renewable energy projects by renewable energy people

renewable energy projects by renewable energy people

Our Services Full lifecycle services across renewable energy sectors 2

Time variant energy yield analysis A case study Presenter: Daniel Marmander Date: 3 rd June 2015

Introduction What we set out to do To assess the effect on P50 yield of the standard method using time invariant compared to a time variant energy yield calculation To determine which parameters would have the greatest effect if changed from time invariant to time variant To see if binning by time of day and month of year would produce the same result as a time step by time step approach 4

Introduction What we have done We have assessed: Impact of TI-specific power curves Impact of rotor equivalent wind speed Impact of time variant wind flow Impact of different binning strategies This is a case study, for a single site. 5

Introduction What we have not done This does not reflect: The absolute accuracy of the various scenarios Quantative statistics it is a case study We have not used turbulence renormalisation to compensate for high/low turbulence, only TI-specific power curves 6

Introduction What, when, where The site is thermally driven, with low inter annual variation but large diurnal variations We have in practise only one wind direction, from the east We have diurnal variations in wind speed ratios between measurements on site We have based our assessment on actual measured wind data and calculated power curves, however the results have been anonymised 7

Introduction Measured wind speed by hour of day and month of year 8

Introduction Measured wind speed by hour of day and month of year 2 m/s 16 m/s 9

Introduction Base case The base case represents an (almost) standard setup: EV wake model Sector wise TI for wakes One flow resource grid, 100 m resolution Hub height (80 m) wind speed used Normal TI power curve Correction for average air density Run on time series, in contrast to frequency distribution 10

Introduction Scenarios Base case Rotor equivalent wind speed, using average shear, 12x24 and instant TI specific power curves, using average TI, 12x24 and instant Air density correction, 12x24 and instant Parameters are changed once at a time (e.g. base case, but with 12x24 air density correction), as well as all at once (e.g. everything on 12x24). 11

Shear Time of day, measured shear 12

Shear Time of year, measured shear 13

Shear Impact of time variant compensation for shear conditions 8.60 8.55 8.50 8.45 8.40 8.35 Rotor equivalent wind speed compensation Very small difference, all below 0.5% Relates to available wind energy Does not predict effect on turbine capacity to convert the energy 8.30 Base case Average: - 0.4% 24x12: -0.4% Instant: -0.2% 14

Turbulence intensity By speed, measured TI 15

Turbulence intensity By time of day, measured TI 16

Turbulence intensity By time of year, measured TI 17

Turbulence intensity Impact of using TI specific power curves 8.60 8.55 8.50 Turbulence intensity specific power curves Very small differences Turbulence renormalisation method has not been used 8.45 8.40 8.35 Does not reflect the influence on wake losses 8.30 Average: 0.0% 24x12: 0.2% Instant: 0.2% 18

Wind speed By time of day, measured wind speed 19

Wind speed Impact of using time variant flow conditions derived from meso-scale model 8.60 8.55 8.50 8.45 Wind flow Average wind speed at hub height is 0.2 m/s higher using time variant wind flow Almost no difference in yield 8.40 8.35 8.30 20 Base case Time of day: -0.3% Wind speeds are either very low or very high Unusually low sensitivity for wind speed changes

Temperature By time of day, measured temperature 21

Air density Impact of using time variant air density 8.60 Air density compensation Significant yield difference 8.55 8.50 No difference between 12x24 and instant 8.45 8.40 Caused by strong diurnal trend for both speed and temperature 8.35 8.30 Base case 24x12: 2.5% Instant: 2.5% 22

Combined results Impact of adjusting for all parameters 8.60 8.55 8.50 8.45 8.40 8.35 All combined Very similar to when adjusting for varying air density only Significant difference against base case Very small difference between 12x24 and instant 8.30 Base case 24x12: 2.0% Instant: 2.2% 23

Conclusions For this case study Very small difference between 12x24 binning and instant time series adjustments. Indicates that 12x24 binning is adequate Air density adjustment is by far the most important factor for energy yield Time variant wind flow makes a large difference in mean wind speed over the site, but has small impact on final energy yield 24

Conclusions In general Time variant modelling might be able to more precisely predict the energy yield It is likely that a 12x24 approach is adequate for most sites There is a need to assess the absolute accuracy of the different approaches, to assure that no over all bias is accidentally introduced By assessing the sensitivity for using 12x24 binning instead of averages, we can get a reasonable idea about the need of a timevariant approach. 25

Thank you for listening Questions? 26