Inputs
Example data table
| Scenario | Series (S) | Parallel (P) | Cold Voc string (V) | Hot Vmp string (V) | Status |
|---|---|---|---|---|---|
| Typical 10S setup | 10 | 2 | ~530 | ~380 | Varies by limits |
| More conservative 9S | 9 | 2 | ~477 | ~342 | Often safer |
| Higher voltage 11S | 11 | 1 | ~583 | ~418 | May exceed max |
Formula used
The calculator adjusts module voltages away from 25°C using temperature coefficients. Coefficients are entered as percent per degree Celsius.
- Voc_cold_module = Voc_STC × (1 + (TC_Voc/100) × (Tmin − 25))
- Vmp_hot_module = Vmp_STC × (1 + (TC_Vmp/100) × (Tmax − 25))
- Voc_cold_string = Voc_cold_module × Series
- Voc_cold_with_margin = Voc_cold_string × (1 + Margin/100)
- Vmp_hot_string = Vmp_hot_module × Series
How to use this calculator
- Enter your controller MPPT window and maximum PV voltage.
- Enter module Voc and Vmp from the datasheet at STC.
- Enter temperature coefficients for Voc and Vmp.
- Set your expected minimum and maximum ambient temperatures.
- Choose a series count and parallel strings, then calculate.
- Confirm hot tracking and cold maximum voltage both pass.
- Use the recommended series range to refine string design.
- Download CSV or PDF for sharing and records.
Voltage behavior across seasons
PV module voltage shifts with cell temperature, so a string that looks fine at 25°C may drift outside controller limits in cold mornings or hot afternoons. Open-circuit voltage rises as temperature falls, while operating voltage at maximum power drops as temperature increases. Typical crystalline modules list Voc temperature coefficients around -0.25% to -0.35% per °C and Vmp coefficients around -0.30% to -0.45% per °C, so a 35°C swing can shift string voltage noticeably. in field conditions. The calculator estimates a cold-case string Voc and a hot-case string Vmp so you can check both extremes before installation.
Tracking window and maximum input
Two constraints must hold together. The MPPT window is where the tracker can regulate power, so hot-string Vmp should remain between the MPPT minimum and maximum. Separately, the maximum PV input voltage is an absolute ceiling; cold-string Voc, after applying margin, must stay below it. The tool reports both checks side by side.
Safety margin in practice
A modest margin adds buffer for measurement tolerance, manufacturing spread, and short voltage spikes. Apply margin to the cold Voc stress case because that challenges insulation and input protection. In highly variable climates, a little more margin can help, but too much padding can reduce tracking headroom during heat.
Choosing series and parallel
Series count sets voltage, while parallel strings scale current and power without changing voltage. Use the recommended series range as a band, then select an integer series count that keeps cold Voc below the controller maximum and keeps hot Vmp inside the MPPT window. After voltage is correct, size parallel strings for energy goals and confirm wiring and controller current ratings.
Recording and exporting results
Good documentation reduces rework and speeds troubleshooting. Save the module datasheet values, temperature assumptions, and the chosen series and parallel layout. Exported CSV and PDF summaries support commissioning notes, maintenance handovers, and warranty discussions. When equipment changes later, rerun the same inputs to confirm compatibility and prevent hidden overvoltage risk.
FAQs
What is MPPT range in a controller?
MPPT range is the voltage window where the tracker can actively regulate and search for the maximum power point. If your string operating voltage sits outside this window, power harvest may drop or the controller may stop tracking efficiently.
Why does cold weather increase string voltage?
As temperature drops, semiconductor bandgap increases and module voltage rises. Voc is most sensitive, so the coldest expected temperature is used to check maximum input voltage and protect the controller from overvoltage.
Should I use Voc or Vmp for MPPT checking?
Use Vmp for MPPT tracking because it represents operating voltage under load. Use Voc for absolute maximum input checks because it represents the highest potential voltage when the array is not loaded.
What safety margin should I choose?
Many designers use 1–3% as a practical buffer for tolerance and transient effects. In very cold or high‑irradiance sites you may increase it slightly, but confirm the resulting series count still stays within the MPPT window at high temperature.
Does parallel wiring affect MPPT voltage?
No. Parallel strings increase current and power while keeping string voltage roughly the same. Voltage checks for MPPT range and maximum input are driven by series count and temperature-adjusted module voltages.
Why might the tool show CHECK even if one test passes?
Because both conditions are required: hot Vmp must be inside the MPPT tracking window and cold Voc with margin must stay below the controller maximum. Failing either side can reduce production or risk hardware damage.