confused need help

kayen

I have a question

Have
* 5 100 watt solar panels 18v each
*4 12v 200 amp deep cell batteries

How can I get started to build my own system.
If I wire series I will get less amps to battery, but i will get larger voltage. ( What is the benefit)
If I wire parrallel I will get stronger current amp to batteries.
I am confused, please help me.I am new and scared that if I wire series I will get less amps.
I want to get the most out of my system. will use for T.V.,dc Fans, led lights and small dc fridge also need to decide the wiring so I can buy controller

Many Thanks

BB.

Re: confused need help

Are you going for a 12 volt DC system? With 5 panels, to use them all, that is your only option (unless you get 1 more or only use 4).

Normally, I like to start with your loads and then design the system....

For this one, since you have the batteries, start with that and then work out from there.

4 x 12 volt batteries * 200 AH per battery. That will be a relatively large 12 volt battery bank--Normally I would suggest 24 volt system--but we can start with 12 volt to see what things look like.

First, normally, we recommend 1-3 days of battery backup power (no sun), and 50% maximum discharge. So using 2 days and 50%, we would get:

• 4x 12 volt * 200 AH * 1/2 days of "no sun" * 0.50 max discharge = 2,400 Watt*Hours per day of DC power
• 4x 200 AH * 1/2 days * 0.50 = 200 AH per day @ 12 volts
• 2,400 WH of DC * 0.85 AC inverter efficiency = 2,040 Watt*Hours of 230 VAC 50 Hz inverter power

So, if you had a 200 watt AC load, you would expect around:

• 2,040 WH per day = 10.2 hours of 200 watts for 2 days (to 50% maximum discharge)

Next, charging your battery bank. Again, a handy rule of thumb is ~5% to 13% rate of charge for the battery bank:

• 4x 14.5 volt batt charging * 200 AH * 1/0.77 solar panel + charger losses * 0.05 rate of charge = 753 Watts of solar panel Minimum rate of charge
• 4x 14.5 volt batt charging * 200 AH * 1/0.77 solar panel + charger losses * 0.10 rate of charge = 1,506 Watts of solar panel for "nominal" rate rate of charge
• 4x 14.5 volt batt charging * 200 AH * 1/0.77 solar panel + charger losses * 0.13 rate of charge = 1,958 Watts of solar panel for "maximum cost effective" rate of charge

So, already, we are looking at 500 watts of solar panels as being a bit on the small size for that large of battery bank.

You can reduce the battery bank size by one or two strings, or buy more solar panels.

Regarding solar irradiation data for your location--You will need to find out how much sun you have (by season)--A quick check shows that the minimum average sun for the region is around 3,000 to 4,000 WH/m² -- I will pick 4,000 WH/m² for this example (by the way, "1 hour of sun" is ~1,000 WH/m² or call it "4 hours of sun" per average day for at least 9 months a year) assuming you are using an 85% watt efficient 230 VAC inverter:

• 500 Watts * 4 hours of sun * 0.52 system losses = 1,040 Watt*Hours of 230 VAC power

If this is mostly DC power, the system derating will be closer to ~61%:

• 500 Watts * 4 hours of sun * 0.61 system losses = 1,220 Watt*Hours of 12 VDC power

Next, the solar array... 500 watts of panel in parallel with Vmp=18volts will give Imp-array~27.8 amps of current. That is a fairly heavy current and it is sort of difficult/expensive to send that amount of current a very long distance at "18 volts"...

So, I need to know how far from the solar array to the charge controller/battery bank the distance will be to calculate wire diameter.

For a larger solar system, I would be suggesting a more expensive solar charge controller and placing the panels in series/parallel (2-4 panels in series, and 1-3 strings or so in parallel). The higher voltage reduces current (Power=Volts*Current). Reduced current allows us to reduce wire diameter (or send the power a longer distance).

Anyway--Lots of questions for you. And I will probably just confuse you if I start going farther out in my assumptions.

-Bill

kayen

Re: confused need help

You are not losing/gaining anything with series/parallel connections... Still the same amount of energy storage in your battery bank. Typically higher voltage battery banks are better for higher powered inverters (keeps current lower in the wiring):

Power = Voltage * Current

So if voltage goes from 12 volts to 48 volts, current will be cut to 1/4 amount. My question is ( What is the importance of the current) I understand the wattage issue, but get lost when it comes to current.

vtmaps

Re: confused need help

kayen wrote: »

If I wire series I will get less amps to battery, but i will get larger voltage. ( What is the benefit)
If I wire parrallel I will get stronger current amp to batteries.

When you choose a charge controller, the controller will take care of the volts and amps to the battery. If your panels are close to the controller you can wire them in parallel and use an inexpensive PWM type of controller. If the batteries are further away and/or you want to get the maximum power out of your panels, use an MPPT type of controller. The MPPT will allow you to wire the panels in series, and it will convert the high volts low amps into lower volts higher amps that are perfectly suited to the battery's needs.

--vtMaps

kayen

Re: confused need help

Very Informative

kayen

Re: confused need help

The MPPT will allow you to wire the panels in series...so must use MTTP to connect series?

waynefromnscanada

Re: confused need help

Hi Kayen. Question on that "small DC fridge".
Do you know the daily power it consumes? Some of them, especially the ones that will run off AC, DC, or propane, are BIG energy hogs compared to the more efficient types with compressors.

waynefromnscanada

Re: confused need help

kayen wrote: »

The MPPT will allow you to wire the panels in series...so must use MTTP to connect series?

Not MUST, but if you don't, you'll loose a HUGE amount of power, possibly most of you're power. Depending on your system arrangement.

kayen

Re: confused need help

I have 2 one that runs off natural gas and the other is dc / 80watt

kayen

Re: confused need help

sorry went and checked, it's 12v/72watts 186L ( medium size )

waynefromnscanada

Re: confused need help

kayen wrote: »

I have 2 one that runs off natural gas and the other is dc / 80watt

The DC 80 watts sounds like an absorption type, same as the propane, only electric heat is used to drive the process. If so, you're looking at almost 2 Kwh per day to run it
If you don't hear a motor running, and instead sometimes hear a slight bubbling sound, then yes, it is absorption like the propane.

kayen

Re: confused need help

runs off 200watt mono solar panel and 100amp deep cycle battery, dont forget the fridge compressor only runs for 20 minutes an hour, also we have plenty of sun

waynefromnscanada

Re: confused need help

kayen wrote: »

runs off 200watt mono solar panel and 100amp deep cycle battery, dont forget the fridge compressor only runs for 20 minutes an hour, also we have plenty of sun

Oh, so it IS a compressor type and NOT absorption! GOOD! So it will use just under 0.6 Kw/hr per 24 hour day, not the almost 2 Kwh/day of an absorption type.

Cariboocoot

Re: confused need help

This might help you understand the reasons for choosing one system Voltage over another: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power