Drag the weather. Watch the voltage.
Move any slider or edit the equipment. The modules, curves, bars and limits respond together.
Virtual rooftop string
Cold cell
10°C
String
16 modules
Inverter limit
1100 V
Each tile is one module in series. More modules raise both cold Voc and hot Vmp.
Live voltage checks
Panel and inverter
Preset values teach the method; check exact ordered equipment against its datasheet.
Editable electrical data
Weather and the working
Cold Voc
This estimates the highest open-circuit voltage on a cold morning. As a panel cools its voltage rises. The result must stay below the inverter’s absolute DC limit.
Hot Vmp
Hot cells pull operating voltage down. Keep this result within the inverter’s MPPT window; check its separate startup voltage on the datasheet.
Trace power through the actual connection.
Tap a numbered test point to jump to its commissioning measurement.
Interactive single line and metering
Approved connection design
0 kW
Dispatch controls
Charging and discharging use an illustrative 90% one-way efficiency. The blackout simulation freezes the ESS and isolates the inverter. An approved islanded backup circuit needs its own transfer and protection design.
Trace the run, then verify voltage drop and cable rating.
Voltage loss is calculated. Current rating stays pending until cable manufacturer and installation data are entered.
Tray cross-section · illustrative packing
DC run controls
The roof temperature is a design condition to use when choosing the manufacturer temperature factor. The +25°C allowance does not itself calculate an ampacity factor. Enter the approved base rating and correction factors for the actual PV cable and installation.
We use 0.023 Ω·mm²/m for warm copper. The current travels out and back. A low loss protects energy harvest over the whole plant life. Voltage drop and cable current rating are separate checks. Confirm insulation temperature rating, installation method, protection, connectors and fire requirements.
Follow the evidence, one reading at a time.
Choose a symptom and enter measured values to see the next decision.
Active symptom
Diagnostic decision map
Test point sketch
Isolate, lock out and prove dead using the approved method. Follow instrument and module manufacturer test voltage limits. These are teaching thresholds, not a substitute for the project acceptance criterion.
Commissioning bench
Record real readings at named test points. A blank acceptance criterion stays pending, never auto-passed.
Clickable field test points
These buttons scroll to the matching record. Carry out each test with the approved method, correct instrument category and manufacturer limits. Isolate and verify before touching DC connectors.
For Voc and Isc, enter the engineer-approved tolerance against the expected value. Insulation acceptance depends on the approved procedure and equipment. The trip result is a recorded observation, not a substitute for a certified relay test.
From one engineer to another.
On the roof, start with the cold number.
Picture the panel voltage as an elastic band. The cells are hot at lunchtime, so operating voltage shrinks. On a clear cold morning it stretches. Count every module in the string before choosing the inverter. The cold open-circuit number is the one that can cross its absolute input limit. The hot operating number tells you whether the MPPT can keep following the array.
When the street goes dark, the inverter must know.
Put yourself in the shoes of a linesman working on a transformer outside the plot. They have isolated the supply and expect the utility conductor to be dead. If your inverter quietly feeds power back into it, that conductor becomes a serious shock hazard. Anti-islanding opens the connection when the grid disappears. Battery-backed operation is possible only through a properly designed, isolated backup circuit.
Why I watch every fraction of a volt on DC.
A building feeder can tolerate some drop because the load still gets the supply it needs. A PV cable drops power that the array could have sold or used, every sunny day for perhaps 25 years. The 1% figure in this lab is a strict design target to start the discussion. Calculate the return path, check the hot copper resistance, then compare cable cost with lifetime yield. Do not forget installation grouping and cable thermal rating.