Estrato and solar savings: why your neighbour saves more than you with the same panels

Picture two homes on the same block, with the same roof, the same orientation and the same monthly consumption. They install the same system, on the same day, with the same installer. A year later, one has saved considerably more than the other.

There is no trick and no botched installation. Solar energy produces kilowatt-hours, but savings are measured in pesos, and the bridge between the two is the tariff. In Colombia that tariff is not the same for everyone: it depends on the property's socioeconomic estrato, on the type of user, and on how much you consume.

It is one of the local particularities that weigh most heavily on the calculation, and one of the least likely to appear in a commercial proposal, where savings are usually presented as a single percentage applicable to anyone.

It is worth separating two things that get mixed together constantly.

A system's output is a physical matter: it depends on installed capacity, the irradiation of your area, the orientation and tilt of the roof, shading and equipment performance. The estrato plays no part whatsoever there. A 4 kWp system on a given roof produces the same whether the property is estrato 2 or estrato 6.

Savings, by contrast, are an economic matter: they are the kilowatt-hours you stop buying multiplied by what buying them used to cost. And there the estrato weighs a great deal, because the effective price per kWh of a subsidised home and that of a home paying the solidarity contribution can be a long way apart.

From that follows a rule the sector's marketing finds awkward: the more expensive your energy, the more profitable it is to stop buying it. Solar energy is not a product that saves everyone the same.

The scheme comes from Ley 142 de 1994, which organises the regime for residential public utilities. Its logic is one of solidarity: higher estratos and commercial and industrial users pay a surcharge on the value of the service, and that surcharge funds the subsidy for the lower estratos.

It is not a hidden item on the bill. It appears as an explicit line — negative if you are subsidised, positive if you contribute — next to the consumption charge. It is the first place to look before believing any savings estimate.

The practical consequence is that two different prices are circling the conversation. The unit cost of the service, which is the one usually quoted in tables and articles, and what you actually pay per kWh once the subsidy or contribution has been applied. Estimating savings with the first when your bill runs on the second produces a number that is wrong from its first line.

Here is the nuance that upends the easy conclusion that 'solar is not for the lower estratos'.

The subsidy does not apply to everything you consume: it covers only up to a threshold, the subsistence consumption, set by the Ministry of Mines and Energy and not the same across the country, because it depends on the municipality's altitude. Anything you consume above that threshold is billed without subsidy.

That means a subsidised home with high consumption has two prices living inside the same bill: some cheap kWh, the subsidised ones, and some expensive ones, those above the threshold. And what a solar system reduces is not an average, but the consumption actually billed to you.

From that comes the nuance almost no quote picks up: when your consumption sits above the subsidised threshold, every kilowatt-hour you stop buying may be avoiding the full tariff rather than the subsidised one. The marginal value of the saving can therefore be greater than the bill's average price suggests. How much greater depends on how your retailer settles the subsidy once the system is running — a question with a concrete answer, and one we come back to below.

That is why ruling a project out on estrato alone is a common mistake. An estrato 2 home with air conditioning and consumption well above the threshold can have a better case than an estrato 5 home with low consumption. The relevant figure is not the label on the property but where your consumption falls relative to that threshold.

The symmetric reading has its own trap. It is true that in estrato 5 or 6 each avoided kWh is worth more, because a contribution is levied on the service. But it does not follow that the project is always better.

A low-consumption home has little to replace, and the cost of an installation does not fall in the same proportion: there are fixed costs — design, paperwork, mounting structure, a day of labour — that weigh the same on a small system as on a mid-sized one. A high saving per kWh on few kWh is still a small saving against the investment.

There is also one concrete question worth putting to your retailer before signing, because it determines the outcome and not everyone answers it the same way: on what base the subsidy or the contribution is settled once the system starts offsetting surplus. It is no minor accounting detail, and we would rather flag it as an open question than publish a general rule we cannot back with the regulation in hand.

What is written down precisely is how the surplus is recognised. Article 25 of Resolución CREG 174 de 2021, as amended by Resolución CREG 101 072 de 2025, draws a distinction for a small-scale self-generator of up to 100 kW running on renewable sources. Surplus that does not exceed the energy you imported over the period is swapped against that import: this is the energy credit. Surplus above it is settled hour by hour at the wholesale spot price, a market value that need not resemble the tariff you pay when you buy.

And there is a detail usually left out: even on the swapped kilowatt-hours the retailer charges the commercialisation component of the tariff. In other words, the energy you export and recover later is not exactly free. That is why consuming on the spot and exporting are not worth the same, why the gap widens the higher your tariff, and why consuming during the day matters more than it seems.

Whatever your estrato, there are parts of the bill a solar system does not touch.

The energy service shares the same paper with other items — public lighting and, in many municipalities, waste collection — calculated on their own criteria, unrelated to your kilowatt-hours. And as long as you remain connected to the grid there are charges tied to being connected, which is exactly what you are buying: permanent backup.

That is why installing more panels does not make every item on the bill disappear. The energy charge can fall a very long way, and surplus accumulates as a credit in your favour, but even on those swapped kilowatt-hours the commercialisation component is still charged, and alongside it sit the charges that have nothing to do with your consumption. A proposal promising a 'zero bill' is describing something the Colombian scheme — energy credits on a bidirectional meter, which is what gets loosely called net metering — does not do.

If something on your bill does not add up, the Superintendencia de Servicios Públicos Domiciliarios is the body that oversees billing and handles complaints.

All of the above boils down to a single number, and you can get it from your own bills today without anyone's help.

Take the energy service charge — not the total on the bill, which may include public lighting, waste collection or other items — and divide it by the kilowatt-hours consumed in that period. The result is what each kWh actually costs you, with subsidy or contribution already baked in.

Do it across twelve months and keep the average: a single month can be distorted by a trip, a hot spell or an irregular billing cycle. That average, together with your monthly consumption in kWh, is the starting point of any honest estimate.

With those two figures you can use our calculator, which gives savings as a range between a conservative and a favourable scenario rather than as a single number, precisely because the value of the surplus is not guaranteed.

A serious proposal has to be able to tell you which tariff it used to calculate your savings. If it does not state it, the number it shows you is not yours: it belongs to a generic case.

Ask for the estimated saving with its assumptions — the tariff used, the irradiation, the self-consumption fraction — and for it to distinguish between the energy you will consume on the spot and the energy you will export. Those are two different savings and blending them inflates the result.

Be wary of any fixed savings percentage announced before anyone has seen your bill. In a country where the price per kWh depends on the estrato, the subsistence threshold and the type of user, a 'save 70%' with no further context is not a calculation, it is a headline.