On Wed, 17 May 2006 11:37:59 -0400, "R.H. Allen" wrote:
JoeSP wrote: Let's assume that the efficiency of the solar collectors is 30% (nowadays a very realistic figure - recent photovoltaic cells are achieving 34% for example), and that we receive eight hours of sunlight per day at about 1 kilo-watt per square meter. Thus we can capture .3 kilowatts per square meter for eight hours, which means we can collect 8 hours x .3 kilowatts = 2.4 kw-hr/d-m2.
Those are some pretty liberal assumptions. For starters, the solar cells with efficiencies higher than 30% are tiny laboratory devices that cost an arm and a leg and haven't been made in quantities large enough to fill a jelly jar, let alone supply meaningful amounts of electricity. And I'm pretty sure that no location in the United States sees 8000 kWh/day insolation, at least not without two-axis tracking.
A while back..I ran into this presentation for renewable and PV.. ref http://cohesion.rice.edu/CentersAndInst/CNST/emplibrary/Hartley%2004May03%20NanoTechConf.ppt see slide 24.. Using the following premises.. 3,800 Billion kWh (US power usage in 2000) 6kWh/m^2/day in desert SW.. (flat plate tilted at latitude) http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/atlas/colorpdfs/208.PDF 25% in additional conversion(*) and transmission loses. (5000km HVDC), PV Panel efficiency 13% National HVDC grid. Larger conductors, no skin effect, reduced corona. and fewer synchronization problems.
Results.. 18,000 sq km.. solar array size.
====== Improvements ==========
Here are some updates, and improvements.. Better PV + trackers...
Commercial Sanyo HIT modules convert solar energy @ 17%. eff.. Dual axis tracker located in desert SW increases output upwards of 50%, annual average now 9 kWh/m^2...
refs: http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/atlas/colorpdfs/169.PDF "Annual average..dual axis tracking flat plate.. " http://www.sanyo.com/industrial/solar/index.cfm?productID=1232 "Sanyo.. HIP-200BA3"
Which reduces the surface area PV panels down to 9,176 sq. km..
Additionally, The trackers located in desert SW produce significantly more power in the summer time which does a fair job of matching increasing A/C loads..
refs.. . average daily solar radiation for June, July, Aug, Sept, Oct. http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/atlas/colorpdfs/162.PDF http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/atlas/colorpdfs/163.PDF http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/atlas/colorpdfs/164.PDF
The apparent disadvantage of trackers is that they need to be spaced apart so they won't cast shadows each other. Assuming tracker space in a 1 to 6 ratio. This would expand the overall land use to (55,000 sq km).. However, spacing them out would have certain advantages.
1. Reduced impact on habitat allows multiple dual uses . Agriculture, homes, roads, etc.. 2. Elevated trackers (height @ central mounting point 7 to 10 meters) allows 99% of ground underneath them to be exposed to direct rainfall and remain as useful habitat. (Trackers would assume a near vertical position and rotate during storm.) 3. Trackers can orient themselves(on edge) in order to protect themselves from high winds, hail , and sand storms. (thus extending their lifespan. 4. Temperature reduction(extra shade) which improves habitat.. Photosynthesis peaks at 93 degrees F and ceases at 104 F.. Keeping the ground temps below 100F improves plant habitat.. 5. Easier maintenance.. Able to move vehicles in between tracked arrays.
===== Conservation and load displacement =====
US's Existing HVAC transmission system has an average ~12% energy loss rate. Loss is higher during summertime peaks ~25%, and is some what lower at nighttime %9 and in the winter 5%.. (I^2R applies)
(Extending HVDC lines closer into the users, and skipping 500/230 KVAC transmission lines, and delivering HVDC directly to 1st set of HV step down substations would eliminate much of HVAC transmission and initial transformer losses... recovering as much as ~50% of current losses).
25 to 35% of our electricity consumption is needlessly wasted.
A little bit of conservation goes a long way. Upwards of 2% can be conserved by building Cable and Sat (200 mil) decoders with a simple circuit so they power down when not in use.. (And wake up on a schedule in order to fetch program guide and record tv programs).
Similar always on problem applies to most electronic devices.. Many are small, but significant 24x7 energy wasters.. Large wall warts is one clue.. Equipment cases warm to the touch is another..
Retire existing CRT, Plasma, and Projection units using hi intensity light sources. And replace them with direct view LCD and/or Projection units using high intensity LED back lights.. (7 to 10% national energy savings.).
More CFL & LED usage (10 to 20% savings.) More efficient A/C, and heat pumps. More efficient refrigerator/freezers.. Computers designed for low energy consumption. More eff power supplies. better processors & video cards. Front loading washers... (1/3 hot water consumption, longer lasting clothes.) Roof or side yard mounted solar hot water heaters. Promote Solar heating Subsidized insulation improvements.
In order to retire some of the old energy hog appliances, the poor and those living in subsidized housing would get them swapped out for free.
15 to 20% of electricity is consumed by the OTHER ENERGY industries.. Oil, NG, Coal... Gas stations, tanker trucks, refineries, pipelines, pumping stations, wells casings, drilling rigs, super tankers, 400 ton trucks, drag lines, shovels, coal trains, railroad tracks, construction of power plants, etc..
A lot of this overhead, pollution, and load goes away, when these industries shrink to less than 1/10th of their current size.
Replacing 80 to 90% of ICE oil and gasoline infrastructure.
Modern EV's using Li-ion tech are roughly 15x more efficient than current conventional autos in combination with the energy losses in the current oil and gasoline infrastructure. (Efficiency of Oil & Gas infrastruction is decreasing with each passing year.. More and more energy is being consumed to recover ever smaller quantities of Oil and NG).
Diverting 15% of our (2000) electricity generation would propel 150 Million EV's for a distance of 19,000 miles..
(Uses 200 wh/mile as a baseline...current Li-ion designs ~100wh/mile).
Household renewable energy production, paired with a EV, would have significant advantages.
======= Lifestyle changes =======
Modern lifestyles are energy intensive.. The more people living a modern lifestyle... The more difficult the problem is to solve.
Abandon the every expanding growth mentality.. GW is visible side effect of ever expanding population/lifestyle and non-renewable energy usage. Either solve the GW/pop problem, or GW will solve it for us with a massive ELE.
Limit free trade in all aspects. That system works against countries who sacrificed resources, and lowest cost in the name of protecting society andor the commons. ref: "Tragedy of the Commons Restated" http://dieoff.org/page109.htm
Increase tele-commuting.. Reduce or stop importing workers. Secure the boarders.. deport the un-invited..
Limit population growth to sustainable levels.. (This already occurred in native pop..)
===== Energy storage & load leveling =====
Use the EV batteries as Grid storage.
This section is dependant on Toshiba's recent claim of a new Li-ION bat tech operating for 50K C/D cycles.
High capacity @home/work charging systems for EV's would also have a intelligent inverter function. They would capable of providing energy back into grid when directed to do so. Note: Not everybody will need the EV's 300 Mile range each every day, participating EV customers would get free energy in exchange.. .
US grid could operate off of EV bats for upwards of two days without an external energy source. This feature would be handy after a hurricane swings on through and disrupts the local grid.
++ Undo some daytime peak demand reduction efforts.
You want the load to be present when PV/widn is at max production. Intelligent thermostats under radio control could receive signals from central energy ops. and alter heating/cooling schedule to match avail power.
Typical 50 gal HW heater stores 10 to 15 kWh of Heat.. (Use mixing values, extra insulation, smart controllers to help manage those loads) Solar HW is much better than electric HW.. Heat pump HW heaters for warmer climates with solar access.
Install PV trackers over widest possible areas.. Florida, Texas, Desert SW, Islands off of California.. Maximize PV production over the widest possible time frame.
Collapse mainland time zones from 4 to 2 in order to shift Commercial energy usage to be in sync with PV energy production. East cost would wake up later, West coast would wake up earlier.
NREL has more realistic discussions at http://www.nrel.gov/ncpv/land_faq.html and http://www.nrel.gov/docs/fy04osti/35097.pdf.
That said, the conclusion reached by this particular type of calculation is fairly robust to changes in the assumptions, so the end result -- even with the crazy starting assumptions -- is actually not too far off the mark.
Then again, as others have pointed out, using nothing but PV to meet our electrical needs is impractical. For that matter, using nothing but
We wouldn't, Hydro (8%) and pumped storage (2%)would still be around..
We would still need a major expansion of wind power.. until it matches PV capabilities..
We would hang onto the combined cycle NG plants and adjust turbines to use various mixtures of CH4 and H2,.. (H2 andor Ch4would be manufactured by during periods of surplus renewable power generation and stored in depleted NG wells.) ..
Operate a limited number of N-plants until we deploy enough renewable and load leveling capacity.
coal, wind, nuclear, or any other single source would be impractical too. It would be technologically feasible, but not practical.
Note: At some point we will need to undo the effects of our past CO2 emissions before the ice caps melt. (Sooner rather than later). This will require using surplus renewable energy in order to improve the efficiency of atmospheric CO2 removal..