Temperature Effects

Temperature effects

  • Normal operating cell temperature (NOCT)
  • Expected temperature at
    • 20C air temperature
    • 0.8 kW/m2m^2 insolation (0.8 sun)
    • 1m/s wind
  • For most modules this is about 45C
  • This is listed on the panel

Temperature

  • We can predict the cell temperature (REEPS2 Eq. 5.23)

Tcell=Tamb+NOCT−20C0.8S T_{cell} = T_{amb} + \frac{NOCT - 20C}{0.8}S

  • If it is hot, the cell temperature rises linearly
  • If it is sunny, the cell temperature rises linearly
  • SS is the insolation in watts per square meter
  • News flash: stuff in the sun gets hot

Temperature Coefficient of Max Power

  • We can predict the maximum power based on the cell temperature

Pmax=PSTC⋅(1−temp coeff⋅(Tcell−TSTC)) P_{max} = P_{STC} \cdot (1 - \textrm{temp coeff} \cdot (T_{cell} - T_{STC}))

  • PSTCP_{STC} power measure in lab under standard test conditions (STC)
  • TSTCT_{STC} cell temperature in lab under STC (25C)
  • temperature coefficient is the temperature coefficient of PmaxP_{max} %/C

Shading/mismatch

  • We use the equivalent circuit model that includes resistances to show these effects
  • These resistances dissipate power and reduce the output power

Shading

  • To mitigate shading issues at the cell level we use bypass diodes
  • To mitigate shading issues at the module level we use microinverters

Maximum power point MPP

Variation in temperature and insolation

Solar Tracking Types

Tracking Insolation

Hourly Temperature Derating

Derate calculator

PVWatts

  • Simple solar photovoltaic estimation tool
  • Created by the National Renewable Energy Laboratory (NREL)
  • Online Calculator

Environmental Technology Center

  • How would we estimate the derate for our panels here?
  • How would we measure it?