Too many panels?

Volvo Farmer · January 2013

Just like any other addiction, if some is good, more is better right?

These popped up on Craigslist today and they are now mine. They are a perfect modular fit for the rest of my system which is made up of (12) 170W 24V nominal panels. These are BP 5170s, which are a mono crystalline panel and I bet they were over four dollars a watt when purchased nine years ago. Eighty cents a watt might seem a little high for used panels, but because of the perfect fit, I snapped them up.

So I have a 800Ahr battery at 24V. These 12 170W panels I have now should theoretically charge at 85A, but I don't remember seeing more than 70 out of them. From a balance of system perspective, I'm now going to have a 3.4KW array on a 800Ahr battery bank, seems a little higher than most on the solar side.

I guess what I want to know is... I think I might be approaching C/8 or possibly C/6 on my charging rate. Do I need to worry about this? My batteries are HuP Solar one. A single string of twelve 2V cells.

Attachment not found.

westbranch · January 2013

Re: Too many panels?

VF, what does HUP say?
What about system efficiency? that would bring the rate down a bit too.

Cariboocoot · January 2013

Re: Too many panels?

I wouldn't expect 85 Amps from 12 170 Watt panels. 70 Amps is very good. 65 would be predicted.

You're Classic isn't going to take all those new panels, so you'll need another controller just to handle them.

The solution is to use a PV disconnect and leave the new array off unless it's cloudy, then turn it on to gain the extra charging power if needed.

The batteries could probably take 160 Amps on occasion, but not regularly. To some degree the amount of current that will flow will be limited by the SOC of the batteries. But I wouldn't just hook everything up and just let it go at whatever rate comes up.

Photowhit · January 2013

Re: Too many panels?

I don't think you have too much solar, I had planned on a 4Kw array for my 800 Amphour 24 volt battery, and was thinking that would be just over 10% charge rate in normal operation. and a max around 14%.

Then I got a great deal on 2.6Kw of array ($1000 and a days work delivered) So if your worried about having too much array I should be shaking in fear! But I figure I'll have a much better chance of keeping the battery topped of during cloudy winter weather.

Where I might have an issue is internally in the E-Panel, as the potential amperage will be pretty high in some spots. I will govern the classic's out put a bit.

NorthGuy · January 2013

Re: Too many panels?

Cariboocoot wrote: »

The solution is to use a PV disconnect and leave the new array off unless it's cloudy, then turn it on to gain the extra charging power if needed.

Or you can install a small air conditioning and run it when there is too much of charging current. Most of the time, that's exactly the time when you would need it.

Eric L · January 2013

Re: Too many panels?

You can program the Classic to limit output amps. If HUP tells you the maximum input amperage, you could use that plus the smallest expected load you'd have going (multiplied by a system inefficiency value if you have one) as the output limit value.

As panel prices fall, I think more people are in this position of having a PV array that can theoretically overcharge the batteries. Luckily, it's a good 'problem' to have and easily fixed with your controller.

newl · January 2013

Re: Too many panels?

One can almost never have enough especially when split orientations are used.

Volvo Farmer · January 2013

Re: Too many panels?

Thanks for all the replies. The panels will be going on a stationary mount optimized for winter sun. I have a 40 amp PWM controller that should handle these, though it will be right on the edge of its specification. All the other panels are on tracking mounts through a Midnite Classic 200.

According to my batteries, my minimum charging system should be 68A and maximum is 136A. So I guess I have nothing to worry about, as I think I'll be around 100A with this upgrade.

Anyone think I'll let the magic smoke out of a Xantrex C40 with eight of these? Imp is 4.72A per panel. I don't know how this controller would react to an edge-of-cloud event on a cold winter day.

stephendv · January 2013

Re: Too many panels?

I like newl's idea of splitting the orientations so you can have a longer solar day, which in off-grid land is better than a peak at noon when you really don't need it/can't use it.

NorthGuy · January 2013

Re: Too many panels?

stephendv wrote: »

I like newl's idea of splitting the orientations so you can have a longer solar day, which in off-grid land is better than a peak at noon when you really don't need it/can't use it.

I don't think this can make a big difference. In the morning, east-facing panels will produce more, but west-facing panels will produce less (or may not produce at all). Similarly, in the evening, west-faced panels will produce more, but east-facing ones will produce less. Therefore, in avarage, you are not likely to benefit much, and may even lose.

stephendv · January 2013

Re: Too many panels?

NorthGuy wrote: »

I don't think this can make a big difference. In the morning, east-facing panels will produce more, but west-facing panels will produce less (or may not produce at all). Similarly, in the evening, west-faced panels will produce more, but east-facing ones will produce less. Therefore, in avarage, you are not likely to benefit much, and may even lose.

I wouldn't go for East-West, rather SE and SW. You're exactly right, that you would lose out on the total generation for the day. But for most off-grid homes, having the energy at the right time is more important than having a greater total amount at the wrong time. I can only speak for my own location, where batteries are in absorb at 12 noon even in winter, if I had more south facing array, there'd be no where to send the extra power. But more SE and SW facing panels would mean more time running purely off solar and not off the battery.

BB. · January 2013

Re: Too many panels?

In available power from solar panels, splitting the array will probably give you less overall power.

However, from the battery life perspective, getting an even charge over 6-8 hours is better than a "quick charge" (higher current) in 4 hours.

That is why Dave Sparks (an off grid installer in the California Sierra Nevada's) still likes tracking arrays--even with their additional costs (and slight increase in maintenance).

Cheap/fixed panels in a large array pointed in different directions may be more cost effective than a smaller array on trackers in that regard.

-Bill

NorthGuy · January 2013

Re: Too many panels?

stephendv wrote: »

I wouldn't go for East-West, rather SE and SW. You're exactly right, that you would lose out on the total generation for the day. But for most off-grid homes, having the energy at the right time is more important than having a greater total amount at the wrong time. I can only speak for my own location, where batteries are in absorb at 12 noon even in winter, if I had more south facing array, there'd be no where to send the extra power. But more SE and SW facing panels would mean more time running purely off solar and not off the battery.

I wasn't talking about whole day, but rather about the amount of energy generated in the morning. What you gain by turning SE array towards the morning sun is likely to be less than what you lose by turning SW array out of the sun.

Similarly, in the evening, what you gain from turning SW array towards the sun could be less than what you lose because your SE array is turned away.

Splitting would make sense if your day was so long that in the morning the Sun would be shining generally from NE, and in the evening - from NW. But, if you do have such a long day in Summer, then your day in Winter is very short and splitted array will hurt you.

westbranch · January 2013

Re: Too many panels?

VF, it looks like you have trackers? How many Watts on trackers?
Maybe you would get longest production, not necessarily maxed out in summer, if the new ones were fixed S . just depends on the ratio of Track:Fixed

Volvo Farmer · January 2013

Re: Too many panels?

I have 2KW tracking. I'm planning on fixing 1.3KW south at latitude+15 degrees tilt. The 250W of homebrew panels in my sig are going away and I'm going to expand the mount for the new panels.

I love my trackers. It is a neat thing to see 50% of rated power coming in a few short minutes after sunrise, and opportunity loads can be shifted until later in the afternoon. I'm already maintaining three trackers and really don't feel like building 2 more. Besides I've run clean out of free H to H satellite dish mounts.

newl · January 2013

Re: Too many panels?

BB. wrote: »

Cheap/fixed panels in a largearray pointed in different directions may be more cost effective than a smaller array on trackers in that regard.

What Bill says is true. For the price of trackers and associated ongoing maintenance, one can easily make up for those costs with fixed panels that will make more consistent power throughout the day than the trackers.

That being said, if space is an issue for panel mounting, trackers can be the better option.

H2SO4_guy · January 2013

Re: Too many panels?

I just lost a C-40 (Trace variety) and it let the magic smoke out of an Exeltech inverter. Hope you think long and hard about pushing it too hard.

Skip

Photowhit · January 2013

Re: Too many panels?

H2SO4_guy wrote: »

I just lost a C-40 (Trace variety) and it let the magic smoke out of an Exeltech inverter. Hope you think long and hard about pushing it too hard.

Skip, that's a pretty odd senerio, the exeltech should be protected and have shut it's self down. Reguardless, I hope you send the inverter back to exeltech or at least inquire, I wonder if they still do $100 rebuild/updating?

How much amperage were you running through the C40? I think we had a post of someone running 80 amps through a C60, and until finally they added a fan... Was your C40 somewhere where it could retain heat? A Trace so I guess it had some age to it?

Volvo Farmer · January 2013

Re: Too many panels?

H2SO4_guy wrote: »

I just lost a C-40 (Trace variety) and it let the magic smoke out of an Exeltech inverter. Hope you think long and hard about pushing it too hard.

I'd be interested in the details here too. The only way I can figure a charge controller can cause an inverter to fail is if the battery voltage gets too high. There's no way my 40 amps into my 800+ahr battery is going to push the voltage up over 32V.

niel · January 2013

Re: Too many panels?

Volvo Farmer wrote: »

I'd be interested in the details here too. The only way I can figure a charge controller can cause an inverter to fail is if the battery voltage gets too high. There's no way my 40 amps into my 800+ahr battery is going to push the voltage up over 32V.

sure it's possible to exceed 32v in time if the pvs aren't being voltage regulated by the cc. a 5% charge rate is quite high if you were thinking it to be low enough on the charge rate to be able to self regulate. i saw first hand a charge rate of a few % push fla batteries to the point of boiling out the electrolyte.

i'm not familiar enough with the exeltech to know what precautions they may have taken for overvoltage, but i'm sure there is probably a limit to that protection in any case.

Cariboocoot · January 2013

Re: Too many panels?

One possible scenario for frying an inverter is to wire it like this:

Panels --> Charge controller --> Inverter --> Batteries

If the resistance between Inverter and Batteries should go high the panels can push the Voltage at the inverter above its maximum during, say, and edge of cloud event and something will go 'poof'.

That's why the recommended wiring is:

Panels ---> Charge controller --> Batteries --> Inverter

H2SO4_guy · January 2013

Re: Too many panels?

There was a single string of 4 Evergreen 210 watt panels with voc of 22.xx and a vmp of 18.xx IIRC. They would usually come in about 82 - 84 voc as a string. The short circuit amperage is 12.11. They go into a 20 amp Midnite breaker then to the charge controller. The charge controller output goes to a Midnite breaker to a Midnite bus bar. The bus bar goes to a Midnite breaker to the inverter. It was as protected as I could have made it that I know of. I will send the inverter off one of these days and see if it can be repaired reasonably.

Skip

Photowhit · January 2013

Re: Too many panels?

I'd say it's well worth looking at having it repaired, NAWS still has the "any inverter made in last 20 years, if repairable, $100" up on the ExelTech section Here;

Exeltech repair Stuff Here

They state; "Over Voltage: Shut off at maximum input voltage, per input conditions. Automatic reset upon fault correction."

Here's a thread from last Summer about people 'popping' fuses in their Exeltech 1100's.

So maybe it's something simple you could fix, odd that they would have a fuse as well, but perhaps that's a good thing.

Too many panels?

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