What advantage of 34V panel compared to 18V?

paul12345

I am looking at a 320W/33.73V panel, producing 9.49 Amp. I have 3 year old panels spec is 150W/17.9V , the 340W only producing an extra 1.12A. What is the advantage in the higher voltage panel compared to the lower? 

This is for an off-grid installation.

BB.

The advantage to the solar panel manufacturer is that they can use less copper in the manufacture of solar panels (and the wiring for the solar array),

Power = Voltage * Current = I^2*R = V^2/R

So, the higher the working voltage, the less current, so smaller AWG wiring.

For you--I depends on what your off grid system is setup as...

In simpler times, we only have PWM charge controllers (pulse width modulation). That is, simple "on/off switching" solar charge controllers.

And the solar panels had to match their output voltage to the battery bank voltage. For example, to charge a 12 volt battery bank @ ~14.7 volts, a Vmp~18 volt solar panel/array was needed. This "higher voltage" allowed for the effects of heat on solar cells (hot cells, lowers Vmp-arrray-hot). And for some wiring voltage drop. This was the most "cost efficient" solar array to connect to a PWM controller charging a 12 volt battery bank.

Then came two changes to the market. One was MPPT (maximum power point tracking) solar charge controllers. These MPPT controllers were (for the most part) buck mode switching power supplies which could take high voltage/low current  from the solar array and efficiently (95% or so) down convert to low voltage/high current needed to charge the battery bank.

This allowed off grid installations to use Vmp-array to be 100 Volts, to even 400 volts with modern solar charge controllers. This allowed us to save on copper costs... A 400 volt solar array can use 1/10th the amount of copper as a 40 volt solar array (P=V*I, 10x the voltage = 1/10 current for same power).

And the whole Grid Tied/Solar Interactive market for solar homes. These systems were much larger than a typical small off grid cabin, and with government subsidies, the huge number of solar panels being made, it was more cost efficient for both 1) high voltage solar arrays (3-10 kWatt arrays) and large format solar panels (from 140 Watt off grid "common" panels, to 200-300+ Watt large format panels--fewer panels to mount, fewer panels to wire, large format panels with higher Vmp-panel voltage--less copper inside--more solar cells in series to make larger panels).

There are disadvantages to higher Vmp panels... One is "mixing" Vmp~30 volt panels with Vmp~18 volt or 36 volt panels... It usually cannot be done on a single MPPT controller. You need a second controller for the "different" Vmp panels. (i.e., one array may run 2 series * 36 Vmp = 72 volt array and another array may run at 3 series * 30 Vmp = 90 volt array.

Another issue is some large format panels have working voltages >50 volts... This panels can be an issue with, for example, a 48 volt battery bank and a choice between 1 series = 50 volts--Too low of voltage to charge a battery bank at ~60 volts; and 2x series for 100 volts and too high of voltage for some MPPT controllers Vpanel input voltage.

In general, today's Vmp~18 volt panels are (roughly) 2x the cost per Watt vs other Vmp=30/36/etc. large format panels.

And if you have a large solar array and it is some distance from the home/power shed, you have newer MPPT controllers that can take upwards of 400 VDC Vmp--At the cost of (for now) of much more expensive high array voltage MPPT controllers.

Clear as mud?

-Bill

NANOcontrol

The higher voltage grid tie also dominates the market so much cheaper per watt than battery voltage panels. Much higher packing density, less wasted space for frame margins gives more power for the same space. 

paul12345

Thanks, I have limited roof space. The more watts I can squeeze into sq. foot, the better.