Interannual variability
The solar resource at any given location fluctuates from year to year. The distribution of annual irradiation values over a sufficiently long record (typically 10–30 years) is well approximated by a normal (Gaussian) distribution, characterised by a mean value and a standard deviation (σ). This standard deviation, expressed as a percentage of the long-term mean, is referred to as the interannual variability.
In PVsyst
- The annual variability is displayed in the "Geographic site" dialog, page "Monthly Weather Data", after importing the data from Meteonorm 9.0.
- If multi-year data are available from a weather data provider, the variability of those data can be evaluated using the tool
Databases > Compare Weather data. The years to be included can be selected, and the "Histo and probabilities" option displays the corresponding distribution plot. - The annual variability value is used in the P90 calculation
Typical magnitude
Annual variability depends on climate type and location. There is a correlation between annual irradiance and annual variability which may be explained by the fact that with sunny climates with many clear days, the possibility of middle or bad days is lower 1.
The table below sumarizes annual GHI variability for Europe (mostly), North America and Africa 1.
| Site | KGPV Climate | Continent | Variability | Lat (°) | Lon (°) | Alt (m) | Period | Source |
|---|---|---|---|---|---|---|---|---|
| Berlin Dahlem (D) | CK | Europe | 7.0% | 52.46 | 13.30 | 58 | 1980–2009 | — |
| Bondville (IL) | CH | North America | 2.4% | 40.05 | −88.37 | 213 | 1995–2008 | SurfRad – NREL |
| Bratislava (SK) | CK | Europe | 3.5% | 48.17 | 17.08 | 195 | 1994–2007 | CIE – ICA |
| Carpentras (F) | CH | Europe | 1.8% | 44.08 | 5.06 | 100 | 1990–2010 | BSRN – Météo France |
| Davos Dorf (CH) | BK | Europe | 3.2% | 46.81 | 9.84 | 1610 | 1981–2010 | WRDC – Met Office |
| Desert Rock (NV) | DM | North America | 1.4% | 36.62 | −116.02 | 1007 | 1999–2008 | SurfRad – NREL |
| El Saler (Spain) | DH | Europe | 2.3% | 39.35 | −0.32 | 10 | 1999–2006 | FluxNet |
| Fort Peck (MO) | DH | North America | 2.5% | 48.31 | −105.10 | 634 | 1995–2008 | SurfRad – NREL |
| Geneva (CH) | CK | Europe | 3.9% | 46.20 | 6.13 | 420 | 1980–2010 | CIE – UNIGE |
| Goodwin Creek (MS) | CH | North America | 3.2% | 34.25 | −89.87 | 98 | 1995–2008 | SurfRad – NREL |
| Ilorin (Nigeria) | EL | Africa | 3.1% | 8.53 | 4.57 | 350 | 1993–2005 | BSRN |
| Lindenberg (D) | CK | Europe | 3.6% | 52.22 | 14.12 | 125 | 1995–2004 | BSRN – DWD |
| Locarno Monti (CH) | CK | Europe | 5.2% | 46.17 | 8.78 | 367 | 1981–2010 | ANETZ – Météo Suisse |
| Murcia San-Javier (Spain) | DH | Europe | 2.4% | 37.78 | −0.82 | 3 | 1985–2008 | — |
| Nantes (F) | CK | Europe | 3.8% | 47.15 | −1.33 | 30 | 1995–2007 | CIE – CSTB |
| Payerne (CH) | CK | Europe | 4.3% | 46.82 | 6.95 | 490 | 1981–2010 | BSRN – Météo Suisse |
| Penn State (PA) | CK | North America | 4.1% | 40.72 | −77.93 | 376 | 1999–2008 | SurfRad – NREL |
| Sion (CH) | BK | Europe | 3.3% | 46.22 | 7.33 | 489 | 1981–2010 | ANETZ – Météo Suisse |
| Sonnblick (A) | BK | Europe | 3.2% | 47.05 | 12.95 | 3105 | 1994–2009 | WRDC – ZAMG |
| Table Mountain (CO) | DH | North America | 1.9% | 40.13 | −105.24 | 1689 | 1996–2008 | SurfRad – NREL |
| Tamanrasset (Algeria) | EM | Africa | 2.4% | 22.78 | 5.52 | 1400 | 1995–2010 | BSRN – Met Office |
| Thessaloniki (GR) | DH | Europe | 2.5% | 40.63 | 22.97 | 60 | 1993–2006 | WRDC – Met Office |
| Toravere (Estonia) | AH | Europe | 5.9% | 58.27 | 26.47 | 70 | 1999–2010 | BSRN – EMHI |
| Valentia (Ireland) | BH | Europe | 3.8% | 51.93 | −10.25 | 14 | 1996–2009 | WRDC – Met Office |
| Vaulx-en-Velin (F) | CK | Europe | 4.3% | 45.78 | 4.93 | 170 | 1994–2010 | CIE – ENTPE |
| Wien / Hohe Warte (A) | CK | Europe | 5.7% | 48.25 | 16.35 | 203 | 1994–2009 | WRDC – ZAMG |
| Zürich Kloten (CH) | CK | Europe | 7.5% | 47.38 | 8.57 | 558 | 1981–2010 | ANETZ – Météo Suisse |
Satellite map
The full map of the inter-annual variation for monthly surface solar radiation was computed by 2 from MERRA-2 satellite data
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P. Ineichen — Global irradiation: average and typical year, and year-to-year variability. Research report, Institute of Environmental Sciences, University of Geneva, 2011. http://cuepe.ch/html/biblio/pdf/Ineichen_2011-global_irradiance_typical_year_and_annual_variability(swc).pdf ↩↩
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Krakauer, N.Y.; Cohan, D.S. — Interannual Variability and Seasonal Predictability of Wind and Solar Resources. Resources 2017, 6, 29. https://doi.org/10.3390/resources6030029 ↩