So, my panels will be coming this week...

Temu

I have ordered a pallet (21) of Suntech 270 STP, 24v panels. This was a group purchase, I'll be using 4 in my off-grid (cabin) application with a bank of 12 Trojan L16, Hi Caps.

I am looking at this invertor:

Outback Power Off Grid Inverter Charger 3500W 24VDC VFX3524

And this controller:

Outback FM-80 Charge Controller MPPT The FLEXmax

Do you think this is a good combination with the panels and set-up I have?

VERY much a newbie here, so please be easy on me!

Thanks!

mike95490

Re: So, my panels will be coming this week...

Temu wrote: »

I have ordered a pallet (21) of Suntech 270 STP, 24v panels. This was a group purchase, I'll be using 4 in my off-grid (cabin) application with a bank of 12 Trojan L16, Hi Caps.

I am looking at this invertor:

Outback Power Off Grid Inverter Charger 3500W 24VDC VFX3524

And this controller:

Outback FM-80 Charge Controller MPPT The FLEXmax

Do you think this is a good combination with the panels and set-up I have?

VERY much a newbie here, so please be easy on me!

Thanks!

270 x 4 =1080w @28V = 38amps DC, so a 80A charger will barely get warm.

What will your battery bank of 12 L-16 end up with for total bank capacity ?
3 strings of 4 series batteries ?
You may have too much battery for your PV

Temu

Re: So, my panels will be coming this week...

mike90045 wrote: »

270 x 4 =1080w @28V = 38amps DC, so a 80A charger will barely get warm.

What will your battery bank of 12 L-16 end up with for total bank capacity ?
3 strings of 4 series batteries ?
You may have too much battery for your PV

I was told to get the 80A in case I desire to add more later...maybe the 60A is a better choice?

I was also told to run 12 batteries, hooked as you mentioned.

Too much battery??? I figured more would be better so as not to drain them down as far?

BB.

Re: So, my panels will be coming this week...

Assuming you got L16RE-2V @ 1110 AH (20 hour rate)... A good starting rule of thumb for charging current is around 5-13% of the 20 Hour bank capacity (roughly):

• 1,110 AH * 0.05 = 55.5 Amps minimum
• 1,110 AH * 0.13 = 144.3 Amps maximum

Assuming 0.77 panel/charger efficiency and ~29 volts battery charging:

• 55.5 A * 29 volts charging * 1/0.77 eff = 2,090 watts of solar panels for "low end" estimate
• 144.3 A * 29 volts charging * 1/0.77 eff = 5,431 watts of solar panels for "high end" estimate

The above numbers are just rough estimates for sizing a system. You can go outside the above recommendations--but there are usually draw backs (lot more generator run-time with too few panels; or lots of extra $$$ spent for too much panels unless you have very heavy daily loads).

Over sizing the battery bank can be a pretty big issue. They take a very long time to recharge (sulfation issues), don't mix very well (need generator for equalization), and large banks have "large" self discharge as they age--leading to the solar panels supplying much of their power just to "trickle charge" the battery bank.

And we have not even discussed your daily loads yet...

-Bill

Temu

Re: So, my panels will be coming this week...

BB. wrote: »

Assuming you got L16RE-2V @ 1110 AH (20 hour rate)... A good starting rule of thumb for charging current is around 5-13% of the 20 Hour bank capacity (roughly):

• 1,110 AH * 0.05 = 55.5 Amps minimum
• 1,110 AH * 0.13 = 144.3 Amps maximum

Assuming 0.77 panel/charger efficiency and ~29 volts battery charging:

• 55.5 A * 29 volts charging * 1/0.77 eff = 2,090 watts of solar panels for "low end" estimate
• 144.3 A * 29 volts charging * 1/0.77 eff = 5,431 watts of solar panels for "high end" estimate

The above numbers are just rough estimates for sizing a system. You can go outside the above recommendations--but there are usually draw backs (lot more generator run-time with too few panels; or lots of extra $$$ spent for too much panels unless you have very heavy daily loads).

Over sizing the battery bank can be a pretty big issue. They take a very long time to recharge (sulfation issues), don't mix very well (need generator for equalization), and large banks have "large" self discharge as they age--leading to the solar panels supplying much of their power just to "trickle charge" the battery bank.

And we have not even discussed your daily loads yet...

-Bill

Yikes! Now you're going WAY over my head. Boy, I should have found this site a long time ago! This set-up I am planning was "said" to be OK from the folks at sunelec, plus it is similar to my neighbors aging system...a bit over 1000w with 12 L16's. He, my neighbor, has almost 9 years on his 16's and is still going strong. He advised the bank of 12.

Probably the biggest load I will ever use will be a washing machine and a small swamp cooler in the summer. It is a small cabin, so even that will not be a major load as it will be used sporadically...probably even just a fan primarily.

The good thing is, at this point, only the panels are on the way!

So you think I should have LESS batteries?

Cariboocoot

Re: So, my panels will be coming this week...

Please note the system specifications in my sig.

You definitely have too much battery at 320 Amps hours * 3 banks: 960. (If these are 'B' type L16's it's worse.)
Even with an FM80 maxed out it will not properly charge such a bank, because the tall case batteries really need 10% charge rate to re-mix electrolyte. They stratify more easily than ordinary "golf cart" type batteries.

That said, 1080 Watts of panels will likely produce a charge current near 30 Amps; good enough for one bank of L16's. At 50% discharge that would give you approximately 3.8 kW hours per day. The panel "harvest" comes in around 3.4 kW hours per day using rule-of-thumb estimates, so it's close. At 25% discharge you'd have 1.9 kW hours to work with and a good margin for cloudy days.

As Bill said, we have not discussed your loads and that really is the place to start designing from. Got to know how much power you need before you can figure out how to get it!

Temu

Re: So, my panels will be coming this week...

Cariboocoot wrote: »

Please note the system specifications in my sig.

You definitely have too much battery at 320 Amps hours * 3 banks: 960. (If these are 'B' type L16's it's worse.)
Even with an FM80 maxed out it will not properly charge such a bank, because the tall case batteries really need 10% charge rate to re-mix electrolyte. They stratify more easily than ordinary "golf cart" type batteries.

That said, 1080 Watts of panels will likely produce a charge current near 30 Amps; good enough for one bank of L16's. At 50% discharge that would give you approximately 3.8 kW hours per day. The panel "harvest" comes in around 3.4 kW hours per day using rule-of-thumb estimates, so it's close. At 25% discharge you'd have 1.9 kW hours to work with and a good margin for cloudy days.

As Bill said, we have not discussed your loads and that really is the place to start designing from. Got to know how much power you need before you can figure out how to get it!

Boy, thank you all for your input. I an not electrical saavy whatsoever and seem to have been misled about "more batteries are better" philosophy. If I am understanding corrrectly now, 8 L16's are more in the ballpark, along with the 60A inverter.

Am I getting closer?

Again, small cabin...minimal needs...biggest load will be a washer maybe twice a week, a vacuum cleaner every other day, no TV, a few low wattage lights for maybe a 2-3 hour period in the evening along with a laptop and bag-type cell phone (always on).

BB.

Re: So, my panels will be coming this week...

A couple of handy meters for measuring power usage... Kill-a-Watt meter for 120 VAC 15 amp circuits--great for use around the home for looking at conservation measures. And for DC Amp*Hour/Watt*Hour measurements, something like one of these is handy.

Basically, need to know the peak loads (watts or amps@volts pump starting, etc.). And need to know how much energy you use in a day (watts*hours; amp*hours @ xx volts).

For example, 4x270 watts of solar panels in moderatly sunny location/season will see around 4+ hours of sun per day. Assuming a system end to end efficiency of 0.52 (solar panels to AC inverter output):

• 4x270 watts of panels * 4 hours of full sun equivalent * 0.52 derating = 2,246 Watt*Hours in typical weather

That is a fair amount of power for a cabin. Assuming a battery bank with 3 days of no sun and 50% maximum discharge (for longer life):

• 2,246 Watt*Hours per day * 1/0.85 inverter efficiency * 3 days of no sun * 1/0.50 max discharge = 15,854 Watt*Hours of battery storage

For a 24 volt battery bank, that would be:

• 15,854 Watt*Hours / 24 volts = 661 AH (at 20 Hour Rate)

That would give you a large bank with a minimum sized solar panels (1,070 Watts of solar panels).

With this setup, you could but the bank in 1/2--Or you could double the panel size for more power. But if you go beyond the rules of thumb--you can have issues.

It would be interesting to hear more about your neighbor's system and how much power they use in a day. It is hard to argue with success.

Regarding battery banks--Here are a couple of battery FAQ's that you can read through:

Deep Cycle Battery FAQ
www.batteryfaq.org

We recommend you start with a paper design first--then figure out the details and hardware needed to support your needs and keep within your cost point.

-Bill

Cariboocoot

Re: So, my panels will be coming this week...

It's a case of "different times, different mores"; used to be that "putting back the Amp hours" was all that mattered. Since then we've learned that putting it back fast enough lengthens battery life. I'd bet your neighbour's system has slowly dropped in actual capacity but he uses such a small portion that it isn't noticeable. If you start out with 1000 Amp hours but only use 200 of it, even losing 50% capacity doesn't show up! (Unless you use a battery monitor, of course.)

But why buy more than you need to, eh? Batteries are really expensive these days!

One bad note about usage: that washing machine. Typically it's a 1/3 HP, high-torque AC induction motor that will have a whonking great start-up draw and chew through 1 kW hour or more per load. Best to run your back-up gen when doing laundry.

My system: I would and will add more panel as soon as I can. It needs 1050 Watts, really. I get away with it now because at high elevation and cooler temps my panels run at 82% efficiency, and the batteries are not tall case. My net charge rate is rough 6.3% - just above minimum. I hold off water pumping and such until batteries are full, then make use of the extra available sunlight.

Just so you know, my typical daily use is 2.4 kW hours. That runs an electric refrigerator, computer/satellite/phone set-up (and printer), 1/3 HP water pump (about 6 minutes a day - use a big pressure tank), 1 HP digester pump (sewage - about 1 minute a day), and the occasional microwave zap along with needed lights/radio/whatever. It works, but it takes some advance thinking.

Temu

Re: So, my panels will be coming this week...

Cariboocoot wrote: »

It's a case of "different times, different mores"; used to be that "putting back the Amp hours" was all that mattered. Since then we've learned that putting it back fast enough lengthens battery life. I'd bet your neighbour's system has slowly dropped in actual capacity but he uses such a small portion that it isn't noticeable. If you start out with 1000 Amp hours but only use 200 of it, even losing 50% capacity doesn't show up! (Unless you use a battery monitor, of course.)

But why buy more than you need to, eh? Batteries are really expensive these days!

One bad note about usage: that washing machine. Typically it's a 1/3 HP, high-torque AC induction motor that will have a whonking great start-up draw and chew through 1 kW hour or more per load. Best to run your back-up gen when doing laundry.

My system: I would and will add more panel as soon as I can. It needs 1050 Watts, really. I get away with it now because at high elevation and cooler temps my panels run at 82% efficiency, and the batteries are not tall case. My net charge rate is rough 6.3% - just above minimum. I hold off water pumping and such until batteries are full, then make use of the extra available sunlight.

Just so you know, my typical daily use is 2.4 kW hours. That runs an electric refrigerator, computer/satellite/phone set-up (and printer), 1/3 HP water pump (about 6 minutes a day - use a big pressure tank), 1 HP digester pump (sewage - about 1 minute a day), and the occasional microwave zap along with needed lights/radio/whatever. It works, but it takes some advance thinking.

Good info and thanks a bunch! I too am at elevation...4200' with lots of sunny, southern exposure...an easy 5 hour a day. Though I didn't think I'd need 1000+ watts, I chose the 4-270's because I won't be using a sun tracker. And yes, my neighbor uses a sunny day to do his laundry! On cloudy days, he has to fire up his genny/welder to pump 'em up!

The thing is, I can only guess at the power I may need...heck, right now, I have a measly 120w panel, a C40, and 2 L16's so I can watch movies on the laptop and have use of a reading light...and the always-on bag phone.

And, since my panel order is on the way, I have to decide on a inverter and controller for now...and what looks to be 8 L16's instead of 12!

I hope this makes sense!

mike95490

Re: So, my panels will be coming this week...

If you do plan on expanding, the FM80 is fine, overkill never really hurts, unless it's battery bank size!

Temu

Re: So, my panels will be coming this week...

mike90045 wrote: »

If you do plan on expanding, the FM80 is fine, overkill never really hurts, unless it's battery bank size!

Thanks! I got schooled on batteries today!

I should have phrased my query accordingly...

"I have 4 Suntech 270 STP 24v panels, what do you recommend for Outback inverter and Outback controller...

and how many L16's should I run with this?"

---

So far, I've decided on the 60A controller and the VFX3524 and 8 L16's.

Now I am wondering if there is a benefit in getting the VFX3548 as opposed to the 24v inverter?

Yes, I am an idiot with this learning curve.

mikeo

Re: So, my panels will be coming this week...

And, since my panel order is on the way, I have to decide on a inverter and controller for now...and what looks to be 8 L16's instead of 12!

I have installed a couple of systems for my neighbors similar to yours. I would use no more then 8 batteries of the Trojan L16 in the 400 amp hour range. I would go with the 80 amp controller because it doesn't cost that much more. This would allow you to double your panels with a 24 volt system should you ever need to. Also I would add a battery monitor like the Trimetric 2020 or similar to complete your system. Don't forget appropriate fuses, breakers and grounding in your installation.

Cariboocoot

Re: So, my panels will be coming this week...

Temu wrote: »

Thanks! I got schooled on batteries today!

I should have phrased my query accordingly...

"I have 4 Suntech 270 STP 24v panels, what do you recommend for Outback inverter and Outback controller...

and how many L16's should I run with this?"

Four. That's 320 Amp hours @ 24 Volt nominal - a good match for your panels.

So far, I've decided on the 60A controller and the VFX3524 and 8 L16's.

Now I am wondering if there is a benefit in getting the VFX3548 as opposed to the 24v inverter?

Yes, I am an idiot with this learning curve.

Everybody's an idiot about what they don't know.

As for the inverter choice ... As good as OB inverters are, they tend towards being pricey. Not only will you need a VFX, but also a MATE or MATE II and preferably a HUB and remote temp sensor to tie all the equipment together and keep settings & data shared.

An alternative you might consider:
Morningstar MPPT controller http://store.solar-electric.com/motr60ampmps.html
Magnum inverter http://store.solar-electric.com/maenms4040wa.html

As for going up to 48 Volt system ... without a definite handle on your loads it is impossible to advise. You usually go up a step in system Voltage for about every 2 kW in consistent power use:
Usage </=2 kW = 12 Volt
Usage </=4 kW = 24 Volt
Usage </=6 kW = 48 Volt
Over 6 kW = dual system.

Roughly speaking.

mike95490

Re: So, my panels will be coming this week...

If you are buying new anyway, I would step up to the 48V system. You can put all the batteries in one series string, and not have to think about equal current sharing. Leaves lots of expansion options, but you have to expand in 48V chunks, not 24V. (batteries, extra panels.....) but the cables and fuses are smaller

rafaelito

Re: So, my panels will be coming this week...

The Outback Inverter you have speced costs less from NAWS than the Magnum and the 3648 is on sale. I like Outback products and would add a Mate (required for programming, but check out the Mate 3 if it is shipping!) and Flexnet DC monitor (provides good monitoring and integration) with Hub 4 (what I just installed in my RV).

48 volts? Why not? Greater efficiency, smaller wiring, same dollars for parts and headroom for expansion. Speaking of parts, I went with midnite solar e-panel plus. Of course, 12vdc was required for my installation.

He'll of a learning curve and many good souls with vast experience (not me) on this board.

You definitely need to consider breakers, combiner box, and balance of system components to complete your installation.



Magnum inverter http://store.solar-electric.com/maenms4040wa.html

As for going up to 48 Volt system ... without a definite handle on your loads it is impossible to advise. You usually go up a step in system Voltage for about every 2 kW in consistent power use:
Usage </=2 kW = 12 Volt
Usage </=4 kW = 24 Volt
Usage </=6 kW = 48 Volt
Over 6 kW = dual system.

Roughly speaking.[/QUOTE]

Cariboocoot

Re: So, my panels will be coming this week...

There are disadvantages to a 48 Volt system too.
For one thing, you need more batteries. That's more expense, more connections, more maintenance. Yes, you get more power. But if you don't need that power, why pay for it? You will also need more panels to charge those batteries because they're more power.
And you can get some array configuration problems in certain areas: a nominal 48 Volt array works fine through MPPT to charge a 24 Volt system. But may be marginal with a 48 Volt system due to wire loss and/or temperature. You might have to go up in array Voltage, and then run in to difficulties with the Voc being too high for the controller in cold weather. Not always, but the possibility is there.

Get a handle on the loads. That's the place to start the design.
Oh; did I say that already?

Temu

Re: So, my panels will be coming this week...

mikeo wrote: »

I have installed a couple of systems for my neighbors similar to yours. I would use no more then 8 batteries of the Trojan L16 in the 400 amp hour range. I would go with the 80 amp controller because it doesn't cost that much more. This would allow you to double your panels with a 24 volt system should you ever need to. Also I would add a battery monitor like the Trimetric 2020 or similar to complete your system. Don't forget appropriate fuses, breakers and grounding in your installation.

Okey-doke...so I went with this:

1 x Outback Power Off Grid Inverter Charger 3500W 24VDC VFX3524 (VFX3524) =
$1,833.96
1 x FM-60 (FM-60) = $508.98

Now I am thinking about 8 of the L16E-AC 370 AH Trojans @$211.16 ea. (local group purchase for that price) as opposed to the 435 AH Trojans.

I got schooled hard on batteries, but I hope this will be OK?

Also, to link the batteries together, can I use 2.0 cable of do I need the 4.0? I've heard differing opinions. I understand 4.0 to go to the inverter.

niel

Re: So, my panels will be coming this week...

go with the largest wire you can for interconnecting the batteries. that's a large capacity bank and will be required to charge/discharge large currents and you want to avoid extra resistances preventing you from doing that very well. this also means if you can have the wires shorter that it would also reduce the resistances the system must face.

Temu

Re: So, my panels will be coming this week...

niel wrote: »

go with the largest wire you can for interconnecting the batteries. that's a large capacity bank and will be required to charge/discharge large currents and you want to avoid extra resistances preventing you from doing that very well. this also means if you can have the wires shorter that it would also reduce the resistances the system must face.

Thanks Niel! Bite the bullet on the 4.0--check.

Now, how 'bout those batteries? The 370 AH better for me, or does that matter in keeping these suckers charged and bubblin'?

Derik

Re: So, my panels will be coming this week...

I have the Outback system, flex 500 dual inverters, fm 80 chager controller and mate.

Not knowing much about solar I installed everything myself and it was much easier than I had expected.

I have 12 L-16RE B's with 9 215 watt panels.

I recently had some low battery issues because I didn't program the charge controller correctly. I have since got everything back in order without the use of a generator.

The opinion here and I agree that for most locations I have too much battery, but because of my southern high desert location things seem to be in order and working well as we approach the shortest day of the year.

Having said that, I would look at the lower amp Trojan t-105's. Time will tell but I kind of wish I would have gottn these over the more expensive L-16RE b batteries.

I have a small shed that is powered with two of these, they are in their 5th year of trouble free service and I have only equalized them once, they show 1.255 on the hydrometer after a day in the sun with only 65 watts feeding them.

In my case my panels far exceed the specifications and thus I am making much more power than I ever expected, this may be the case with you as well depending on your location.

Talk to you neighbor.

niel

Re: So, my panels will be coming this week...

trojans like the 10% rate of charge give or take a few %. i didn't go into figuring what current you will get from the pvs, but i'm sure you can do some rough math to get a %.