How to Work Out How Much You Save with Solar Panels
Table of Contents
Before installing solar panels, the most important question is always the same: how much will I actually save, and how many years will it take to recoup the investment? There’s no single answer, because the saving depends on your consumption, your location, your roof’s orientation and, above all, how much energy you use during daylight hours. The good news is that it can be estimated with a simple method and a few reference figures.
In this guide we explain, step by step and with a worked example, how to calculate your annual saving with solar panels and your payback period, which variables affect the result, and how the 2026 incentives change things. Every figure comes with its source and confidence level.
Your annual saving is calculated like this: (energy you self-consume × electricity price) + (surplus you export × compensation price). As a reference point, a household with a 5.5 kW installation saves in the order of €1,000/year and pays it back in 6–7 years without incentives (APPA Renovables, 2025). The 2026 income tax deductions shorten that period.
The calculation method in 4 steps
Working out your saving means chaining together four estimates. Here’s each one with its formula.
Step 1. Estimate how much energy your panels will produce
Annual production depends on the capacity you install (in kWp) and the useful sunlight hours in your area. The formula validated by IDAE (Spain’s energy agency) is: Production (kWh/year) = kWp × PSH × 365 × PR
Where:
- kWp: the peak capacity you install.
- PSH: peak sun hours for your area (useful daily solar energy). These range from ~3.9 in the north to ~6 in the south.
- PR (performance ratio): between 0.75 and 0.85; accounts for losses from temperature, the inverter, cabling and dirt.
Practical shortcut: in Spain, each kWp installed produces between 1,100–1,300 kWh/year in the north and 1,500–1,700 kWh/year in the south. For a precise figure for your address, use the European Commission’s free official PVGIS tool.
Step 2. Work out your self-consumption percentage
You don’t use all the energy you produce at the moment you produce it: part of it you consume (self-consumption) and part you export to the grid (surplus). Your self-consumption percentage is decisive, because every kWh you consume is worth far more than every kWh you export.
- Without a battery and with low daytime consumption: around 30–40%.
- With a battery or high daytime consumption: between 70% and 90%.
Step 3. Calculate your annual saving
You now have everything you need for the core saving formula:
Saving (€) = (kWh self-consumed × purchase price) + (kWh surplus × compensation price) | ||
Legal limit to bear in mind (RD 244/2019): compensation for your surplus can never exceed the cost of the energy you draw from the grid in the same billing period. In other words, your energy charge can fall to €0, but surplus isn’t paid out in cash and doesn’t build up as credit in your favour. Fixed costs (contracted power, network charges and taxes) still apply. | ||
Step 4. Calculate the payback period (how many years to recoup the investment)
Payback (years) = Net cost (after incentives) ÷ Annual saving |
A solar installation’s working life exceeds 30 years with minimal maintenance (APPA Renovables, 2025), with the modules retaining around 92% of their output at 25 years. Once it’s paid for itself (usually between year 6 and year 9), the rest of its life is essentially free energy.
Verified reference figures (2026)
These are the values you can use to make your own estimate. It’s worth updating them before you decide, because electricity and surplus prices fluctuate.
| Variable | Valor de referencia | Fuente |
|---|---|---|
| Producción norte de España | 1.100–1.300 kWh/kWp/año | PVGIS (Comisión Europea) |
| Producción centro peninsular | 1.200–1.350 kWh/kWp/año | PVGIS |
| Producción sur de España | 1.500–1.700 kWh/kWp/año | PVGIS |
| Ratio de rendimiento (PR) | 0,75 – 0,85 | IDAE / sector |
| Precio luz hogar (mercado libre) | ≈ 0,15 – 0,20 €/kWh | OCU / comercializadoras |
| Compensación de excedentes | 0,06 – 0,10 €/kWh | Comercializadoras / OCU |
| Coste instalación residencial (5,5 kW) | ≈ 6.682 € (1.215 €/kW) | APPA Renovables 2025 |
| Rango de coste por kWp | 900 – 1.500 €/kWp | UNEF / instaladores |
| Consumo medio del hogar | ≈ 3.000 – 3.500 kWh/año | IDAE (SPAHOUSEC) |
| Producción por panel (450–460 Wp) | 600 – 750 kWh/año | Sector |
What makes your saving vary
Two homes with the same installation can save very different amounts. These are the factors that weigh most:
- Your consumption profile. The more energy you use during daylight hours, the higher your self-consumption and the more you save (each kWh is worth €0.15–0.20 rather than €0.06–0.10).
- Your geographic area. An installation in Almería can produce close to 50% more than the same one on the Cantabrian coast.
- Orientation and tilt. South-facing with a 30–35° tilt is optimal; east or west can lose between 10% and 30%.
- Nearby trees, chimneys or buildings reduce output.
- Sizing. Oversizing generates surplus that’s paid for at a lower rate; the usual approach is to size the installation at 70–80% of your consumption.
- Your tariff and compensation price. Choosing the right tariff and company is key: that’s where it’s easiest to gain or lose savings.
- Physical or virtual battery. These lift the share you actually use from 30–50% to 70–90%.
- Rises in the electricity price. Every increase automatically improves the return on your panels.
Solar electricity tariff prices
What about backup during a power cut?
Important: because of mandatory anti-islanding protection, a normal installation shuts down during a power cut, even with sun and a battery. To keep your supply running you need a hybrid inverter with a backup function plus a switching system (a backup box, roughly €2,000 as a guide), which typically powers only critical loads (fridge, lighting, communications). The Iberian blackout of April 2025 sharply increased interest in this feature.
A worked example with numbers
Let’s look at the full calculation for a detached house in southern Spain. It’s an illustrative example: your result will depend on your own variables.
-
Variable Valor del ejemplo Potencia instalada 5 kWp Coste de la instalación 7.000 € Producción anual (5 × 1.600) 8.000 kWh/año Consumo anual del hogar 4.000 kWh/año % de autoconsumo (sin batería) 35% → 2.800 kWh autoconsumidos Excedentes vertidos 5.200 kWh Ahorro por autoconsumo (2.800 × 0,20 €) 560 € Compensación de excedentes (5.200 × 0,07 €) ≈ 364 € (sujeto al límite legal) Ahorro anual estimado ≈ 900 € Deducción IRPF 10% (base 5.000 €) 500 € (en la Renta 2026) Coste neto tras deducción ≈ 6.500 € Amortización (6.500 ÷ 900) ≈ 7,2 años
How the result changes when you move one variable
- With a battery (80% self-consumption): the saving rises to ~€1,390/year, though the investment increases by €2,500–4,500.
- In the north (1,150 kWh/kWp): the saving falls to ~€700/year and payback stretches to 9–10 years without incentives.
- With high daytime consumption (50% self-consumption): the saving exceeds €1,000/year and payback drops to ~6 years.
For businesses or SMEs with high daytime consumption (15–20 kWp), the self-consumption percentage is higher and payback is usually shorter: between 5 and 8 years.
How the 2026 incentives affect payback
Incentives don’t change your annual saving, but they reduce the net cost of the installation, and therefore shorten your payback period. The main ones in force in 2026 are:
- Income tax deduction for self-consumption (RDL 7/2026): 10% for individual homes and 20% for residential buildings, on a maximum base of €5,000 (batteries included), for installations carried out in 2026.
- Energy efficiency deductions: 20%, 40% or 60% depending on the certified improvement, extended until the end of 2026 (homes) and 2027 (buildings).
- Municipal reductions (IBI / ICIO): discretionary and variable by council; worth checking in your own municipality.
One important nuance: these deductions apply to the investment in the physical installation, not to services such as a virtual battery. For full details of incentives and grants, see our dedicated guide.
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Questions? We answer them
How much do you save a year with solar panels on a home?
It depends on your consumption, your area and your self-consumption percentage, but it’s usually between €600 and €1,200/year. As a reference, APPA Renovables puts the saving from a typical 5.5 kW installation at around €1,038/year.
How do you calculate the saving with solar panels?
In four steps: estimate production (kWp × PSH × 365 × PR), work out your self-consumption percentage, apply the saving formula (self-consumption × electricity price + surplus × compensation price), and divide the net cost by the annual saving to get your payback period.
How many years does it take for solar panels to pay for themselves?
Typically between 6 and 9 years without incentives, and between 4 and 7 years with the 2026 deductions, depending on your area and self-consumption. The installation’s working life exceeds 30 years.
How many solar panels do I need for my consumption?
Divide your annual consumption by the output of each panel (600–750 kWh/year). An average household is usually covered by 5–8 high-output panels (3–5 kWp). The recommended approach is to size the installation at 70–80% of your consumption.
How much does a solar panel produce per year in Spain?
Each kWp installed produces between 1,100 and 1,300 kWh/year in the north and between 1,500 and 1,700 kWh/year in the south. A 450–460 Wp panel generates in the order of 600–750 kWh/year.
What is the self-consumption percentage and why does it matter so much?
It’s the share of the energy you produce and consume there and then, rather than exporting it. It matters because every kWh you self-consume saves you the full electricity price (€0.15–0.20), whereas every kWh exported is only compensated at €0.06–0.10. Without a battery it’s around 30–40%; with a battery, 70–90%.
How much do they pay for surplus energy?
Between €0.06 and €0.10/kWh on the free market, depending on the supplier. By law, compensation can never exceed the cost of the energy you draw from the grid in that period.
At what level of consumption do solar panels become worthwhile?
As a rough guide, from around 2,500–3,000 kWh/year, particularly if a significant share of your consumption falls during daylight hours. Below that, payback stretches out.
What incentives shorten payback in 2026?
The income tax deduction for self-consumption (10–20%), the energy efficiency deductions (20–60%) and, in some municipalities, IBI reductions. They don’t increase your annual saving, but they reduce the net cost and shorten the payback period.
Rafa Loza es experto en el sector energético, fundador y CEO de Quecomparo.es, un comparador de tarifas independiente y gratuito, donde ayudan a miles de usuarios a reducir su factura de luz, gas o telefonia.
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- Rafa Loza
- Rafa Loza
