How many panels do I need?

At some point in your search it'll happen: someone you know says they installed 6 panels, someone in a Facebook group swears 4 is more than enough, and an ad offers you a "kit of 8" as if it were one-size-fits-all. Three different numbers, all three stated with total confidence. So which one is yours?

Short answer: the one your consumption justifies and your roof allows, in that order. Useful answer: read on, because understanding where the number comes from will help you evaluate any quote you receive.

The starting figure is how much energy you consume per month, and it's on your bill: the kWh. Not the amount in pesos. The kWh, which appear in the consumption breakdown.

One tip before going further: don't look at a single bill. Consumption varies a lot across the year, with air conditioning in summer and heating or longer lighting hours in winter. The right approach is to look at the last six bills, or better still twelve, and take the average. Sizing against the January bill leads to an oversized system; against the May one, to an undersized system.

Conceptually the calculation goes like this: each kWp of panels generates, in Argentina and depending on the region and roof conditions, a reasonably predictable number of kWh per year. From your annual consumption and that expected yield you get the capacity you need, and from there the panel count.

We're deliberately not giving you a "divide by this number" formula: real yield depends on your location, orientation and shading, and that's exactly where a generic calculation turns into a promise that can't be kept. What you can verify with what you have: that the starting point is YOUR actual consumption. If nobody has asked you for bills yet, offer them: it takes a minute and turns a general estimate into a number for your home.

Intuition says "I want panels so I never pay for electricity again". And here we have to be honest: covering 100% of your consumption is almost never the best purchase.

The reason is how the credit works. What you generate and use on the spot saves you the full price of the kWh. What you generate in excess is fed to the grid and credited back (only in provinces where this is permitted and regulated), but at a lower value. So the first panels, the ones covering your daytime consumption, are the best deal. The last ones, generating surplus almost all year, are the worst. A system covering a good share of your consumption usually returns more per peso invested than one chasing a zero on the bill.

Besides, a literal zero doesn't exist: the fixed connection charges are paid either way. The bill drops a lot; it doesn't disappear. We'd rather you heard that from us than from your first bill.

If budget or roof space leaves you torn between two sizes, there's an asymmetry working in your favour: expanding later is relatively straightforward, shrinking is impossible.

A good system is designed leaving the door open: roof space reserved, electrical installation planned to grow. If next year you add an electric car or a pool, you add panels on top of what you already have. That's why it's worth telling your installer your plans: "I'm thinking of putting air conditioning in the bedrooms" is a sizing input, not small talk. There's a whole article on what makes a system expandable.

When the quote arrives, the panel count should come with:

• Your consumption as the starting point: they asked you for bills, ideally several
• A generation estimate for your case, not a generic savings percentage
• The sizing logic explained: what share of your consumption it covers and why that point
• The surplus stated plainly: how much you'd generate in excess and what it's worth
• Your future plans considered, or at least asked about

The panel count is the conclusion of a line of reasoning. Ask to see the reasoning, not just the conclusion: any well-made proposal has one behind it, and seeing it will give you confidence to decide.