Which inverter?

Saggys · December 2013

I will be installing a off grid system for our cabin this spring. It will have LED lighting, LCD TV/DVD, toaster, coffee maker and most importantly ceiling fans. I have two inverters, a Trace DR1524 and a Trace PS2512, they are both modified sine wave inverters but the PS is basically a SW series without the control panel and offers more steps in the creation of its output wave form. 900 watts of PV will feed either two L16's or four T105's depending on which inverter I select. Charge controllers will be PWM which I already have.
I am leaning towards the 12volt inverter because of the ceiling fans (should operate quieter) and the better quality inverter. I can keep my cable runs from my pole mounts to charge controller at 50 feet or less. Also I will have some panel shading in early morning and late afternoon. The panels are 12volt and if wired two in series if one of the two panels is shaded I would lose both panels output. I have all equipment to do either inverter set up other than the batteries, also I am not interested in a MPPT controller at this time as I am happy with my obsolete equipment choices.

Blackcherry04 · December 2013

Re: Which inverter?

Saggys wrote: »

I will be installing a off grid system for our cabin this spring. It will have LED lighting, LCD TV/DVD, toaster, coffee maker and most importantly ceiling fans. I have two inverters, a Trace DR1524 and a Trace PS2512, they are both modified sine wave inverters but the PS is basically a SW series without the control panel and offers more steps in the creation of its output wave form. 900 watts of PV will feed either two L16's or four T105's depending on which inverter I select. Charge controllers will be PWM which I already have.
I am leaning towards the 12volt inverter because of the ceiling fans (should operate quieter) and the better quality inverter. I can keep my cable runs from my pole mounts to charge controller at 50 feet or less. Also I will have some panel shading in early morning and late afternoon. The panels are 12volt and if wired two in series if one of the two panels is shaded I would lose both panels output. I have all equipment to do either inverter set up other than the batteries, also I am not interested in a MPPT controller at this time as I am happy with my obsolete equipment choices.

I'd opt for the the PS 2512 based on your loads and having ceiling fans on MSW for 20 years, they tend to be very annoying. The age of both Inverters is kind a problem, so with that in mind I'd buy the t-105's where you could reconfigure them and use the other as a emergency spare.

BB. · December 2013

Re: Which inverter?

You have three loads which are problems... the Fans, Toaster, and Coffee maker are all something you really need to confirm.

The Fans because they may take a fair amount of power and operate 10+ hours per day... That can add up in Watt*Hours very quickly.

The Toaster and Coffee Maker do not run very long, but take a lot of power (probably 900-1,500 watts). That is a lot of power. And the coffee maker if you leave the hot plate on can take a lot of energy. And some coffee makers have been found to take a fair amount of power when "off" (standby).

Get a Kill-a-Watt type meter and start measuring your loads and figuring out how many Watt*Hours (kWatt*Hours) per day you will need to supply (and peak wattage).

Also, double check the voltage drop from the panels to the charge controller. 50 feet of wire run is not insignificant. And if you run the array at 12 volts--Makes the problem even worse. A 24 volt battery bank + PWM controller may be a better fit...

Using a simple voltage drop calculator:

900 watt array / 17.6 volts Vmp = 51 amps (guess)
51 amps with 3% drop (17.6*0.03=0.5 volt drop) and 51 amps -> 2/O awg cable will give 0.5 volt drop (12 volt PWM controller)
25.5 amps @ 35.2 volt array 3% drop or 1.1 volt drop and 50 feet -> 6 awg cable will give 1.2 volt drop (24 volt PWM controller)
12.75 amps @ 70.4 volt array 3% drop or 2.1 volt drop and 50 feet -> 10 awg cable will give 1.5 volt drop (MPPT controller)

-Bill

Saggys · December 2013

Re: Which inverter?

I actually have two PS2512's (spare) with the SWRC and stacking cable although I am only going to use one. The DR1524 is NOS so it should be good? I also have a Onan LP 2.5kw generator for low periods of sunlight and to run when loads are heavy. The panels would be six 75 watt panels x2 on pole mounts going to power shed disconnects so wire size would be less with two separate charge controllers. What about the shading I experience early morning and late afternoon? Would I get better yield with 12volt configuration? Thanks for the replies.

The ceiling fans would be used in the summer for bed time and to circulate heat from the woodstove in the winter months, I would not try to use them 10 hours a day

BB. · December 2013

Re: Which inverter?

Even if you use two separate controllers--Wire size will be 1/2 per controller, but 2x the amount of wire--So coppers costs will still be about the same.

Wire gauge goes 3 numbers for 1/2 (or 2x) diameter, so the above calculations will be around +3 AWG smaller for the same voltage drop (with 1/2 the current).

2/O cables is (roughly) $2.50 per foot -- Or around $250 for 100 feet of cable for a 12 volt PWM system.

-Bill

Saggys · December 2013

Re: Which inverter?

Good point Bill. How about the shading?

waynefromnscanada · December 2013

Re: Which inverter?

One point I think was missed - - some coffee makers and even some toasters now have electronic controls which may not work properly on MSW, and MAY even let out some smoke. Just something to be aware of.
Shading - - - PV cells are in series, so any one cell in it's series string will basically shut down the whole string if it gets shaded. Think of the older Christmas lights where if one in the string goes out, they all go out.
Many solar panels however have more than one series string per panel, so in those cases, one cell shaded would only shut down part of the panel.

BB. · December 2013

Re: Which inverter?

As Wayne says, shading is bad-Solar Electric Panels need full/direct sunlight to output full voltage/current... At the very least, shading part of one panel will take out the entire panel's worth of output.

If you have series strings on PWM controllers, shading part of one panel will (usually) take out the production of the entire string.

There are ways around some shading, but it does not usually increase output that much--One person here figure out that his panel was two parallel strings of cells, and if he put the panel in "landscape", snow which would collect/melt last on the bottom edge of the panel would only cut 1/2 of the panel/strings's output.

In the end, if you can reduce shading (shorten/move vent stacks, trim trees, move panel away from chimney, make sure there are no overhead wires/ropes/cables, etc.)--All those will do a much better job of giving you more output.

-Bill

westbranch · December 2013

Re: Which inverter?

With the distance involved ~ 100 ; return, you might make a $$ case for a MPPT CC as you could go with smaller wire and less of it, as you could use 3 panels in series, and stay @12 v.

Saggys · December 2013

Re: Which inverter?

That is one of the reasons I want to stick with a 12 volt system. If all panels are wired in parallel I will only lose the panel shaded. Early morning and late afternoon are the times the panels will experience some shading. We are in a heavily forested area and I have already cut enough trees down! My current 12volt temporary system has been working well enough for us for lighting, toaster, coffee pot and its design is far from ideal. This is mainly weekend use with a week in deer hunting season.

westbranch · December 2013

Re: Which inverter?

sounds like it is turning into a permanent system, rather than temporary...

Vic · December 2013

Re: Which inverter?

Saggys wrote: »

... I have two inverters, a Trace DR1524 and a Trace PS2512, they are both modified sine wave inverters but the PS is basically a SW series without the control panel ...

Am a bit tardy to this conversation, but, The PS2512 IS a Pure Sine wave Inverter. Believe that this is that the PS in the model number means:

http://www.altestore.com/store/Inverters/Off-Grid-Inverters/2000-to-2999-Watts/Xantrex-Ps2512-2500W-12V-120Vac-True-Sinewave/p3565/

FWIW, Vic

Saggys · December 2013

Re: Which inverter?

westbranch wrote: »

sounds like it is turning into a permanent system, rather than temporary...

So True! Thanks everyone for the insight. I am going to run the twelve volt system and the expensive copper, if things do not work out I can switch the panel configuration in the combiner and switch to the DR1524 and the wire will be oversized.
I think the PS stands for Power Station, it is a 30+ to a 50+ step modified sign wave inverter.

Blackcherry04 · December 2013

Re: Which inverter?

A stepped sine wave inverter produces another “in between” AC wave form. Instead of having a single positive or negative pulse punctuated by an “off” period between, a stepped sine wave inverter is able to produce a series of different voltage levels which can be arranged to produce what is often described as a “Mayan temple” shape. The number of steps varies as the battery voltage changes. At higher battery voltages, there are fewer, but taller steps; at lower battery voltages, there are many shorter steps.

This approach produces a wave form with a much lower THD than a modified square wave inverter and offers good performance and DC-to-AC conversion efficiencies of more than 90%. Some of these inverters are even able to be grid-tied since the THD is low enough to meet UL and utility requirements.

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Which inverter?

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