How to tell whether your home is a good fit for solar energy

You do not need to be an expert to make a first assessment. Review these points before going further:

It is the first question and it is usually answered badly, because people think in total square metres rather than usable area.

Usable area is the part of the roof left after subtracting everything in the way: chimneys, water tanks, aerials, skylights, the shade those same elements cast, and the walkways required by regulation and maintenance. On a hipped roof, moreover, only one or two planes are usually usable.

As a practical order of magnitude, a current module takes up around two square metres and contributes a fraction of a kilowatt. A typical residential system of 3 to 5 kWp therefore needs on the order of 15 to 30 free, well-oriented square metres, not the total surface of your house.

One detail that changes the sums: modules cannot be placed flush against each other if the roof is flat and they sit on tilted structures, because they shade one another. On a flat roof, the spacing between rows can take up as much surface as the modules themselves.

In Colombia, because of the proximity to the equator, the sun stays high all year and day length barely varies. Differences in output from orientation are considerably smaller than in countries with marked seasons, where a badly oriented roof can be ruled out outright.

That does not mean it makes no difference. A north- or south-facing plane, with a moderate tilt, is still better than a west-facing one. But the penalty of an imperfect orientation is usually a few percentage points of annual output, not half of it.

There is an interesting nuance: orientation changes not only how much you produce, but when. An east-facing plane concentrates output in the morning; a west-facing one, in the afternoon. If your consumption is concentrated late in the day, a west-facing orientation can deliver more in real savings even if it produces somewhat less in total, because it increases self-consumption.

What does penalise clearly is shade. An area shaded for much of the day greatly reduces output, and on a system with a central inverter the effect can be disproportionate: the modules are connected in a string, and shade over one drags down the performance of the whole string.

A solar system lasts around twenty-five years. The roof it is installed on does not always.

If your tiles or sheeting are close to the end of their service life, installing on top means that when the time comes to replace them the system will have to be dismantled, the roof changed and the system reinstalled. That double job has a cost nobody includes in the initial quote, because it happens years later.

The rule of thumb is simple: if the roof has fewer years left than the system, it is worth renewing it before rather than after. It is an uncomfortable conversation once you have decided to invest in panels, but far cheaper than the alternative.

The material also drives the mounting cost. Clay tile, metal sheeting and flat slab take different structures, with different prices and complexity. Clay tile is the most delicate: it requires specific components and a careful hand so watertightness is not compromised.

Consumption is what defines the size of the system, but there is a second variable that is almost never mentioned and that weighs just as much: what time of day you consume.

The energy you use while the system is producing saves you the full tariff. What you export is offset according to what the regulation sets, at a value that need not match it. Two homes with the same monthly consumption and the same system can save different amounts if one is empty all day and the other is not.

That does not disqualify anyone: a home with mainly night-time consumption still saves, just less per kWh generated. But it should be reflected in the savings estimate you are shown. If a proposal values all generation at the full tariff without asking about your schedule, it is being optimistic.

As for magnitude, low consumption does not prevent installing: it makes a small system perform proportionally worse, because the fixed costs — design, mobilisation, legalization — are spread across less capacity.

It is the most common case in Colombian cities and the one that causes the most confusion.

In a complex or building, the roof is usually common property, not owned by any particular apartment. Installing there for the consumption of a private unit requires authorisation from the owners' assembly under Ley 675 de 2001, and in many cases implies exclusive use of a common area that has to be formalised.

There is a considerably simpler variant, which is for the condominium to install for its own consumption: common-area lighting, pressure pumps, lifts, the concierge desk. That consumption is daytime and continuous, which fits generation well, and the decision rests with the assembly without needing to resolve individual rights over the roof.

If you have a terrace or roof in private use — a penthouse, a house inside a gated complex — the case is much closer to that of a single-family home, though it is worth checking the condominium bylaws in case there are aesthetic restrictions.

Almost none of these factors is disqualifying on its own, and it is worth knowing what can be compensated for and what cannot.

A partially shaded roof can be resolved with microinverters or power optimizers, which confine the effect of shade to the affected modules instead of dragging the whole string down. They cost more, but on a roof with partial shading they recover much of the lost output.

Limited area is compensated for with modules of higher capacity per square metre. Low consumption does not prevent installing a small system, although its cost per kWp will be higher. And a complex roof is resolved with a suitable structure, at its own extra cost.

What has no reasonable fix is a roof with heavy shade for most of the day, or one needing imminent replacement. In those two cases the honest answer is to wait or look for another surface.

The technical visit is what confirms what is viable in your case. No remote assessment, including this one, replaces it.