System Sizing Flashcards
Which of the following was NOT one of the limitations to array size covered in Grid-Direct System Sizing chapter?
1. client/homeowner familiarity with PV systems
2. client/homeowner budget
3. energy production goals
4. space
- client/homeowner familiarity with PV systems
The chapter focused on space, budget, and energy production goals as the most obvious limitations to array size.
true or false. Producing more energy than is used on an annual basis is always good financial sense and often incentivized by electric utilities
false
Producing more energy than is used on an annual basis rarely makes financial sense for most net-metered systems and may not even be allowed by some utilities. However, in areas with feed-in-tariffs, this may not be a limiting factor for system size
true or false. Temperature has a dramatic effect on PV voltage
true
Temperature - and specifically cell temperature - has a dramatic effect on PV voltage. It’s important to consider both high and low temperatures (and the resulting voltages) when matching an inverter with an array. If high and low temperatures are not accounted for, then the system might go offline, underproduce, or be unable to turn on during hot summer days when the voltage is low; likewise, during clear, cold winter days, the array voltage might exceed the rating of the inverter and other electrical components in the system
true or false. Every source circuit must have precisely the same number of modules if the inverter only has the ability to track one maximum power point
true
Desired array size in STC watts ______________ = How many modules are needed
1. Current STC range
2. Voltage STC range
3. Module size in STC watts
4. Module dimensions in square inches
- Module size in STC watts
Calculate how many modules are needed by identifying the desired array size in Standard Test Conditions (STC) watts and dividing by module size in STC watts
Which of the following circumstances would make choosing a higher power ratio unwise?
1. Especially expensive modules are being used.
2. The site is especially hot.
3. The utility imposes limits on AC kW but not DC kW
4. The site has suboptimal conditions (such as shading, un-ideal array tilt or orientation).
1.Especially expensive modules are being used.
There are situations where a higher power ratio makes a lot of sense, including climates that are hot, smoggy, hazy and or/dusty year round, as well as shaded locations. These locations are unlikely to see Standard Test Conditions (1000 W/m2, 25ºC cell temperature, 1.5 atmosphere) very often, so minimal power clipping is expected.
When PV modules are inexpensive, it can be financially beneficial to add modules so that during the earlier and later times of the day when irradiance is lower, the larger array will allow the inverter to operate at full power for longer periods of time.
true or false. A lower power ration is more likely to be a sensible option for a high elevation, cold climate location
true
Some project locations will not gain much from a higher power ratio. Areas which are higher in elevation have a thinner atmosphere and higher irradiance, which will cause the PV array to operate closer to (and sometimes even higher than) its STC rating. Additionally, snow is reflective and can cause the array to have a higher output. For these reasons, systems in snowy locations may benefit from a lower power ratio.
Some inverters operate better at lower power ratios, so it is always important to refer to the manufacturer’s instructions.
To ensure that an array will comply with inverter (or Module Level Power Electronics) operating parameters, you should check the _____________ to identify the highest voltage and the _____________ to identify the lowest voltage your array is likely to experience.
blank 1: VOC on the coldest day
blank 2: VMP on the hottest day
