Download Renewable Energy Lecture: Hydroelectricity and Wind Energy and more Slides Energy and Environment in PDF only on Docsity! Hydro and Wind Spring 2013 Lecture 14 1 Renewable Energy I Hydroelectricity Wind Energy Renewable Resources • Renewable means anything that won’t be depleted by using it – sunlight (the sun will rise again tomorrow) – biomass (grows again) – hydrological cycle (will rain again) – wind (sunlight on earth makes more) – ocean currents (driven by sun) – tidal motion (moon keeps on producing it) – geothermal (heat sources inside earth not used up fast) Renewable Energy Consumption Energy Source QBtu / % (1994) QBtu / % (2003) QBtu / % (2011) Hydroelectric 3.037 / 3.43 2.779 / 2.83 3.171 / 3.26 Geothermal 0.357 / 0.40 0.314 / 0.32 0.226 / 0.23 Biomass 2.852 / 3.22 2.884 / 2.94 4.511 / 4.64 Solar Energy 0.069 / 0.077 0.063 / 0.06 0.158 / 0.16 Wind 0.036 / 0.040 0.108 / 0.11 1.168 / 1.20 Total 6.351 /7.18 6.15 / 6.3 9.135 / 9.39 much room for improvement/growth, but went backwards from 1994 to 2003! Slide copied from Lecture 11 Another look at available energy flow • The flow of radiation (solar and thermal) was covered in Lecture 11 – earth is in an energy balance: energy in = energy out – 30% reflected, 70% thermally re‐radiated • Some of the incident energy is absorbed, but what exactly does this do? – much goes into heating the air/land – much goes into driving weather (rain, wind) – some goes into ocean currents – some goes into photosynthesis Docsity.com Hydro and Wind Spring 2013 Lecture 14 2 The Renewable Budget Outstanding Points from Fig. 5.1 • Incident radiation is 1741015 W – this is 1370 W/m2 times area facing sun (R2) • 30% directly reflected back to space – off clouds, air, land • 47% goes into heating air, land, water • 23% goes into evaporating water, precipitation, etc. (part of weather) • Adds to 100%, so we’re done – but wait! there’s more… Energy Flow, continued • 0.21% goes into wind, waves, convection, currents – note this is 100 times less than driving the water cycle – but this is the “other” aspect of weather • 0.023% is stored as chemical energy in plants via photosynthesis – total is 401012 W; half in ocean (plankton) – humans are 7 billion times 100 W = 0.71012 W – this is 1.7% of bio‐energy; 0.0004% of incident power • All of this (bio‐activity, wind, weather, etc.) ends up creating heat and re‐radiating to space – except some small amount of storage in fossil fuels Q2 The Hydrologic Cycle Lots of energy associated with evaporation: both mgh (4% for 10 km lift) and latent heat (96%) of water Docsity.com Hydro and Wind Spring 2013 Lecture 14 5 Wind Energy The Power of Wind • We’ve talked about the kinetic energy in wind before: – a wind traveling at speed v covers v meters every second (if v is expressed in m/s) – the kinetic energy hitting a square meter is then the kinetic energy the mass of air defined by a rectangular tube – tube is one square meter by v meters, or v m3 – density of air is = 1.3 kg/m3 at sea level (and 0°C) – mass is v kg – K.E. = ½(v)·v2 = ½v3 (per square meter) Wind Energy proportional to cube of velocity • The book (p. 134) says power per square meter is 0.61v3, which is a more‐or‐less identical result – accounts for above sea level and more typical temps. • If the wind speed doubles, the power available in the wind increases by 23 = 222 = 8 times • A wind of 10 m/s (22 mph) has a power density of 610 W/m2 Q Can’t get it all • A windmill can’t extract all of the kinetic energy available in the wind, because this would mean stopping the wind entirely • Stopped wind would divert oncoming wind around it, and the windmill would stop spinning • On the other hand, if you don’t slow the wind down much at all, you won’t get much energy • Theoretical maximum performance is 59% of energy extracted Docsity.com Hydro and Wind Spring 2013 Lecture 14 6 Practical Efficiencies • Modern windmills attain maybe 50–70% of the theoretical maximum – 0.5–0.7 times 0.59 is 0.30–0.41, or about 30–40% – this figure is the mechanical energy extracted from the wind • Conversion from mechanical to electrical is 90% efficient – 0.9 times 0.30–0.41 is 27–37% Achievable efficiencies Typical Windmills • A typical windmill might be 15 m in diameter – 176 m2 • At 10 m/s wind, 40% efficiency, this delivers about 40 kW of power – this would be 320 kW at 20 m/s – typical windmills are rated at 50 to 600 kW • How much energy per year? – 10 m/s 610 W/m2 40% 240 W/m2 8760 hours per year 2,000 kWh per year per square meter – but wind is intermittent: real range from 100–500 kWh/m2 – corresponds to 11–57 W/m2 average available power density • Note the really high tip speeds: bird killers – but nowhere near as threatening as cars and domestic cats! Average available wind power recall that average solar insolation is about 150–250 W/m2 Docsity.com Hydro and Wind Spring 2013 Lecture 14 7 Comparable to solar? • These numbers are similar to solar, if not a little bigger! – Let’s go to wind! • BUT: the “per square meter” is not land area—it’s rotor area • Doesn’t pay to space windmills too closely—one robs the other • Typical arrangements have rotors 10 diameters apart in direction of prevailing wind, 5 diameters apart in the cross‐wind direction – works out to 1.6% “fill factor” Q 5 diameters 10 diameters rotor diameter wind Current implementations • Rapidly developing resource – 1.4 GW in 1989; 6.4 GW in 2003; 60 GW by end of 2012 – fast‐growing (about 25% per year) – cost (at 5–7¢ per kWh) is competitive – expect to triple over next ten years • Current capacity: ~60 GW – but should only count as 15 GW of continuous Texas overtook California in 2007; Iowa coming up fast ht tp :// w w w. w in dp ow er in ga m er ic a. go v/ w in d_ in st al le d_ ca pa ci ty .a sp Flies in the Ointment • Find that only 25% of rated capacity is achieved – design for high wind, but seldom get it • 3% of electrical supply in U.S. is now wind – total electrical capacity in U.S. is 1051 GW; average supply 451 GW – limited tolerance on grid for intermittent sources • lore says 20%, but could be substantially higher in nationwide grid • If fully developed, we could generate an average power almost equal to our current electrical capacity (764 GW) – but estimates vary widely – some compute < 2000 GW practically available worldwide – and struggle to deal with intermittency hits at some point Q Docsity.com