Why a business recovers its solar investment sooner than a home

A photovoltaic module does not know whether it sits on a house or on a warehouse. The difference between the residential and the business case is not in the equipment: it is in four economic conditions that in a company tend to occur together and in a home almost never do.

They are worth listing because each can be checked inside the company before requesting a single quote, and because together they explain why two projects of the same installed capacity can have very different returns.

It is also worth saying the opposite from the start: none of this makes solar a good idea for every company. There are conditions that push the other way, and they have their own section.

This is by far the heaviest factor, and it is purely a matter of timing.

A grid-connected system generates during the day. The energy you consume at that same instant saves you the full tariff; what is left over is exported to the grid and offset according to article 25 of Resolución CREG 174 de 2021, as amended by Resolución CREG 101 072 de 2025, at a value that need not match that tariff. Self-consuming and exporting are not worth the same.

A typical family home has the problem of emptying out precisely during the hours of highest generation: people leave for work and come back when the sun is already dropping. An office, a workshop, a shop, a data centre or a pumping system have the opposite pattern, with demand concentrated in working hours.

The result is that in a company a far larger share of what is generated turns into full tariff avoided. It is the same system producing the same amount, but each kilowatt-hour is worth more.

The Colombian utilities regime, set out in Ley 142 de 1994, funds the subsidy for the lower estratos with contributions from the higher estratos and from commercial and industrial users, who pay a solidarity contribution on the value of the service.

Translated into the solar project: the company sits on the expensive side of that equation. Its effective price per kilowatt-hour is higher than that of a good share of the country's households, and since savings are avoided kWh multiplied by what buying them used to cost, each unit saved yields more.

The corollary is that the figure to take into the assessment is not the unit cost that appears in general tables, but the effective price per kWh you get by dividing the energy service charge by the kilowatt-hours billed, averaged over twelve months.

Ley 1715 de 2014, amended by Ley 2099 de 2021, establishes four mechanisms for non-conventional renewable generation projects, and Decreto 829 de 2020 sets out the procedure on a project certified with UPME.

Those mechanisms carry an implicit requirement that leaves most households out and most formal companies in: you need a tax position that allows you to use them. The income tax deduction and accelerated depreciation are only worth something if there is enough taxable income to apply them against.

That is where the project stops being a technical decision and becomes a joint one with the finance function. The benefit is not a discount the installer applies to the invoice: it is a procedure with its own calendar, and the order of the steps matters.

It is also where you should be wary of a proposal presenting the incentives already deducted from the price as though they were automatic. They are not, and presenting them that way distorts the comparison between quotes.

A solar project has costs that barely change with size: the design, the site visit, mobilising the crew, the connection process, commissioning.

On a small residential system those fixed costs are spread over few kilowatts peak and weigh heavily on the final price per kWp. On an installation of tens or hundreds of kWp they are spread over many more, and the unit cost falls.

Technical factors push the same way: large, clear roofs without the shading of a residential neighbourhood; three-phase supply; and the option of working with higher-capacity inverters, more efficient per installed watt.

That is why comparing quotes on their bottom line is an even worse mistake in the business world than in the residential one. The unit of comparison is the cost per installed kWp, with the same scope declared in both proposals.

The first real obstacle is neither technical nor financial: it is who owns the building. A company operating from a leased warehouse has to settle who invests, what happens when the lease ends and who keeps the asset. That is a conversation to have with the landlord before requesting quotes, not after.

The second is the time horizon. A project assessed over twenty years makes no sense if the company expects to move in three, unless the contractual structure allows for that scenario.

The third is the state of the roof. A roof due for replacement in the short term has to be dealt with before anything is mounted on it, and some structures need reinforcing to take the extra load. That cost belongs to the project even if it is not solar, and leaving it out of the proposal is one of the classic sources of cost overrun.

The fourth is the consumption profile. Not every company consumes during the day: an operation with a night shift, a cold room running in the small hours or an evening-trade business look, in this respect, more like a home than a factory.

When there is plenty of roof available a predictable temptation appears: fill it. It is the mistake that most often turns a good project into a mediocre one.

Sizing by available square metres instead of by the consumption curve produces a system that over-generates in the middle hours, exports that surplus and sees it offset at a value that does not match the tariff avoided. The investment rises in proportion to size; the saving does not.

Correct sizing starts from the company's consumption data — ideally the hourly curve if the retailer can supply it, and otherwise twelve months of bills — and looks for the point where self-consumption is maximised without producing a systematic surplus.

If a proposal arrives with a capacity it does not explain, that is the question to ask before any other: why that capacity and not a smaller one.

A proposal that will go before an investment committee needs things a residential quote does not usually carry, and asking for them up front saves a whole review cycle.

Ask for the estimated annual output with its assumptions stated — the irradiation used and the performance ratio — not a bare figure. Ask for the cash flow with and without incentives, because those are two scenarios with different probabilities. Ask for the brand and model of modules and inverter, not 'equivalent', and for the module, inverter and installation warranties separately.

Ask too who takes on the UPME certification and who the connection process with the grid operator, with timescales. And verify RETIE compliance, which is not negotiable in exchange for a discount.

With that, the decision stops being an act of faith in the salesperson and becomes what it should be: an investment assessed with its assumptions on show.