Why HT Industrial Consumers Need a Different Solar Design Than LT Rooftop Systems

A factory consumes 20 lakh units of electricity a year.

The management decides to install industrial solar. The roof has enough space, the annual consumption is high, and the financial case looks attractive.

So the first calculation seems simple:

Annual units → required solar capacity → number of panels → installation.

That approach may work as a rough starting point.

For an HT industrial consumer, however, it is nowhere near enough to finalise the system.

An industrial facility taking electricity at high tension operates in a very different electrical and commercial environment from a smaller LT rooftop consumer. The difference is not simply that an HT system is “bigger.”

HT consumers can have substantial maximum demand, contract demand, transformers, protection systems, complex internal distribution, multiple production loads and time-dependent consumption patterns. Their electricity economics can also depend on when power is consumed, not merely how many units appear on the monthly bill.

That changes how industrial solar should be designed.

The real objective isn't:

How many solar panels can we install?

It is:

How should solar integrate with this factory's electrical system, operating load and tariff structure?

LT vs HT: Why the Difference Matters

LT means Low Tension, while HT means High Tension.

A smaller LT commercial or industrial installation may have relatively straightforward consumption and electrical infrastructure.

An HT industrial facility can look very different.

Think of a large manufacturing plant containing:

• production machinery;
• motors;
• compressors;
• furnaces or process equipment;
• chillers;
• HVAC;
• multiple transformers;
• large motor-starting loads;
• power-factor correction;
• DG backup; and
• multiple internal distribution panels.

The factory may operate one, two or three shifts.

Its load may change dramatically from one production line to another.

So a 1 MW industrial solar installation at such a facility cannot simply be treated as a scaled-up version of a 100 kW LT rooftop plant.

Start With the Load Profile, Not the Electricity Bill

Suppose two factories each consume:

20 lakh units/year

At first glance, they appear to need a similar solar system.

Now look at how they operate.

Factory A

Operating hours: 8 AM–6 PM

Most machinery runs during the day.

Factory B

Operating hours: 24×7

Large loads continue through the evening and night.

Annual consumption is identical.

But the solar opportunity isn't.

Factory A may be able to consume a large portion of solar generation directly.

Factory B may still have excellent daytime solar utilisation, but solar alone cannot address much of its night-time requirement.

This is why an HT project should ideally be modelled using:

15-minute or hourly load data

rather than only monthly electricity bills.

You need to know:

When does the factory consume power?

Not just:

How much power does it consume?

Consider a 24-Hour Factory

Imagine an HT industrial facility with the following simplified load:

Time	Factory Load
6 AM	600 kW
9 AM	900 kW
12 PM	1,200 kW
3 PM	1,100 kW
6 PM	900 kW
9 PM	750 kW
Midnight	650 kW

Now suppose its industrial solar system produces:

Time	Solar Output
6 AM	0 kW
9 AM	300 kW
12 PM	750 kW
3 PM	600 kW
6 PM	50 kW
9 PM	0 kW
Midnight	0 kW

At noon:

Factory demand = 1,200 kW

Solar generation = 750 kW

Approximate grid requirement = 450 kW

At 9 PM:

Factory demand = 750 kW

Solar generation = 0 kW

Grid requirement = 750 kW

Solar hasn't reduced the factory's electricity requirement.

It has reduced how much of that requirement needs to come from the grid during solar-generation hours.

That distinction is fundamental to HT solar design.

Maximum Demand Adds Another Dimension

An HT consumer's electricity economics can involve more than energy consumption.

GERC's FY 2026–27 tariff framework, for example, defines maximum demand based on the average kW/kVA supplied over the applicable demand interval and defines contract demand as the maximum kW/kVA for which supply facilities are provided. Gercin

That means a factory should not evaluate solar only through:

Annual solar generation × ₹/unit

It should also understand what happens to its grid-demand profile.

Consider an illustrative facility.

Without Solar

Daytime factory demand:

1,500 kW

Grid requirement:

1,500 kW

With Solar

Factory demand:

1,500 kW

Solar generation:

700 kW

Grid requirement:

800 kW

During that interval, solar has significantly reduced grid draw.

But now imagine the factory reaches its monthly maximum demand at:

7:30 PM

Factory demand:

1,600 kW

Solar generation:

0 kW

Grid requirement:

1,600 kW

The solar system may save a substantial number of units during the month while having little or no effect on the demand-setting event.

This is exactly why an HT solar proposal should not automatically promise:

“Solar will reduce both your energy and demand charges.”

The load data has to prove it.

Time-of-Use Tariffs Make Timing Even More Important

For HT consumers, the value of electricity can also vary according to time.

This is particularly relevant in Gujarat in 2026.

GERC's FY 2026–27 DGVCL tariff order discusses Time-of-Day charges for consumers with maximum demand above 10 kW and identifies the role of peak periods in encouraging consumers to shift consumption toward periods that better align with available generation. Gercin

Torrent Power Ahmedabad's FY 2026–27 tariff order likewise incorporates revised peak periods and a daytime consumption rebate for applicable HT categories. It records peak periods of 6 AM–8 AM and 5 PM–11 PM, while shifting the earlier night-time rebate toward daytime/solar-hour consumption. Gercin

That creates an important engineering and financial question:

At what times is the factory buying its most valuable grid electricity, and how much of that consumption can solar actually displace?

A unit generated at noon and a unit required at 8 PM may not have identical economic value.

10 Lakh Solar Units Can Have Different Value at Two Factories

Consider two HT factories.

Both install systems generating:

10 lakh units/year

Factory A

Uses almost all generation directly during operating hours.

Factory B

Has lower daytime load and significant consumption outside solar hours.

Even if annual generation is identical, the economic outcome can differ because of:

• self-consumption;
• export treatment;
• time-of-use tariffs;
• banking or settlement rules where applicable;
• demand profile; and
• tariff structure.

So the KPI for solar for industries should not simply be:

Annual Generation = 10,00,000 units

It should include:

How many of those units create useful financial value for this particular factory?

HT Solar Must Integrate With Existing Electrical Infrastructure

For a small rooftop system, the electrical architecture may be relatively straightforward.

A large industrial facility can contain:

11 kV/22 kV or other applicable incoming supply

HT switchgear

transformers

LT panels

multiple distribution boards

DG sets

protection relays

APFC systems

and sometimes multiple buildings or load centres.

The solar plant needs to be designed around that architecture.

Suppose a factory has three transformers:

Transformer A → Production Line 1

Transformer B → Production Line 2

Transformer C → Utilities + HVAC

Where should solar be integrated?

At one LT bus?

Across multiple buses?

At HT level?

The answer depends on system capacity, load distribution, existing equipment ratings, protection philosophy and site configuration.

There is no universal answer.

That's why large solar panels for industrial use cannot be designed properly from a Google Maps roof measurement and one electricity bill.

Transformer Loading Needs to Be Understood

Consider a factory with a:

2,000 kVA transformer

and a large proposed rooftop solar system.

An inexperienced approach might simply connect solar to the nearest available panel.

But engineers need to understand the direction and magnitude of power flows under different operating conditions.

For example:

Factory Running Normally

Factory load: 1,500 kW

Solar: 700 kW

Grid contribution: 800 kW

Straightforward.

Now suppose production stops temporarily:

Factory load: 200 kW

Solar: 700 kW

There is now:

500 kW of surplus generation

Where does it go?

Whether export is permitted and how the system should respond depends on the project's connection and regulatory arrangement.

The electrical design therefore needs to consider not only maximum factory load but also:

minimum daytime load.

That is a major sizing parameter for behind-the-meter industrial solar.

Minimum Load Can Be More Important Than Maximum Load

Imagine an HT factory with:

Peak demand = 2 MW

Management concludes:

“Let's install 2 MW solar.”

But during weekends and production shutdowns, the factory load falls to:

300 kW

On a sunny Sunday, the solar plant could potentially generate far more electricity than the facility is consuming.

If export is limited or economically unattractive, this can result in curtailment.

Now the 2 MW design may not be optimal without:

• export capability;
• zero-export control;
• load management;
• storage; or
• another appropriate energy arrangement.

This is why industrial system sizing should consider:

maximum load

and

minimum daytime load.

Annual consumption alone hides both.

Protection Design Becomes More Important as Capacity Grows

A large industrial solar plant changes the electrical network inside the factory.

Engineers may need to evaluate:

• short-circuit levels;
• relay coordination;
• anti-islanding protection;
• over/under-voltage protection;
• over/under-frequency protection;
• breaker ratings;
• transformer capacity;
• cable sizing;
• earthing;
• surge protection; and
• grid-synchronisation requirements.

For an HT-connected facility, solar should behave correctly not only during normal generation but also during:

grid faults

power failures

DG operation

maintenance

and

system switching.

This is why the inverter is not simply another machine connected to the factory.

It becomes part of the electrical power system.

DG + Solar Requires Special Attention

Many factories have diesel generators for backup.

Now consider what happens during a grid outage.

The grid disappears.

DG starts.

What happens to the solar plant?

Can solar operate with the DG?

Should it disconnect?

If coordinated operation is intended, how will generation and DG loading be controlled?

Suppose:

DG capacity = 1,000 kVA

Factory emergency load = 500 kW

Solar generation = 700 kW

Without the correct control philosophy, the operating condition can become problematic.

The solution depends on the system architecture and equipment.

The important point for factory owners is:

“We already have DG backup” is not the end of the solar discussion.

It is the beginning of another engineering discussion.

Power Quality Matters in an Industrial Environment

Industrial facilities can contain:

• variable-frequency drives;
• welding equipment;
• large motors;
• furnaces;
• rectifiers;
• compressors; and
• other nonlinear or rapidly changing loads.

These can influence harmonics, voltage behaviour and power quality.

Solar inverters also interact with the electrical system.

A large industrial solar installation therefore deserves proper electrical studies where required rather than assuming that a technically compliant inverter will automatically solve every site-level interaction.

This becomes increasingly important as solar penetration rises relative to the facility load.

Solar Sizing Should Follow the Factory's Production Cycle

Consider a textile unit.

Production operates:

24×7 for eight months

but slows substantially during the remaining four months.

Now consider an engineering plant operating:

Monday–Saturday

with almost no Sunday load.

And a food-processing factory with a:

four-month seasonal production peak.

All three could consume the same annual number of units.

Their optimum solar designs could still differ.

For an HT consumer, ask for at least:

12 months of electricity bills

and, where available:

interval load data across representative working and non-working days.

Then overlay expected solar generation.

That is much stronger than sizing from:

Annual units ÷ assumed generation/kW.

Illustrative: Same 1 MW Solar, Different Factory

Consider a 1 MW solar plant expected to generate an illustrative:

15 lakh units/year

Now compare two factories.

Factory A

Directly consumes 95% of solar generation.

Useful direct solar energy:

14.25 lakh units

Factory B

Can directly use only 65%.

Useful direct solar energy:

9.75 lakh units

Difference:

4.5 lakh units/year

At an illustrative electricity value of ₹8/unit:

₹36 lakh/year

Same 1 MW system.

Same solar generation.

Potentially very different direct-consumption value.

The treatment and value of any surplus would depend on the applicable arrangement, so this example intentionally focuses only on direct utilisation.

This is why industrial solar should be designed against the load curve.

Rooftop Solar May Only Be the First Layer for HT Consumers

Large HT consumers often have another challenge:

Their electricity requirement is much larger than their available roof.

Suppose a factory consumes:

1.5 crore units/year

The technically suitable rooftop can support a solar system producing:

25 lakh units/year

Even a perfectly designed rooftop plant addresses only part of the requirement.

That doesn't make rooftop solar a poor investment.

It means the factory's energy strategy may need multiple layers:

Rooftop industrial solar

Captive / group-captive / open-access renewable power

Grid

Storage where economically justified

Mercom reported in July 2026 that open access is expected to remain an important route for large industrial consumers specifically because rooftop solar is constrained by available space. Mercomindia.com

Earlier in 2026, industry participants similarly described rooftop solar as the logical first step before evaluating open access for larger C&I requirements. Mercomindia.com

Industrial Solar Is Growing But Residential Design Logic Shouldn't Follow It Into Factories

India added 6.6 GW of rooftop solar in the first half of 2026, up 131% year over year. Industrial projects accounted for 10% of Q2 additions, while Gujarat was one of the country's leading rooftop markets. Mercomindia.com

This rapid growth is encouraging.

But residential and industrial rooftop projects solve very different problems.

A residential system may primarily be designed around:

household consumption + available roof + applicable net-metering arrangement.

A large HT industrial system can require analysis of:

energy consumption + maximum demand + contract demand + load curve + tariff timing + transformer architecture + protection + DG integration + export conditions + future production.

That is a fundamentally different design exercise.

Where Do Industrial Solar Batteries Fit?

For some HT consumers, industrial solar batteries can add another layer of control.

Suppose a factory produces surplus solar around:

1 PM–3 PM

but experiences a high grid-demand period around:

6 PM–8 PM.

Storage could potentially shift some energy from the first period into the second.

For example:

Surplus solar available:

500 kW for 2 hours

Energy:

1,000 kWh

A suitably designed battery could store part of that energy for later use, subject to efficiency, usable state of charge and system constraints.

But battery sizing must answer two different questions:

How much power is required? — kW/MW

For how long? — kWh/MWh

A battery should not be added simply because the factory is an HT consumer.

Mercom reported in May 2026 that C&I energy procurement is increasingly moving beyond rooftop solar alone toward combinations of renewable energy and battery storage as businesses seek better alignment between clean generation and their actual operating requirements. Mercomindia.com

Storage should solve a measurable problem.

Future Production Expansion Should Be Designed In

Suppose a factory currently operates with:

Maximum demand: 1,500 kVA

Management plans to add a production line next year.

Expected demand:

2,200 kVA

If the solar plant is designed only around today's operating profile, the facility may need major modifications later.

Future planning can affect:

• inverter architecture;
• transformer loading;
• connection point;
• switchgear;
• cable routes;
• rooftop allocation;
• monitoring; and
• potential storage integration.

For a 25-year energy asset, asking about the factory's next five years of production is entirely reasonable.

An HT Solar Proposal Should Show More Than Payback

A serious industrial proposal should ideally include:

Metric	Project Data
Annual electricity consumption	___ kWh
Maximum demand	___ kW/kVA
Contract demand	___ kW/kVA
Minimum daytime load	___ kW
Proposed solar capacity	___ kW
Expected annual generation	___ kWh
Expected direct consumption	___%
Expected surplus/export	___ kWh
Existing transformer capacity	___ kVA
Connection level	___ kV
Annual grid energy displaced	___ kWh
Estimated annual savings	₹___

Then include an hourly or interval-based graph showing:

Factory Load vs Solar Generation vs Grid Import

That single chart can expose design problems that an attractive “3-year payback” headline hides.

Five Questions HT Consumers Should Ask Their Solar EPC Company

1. Have you analysed our interval load data?

If the design uses only monthly bills, ask why.

2. Where exactly will solar connect to our electrical network?

The proposal should identify the connection architecture not just the roof layout.

3. What happens when production load falls below solar generation?

Ask about export, curtailment and control strategy.

4. How does the solar system interact with transformers, protection and DG backup?

These should be engineered, not assumed.

5. What percentage of solar generation will we actually use economically?

Annual generation alone isn't enough.

These questions help distinguish an industrial solar engineering proposal from a scaled-up rooftop quotation.

The Enersol Approach: Design Around the Factory, Not Just the Roof

For Enersol, an HT industrial project should begin with three datasets:

The electricity data.

The electrical system.

The production pattern.

The electricity data tells us consumption, maximum demand and tariff exposure.

The electrical study shows transformers, switchgear, connection points, protection and existing infrastructure.

The production profile tells us when electricity is actually required.

Then comes the roof and solar-resource assessment.

Only after these pieces are brought together should the final solar panels for industrial use be sized and the electrical architecture locked.

For some factories, rooftop solar may address a substantial share of daytime energy.

For larger HT consumers, rooftop solar may become the first layer of a wider strategy involving captive/open-access renewable energy and potentially industrial solar batteries.

The goal isn't simply to install the maximum possible MW.

It is to make every installed MW work intelligently with the factory.

Final Thoughts

HT industrial consumers should not buy solar as though they are buying a larger version of an LT rooftop system.

The difference goes far beyond capacity.

HT facilities can have:

• complex load curves;
• maximum and contract demand;
• time-dependent tariffs;
• multiple transformers;
• large motors and process loads;
• DG systems;
• protection requirements;
• 24-hour production.

That changes both the engineering and the economics.

India's industrial rooftop solar market is growing quickly, with industrial installations representing 10% of Q2 2026 rooftop additions. Mercomindia.com At the same time, C&I consumers are increasingly combining rooftop solar with open access and storage as their energy strategies become more sophisticated. Mercomindia.com

For a factory owner, the actionable takeaway is simple:

Before approving an industrial solar installation, ask for more than a capacity recommendation.

Ask for:

your load curve,

the solar-generation curve,

the proposed electrical connection architecture,

and

the resulting grid-import profile.

If those four pieces are missing, you may know how many panels you're buying.

But you still don't know whether the solar system has been designed for your factory.