Max S. Dunn

Ed: Woods Seminar: Solar Thermal

Posted by: Max Dunn on November 14, 2008 07:54:55

Speaker: John O’Donnell

I have been skeptical of solar thermal because it seemed like the cost was higher than PV due to it needing turbines and other power-plant equipment. However, John showed costs of $110 mWh for solar thermal versus $120 for coal (with a $30/ton CO2 tax). He also brought up a very good point that solar power only lasts to about 5 or 6 pm, but peak hours go to 8pm in the summer. So no matter how much solar power we have, it won’t eliminate the need for any peaking plants. And while batteries cost $500/kWh, storing heat as supercritical water or molten salts costs only about $50/kWh. With storage, solar thermal could supply 95% of energy in US, versus only about 20% for wind and PV. So while solar thermal plants are still only economical in large installations, it seems like they might be a good component of a sustainable energy future.

Overview

• Solar thermal was the first solar power used to heat steam in 1914 in Egypt
• Solar thermal is important because the heat can be stored
• Solar thermal produces 4 times the jobs and economic impact of fossil fuel plants
• $800 million in last 15 months have flowed into this sector

Background

• Electric power is the fastest growing part of worldwide energy use
• EIA says electricity use will double by 2030
• 50% of power comes from coal in US
• CO2 released: 1400 lbs per 1mw overall, 2200 lbs for coal
• Power generation in the US uses half of all potable water
• Wet power plant 8% to 9% more efficient than a dry plant
• It is not possible in CA to build a wet plant

Energy Future

• EIA estimates that increase in electricity production will mainly come from coal
• 16 TWh annually of worldwide energy use
• Solar is by far the largest possible source of renewable power, much more than wind

Solar Thermal

• Solar thermal now competitively priced in US
• At $30/ton CO2 economics drive deployment
• Solar thermal can deliver 90% of grid power with storage
• Thousands of megawatts in contract/construction now
• We now have 8 year extension of the 30% solar credit (it took 10 times to pass)
• In CA in June uses 20 GW in the morning, and 60 GW at the peak
• Peak summer load is growing 2 times faster than overall load.
• This means that the peak power is fueled by the most inefficient plants
• Peak hour demand extends to 8pm, so solar without storage will not be able to help with peak power – we still need the same number of plants

Types of Solar Systems

• Two categories of systems that focus light on a point (need tracking in 2 dimensions) systems that focus on a line (need 1 dimension tracking)
• Four types: dish, tower, trough, linear fresnel
• Concentrates 50-3000x
• In typical coal plant about 40% efficient, in solar 35% up to 50% for combined cycle
• Radiative heating runs to the 4th power of the temperature
• So point absorbers try to drive the area down to reduce heat emissions, this pushes materials
• Companies:
  • Stirling: Stirling Energy Systems, Infinia
  • Tower: Abengoa, Solar Reserve, Brightsource, Torresol
  • Trough: Solar Millenium, Acciona, Abengoa
  • Linear fresnel: Ausra
• Moving mirrors called heliostats
• Best developed solar technology today, Solar Two uses molten salt. 88% of sun that heat it converted to heat in salt
• Molten salt works well as long as it stays above 180 degC (and is stable to 600 degC), otherwise it will solidify and there will be major problems
• Osra is building 180 MW plant that occupies one square mile
• Ideally would like material that absorbs light at 0l2 to 5 um, but then doesn’t emit the infrared heat above this.
• Selective surfaces approach this

Energy Storage

• It is a lot cheaper to store energy as heat than as electricity. Example laptop battery for $100 and thermos for $5 holds the same amount of energy
• Batteries run about $1000/kWh but solar storage is about $50/kWh
• Storage plants are more expensive but then turbine produces power for more time, so a 12 hour storage system costs about the same as one with no storage
• There is no single storage technology that works best with all types of solar thermal systems
• Commercially available: hot salts, supercritical water
• Water storage gets about 90% exergy efficiency and loses only about 1% per day. Biggest cost is vessel and valves
• Andasol 1 uses molten salt storage. Two tanks one at 292 degC and another at 386 degC.
• CA pays twice as much peak electricity from noon to 8pm from M-F
• Natural gas likely to double in price in the next 5 to 6 years
• Storage systems allow producer to delay generation until noon for maximum revenue

Solar Thermal Advantages

• Above 20%, wind become very expensive because of storage and integration cost
• Solar thermal doesn’t have these problems until it reaches 94%
• Solar thermal can supply over 95% of US grid power (Miles & Morgan, SolarPACES 2008)
• Electric cost with carbon tax $30:
  • Nuclear $150Mwh,
  • IGCC $125
  • Coal $120
  • Gas peaker $185
  • Solar thermal $110
• US could be powered by 92 mile square, or 10% of BLM land
• We have transmission technology today. We already move hydro-power to LA. Only 3% energy loss per 1000km.
• We built 25% of the US grid in 10 years, with no government policy, so it would be possible to convert
• Solar Power Energy graph: http://tinyurl.com/perez-v-08

Questions

• Biggest challenge is cost of capital. Newest technology is most efficient, but most unsure, so this drives up the cost of capital
• Many hydro plants have radically reduced output and some will be closed in the future. So we can put wind and solar thermal at these locations and ship over underutilized lines