High (?) Voltage Systems?

[crxvfr]

I have a 200 watt 24 volt mono panel that is supposed to make 5 amps?
Maximum Power Current (Imp) - 5.4

Now I have some amorphous panels that say this:
Maximum power (Pmax) 43.0W
Voltage at Pmax 71V
Current at Pmax 0.616A
Open-circuit voltage (Voc) 101V
Short-circuit current (Isc) 0.787A
Guaranteed minimum Pmax 38.7W

Only .6 of an amp compared to the 5.4 of a the mono 24v panel?

The manual says: Because these modules are designed specifically for medium and
high-voltage arrays, they can provide savings beyond
their competitive price tags. A 200-volt array, for example,
needs only three modules in series instead of the twelve
needed with traditional modules, which can reduce interconnection
time and materials.

For all I know these things could have been made in the 70's and those numbers are bunk in recent terms.
But what are the advantages of higher volt systems?
In what direction should I be thinking? They are Solarex Millennia. Are they any good?

[Sunking]

what are the advantages of higher volt systems?

Because higher voltage is much more efficient. Higher voltages means lower current for a given power level. Lower current means smaller wires (less expensive) and less power losses on the wiring from current flowing. This is the exact reason electric companies transport and distribute electricity at very high voltages. Transmission voltages go up as high as 800,000 volts here in the US, and up to 1 million volts in some countries.

Each time you double the voltage, you improve the efficiency 400% for a given wire size and power level. In a 12 volt system you can loose up to 30% of your power just in the wiring losses.

At 1000 watts @ 12 volts is 83.3 amps. At 48 volts the current drops to 21 amps.

[Mike90250]

Only .6 of an amp compared to the 5.4 of a the mono 24v panel?

Voltage at Pmax 71V
Current at Pmax 0.616A

71 * .616 = 43.736 watts. Doing fine. Wire it up with 18 gauge wire and enjoy. .6 amp high voltage sure saves copper costs.

[crxvfr]

At 1000 watts @ 12 volts is 83.3 amps. At 48 volts the current drops to 21 amps.

Current dropping is a good thing? Seems you would want plenty of current?!?

So then, all that fuss about smaller wires?

There has to be more.

..like maybe a higher voltage could charge a higher voltage battery system, (which would also be more efficient?) and cause a slower draw that would make reserves last longer? Am I getting this? If it lasts longer, would it reduce the amount of batteries required?

Wire it up with 18 gauge wire and enjoy

No way. Really? I have 22 of them.

Maybe scratch the remark I just made about all that fuss about smaller wires.

[Mike90250]

Look at the battery cable on your car, (12V fat as your finger)
and then to the back of your house, at the house feeder (120V size of a pencil)
and the distribution line that feeds the block of houses (16,000V, size of the lead in a pencil)

It's called POWER or WATTS. You can trade one for the other, and still have the same amount of work. Like a big 440 V-8 engine at 4500 RPM, or a 4 banger at 9200 RPM

One gets power at low RPMS, other at higher RPMs. Volts and amps.

[crxvfr]

Thanks for being so patient with me.

So if I wire all 22 panels in parallel it will only come to 13.2 amps @ 71 volts?

22 panels * .6 amps = 13.2 amps @ 71 volts?

So I would be able to use my little morningstar sunsaver mppt because its voltage limit is 75 and amp limit 15? Sweet! (hopefully)

Am I thinking right? If I am, I think I'm beginning to see the light.

If I use it with my big 200 watt 24 v mono panels @ 5-6 amps and 35+ volts per, I can only hook 2 panels before I hit the voltage AND amp limit!?!

[Mike90250]

So I would be able to use my little morningstar sunsaver mppt because its voltage limit is 75 and amp limit 15? Sweet! (hopefully)

No, the MS MPPT amp limit, is on the OUTPUT. But the 15 amps, is amps, regardless of the voltage (12 or 24) rated 200W @ 12V battery, or 400W @24V battery.

This is where the magic of MPPT happens. for a 12V battery, you only need 2.8A @ 70V, to have to controller down convert that to 15A @ 12V. So you can save losses on the long array wires on the roof & wall, 3A should be fine in a 18ga wire, for a long ways. if it was a 12V panel array, you would need at least #8 or 6 wire.

[Sunking]

crxv how are your math skills? Do you understand simple high school algebra?

When working with DC there is a physical law called OHm's Law. It consist of 12 formulas with four variables called:

E = Volts. Sometimes expressed as "V"
I = Current in Amperage or Amps. Sometimes expressed as "A"
R = Resistance
P = Power measured in Watts. Sometimes expressed as "W"

The Formulas are:


So if you know any two variables, you can solve the other two. For example if I have a source of power like a solar panel and I know the output power is 100 watts, and the voltage is 18 volts, then I know the current I = W/E = 100 / 18 = 5.55 amps.

If you understand this please reply and I will go a little deeper.

If your math skills are good, you do not have to remember all 12 forumlas. For example in college DC electronics th efirst test in week one is what are the 12 Ohm's Law formulas. I did not have to memorize all 12, I only had to remember 2 of the formulas. From those 2 I could solve for the other 10 with algebra. For example if I know EI=P, then I also know E=P/I and I = P/E

[Sunking]

OK here is a real life application. 2 designs, 1 using 12 volts solar panels, and an identical one using 70 volt panels. Both will bee 500 watt solar panel wattage, 12 volt batteries, and the distance between solar panel and controller is 50 feet 1-way.

OK a 12 volt 500 watt solar panel array operating voltage or Vmp is 18 volts. so the current flowing between the panel and controller is 500 watts / 18 volts = 28 amps. The minimum size wire you can use to NEC is #12 AWG. The loop resistance of 50 feet of 12 AWG is .2 Ohms. We know P = I^2 R = 28 x 28 x .2 = 157 watts. So we loose 157 watts out of 500 watts as heat on the wiring between the solar panel and controller. We just lost 31.4% of our power.

Ok same set up,except we now use a 70 volt panel. 500 watts / 70 volts = 7.1 amps. Use the same 12 AWG wire and we loose 7.1 x 7.1 x .2 ohms = 10 watts out of 500 (.02%) on the wiring between the panel and controller.

Which is better or more efficient? Lower or higher voltage? Loose 31.4 % or .02%? If you voted for Obama you would choose 31.4% because; it helps the economy. You would have to buy more panels to make up for the losses which creates more green jobs in China, As Obama would say: "Anyone who looks at the facts would know that. Don't let the Right Wing Christian Republicans confuse you with numbers".".

[crxvfr]

crxv how are your math skills? Do you understand simple high school algebra?

I took business math not alg-geom-trig-calc, but yes, I did have an algebra class years and years ago. I struggle with complex algebra but I am familiar with ohms law.

One of the things that's throwing me off is the terminology and trying to do equations given in different terms.

....but I do like your analogies

I am busy at work today but when I get home I will try to digest what you guys are telling me so I can ask smarter questions.

Many many thanks to you guys for helping me to learn despite my baby steps.

[crxvfr]

Ok, going back to where I was first confused, I said that 22 43 watt, 71 volt panels * .6 amps = 13.2 amps @ 71 volts & 946 watts. This seems to be right to me.

My sunsaver says:

Nominal Battery Voltage 12 or 24 volts
• Max. Battery Current 15 amps
• Battery Voltage Range 7-36 volts
• Max. PV Open Circuit Voltage 75 volts
• Nominal Max. PV Input
12 volt battery 200 Watts
24 volt battery 400 Watts
• Output Rating 15 amps load control
• Self Consumption 35 milliamps
• Transient Surge Protection 4 x 1500 Watts

Does Battery Voltage Range mean I can have 36 volt batteries?

Now, the 75 volt sunsaver limit handles the 71 volts from the panels.
And 946 watts/71 volts = 13.2 amps generated by the panels, right?
The only amp rating I see, Mike says is for output, so I don't know what to do with that number, but surely the sunsaver, as small as it is, can handle 13.2 amps of panels right?

Then Mike said:

No, the MS MPPT amp limit, is on the OUTPUT. But the 15 amps, is amps, regardless of the voltage (12 or 24) rated 200W @ 12V battery, or 400W @24V battery.

...or 600 watts at 36 volts?

This is where the magic of MPPT happens. for a 12V battery, you only need 2.8A @ 70V, to have to controller down convert that to 15A @ 12V. So you can save losses on the long array wires on the roof & wall, 3A should be fine in a 18ga wire, for a long ways. if it was a 12V panel array, you would need at least #8 or 6 wire.

Ok, so no on the sunsaver?, ...or maybe at least up to 400 or possibly 600 watts?... or no on my guess at interpreting amp limits?, ...or no on the idea of feeding it 13.2 amps when it only needs 2.8 to do it's thing? ...or no on my math?

And Sunking, I have heard some of those right wing christian republicans say some pretty stupid things. And it was under jr's watch that we lost our bill of rightsto something curiously named the patriot act. Obama promised change. He picked right up where jr left off. They all are working for the same thing. Global Homogenization.

Ya know who my guy is? Ron Paul. Today he explained to an empty room (only he and a few others showed up), ...we are fighting a non-war. We are at war with no country. We're fighting a few thousand people, that have no tanks, no planes, no navy, with 100,000 troops and doing badly, even replacing generals while we continue to operate foreign bases in 130 different countries as we go farther and farther in debt at home. What is going on?

Ya see, I can never really take a talk about politics seriously because it's all phony. They know exactly what they are doing. That curiously named document I mentioned was thousands of pages long and it appeared almost overnight. Our current vp had a large hand in it. Am I supposed to believe that they can come up with something like that overnight when nowadays, they can't even read a bill? C'mon.

I'm with you in spirit brother, but not willing to believe in one party or the other. ...or the media for that matter. If I have to choose, I go for the conservative side of things, but the have tarnished that word too. ...I am no protester, no dissident, no domestic whatever. I am trying to learn to embrace what's coming, whatever it may be. For whatever reason, I'm sure things are going, and are going to go just the way they're supposed to, I've been watching.

You can carry on politically like that with me if you want though. It's fun, ....but be aware my perspective on world view is strange and "not like the other ones".

[Mike90250]

Lets' keep blatent political talk off the electrical data boards , please.

As to the sunsaver capacity at 36V, I thought it was 12 or 24v only, the tristar MPPT goes up t048 though. not many 36V systems though.

[crxvfr]

Whoops, didn't mean to get you in trouble Sunking.

See? We are not allowed to talk about it.

And Mike, I understand. Sunking gets me going because he is right about alot of things and is some kind of super-genius when it comes to governmental issues and laws concerning solar power, which is an issue. I am inclined to tell him what things looks like from the outside but I understand it reflects badly on the forum. If I thought SK would recognize my username I would pm him.

But yeah, ok. I need a bigger controller.

I'm not sure if it will handle 36v batteries.

If that's what "battery voltage range" means, then yes, but then it does say 12 or 24 volt batteries!?!

That's what I mean about getting confused on the terminology.

[Sunking]

Lets' keep blatent political talk off the electrical data boards , please.

I understand and apologize. It is hard to resist the politcal side since RE is 99% a political issue.

[Sunking]

Whoops, didn't mean to get you in trouble Sunking.

You did not get me in trouble, I don't need any help doing that.