Building A Solar Society Oct08
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Transcript of Building A Solar Society Oct08
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Building a Solar Society
Ken ZweibelDirector
GWU Institute for Analysis of Solar Energy
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What are our problems?
• Carbon dioxide
• Oil supply
• Energy prices
• World conflicts over energy
• Trade imbalance
• Economic vitality
• Can we use solar to solve these problems?
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Electric Transportation
• Plug‐in hybrids– Daytrips – electricity
– Range – fuel
– Charging
– Efficient electric motors (90%, instead of 30% internal combustion engines)
– 10 c/kWh electricity is close to $1.5/gallon gasoline equivalence
– This is not “business as usual”
– THIS IS A HUGE OPPORTUNITY FOR CHANGING OUR ENERGY WORLD!
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Transforming Our Energy
• If we move to electric transportation we can
– Get off foreign oil
– End dependence on others
– Remove the irritation causing global tensions
– Stabilize energy prices
– Stimulate our economy instead of bled dry by imports
– And lower our transportation costs at the same time!
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How can we do this?
• Make MUCH more electricity with– Coal
– Nuclear
– Wind
– Natural gas
– Solar
• Or maybe not…
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Electricity Options
• Coal makes too much carbon dioxide
• Natural gas is too supply limited
• Nuclear…is nuclear
• So that leaves wind and solar
–Wind is fine, but too small
• Potential for 20%‐30% of current electricity
– So, solar…
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There’s Plenty of Solar1 day of unconverted US solar energy: 48,000 TWh
1 year of US electricity: 4000 TWh
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Let’s Remind Ourselves that Solar Already Exists
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How does solar solve our problems?
• We use solar and some wind to produce almost every new kWh we need to meet transportation demand– Energy self‐sufficiency AND– Elimination of the carbon dioxide in gasoline
• Won’t people charge at night?– Yes, initially, and for that we use wind and fossil fuels– But we displace those same fossil fuels during the day with solar
– And when we produce enough solar, we shift to daytime charging
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To Repeat…
• We can use solar and a wind to charge our plug‐in hybrids
• We may not need any more fossil fuels to do it• We may not need any more nuclear to do it• We can do it without carbon dioxide emissions, eliminating almost all carbon dioxide from the transport sector
• And we can save money doing it
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Aren’t there some devilish details?
• Cost of solar
• Land for solar
• Intermittency
• Demand & supply mismatch
• Transmission
• Speed of adoption
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Problems and Solutions
• Let’s look at each of these
• First, how much energy are we talking about?
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How Much Electricity?
• 5.3 Quads used to move vehicles• Losses
• 15% electric to battery• 10% motor• 10% electric transmission from source
• 5.3 Quads needs 7.7 Quads before losses• Let’s replace 70% (somewhat arbitrary), so we need 5.4 Quads of electricity
• 1600 TWh (1 Q is about 300 TWh)
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How Much Solar?
• Let’s add ~10% for demand growth during replacement
• We need 1800 TWh/yr of new non‐carbon production
• If 800 TWh of this is wind (equivalent to 20% of today’s electricity, a common goal)…
• Then we need 1000 TWh of solar• At 1.6 kWh/W installed, this is 625 GW of new solar capacity
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How Much Land Is 625 GW Solar?
• Ignore rooftops to first order
• About 16,000 km2 (126 km on a side)– Assuming 40 W/m2 of land use
• Less than 0.2% of US land area (9 million km2)
• Is this a lot?
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Hydro and Solar Land Use
Hydro• 1% US land
• 7% electricity
• 280 TWh
Solar• 0.2% US land
• 1000 TWh (25% US electricity)
• 16 times more land efficient than hydro!!!!
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Can We Do This Quickly?
• Current world PV production is about 5 GW/yr
• At a growth rate of 50% per year, and assuming 1/3 goes to the US, we accumulate 625 GW of installed PV in the US in 2020 (12 years)– We use PV as a proxy for all solar in this calculation (adding solar thermal electric would make this easier)
– Pinch points require further examination
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But how much would it cost?
• Many ways to calculate cost• Key is, in comparison to what?• The most direct answer:
– In comparison to buying gasoline over $2.5/gallon, it is cheaper
– In comparison to buying gasoline that is continuously escalating, it is transformationallycheaper
– In comparison with today’s coal, it is more expensive, but avoids carbon dioxide
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This Assumes
• Solar electricity is
– 15‐20 c/kWh in the US Southwest and CA
– 20‐25 c/kWh elsewhere due to less sunny conditions or long‐distance transmission costs
• Used in plug‐in hybrids, 20 c/kWh solar is equivalent to about $2.5/gallon gasoline
• Technical roadmaps exist for solar at 10 c/kWh or less in the Southwest– But commodity inflation may overtake those cost reductions
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Comparison of Plug‐In Hybrid Options*
CO2 Emissions of Plug‐in Hybrids (g/mi)
0100200300400500600
Gasoline SolarElectricHybrid
USElectricMix
Hybrid
*Not including battery costs and battery CO2 footprint.
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Solar versus Coal
• Today’s coal‐based electricity is about half the price of solar (for new installations)
• The following assumptions make using coal or solar the same within 1% for a 12‐year program:– Today’s solar is twice the cost of coal– Coal increases by 3% per year and solar decreases by 3% per year (cost weighted by increasing annual installations)
• Over the course of a 12‐year program, solar and coal could be the same cost
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What Issues Are Left?
• Intermittency
• Supply & Demand Mismatch
• Transmission
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Transmission
• Transmission is valuable because solar intensity in some regions is 50% higher than most places – Implies 33% lower price
• For long distances – High‐voltage lines lose less per mile (I2R loss)– DC loses less than AC (wavelength‐driven loss)
• A High‐Voltage (HV) DC line– Loses 3% per 1000 km– Line costs 0.25 c/1000 km at solar capacity factor– 1% loss and 1.7 c/kWh capital cost at downlink– 10% loss at 3000 km implies another 1.2 c/kWh (at 12 c/kWh)– Total implied cost is about 4 c/kWh at 3000 km
• So total cost is 15 c/kWh + 4 c/kWh = ~20 c/kWh for transmitted solar
– Requires right‐of‐way access
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Siemens has built several GW of high‐voltage DC transmission lines worldwide. This is a 235‐MVA‐HVDC power transformer for the Australia‐Tasmania undersea cable. An even larger line is
being built in China (2400 km with a power transmission capacity of 6.4 GW)
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Transmission Opportunities
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The Sun Is Always Shining: Siemens HV DC Vision
Siemens 2007, EPRI, DC_Solutions_EPRI_Conference_09-07_V_1b, slide 47
12,000 mile transmission, about equivalent to storage losses (0.9720>0.5)Can balance night/day (east-west) and seasons (north-south)
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Supra‐Regional
• International transmission– Could be cheaper than storage (capital plus losses)
– Removes sudden peaks and valleys due to geographic distribution (avoids correlated cloud events)
– East – West• Extends daylight hours
• Eventually could be “24 hour”
– North – South• Ameliorates seasonal solar variations (always about the same output)
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Example of Geographic Smoothing
“Capacity Valuation Methods,” SEPA 02-08, Hoff, Perez, Ross, Taylor, 2008
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Transmission corridors will pick up wind along the way to East Coast
Add distributedsolar along theway as well
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Wind and Sun Are Complimentary
High Plains Express Feasibility Study, June 2008, p. 35
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Increased Capacity Use with Wind and Solar Lowers Transmission Cost
“We found that by blending wind and solar for geographically diverse sites, we can achieve a more consistent product for delivery, thereby offering the potential for reducing integration costs and improving the economics and acceptability of renewables.” Jerry Vainineti (co‐author)
From High Plains Express Feasibility Study, HV AC, for wind and solar combination
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What Does Transmission Do?
• Access to better (cheaper) resource
• Can combine with wind
• Geographic diversity smoothes output, reducing size of abrupt changes (a key variability issue)
• Reduces day‐night and seasonal variations if very long distances
• Partial replacement for storage
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What’s Left?
• Further solutions for solar variability– We may not have long‐distance transmission in a timely manner due to access issues
– Machines and consumers do not run on varying electricity
• Mismatch between solar and demand
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Solar Variability
• Night
• Seasons
• Storms
• Cloudiness
• Transient clouds– Gap and peak ramp rates
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Variability Solutions• Fast, short‐term gaps
• Transmission• Geographic diversity of sources• Draw down from plug‐in hybrid batteries• More flexible fossil fuel generators
• Moderately fast gaps• Normal fossil fuel backup
• Growth in evening peaks• Storage (e.g., compressed air, CAES)• East‐west transmission• New fossil fuel generators
• Nighttime demand for charging plug‐ins• Wind • Fossil fuel moved from daytime (and replaced with solar)
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Demand Mismatch
• Solar shape (midday maximum; seasonally varied)
• Demand variability (regional, season)• Spring and Fall midday solar oversupply
• Charge plug‐in hybrids• Charge compressed air
• Winter demand– Fossil fuel back‐up–CAES and North‐South transmission
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How Can We Do This?
• More flexible fossil fuel generation, even if it requires replacing existing generators with specialized ones– Because solar requires flexible “load following” to compensate for its variations
• Almost no new conventional energy generation– Everything from wind and solar, some new storage– Possibly some natural gas growth for evening peak growth
• Smarter grid that allows more responsive movement of supplies to demand, and movement of oversupply to storage or elsewhere
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Principles
• Avoid storage except plug in hybrids as much as possible
– Doubles cost of electricity
• Do not store fossil fuels – increase carbon dioxide emissions by turnaround losses
• Store lowest cost non‐carbon dioxide electricity
– Wind, existing nuclear, then solar
• Store excess solar in plug‐in hybrids Fall and Spring midday
• Explore long‐distance transmission to offset storage
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Denoument
• Instead of thinking of shutting down existing coal plants with solar, we should be thinking of eliminating foreign oil and using our existing fossil fuel plants to backup solar energy
• This will avoid the issue of abandoned assets (which still have to paid for), while addressing our key problems – oil prices and carbon dioxide emissions
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Total Value
• Energy self‐sufficiency
• Avoided CO2
• Price stability (and no fear of others’ price and political manipulation)
• Reduced global tension
• Local jobs and well‐being
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The morning after (a sober re‐examination)
• Depends on success of plug‐in hybrids
– Will batteries work?
– What will they cost (money and CO2)?
• Growth rates mean oversight of
– Pinch points and shortages
– Prices
– Local content
– Financial manipulation
• Needs “the right” government involvement