The most expensive mistake in domestic solar is buying more than you can use. Here is how sizing actually works.
Most people arrive at a number of panels before they have looked at a bill. It is worth doing it the other way round.
Start with consumption, not roof space
Your annual usage in kWh is on your electricity bill. That figure, more than anything about your roof, determines what size system makes sense. A household using 4,000 kWh a year and one using 7,000 need meaningfully different systems.
Why oversizing costs you
Generation you do not use is exported. Export is paid at a lower rate than you pay to import, so every unit you export rather than consume is worth less to you than one you use. Beyond a certain point, adding panels adds cost faster than it adds value.
What the roof decides
- Orientation. South is best; east and west still work and can suit morning and evening usage.
- Pitch. Most Irish roof pitches are within a workable range.
- Shading. Trees, chimneys and dormers change panel layout and sometimes the inverter choice.
- Condition. Older roofs are assessed before anything is mounted.
The grant is pro-rata
Worth factoring in: the SEAI grant scales with system size up to the €1,800 maximum. A 2.5kWp system draws about €1,500 rather than the full amount.
What we do
We ask for your bills, look at the roof properly, and design to your actual consumption. If that means a smaller system than you were expecting, we will say so — a system sized to your house is worth more than a bigger one sized to a quote.