Monitoring and Performance Evaluation – SS2 Solar Photovoltaic Installation & Maintenance Lesson Note (Second Term)

Monitoring means watching a solar system after installation to check that it is producing power, that the energy matches what the house uses, and that faults are caught early. Performance evaluation means comparing what the system should do with what it is actually doing. Technicians use meters, apps and performance graphs to do this.

Behavioural objectives

By the end of the lesson, students should be able to:

• state why a solar system is monitored after installation;
• name the hardware meters used for monitoring and say what each one measures;
• describe how remote monitoring with an inverter, a cloud server and an app works;
• read a daily production graph and give likely causes of dips, low flat output and sudden stops;
• explain what Performance Ratio (PR) means and list ways to improve system performance.

Why monitor a solar system?

Imagine you buy a car, but the dashboard is missing. You would not know how much fuel you have, how fast you are going, or if the engine is overheating.

In solar design, monitoring is our dashboard. We do not just walk away after installation. We watch the system to see:

1. Is it working? (Are the panels actually producing power?)
2. Is it enough? (Is the energy produced matching what the house is using?)
3. Is it failing? (Can we see a problem coming before the lights go out?)

Performance evaluation simply means comparing what the system should do with what it is actually doing. With meters and apps, we can show a customer that the system is working properly, or catch a small fault before it becomes a big one.

Which hardware meters are used for monitoring?

Before we use computers, we use physical meters. These are the “eyes” of the technician.

• The energy meter (kWh meter): This shows the total energy used by the house. If the house uses 10 kWh but the panels only produce 5 kWh, the batteries will eventually die.
• The multimeter: This is a handheld tool used to check the “health” of specific parts. We use it to check the voltage of a single battery or the current coming from one string of panels.
• DC clamp meter: This is a special tool that can measure the current flowing through a wire without touching the bare metal. You just “clamp” it around the wire.

How does remote monitoring work?

Most smart inverters now come with a Wi-Fi or GPRS module. This allows the solar system to talk to the internet.

How it works

1. The inverter collects data every minute.
2. It sends this data to a “cloud” server.
3. The technician (you) or the owner logs into an app on a smartphone to see the performance.

What the app shows you

• Real-time power: How many watts are coming from the sun right now.
• Battery percentage: Is the battery at 90% or 20%?
• Historical data: A graph showing how much power was produced last week compared with this week.

How do you read a performance graph?

As an SS2 student, you need to be able to look at a graph and tell a story.

On a perfect sunny day, the production graph looks like a bell, so it is called the bell curve. It starts low at 7:00 AM, reaches its peak at 12:00 PM (noon), and goes down by 6:00 PM.

• What if the graph has “dips” at noon? This usually means clouds were passing over.
• What if the graph is flat and low? The panels might be very dirty, or there is a “shading” problem from a nearby tree.
• What if the graph stops suddenly? A fuse might have blown or the inverter shut down due to heat.

What is Performance Ratio (PR)?

In professional solar design, we use a term called the Performance Ratio (PR). It is like a student’s exam score for the system.

PR compares the energy the system actually delivers with the energy it should deliver for the sunlight it receives. If a system has a PR of 80%, it delivers 80% of the expected energy, while 20% is lost to heat, wire resistance or dust.

How to improve performance

1. Keep it cool: Make sure the inverter is in a well-ventilated room.
2. Keep it clean: Wash the panels regularly.
3. Check connections: Loose wires cause “resistance”, which steals your power.

Evaluation

1. What does performance evaluation mean?
2. State the use of each of these tools: energy meter, multimeter, DC clamp meter.
3. Describe the three steps by which data gets from the inverter to a smartphone app.
4. A production graph is flat and low. Give two possible causes.
5. A system has a PR of 80%. What does this mean, and what are the three causes of the 20% loss?

Assignment

1. List the three things the monitoring app shows the technician or owner.
2. Describe what the production graph of a perfect sunny day looks like, including the times of the start, the peak and the end.
3. Explain three ways to improve the performance of a solar system.