# Any opinions/suggestions on my emergency power setup?

Registered Users Posts: 33 ✭✭

Could someone check my system to see if I got this right before hooking it all up?

Two 160W panels in series and two 165W panels in series, then parallel these two into a 40A MPPT controller. I will use a 15A dc circuit breaker in each series line before I parallel them.

160W panel specs: Vmpp = 18.5V, Impp = 8.65A    This line will be 37V @ 8.65A

165W panel specs: Vmpp = 18.1V, Impp =9.12A      This line will be 36.2V @ 9.12A

So in parallel, the voltage will be pulled down to 36.2 but the amps will be 17.77, for 643.2W, right?

Are the different specs between the 160W and 165W panels are small enough to not affect the MPPT finding the max power point?

Battery bank is two 12v VMaxTank 155AHr SLA batteries in series for a 24V Go Power 1500W Inverter, fused for 110 amps.

I'm open to suggestions on different wiring strings. The controller can take up to 150V Voc.

From using a calculator on another website this should keep my Fridge (1080 Whr/day) running 24/7 but only 1.5 days without sun. But I live in Nevada where cloudy days are almost newsworthy because they are so rare. I built this with the idea of an emergency power source for my fridge, (and for a fun experiment too).

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• Solar Expert Posts: 2,401 ✭✭✭✭✭
The panels ratings are close, my choice would be to put one 160 and one 165 in series per string, that way the combination of each string would be equal. As far as the calculation for battery size, load, array capacity, hours of sun, efficiency and losses, there are smarter people at this than i, so will leave that alone.

1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank
900W  3 × 300W No name brand Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal as a backup system.
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergencies and welding.
The panels are so close in Imp and Vmp, it does not matter which way you choose to series+parallel them...

Vmp is within ~5% and Imp is within 3%... Both are "close enough" to be pretty much ignored. I am not sure you could measure a difference at the charge controller as to how you series/parallel them. McGivor is probably correct, since Imp is a closer match, mixing the two panels in series would give you a better Vmp parallel match. Panel ratings are typically ~3-5% tolerances anyway.

Sizing of solar array to battery bank:
• 155 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 292 Watt array minimum
• 155 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 584 Watt array nominal
• 155 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 759 Watt array cost effective maximum
A ~650 Watt array is a nice size for that battery bank.

A 155 AH @ 24 volt battery bank is good for (155 AH / 200 AH per 1 kWatt) ~ 775 Watt max continuous rated AC inverter (recommended for flooded cell lead acid batteries). So--Your 1,500 Watt inverter is a bit on the large size--Since you have SLA (possibly AGM?)--It is possible that they will have better surge power support vs simple Flooded Cell batteries.

A 1,500 Watt inverter could draw as much as:
• 1,500 Watts * 1/0.85 inverter eff * 1/21.0 volts battery cutoff = 84 amps
And using an NEC deratings of 1.25 for wiring/breaker/fuse ratings:
• 84 amps * 1.25 NEC deratings = 105 Amp branch circuit wiring
I would suggest getting a circuit breaker vs a fuse--That way you can really "turn off" the AC inverter and ensure no draw (some inverter with on/off may draw a bit of current when off--double check yours if it has on/off control).

It is close for running a standard 120 VAC US refrigerator--You may have to run a second parallel string of batteries--But it is certainly worth a try (i.e., will the fridge start in the morning after discharging the battery bank over night?).

A standard 2 days/50% discharge of battery bank:
• 155 AH * 24 volts * 0.85 inverter eff * 1/2 days * 0.50 max discharge = 791 WH per day
Most refrigerators take around ~1,000 to 2,000 WH per day (get a Kill a Watt meter to measure yours). Overnight with full sun next day would seem to work OK for your needs (turn off ice maker, keep doors closed as much as practical will help).

And regarding sun:
• 1,500 WH per day (guess) * 1/0.52 off grid system eff * 1/650 Watt array = 4.4 hours of sun "break even" per day
4.4 hours of sun is a fair amount of sun. For Las Vegas:

### Las VegasAverage Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 54° angle from vertical:
(For best year-round performance)  Jan Feb Mar Apr May Jun 4.63 5.11 6.32 6.70 6.74 6.63 Jul Aug Sep Oct Nov Dec 6.27 6.06 6.15 5.85 4.99 4.58
So, during winter, you would be "squeaking through" (if 1,500 WH per day)--But looks doable.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 33 ✭✭
edited January 2017 #4
Thanks for the evaluation guys.

While a stationary panel mount is convenient, I though of something different.

I'm going to mount my 4 panels on this big 15' sturdy aluminum tube, elevate one end of it so the panels face the angle of the winter sun, and I can simply rotate the tube 3 times a day (morning-noon-evening) to have dawn to dusk sun tracking. In summer, the tube will need to be parallel to the ground so I'll need to elevate the other end too. The panels will see-saw from dawn to dusk.

I'm thinking with a TV antenna rotor mounted to one end of the tube, all I would need is some computer control to auto-track for me. The rotor should also hold the tube steady on windy days. (Wind is probably the one big sticking point of this. With enough of it the tube could spin around over and over, so until I get a rotor, I'll have to find a quick release clamp to hold it where I set it.)
• Solar Expert Posts: 5,114 ✭✭✭✭
Does that fridge have a 'linear compressor' or is it an old style rotary compressor, if the latter you need to determine the start up (locked rotor) surge  and that will be the biggest issue to be overcome, ie if it is a newer 'inverter type' of fridge  you might be able to get away with an inverter as low as 1000W but if an older fridge you probably need a minimum of 2000W to start the compressor.... and you will need more than 2 x 12V 155A batteries to run the fridge for more than 1 1/2 days if it is an older compressor.  Please clarify... I have a 2 year old GE fridge and it runs off a 1500W inverter peak draw with a surge draw< 40A, more like 30A, and then it tapers to <5 before shutting down...
hth

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• Solar Expert Posts: 8,011 ✭✭✭✭
St8kout said:
......I'm going to mount my 4 panels on this big 15' sturdy aluminum tube, ......
I hope it is VERY sturdy.  Aluminum is not nearly as strong as steel.
Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

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• Registered Users Posts: 33 ✭✭
edited January 2017 #7
Does that fridge have a 'linear compressor' or is it an old style rotary compressor, if the latter you need to determine the start up (locked rotor) surge  and that will be the biggest issue to be overcome, ie if it is a newer 'inverter type' of fridge  you might be able to get away with an inverter as low as 1000W but if an older fridge you probably need a minimum of 2000W to start the compressor.... and you will need more than 2 x 12V 155A batteries to run the fridge for more than 1 1/2 days if it is an older compressor.  Please clarify... I have a 2 year old GE fridge and it runs off a 1500W inverter peak draw with a surge draw< 40A, more like 30A, and then it tapers to <5 before shutting down...
hth

It's a GE Adora side-by-side about 4 years old. The Kill-a-watt meter jumped to 744W for about a second, then down to 142W for a bit, then down again to 134W. At rest it draws 2W. The inside placard list 11.6A so that's about 1400W. The Go Power has a surge rating of 2000W, so no problem there.
• Registered Users Posts: 33 ✭✭
edited January 2017 #8
mike95490 said:
St8kout said:
......I'm going to mount my 4 panels on this big 15' sturdy aluminum tube, ......
I hope it is VERY sturdy.  Aluminum is not nearly as strong as steel.

Here's the thing. It came with my pool cover to roll/unroll it. That cover was fairly heavy, especially when wet.

It's actually three-10' sections. Two sections telescope snugly into the center section on each end by 2-3 feet, as needed to adjust to the pool width, and are secured with sheet metal screws. I plan on removing one end section and slide the other end halfway in. I could make it as short at 10' but I think I need 15' for what I have planned.

The tube is not round but has several flat edges, and with the telescopic inner tube inserted, it is quiet strong. During the winter, the tube will be at an angle to the ground, so the weight is not really pushing down on the center of it. In Summer, the supports I'm working on will be closer in to the panels, which are 58" long, so the weight is only on about 60" of the tube.

I could be wrong and the tube could crack under the weight, but I think I have it right. I'll keep a close eye on it.

I originally wanted a "top of pole" mount, but for some reason I can't find a 3-4" diameter schedule 40 pipe anywhere in town. I could order one but they want several hundred dollars, so forget that. I even thought of using a chain link fence post and filling it with concrete, but some people said the concrete would eventually crack and the pole would buckle. The largest diameter steel or iron pipe Home Depot and Lowes carry is 2" schedule 40 black steel. Not too sure about using that with the winds we sometimes get here. But then again I could maybe bundle 3 of them together. Hmm.

• Solar Expert Posts: 2,401 ✭✭✭✭✭
St8kout said:
Does that fridge have a 'linear compressor' or is it an old style rotary compressor, if the latter you need to determine the start up (locked rotor) surge  and that will be the biggest issue to be overcome, ie if it is a newer 'inverter type' of fridge  you might be able to get away with an inverter as low as 1000W but if an older fridge you probably need a minimum of 2000W to start the compressor.... and you will need more than 2 x 12V 155A batteries to run the fridge for more than 1 1/2 days if it is an older compressor.  Please clarify... I have a 2 year old GE fridge and it runs off a 1500W inverter peak draw with a surge draw< 40A, more like 30A, and then it tapers to <5 before shutting down...
hth

It's a GE Adora side-by-side about 4 years old. The Kill-a-watt meter jumped to 744W for about a second, then down to 142W for a bit, then down again to 134W. At rest it draws 2W. The inside placard list 11.6A so that's about 1400W. The Go Power has a surge rating of 2000W, so no problem there.

What is being referred to is the inrush current, the current it takes to start from stall which can be as high as 8 to 10 times the maximum rating for a few milliseconds, a Kill-a-watt meter cannot capture this, you would need a clamp on ammeter with inrush feature. Not saying it won't work, just don't be surprised if it doesn't. Is it a pure or modified sine wave, modified are not the best for motors.
1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank
900W  3 × 300W No name brand Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal as a backup system.
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergencies and welding.
• Registered Users Posts: 33 ✭✭
mcgivor said:
St8kout said:
Does that fridge have a 'linear compressor' or is it an old style rotary compressor, if the latter you need to determine the start up (locked rotor) surge  and that will be the biggest issue to be overcome, ie if it is a newer 'inverter type' of fridge  you might be able to get away with an inverter as low as 1000W but if an older fridge you probably need a minimum of 2000W to start the compressor.... and you will need more than 2 x 12V 155A batteries to run the fridge for more than 1 1/2 days if it is an older compressor.  Please clarify... I have a 2 year old GE fridge and it runs off a 1500W inverter peak draw with a surge draw< 40A, more like 30A, and then it tapers to <5 before shutting down...
hth

It's a GE Adora side-by-side about 4 years old. The Kill-a-watt meter jumped to 744W for about a second, then down to 142W for a bit, then down again to 134W. At rest it draws 2W. The inside placard list 11.6A so that's about 1400W. The Go Power has a surge rating of 2000W, so no problem there.

What is being referred to is the inrush current, the current it takes to start from stall which can be as high as 8 to 10 times the maximum rating for a few milliseconds, a Kill-a-watt meter cannot capture this, you would need a clamp on ammeter with inrush feature. Not saying it won't work, just don't be surprised if it doesn't. Is it a pure or modified sine wave, modified are not the best for motors.

Oh, I'm a firm believer in pure sign wave and I try to warn people away from modified.

The placard does say 11.6A, (1400W). I thought I read somewhere that energy efficient appliances have soft start built in. Plus I've run it with my little Yamaha EF2000i inverter gen, which is rated at 1600W with a 2000W surge (not much different than my Inverter). We had a 6 hour blackout and the gen never missed a beat. I was also running my 55" TV and directv box (maybe 120W total), one of the many advantages of satellite TV. Not affected by blackouts.

• Registered Users Posts: 3,016 ✭✭✭✭✭
A couple of thoughts on your tracker pole idea.

First, you may want to quantify your expected harvest gains with tracking vs fixed tilt. Time of day tracking won't help much in winter as the suns path is mainly in the south. In summer the gains can be significant, but do you have a way of using the extra harvest?

Second, wind load is likely to be more of an issue than just the weight of the panels in design of structure.
Off-grid.
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
• Registered Users Posts: 33 ✭✭
edited January 2017 #12

Well, this is my first effort in building an emergency power supply (and on a somewhat limited budget). Sure, I could simply buy more panels and build a fixed mount, but my rotating pole idea is easy and cheap. Rotating them 3 times a day during a blackout (morning-noon-evening) should give me way more power than a fixed position, and is certainly easy to do. Of course, I won't need to rotate them until there is a blackout.

I've often thought that if we had a major power outage in the summer (due to say, an earthquake), without air conditioning I'd have to pack a bag and leave. It can get up to 120 degrees here. So with my solar system I could run a small window A/C (500-600W) in a small room to ride it out. Of course, I would not be able to run it at night unless I add way more batteries, but it also gets much cooler here at night so I can just use fans. And as soon as the sun comes up (around 5:30am in the summer) the batteries start charging because I'll have the panels already aimed east from the night before. By 6am the sun is already plenty bright.

Yeah, it's somewhat theoretical in that I have not tried it in the real world yet. And maybe sometime in the future I'll buy more panels and build a fixed mount, but for now this is my plan.

Wind can be a problem so I plan for the panels to be below the height of the walls in our subdivision. Everyone's back yard has 6-7' stone walls and winds come mostly from the west. I have a spot picked out on the west side of my yard that gets full sun all day long, but far enough from the west wall to still get full sun well into the afternoon/evening.

One end of the pole will be mounted to some poles I'll be cementing into the ground. I certainly don't want to wake up and find the panels in my swimming pool. Right now it's too cold to pour concrete so I'm on hold.

• Solar Expert Posts: 4,765 ✭✭✭✭
St8kout said:
...So with my solar system I could run a small window A/C (500-600W) in a small room to ride it out...
NO, you could not.

At high temps, your duty cycle would be almost continuous. A Small window unit will use roughly 500 Watts. Your system, while 650 Watts of array, will normally produce only 650 x .75= @490 watts, in addition, your inverter will use roughly 15% of that for an AC production of about 425 watts, and this is with out any storage(battery) or any other loads or losses.

Likely your production will be even less with very hot panels and of 155 ah at 24 volts, won't run the ac for very long and require recharging. Through put for use of stored energy is roughly 50% total losses.
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
• Solar Expert Posts: 814 ✭✭✭✭
St8kout said:

Well, this is my first effort in building an emergency power supply (and on a somewhat limited budget). Sure, I could simply buy more panels and build a fixed mount, but my rotating pole idea is easy and cheap. Rotating them 3 times a day during a blackout (morning-noon-evening) should give me way more power than a fixed position

No, it won't.  You might get 20% more power but that's about it.  If you have the money/time I'd just add another panel.

I've often thought that if we had a major power outage in the summer (due to say, an earthquake), without air conditioning I'd have to pack a bag and leave. It can get up to 120 degrees here. So with my solar system I could run a small window A/C (500-600W) in a small room to ride it out.

To do that you'd need a beefy inverter, a good battery (i.e. low resistance to handle starting surge) and about 1000 watts of panels.  If you want to run it close to sunset make that 2000 watts.

Of course, I would not be able to run it at night unless I add way more batteries, but it also gets much cooler here at night so I can just use fans. And as soon as the sun comes up (around 5:30am in the summer) the batteries start charging because I'll have the panels already aimed east from the night before. By 6am the sun is already plenty bright.

"Plenty bright" does not equal "full power" - in the morning and evening the sun has to traverse a lot more atmosphere.

• Registered Users Posts: 107 ✭✭✭
Hold on a minute... Air Conditioning in an emergency?  Oh, maybe you are married:-).
Why not use a 12V pump to draw water from the swimming pool and pass it through a radiator in your room?
Camden County, NJ, USA
19 SW285 panels
SE5000 inverter
grid tied
• Registered Users Posts: 3,016 ✭✭✭✭✭
Use the pool water for a swamp cooler?
Off-grid.
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
• Registered Users Posts: 33 ✭✭
edited January 2017 #17

Hey, I'm in Vegas, and every summer I see my outdoor thermometer pinned at 120 degrees in the shade. Not kidding. And when the wind blows it's like a blast furnace.

I actually thought about trying to use the cold pool water with some kind of radiator, but small window A/Cs are cheap (plus I already have one). When my HVAC shut down on a Friday and the repair shop said they were booked until Monday afternoon, I pulled it out of storage and it was a life saver. People do die from extreme heat, and I'd prefer not to be one of them. It can stay above 100 degrees for some 4-5 months or so. It's not too bad for a little while, but being that hot all day long is very miserable.

Photowhit: Yeah, I figured it might be pushing it and when we get closer to summer I might buy more panels. I planned to see just how much drain there would be on the batteries once it's up and running and go from there.

Bill Novak: I found this solar calc website, http://pvwatts.nrel.gov and you can plug in different figures to see the result. On a yearly basis, it shows a 46% increase with 2 axis tracking over a fixed roof mount. Am I missing something? I used .6Kw for panel output.

Fixed mount = 1041KWh

2 axis tracking = 1523 KWh

1523-1041=482

482/1041=.463 x 100= 46.3% increase.

If I'm not mistaken I would need to add 277W worth of panels to a fixed mount to get the same power as 2-axis tracking.

I'm not trying to start an argument or anything as I'm the new guy who doesn't even have a system up and running yet. lol.

• Solar Expert Posts: 2,401 ✭✭✭✭✭
Heat is the solar enemy, battery life is reduced, panel output is reduced, refrigerator and AC demand increases it's  tough to get through those temperatures, I have to endure only 2 months of 120 Deg F and have been in Vegas in July/August and undestand what you are talking about. My question is how often do you have outages?  Seems a lot of expense for a backup system, not to judge. If you were to have an array to run AC while the sun shines and transfer to grid for night, would save on the utility bill rather than panels sitting in the sun without using their potential energy. A battery kept in the cooled space would last significantly longer, as would related electronic devices, charge controller, inverter etc. Note, if a battery is not used much, the investment will be wasted, it will die over time rather than through useage.

Running a refrigerator in such heat increases demand significantly, around 50% and would be better off in a conditioned environment. If appliances such as an INVERTER  mini split and refrigerator were used, in conjunction with good insulation, my belief is it's doable, in fact that is my plan for next month, albeit I do not have grid. The inverter units would allow a smaller inverter as there is no inrush to worry about and both will use less than an old technology refrigerator and window rattler AC unit and the mini split is quite.

So going back to your original post, if you were just considering a refrigerator, I doubt that your array or battery are large enough in 120 Deg temperatures, in fact I'm pretty sure as I first tried 200Ah at 24V with a more efficient refrigerator and that was marginal, found out that adding 35W fan overnight, 6 hours,  was enough to drag the battery down too far. My array, at 1500W, was not a problem but had to increase the bank to 300Ah to stay within safe limits of discharge. My plan to do AC involves building a completely new and seperate system of 300Ah at 48V and a 1000W array , leaving the existing system as is, since it works. Solar is NOT cheap especially off grid, building a system to cover odd outages is not something I would consider because your needs will exceed your expectations, as you have alluded to, the need for AC. Just some thoughts to consider, if it is an emergency system, base it on minimalist expectations.
1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank
900W  3 × 300W No name brand Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal as a backup system.
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergencies and welding.
• Solar Expert Posts: 4,765 ✭✭✭✭
St8kout said:
Photowhit: Yeah, I figured it might be pushing it and when we get closer to summer I might buy more panels. I planned to see just how much drain there would be on the batteries once it's up and running and go from there.
No you are not "pushing it", it's not realistic at all!

I've been there and done that, when it comes to running and air conditioner on a small system. With a well insulated cabin, 6" walls, built in the shade, I was able to run 5 hours+/- on battery system of 4 golfcart batteries with about 230ah at 24 volts and 1000 watts of array, I increased the system to about 1600 watt array to give me more daytime running. I also shut down the fridge to give me more running time on some summers.

St8kout said:
Bill Novak: I found this solar calc website, http://pvwatts.nrel.gov and you can plug in different figures to see the result. On a yearly basis, it shows a 46% increase with 2 axis tracking over a fixed roof mount. Am I missing something? I used .6Kw for panel output.

Fixed mount = 1041KWh

2 axis tracking = 1523 KWh

1523-1041=482

482/1041=.463 x 100= 46.3% increase.

If I'm not mistaken I would need to add 277W worth of panels to a fixed mount to get the same power as 2-axis tracking.

The site is for grid tied systems, Off grid systems don't work the same.

Off grid systems must have greater losses as they must fully charge a battery regularly. Think of the grid as a battery bank that is never full. It will take the energy if it can be produced. If you do a grid tied system it is accurate. In general you need about 3x the amount of array to produce as much usable electric in an off grid system. I can expand on this later. but energy going into the grid losses about 1-3% going through the inverter. In an off grid system, using stored energy the losses are roughly 50% through the charge controller, battery, wiring and inverter.

You have used the figure of .6 kw for output. Realistically your 650 watt array will produce about 75% of it's panel rating, or about 650x.75= 487.5 watts, though likely even less with your high panel temperatures. You might be able to find the NOCT (Normal Operating Cell Temperature) values for your panels.

Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
• Solar Expert Posts: 814 ✭✭✭✭
St8kout said:
Bill Novak: I found this solar calc website, http://pvwatts.nrel.gov and you can plug in different figures to see the result. On a yearly basis, it shows a 46% increase with 2 axis tracking over a fixed roof mount. Am I missing something? I used .6Kw for panel output.
Two issues there:

1) Those numbers are for a full time (constant adjustment) 2 axis tracker.  That's not the same as "elevating the end of a big 15' sturdy aluminum tube" and "Rotating them 3 times a day during a blackout."  1-axis performance would be much closer to what you will receive.

2) The NREL site gives you energy over a whole year.  If you are off-grid, you care about energy changes day by day - which is very different than yearly energy divided by 365.
• Registered Users Posts: 33 ✭✭
edited February 2017 #21
St8kout said:
Bill Novak: I found this solar calc website, http://pvwatts.nrel.gov and you can plug in different figures to see the result. On a yearly basis, it shows a 46% increase with 2 axis tracking over a fixed roof mount. Am I missing something? I used .6Kw for panel output.
Two issues there:

1) Those numbers are for a full time (constant adjustment) 2 axis tracker.  That's not the same as "elevating the end of a big 15' sturdy aluminum tube" and "Rotating them 3 times a day during a blackout."  1-axis performance would be much closer to what you will receive.

2) The NREL site gives you energy over a whole year.  If you are off-grid, you care about energy changes day by day - which is very different than yearly energy divided by 365.

Yeah, I know it's for grid tie but I was using it only to find the difference between fixed and tracking. I also ran the figures for just one month in the summer and it still came out to 46%.

Still, it does show that the max I can hope for is a 46% boost. During an emergency I'll have no problem with making smaller adjustments throughout the day if I'm coming up short on power.

On the 2 axis tracking, one axis is for seasonal adjustments so that won't be often. Once a month if that much.

Lastly, I guess I should point out that this started as a fun 'tinkering' project at first, and I'm also a bit of a 'prepper' although I hate that word. I grew up in hurricane country where we've been without power for weeks, and I didn't like it one bit. No hurricanes expected in Vegas but there is a very real chance of earthquakes, which could possible cause a very long term blackout. And of course Vegas is also on the terrorist's list as an ideal spot to hit. They've found pics of Vegas on known terrorist websites. I'm kind of thinking they'd love to turn off all those bright lights. Anyway, for any kind of SHTF scenario, I've been slowly but surely looking how to handle such things. I'm not one to sit and wait for the government to come to my rescue. I prefer to be at least a little self sufficient.

I know you can't prepare for every single possibility, but it's never a bad idea to have at least a few weeks of food and water on hand for such things. I keep about 4 months worth.

It's funny on the earthquake thing. My homeowner's insurance guy told me nobody here buys earthquake insurance. I asked him to give me a rate anyway. He had to make some phone calls and came back with, "Wow, I had no idea." I forget the exact figure but it was outrageous, as if I was in California. So on one hand they say earthquakes are rare, but on the other hand they want a fortune for insurance, as if they know something we don't. Now you have to assume they've done their homework when they gave me this rate, and it's so high you normally would not want to pay that much.

• Solar Expert Posts: 1,098 ✭✭✭✭
Photowhit said:

The site is for grid tied systems, Off grid systems don't work the same.

Off grid systems must have greater losses as they must fully charge a battery regularly. Think of the grid as a battery bank that is never full. It will take the energy if it can be produced. If you do a grid tied system it is accurate. In general you need about 3x the amount of array to produce as much usable electric in an off grid system. I can expand on this later. but energy going into the grid losses about 1-3% going through the inverter. In an off grid system, using stored energy the losses are roughly 50% through the charge controller, battery, wiring and inverter.

You have used the figure of .6 kw for output. Realistically your 650 watt array will produce about 75% of it's panel rating, or about 650x.75= 487.5 watts, though likely even less with your high panel temperatures. You might be able to find the NOCT (Normal Operating Cell Temperature) values for your panels.

In an off grid system, unless you can make full use of "opportunity loads" throughout the second half of the day you will be losing lots of potential power when your CC is in Absorb or float modes, provided it is designed right. Off grid people know of and take advantage of this potential.

2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

• Solar Expert Posts: 4,765 ✭✭✭✭
In an off grid system, unless you can make full use of "opportunity loads" throughout the second half of the day you will be losing lots of potential power when your CC is in Absorb or float modes, provided it is designed right. Off grid people know of and take advantage of this potential.
I don't think this helps much for the original poster. Even with the best use of opportunity loads, he's NOT going to run a air conditioner from his small system. The 650 watts of array won't run it by it's self and the battery bank won't run it long. He'll need to up the array and likely the battery bank for the system to do what he wants.

I hope he'll try it out, no reason not to, over a couple days... Perhaps with a clamp meter so he can see which way the energy is running from his battery bank when trying to run the air during the day.
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
• Registered Users Posts: 33 ✭✭
edited February 2017 #24

Yeah, I know it's a small system. I was originally going for just running my fridge, then I started looking into maybe running a small A/C only during the day. At night I could use the battery bank to run a fan, and it would start recharging in the morning when I aim my array to the East the night before.

Someone locally is selling new-in-box MiaSole CIGS panels, 111 Watt for \$50 each. They have a high nominal operating temp of 120 F, which as I mentioned before is 'normal' during the summer.

It says they are frameless so mounting costs are higher (one of the reasons they say is why they failed to catch on and went belly up.)

I'm thinking of two strings, one with my four-160W panels in series, and the other with four-111W panels in series, then parallel these two strings. The Vmp of one string is 77.6V, and the other is 73.2V.

What do you guys think? I'm considering buying 4 of them to add 444 Watts. It will just about max out my charge controller's input wattage, but then again, I know you don't always get the advertised rated wattage from a panel.

• Solar Expert Posts: 4,765 ✭✭✭✭
https://lasvegas.craigslist.org/for/6002781251.html

They are new sealed, have frames, Poly panels, 2 in series will give you 480 watts at a VMP of 74.2.

Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
• Solar Expert Posts: 4,765 ✭✭✭✭
Here is some information about the different panels, from someone else;
http://energyinformative.org/solar-cell-comparison-chart-mono-polycrystalline-thin-film/

While they do say Thin film in reference to heat is;
"Relatively low impact on performance"

"Tend to degrade faster than crystalline-based solar panels"
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
• Solar Expert Posts: 4,765 ✭✭✭✭
Most of the 'loss' in heat is in voltage, if you are using inexpensive PWM charge controllers, be sure to keep your batteries, panels and charge controller near each other. The voltage loss will be a less significant factor in the applied wattage, so long as you have sufficient voltage.
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
• Registered Users Posts: 33 ✭✭
edited February 2017 #28
Photowhit said:
https://lasvegas.craigslist.org/for/6002781251.html

They are new sealed, have frames, Poly panels, 2 in series will give you 480 watts at a VMP of 74.2.

Wait, the 240W panel shows a Vmp = 29.5v. I think you were looking at the Voc = 37.1v.

Not sure how to wire them with my 160W panels without using a separate controller in parallel. Any idea's?

So here are the specs of what I now have:

Two -160W panel specs: Vmpp = 18.5V, Impp = 8.65A

Two -165W panel specs: Vmpp = 18.1V, Impp =9.12A

The 240w panel specs: Vmp = 29.5V, Imp = 8.1A

If I wire them all in series, Voc = 164V, which exceeds the contoller's max Voc of 150V.

So I can only add one - 240W panel for a total array of 830W, and I only gain about 190W because Imp gets pulled down to 8.1A, right?

• Solar Expert Posts: 2,401 ✭✭✭✭✭
Base your PV voltage on battery voltage, ideally you need to be roughly  2× battery voltage with  MPPT, reason why 60 cell panels are a perfect fit, 29.5V is close to 24V double voltage for a 12V system. The 160/165 W panels you have are 36 cell, the closest you can get is series 160&165 make 2 strings, parallel the 2 for about 36 vmp. which I believe is where you started this discussion.
1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank
900W  3 × 300W No name brand Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal as a backup system.
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergencies and welding.
• Solar Expert Posts: 4,765 ✭✭✭✭
St8kout said:
Photowhit said:
https://lasvegas.craigslist.org/for/6002781251.html

They are new sealed, have frames, Poly panels, 2 in series will give you 480 watts at a VMP of 74.2.

Wait, the 240W panel shows a Vmp = 29.5v. I think you were looking at the Voc = 37.1v.

Not sure how to wire them with my 160W panels without using a separate controller in parallel. Any idea's?

So here are the specs of what I now have:

Two -160W panel specs: Vmpp = 18.5V, Impp = 8.65A

Two -165W panel specs: Vmpp = 18.1V, Impp =9.12A

The 240w panel specs: Vmp = 29.5V, Imp = 8.1A

If I wire them all in series, Voc = 164V, which exceeds the contoller's max Voc of 150V.

So I can only add one - 240W panel for a total array of 830W, and I only gain about 190W because Imp gets pulled down to 8.1A, right?

Sorry, I was having a hard time reading the info panel, you will want \$70-75 volts VMP. I think there is another in your area craigslist, other than the same seller Topoint panels which are in the range, but a bit more expensive per watt.
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
• Registered Users Posts: 33 ✭✭
edited May 2017 #31

Finally got it all up and running, and after looking at it on paper for so long, I almost can't believe how well it's working. It's currently running my small 5000 btu A/C with power to spare. I found THE smallest wattage A/C on the market (rated 410 watts but never draws more than about 380 watts, and it cools like a champ.) As long as the sun is shining it's not drawing any power from the battery bank at all. Of course, during an actual blackout I'll plug in my fridge instead, and it should be able to run it 24/7 as it uses less power than the A/C.

As you can see from the meter, I'm getting 29.6v at 15.6 amps from the panels. It only shows how much power it needs from the panels, not how much they are actually producing. Without a load it reads at around 41v at 0.1 amp.

The mounting for the panels is simple, easy, and practical, although I'll admit not professional or as nice as a roof mount. It's two-axis tracking. Adding or removing the cinder blocks makes for seasonal tracking, and I'll need to add another block when summer gets here. The array see-saws for dawn to dusk tracking. 8' aluminum pole, 2 Unistrut bars, 2 U-clamps, a couple of 2x4s and the cinder blocks, to build it. Digging the hole to cement the 2x4s in was the hardest part as our soil is more rock than dirt. My Realtor told me they use explosives to install swimming pools as it's the easiest way to go when building new subdivisions.

I have not bothered to determine just how much more power I can get from dawn to dusk tracking. I do know that I need to rotate it by around 1 pm from when it's aimed east for the morning sun, otherwise the A/C starts drawing battery power. I rotate it back to the east after the sun goes down, ready for the next day.

Thanks for all the help and advice.

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