4 busbar vs 2 Busbar solar panels which one to choose ?

Re: 4 busbar vs 2 Busbar solar panels which one to choose ?

drraptor wrote: »

Solar Irradiance in my area is 1800 KWh/m²
while Solar Insolation is given below in the table.

I am not sure where the 1,800 KWh/m² is coming from.

There are many ways of listing the amount of "sun" you get per day/year, etc...

Your table below:

Average Solar Insolation figures

Measured in kWh/m²/day




Jan
Feb
Mar
Apr
May
Jun


3.25
4.28
5.35
6.39
7.31
7.22


Jul
Aug
Sep
Oct
Nov
Dec


6.11
5.66
5.50
5.00
3.92
3.19



http://solarelectricityhandbook.com/solar-irradiance.html

Note the "Measured in kWh/m²/day" comment.

Thank makes your numbers (January) 3.25 * 1 kWh/m²/day = 3.25 kWh/m²/day.

We slang that as 3.25 hours of sun per day (3.25 hours of noon-time equivalent sun per day).

So, for San Francisco California (really SFO airport), using PV Watts for a 1 kWatt fixed array with 0.52 off grid efficiency:

"Station Identification"
"City:","San_Francisco"
"State:","California"
"Lat (deg N):", 37.62
"Long (deg W):", 122.38
"Elev (m): ", 5
"PV System Specifications"
"DC Rating:"," 1.0 kW"
"DC to AC Derate Factor:"," 0.520"
"AC Rating:"," 0.5 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 37.6"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:","12.5 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 3.62, 54, 6.75
2, 4.59, 62, 7.75
3, 5.22, 79, 9.88
4, 6.11, 89, 11.12
5, 6.36, 95, 11.88
6, 6.47, 94, 11.75
7, 7.01, 105, 13.12
8, 6.67, 99, 12.38
9, 6.62, 95, 11.88
10, 5.41, 80, 10.00
11, 3.87, 55, 6.88
12, 3.35, 50, 6.25
"Year", 5.45, 958, 119.75

I get 3.62 hours of sun per day (and an average of 54 kWH per month) for January:

3.62 hours of sun * 1,000 Watt array * 0.52 off grid system eff = 1,882 Watts of "average usable" AC power per day

But that is really spread out over 9 hours of the day. Using January 15th hourly output (1966 was the "representative" average day over ~20 years of measurements):

1966, 1, 15, 08:00, 0
1966, 1, 15, 09:00, 107
1966, 1, 15, 10:00, 241
1966, 1, 15, 11:00, 340
1966, 1, 15, 12:00, 399
1966, 1, 15, 13:00, 407
1966, 1, 15, 14:00, 374
1966, 1, 15, 15:00, 302
1966, 1, 15, 16:00, 191
1966, 1, 15, 17:00, 25
1966, 1, 15, 18:00, 0

So a panel rated @ Standard Test Conditions (STC) of irradiance of 1000W/m , spectrum AM 1.5 and cell temperature of 25℃.

Will output higher current or voltage in my area ? And what is the difference btw the thermal characteristics of Polycrystalline and Mono-crystalline.

More or less, current is proportional to the amount of direct sunlight hitting the array. Very little direct light, very little output current.

Vmp (voltage maximum power) is a combination of minimum sunlight (solar panel needs "week morning or evening direct sun to "hit" Vmp), and at that point Vmp is a function of solar cell temperature. Vmp is rated at STC (standard test condition of ~25C cell temperature). In warm climates, the sun heats up the solar array and causes Vmp to fall (by ~20% drop in very hot/sunny weather).

In sub freezing weather (and below) Vmp-array-cold can exceed Vmp-stc.

how does cell temperature affect Voltage and current ? I know extremely low temperature increases the Cells voltage e.g a panel rated at 37.8 will output at ~40V.

Technically, Imp-current rises as the temperature increases. And Vmp falls as the temperature increases. Since the Tcoeff for Voltage is about 10x greater than the Tcoeff for Amperes, we tend to "ignore" the effect of cell temperature on panel output current.

And Power Tcoeff is (mostly) driven by the Voltage Tcoeff. Panel power will fall with increasing cell temperature.

It gets more complex because PWM type charge controllers really only "control" panel Imp current--So PWM controllers have little output change with respect to temperature (as long as Vmp>~17.5 volts for a 12 volt battery bank).

MPPT charge controllers are "constant power" down converters... So their maximum output power is affected by panel temperature. Power=V*I, so change in V will give change in available power power.

When designing an off grid solar power system... Your "critical points" are Vmp-array-Hot (minimum voltage needed to charge the battery bank or "run" the GT inverter) and Voc-cold (very cold arrays have high Voc output voltage--which can damage a charge/GT controller).

For a 140-150 volt input MPPT charge controller in a cold climate--A maximum Vmp~100 VDC will give a maximum Voc~140-150 VDC.

Is this calculator any good http://www.sunearthtools.com/solar/payback-photovoltaic.php ?

Financial models are only as good as your assumptions... In the US, we have a claimed ~1-3% inflation rate--In my life it is over 12% from what I have seen and paid for. Also, wages are not keeping up with inflation.

I personally do not see Solar Power as an investment. It can result in a savings of energy costs (utility power + solar subsidies) or for off grid homes where utility power is very expensive to bring lines out, or simply not available. Subsidies will change over time (there is not utility and PUC push back against GT solar in some locations now). Add that Americans move (at least used to) move once every ~7 years--Will your system give you a good return on investment before you move--And how much would a home buyer pay you for the system.

I know my ~$35k installation would cost around $10k if installed new today... Why would somebody pay >$15k for a 10 year old solar array+AC inverter?

and will this sun position calculator be of any help http://www.sunearthtools.com/dp/tools/pos_sun.php?lang=en

Probably fine--But you still need a good model for the shading on your array. My guess--Any one panel that is shaded will kill production for that entire solar array string. I have two strings on my GT inverter, shading on one panel will kill array production by ~50% (close enough for solar work).

-Bill