Can My Solar Array Run My AC?

[Gone2long]

OK folks, here is that other thread I warned you about.

I have a 420W per hour solar array and a small, 230V AC which draws only about 2.15 A and 495W.

I would like to run it off my solar array using a 1,000W, 12V-230V inverter. Would this work?

I understand that a critical issue would be battery storage, but assuming (for the sake of argument) that I have enough storage capacity, should the system handle the load?

As a corollary concern, let me note that I have used a small, 150W inverter connected directly to my house batteries with alligator clips. Every time the solar controller diverted power from the batteries (in order to avoid overcharging) the inverter would fault out, and eventually it just conked out.

Could that happen with a 1,000W inverter running the AC?

Thanks for your input,

G2L

[tkeithlu]

Without doing the calculations for draw, charging, and storage, I'm betting that the start up spike on your AC will flip out the inverter. Then the start point on the calculation, 420w from the solar array (under ideal conditions, remember) versus 495w running (not starting) the AC makes it sound like a loser. People with far more 120v expertise than me will now step in.

[four winds]

Even your small AC would be drawing about 40 amps continuous from your 12v battery bank. Running it only four hours during the day would likely be greater than all other daily demand on the system. Which would be practically impossible to replenish with a 420 watt solar array.

A genset is likely the only viable alternative for AC onboard off the dock.

[TacomaSailor]

The real question is "Can my inverter start my AC?"

A 2nd question is "what kind of AC wave form does the AC compressor require?"

Find the AC specs - what is the current draw for starting and how long does that last?

For example: a Wagan 1000 watt inverter can supply 2,500 watts for ?? milliseconds (specs don't tell how many). The Wagan sales specs says the 1Kw Wagan inverter can start a small AC compressor.

I've burned out several small AC motors while trying to run them on modified wave form inverters. What does you AC compressor motor manual say? How sensitive is the compressor to AC line frequency?

What shape AC wave does your inverter deliver? How does that wave form change during AC compressor startup and what does it do to the frequency?

The cruisers I hung out with in the tropics who had AC on the boat ran it during the late evening to cool the sleeping area. Your solar panels will be of little value at that time.

How big is your battery bank? If you are pulling 42 amps (495 watts/12.5V/.94 efficiency) then you probably want at least 800 amp hours of capacity to not exceed a 20-hour pull down rate from the battery bank.

A 420 watt solar array will need about 1.5 hours of sunshine time (directly overhead) to replace each hour of AC power draw. But, that leaves no spare charging capacity to replace the current draw from other domestic uses.

Your whole system seems a little small for AC off the solar.

[tkeithlu]

All these contributions fit together. The sum answer to your question "Will it work?" is "No."

[SV DestinyAscen]

No. And even if your inverter can handle it your battery system won't stay replenished for long.

[Gone2long]

Originally Posted by four winds

Even your small AC would be drawing about 40 amps continuous from your 12v battery bank. Running it only four hours during the day would likely be greater than all other daily demand on the system. Which would be practically impossible to replenish with a 420 watt solar array.

A genset is likely the only viable alternative for AC onboard off the dock.

Pardon my ignorance as I am a newbie in all this solar stuff, but what I guess you mean is that, when the inverter draws 495 Watts from a 12V system, that ends up being 41.25 or so Amps per hour, instead of the 2.15A when I use the AC on a 230 AC line. Correct?

That being the case, I would be using 40+ amp hours per hour. Demand on the system other than the AC would be extremely negligible, or, if I turn everything else off, non-existent. So, if I had 420 amp hours of battery storage, perfect sunlight, a 100% operative system, and ran nothing but the AC, I would run my batteries to zero in about 10 hours. Make sense?

I usually have perfect sunlight, but I understand that the batts should never go that low and that sytems usually get no where near 100% functionality, so we are just talking theory here. But the theory, or lets say, hypothetical capabilities of the system under optimum performance, is what I (as a complete novice) am trying to understand.

Thanks for your help,

G2l

drawn Maybe this is my ignorance talking here, but I don't get how

[Gone2long]

Thanks for the details. Will go back to some of the earlier research I did to make sure I understand all of it. If you have time, check my earlier post above and critique it, in terms of the real specs that you just posted.


Thanks again,


G2L

[Gone2long]

Originally Posted by tkeithlu

All these contributions fit together. The sum answer to your question "Will it work?" is "No."

Definitely seems like the consensus. But, just out of curiosity, how do folks end up running inverters at all when the 150 W inverter I was using faulted out every time the controller diverted power? This happened even if there was no load on the inverter.

Thanks


G2L

[leftbrainstuff]

Your current draw seems at least a magnitude low for your AC. 2.15A is probably just a fan load.

The problem you have with AC is the inefficiencies due to power factor and load spiking. You can't apply DC math.

All those domestic appliancies, like AC, are very rf noisy, power hogs and designed for big fat grid power. The controllers and motors aren't designed for what you are trying to achieve. Even if you do get it to run expect frequent failures.

The simple answer to your question is no your specs aren't sufficient.

Read some of the threads from cat owners. There are some cruisers running big solar arrays (+1kW) and big lithium ion battery banks who heat water and run AC. This will give you an idea of the cost and complexity to reliably run AC off grid.

[Gone2long]

Originally Posted by leftbrainstuff

Your current draw seems at least a magnitude low for your AC. 2.15A is probably just a fan load.

The problem you have with AC is the inefficiencies due to power factor and load spiking. You can't apply DC math.

All those domestic appliancies, like AC, are very rf noisy, power hogs and designed for big fat grid power. The controllers aren't designed for what you are trying to achieve.

The draw I stated is correct for AC current. See my previous thread on running the AC off a generator.

Also, current spikes are millisecond events and do not effect the AC's functionality on a normal AC line. Mine wont trip even a 15A breaker. However, could very well be a different story when connected to a 12V inverter. I have heard, for instance, that inverters "don't like spikes".

Thanks for your input,

G2L

[four winds]

Originally Posted by Gone2long

Pardon my ignorance as I am a newbie in all this solar stuff, but what I guess you mean is that, when the inverter draws 495 Watts from a 12V system, that ends up being 41.25 or so Amps per hour, instead of the 2.15A when I use the AC on a 230 AC line. Correct?

That being the case, I would be using 40+ amp hours per hour. Demand on the system other than the AC would be extremely negligible, or, if I turn everything else off, non-existent. So, if I had 420 amp hours of battery storage, perfect sunlight, a 100% operative system, and ran nothing but the AC, I would run my batteries to zero in about 10 hours. Make sense?

I usually have perfect sunlight, but I understand that the batts should never go that low and that sytems usually get no where near 100% functionality, so we are just talking theory here. But the theory, or lets say, hypothetical capabilities of the system under optimum performance, is what I (as a complete novice) am trying to understand.

Thanks for your help,

G2l

drawn Maybe this is my ignorance talking here, but I don't get how

G2l, I knew I could count on others to provide additional caveats to your idea.

To your post quoted, I would say you are correct and understand the basic reasoning when pondering this subject.

You asked could your array handle this task. You state about 10 hours of run time, which is correct. You state 420 ah used, let's say over two days. Of course, considering the idealist parameters you set, reality is a little more ah.

So now just calculate the ah available from your array on your idealist perfect day. Solar insolence maps suggest five full sun hours for Florida, for example.

Determine how many days it will take to charge the bank. You know then, the intervals of usage of AC and it is supported. I wont be daily.

And you will find the answer ,for you, about the array's fitness for use.

[dlymn]

My 6kw home system gives me 6kw for a little while a few days a year. Solar Panels on a boat will almost never produce what the manufacturers claim. Different latitude, movement of sun, movement of boat, shading, dirt and salt on panel etc all have a negative impact.
Furthermore a 400w reverse cycle AC won't actually do much cooling. We run an 800w unit and it struggles to drop the cabin by 5 degrees when the outside temperature is 35 centigrade.
When you do your drain calculations, don't forget to include the other equipment that might also be operating (fridge, charging computers etc, lights). You should also not discharge your lead acid batteries to dead flat. I always work on 40% discharge and so a 200 ah battery will only provide 80ah of available energy
You won't get a great charge when you're sailing because you will never have the panels at constant optimum angle. You'll only be stable when you're tied up and maybe next to shore power.
Have you also figured out how you're going to discharge the heat the unit collects or is it a split system?

[dlymn]

Originally Posted by four winds

G2l, I knew I could count on others to provide additional caveats to your idea.

To your post quoted, I would say you are correct and understand the basic reasoning when pondering this subject.

You asked could your array handle this task. You state about 10 hours of run time, which is correct. You state 420 ah used, let's say over two days. Of course, considering the idealist parameters you set, reality is a little more ah.

So now just calculate the ah available from your array on your idealist perfect day. Solar insolence maps suggest five full sun hours for Florida, for example.

Determine how many days it will take to charge the bank. You know then, the intervals of usage of AC and it is supported. I wont be daily.

And you will find the answer ,for you, about the array's fitness for use.

The five full sun hours is calculated by averaging daily light availability over a year, In high summer, you might get so much light that your batteries are fully charged, equipment is being energised and energy goes to waste.In winter you might get so little energy that the batteries won't get fully charged let alone supply spare energy to operate equipment in real time. Our experience is that, in reality, over summer you can depend on getting 3 hours of full charge on average. Our panels are in a fixed position and so only get full light square to the panel for a moment every day.

[StuM]

Originally Posted by Gone2long

Pardon my ignorance as I am a newbie in all this solar stuff, but what I guess you mean is that, when the inverter draws 495 Watts from a 12V system, that ends up being 41.25 or so Amps per hour, instead of the 2.15A when I use the AC on a 230 AC line. Correct?

First thing you should do is learn the basics of Amps, Watts and Volts, including the difference between Amps and Amp hours ( and why "amps per hour" is nonsensical).

You may like to start here: http://www.cruisersforum.com/forums/...ml#post1933764)