The nightmare begins!! Where to start power consumption calcs?

[captmikem]

Originally Posted by Zai

Thanks for all of the info!

Helps me re-think things a bit, for example: that the chart plotter uses much more of the daily budget than I thought, what about durring long passages to switch it off for the most and only using it to verify once in a while (durring daylight hours)? Running the radar on standby for the most and transmitting on a regular schedule (every half hour for example)? On longer passages not running the fridge (dried foods and/or canned). On cloudy days doing more manual steering, etc.

Now I am getting inspired, thanks again!

Zaj,
Folks nowadays expect a fix a second, When you are crossing an ocean, we used to be happy with a morning and evening star fix. We were ecstatic when satnav would give us 2 or 3 fixes per day. Honestly, once you leave shore, a noon and midnight fix off your gps is really all you need until you start closing the coast. And Radar, having to crank it up and look at it makes it not really the best for collision avoidance except in low visibility or when you see something on the horizon and want to check it out, because otherwise it is just sitting there using up power, and you have to look at it for it to be useful, which after a while of not seeing anything you tend to neglect. Radar alarms are fine, but when you start getting sea returns, your alarm is either beeping all the time or if you turn the sea clutter up you miss targets. (and it Sucks up the power!) Nowadays with AIS being required on all commercial ships, it is so much better, like having ARPA without spinning a radar. You could actually get a small cheap Lowrance chartplotter and hook your AIS up to it, would not draw much, you would have your position continuously (might have to plot it on a paper chart) and have your AIS alarm for any traffic. Don't forget people have been using their eyes and senses for many many years, you can do the same.

As for consumption, Paul is correct, you can make a guess, but it is only theoretical. Corrosion at terminals throws it off, turning reading lights on, listening to or transmitting on your ssb, water pumps, all kinds of things. A battery monitor is the best real time indicator ( I use a Link 10 but there are others just as good) it is like a fuel gauge for your battery. Also charge controllers that make the best use of your alternators (I run two off my main engine) make a world of difference in how long you have to run your engine to replace the charge. If you have an efficient fridge you can charge it every couple of days when you charge your batteries.

And just a word about batteries here, I had a fortune in Odyssey agm batteries, 4 of their 2250’s and 8 2150’s and they all went south after 3 years. Now I have two 8d sealed batteries for 1/5th the price and a couple of 31’s they work just as well.

Hope this helps, and good luck to you.
Michael

[MarkSF]

Originally Posted by Zai

My original thoughts are a battery bank of aprox. 500 amps (gel or AGM), 450 watts solar (9 hours/day), 400 watts wind (calculate at 200 watts for 4 hours a day).

A good start would be getting the terminology right. The battery bank is 500 Ah, or amp hours. I'm presuming you mean the solar will give 450 Wh, or watt hours, equaling 50 watts for 9 hours.

If you say 450 watts for 9 hours a day that would be 4.05 kWh, which is a big difference.

"400 watts wind (calculate at 200 watts for 4 hours a day)" Huh? That should be 800 Wh.

Watts and amps are rates of usage, like flow. Watt hours and amp hours are quantities, like gallons. Think of your batteries as having so many gallons of electricity in them. You can use them slowly, say over 10 hours those batteries will give 50 amps. Over 1 hour they will give 500. (well, it's more complicated that that because you get MORE total power at lower rates)

The battery capacity governs how much power you can use over a day. Please note that you should only use half the capacity, or 250 Ah to preserve the battery life. Over a longer voyage, you must replace that used capacity every day.

Here's my calculation : you have 50w of solar for 9 hours a day. That's 450 Wh, which at 12V is 56 Ah. You have 200W of wind, for 4 hours a day. That's 800 Wh, or 67 Ah. So you can use a total of 123 Ah per day.

Add up the realistic usage of your boat systems in Ah, per day. Sticking to the same units will help preserve sanity.

[CLady]

My AGM house battery is rated at 500 ah of which I figure drawing no more than 250 ah when figuring power useage.

[kas_1611]

Calculate on the worst case scenario - that is everything pulling maximum power - so you have an energy reserve more than capable of meeting that demand.

So if your fridge pulls 3amps but runs for 20mins per hour, for example, calculate based on 3amps per hour as if the compressor is running non stop. Unlikely I know but better safe than sorry.

Then figure out where you can save power. Swap to LED lights everywhere, insulate the fridge, turn down the backlighting on instruments to as low as they will go (mine are on 0% backlight and the effect is dramatic), don't leave USB chargers (or any type of charger/convertor) in the 12v sockets when not in use, unplug/switch off everything if not physically using it etc etc. If you haven't got a battery monitor fit one as this will show you clearly how much power you are actually using rather than theoretical.

One thing that confused me was your claim to have wind power for 4 hrs a day. If you are sailing then your wind genny should be turning under the apparent wind so you'll be generating constantly and even if you are on anchor unless it is absolutely flat calm you'll have some amps coming in from both the wind and solar generation. Again a battery monitor or incomming ammeter will show exactly how much.

As an example we have a 135Ah battery, 2x35w flexible solar panels and an average daily power use of 60Ah. On an average day under sail the panels provide enough power to balance the drain with the chartplotter, instruments, VHF and fridge on. On a brighter day they actually provide an extra amp than we drain. On anchor without the instruments but listening to the stereo the panels, on a bright day, easily match the demand and will keep the batteries topped up. We can do over 2 days on anchor without having to worry about dropping below 50% charge as long as the sun is shining of course.

Hope that helps

[sailorboy1]

Originally Posted by Zai

My original thoughts are a battery bank of aprox. 500 amps (gel or AGM), 450 watts solar (9 hours/day), 400 watts wind (calculate at 200 watts for 4 hours a day).

To just get right down to it, I feel this is enough power. I would get more solar and less wind if possible.

[Zai]

Originally Posted by MarkSF

A good start would be getting the terminology right. The battery bank is 500 Ah, or amp hours. I'm presuming you mean the solar will give 450 Wh, or watt hours, equaling 50 watts for 9 hours.

If you say 450 watts for 9 hours a day that would be 4.05 kWh, which is a big difference.

"400 watts wind (calculate at 200 watts for 4 hours a day)" Huh? That should be 800 Wh.

Watts and amps are rates of usage, like flow. Watt hours and amp hours are quantities, like gallons. Think of your batteries as having so many gallons of electricity in them. You can use them slowly, say over 10 hours those batteries will give 50 amps. Over 1 hour they will give 500. (well, it's more complicated that that because you get MORE total power at lower rates)

The battery capacity governs how much power you can use over a day. Please note that you should only use half the capacity, or 250 Ah to preserve the battery life. Over a longer voyage, you must replace that used capacity every day.

Here's my calculation : you have 50w of solar for 9 hours a day. That's 450 Wh, which at 12V is 56 Ah. You have 200W of wind, for 4 hours a day. That's 800 Wh, or 67 Ah. So you can use a total of 123 Ah per day.

Add up the realistic usage of your boat systems in Ah, per day. Sticking to the same units will help preserve sanity.

You are correct in as the battery bank I am planning is 500 amp hour.
The solar panels are 450 watts total calculating 9 hours of such production maybe is not realistic? I think I need to adjust that, but that is why I am posting here, to get you guys input who have been there done that. :-)

The wind generator is a Silent Wind. I have calculated it at half of the rated max output for a period of 4 hours a day (maybe too little?) Max is 400 watts, it puts out 200 watts at about 22 knots of wind and about 100 watts at about 17 knots.

After all of the input I am considering to bump the solar to 600 watts.
Of course I will use a battery management system to monitor the whole lot and make adjustments from there, but I am trying to nail it as close as possible the first time around.

I like the weight of those Renogy panels (I have not bought any panels as of yet). Planning to build an arch out of aluminum and have it hard anodized (weight consideration) to mout the solar on and double as a way to lift the dingy. The wind generator will mount to one side (port).

Thanks again for steering me in the right direction!

[oleman]

I have a modern power consumption meter. It will accurately measure 100A AC at 80 - 300 VAC 60 cycle. It is small enough to fit in a tea cup.
AND COST around $30 American at a website in China.
To my surprise is is also fairly accurate.
This is a panel meter and requires a competent electrician to properly install it.
It could guard a single branch or the total consumption of the whole vessel.

[Lars_L]

The power from the wind generator is the hardest to calculate. But it’s possible to simplify the calculation.
You sail in the trade wind that blows 20 knots.
You sail in 6 knots.
The wind comes in from straight behind, then will the wind generator get 20 – 6 = 14 knots.
Lock in Silent winds power diagram. I guess that it gives 50 W @ 14 knots.
50 W in a 12 V system corresponds with 50 / 12 = 4.2 A.
You will have this wind day around and that will give you 24 hour * 4.2 Ampere = 100 Ah.

The big problem with the calculation of the wind generator is that if the wind goes down to the half, the power output will be 1/8.
An example.
Silent wind gives 400 W @ 26 knots.
The wind goes down to 13 knots. (the half)
The output power will go down to 50 W. (1/8)

What wind speed do the wind generator get? It is not what the wind instrument, which sits in the top of the mast shows, it is much less, and it’s hard to guess. A handhold instrument that you hold beside the wind generator is more exact. A small wrong in the measure of the wind speed will do a big impact on the produced power.

In may home area (N 55°) I calculate that a 100 W solar panel gives an average of 1 A day around = 24 Ah.


Oleman. An instrument that is made for AC do not work with DC.

[monte]

You're on the right track Zai. Personally I'd leave the wind gen till later unless you are planning on a long passage in the immediate future. Shading the panels will probably be an issue mounted on the arch. Take a look at markJ,s panels, I think I saw a picture he posted on here. On an arch and easy to angle if need be, lifts the dinghy as well ..

[Dody]

Hi together,

I really appreciate all your previous posts and I agree on most of them.

But, in my opinion, the first question to be asked is: what do you want to do with your boat? Concerning electricity consumption this is the major point to determine what is important.

A few years ago when designing my new electric system I was struggling with the same question. Somehow I have the feeling that my priorities did and do point in a very different direction.

My boat is composite (wooden frames and planks, ply diagonal and 7 mm fibreglass on the outside from the beginning), launched 1960, 22 Tons, I'm mainly sailing on my own.

Priorities for me were the worst-case scenario:
- if I have a leak I want to be able to run my electrical bilgepumps (+ use the engine intake if the engine is not under water etc.) to have my hands free to find the leak and do something about it, if need be for 24 hours or more.
- at the same time be able to run my autopilot which takes 8-10 Amps
- at the same time run my radar with the alarm set (28 Watts)
- and still have enough power to run my nav-lights, the VHF, at least the handheld GPS, a cabinlight for the nav and occasionally the SSB.

In this scenario I considered everything else as luxury and not needed. But, I wanted my setup to be capable to cope with a situation like this.

After all this was calculated and worked out, I sat down to find out about the consumption of electricity needed at anchor or on a normal passage without things going wrong and found out that I've got plenty. So I set it all up as worked out for the worst case scenario.

Someone enjoying sailing around in the bay with a nice breeze for a day won't have to cope with fog, weatherforecasts nowadays are getting better and better. He won't need to fight a leak for 24 hours or more, help is in the vicinity. He might have crew to give him a hand with steering and being on watch, so no need to run the autopilot constantly or the alarm of the radar.

Just a different approach ...

Cheers & fair winds
Dody

PS: I've got 3 analogue Amp-Meters, one of them in the cockpit and analogue Volt-meters, also one in the cockpit. Lots of nice things can be done with these smart battery-monitors, but once things go pearshape you won't get a proper reading any more which means you can't react before more things go wrong.

[Frugal]

The one day you get all the sums right will be a milestone. The other 364 days per annum will be a millstone of not enough power or not at the right time. May I suggest you discount the wind generator. If it's making a lot of power then you will be seeking a friendlier spot. Try going for the maximum wattage of solar panels you can mount, use reliable regulators and mount a similar amp/hours of batteries as per watt of panels. If you are in less than 35 degrees of latitude you will probably have excess power on most sunny days.
It is a pleasure to run the toaster, microwave, deck lights etc, with a surplus of power and forgo them when it's not sunny.
I run 680 watts of panels, 1 MPPT regulator 2 PWM regulators into 700 a/h of gell cells (Fiamm monolites ) and a 400 watt wind generator.
The setup allows for up to three days of cloudy weather without starting the main engine.
Base consumption is the fridge and freezer at around 100 a/h per day.
The panels have produced up to 240 ah per day but average around 180.
The cost of extra solar panels will be long forgotten but their benefit will remain.
Cheers

[Lars_L]

Originally Posted by MarkSF

A good start would be getting the terminology right. The battery bank is 500 Ah, or amp hours. I'm presuming you mean the solar will give 450 Wh, or watt hours, equaling 50 watts for 9 hours.

If you say 450 watts for 9 hours a day that would be 4.05 kWh, which is a big difference.

"400 watts wind (calculate at 200 watts for 4 hours a day)" Huh? That should be 800 Wh.

Watts and amps are rates of usage, like flow. Watt hours and amp hours are quantities, like gallons. Think of your batteries as having so many gallons of electricity in them. You can use them slowly, say over 10 hours those batteries will give 50 amps. Over 1 hour they will give 500. (well, it's more complicated that that because you get MORE total power at lower rates)

The battery capacity governs how much power you can use over a day. Please note that you should only use half the capacity, or 250 Ah to preserve the battery life. Over a longer voyage, you must replace that used capacity every day.

Here's my calculation : you have 50w of solar for 9 hours a day. That's 450 Wh, which at 12V is 56 Ah. You have 200W of wind, for 4 hours a day. That's 800 Wh, or 67 Ah. So you can use a total of 123 Ah per day.

Add up the realistic usage of your boat systems in Ah, per day. Sticking to the same units will help preserve sanity.

Think the battery as a tank. The volume you have filled up the tank with is the amount of energy it stores. The volume is measured in Wh (watt hours) and that will be the most correct way to measure the energy. If the tank has vertical sides, and if you see the tank from above, it has an area of 12 V (volt). The filled level is then measured in Ah (ampere hours) and direct related to volume that’s stored in the tank or the energy it contains. This is a common way to measure the stored energy. A problem is that the sides are not smooth, they have great bubbles, and the area will vary between 10.5 V and 14.4 V. If you measure the level (Ah), the measure of the volume (energy Wh) will not be more accurate than that.

[Paul Elliott]

Originally Posted by Zai

You are correct in as the battery bank I am planning is 500 amp hour.
The solar panels are 450 watts total calculating 9 hours of such production maybe is not realistic? I think I need to adjust that, but that is why I am posting here, to get you guys input who have been there done that. :-)

I think that rated Watts * 5 hours/day is a more likely output. If you're in the tropics and keep the panels pointed at the sun it's going to be better, but on a sailboat orientation and shadows (and clouds) are a big factor.

So, 450W (rated) * 5 = 2250 Wh/day. Assume a 13V battery charging voltage, and a 90% efficient MPPT controller, and that's about 156 Ah per day.

All very approximate though. I'm sure some people do better.

[SURV69]

Gee ...

if required amps(or watts), were pounds ... all these boats would sink under their own weight.

[CLady]

Your latitude impacts your solar value.
I figured 6 hours per day solar value in 38N Lat to 22N Lat. In the squally regions, figure a little less.