Peak Sun Hours (HSP): explained simply to get your solar installation right
If you've ever read that “your area has 4.5 HSP” and didn't understand anything, don't worry. Peak Sun Hours (HSP) are a way to express how much solar energy reaches your panels each day as “equivalent hours of strong sun” at 1,000 W/m².
Why do HSP matter to me?
- To estimate the production of your panels in kWh per day.
- To choose the right panel power (without undersizing or oversizing).
- To size batteries in off-grid systems and anticipate winter performance.
- To calculate pumping: hours of operation at full power and daily flow rate.
The easy formula (the one you'll always use)
Daily production (kWh) ≈ Panel power (kWp) × HSP × 0.80–0.85
Example: 2 kWp × 4.0 HSP × 0.85 ≈ 6.8 kWh/day.
Losses: the factor 0.80–0.85 accounts for temperature, cables, inverter, dirt, and shading.
Key concepts
- Round-trip efficiency: energy that comes out of the battery compared to what went in when charging (typical lithium ≈ 90–95%).
- DoD (Depth of Discharge): % of the nominal capacity you can use without shortening lifespan (typical lithium 80–90%; lead-acid ≈ 50%).
- Reference HSP: unless otherwise indicated, calculated for south orientation and optimal tilt (module almost perpendicular to the radiation).
Example 1 — Off-grid home (no grid, lithium batteries)
Objective: country house with 5 kWh/day. Area with HSP 4.2.
- Panels: 5 ÷ (4.2 × 0.8) ≈ 1.49 kWp → we recommend 1.8–2.2 kWp due to clouds and degradation.
-
Battery (lithium): 1 day of usable autonomy. With round-trip efficiency 90% and DoD 80%:
Useful energy required = 5 ÷ 0.9 = 5.55 kWh → Nominal capacity = 5.55 ÷ 0.8 = 6.9 kWh → recommended lithium battery 7–10 kWh (if lead-acid, you would need approximately double the nominal due to lower DoD). - Inverter: microwave peaks + pump + fridge → 3 kW with good overload capacity.
Result: balanced system for daily use; more margin in winter if you schedule consumption with sunlight.
Example 2 — Self-consumption in grid-connected home
Objective: home with 18 kWh/day aiming to cover 60–80% with solar. HSP 4.5 area, south-facing roof 25°.
- Target production: 12 kWh/day.
- Panels: 12 ÷ (4.5 × 0.85) ≈ 3.1 kWp → we recommend 3.6–4.0 kWp (better coverage in winter and cloudy conditions).
- Inverter: 3–4 kW (ideally 2 MPPT if there are two roof sections or shading).
Important note: Published HSP usually assume south orientation and optimal tilt. If your roof faces east/west or is very flat, the effective HSP decreases; compensate with more panels or correct with an orientation/tilt factor.
Example 3 — Water pumping to storage tank
Objective: pump 10 m³/day to 40 m (well without grid). Typical solar pump brand (Lorentz, Ziri, Grundfos, Acrosun…). HSP 5.0 area.
- Select the pump by hydraulic curve (flow at 40 m) and the manufacturer will provide the minimum required PV power (e.g., 1.6 kWp for your flow/TDH).
- With that installed power, the pump delivers its nominal performance for approximately HSP hours per day: full power hours ≈ HSP.
- During the remaining hours with lower irradiation, the pump keeps running, but with less flow. For a conservative estimate, use:
Daily volume ≈ Nominal flow × HSP × 0.85
(0.85 accounts for losses and that not all HSP are exactly at peak power). Adjust with the manufacturer's charts for greater accuracy.
Tip: in storage tank pumping, the “storage” is the water: usually batteries are not needed, just proper PV sizing and a solar controller/inverter.
How to determine your HSP
- Reference: HSP calculated for south and optimal tilt (modules as perpendicular as possible to the radiation).
- For off-grid systems, use monthly HSP and design for the critical month (winter).
- If your roof is east/west or flat, adjust the effective HSP or add 10–20% more panel.
Base HSP table (30° tilt, south orientation)
| Country | Province | Maximum summer HSP (h) | Minimum winter HSP (h) | Annual average HSP (h) | Notes |
|---|---|---|---|---|---|
| Spain | Madrid | 7,660 | 2,427 | 5,069 | 30° and optimal tilt |
| Spain | Seville | 7,118 | 2,757 | 5,155 | High irradiation |
| Spain | Barcelona | 6,427 | 2,402 | 4,496 | Coastal |
Indicative values; vary due to cloud cover, shading, and real conditions. For a professional project, use manufacturer data and curves and simulate losses.
Compatibilities / Limitations
- East/west roofs: distribute daily production better but reduce effective HSP compared to south (compensate with +10–20% more panel).
- Partial shading: separate strings, optimizers, or microinverters as appropriate.
- Hot climates: use a 0.80 factor and leave ventilation under the panel.
- Off-grid in winter: design with minimum HSP or add backup (generator/grid charging).
Maintenance
- Clean when you see persistent dust/salt.
- Annual inspection of tightening, protections, and production vs. expected HSP.
- Monitor module temperature and the impact of seasonal shading.
Typical mistakes (and how to avoid them)
- Confusing “hours of light” with HSP: HSP are equivalent hours of sun at 1,000 W/m².
- Forgetting losses: apply 0.80–0.85 in quick calculations.
- Designing for summer: in off-grid systems, winter is the key period.
- Not checking Voc/Isc with temperature: check string limits in cold/heat.
Quick FAQs
Can I use only annual HSP? Yes, for a first estimate; to refine, use monthly HSP and design for the worst period.
Do I need batteries if I have grid connection? Not necessarily; scheduling consumption at midday already improves savings. The battery increases the % of self-consumption.
Does the same HSP work for everything? HSP measures available solar energy; usable kWh depend on the system and its losses, which is why we apply 0.80–0.85.
Would you like us to do your calculation?
Tell us location, consumption, and whether it is off-grid, self-consumption, or pumping. We will prepare estimated production, actual losses, and suitable materials for you.
