Ready, Shoot, AIM!!!!!

[rachelsdad]

So proud me goes out to replace my 4 24v Chevy Volt batteries and decides to upgrade to 4 24v 100 ah LiFePo batteries. Basically doubling my bank capacity and adding some charge protection, BMS and a rudimentary reporting system

Cool...gonna scrap the propane fridge, go electric...nice, but really no other upgrades needed. I have about 25 light fixtures with 40watt LED bulbs pulling less than 5 watts each and a few AC/DC ceiling fans. Don't think I've ever had more than half of them on at once, in fact typically only 6 or so.

Mainly summer use, the lights aren't on much before 7 p.m. spring summer and fall and I turn in before 10, so use is negligible. But if wife and daughter ever decide to spend some time up there there shouldn't be an issue with those night birds.

So then I start thinking....(for once), I have 9 x 260 solar panels.... figure 90% efficient..85%?? What would be my total input for a "good" day of sun?

 

[sunshine_eggo]

So proud me goes out to replace my 4 24v Chevy Volt batteries and decides to upgrade to 4 24v 100 ah LiFePo batteries. Basically doubling my bank capacity and adding some charge protection, BMS and a rudimentary reporting system

Cool...gonna scrap the propane fridge, go electric...nice, but really no other upgrades needed. I have about 25 light fixtures with 40watt LED bulbs pulling less than 5 watts each and a few AC/DC ceiling fans. Don't think I've ever had more than half of them on at once, in fact typically only 6 or so.

Mainly summer use, the lights aren't on much before 7 p.m. spring summer and fall and I turn in before 10, so use is negligible. But if wife and daughter ever decide to spend some time up there there shouldn't be an issue with those night birds.

So then I start thinking....(for once), I have 9 x 260 solar panels.... figure 90% efficient..85%?? What would be my total input for a "good" day of sun?

Simulate your array at your location on PVWatts.

 

[rachelsdad]

Looking at it.

Would 260 x 9 be my DC size? ??

Or by s/f: Panels are 5' x 3'. 135 s/f? Only 2kw?

 

[Mattb4]

...

So then I start thinking....(for once), I have 9 x 260 solar panels.... figure 90% efficient..85%?? What would be my total input for a "good" day of sun?

There is a standard hour average based on location and Season. Typically about 5 hours Summer and 2 hours Winter. You may have more or less depending on shading or mounting arrangements. It can be calculated on the net at places like : http://www.solarelectricityhandbook.com/solar-irradiance.html

How to use this number. Take you panels watt rating and multiply it by the average hour. Your case of 2340W of panels times 5h would give you a days production of 11,700Wh or 11.7kWh.

 

[sunshine_eggo]

Looking at it. Would 260 x 9 be my DC size? ??

260 * 9 = 2340W = 2.34kW

 

[Koyaanisqatsi]

There is a standard hour average based on location and Season. Typically about 5 hours Summer and 2 hours Winter. You may have more or less depending on shading or mounting arrangements. It can be calculated on the net at places like : http://www.solarelectricityhandbook.com/solar-irradiance.html

How to use this number. Take you panels watt rating and multiply it by the average hour. Your case of 2340W of panels times 5h would give you a days production of 11,700Wh or 11.7kWh.

That site doesn't have but a small number of cities in California, none of which are even close to where I am, and thus not accurate for my area. Is there a service like this that either accepts lat/lon coordinates or has more complete coverage of cities?

 

[Mattb4]

If the city is East or West of you and ~100 miles it likely would give similar results. Possibly find North and South cities from you and average them to get an approximation for irradiance number.

Heck with all the AI stuff nowadays you likely could search for your location on the 'net and get numbers.

 

[sunshine_eggo]

That site doesn't have but a small number of cities in California, none of which are even close to where I am, and thus not accurate for my area. Is there a service like this that either accepts lat/lon coordinates or has more complete coverage of cities?

Simulate your array at your location on PVWatts.

The output of PVWatts includes average hourly numbers by month.

 

[rachelsdad]

Here are the results for my area in the ADK's:

March: 4.75 April 4.97, May 5.68 June 5.51, July 5.86, August 5.58, September 4.69 & October 3.02

​

It's a camp, only used weekends mostly with two (hopefully three this year), full week stays.

So...if this:

How to use this number. Take you panels watt rating and multiply it by the average hour. Your case of 2340W of panels times 5h would give you a days production of 11,700Wh or 11.7kWh.

is in fact the right approach I should be in good shape.

Am I wrong?

I don't have room for more panels on the roof so maybe replace with more powerful?

 

[Mattb4]

...

I don't have room for more panels on the roof so maybe replace with more powerful?

Since panels are rated by efficiency and square foot of coverage (STC-Standard test conditions is 1000W per square meter) it is difficult to find a larger wattage but with less area covered. Most large wattage panels are ~20% efficient and a gain of 1 or 2 percent does not make for a huge size change. If your panels are really old and are about 15% efficient than updating them to new 20%+ panels might be worth it.

 

[rachelsdad]

They are 7 years old. Thanks for the feedback!

 

[Mattb4]

They are 7 years old. Thanks for the feedback!

You can calculate their efficiency if you know their size and rated wattage. Width X length (leave out frame) to give you amount of square meters.

 

[rachelsdad]

260 watts

39.41 x 65.94, with frame would equal 18 s/f...including frames, no measurement on spec sheet for frame but

There are 60 cells in each panel that are 6.14*6.14" arranged 10 x 6. Soooo

3.07 ft x 5.11 = 15.708 s/f or

1.67 meters x 1 meter...so 1.67 s/meters..(I hate metric...this just looks wrong).

 

[Hedges]

Here are the results for my area in the ADK's:

March: 4.75 April 4.97, May 5.68 June 5.51, July 5.86, August 5.58, September 4.69 & October 3.02

​

It's a camp, only used weekends mostly with two (hopefully three this year), full week stays.

So...if this:

How to use this number. Take you panels watt rating and multiply it by the average hour. Your case of 2340W of panels times 5h would give you a days production of 11,700Wh or 11.7kWh.

is in fact the right approach I should be in good shape.

Am I wrong?

I don't have room for more panels on the roof so maybe replace with more powerful?View attachment 276078

Left and right looks like it gets shading by trees.
Which direction is South?

How about an awning of PV panels over the "garage door" facing the lake?
You could fit several big ones there and pick tilt angle.

 

[Mattb4]

260 watts

39.41 x 65.94, with frame would equal 18 s/f...including frames, no measurement on spec sheet for frame but

There are 60 cells in each panel that are 6.14*6.14" arranged 10 x 6. Soooo

3.07 ft x 5.11 = 15.708 s/f or

1.67 meters x 1 meter...so 1.67 s/meters..(I hate metric...this just looks wrong).

15.708sqft=1.459sqm (just use google to convert) since STC is 1000W/sqm if panels was 100%eff you would have 1460W But you have 260W. 260W/1460W= 17.8% (most likely 18%eff panels).

 

[rachelsdad]

South is garage door side. The trees on the East do impede a bit but have been cut back since this photo was taken, West side don't interfere at all, just the angle looks like it would.

Ok hate to sound like an idiot...(which I am, that is why I had a pro install)....but what does that mean as far as ability to charge my 4 batteries?

 

[rachelsdad]

Left and right looks like it gets shading by trees.
Which direction is South?

How about an awning of PV panels over the "garage door" facing the lake?
You could fit several big ones there and pick tilt angle.

I would probably have to mount them flat on the wall, as we average about 10' of snow up there a year and it would need a pretty stout framing.

Not sure the APA would like that though. My spot is one of the more restricted areas of the ADK's albeit with private ownership.

Adirondack Park Agency

 

[Bluedog225]

First, very cool cabin.

Others will know better, but I think there’s some significant room for improvement on your panel placement.

If that garage is the south facing wall, that means you’re going to get pretty good sun with a more vertical panel (maybe angled out at foot at the bottom) in the winter and I can’t help but think you’re going to get some great reflected or irradiance from the water. That is, almost vertical and mounted below the window.

Similarly, a deck mounted railing of two or three near horizontal panels to match the ones above the garage. All mounted facing the same orientation and on the same string.

I can see a big 400 watt panel or two on that south facing roof that will be producers.

And I think (check this) that if you have panels facing different directions, you ought to put them on different MPPTs. I can see about 4 panels. So they are all different orientations?

 

[Bluedog225]

Edit to add-Tell the park agency that you can have solar or run a diesel generator all night. Which do they prefer?

 

[Hedges]

Vertical should be fine, considering you will get light reflected off water. And especially helpful in winter, if that is South facing.
Like the guys with vertical fences of panels in the snowy north.

Are your roof panel mounts designed for the snow load? Number of rails, and sometimes staggering to spread over more rafters.

See if you are allowed flat on the wall. Adds significantly to total wattage.

 

[Hedges]

South is garage door side. The trees on the East do impede a bit but have been cut back since this photo was taken, West side don't interfere at all, just the angle looks like it would.

Ok hate to sound like an idiot...(which I am, that is why I had a pro install)....but what does that mean as far as ability to charge my 4 batteries?

Good, South.

Batteries accept some charge current (reduced at low temperature, so set BMS temperature limits considering what current is available.

PV wattage divide by battery voltage equals battery current (after applying any efficiency losses.)
Batteries can accept higher current at lower than full voltage which is convenient.

Panels at different orientations need to be in different series strings, but can be paralleled into a given MPPT input if similar string voltage.
Area presented to sun (use Trig) should approximately give ratio of power produced to rated power.
But with the added panels vertical, when they produce max the roof panels will produce near zero.
So charge current from roof panels when sun directly overhead can be considered pretty much separate from when panels on wall produce their max. A bit more than that maybe due to sun reflecting off water.

Just want to make sure you don't exceed rated charge current and have BMS disconnect.

"4 24v 100 ah LiFePo" = 10kWh
0.5C x 10kWh = 5kW charge rate allowed.
You're fine. Have about 2.5kW so far, and even if you add 2.5kW more at a different angle, you won't exceed 5kW.

Maybe set temperature limit where 3kW, 0.3C would be acceptable.

From one of these brand's tables, I think 7 degree C lower limit is probably OK. See what specs you can find for your cells.

Post in thread 'Why you cannot charge LiFePO4 below 0 degrees Celsius'

Jan 26, 2021

Since this topic is gaining interest again, here are a few more tables showing the same trend as the Ganfeng Datasheet for other manufacturers

CALB SE series datasheet is the clearest but least detailed (and doesn't acknowledge SOC):



ETC 228 is quite similar in presentation to Ganfeng, but min of 0*C and SOC doesn't appear too important:


Here is the Ganfeng table again for comparison (the only one shows that shows...

• Dzl

• 
• 

Got battery heaters? Insulation?

 

[rachelsdad]

@Hedges
Got battery heaters? Insulation?
No need, I don't go up past early November. They have low temps cut off as well, (LiTime). But I take 'em home for cold and security.

It's on an island, (that's just the boathouse where the panels are mounted on the roof), and temps reach negative quite often up there...really not much to do, I don't hunt or snowmobile, (I do winter backpacking but never thought of heading there). I used to take my 8 6v 100 lb. lead batteries home every fall, fun in a boat! The 4 Chev Volt Batteries were lovely, 24 lbs., I could put them in my pocket. These new ones weigh 48 lbs., still pretty easy vs. the lead but that will get old some day I'm sure. Right now they're sitting in my office at 71! This will be the first year I've used them

@Bluedog225


And I think (check this) that if you have panels facing different directions, you ought to put them on different MPPTs. I can see about 4 panels. So they are all different orientations?
There are four on the east, one south and four more on the west side of the roof, all going into my one Magnum MS4024 Inverter/Charger.

Edit to add-Tell the park agency that you can have solar or run a diesel generator all night. Which do they prefer?

In my application that was my approach...worked real well!

I think I am in good shape based on my understanding of the help so far. I'll run them this year with the existing set up.

Thank you everyone!

 

[Bluedog225]

And of course, if you pm me the address, I’ll be glad to look your system over in person, for a week or two.

All part of the diysolarforum service.

 

[rachelsdad]

And of course, if you pm me the address, I’ll be glad to look your system over in person, for a week or two.

All part of the diysolarforum service.

Any time any day. My wife and daughter rarely come up anymore. Unlike most Adirondak lakes this is not tannic at all, the fish taste like sushi....bass, landlocked salmon..I could swallow the perch whole. Blue collar, not like Lake Placid or Champlain. More loggers than financiers up here. I get along with everyone fairly well since I drink PBR at the local bar and usually swing the bar..for a total of $8-$12!!!

 

[12VoltInstalls]

There’s a lot of great responses here.
I have thoughts interstitial below that you may or may not find useful

is in fact the right approach I should be in good shape.

I’m in Vermont. I know ‘the struggle’ at these latitudes.

don't have room for more panels on the roof so maybe replace with more powerful?

Have you actually been low on power?
Since you say you don’t get up there in the winter, the roof still has room for options.
However, I personally would utilize the front wall of the boathouse - at the low price of panels these days I’d pick the wall and ignore the suboptimal angle (loses some output potential) and run with it. Your existing roof panels are more suboptimal imho and you’ve been using them fine.

what does that mean as far as ability to charge my 4 batteries

Guessing a similar latitude (it’s close enough to me) I’m guessing that you batteries (roughly ~10kWh storage) could fully charge in one good sun June day if they were fully “empty.”

would probably have to mount them flat on the wall, as we average about 10' of snow up there

The front wall with four 300W panels (1200W total) would be a substantial addition with a potential of ~50% charging capacity of the batteries.

Vertical should be fine, considering you will get light reflected off water. And especially helpful in winter, if that is South facing.
Like the guys with vertical fences of panels in the snowy north…..See if you are allowed flat on the wall. Adds significantly to total wattage.

Agreed. It’s an excellent strategy.
All my panels are vertical and have been for 3-4 years now. I never lose charging ability due to snow or ice accumulation- although that is a nonissue for the LuckyADK OP

gonna scrap the propane fridge, go electric

I have a little piece of property here in VT with an offgrid RV that I severely modified for 4-season -20*F weather. In a camper elimination of venting for the ‘fridge’ and going electric household fridge cut my heating costs by about a third.
In your case it might not save a ton of money but it’s going to be worth it to unpropane yourself a bit in a remote locale just in convenience factor! Bonus is even used RV refrigerators sell for around the price of a low-wattage ~10CF

You are def going in the right direction imho