How many kilowatts per day do you use?

[valhalla360]

Originally Posted by haiqu

Valhalla: Yeah, that's why we average it over a day. That's what MOST of the people in this thread understand by the "per day" part of the statement. All but the utterly pedantic anyhow.

Actually, daily consumption is never used as an end product. Other than as an intermediate step it really doesn't have much use, so the average demand numbers is the pedantic part.

Input: Solar panels are not rated in average daily output. Generators do not typically run at peak output all day, a 30amp cord doesn't typically run at 30amps.

Output: Lights come on at night, pumps only run when there is a leak, Fridge only runs when the interior starts to warm up.

[Paul Elliott]

Originally Posted by sailorchic34

Watt is a quantity of one joule for one second.

No, a Watt is a rate of one joule per second. Definitely not the same thing. For that matter one millijoule per millisecond is also a Watt.

Originally Posted by Dennis.G

What is the distance covered if one is going 5 knots for 24 hours? Well, we could say 730,080 feet, but easier would be 5 knot x 24 hours = 120 knot-hours. (knot-hours of course analogous to Watt-hours, a quantity of something).

I love it!!!

[Paul Elliott]

Originally Posted by valhalla360

Actually, daily consumption is never used as an end product. Other than as an intermediate step it really doesn't have much use, so the average demand numbers is the pedantic part.

Input: Solar panels are not rated in average daily output. Generators do not typically run at peak output all day, a 30amp cord doesn't typically run at 30amps.

Output: Lights come on at night, pumps only run when there is a leak, Fridge only runs when the interior starts to warm up.

I beg to differ with you. My boat is solar powered 98% of the time. My solar panels put out power that both feeds the existing loads and puts power into the batteries. Over a 24-hour period (or a week, or a month), the panel output had better exceed my average consumption or I need to run the engine or plug in to shore power. The batteries take care of peak loads, and the peak output of the solar panels is virtually irrelevant.

Daily consumption averages aren't pedantic -- in my case they are crucial.

[TheThunderbird]

Originally Posted by haiqu

Mediterranean type weather (cool but never cold).

Laptop(**) with OpenCPN, internet via 4G wireless modem/router, 100% LED lighting, independent solar instruments (Tacktick), VHF Radio, Marine/Ham HF Radio, soldering iron, phone, AIS, GPS, rechargeable Bluetooth headphones, small inverter, Ryobi 18V tools, bilge pump, water pump, electric macerator head, ultrasonic antifoul.

3 x 80W solar panels and 2 x 105AH AGM batteries which delivers about 450W-600W per day on average (allowing for 6 hours of sunlight and the inefficiencies of this system).

All cooking and occasional water heating is butane and I don't have (or need) refrigeration, airconditioning, cabin heating, deep freeze or - heaven forbid - electric cooking. There is no engine on either of my yachts and I have a manual windlass on both. The system is totally off-grid, I never connect to shore power.

(**)Laptop has been optimized for low power with SSD drives.

Quite illuminating..

SOLAR
Rated solar power is 80x3=240w running for say 6H/day (out of daylight of max 15H in full summertime...)
However you mention 450/600W drawn, I assume it being WxHours, or Wh.

It is equivalent to 2.0-2.5hours of your solar battery max output, out of a 6h/day assumption.

Which means efficiency of say 35-40% of nominal power, correct!?

BATTERIES
Nominal output of say 1000Ah is calculated on a slow discharge of 20h !!!
More likely, on a 10h practical cycle, rated power is 20% less, so it is 800Ah.

Assuming to use no more than 15-20% of it (max 30%,.. the more, the shorter battery life...) we have 120-160Ah @12V, or 1400-1900 W.
It is 140-190W along the 10h long assumption, or more likely some intermittent use with peaks 3-5X larger (1kW).
However, I was able to run a 2kW induction hob out of 700Ah pack, for 10'

IN SHORT
Solar supplement continuous Low consumption (LED driven) and battery floating
Batteries meet impulsive demands, and moderate charges of say FEW HUNDRED W for a short time, including inverters ...

FOR ANYTHING larger, there is Mastercard shore power, or a generator. I consider having it a SAFETY ITEM, and a way to INDEPENDENCE.

[valhalla360]

Originally Posted by Paul Elliott

I beg to differ with you. My boat is solar powered 98% of the time. My solar panels put out power that both feeds the existing loads and puts power into the batteries. Over a 24-hour period (or a week, or a month), the panel output had better exceed my average consumption or I need to run the engine or plug in to shore power. The batteries take care of peak loads, and the peak output of the solar panels is virtually irrelevant.

Daily consumption averages aren't pedantic -- in my case they are crucial.

Daily CONSUMPTION (ie: amp-hr or watt-hr) average is useful (average watt or amp draw has no real use). Solar panels aren't rated in average daily watts output.

You get to the daily consumption by taking the instantaneous consumption of all the devices and how long each is on (you can get an amp-hr or watt-hr meter which does it for you but that's just a different way to get to the same calculation). That results in amp-hr or watt-hr. While there is an associated average amps or watts per day, it has to be converted back to amp-hr or watt-hr to size the battery bank or the solar panels.

Let's say you have an average of 200watts over a typical day. You don't go out and buy a 200watt panel and call it good or you will find that you don't have nearly enough because the panel doesn't produce 200watts for 24hrs under the best of conditions.

To figure out how much solar you need from the average wattage, you would have to convert that 200watt average back to watt-hrs (ie: 4800watt-hrs in the example) and then estimate how long the solar panels will generate thier rated watts). If they put out thier average rating for 5hrs per day, you would need, 960 watts of solar panels.

So why convert watt-hr to daily average watts to convert back to watt-hr?

(note: I am ignoring inefficencies and daily varation to simplify the explainaiton)

[TheThunderbird]

Originally Posted by Paul54

Watts per hour or watts per day. Is it really all that confusing?

YES, IT IS
IN DEED, IT IS...


WATT X HOUR ..... :-) MULTIPLICATION

WATTS x Hour / DAY :-) DIVISION


1st is a consumption, energy used
2nd is the above overall, on a daily cycle

[haiqu]

Originally Posted by NorthernIsland

Why would the latter sentence be obfuscated? Obviously it has nothing to do with electricity generation capability or total loads.

It's obfuscated because it introduces an arbitrary, Time.

[haiqu]

Originally Posted by Dennis.G

The power company will bill you for the kilowatt-hours (kWh) you consume, because that is the measurement every electrical utility uses - good enough for them. Nobody "consumes" 3 kw a day. If your average power usage over a day was 3 kw, you would have consumed 72 kWh of energy that day.

If your average power usage over a day was 3kW, you would have consumed 72 kW of power that day. Swapping over an energy unit isn't necessary.

[haiqu]

Originally Posted by TheThunderbird

Quite illuminating..

SOLAR
Rated solar power is 80x3=240w running for say 6H/day (out of daylight of max 15H in full summertime...)
However you mention 450/600W drawn, I assume it being WxHours, or Wh.

It is equivalent to 2.0-2.5hours of your solar battery max output, out of a 6h/day assumption.

Which means efficiency of say 35-40% of nominal power, correct!?

BATTERIES
Nominal output of say 1000Ah is calculated on a slow discharge of 20h !!!
More likely, on a 10h practical cycle, rated power is 20% less, so it is 800Ah.

Assuming to use no more than 15-20% of it (max 30%,.. the more, the shorter battery life...) we have 120-160Ah @12V, or 1400-1900 W.
It is 140-190W along the 10h long assumption, or more likely some intermittent use with peaks 3-5X larger (1kW).
However, I was able to run a 2kW induction hob out of 700Ah pack, for 10'

IN SHORT
Solar supplement continuous Low consumption (LED driven) and battery floating
Batteries meet impulsive demands, and moderate charges of say FEW HUNDRED W for a short time, including inverters ...

FOR ANYTHING larger, there is Mastercard shore power, or a generator. I consider having it a SAFETY ITEM, and a way to INDEPENDENCE.

Consumption is 450-600 watts in a day, not watt hours.

Apart from that, these looks like random thoughts. Was there a question?

I could do a complete analysis of my power usage, panel and battery sizing calculations and even allow for their inefficiencies if it makes you happy. The system was purposely designed and not just thrown together.

[NorthernIsland]

Originally Posted by haiqu

If your average power usage over a day was 3kW, you would have consumed 72 kW of power that day. Swapping over an energy unit isn't necessary.

Why not read Stu's previous posts explaining this in detail...

Sent from my HTC VLE_U using Cruisers Sailing Forum mobile app

[StuM]

Originally Posted by haiqu

If your average power usage over a day was 3kW, you would have consumed 72 kW of power that day. Swapping over an energy unit isn't necessary.

Still don't get the fundamental difference between Power and Energy do you?
You consume Energy. Power is just the rate at which you consume Energy.

You can't "use" or "consume" power. If you consumed power, your 40 horse power engine would soon be powerless as would your 200 Watt solar panel.

Power is Watts. Energy is Watt hours.

You would have consumed 72 kWh of ENERGY that day.

[valhalla360]

Originally Posted by haiqu

If your average power usage over a day was 3kW, you would have consumed 72 kW of power that day. Swapping over an energy unit isn't necessary.

Please share the math and show your work.

I know exactly what your mistake was but let's see if you can figure it out. hint: it might have to do with a missing hours unit.

Just for giggles: a 30amp cord at 120v is only rated to handle 3.6kw (theoretically but in reality a bit less). You could need a cord rated to handle 600amps to handle 72kw. Even if you were talking euro 240v power, you would need a 300amp cord to handle 72kw.

[valhalla360]

Originally Posted by haiqu

It's obfuscated because it introduces an arbitrary, Time.

Nothing arbitrary about it. You have no clue what the total consumption is unless you incorporate time.

When you turn the engine over on your boat, the amps/wattage draw is huge it could easily be in the 2000-5000watt range (depending on engine size). But if you immediately turn the motor off, you will find that the batteries are still very close to fully charged because the TIME was only a few seconds.

On the other hand, lets say you have a huge 1000amp-hr battery bank and lets assume you accidentally disconnected the solar and left on a single tiny 12w bulb by accident. You come back in a month, you find the batteries dead because while the wattage was tiny for such a large battery bank, the TIME was huge.

Absolutely nothing arbitrary about the impact of time. It's clearly a critical component when looking at energy consumption.

[Dockhead]

Originally Posted by valhalla360

I would think running the generator, you would be more concerned. . . .
.

Not really. The generator is pumping out up to 6.5kW, and a load of plus or minus a kilowatt is not felt at all. A little extra load is even good sometimes.

[valhalla360]

Originally Posted by Dockhead

Not really. The generator is pumping out up to 6.5kW, and a load of plus or minus a kilowatt is not felt at all. A little extra load is even good sometimes.

If the generator will be running regardless of load, you have a good point. While it will impact the fuel consumption, ON or OFF will have a bigger impact.

But presumably if you are running a 6.5kw generator you are running air/con or electric heat or other heavy loads that will vary in duration so there is presumably a fairly strong correlation between kwh consumed and fuel consumption...and thus cash spent on fuel.