Lesson 6 – T: Transform Your Learning: How Do We Build and Use Photovoltaic Panels?

T: Transform Your Learning

Use Panel Specifications to Make an Engineering Decision

Now you will use panel information the way an engineer would. Instead of looking only at the biggest watt number, you will compare several panel specifications and decide which panel is the better fit for a real situation.

Percent Change in Power

In the below scenario, you’ll look at multiple panel specifications to make a engineering design decision. Before you jump in, here is an example of how to determine how higher temperature may reduce output.

Panel	Standard Test Condition	Actual Temperature	Temperature Coefficient
Panel A	25°C	45°C	–0.38% per °C
Panel B	25°C	45°C	–0.20% per °C

Percent Change in Power: Panel A

To calculate the output of the panel, you use this formula:

Percent change in power ≈ (temperature coefficient) × (temperature change from 25°C)
Percent change in power = (.38%) x 20 = 7.6% lower than the rated power

Percent Change in Power: Panel B

To calculate the output of the panel, you use this formula:

Percent change in power ≈ (temperature coefficient) × (temperature change from 25°C)
Percent change in power = (.30%) x 20 = 6.0% lower than the rated power

Based on these calculations, the panel that keeps most of its power on this day is Panel B, which only drops 6% of its rated power.

Scenario: Hospital Solar System

A hospital needs a small solar system for lights, vaccine refrigeration support equipment, and device charging. The site is hot for much of the year, and the roof area for solar panels is limited. Two panel options are available.

Panel	Rated Power	Efficiency	Temperature Coefficient
Panel X	360 W	20%	-0.34% per degree Celsius
Panel Y	340 W	18%	-0.26% per degree Celsius

Assume the site receives 5 hours of strong sunlight per day.

Estimate Daily Energy

Use the formula below:

Daily Energy = Rated Power x Sun Hours

Panel X daily energy: 360 W × 5 h = 1800 Wh per day
Panel Y daily energy: 340 W × 5 h = 1700 Wh per day

Compare the Panels

Which panel has more power under standard conditions?

Panel X has more rated power under standard conditions because it is listed at 360 W, while Panel Y is listed at 340 W. The difference is 20 W, so based on rated power alone, Panel X would be expected to produce more power in standard test conditions. This answer uses the numbers in the table as evidence.

What about when there are extreme conditions or constraints?

Think about or jot down:

Which panel may hold onto more of its output in high heat?
Which panel may be more useful when roof space is limited?

Make a Recommendation

If you had to choose one panel and explain your choice, which panel would you choose and why? Your explanation should include:

At least one number
At least one comparison
At least one trade-off

Check Your Understanding

How does connecting cells in series change a panel’s electrical output?
How does connecting cells in parallel change a panel’s electrical output?
Why is rated power not the only thing engineers consider when choosing a panel?
Which panel would you recommend for the mini-grid scenario, and what evidence supports your choice? Describe one trade-off involved in your recommendation.

Closure: Connecting Lesson 6 to Lesson 7

In this lesson, you learned that photovoltaic panels are made from many smaller cells and that their design affects how much voltage, current, and power they produce. You also learned that engineers choose panels by comparing more than one specification. In the next lesson, you will continue thinking like a solar engineer by connecting what you know about solar supply to the energy demand of a full mini-grid system.

Final Takeaway

A photovoltaic panel is more than just a big watt number. It is made of many cells wired in series and parallel, and engineers look at the panel’s specifications and trade-offs to match it to real-world needs. By considering all of these factors, they can design a solar system that works well in its specific environment.