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What is Solar Irradiance & How Does it Affect Solar Farms?

Updated: Apr 1

photograph of a golden sunset over flat land

Solar irradiance refers to the power per unit area received from the sun in the form of electromagnetic radiation. It represents the amount of solar energy that reaches a given surface area per unit of time. Irradiance measurement is in watts per square meter (W/m²).

Types of Solar Irradiance

There are three types of solar irradiance that represent the power from the sun that reaches Earth’s surface.

  • Direct Normal Irradiance (DNI): DNI represents the amount of solar irradiance that is directly received from the Sun in a perpendicular direction. It refers to the solar radiation that reaches the Earth's surface without any obstructions or scattering from the atmosphere.

    • DNI is measured in watts per square meter (W/m²). This measurement is important for concentrated solar power (CSP) systems. These systems use mirrors or lenses to concentrate sunlight onto a receiver. This receiver generates electricity or heat.

  • Diffuse Horizontal Irradiance (DHI): DHI refers to the solar irradiance that arrives at the Earth's surface after being scattered or diffused by the atmosphere and clouds. It is the portion of solar radiation that arrives from different directions due to scattering by molecules and particles in the atmosphere.

    • DHI is also measured in watts per square meter (W/m²) and is relevant for both solar photovoltaic (PV) systems and CSP systems.

  • Global Horizontal Irradiance (GHI): GHI represents the total amount of solar irradiance received on a horizontal surface, taking into account both direct solar radiation and diffuse solar radiation. It is the sum of the direct normal irradiance (DNI) and the diffuse horizontal irradiance (DHI).

    • GHI is typically measured in watts per square meter (W/m²) and is widely used in the evaluation, design, and performance assessment of solar PV systems.

Solar Farms and Solar Irradiance Relationship

Solar farms, also known as solar power plants or solar photovoltaic (PV) installations, rely on irradiance to generate electricity. Solar panels, which are the primary components of solar farms, convert sunlight into electricity through the photovoltaic effect. The amount of electricity generated by a solar farm is directly influenced by the intensity of irradiance it receives. Irradiance from the sun does affect the probability of a solar farm being built in a particular location. The primary reason for this is the need for a certain level of solar irradiance in order to generate electricity efficiently. This in turn makes solar farms economically viable. Developers assessing the feasibility of a solar farm project consider the solar resource potential of the site. This potential is closely tied to irradiance. A location with high solar irradiance is more likely to be chosen for the construction of a solar farm because it ensures greater energy generation and higher returns on investment. Interestingly, even though the solar resource potential may seem like the most crucial factor for development, tax incentives actually drive development more. LandGate provides free property reports and solar lease estimates for landowners. See how much you could expect to lease your land for a solar farm through our nationwide free data intelligence and marketplace.

Solar farms typically require a minimum level of irradiance to operate optimally. If a location has consistently low irradiance, it may not be suitable for large-scale solar energy production. Solar panel technology has made it possible to generate electricity in areas with lower solar irradiance, for example in the northeast of the US where incentives are greater. Solar irradiance is a crucial factor that directly impacts the energy production potential and financial viability of a solar farm project, but other factors such as tax incentives, proximity to electrical infrastructure, and buildable acreage may ultimately be the deciding factor.

Performance of Solar Farms

Several factors can affect irradiance and, consequently, the performance of solar farms. These factors include:

  1. Time of day: Solar irradiance is highest when the Sun is at its highest point in the sky, typically around noon. It gradually increases after sunrise, reaches a peak around midday, and then decreases as the Sun sets.

  2. Season: Solar irradiance varies with the seasons due to the tilt of the Earth's axis. In general, solar irradiance is higher during summer and lower during winter.

  3. Weather conditions: Cloud cover, atmospheric haze, and other weather phenomena can obstruct sunlight and reduce solar irradiance. Overcast skies, for example, significantly diminish the amount of sunlight reaching solar panels.

  4. Latitude and geographical location: Solar irradiance is generally higher near the equator and decreases as you move closer to the poles. Regions closer to the equator receive more direct sunlight throughout the year, resulting in higher solar irradiance.

The highest solar irradiance is typically found in areas with abundant sunshine, such as deserts or regions with clear skies and minimal cloud cover. Countries located near the equator, such as those in the Sun Belt region (e.g., lower parts of the United States), generally experience higher solar irradiance.

Solar Farms in Locations with Lower Solar Irradiance

It's important to note that solar farms can still be productive in regions with lower irradiance, as long as they receive an adequate amount of sunlight for power generation. Landowners can still establish solar farms in states with low solar irradiance, especially if there are state incentives for solar farm development. While solar irradiance is an important factor for optimal energy generation, advances in solar technology and the availability of supportive policies can make solar farms viable even in regions with less solar resource potential.

  1. Policy incentives: States with low solar irradiance may offer attractive incentives and policies to promote renewable energy development, including solar farms. These incentives can include financial incentives such as tax credits, grants, or favorable financing options, making the project financially viable despite lower solar irradiance.

  2. Technological advancements: Solar technology continues to improve, with increased efficiency and reduced costs. This allows solar farms to generate electricity even in areas with lower solar irradiance. Advanced solar panels and tracking systems, as well as energy storage solutions, can enhance energy production and grid integration.

  3. Diversification of energy sources: Building solar farms in states with low irradiance can be a part of a larger strategy to diversify energy sources and reduce dependence on traditional fossil fuels. Solar farms can complement other renewable energy sources, such as wind or hydro, to provide a balanced energy mix.

It's worth noting that the economic feasibility of a solar farm in a low solar irradiance area would require careful evaluation, considering factors such as available land, grid infrastructure, project financing, and the specific state incentives and policies in place. However, with the right combination of supportive policies, technological advancements, and financial incentives, solar farms can still be a viable option for landowners in states with less solar irradiance. LandGate combines irradiance data, electrical infrastructure, tax incentives and much more to calculate valuations based on parcels across the United States. We offer free Property Reports for landowners containing solar lease estimates custom to their parcels, and a host of solutions for solar developers.


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