Temperature Effects
Temperature effects
- Normal operating cell temperature (NOCT)
- Expected temperature at
- 20C air temperature
- 0.8 kW/m^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)
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
- S 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
P_{max} = P_{STC} \cdot (1 - \textrm{temp coeff} \cdot (T_{cell} - T_{STC}))
- P_{STC} power measure in lab under standard test conditions (STC)
- T_{STC} cell temperature in lab under STC (25C)
- temperature coefficient is the temperature coefficient of P_{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?