ah / day to 60-65?



If I had to run my engine 2 hours a day, I'd find much better ways to manage my electrical system, and have.


These days, "Most people..." use everything BUT their alternators.

[newhaul]

Originally Posted by Stu Jackson

Would it be possible to only have to run your engine for one hour only every three days with the same loads which with good management can be reduced from 100 ah / day to 60-65?



If I had to run my engine 2 hours a day, I'd find much better ways to manage my electrical system, and have.


These days, "Most people..." use everything BUT their alternators.

you mean like these

[CatNewBee]

There are some power hogs to consider.

Number one are fridges and freezer. They run all day long. Depending on what you have this could be a big chunk. We have 2 fridges and a freezer, they draw constantly between 15 and 20A, so for the 24h day around 350...400Ah depending on outside temp and ice build up inside.

Next is Navionics, instruments, Radar Auto pilot. On a monohull you can use a wind vane instead, but for motoring you will need one. 5..15A i would say, 10h sail means 50..150Ah consumption.

Lights is easy, use LED for navigation lights, anchoring and interior. Consumpiuon daily maybe 15..20Ah.

Watermaker is an issue too, 100l water take 60Ah, depending on your usage and crew size, we need it daily.

Then notebooks, pc, tablets, camaras, phones etc. This could summ up too. I would say 5..20Ah

If you use an inverter, very likel there will be some heavy loads. E. G.for a microwave, instapot, induction plate, toaster, ice maker or whatever.

Not uncommon are warm water boiler, real power hogs, but some use the engines primary cooling circuit to make warm water and can hold it for about 2..3 days warm wor washing dishes or so, otherwise running on inverter it will add up 150Ah for a heatup. As cruisers off grid, you may consider a washing machine, add another 100Ah for the water and electricity per load.

On our cat we produce and consume 8kWh in average daily, by solar and stored in a LiFeYPO4 1000Ah battery good for 3 days+ bad weather without rationing power. Solar is a 1650Wp array, that delivers this 6...9kWh per day, no alternators or generator contribution.

A problem under way is the higher demand for the electronics and autopilot, while sails shading part of the solar array, so instead og 9kWh in sunny days, there are only 5..6kWh, not fully covering our consumption. But the buffer is usually big enough for a 4..5day passage without the need to make water (600l capacity) or run the generator. We need 2h generator time to charge 600Ah because of the Lithium battery, would not work with lead acid.

[CatNewBee]

... In your case on a monohull I would say 1/2 of it, 500Ah LFP or 800Ah FLA if you have a generator, may be less, 400...600Wp solar or 450Wp solar plus wind generator if you not motor frequently. Other wise you may need to run your engine some hours per day for charging or may have to limit your consumption.

It really depends on you, what you need and use.

[mvweebles]

"1650 Watts of panels?" That's close to 10-12 Sq meters. Impressive! One of the benefits of having a cat...

To OP - there are four general buckets of consideration: (1) energy usage/budfet: austere (100a/day) to luxury (+400a/day). Underway, electronics and A/P are the hogs. At anchor, refrigeration is the hog. (2) Desire/ability to be off grid and not run either a generator or your engine for charging. (3) Physical limitations forbbatteries and solar panels. And (4) Budget. If you are willing to design for at-anchor and know that when you're underway you will have go run the engine a couple hours a day, greatly reduces sizd/cost of the system.

As a starting point, would say a base system of 100ah/day energy usage budget is on the austere side with 200ah of battery storage (two 6v golf cart batteries or equivalent) with two solar panels. From there, you can multuply the base system as needed - if your needs are closer to 200ah/day, then double the base system (may only need 3 panels). And so on. Sooner or later you will hit a barrier in one of the four buckets listed above. But leave room for expansion where possible. As an aside, would recommend coughing up additional money for top quality system components (charger/inverter, MPPT solar controller, Balmar regulated alternator, State of Charge meter, etc). In my opinion, going cheap is false economy.

Good luck. Would be interested in what direction you go.

[mikedefieslife]

Originally Posted by Pizzazz

Technically, batteries should only cover you during the night when your consumption is very low and you sleep.

I'm not sure about that. Currently in Madeira. It has thick cloud every afternoon and offers near 0 solar charging during that time. In fact since I've been in the Atlantic it has been cloudy for 50% of the time, so the OPs cruising destination is vitally important to how he equips his boat in terms of energy generation.

[noelex 77]

Originally Posted by CatNewBee

It really depends on you, what you need and use.

Exactly.

Power usage varies so enormously that it is not a great idea to rely on what others are using as a prediction for your likely consumption.

If the goal is to use solar and wind rather than a generator, the minimum number where the boat runs well and the crew are comfortable is very important. Reducing this number as much as practical is important and with careful selection of systems and devices significant savings are possible with little sacrifice in functionality.

Most of the time the production will be much higher than this minimum number and using systems such as electric cooking to take advantage of this extra power is worthwhile. There is nothing wrong with using heaps of power, providing you are also producing heaps of power.

[CatNewBee]

Originally Posted by mvweebles

"1650 Watts of panels?" That's close to 10-12 Sq meters. Impressive! One of the benefits of having a cat...
.

5 Panels at 156 cm x 105 cm, 330Wp each, 8.2 sqm in total, not that bad...

[Pizzazz]

Originally Posted by mikedefieslife

I'm not sure about that. Currently in Madeira. It has thick cloud every afternoon and offers near 0 solar charging during that time. In fact since I've been in the Atlantic it has been cloudy for 50% of the time, so the OPs cruising destination is vitally important to how he equips his boat in terms of energy generation.

My point was that if you charge from an engine/generator, you do not want to run it while you are sleeping. So, it makes no difference if you run the engine for two hours a day or four six hours every three days. Hence you need minimal batteries. Actually, I think the battery bank should be sized to your largest load, typically the inverter powering an AC device.

The only reason I am against solar is that it looks ugly on a small boat like mine. May be foldable panels that you put out an anchor. Also, for my type of sailing I use the engine a lot in coastal work as the winds in SoCal are typically variable. I think most people use the engine more than they want to admit.

[CatNewBee]

The problem with lead acid batteries is, they have a very small acceptance rate, especially over 80%SOC, so two hours per day will not charge them to full.