Sizing a photovoltaic system is the most important step — a system that is too small does not cover consumption, and one that is too large is an unprofitable investment. Here's how we do the math right.

1. Calculate your actual consumption

It starts with energy bills from the last 12 months. Add up the kWh consumed and divide by 365. Thus you get the average daily consumption. A typical house in Romania consumes 15-25 kWh/day, and one with a heat pump reaches 40-60 kWh/day in winter.

2. Determine the power of the installation (kWp)

General rule: in Romania, 1 kWp installed produces ~1,300 kWh/year. So for an annual consumption of 5,000 kWh you need at least 4 kWp.

For full autonomy we recommend to oversize by 20-30%: if you need 4 kWp, install 5 kWp to cover network losses as well.

3. Available space and orientation

• South facing roof, inclined 25-35° → maximum yield
• East-west roof → 90% of south roof production
• Flat → we add inclined structure, efficiency 92%
• 1 kWp = ~5-6 m² roof

4. System type: On-Grid, Off-Grid or Hybrid

On-Grid: connected to mains, no batteries. The cheapest, ideal for daily consumption (homes with telework).

Off-Grid: isolated, with batteries. For cottages or homes without a grid. Requires more careful sizing.

Hybrid: combine both — produce, store and inject surplus into the grid. Recommended for autonomy + prosumer status.

5. Storage capacity

For typical nighttime autonomy, LiFePO4 battery sized at 50% of daily consumption. For a house with 20 kWh/day consumption, 10-15 kWh storage is optimal.

Practical example

House with 4 people, annual consumption 6,000 kWh:

• System 5-6 kWp TOPCon panels
• Hybrid inverter 5 kW
• LiFePO4 10 kWh battery
• Investment: ~12,000-15,000 € turnkey
• Payback: 6-8 years

La EcoSolaris we do free sizing based on your invoices. See the range of products or contact us for a personalized offer.