cabin solar system

[metamorphesis]

hello, i am about to order 6x100w amorphous panels for a small cabin. they seem a good price at $200 each. i only plan to run a small fridge, laptop and a few led lights. i know i probably dont need this many panels but may add a few more appliances in time and wanted to keep the panels same. i only have 2x 100ah batteries atm and plan to have them in a 24v setup. my question is the panels have a max voltage of 90v and from the 24v controllers ive seen mostly accept 50v max. 48v controllers seem take higher voltages but are more expensive. any help would be greatly appreciated.
phil
australia

[Mike90250]

are you sure you want amorphous panels? Best check the warranty, most of them loose a fair amount of power the first 2 years.

600W will not be enough to run a fridge and other stuff year round. Maybe for 3 summer months with long days.

You need to calculate your loads first, and then plan a system.

[Naptown]

90 volts. is that maximum system voltage or the actual output of the modules?
I have no experience with thin film but a 90 volt output voltage on a module rated at 100 watts seems high. If all 6 together output 90 volts wired in series you may be able to come up with a lower voltage output by varying string sizing from say six in series to 2 strings of 3

[russ]

Hi Metamorphesis - Welcome to Solar Panel Talk!

To calculate the loads -

1) lamps - more or less wattage X hours of use.

2) fridge and other appliances - you need to use a meter like Kill A Watt to measure actual consumption over 24 hours or more.

Russ

[Mike90250]

90 volts. is that maximum system voltage or the actual output of the modules?.....

Sure, if the modules are designed for grid tie use.

[GreenPowerVideos]

Calculating what you really need

Meta-

Indeed Mike is right.

You won't have enough power to do what you want.

You first calculate your daily power needs by identifying the power use of each item by looking at the plate on the rear of the item.

Say a refridge uses 500W. It actually draws about twice that to start the compressor.
So, your inverter must be sine-wave so that it can actually spin up the motor in the compressor. It also has to have a surge capacity of over 1KW.

That fridge is probably on for 20% of the day - considering the season it is operating in. So, 20% of 24 hours at 500W = 2.4 KWH per day.

Knowing that panels will produce one KWH a month for each 6 watts of panels, you'll
need 432 watts of panels just for the fridge. That's before losses. You really need to add 15-20% for battery & inverter losses etc.

Amorphous panels are cheap because they decay in output over time. I'd never use them. Buy name-brand polycrystalline or mono-crystalline panels at about the 200 watt size. They have dropped in price...

Wiring of panels is determined by the voltage you require at the charge controller input. This is determined by the distance of the panels to the battery/charge controller box, the battery bank voltage and the charge controller max input voltage.
You have to know how to read the panel's label. There are several items listed. Voltage under load and current in circuit are the most important. You do not want to exceed the battery bank by more than 3X voltage.... or charge controller efficiency goes down. You also want a MMPT charge controller.

My goal is to teach everyone how to do this safely. You can't learn it from youtube videos. I'm glad to answer questions, but there is a lot to know. It isn't rocket science
(OK, I am a rocket scientist), but it takes dedication to learning the ropes. You can cause an explosion of the battery bank... acid all over... fires etc. It is serious.
Even if you are lucky enough to hook it up -and it sort of works, it will fail in the long-term if you don't follow standard electrical principals.

Best of luck!

Bob Nagy

[metamorphesis]

thanks everyone for ur help. just glad i didnt order the thin film panels i think i am going to relook at my fridge choice, panel outputs etc. i will post some things i have in mind to see what ppl think.maybe a 12v 80litre fridge would use less amps and not have the big draw on startup. i also have a 1800w generator that i was going to use on low light days. i have seen on ebay inverters that also have battery charging ability. around 30amp 3 stage...is this possible to run off such a small generator?
thanks again for ur help

[metamorphesis]

hi everyone and thanks again for your help so far.
i have now been looking at mono panels around the same size. am thinking 2x 250w. here are the specs..
Rated Power - 250W
Max Power Voltage - 48V
Max Power Current - 5.21A
Open circuit Voltage - 57.6V
Short circuit Current - 5.62A
Net Weight - 20.5kg
Dimensions - 1580 x 1050 x 46mm
Temperature range - -45 to 85 deg C
Frame Material - Aluminium
Output Tolerance - 3%

Max System Voltage - 1000V
I am hoping to use with a 24v battery system. can anyone tell me if these panels are suitable?
also wondering about these inverter that have upto 50amp charging and if they would be any good using my 1800w generator to charge batteries when no sun....

http://cgi.ebay.com.au/2400W-Pure-Sine-Wave-Inverter-50Amp-Charger-24V-/150512502956?pt=AU_Boat_Parts_Accessories&hash=item230b3e88ac

otherwise i was thinking of a small 24v inverter and a seperate charger to use with my generator..does anyone know how many amp charger i can use with an 1800w generator?

I am still thinking of a 12v/24v fridge as this will be my highest power consumer and am hoping to use only 2x 100ah deep cycle batteries.

regards
phil
australia

[Mike90250]

Rated Power - 250W
Max Power Voltage - 48V

With these panels, you would need a MPPT charge controller, and to manage 500W, will have to be one of the expensive ones from Morningstar, Blue Seas, Rogue, Outback or Xantrex. With a PWM controller, you will loose half the PV array power, charging a 24V battery bank.

If you locate panels with a 30-35V Max Power Voltage, you could use a PWM controller, and not loose as much power.

[Naptown]

Plan on replacing batteries periodically. The better you maintain the charge etc the longer they will last.