Why Copying Another Solar Installer’s Design Can Go Very Wrong

There is a sentence I have heard many times in solar:

“This is the exact system we installed for another customer. It worked perfectly, so let’s do the same thing here.”

It sounds reasonable.

Why reinvent the wheel when somebody else has already done it?

The problem is that solar systems are not templates.

A system that works perfectly in one house can perform badly in another house, even if both customers have the same number of bedrooms, the same inverter size and seemingly similar appliances.

I have learnt to be very careful whenever someone tells me:

“Just copy the design.”

Copy the concept if it makes sense.

Copy the experience.

Copy the lessons.

But don’t blindly copy the numbers.

Because the numbers belong to the particular system they were calculated for.

Two houses can look identical on paper and still be completely different

Let’s say two customers both have:

• 4-bedroom houses
• 2 air conditioners
• 1 refrigerator
• 1 freezer
• TVs
• Fans
• Lights
• A water pump

Someone may look at this and say:

“Easy. Install the same system in both houses.”

But I would still ask questions.

Are the ACs the same size?

Are they inverter ACs?

How often are they used?

Does one customer leave the AC running throughout the night?

How big is the freezer?

Does the other customer use an electric cooker?

Does one house have a borehole pump?

Does one customer work from home?

Are there computers, servers or other equipment?

What are the customer’s expectations?

Do both customers want the same backup time?

Are their roofs equally suitable for solar panels?

Are the panel installation conditions the same?

There can be a huge difference between the two houses.

So the fact that the buildings look similar doesn’t mean the energy requirements are the same.

The load is not determined by the number of rooms

This is one of the first mistakes I see.

Someone says:

“It’s a 3-bedroom house, so use a 5kVA inverter.”

Why?

The number of bedrooms does not tell me how much electrical power the house consumes.

I have seen modest homes with very demanding loads.

I have also seen large houses where the essential electrical load is relatively small.

A house with one AC that runs occasionally is not the same as a house where three ACs run every night.

A customer with a water pump, electric cooker and water heater has a different energy profile from someone who doesn’t use them.

So when copying a previous installation, the first thing I want to copy is not the equipment list.

I want to understand why that equipment was selected in the first place.

The battery requirement can be completely different

This is where copying someone else’s design can become particularly expensive.

Imagine Installer A installed:

10kWh lithium battery

for Customer A.

Customer A uses the battery mainly for:

• Lights
• Fans
• TV
• Refrigerator
• Internet equipment

and the system comfortably gets through the night.

Customer B sees the installation and says:

“I want exactly the same thing.”

But Customer B wants to run:

• Two ACs
• Freezer
• Refrigerator
• Fans
• TVs
• Lights
• Pump

throughout the evening.

The same 10kWh battery is now being asked to do a completely different job.

Customer B may conclude:

“This battery is bad.”

But the battery may be perfectly fine.

The design was copied without copying the conditions under which it was designed.

The inverter may be the wrong size

The same problem applies to the inverter.

If another installer used a 5kVA inverter successfully in one home, that doesn’t mean every similar-looking home needs a 5kVA inverter.

I need to consider:

• Expected running load
• Simultaneous loads
• Motor/compressor starting requirements
• Surge capability
• Inverter operating limits
• Future loads

A refrigerator and an air conditioner don’t behave like a few LED bulbs.

Loads with motors and compressors can have starting demands that need to be considered.

So I don’t select an inverter simply because:

“My last customer used this one.”

I select it because the current system requires it.

And the PV design can be completely different

This is another area where blindly copying a previous installation can cause trouble.

Someone might say:

“The last system used 12 × 550W panels. Let’s use 12 × 550W here.”

That may or may not be correct.

I want to know:

What inverter is being used?

What is its maximum PV voltage?

What is its MPPT operating range?

What is its maximum PV current?

What is its maximum PV power?

What are the panel specifications?

How many panels are in each string?

How are the strings distributed across the MPPTs?

What happens to the string voltage under different temperatures?

The panel count is only the beginning.

The string configuration matters.

Two systems with the same number of panels can have completely different PV configurations.

And a configuration that is acceptable for one inverter may be completely wrong for another.

The roof can change everything

This is something a person copying designs from photographs may completely miss.

You see another installation with 16 panels.

The roof looks spacious.

So you decide:

“I’ll use the same arrangement.”

Then you arrive at your customer’s house.

The roof has:

• Different orientation
• Different pitch
• Partial shading
• Water tanks
• Satellite dishes
• Roof structures
• Trees nearby
• Limited usable space

Suddenly the previous design doesn’t fit.

You have to change the string arrangement.

You may have fewer usable areas.

Shading may affect some panels.

The panel layout may have to change.

This is why I don’t design a PV array from a WhatsApp photograph of somebody else’s roof.

I inspect the actual installation conditions.

Even the weather and environment matter

Solar doesn’t operate under laboratory conditions.

Real-world conditions matter.

Dust.

Heat.

Cloud cover.

Rain.

Harmattan.

Shading.

Panel orientation.

Ventilation.

All of these can influence system performance.

An installation that performs well in one location and environment should not automatically be expected to produce exactly the same result somewhere else.

Even within Nigeria, conditions can vary.

And the customer shouldn’t be sold an unrealistic expectation based on another person’s experience.

The battery voltage matters too

Another common mistake is copying battery quantities without looking at the system architecture.

For example:

“That installer used two batteries. Let’s use two batteries.”

Two batteries of what voltage?

What capacity?

What chemistry?

What discharge rating?

What BMS?

How are they connected?

What does the inverter support?

What does the manufacturer permit?

Two batteries in one system do not automatically mean two batteries will be appropriate in another.

The number of batteries is not the design.

The electrical relationship between the batteries and the rest of the system is the design.

Different brands can change the design

This is something customers often overlook.

Suppose another installer used:

Inverter A + Battery A + Panel A

and everything worked well.

You decide to use:

Inverter B + Battery B + Panel B

but keep exactly the same numbers and configuration.

Why?

The new inverter may have different PV limits.

The battery may have different charge/discharge limits.

The communication requirements may be different.

The recommended settings may be different.

The MPPT arrangement may be different.

The equipment may have different operating conditions.

So copying the quantity without checking compatibility is dangerous.

“But it worked for my friend”

This is one of the hardest things to explain to customers.

A customer may say:

“My friend installed this exact system and it works perfectly.”

Good.

I’m happy for your friend.

But your friend’s electricity consumption is not necessarily yours.

His usage pattern isn’t yours.

His roof isn’t yours.

His equipment isn’t necessarily yours.

His battery isn’t necessarily yours.

His expectations aren’t necessarily yours.

So his experience is useful information.

It is not your system design.

I would rather use your friend’s installation as a reference point and then calculate your own requirements.

Copying can also spread mistakes

This is the part that concerns me most.

Imagine an installer makes a mistake.

Perhaps the PV string configuration is wrong.

The customer doesn’t notice immediately.

The system still produces some power.

Another installer sees the installation and thinks:

“This is how they do it.”

He copies it.

Then another installer copies him.

Before long, a bad practice has become:

“Industry standard.”

That’s how mistakes spread.

Experience is useful, but experience must still be questioned.

I don’t want to copy something simply because it has been done many times.

I want to know whether it is correct.

A quotation is not a design

This is another distinction I think customers should understand.

Someone can send you a quotation that says:

5kVA inverter
10kWh battery
5kW solar panels

That is a list of equipment.

It doesn’t automatically tell me whether the system is correctly designed.

I still want to know:

Why 5kVA?

Why 10kWh?

Why 5kW PV?

What loads were considered?

What backup time is expected?

How is the PV configured?

What are the cable requirements?

What protection is required?

How will the system be expanded?

The equipment list is only the visible part.

The design is the reasoning behind the equipment list.

What I would copy from another installer

There are things I absolutely encourage installers to learn from one another.

If another installer has developed a good installation method, learn from it.

If they have discovered a common failure, learn from it.

If they have found a better way to organise a system, study it.

If they have experience with a particular inverter, learn from that experience.

If they have developed a good commissioning checklist, use the idea.

That’s how industries improve.

But I would not blindly copy:

• Inverter size
• Battery capacity
• Panel quantity
• Panel string configuration
• Cable sizes
• Protection arrangement
• Battery settings

without verifying that they are appropriate for the new installation.

Learn from another installer’s design. Don’t blindly duplicate it.

What I check before designing a system

When I am approaching a new installation, I want to start with the new customer.

I look at:

1. The actual loads

What appliances are there?

2. The usage pattern

How long are they used?

3. Simultaneous demand

What can be running at the same time?

4. Energy requirement

How much energy does the customer need over the relevant period?

5. Inverter requirements

What power and surge capability are required?

6. Battery requirements

How much usable energy is required, and what discharge capability is needed?

7. PV requirements

How much solar generation is required, and can the inverter accept the proposed array?

8. Installation conditions

What does the roof, equipment location and environment look like?

9. Future expansion

What might the customer add later?

Then I select the equipment.

Not the other way around.

The dangerous part is that copying can appear to work

This is why the mistake is so easy to make.

A poorly copied system doesn’t necessarily fail immediately.

The inverter may turn on.

The panels may produce power.

The battery may charge.

The customer may be happy.

Then a few months later, problems begin.

The battery isn’t lasting.

The inverter is overloaded.

The system struggles during cloudy weather.

The PV isn’t charging the battery adequately.

The inverter starts showing faults.

The customer adds another AC and suddenly everything changes.

Then everybody starts asking:

“What happened?”

The answer may be that the system was never designed for that particular customer in the first place.

The best solar installers don’t copy systems — they understand systems

This is what separates installation from engineering thinking.

An installer should be able to look at another person’s system and ask:

Why did they choose this?

What assumptions were made?

What loads were considered?

What equipment was available?

What limitations did that system have?

Then take the lessons and apply them appropriately.

That’s much more valuable than copying a shopping list.

Because when you understand the design, you can adapt.

When you only memorise the design, you can only repeat it.

Final thoughts

I don’t have a problem with installers learning from one another.

I actually encourage it.

The solar industry needs knowledge sharing.

But there is a big difference between learning from another installation and duplicating another installation without doing your own calculations.

The next house is not the previous house.

The next customer is not the previous customer.

The next inverter may not be the same inverter.

The next battery may not be the same battery.

The next roof may not have the same conditions.

And the next customer’s expectations may be completely different.

So when someone tells you:

“Don’t worry. We installed this exact system somewhere else.”

My next question would be:

“Good. But why is this exact system right for this customer?”

If the installer can answer that with proper reasoning, I’m listening.

If the answer is simply:

“Because it worked for the other customer.”

Then I would start asking a lot more questions.

A good solar design can be inspired by experience.

It should never be replaced by experience.