1. SHP – Columbia University
Energy from wind
Diego Villarreal
SHP – Columbia University
November 21, 2015

2. Why wind? Renewable form of energy No CO2 emissions Clean power
Relatively simple setup (although lots of land).
Ultimately another form of solar energy.
Technology is well understood (mature tech)
So what are the potential issues with wind?
NIMBY’ism
Ultimately limited by power density (more on this later).
Intermittency.
Grid integration

3. Physics of wind
Power of wind has been used for thousands of years to convert KE into mechanical work for pumping water and crushing grains (think Holland!).
Modern wind turbines converts wind power into electricity. But what does this mean?
Wind power using first principles:
KE = ½ mv2
P = KE/unit time
From basic fluid mechanics, mass flow rate (mass per unit time):
Power ~ cube of the velocity
Power ~ density of air
Power ~ rotor swept area =

4. Theoretical limits of wind power
The amount of power you can extract from wind is limited by physics, not design.
Extracting KE form wind results in a pressure drop.
If 100% of energy was extracted, velocity at the other side of the disk would drop to zero (conservation of momentum).
This would inhibit the air from flowing through, dropping power to zero.
This is called the Betz limit ~ 59% (will skip derivation in the interest of time).
Maximum efficiency of wind turbine (independent of design) ~ 59%.

6. Power Curves

8. So how much energy do we expect to extract from a wind turbine?
What wind velocity do we use?
Power ~ cube of the velocity, so using wrong velocity is a big deal.
Thus we use probability density functions to determine the correct sites and economics

9. Rayleigh Distribution
Weibull Distribution

10. US Wind Resources

11. US Wind Resources

12. Wind turbines are big!
Typical 1.5 MW turbine

13. Global Renewables

14. Wind electricity in the USA
Source: EIA 2013

15. Wind electricity in the USA
Source: EIA 2013

16. Countries with the most installed wind
US = 4,106 billion kWh

17. 2012 capacity additions (US)
Which states added the most capacity in 2012?
What is the expected CAGR of wind for the next 5 yrs?

18. Renewable Portfolio Standard
Policy mandating that a % of energy in a particular state come from renewables.
Certified generators earn certificates for every unit of electricity they produce and can sell these along with their electricity to supply companies.
Renewable Energy Credits – Bought and sold in to meet targets. Can be a huge source of revenue for wind projects

19. But the wind is always blowing somewhere, right?

20. The issue of power density
One of the problems with wind is its power density (W/m2).
But what is power density?
Energy density is easy. It is simply energy per unit weight:
J/g
MJ/kg
But power density is a bit more tricky (depends how you define it). We’ll use a measure of energy flux over horizontal area of land or water surface.
Assumptions:
3 MW turbine with a rotor diameter of 112m.
The wind turbines require spacing of 6 diameters between each one.
CF = 0.3
What is the peak power density of wind?
Actual?

21. Power density of other sources
POWER DENSITY LOW (W/M2)
POWER DENSITY HIGH (W/M2)
WIND 1 2
COAL
100
1000
GAS
200
2000
SOLAR (PV) 4 9
SOLAR (CSP) 10
BIOMASS
0.5
0.6
Changing the power density-determined infrastructure of energy systems that were created over more than a century for electricity generation from fossil fuel combustion will not be easy.
This new energy infrastructure would increase fixed land requirements.
Most of the area occupied by large wind farms could be used for crops or grazing but other land uses would be excluded.
Transmission lines to concentrate low power density systems will be required and .

22. Storage will ultimately be required
What storage methods can we use to store wind power?
Which ones do you think are the most cost effective?
Is there GW scale storage available?

23. Economics of wind LCOE of wind in good locations ~ $0.06-0.08/kWh.
Coal ~ $0.06
On top of this, wind farms in US can sell RECs, use PTCs, ITCs, etc.
If price on carbon wind is less expensive than coal.
1 MW turbine cost < $2m

24. Economics of Wind All costs fixed – turbines, site, connection charges
Minimal variable costs
So average cost is 4-6 cent/kWh but marginal cost is zero
Cost of one extra unit of energy is zero
So if there is a choice always use wind before using any fossil fuel
Renewables are first in the “dispatch order” or “dispatch curve”

25. ‘Life cycle’ of electricity

26. What does the load (demand) look like?

27. Who gets to go first?

28. How is price set How is price of electricity set in wholesale markets?
Looking at the generation stack, you can see how price is calculated. If load is about 90 GW (Gigawatts), which is the amount of power consumed by about 75 million homes on an annual average basis, we draw a vertical line at 90 GW (in blue, below) and then draw a line across at the intersection with the stack (the orange line). As you can see, the lower orange line intersects the price axis at about $35 per Megawatt-hour (MWh). Now, if it is a hot summer day and lots of air conditioning is being used, then, for the same system, we might see a load of 145 GW. In this case, draw the blue vertical demand line, and then project the orange line over, and you see we get a price of about $150 per MWh. This explains why power prices can be so volatile, varying from close to zero at some hours up to, possibly, several thousands of dollars, all within the same day.

29. By the hour

30. The intermittency issue
One of the biggest issues with wind is its intermittent nature.
When & with what intensity the wind will blow is not easy to predict.
Intermittency can be a problem.
At low penetrations, not a big deal. At higher penetrations (>30%) grid interconnection and GW size storage required.
Other issues:
Average Capacity Factor greatly varies by region.
On average, wind is dilute (power density issue)

31. Case study - Denmark Can you identify any issues?
Can you spot any trends?

32. 32

33. 33