## Location & Climate

**Location:** Corvallis, OR

**Record low:** -22°C (-7°F)

**Average low:** 1°C (34°F)

**Average high:** 28°C (82°F)

**Record high:** 42°C (108°F)

## Photovoltaics

**Module:** SolarWorld 175 W

**Voc:** 44.4 V

**Vmp:** 35.8 V

**Temperature coefficient:** -0.33%/°C

**Mount type:** Parallel-to-roof mount (4 in. from roof surface to back of module)

## Equipment

**Inverter:** PV Powered 5200

**Maximum Voc:** 500 VDC

**Minimum Vmp:** 240 VDC

## Calculations

**Step 1.** Calculate the adjusted voltage for low temperatures.

Vadj = 44.4 V x {1 + [(-22°C – 25°C) x -0.33%/°C]}

Vadj = 51.3 V

Determine the maximum number of these modules in series for this inverter at this location:

Maximum number per string:

Component’s max. Voc ÷ Vadj for low temperatures

500 VDC ÷ 51.3 V = 9.7 modules

Round down to the next whole number—in this case, nine modules is the maximum number in series.

**Step 2.** Calculate the adjusted voltage for high temperatures.

**Vadj = 35.8 V x {1 + [(28°C + 35°C – 25°C) x -0.33%/°C]}**

(Note the additional temperature—35°C—due to the racking method.)

**Vadj = 31.3 V**

Determine the minimum number of these modules in series for this inverter at this location:

Minimum number per string:

Component’s min. Vmp ÷ Vadj for high temperatures

240 VDC ÷ 31.3 V = 7.7

Round up to the next whole number—in this case, eight modules is the minimum number in series.

Comparing these calculations to those for other equipment will determine if you may be better off with a different combination of equipment. The minimum value calculated should always be carefully considered and is rarely the best choice. In this example, if strings of eight modules are used, the resulting Vmp on an average day will only be 250.4—precariously close to the low value (240 VDC) of the sample inverter’s operating window.