How Many Watts of Solar?

[newhaul]

Originally Posted by KP44

I do carry a hand grinder. But with a big inverter that we almost never use - I grind fresh coffee. I turn on the inverter, grind for 20 seconds, and turn the inverter off. Very little power needed.
It is nice to have the inverter for power tools. But most newer power tools use a battery. I can charge the batteries with a 100 watt cigarette-lighter inverter. So really not much need for the big inverter.

The optimum efficiency point for an inverter is to use it at about 80% capacity.

I run my 300 watt rice cooker on my 400 watt inverter

Most coffee grinders will be happy on a small 100 watt inverter .

[john61ct]

Originally Posted by newhaul

There are so many problems with that estimate.

Pretty sure was tongue in cheek.

Highlighting the fact there are too many variables for any pat answer to apply universally.

Except for mine of course 8-)

[KP44]

Originally Posted by newhaul

900ah Fla gives about 450 usable that's good so you need about 900 watts solar to charge that if just solar.
Now switching to Lfp you would need estimated 600 ah capacity at about 25% of the weight . And due to charging acceptance you could likely get by with 400 watts running thru an mppt controller.

If I used the entire 450 amp hours in a day, I would want at least 1,000 watts of solar.
But I only use about 130 amp hours on heavy days. Less if the refrigeration is off part-time. All my lights are LEDs. So 400 watts of solar is good and the batteries are never drawn down near 50%.

[newhaul]

Originally Posted by john61ct

Pretty sure was tongue in cheek.

Highlighting the fact there are too many variables for any pat answer to apply universally.

Except for mine of course 8-)

here is my basic to estimate for potential customer
1 watt per ah of Fla.
1.5 watt per ah for Lfp. ( consider you need about 30% less Lfp capacity )
once they hire me then we get deeper into the specifics.

[KP44]

Originally Posted by newhaul

The optimum efficiency point for an inverter is to use it at about 80% capacity.

I run my 300 watt rice cooker on my 400 watt inverter

Most coffee grinders will be happy on a small 100 watt inverter .

I have not heard the 80%. I charge power tool batteries and run laptops on a little 100 watt inverter made for a cigarette lighter plug. It will probably run the coffee maker.

The smaller inverters have much less power draw, so I endorse the 100 watt and 200 watt size unless you're going to run a microwave. It depends upon your preferences. We hardly used the microwave and left it ashore. But we have a good propane stove.

[LoudMusic]

Originally Posted by john61ct

Pretty sure was tongue in cheek.

Highlighting the fact there are too many variables for any pat answer to apply universally.

Except for mine of course 8-)

[newhaul]

Originally Posted by KP44

I have not heard the 80%. I charge power tool batteries and run laptops on a little 100 watt inverter made for a cigarette lighter plug. It will probably run the coffee maker.

The smaller inverters have much less power draw, so I endorse the 100 watt and 200 watt size unless you're going to run a microwave. It depends upon your preferences. We hardly used the microwave and left it ashore. But we have a good propane stove.

check on the bottom of the grinder it will tell you how many watts it draws .
As far as a coffee maker well my drip pot draws 900 watts i use my 1500 watt unit.
My perk pot draws 700 so I use my 750 watt unit.
Everything else I run on my 400 watt unit.

[kmacdonald]

On my Capri 22 I have a 20AH lithium battery and a 60W solar panel. No other method to recharge the battery. It easily supplies all the power needs for: VHF, Nav Lights, cabin lights, laptop and phone charging.

[kmacdonald]

Originally Posted by Paul L

Well with 2 and half hours of cruising experience you clearly have more cruising experience than some self professed experts.

Nominated for post of the year.

[a64pilot]

A big issue with calculating just how much Solar you need and not having more than that is that not every day is cloudless, there are many days that are less than optimum for Solar, and if you don’t have excess Solar, then those days your not fully charging your bank, or your running your motor or generator etc to make up the difference.

Calculating how much Solar you need and only installing that much is the same as calculating exactly how much fuel you need of get to somewhere, and only taking that much fuel.

A prudent person carries a reserve. Plus having more Solar is not necessarily so much about increasing production in AH as it is about increasing the number of hours in a day that your Solar output exceeds your electrical usage, thereby increasing the number of hours of charge your bank sees.

[Mike OReilly]

Originally Posted by a64pilot

….A prudent person carries a reserve. Plus having more Solar is not necessarily so much about increasing production in AH as it is about increasing the number of hours in a day that your Solar output exceeds your electrical usage, thereby increasing the number of hours of charge your bank sees.

This is why I say the simple answer it to just maximize your solar capacity. On a monohull this maximum will be modest.

Actually, using this focus one could turn the standard approach to electrical systems on its head. Instead of calculating typical ah demands, matching that to a battery bank, and then planning your charging system — instead of all that you could start with your solar charging system, then work the other way to arrive at what your typical daily ah load can be. This would then define what electrical systems you can install.

[sailorboy1]

I think that the "as much as you can fit" is an example of the "everything on a boat can be fixed, with the proper application of cash" method of boating.

With enough buts, sometimes, ifs you can vary any real answer. Doesn't really change that there is in fact a real answer even if it isn't perfect.

[a64pilot]

Panels can be had cheaply, maybe not the exotic marine ones though.
I think I paid .50c a watt for mine, they were left over panels from a residential installer, they buy pallets I guess and often have a few left over.
Next buyer wants all the panels to look the same, and doesn’t want left over panels.
I bought what they had left over, 6 250W panels, 4 Canadian Solar and 2 Mage I believe.
So I have $500 in my Kilowatt or panels, the frame was scrap aluminum extrusions from work.
The Outback was about $400 I think, and I likely have about $100 in wire etc.
So my Kilowatt costs all in about $1,000.

I could easily have spent way more than that for less than half the output by paying to have things done, way more.

Right now, because it’s heavily overcast from an approaching front, I’m making 20 amps from that kilowatt of panels, sunny day at least three times that, but even only 20 is charging the bank, if I had less Solar it wouldn’t be.

[john61ct]

Which comes full circle to

install as much panelage as you're willing to fit, and

do not rely on only your solar

[newhaul]

Originally Posted by john61ct

Which comes full circle to

install as much panelage as you're willing to fit, and

do not rely on only your solar

properly sized solar is all you need for at least 8 months out of a year.

200 is plenty from mid spring to mid fall .
Then I put out my extra 200 worth of flex panels and I'm still good but for heavy snow days.