What is Solar Irradiance & How Does it Affect Solar Farms?
- Craig Kaiser
- May 6
- 5 min read
When it comes to solar energy, one term you’ll hear often is "solar irradiance." But what exactly does it mean, and why is it so important for solar farms? Solar irradiance is essentially the measure of sunlight hitting a specific area, and it’s a key factor in determining how much energy a solar farm can produce. In this resource, we’ll break down what solar irradiance is, how it works, and why it’s critical for the efficiency and performance of solar power systems.
What is Solar Irradiance?
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. The three types of solar irradiance are Direct Normal Irradiance (DNI), Diffuse Horizontal Irradiance (DHI), and Global Horizontal Irradiance (GHI).
1) 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.
2) 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.
3) 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.
How Does Solar Irradiance Affect Solar Farms?
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 affects 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. 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. 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 Irradiance Impacts on the Performance of Solar Farms
Several factors can affect solar irradiance and, consequently, the performance of solar farms. These factors include:
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.
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.
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. However, the impact of weather on solar panel performance is supringly minimal.
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. Arizona, New Mexico, Nevada, California, Florida, and Texas are the states with the highest solar irradiance. These states receive the most sunlight on average due to their geographical location, climate, and terrain.
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.
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.
Technological advancements: 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.
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.
LandApp combines irradiance data, electrical infrastructure, tax incentives and much more to calculate valuations based on parcels across the United States. To uncover your property's potential for a solar lease, find your land on our map to create our free property report today: