grid tie panel size

levsmith

Hey everyone, I will be building an off grid house here soon and am wondering if there is any kind of standard size for grid tie systems. I tried calling the local dealer but they are closed until after the holidays and I want to buy a charge controller while NAWS has their 5% off sale. I think the dealer here mainly just does grid tie and I'm going to try to get about 4 panels depending on the size the next time they do a grid tie job. I will be getting an mppt charge controller, so the voltage doesn't necessarily matter, I would just like to make sure the panels aren't some uncommon size. Everything I have seen up to 320 watts shows that it to will work with the charge controller I am looking at. So is there is any kind of standard size?

bill von novak

levsmith wrote: »

Hey everyone, I will be building an off grid house here soon and am wondering if there is any kind of standard size for grid tie systems. I tried calling the local dealer but they are closed until after the holidays and I want to buy a charge controller while NAWS has their 5% off sale.

First recommendation - do NOT start on your system by buying things that are on sale. You will most likely realize you can't use it, or will realize that the thing you bought will force you into poor decisions on other parts of your system. Start with a load analysis then work backwards from there.

levsmith

bill von novak wrote: »

First recommendation - do NOT start on your system by buying things that are on sale. You will most likely realize you can't use it, or will realize that the thing you bought will force you into poor decisions on other parts of your system. Start with a load analysis then work backwards from there.

Oh I have the load analysis done as much as I can. Its somewhat difficult to figure with a completely new house that hasn't been built yet but have it as close to done as I can. I already know how many watts I need and the controller I want, which is one that will allow me to expand the system in the future as I add loads. I just figured it might be a good time to buy the controller since that 5% off will save me over 30 bucks on a $600 controller but have no idea what size panels are normally used in professionally installed grid tie systems. $30 may not sound like much but every little bit helps because things will be tight financially to be able to get it built by next winter. I won't be doing a bank loan on the cabin or solar, it's all coming out of my pocket, other than the loan on the land, so saving money anywhere I can is important.

vtmaps

levsmith wrote: »

so saving money anywhere I can is important.

All the more reason to follow Bill Von Novak's advice and slow down and don't buy anything until you have a design for the entire system.

You asked about the size of the panels... but you didn't say anything about where and how they will be mounted. That would affect my judgement of what size panels to buy.

--vtMaps

levsmith

vtmaps wrote: »

All the more reason to follow Bill Von Novak's advice and slow down and don't buy anything until you have a design for the entire system.

You asked about the size of the panels... but you didn't say anything about where and how they will be mounted. That would affect my judgement of what size panels to buy.

--vtMaps

Sorry I didn't mention much, I was only curious if there was a standard size panel used. I do pretty much have the entire system designed and have all components from the batteries to the inverter already (I built a backup battery system for my current house that is charged from the grid to use during some of the extended power outages here, and it works great!) The only parts I am missing is the panels, charge controller and any wiring, breakers, combiner boxes, etc. in between those components.

The panels will be pole mounted and the only limiting factor there is the total square ft of panels, it can be adjusted for different size panels. Thanks

BB.

The "standard" solar panels used in larger systems these days are typically around 200 Watts and above. And they are (usually) either 60 cell (Vmp~30 volts) or 72 cell (~36 volt Vmp) panels.

One of the issues with solar panels is they need to be sized/matched to the Solar Charge controller or the GT Inverter... There is usually a working voltage (for typical MPPT type solar charge controllers, for a 12 volt bank, Vmp is in the range of ~18 to 100 VDC, for a GT inverter the range may around 200-400 VDC).

And if you use the "Cheap" PWM type controller, you need for the Vmp-array voltage:

12 volt bank -- Vmp ~ 18 volts
24 volt bank -- Vmp ~ 36 volts
48 volt bank -- Vmp ~ 72 volts

As you can see, a 60 cell panel does not work "efficiently" with a DC battery bank and PWM controller.

For an MPPT type solar charge controller, the top voltage is typically around Vmp~100 VDC, and the bottom voltage is the same as the PWM chart. Typically, the "optimum" voltage range is around 2x the battery charging voltage (i.e., 12 volt bank charging at 14.8 volts would be Vmp-array~29.6 volts or Vmp~30 volts).

Typically, panels that are under 140 Watts and Vmp works with DC battery bank and PWM controllers can be almost 2x as expensive as the GT solar panels ($$$/Watt pricing).

140 Watt or smaller panels can be small enough to ship best way (bus, UPS, etc.). Larger panels typically have to ship by truck. Panels over ~175 Watts typically need two people to move around safely and install.

Note that shipping costs are not small--Especailly if you are buying one panel or less than a full pallet at a time (repackaging costs, and truck costs based on foot print of pallet, etc. drive up costs).

Make sure you have costs of panel to your front door (or local freight terminal).

-Bill

levsmith

Thanks Bill, that's exactly what I was looking for. I am hoping to combine shipping on panels the next time the local company does an install. Buying 3 or 4 panels with freight shipping makes the cost pretty high per watt. I won't have to worry about a GT inverter as this will be off grid. I also didn't know about the optimum charging voltage being 2x the battery voltage. I am looking at the midnite solar classic 200 which is 200 volts max. I was planning on wiring the panels in series to keep the voltage up and the wire size small. I may just have to settle with the extra losses of converting from a high array voltage to a low battery voltage for now as I do plan to upgrade the system to 48 volts eventually, I'll just use what I have for my battery backup until that time comes. Thanks again!

Just so people know, this system isn't going to be your ideal perfect install and I know that and it's something I am willing to live with until I can get my current house sold and be able to afford a proper install, and if I can, I will be using components that I will be able to use when that time comes so that I don't have to buy twice

vtmaps

levsmith wrote: »

I also didn't know about the optimum charging voltage being 2x the battery voltage.

That's not really the rule, but it sort of works. What you need for input voltage is the maximum battery voltage plus a few more volts. The "few more volts" is to allow the MPPT controller to sweep the voltage and find the max power point. Consider a 12 volt panel with a Vmp of 18 volts... you need a charger output of up to 15.5 volts to charge a 12 volt battery. A PWM controller can charge the battery with 18 volts in and 15.5 volts out. An MPPT controller might need a bit more input voltage than 18 volts in order to function properly.

Solar panels with 60 cells have a Vmp of about 30 volts. You put them in parallel (30 volts) for a 12 volt system. You put 2 of them in series (60 volts) for a 24 volt system, and you put 3 in series (90 volts) for a 48 volt system. All of those voltages are higher than they need to be, for example a 24 volt battery needs charging up to 31 volts, and an input of 45 volts would be near optimal, but with 60 cell panels your choices are 30, 60 or 90 volts.

levsmith wrote: »

I am looking at the midnite solar classic 200 which is 200 volts max. I was planning on wiring the panels in series to keep the voltage up and the wire size small. I may just have to settle with the extra losses of converting from a high array voltage to a low battery voltage for now as I do plan to upgrade the system to 48 volts eventually,

Don't do that unless the distance is extreme between the combiner and the controller. The Midnite Classic 150 can handle more power, is more efficient, runs cooler, and is less expensive than the Classic 200. By putting your panels at a higher voltage you will decrease your losses in the cable, but you may be just moving those losses from the cable to the controller. How large is the array and how far from the controller?

--vtMaps

levsmith

vtmaps wrote: »

That's not really the rule, but it sort of works. What you need for input voltage is the maximum battery voltage plus a few more volts. The "few more volts" is to allow the MPPT controller to sweep the voltage and find the max power point. Consider a 12 volt panel with a Vmp of 18 volts... you need a charger output of up to 15.5 volts to charge a 12 volt battery. A PWM controller can charge the battery with 18 volts in and 15.5 volts out. An MPPT controller might need a bit more input voltage than 18 volts in order to function properly.

Solar panels with 60 cells have a Vmp of about 30 volts. You put them in parallel (30 volts) for a 12 volt system. You put 2 of them in series (60 volts) for a 24 volt system, and you put 3 in series (90 volts) for a 48 volt system. All of those voltages are higher than they need to be, for example a 24 volt battery needs charging up to 31 volts, and an input of 45 volts would be near optimal, but with 60 cell panels your choices are 30, 60 or 90 volts.



Don't do that unless the distance is extreme between the combiner and the controller. The Midnite Classic 150 can handle more power, is more efficient, runs cooler, and is less expensive than the Classic 200. By putting your panels at a higher voltage you will decrease your losses in the cable, but you may be just moving those losses from the cable to the controller. How large is the array and how far from the controller?

--vtMaps

Thanks for the reply. Good news is I called NAWS and I was told they normally have sales around black Friday as well so I will be holding off until then. The reason I was looking at the 200 over the 150 is from the results on midnites string calculator. In almost every test I did with their calculator, the 200 seemed to be a better fit. I can't tell you how many times I saw the "marginal" or "too high" voc and "always" in hypervoc on the 150 when the 200 showed it being OK. Maybe I need to play around with putting fewer in series and more strings in parallel.

The array will start out at around 1000 watts, depending on what size panels I can get and hopefully be about 4000 watts once I get the house sold and upgrade the system to 48 volts. The array will be about 150 ft from the controller

vtmaps

levsmith wrote: »

The array will start out at around 1000 watts, depending on what size panels I can get and hopefully be about 4000 watts once I get the house sold and upgrade the system to 48 volts. The array will be about 150 ft from the controller

4000 watts over 150 feet is going to require some serious cable.

On a 48 volt battery, the classic 200 has maximum power limits of 3796 to 4550 watts, depending on input voltage. In order to get 4550 watts through it you must have an input voltage of 70 volts. At 140 volts input the power is down to 3796 watts. The reason the power is so derated at higher voltage is because the controller makes a lot of heat at higher voltages and limits itself to keep from burning up.

Therefore, you will either need 2 of the Classic 200s and 2 pair of cables, or you will use a Classic 150 and some EXPENSIVE cable. Other options are to consider the xantrex 600 volt controller, or to consider putting batteries and inverter near the array and transmitting AC back to the house... perhaps a power shed half way between array and house.

--vtMaps

bill von novak

levsmith wrote: »

The array will start out at around 1000 watts, depending on what size panels I can get and hopefully be about 4000 watts once I get the house sold and upgrade the system to 48 volts. The array will be about 150 ft from the controller

A few things here.

1) At 4000 watts grid tie is going to be a lot easier. Is there a reason you don't go with just straight grid tie? Will you be entirely off-grid? If you want backup with a grid installation, GT inverters like the SMA inverters with "secure power" will provide that without needing all those charge controllers / heavy wiring.

2) What do you mean "upgrade to 48 volts?" Surely you will not buy components for a 12 or 24 volt system, then buy the 48 volt parts later and toss the older parts?

levsmith

vtmaps wrote: »

4000 watts over 150 feet is going to require some serious cable.

On a 48 volt battery, the classic 200 has maximum power limits of 3796 to 4550 watts, depending on input voltage. In order to get 4550 watts through it you must have an input voltage of 70 volts. At 140 volts input the power is down to 3796 watts. The reason the power is so derated at higher voltage is because the controller makes a lot of heat at higher voltages and limits itself to keep from burning up.

Therefore, you will either need 2 of the Classic 200s and 2 pair of cables, or you will use a Classic 150 and some EXPENSIVE cable. Other options are to consider the xantrex 600 volt controller, or to consider putting batteries and inverter near the array and transmitting AC back to the house... perhaps a power shed half way between array and house.

--vtMaps

Thanks vt, can I ask where you got your numbers from? Is there a chart showing watts and volts max? I can probably get it from the string calculator but having the documentation on hand would be nice. Is the xantrex 600 even more inefficient than the classic 200? What is the advantage to the 600 if the 150 volt is better than the 200 classic?

I have thought about a remote power shed. I will have a garage a little closer, about 100 feet from the array but that's still quite a run for wire. The array will be very close to my well so although I don't need a well house if I keep all water lines below the frost line, maybe I will build one anyways and house the power components and batteries in it and run 120 from there to the house. I just prefer to have everything in somewhat of a climate controlled area if possible, the pump house would be pretty cold in the winter and hot in the summer.

levsmith

bill von novak wrote: »

A few things here.

1) At 4000 watts grid tie is going to be a lot easier. Is there a reason you don't go with just straight grid tie? Will you be entirely off-grid? If you want backup with a grid installation, GT inverters like the SMA inverters with "secure power" will provide that without needing all those charge controllers / heavy wiring.

2) What do you mean "upgrade to 48 volts?" Surely you will not buy components for a 12 or 24 volt system, then buy the 48 volt parts later and toss the older parts?

I'm sure GT would be a lot easier but there is a reason I won't be doing grid tie. The nearest power line is 1/2 mile away from the property and the power company quoted me 16k dollars to bring power to my location. I can easily go completely off grid for that price.

The only large expense when I upgrade to 48 volts is the inverter. The charge controller will be mppt so battery voltage isn't an issue there, the same inverter will work on 48 volts as well as 12. The batteries can be rewired to go from 12v to 48v. Since I already have a 12 volt inverter right now I think that's the way I will start, since 48 volt inverters are in the 1000's of dollars. When the time comes, I'll buy the 48v inverter, rewire the batteries, and change the setting on the charge controller.

vtmaps

levsmith wrote: »

Thanks vt, can I ask where you got your numbers from? Is there a chart showing watts and volts max? I can probably get it from the string calculator but having the documentation on hand would be nice. Is the xantrex 600 even more inefficient than the classic 200? What is the advantage to the 600 if the 150 volt is better than the 200 classic?

I have no personal experience with the xantrex 600 volt controller. By specification, it is reasonably efficient. It's been discussed on this forum. It might be a better choice for your situation.

As for my numbers... they come from Midnite. Midnite has online a downloadable Classic Power Chart that gives the limits. By the way, the engineers and founders of Midnite (and Outback) recommend that their controllers not be run at maximum power continuously by design, it shortens their life... they get hot. Remember, these numbers in the chart are the absolute max... this is the point where the controller begins limiting its power so as to avoid melting. It's not good to design a system which is on the verge of melting all the time.

One thing you can see from the power charts is just how much power you sacrifice by using a higher input voltage. That also tells you something about the efficiency of the controller... the reason the power is derated at higher voltages is because at higher voltage the controller is less efficient. That means it is taking more of the energy and turning it into heat.

Have you tried running a voltage drop calculator on 4000 watts over 150 ft (300 ft round trip) with a Vmp of 90 volts? You will need #2 copper as a bare minimum. If you buy 72 cell panels (Vmp about 37) and put them in strings of 3 (Vmp of 111), you can probably get by with #4 copper.

With an input voltage of 111, the Classic 150 can handle 4438 watts, so a 4000 watt array is a reasonably conservative design for that controller.

--vtMaps

SkiDoo55

If I was putting in a 4000 W system from the start and had a large distance to run would consider the XW MPPT 80-600 charge controller. But keep in mind that you need to have realistic min 10 ea 60 cell panels in series to make it work. Operating voltage is 195-550 vdc. Will take 4800 W nominal at 48 volts. You can go to Schnieder site and download the design tool (Free) and play with the components and distances, to see what works. At 48 Vdc @96% and can reduce wire size for the array to controller. If burying wire I would still recommend putting it in conduit to help protect from nawing critters and damage from rocks in the soil cutting into and shorting it out. Makes it easier to repair. Or replace without having to retrench it.

softdown

How cold does it get in your part of Kansas? Hyper VOC could possibly become an issue with three 72 cell panels. I could only use two panels due to Hyper VOC concerns with the Outback FM80. Bit it can get mighty cold here.

softdown

They made a kazillion 72 cell 24 volt panels with 5" cells. Now they use 6" cells and have went from ~190 watts to over 250 watts/panel. I think this is good but the panels have become slightly harder to handle. But...fewer panels are needed. Bigger panels are a lot more cost efficient as has been pointed out.

inetdog

levsmith wrote: »

I'm sure GT would be a lot easier but there is a reason I won't be doing grid tie. The nearest power line is 1/2 mile away from the property and the power company quoted me 16k dollars to bring power to my location. I can easily go completely off grid for that price.

Do not look only at the original install price of the system!
Once you have made your initial investment and also allow for replacing the battery bank every four years or so (if you take good care of it) you will find that your cost per kWh of energy will be somewhere from two to ten times the cost of utility power, and that higher cost of energy will go on for the life of the system.
Look at how much energy you use per year and figure the cost of that energy from the Power Company (POCO). Then figure out what you would pay for your own "free" solar power each year (at a minimum cost for an ideal system of $.50/kWh and a more realistic value between $1.00 and $2.00 per kWh.

Then look at how long it would take for that difference to pay off the $16k cost to bring in grid power.

Users who are forced to live off grid by much higher installation costs or do so as a matter of lifestyle choice will have to reduce their monthly energy consumption to far less than they are accustomed to, with the associated lifestyle changes, before solar power becomes affordable. With current technology it will never be as cheap as POCO power, so make the cost comparison over at least a ten year period.

vtmaps

softdown wrote: »

How cold does it get in your part of Kansas? Hyper VOC could possibly become an issue with three 72 cell panels. I could only use two panels due to Hyper VOC concerns with the Outback FM80. Bit it can get mighty cold here.

There's a big difference between the Outback FM80 and the Midnite Classic 150 with regards to high input voltage... the FM80 will be damaged by 150 volts, but the Classic will enter hyperVoc mode. In this mode it produces no power, but is not damaged. Remember, at times when hyperVoc occurs there is no solar gain anyway. By the time the sun is high enough to produce some power, it will have warmed the panels enough to get them below 150 volts.

--vtMaps

softdown

I was told that my FM80 could get fried by Hyper VOC before the sun really rose. There is maximun voltage but no amps to turn the CC on and draw down the voltage. Was informed of this on Outbacks board.

At any rate, it is easy to compute with the Midnite string tool. Outbacks string tool is more....mystical.

It only takes once....and Hyper VOC damage is not covered by warranty.

vtmaps wrote: »

There's a big difference between the Outback FM80 and the Midnite Classic 150 with regards to high input voltage... the FM80 will be damaged by 150 volts, but the Classic will enter hyperVoc mode. In this mode it produces no power, but is not damaged. Remember, at times when hyperVoc occurs there is no solar gain anyway. By the time the sun is high enough to produce some power, it will have warmed the panels enough to get them below 150 volts.

--vtMaps

softdown

My costs for grid power was much higher than this. Today....I might just cough up $16,000 for grid power. The problem with solar? Batteries....batteries....batteries. There are 100 ways to destroy a battery and/or battery bank.

Babysitting solar equipment is something I would rather not have to worry about 24/7. But then....I just replaced a battery a couple days ago.

Solar is very badly in need of better battery technology. Batteries are far too:
1) Expensive
2) Short lived
3) Delicate

.....and they keep going up....faster than inflation.

inetdog wrote: »

Do not look only at the original install price of the system!
Once you have made your initial investment and also allow for replacing the battery bank every four years or so (if you take good care of it) you will find that your cost per kWh of energy will be somewhere from two to ten times the cost of utility power, and that higher cost of energy will go on for the life of the system.
Look at how much energy you use per year and figure the cost of that energy from the Power Company (POCO). Then figure out what you would pay for your own "free" solar power each year (at a minimum cost for an ideal system of $.50/kWh and a more realistic value between $1.00 and $2.00 per kWh.

Then look at how long it would take for that difference to pay off the $16k cost to bring in grid power.

Users who are forced to live off grid by much higher installation costs or do so as a matter of lifestyle choice will have to reduce their monthly energy consumption to far less than they are accustomed to, with the associated lifestyle changes, before solar power becomes affordable. With current technology it will never be as cheap as POCO power, so make the cost comparison over at least a ten year period.

Vic

softdown wrote: »

I was told that my FM80 could get fried by Hyper VOC before the sun really rose. There is maximun voltage but no amps to turn the CC on and draw down the voltage. Was informed of this on Outbacks board.

At any rate, it is easy to compute with the Midnite string tool. Outbacks string tool is more....mystical.

It only takes once....and Hyper VOC damage is not covered by warranty.

As vtmaps mentioned, HyperVoc is a term coined by Midnite. It is specific to their MPPT CCs, only. By definition, HyperVoc on the Midnite CCs is the extra NON-OPERATING input voltage cushion, where the CC is NOT destroyed by Excessive Voc. The NidNite KID has some HyperVoc capability, but believe that it is still limited to 162 V Max, non-operating Vin.

HyperVoc Link:http://midnitesolar.com/pdfs/whyHyperVOC.pdf

The permissible range of of Hyper Voc (again, only with respect to the Midnite MPPT CCs) is the number in the Classic's model number plus the nominal battery voltage, and only up a maximum of 48 V for this adder. So a Classic 150 on a 48 V system Ceases operation at 150 volts, but should not be damaged for this excessive Voc until the CC Vin exceeds 198 volts. (have seen it stated at one place in the MN docs as a HyperVoc limit of 200 V A Classic 150 on an uncommon 72 Volt nominal battery is still limited to 198 V without damage.

In reality, regarding CCs other than the MidNite Classics and KID, Excessive Voc input to those CCs should not be called HyperVoc, but perhaps just that Excessive Voc, or damaging Voc, or Warranty-Voiding excessive Voc ... or ...

On another Forum, believe that I was the guilty party suggesting that you use the MidNite Classic String Sizer, ONLY for the easy data entry, and NOT for any reference to HyperVoc, or Max current capability of your FM 80.

FWIW, Vic

softdown

Fair enough. Now back to the original point. If the OP has possible weather below approx neg.15 F....then three panels may not be advisable with the FM60/80. This is using data with the older, smaller 5" cells on 72 cell panels. Pretty common knowledge that Midnite deals with Hyper VOC better...but almost everyone seems to wind up with the FM60/80...from what I see.

Midnite sizing tool:

http://www.midnitesolar.com/sizingTool/index.php

Vic

softdown wrote: »

Fair enough. Now back to the original point. If the OP has possible weather below approx neg.15 F....then three panels may not be advisable with the FM60/80. This is using data with the older, smaller 5" cells on 72 cell panels. Pretty common knowledge that Midnite deals with Hyper VOC better...but almost everyone seems to wind up with the FM60/80...from what I see.

YES, you are correct about the MidNite MPPT CCs handling HyperVoc better than ANY other MPPT CC on the planet, because it is their WORD. Technically, NO other CCs use HyperVoc, although it appears that MidNite has no official Copyright on it.

Believe you are using HyperVOC in reference to EXCESSIVE Voc. Seems that HyperVOC is a protective function built-into ONLY MidNtte Classics and KIDs, to put too fine a point on it.

Three 72-Cell PVs can easily have an excessive Voc for many MPPT CCs. We run strings of three 72-cell PVs on one system, and have ten-year absolute high Vin of 140 V on one MX-60, and 141 on another.

The MX-60, and FM CCs have been popular in the past ... would guess that in the past few years that the MidNite Classics and KIDs (for moderate size systems), may be doing more sales volume, than the FMs ... Opinions. Vic

softdown

Problem I have with the KID is that by the time you add the accessories to bring it "up to snuff" you could have about got an FM60/80. Outback is still as respected as anyone. Midnite have the advantage with dealing with higher voltages....which incidentally acts to bring down the amperage capabilities.

People in cold climates just need to be aware of HyperVOC. I'm going to continue using that term because it is universally recognized. Though I appreciate the background that you brought to the subject.

softdown

I am looking at the Midnite Classic by two different vendors. NAWS (us) states 5 year warranty. Another vendor states 2 year warranty. What could be going on?

I could see a charge controller failing after 3-4 years. Wouldn't be that rare.

levsmith

Sorry everyone, been a little while since I've been able to get on. According to intellicast, the record low here is -19F.

vtmaps

levsmith wrote: »

Sorry everyone, been a little while since I've been able to get on. According to intellicast, the record low here is -19F.

If our low for any particular winter was -19°F, we would say that was a warm winter. But I want to mention that for design purposes you should use about -30°F.

The reason is radiative cooling. Record low temperatures tend to occur on still, clear nights. On these nights, surfaces radiate their heat into space and become colder. The cold surfaces cool the air by conduction. The coldest air is at ground level.

Record low temperatures are air temperatures and are measured a few feet off the ground. Usually the record low temperature occurs around dawn. It occurs at dawn because the first rays of sunshine cause breezes that stir up the cold air from ground level to the level of the measuring thermometer.

My point is that your solar panels are a surface and will cool at night by radiative cooling. They will be colder than your record low temperature. Design for that.

--vtMaps

levsmith

vtmaps wrote: »

If our low for any particular winter was -19°F, we would say that was a warm winter. But I want to mention that for design purposes you should use about -30°F.

The reason is radiative cooling. Record low temperatures tend to occur on still, clear nights. On these nights, surfaces radiate their heat into space and become colder. The cold surfaces cool the air by conduction. The coldest air is at ground level.

Record low temperatures are air temperatures and are measured a few feet off the ground. Usually the record low temperature occurs around dawn. It occurs at dawn because the first rays of sunshine cause breezes that stir up the cold air from ground level to the level of the measuring thermometer.

My point is that your solar panels are a surface and will cool at night by radiative cooling. They will be colder than your record low temperature. Design for that.

--vtMaps

That makes sense. Thanks for mentioning it!

softdown

Keep wondering how cold it was to record 141 volts with three 72 cell panels. You have data sheets....and you have the real world.

Vic wrote: »

YES, you are correct about the MidNite MPPT CCs handling HyperVoc better than ANY other MPPT CC on the planet, because it is their WORD. Technically, NO other CCs use HyperVoc, although it appears that MidNite has no official Copyright on it.

Believe you are using HyperVOC in reference to EXCESSIVE Voc. Seems that HyperVOC is a protective function built-into ONLY MidNtte Classics and KIDs, to put too fine a point on it.

Three 72-Cell PVs can easily have an excessive Voc for many MPPT CCs. We run strings of three 72-cell PVs on one system, and have ten-year absolute high Vin of 140 V on one MX-60, and 141 on another.

The MX-60, and FM CCs have been popular in the past ... would guess that in the past few years that the MidNite Classics and KIDs (for moderate size systems), may be doing more sales volume, than the FMs ... Opinions. Vic

Vic

softdown wrote: »

Keep wondering how cold it was to record 141 volts with three 72 cell panels. You have data sheets....and you have the real world.

The low temperature recorded for those times, was about +20 F.

All of the PV modules in use at that time were Shell Solar SQ175PCs. These run an STC Vmp of 35.4 V, and 44.6 Voc.

Running strings of three of these PVs is at the very hairy edge of acceptable. Only works in very moderate, temperate environments. AND, the lightly-loaded string Vmp (really approaching Voc for the temperature of the PV, while operating) easily runs into the 122 V range, as input to the CCs. This is an efficiency hit of several percentage points.

Of course, using higher voltage-tolerant CCs increases the flexibility of the string configuration.

Chose this configuration, because the longest run from the PVs into the CCs was about 80 feet, and wanted to be able to use PV string voltage to heat domestic water, directly.

The PV racks are on a roof that is about 75 feet long.

In general, this three PVs per string configuration will NOT work for many applications. Furthermore, the current 72-Cell PVs have even higher Vmps -- about 36.5 V, and some have about 1 V higher Vocs, even more marginal for current production PV Modules. Some have about 1V lower Vocs, but not recommended, for CCs with 150 V absolute maximum PV input voltages.

With your very cold seasonal temps, strings of three with an FM, or other 150 V Max input CC, are of course are out of the question.

FWIW, Vic