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A Norwegian-Swedish research group has used multiple linear regression to assess whether 128 existing wind power plants in the Nordic countries could potentially be converted into wind-solar power plants with cost-optimal PV capacities and good net present value (NPV) levels. Their modelling could potentially be used across countries and latitudes.
A group of researchers from Norways Institute for Energy Technology (IFE) and Swedens Uppsala University has outlined a new strategy for converting wind farms into hybrid wind-solar installations.
“Wind-solar hybrid plants can be valued differently depending on market conditions,” Øyvind Sommer Klyve tells pv magazine . “In some cases, offering a firmer output curve, such as a solar-wind hybrid typically achieves, can generate additional revenue if the end consumer would pay for the firmer output in addition. Conversely, there may be market situations where power prices are high enough that you might not want solar and wind assets to share grid-connection infrastructure if that would lead to power curtailment. There may also be regulations that prohibit building solar-wind hybrids.”
The research group used multiple linear regression (MLR) analysis to investigate how 128 existing wind power plants in Norway and Sweden could potentially be converted into cost-optimal wind-solar power plants with PV capabilities and good net present value (NPV) levels. MRL is a model that estimates the relationship between a quantitative dependent variable and two or more independent variables using a straight line.
In their modelling, the scientists assumed that solar power generation is sold to the day-ahead market and is reduced when the sum of PV and wind generation exceeds the point of interconnection (PDI) of the hybrid installation. “All 128 wind power plants investigated have average capacity factors above 15%,” the scientists specify. “Those with lower capacity factors were considered to be failed or small-power wind turbines and were eliminated in a previous step.” A total of 22 wind power plants were previously filtered out in that step.”
They also assumed that there is no shading on the installation, that snow losses can be neglected and that the terrain is suitable for the installation. “These assumptions will lead to a positive bias in the modelled capacity factors, especially in the northernmost bidding areas, which are more mountainous and snowy than the southern bidding area locations in the Nordic countries,” they further explained, noting that the NPV calculation only included revenues and costs related to the PV system.
The model identified three key parameters for retrofit system viability: A high average PV capacity factor; a low average wind capacity factor; and a strongly negative Pearson correlation factor between the hourly PV and wind generation profiles. The Pearson correlation coefficient is the most common way to measure a linear correlation between two variables.
The researchers found that a strong anticorrelation alone could easily decide whether retrofitting an existing wind power plant into a wind-solar hybrid is economically viable. “In this context, many of the most cost-effective retrofit cases occurred at sites with the weakest anticorrelation, and the positive impact of anticorrelation on NPV only became apparent after performing an MLR analysis that also considered PV and wind capacity factors.”
Their analysis also showed that sites with high levels of solar radiation and low-performance wind power plants should be prioritized, while areas with high hourly anticorrelation between wind and solar power should be neglected.
“The hourly correlation coefficient between PV and wind generation profiles is a better indicator of techno-economic feasibility than diurnal or seasonal correlation coefficients,” they added. “The slope coefficients of the derived MLR model can be multiplied by the average wind and PV capacity factors and the anti-correlation of a wind site to obtain an initial estimate of the site’s techno-economic PV retrofit potential.”
The research group also stressed that its new methodology can be applied in any country or latitude. It was presented in the study “ Retrofitting wind power plants into hybrid PV–wind power plants: Impact of resource related characteristics on techno-economic feasibility”, published in Applied Energy . |
