Wattage Usage on a 30' sailboat

[a64pilot]

When those Walmart 12V batteries die, replace them with Costco / Sams Club 6V golf cart batteries, longer life and more AH per $ than anything else.
If $$ is an issue, don't let someone talk you into expensive AGM or Gel batteries, they may or may not be better, but they are unquestionably more expensive

Consider if possible the eventual purchase of a good little suitcase genset, the Honda 2000 is well though of and if you keep an eye out maybe you can find one used at a good deal.
Better (cheaper) in the long run to run a suitcase gen as opposed to your engine, although the return on investment may be pretty long

[Chuck Hawley]

This is the evergreen question, isn't it? As soon as we break free of our shore power cords, we face the dreaded Energy Budget issues. While at West Marine, I created an Excel spreadsheet to help cruisers and racers anticipate their usage, storage, and charging needs. There's been a pile of additional quality information since then on forums like this, and there have also been easier methods to understand one's usage and one's instantaneous capacity. Here are some thoughts from the original West Advisor...

1. Check out the information here on calculating your energy needs. You'll also find good information here.

2. It boils down to knowing your daily consumption, having enough capacity to handle your daily consumption, and having enough charge capacity to recharge in a reasonable amount of time.

3. I am going to guess that you will need 50Ah per day. When I sailed to Hawaii in 1980 and 1982, I had very simple boats and was able to use a single 50W solar panel exclusively. My loads were an efficient Autohelm autopilot, an interior light, a strobe light, and a VHF radio. I could not run my tricolor light all night, but did turn it on when I saw traffic. My consumption was in the range of 24Ah per day. I used a single Group 27 battery and probably cycled it more than optimum, but nothing lasts forever.

4. There's nothing magic about a 50% level of discharge. Less (shallower discharges) will result in more cycles. Deeper will result in fewer cycles. It is possible that there is a better % than 50% for lifetime energy storage, but we've repeated 50% DoD for so long that it has become a virtual truth. I suspect that discharging to 30% DoD would be imperceptibly worse and would give you more energy per cycle. Lower voltage, but more energy.

5. A $200 multifunction meter makes all of this So Much Less Confusing. It's hard to look at your battery system and make heads or tails out of it. Monitoring with a Blue Seas or Victron meter is a really good idea.

Cheers,

Chuck

[Stu Jackson]

Chuck summarized it very well.

Here is another energy budget spreadsheet:

The All-Important Energy Budget:
Energy Budget

Record of Daily Energy Use of 100 ah per day:

"Breaking In" New Wet Cell Batteries

There is sooo much written on solar these days you'd have to be living under a rock to miss it.

Here's a good source that I got from a solar discussion on this very forum:

https://handybobsolar.wordpress.com/

[SURV69]

This is a learning exercise and I think I have my energy needs covered. The facts ... well, they might say otherwise, but I think I'm close.

I'm taking heed of those of you's who feel I won't meet my needs, as you may well be right and you have experience... my plan does include adding more panels, but not as yet.

I'm using the 4 30watt panels because I don't want to get involved with an elaborate installation. Eventually, the 4 30watt units will be placed at the lifelines, and a new array will be on the back of the boat(behind the backstay). The idea of panels for a bimini doesn't seem feasable for me ... I wish could be.

So, some time in late summer, I hope to 2 larger solar panels, and although I'd like 100+watt panels ... well ... the boat is only 29 feet long with a 9' beam.

In any case, I can only add what I have room for and eventually my available power will control how I use it ... as most people ... I'll learn how to cope.

This is why I'd like to hear from others who are "coping" ... getting by with less than the most ideal of solar panel usage.

I have looked at and contemplated 100watt & even 300watt panels, but seriously, if I had room for 400-600 watts panels and umpteen batteries, I wouldn't be asking for ideas .... I'd be bragging about my system.

[MarkSF]

Originally Posted by SURV69

I have just bought 4 30 watt/12 volts panels and a 20A controller for my Bristol 29, which I plan on living in and cruising full-time. I chose the 30 watt panels because I didn't want to spend a lot of time installing my first choice(2x100watt). I also have 2 690AH starting batteries and a 800+ AH battery(left it at home) ... all wetcell batteries. I might add another large house battery later(along with 2 40-80 watt panels) My alternator delivers 40 amps when the engine runs.

I cook on an alcohol stove, use minimal lighting and am operating on a 2A notebook computer. My fridge is a Frigoboat which draws 3A per hour of running, which is about 15 minutes per hour(daytime), and about 5-10 minutes each hour at night. Beginning last years I've learned to "enjoy", heat and tolerate cold. My 7"TV draws about 1/2A and my mp3 player(with speaker), draws about 1/6A.

My computed amperage, daily is expected to be about 35 or so amps on average.

For summer, I expect the 120 watts should suffice and deliver about 40+ amps daily.

I'm figuring that rainy/cloudy days will reduce wattage, but these days might also reduce fridge running time and hopefully keep me covered.

I know there are lots of sailors with hundreds of wattage, and with wind vanes to boot, but I'd like to hear from those who have operated in the 100W to 200W range ... and hear what they think of their system setups.

The most important thing is to understand the difference between amp/hours, amps, and watts, and then not to freely mix them in your posts and calculations, as they are completely different things.

For example, what on earth does this even mean?

"which draws 3A per hour of running"

[Pete7]

Originally Posted by SURV69

This is a learning exercise and I think I have my energy needs covered. The facts ... well, they might say otherwise, but I think I'm close.

In some respects your task is even more difficult than than of arranging solar on a large yacht. You have limited space for both panels and batteries and at a guess a limited budget. A large bank of 6v batteries would be very nice, but its not going to happen, space and cost rule that out. You also may have to accept that some panels will be in shade at some point during the day, well then so be it.

In summary then 3 steps are needed.

1. measure what you use and what the panels generate as chuck suggested.
2. Maximise the power generation from the panels.
3. Minimise the power needed, so insulate that fridge.

Pete

[StuM]

Quotes:
Surv69:
25-35 Amps at 12 volts to be needed daily...
down-draw my batteries by 20 amps or...
120-150 or so watts per hour.

Pete7:
30-40 amps per day...

zstine:
420w daily use

MikeFeergie:
I battle to draw less that 120 amps a night

Puhlease! (Here I go again!)

As MarkSF says - you guys need to understand the differences. Please read here:

http://www.cruisersforum.com/forums/...ml#post1933764

[kmacdonald]

I have a 22' sailboat used on weekends with a 60W panel. It charges a 20AH lithium battery that powers anchor light, 2 cell phones, laptop, depthfinder. I am going to change it out for a smaller, lighter 30W panel. The 60W was at least triple the size needed.

[Pete7]

Originally Posted by StuM

Quotes:
Surv69:
25-35 Amps at 12 volts to be needed daily...
down-draw my batteries by 20 amps or...
120-150 or so watts per hour.

Pete7:
30-40 amps per day...

zstine:
420w daily use

MikeFeergie:
I battle to draw less that 120 amps a night

Puhlease! (Here I go again!)

As MarkSF says - you guys need to understand the differences. Please read here:

http://www.cruisersforum.com/forums/...ml#post1933764

Why do I feel like I have just had my homework marked by the Headmaster

[kmacdonald]

Originally Posted by Pete7

Why do I feel like I have just had my homework marked by the Headmaster

Because "amps" is a measure of current, not energy.

[SURV69]

Canada has their language police and in America we have home-owner's associations.


In Germany, in the 1940's they had the nazis.

Give a little latitude to those of us(me), evidently too stupid to understand the proper usage of A, Ah, wattage and voltage.

[mitiempo]

Originally Posted by SURV69

Give a little latitude to those of us(me), evidently too stupid to understand the proper usage of A, Ah, wattage and voltage.

Electrical issues have to be accurate, not just close.

If you use 120 amps you use 120 amps all night. You also use 120 amps in one minute.

Amps is the amount of water out of the hose.

Amp Hour (AH) is the amount of water x the time it flowed.

It is important.

[SURV69]

while I understand the perceived need for proper terminology, keep in mind that if a person is talking about 12 volt panels, it can generally be assumed that a 12 volt system is being discussed.

and ... if a person talks about a TV drawing 4 amps, it can be generally assumed to be per hour, since 4 amps per minute or per 24 hours is obviously, each grossly incorrect.

Typically, if a person's target is to operate certain items that will somewhat approximate what 4, 12volt, 30watts panels might deliver, the general premise could be that someone wants to make use of items would require something in the area of 500-600 watts ... most likely at 12 volts and therefore at something approximating 30 or so amps, and probably per day, as in 24 hours. With no more specificity than just given, most people would know the time frame and could continue the discussion without basically stating that without more specificity, the given figures are, almost contemptuously worthless.

If someone stated that Hank Arron hit 45 homeruns ... virtually nobody would have to ask if it was in one game or one lifetime.

[mitiempo]

Most people like to learn.

I guess some don't.

[Jim Cate]

and ... if a person talks about a TV drawing 4 amps, it can be generally assumed to be per hour, since 4 amps per minute or per 24 hours is obviously, each grossly incorrect.

And you, sir, have obviously not understood the helpful explanations that have been offered above.

For, you see, a TV that draws 4 amps will do so for one second, one minute, one hour...
and your statement is "grossly incorrect".

You really should read StuM's link, for it does a good job of gathering all this nomenclature together in an understandable format.

Jim