Siemens Solar utility and building systems: seven plants

At the large end are the utility and building systems. They show how the same silicon technology was scaled: from 6 modules operating a 115 kV switch to 12,240 modules at Kerman. Where the notes allow it, we check the stated figures against the component lists.

New Munich Trade Fair Centre, Germany

System components as published:

• 7,812 frameless 130 W modules with 84 mono-crystalline cells each (SM130-L)
• 3 × 330 kVA inverters in master-slave-slave mode
• 4,000 VAC feed into a 20,000 V transformer
• South-facing at 28° tilt
• Array: 21 modules in series by 372 in parallel (340 to 420 VDC)
• Design output 1,000,000 kWh a year, 4 % of the centre’s needs and over 50 % when no events are on

Our arithmetic:

• 21 × 372 = 7,812 modules ✓. 7,812 × 130 W = 1,015.6 kW ✓ (stated 1,016 kW).
• 7,750 m² of array for 1,016 kW is 131 W/m², close to the 129 W/m² we calculate for the SM55.
• 1,000,000 kWh ÷ 1,016 kWp is about 984 kWh per kWp (calculated).
• The note equates one million kWh with the average demand of 340 German households, or about 2,900 kWh each.

The note calls this the world’s largest rooftop PV plant at the time.

Battle Creek Environmental Magnet School, St. Paul, Minnesota

System components as published:

• 234 × M55 modules pre-mounted on Unistrut racks (36 × Unistrut P4000 racks)
• 9 × PV source circuit protectors
• 3 × 4 kW Omnion inverters

Our arithmetic:

• 234 × 55 W = 12.9 kW against the stated 12 kW, so the rating used is about 51 W per module. 15,000 kWh ÷ 12 kW is about 1,250 kWh per kWp (calculated).

The array is suspended over a roof that was designed only for snow loads, which is why it was prebuilt on racks.

PVUSA US-2, Kerman, California

System components as published:

• 12,240 × M55VJ mono-crystalline modules on eight tracker rows
• 650 kW peak DC
• Two Omnion three-phase inverters to 12.5 kV, tied to PG&E Kerman feeder 1104

Our arithmetic:

• 12,240 × 53 W = 649 kW, close to the stated 650 kW. But the fact sheet also lists 1,224 panels of ten 55 W laminates (550 W each), which would be 673 kW: the 650 kW figure matches 53 W per module, not 55 W.
• The sheet gives 502 kWac at PVUSA test conditions from two 275 kVA Omnion inverters, a DC to AC ratio of 650 ÷ 502 = 1.29.
• Array circuit 144 modules in series by 85 in parallel = 12,240 ✓. Design output 1,200,000 kWh a year, about 1,850 kWh per kWp (calculated: 1,200,000 ÷ 650).

The plant was built to demonstrate PV grid support: relieving overloaded summer-peaking distribution feeders.

Sacramento Municipal Utility District, Hedge Substation

System components as published:

• 400 panels of twelve 53 W modules = 4,800 modules
• Array circuit as published: 24 modules in series by 400 in parallel

Our arithmetic:

• 400 × 12 × 53 W = 254.4 kW ✓. But 24 in series × 400 in parallel would be 9,600 modules, twice the stated 4,800; the note is internally inconsistent. 24 × 200 = 4,800 would fit.
• 440,000 kWh ÷ 254 kW is about 1,730 kWh per kWp (calculated; this is a single-axis tracking array).

PHALK 500, Mont-Soleil, Switzerland

System components as published:

• 1,320 panels of eight 53 W laminates, panels bonded in a temporary facility near the site
• One ABB inverter into the 16 kV network

Our arithmetic:

• 1,320 × 8 × 53 W = 559.7 kW ✓ (stated 560 kW), panel power 424 W. 4,575 m² for 560 kW is 122 W/m².
• Array circuit 48 modules in series by 220 in parallel = 10,560 ✓. Design output 700,000 kWh a year, about 1,250 kWh per kWp (calculated). Inverter: one 500 kVA ABB, 16 kV, 50 Hz.

The structures are laid out irregularly on the hillside for a more natural look than rigid rows.

X-Calak, Quintana Roo, Mexico: village hybrid power

System components as published:

• 6 × 10 kW wind turbines
• 234 × M75 modules (11.2 kW)
• 216 × 1,640 Ah batteries (as written in the note)
• 1 × 40 kW three-phase inverter
• PV/wind supervisory and control system
• Existing 125 kW diesel generators

Our arithmetic:

• 11.2 kW ÷ 234 modules = 47.9 W per module, matching the 48 W quoted for the M75 in the Argentine note.
• Read literally, 216 batteries of 1,640 Ah would be about 354,000 Ah, far too much for an 11.2 kW array. We read it as 216 two-volt cells in series (a 432 V bank of 1,640 Ah, about 708 kWh), which is our interpretation, not the note’s wording.

The note credits the hybrid system with helping stem migration to cities and supporting the tourist and fishing industries.

Solar-powered motor operators on 115 kV switches, Marietta, Georgia

System components as published:

• 6 × M55 modules (300 W array)
• 24 V, 200 Ah battery bank
• 2 × 24 V motor operators
• 1 remote terminal unit and a radio link

Our arithmetic:

• 6 × 55 W = 330 W, against the stated 300 W. 24 V × 200 Ah is 4.8 kWh nominal for a load that only operates a motor occasionally.

Distribution lines are not always available, so AC transformers to motorise remote switches are in many cases impractical; solar avoids sending crews to the field.

Scale in one table

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