5 Solar Mistakes That Immediately Tell Me an Installer Doesn’t Know What He’s Doing

There are some things I see on a solar installation that immediately make me stop and ask questions.

Sometimes it is not the brand of inverter.

It is not even the price of the system.

It is something much simpler.

The way the cables are connected.

The way the panels are configured.

The way the battery is being charged.

The protection that is missing.

Or, sometimes, the installer cannot explain why he designed the system the way he did.

I am not saying an installer has to know everything.

Nobody does.

But there are certain mistakes that are difficult to excuse, especially when someone is presenting himself as a professional.

Over the years of working around solar systems, I have learnt that a solar installation can tell you a lot about the person who designed it.

Here are five mistakes that immediately make me question an installer’s knowledge.

1. He sizes the inverter by guessing the customer’s appliances

This is probably one of the biggest red flags.

A customer says:

“I have two TVs, one fridge, one freezer, four fans, lights and an AC.”

And the installer immediately says:

“You need a 5kVA inverter.”

Based on what?

That’s the question.

Solar system sizing should not be based on casually counting appliances and picking an inverter size from memory.

I want to know the actual power requirements.

What is the running power?

Which appliances operate at the same time?

Which appliances have motors or compressors?

What are the starting or surge requirements?

How long are the appliances expected to run?

What is the customer’s actual objective?

Are they trying to power essential loads only?

The whole house?

Certain appliances during the day?

Everything through the night?

These questions matter.

A refrigerator, freezer, water pump and air conditioner don’t behave like a television or LED bulb.

Some loads have significant starting requirements.

So when an installer says:

“Don’t worry, 5kVA will carry everything.”

without doing any meaningful assessment, I immediately become uncomfortable.

And there is another problem.

Inverter power and battery energy are not the same thing.

A 5kVA inverter tells you something about the power the inverter can handle under its specifications.

It does not tell you how many hours the battery will run your house.

That is a completely different calculation.

A professional installer should understand the difference.

2. He connects solar panels without checking the inverter’s PV limits

This one really worries me because it can create a serious system-design problem.

I have heard statements like:

“Just connect the panels. The inverter will regulate it.”

No.

That’s not how I approach PV design.

Before connecting a solar array, I want to know what the inverter allows.

What is the maximum PV voltage?

What is the MPPT operating-voltage range?

What is the maximum PV input current?

What is the maximum recommended PV power?

How many MPPT trackers are available?

How are the panels going to be arranged across those MPPTs?

Then I look at the panel specifications.

The panel’s:

• Voc
• Vmp
• Isc
• Imp
• Rated power

all matter.

And temperature matters too.

One of the mistakes I see is calculating the PV string using the panel voltage under normal conditions and forgetting that Voc changes with temperature.

A cold panel can have a higher open-circuit voltage than it does under warmer conditions.

That means a string that looks acceptable on paper under one condition could approach or exceed the inverter’s maximum PV voltage under another.

That’s why I don’t just count panels.

I design the string.

For example, if someone tells me:

“This inverter can take 6kW of solar, so let’s just put any combination of panels that adds up to 6kW.”

I would stop there.

The total wattage is only one part of the design.

The voltage and current also have to stay within the inverter’s specifications.

3. He doesn’t understand battery charging and discharging

This is another one that tells me very quickly whether someone understands the system or is simply connecting equipment.

I’ve seen installations where the installer knows how to connect positive to positive and negative to negative, but cannot explain the battery settings.

That’s not enough.

The battery is one of the most expensive components in many solar systems.

You need to understand how it is supposed to operate.

For lithium batteries, for example, the battery management system plays an important role in protecting the cells.

Depending on the battery and inverter, communication between the BMS and inverter may also be important.

The correct charging and discharge parameters should follow the battery manufacturer’s specifications.

For lead-acid batteries, things such as charging voltage, depth of discharge, temperature and maintenance can significantly affect battery performance and lifespan.

So if an installer says:

“I normally use this setting for every lithium battery.”

That is a red flag.

Different batteries have different specifications.

Even when two batteries have the same nominal voltage and capacity, they should not automatically be treated as identical.

And I pay particular attention when installers mix batteries.

For example:

“We already have one battery. Let’s add another one from a different brand.”

That may not be appropriate.

Battery chemistry, voltage, capacity, BMS behaviour, age, internal resistance and manufacturer requirements all matter.

You cannot treat batteries like rechargeable torches and simply connect anything together because the voltage looks the same.

4. There is no proper protection or earthing

This is one of those things that some customers don’t notice until something goes wrong.

A solar installation isn’t complete simply because the inverter is producing electricity.

I want to know how the system is protected.

Depending on the system design, this can involve appropriate:

• DC isolators
• Fuses
• DC breakers
• AC breakers
• Surge protection devices
• Battery protection
• Earthing and bonding
• Isolation points

The exact protection arrangement depends on the equipment and installation.

But when I see a large solar system with almost no meaningful protection, I start asking questions.

The same goes for earthing.

If an installer cannot clearly explain the earthing arrangement, that’s concerning.

Earthing isn’t something you add at the end because the customer asked:

“Where is the earth wire?”

It should be considered as part of the system design and installation.

And there is a difference between simply connecting an earth conductor and actually understanding what needs to be bonded and earthed.

5. He cannot explain why he designed the system that way

This one is probably my biggest test.

I can forgive someone for making an honest mistake.

What I don’t like is an installer who cannot explain his own work.

Ask him:

“Why did you choose this inverter?”

If the answer is:

“That’s what I normally use.”

Ask:

“Why this battery capacity?”

“That’s what the customer can afford.”

Ask:

“Why this number of panels?”

“That’s how many will fit on the roof.”

Ask:

“Why did you use this cable size?”

“The supplier gave me this one.”

Ask:

“What can this system realistically power?”

“Everything.”

Now I’m worried.

A professional installer should be able to explain the decisions behind the system.

Not necessarily with complicated engineering language.

Just logically.

“Your estimated peak load is around this level, so I selected this inverter with enough operating and surge capacity.”

“Your expected daily energy consumption is approximately this much, so this battery gives you the required usable energy within the intended operating limits.”

“This PV configuration keeps the voltage and current within the inverter’s MPPT limits.”

“I selected this cable size based on the expected current, cable length and allowable voltage drop.”

That’s a completely different conversation.

One more thing: the installation should look intentional

I don’t believe a solar installation has to look like a showroom to be good.

But when I look at an installation, I should be able to understand what the installer was trying to achieve.

Cables should be properly routed.

Connections should be properly terminated.

Equipment should have adequate ventilation where required.

Panels should be securely mounted.

Components should be accessible for maintenance.

Labels should be used where appropriate.

There shouldn’t be a collection of random cables hanging around the inverter room with no clear organisation.

Good workmanship is not about making the installation beautiful for Instagram.

It is about making it safe, reliable and maintainable.

A customer should not be afraid to ask questions

One mistake I see customers make is assuming that asking technical questions will make them look ignorant.

It doesn’t.

You are spending your money.

Ask.

If an installer says you need a 10kVA inverter, ask why.

If he says you need 15kWh of battery, ask why.

If he wants to install 12 solar panels, ask how he arrived at that number.

If he recommends a particular battery, ask why.

If he says you can run your air conditioner all night, ask what battery capacity and load assumptions that promise is based on.

A competent installer should welcome reasonable questions.

You don’t have to understand every technical detail.

You just need to know that the person designing the system actually understands it.

And installers should also be honest with customers

This article isn’t an invitation to insult installers.

I have seen customers make unreasonable demands too.

Someone wants to run:

• Several air conditioners
• Multiple refrigerators
• Freezers
• Water pumps
• TVs
• Computers
• Electric cookers
• Water heaters

and still wants a tiny inverter and a small battery because:

“I don’t want to spend too much.”

At some point, the installer has to say no.

That’s part of being a professional.

Don’t promise what the system cannot deliver simply because you want to collect the job.

Tell the customer what is possible within the budget.

Maybe the customer can start with essential loads.

Maybe they can expand later.

Maybe they need to increase the battery.

Maybe they need more PV.

Maybe the inverter needs to be larger.

That’s better than making promises that the system cannot keep.

The biggest red flag of all

If I had to reduce everything in this article to one point, it would be this:

If an installer cannot explain his design, don’t be in a hurry to give him your money.

I don’t expect every installer to speak like an electrical engineer.

I don’t expect everyone to memorise every inverter manual.

But I expect a professional to understand the system he is selling and installing.

He should know why the components were selected.

He should understand their limitations.

He should know how they should be connected.

He should understand the basic calculations behind the system.

And most importantly, he should be honest about what the system can and cannot do.

Final thoughts

Solar installation is not just about connecting panels to an inverter and connecting an inverter to a battery.

There is engineering behind it.

There is system design.

There is electrical protection.

There is energy management.

There is configuration.

There is commissioning.

And there is responsibility.

So the next time you are about to hire an installer, don’t only ask:

“How much?”

Ask:

“Why?”

Why this inverter?

Why this battery?

Why this number of panels?

Why this cable size?

Why this protection?

Why this configuration?

If the installer can confidently explain the reasoning behind the system, that’s a good sign.

If every answer is:

“Don’t worry, I’ve been doing this for years.”

Then I would worry.

Because experience is valuable.

But experience without understanding can simply mean someone has been repeating the same mistakes for years.

And in solar, the customer is the one who eventually pays for those mistakes.