21-05-2025
How solar power forecasting can help maximise your solar panels
Analysis: As solar becomes a significant part of our energy system, there are challenges in effectively forecasting and managing solar energy production
By Maeve Upton and James Sweeney, UL
In recent months, Ireland has seen a rapid surge in solar energy production. A new record for grid-scale solar power was set on the March 25th last, reaching 750 Megawatts at a single moment - enough to power about 750,000 homes at once.
But as electricity from solar becomes an increasingly significant component of our energy system, challenges arise in effectively forecasting and managing variability of solar energy production, at both household and national levels.
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Solar panels convert sunlight or solar irradiance, into electricity, which varies throughout the day. The amount of power produced depends on several factors, including the characteristics of the panel and the solar irradiance it receives. There are many different solar panel systems available with varying panel characteristics. If you're considering installing solar panels, check out this guide which covers everything from panel selection to financial incentives.
Solar irradiance is the amount of sunlight reaching the ground and is the biggest drivers of variability in electricity production. During the day, the three main sources of variability are the sun's position, cloud cover and panel temperature.
Position of the sun
The sun follows a predictable daily (diurnal) cycle—rising in the east and setting in the west —and also changes with the seasons. In the northern hemisphere, the sunniest months are typically May and June.
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Cloud cover
Cloud cover can block or scatter sunlight, significantly reducing the amount of solar irradiance reaching the surface of the solar panel. Solar power output drops each time a cloud passes over the solar panel. Unlike the sun's position, cloud cover is much harder to predict, especially in Ireland's temperate maritime climate.
Higher temperatures
Higher temperatures can reduce the efficiency of the solar PV panel. Though weather forecasts can quantify this, the effect on solar power output requires local-level estimates.
What is solar power forecasting?
Solar power forecasting is the process of predicting the amount of solar radiation (sunlight) reaching Earth's surface at a specific location and time. This is crucial for managing solar energy production, integrating renewable energy into power grids and ensuring energy system stability.
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How does it work?
To forecast solar power at a specific time and location, we need three key components: input data (solar PV system such as orientation and weather), astronomical calculations on the sun's position and a model combining them. The input data provides information about weather conditions, while astronomical calculations determine the position of the sun. These elements are combined within a forecasting model to estimate the solar power output.
The input data has three main sources. The most accurate is ground-based measurements from meteorological stations managed by Met Éireann. They record high quality solar irradiance data in real time, but are limited to their 20 stations around Ireland.
An alternative source is reanalysis datasets, which provide estimates of solar irradiance by blending historical weather observations with advanced numerical weather models. While reanalysis data offers consistent and spatially complete coverage, it is not available in real time and typically lags by about five days.
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The final source is satellite data, which provides valuable observations of solar irradiance and cloud cover. However, these measurements can vary significantly if the instruments are not regularly calibrated and maintained, an effort that requires consistent investment and funding.
In addition to these data sources, astronomical calculations are performed to determine the sun's position in the sky and day length based on the time of year. These calculations are essential for accurately estimating the potential solar irradiance.
Once we've selected our input data and calculated the sun's position, we apply models to convert solar power observed on a horizontal (flat) surface to that received on a tilted surface—matching the orientation and size of the specific solar panel system. This step is crucial for estimating how much power a real system could generate.
If you're curious about what your solar panels could do, check out the GREEN-GRID app. This uses advanced data-driven modelling tools to estimate real-time solar power, giving hourly insights for homeowners across Ireland.
What are the challenges for solar power in Ireland?
While Ireland's progress in solar power adoption is promising, several challenges complicate accurate forecasting and integration into the grid. These challenges highlight the need for better forecasting and more flexible grid systems to ensure that the growing share of renewable energy is fully captured and effectively used.
From a forecasting perspective, models can be highly effective but their accuracy is limited by the quality and resolution of the input data the integration side, one significant challenge is dispatch down, when renewable energy, particularly wind and solar, is reduced or curtailed because the electricity grid cannot accommodate all of the power being generated at a given time. As a result, some renewable energy is available but not used, which can reduce the overall efficiency of the system and delay the full benefits of clean energy investment.
Another issue is the limited visibility of microgeneration, such as roof-top solar, which is often excluded from official reports. Similarly, embedded generation, which refers to electricity generated and used locally, is not consistently measured, though recent reports suggest improvements are planned.
