Solar panels for your home

A grid-connected system turns sunlight into electricity that powers your home there and then. What you do not consume at that instant is exported to the grid and offset on your bill; what you need when there is no sun you draw from the grid as normal.

That means it does not change the way you live: there is no consumption to ration, no batteries to watch, nothing to give up at night. The installation is invisible in daily use and its effect shows up on the bill.

What does change is the structure of your spending: you go from paying for energy every month for as long as you own the house to an up-front investment that replaces a good part of that spending for 25 years or more.

The starting point is your monthly consumption in kilowatt-hours (kWh), which appears on your bill. With that figure and the solar radiation in your city, the system capacity is estimated in kilowatts peak (kWp).

A common mistake is to size by the size of the home. There is no relation: a large house with few occupants and no air conditioning can use less than a small apartment with an electric water heater. Consumption rules, not square metres.

A system can cover anything from part to all of your consumption. Covering 100% is not always the most cost-effective: it depends on the space available on your roof, on your budget and on how your consumption is spread through the day. The detail of the calculation is worked through in the sizing guide.

The theoretical calculation runs into a physical limit. As a reference, each kWp needs roughly 5 to 7 m² of well-oriented, unshaded surface, and the usable area is always smaller than the total area: you have to subtract walkways, edge setbacks, tanks, aerials and air-conditioning units.

In Colombia, being close to the equator, the penalty for not facing south is far smaller than at high latitudes. East- or west-facing roofs produce somewhat less in total, but they shift generation towards the morning or the afternoon, which sometimes fits the home's real consumption better.

What does weigh heavily is shade. A growing tree, a neighbouring building adding a floor or a badly placed tank have a disproportionate effect, because in a series string the shaded panel constrains the rest. If the shade is unavoidable, there are solutions — microinverters or optimizers — that limit the damage.

And the structure matters: the roof has to take the weight and the anchor points have to stay watertight. It is where most problems show up afterwards, which is why the installer's workmanship warranty deserves attention.

When your system produces more than you are consuming at a given moment, the surplus is exported to the grid. Net metering lets you deduct that energy from your bill, within the framework of CREG Resolution 174 of 2021 for small-scale self-generators.

In practice the grid acts as backup at no extra cost and with no conversion losses. Adding batteries purely to save usually worsens the return, because they increase the investment without increasing the saving proportionally.

Batteries make sense for a different reason: continuity. If you suffer frequent outages or need certain equipment to keep running during a blackout, the calculation is no longer about profitability but about the cost of being without power.

This is the expectation most worth setting straight before you ask for quotes. A solar system reduces the kilowatt-hours you buy from the grid; on those avoided kWh you stop paying the unit cost of energy.

It does not reduce the items that travel on the same bill but are not energy: the public lighting levy, waste collection in some municipalities, or financing and insurance contracted through the retailer. Nor does it eliminate the bill entirely, because as long as you stay connected you keep a commercial relationship with your operator.

And there is a very Colombian factor that changes the result a lot: the socio-economic stratum. Low strata receive a subsidy on part of their consumption and high strata pay a solidarity contribution, so the effective price per kWh varies considerably. The more you pay per kWh, the more each kWh you stop buying is worth. In a subsidised household with high consumption, moreover, the kWh above the subsidy threshold are the most expensive and are precisely the first ones solar replaces.

The physical installation of a residential system is usually done in a few days. What stretches the project is not the installation but the steps before and after.

Beforehand there is a technical site visit that measures the real area, assesses shading, checks the structure and the panelboard, and works out where the cabling will run. Afterwards comes the connection process with the grid operator, the stage with the most variability in the whole project and one worth building into the schedule from the start.

During the work there will be activity on the roof, conduit runs and a brief interruption of supply when connecting. None of that requires you to move out, but it is worth agreeing in writing who is liable if a leak appears in the roof: it is the most common damage and the one that generates the most disputes.

Besides paying cash, there are consumer credit lines and green loan products aimed at energy efficiency, and some installers offer direct financing. Which one suits you depends on the rate, the term and on whether the estimated monthly saving covers the instalment or not.

The useful comparison is not simply 'instalment versus saving', but the total cost of the loan against the savings accumulated over the term. An instalment that fits the monthly saving can still be expensive if the rate is high and the term long.

If you file income tax, it is also worth reviewing the tax benefits of Laws 1715 of 2014 and 2099 of 2021 with your adviser: they depend on your situation and require certification of the project with UPME, so they are not an automatic discount.