Interior Secretary Salazar, Senator Reid announce ˜Fast-Track initiatives for up to 100,000 MW of solar energy development on Western lands

The Bureau of Land Management has nearly 160 active solar project applications, “with a projected capacity to generate 97,000 megawatts of electricity” — equal to nearly 30% of the nation’s household electrical consumption.  Last week, Secretary of the Interior Ken Salazar and Senate Majority Leader Harry Reid (D-NV) announced a series of initiatives to fast-track those projects.  I am excerpting a post from guest blogger Craig Severance on what the BLM initatives might mean.  At the end, he discusses a key low-carbon bridging technology, the “hybrid solar/natural gas” plant, which can provide fully dispatchable all-weather power available 24/7 with total generation costs of 7 to 8 cents per kWh.  See also “Natural gas game changer, Part 3” and “Concentrated solar thermal power Solar Baseload “” a core climate solution.”

Map of SW Solar Resources on BLM Lands. Source: BLM.

Measures announced Monday by the U.S. Department of the Interior identified initial solar project areas for the extremely sunny desert areas of the U.S. Southwest.  These Solar Energy Study Areas could site utility-scale solar projects totaling 100,000 MegaWatts (MW) capacity. By comparison, the extremely successful U.S. wind energy industry had total installed capacity by the end of 1st Qtr 2009 equaling 28,206 MW, and “new nuclear power” Generation III+ nuclear plants installed worldwide to date equals zero MW.

Salazar, Reid announce BLM Plans to “Fast-Track” Solar. On Monday, U.S. Interior Secretary Ken Salazar, appearing in Las Vegas with Senate Majority leader Harry Reid (D-NV), announced Bureau of Land Management (BLM) plans to move quickly on solar projects in the desert Southwest.  Plans to “Fast-Track” solar include:

  • Identification of 24 “Solar Study Areas” in 6 Western States, on land administered by the BLM. (Click here for detailed state-by-state maps of the Solar Study Areas.)
  • In-depth evaluation of these 24 areas will begin immediately for their suitability for “large-scale solar energy production”.
  • The 24 areas will be segregated from new mining claims and other actions initiated by third parties under public land laws.  Existing claims will be honored. This segregation will allow solar resource plans to be evaluated and authorized first before conflicting new resource claims would be considered.  The BLM noted that “most of the solar energy study areas are located in alluvial valleys are unlikely to contain significant mineral values”.
  • 4 new BLM Renewable Energy Coordination Offices — in Nevada, California, Arizona, and Wyoming (which has major wind resources) will be opened to expedite processing of renewable project applications  The NV office opened Monday.
  • The BLM has already received applications for 158 SW solar projects.   The new processes are expected to complete study area evaluations by the end of 2010, with construction of approved projects to begin thereafter.

Optimum Areas Selected. The announcement by Interior follows exactly two weeks after release on June 15th of the Western Governor’s Association “Western Renewable Energy Zones – Phase 1 Report”, a collaborative effort of the Western Governors, the U.S. Dept. of Energy, the Interior Department, and the Federal Energy Regulatory Commission.  BLM’s “Solar Energy Study Areas” were clearly developed in concert with the Western Governor’s Association project.

The “Western Renewable Energy Zones” (WREZ’s) study was aimed at finding areas which had very concentrated, high-quality renewable energy resources.  These “hub” areas would then be the logical places to construct renewable energy generation projects, and the transmission lines to serve them.  In the WREZ study, public comments were taken from utilities, businesses, environmental and wildlife groups, local governments and citizens.

The Solar Energy Study Areas of BLM further selected only those areas with limited impacts on wildlife, other natural resources or other land users.  (In other words, land where no one would care if you put a large solar farm.)  This might seem to favor very remote areas.  However, it is also very important to be close to existing or proposed transmission corridors, and be accessible by roads. The slope of the terrain was also considered in finding the most optimum areas.

Though a major effort, a map of the optimal Western Renewable Energy Zones was developed in just a year’s time, aided by consulting firm Black & Veatch.  Below is the portion of the WREZ map covering the SW states, including solar WREZ areas (orange) identified:

Western Renewable Energy Zones in SW States.  Source: WREZPh1

Relative Size of Circles Reflects MWh/yr Potential Generation
(Orange = solar; Blue = wind; triangles = geothermal sites)

Public Lands Crucial to Solar Utility Scale Projects. Wind farm developers have had few problems siting massive wind farms on existing farmland, because of the very small “footprint” per acre of the wind turbines.  Farmers can receive lucrative cash royalty payments for allowing the wind farm on their land, yet still continue to farm undisturbed right around the base of the wind turbines.

This simply will not be the case with large “solar farms” consisting of acres of solar collection mirrors, trough collectors, or photovoltaic panels.  Of necessity, collecting the solar rays that fall upon the land requires using most of the land area, either for the collectors themselves or for access pathways.

Installation of large utility-scale solar farms thus would require purchase of any land used, at a high cost for the projects, if not for the availability of largely unused Federally-owned lands.  Hence, the BLM lands hold the key to siting of large solar projects in the Southwest.  Though the BLM will charge leasing fees to solar developers, these will be market value based for a solar project, and thus reasonable enough to allow the projects to succeed.

Transmission Corridors to Follow. While many of the 24 Solar Energy Study Areas are close to already-existing transmission lines, many have no access to transmission lines, or the existing transmission lines would need to be upgraded.  The WREZ Phase I study was in fact by definition an effort to define the best renewable energy areas to develop which would need transmission corridors to deliver the power to market.  (For instance, rooftop solar PV within cities was not considered in the WREZ study, a limitation that may prove important if PV prices soon tumble.)

The identification of the BLM study areas, and even final project approvals for the solar farms to be built, will thus not be the final step to development of these resources.  Once projects are identified for development, tandem efforts to develop transmission corridors to serve those projects will be needed.  This is a major reason for inclusion of the Federal Energy Regulatory Commission (FERC) in the WREZ study from the beginning.

Central Power Plants Located Far From Loads. The “solar farm” generating plants to be located on BLM lands will essentially be “central power plants” in the traditional sense — large multi-MW generators connected to the utility grid by transmission lines.

This is in direct contrast to “distributed” power generation projects, such as rooftop photovoltaic solar collectors that serve a single or a few buildings, or a substation area.

The advantages of the “central power plant” model of the Solar Energy Study Areas is that the most concentrated, highest value (i.e. sunniest) areas were selected.  Therefore, locating solar generating plants in these areas will produce more power for each dollar spent on building the plant.  It is just a fact of life, however, that very few people chose to live near these very sunniest areas of the Southwest (probably because they were just too sunny, hot, and dry.)

The other advantage of locating in the desert is that types of facilities that cannot be roof-mounted can be built there.  While it might be possible to find rooftops in L.A. to install solar photovoltaic panels, you won’t find any land you can afford in L.A.  If the most economical and reliable solar designs use technologies other than rooftop PV, therefore, they will need to be located on public lands.

What Kind of Solar Generating Projects Will Be Built? There are many designs proposed, but one of the most economical may be combination solar thermal/natural gas power plants, such as proposed by solar thermal company Ausra.

In these power plants, water runs in tubes through mirrored troughs which focus the sunlight on the tubes and heat the water, which then drives a steam turbine.  That’s the “solar thermal” part of the combination.

The “combined cycle gas turbine” part of this “hybrid solar/natural gas power plant” is a gas turbine that first generates power from burning the natural gas in jet-engine-like “turbines” that spin blades to generate power.  Then, the very hot exhaust gases are used to heat water which drives a steam turbine.

In the “hybrid solar/natural gas” power plant, both the solar thermal and the natural gas turbines would share the same steam turbine.  Not only does this save on construction costs, but it results in a power plant that can run very efficiently from a thermal standpoint.  As the solar resource cools off at night, the gas turbines can gradually be ramped up to provide just enough heat to keep the operating fluid at optimum temperature.  Then, as the solar becomes available during the day, the gas turbines can be gradually ramped down and shut off.

Not “Sunny Day” Power Plants. The solar thermal/natural gas plant is thus NOT a “variable” power resource the utilities cannot predict.  It would be fully dispatchable power available 24 hours a day/7 days a week.  A seamless operation of one coordinated power plant, not a “sunny days” power plant.

Ausra CEO Bob Fishman predicted at the Boston Going Green conference in March, that this combination design could lower total generation costs to around 7 to 8 cents per kWh.  In contrast, Fishman said the solar thermal plant if built without the natural gas turbine, would produce electricity at total generation costs of around 12 to 13 cents/kWh.

With natural gas supplies in the U.S. now at very abundant levels and low prices, these hybrid solar/natural gas plants could prove the most economical and reliable solar generators for several decades.  A real powerhouse of economical and reliable low-carbon electricity for the Western United States.

In future decades, as energy storage solutions advance, and our natural gas resources eventually diminish, other means to “back up” the solar power resources will prove valuable.

[JR:  I would add that the most obvious energy storage solution is large-scale deployment of plug-in hybrids (along with electric cars), a core climate solution, which just happens to be a top priority of the Obama administration and a major component of both the stimulus bill and the Waxman-Markey climate and clean energy bill.]

26 Responses to Interior Secretary Salazar, Senator Reid announce ˜Fast-Track initiatives for up to 100,000 MW of solar energy development on Western lands

  1. Modesty says:

    There’s obviously a lot to be excited about in here. But this is the first time I’ve seen you mention NEW natural gas plants (albeit of a very different kind) in a positive context. (I realize the article is not yours.)

    Your earlier game-changer proposed the use of already existing but underutilized plants, which really seems brilliant and straightforward.

    But the hybrid proposal above could entail a generation of new investment in natural gas.

    “In future decades, as energy storage solutions advance, and our natural gas resources eventually diminish, other means to “back up” the solar power resources will prove valuable.”

    This suggests a whole new generation of natural gas plants (hybrid).

    That’s more natural gas than I bargained for.

    What would we be locking-in, with this proposal?

    [JR: I’ll try to get Craig to do a follow up post on this at some point. This plants probably have a factor of five (or more) lower emissions per kwh than coal, so I can’t lose a lot of sleep over them — nor would I expect a lot of them to be built. Obviously, utilities would only get the renewable credit for the CSP kwh.]

  2. Mark Shapiro says:

    Another storage option is battery swapping proposed for Shai Agassi’s Project Better Place. No one knows how the economics will work, but it’s certainly worth trying.

    The main advantage that battery swapping offers is that the unused batteries are always connected to the grid, while the PHEV batteries are plugged in some lower fraction of the day (maybe much lower).

    Also, leaving more of the battery with the Swapper lowers the weight of the vehicle, lowering cost and raising efficiency.

    Better Place has already demonstrated battery swapping technology. Let’s watch closely.

  3. Omega Centauri says:

    “Farmers can receive lucrative cash royalty payments for allowing the wind farm on their land, yet still continue to farm undisturbed right around the base of the wind turbines.

    This simply will not be the case with large “solar farms” consisting of acres of solar collection mirrors, trough collectors, or photovoltaic panels. Of necessity, collecting the solar rays that fall upon the land requires using most of the land area, either for the collectors themselves or for access pathways.”

    This may not have to be the case. One startup, CoolEarthSolar, is pushing a concept of stringing concentrated photovoltaic modules from pole mounted cables. The land underneath could still be utilized for farming and ranching, although clearly the esthetics would be affected. The major unknown is whether they can reach the targeted low capital and operating costs targeted in their business plan. Their concept relies on the use of low cost inflated mylar reflectors.

  4. Leif says:

    A storage solution that also does not seem to get enough attention is compressed air.
    It can be run thru a pipeline or used on site. Air tools are ubiquitous, reliable and affordable.
    Air motors are available for automobiles, fork lifts and more.
    Recharging is quick and safe. Air tanks are easy to build and lighter than batteries. No harmful or dwindling chemicals required. Safe to transport. Idealy suited for remote locations. ie. A farm could have a windmill and run the whole farm including making off production electricity on compressed air. One resourceful farmer that I read about bought a used raliroad tank car as a storage tank. Extra capacity easily sold to the neighbors. No foreign resources required. The list goes on.

  5. Anthony Watts says:

    Having done two solar projects myself, one on my home and one for a local school, I applaud a solar solution of otherwise unusable land.

    But the rub is that it should be viewed not as added capacity, but as an offset to existing, since solar does not work at night, other types of generation must kick in then. On the plus side, solar helps immensely with peak daytime load.

    [JR: One thing the country has is excess capacity at night — and even more so with all the wind coming on. Concentrated solar plus wind, with some back up by natural gas, and of course demand response (plus efficiency), pretty much covers everything new we could need at this point. And yes it can be an “offset” to existing capacity.]

    Leif, compressed air is a worthwhile idea. Tied with solar and a air motor/generator it could provide a viable energy storage solution without need for chemical based storage.

  6. Christian Hernandez says:

    “equal to nearly 30% of the nation’s household electrical consumption”

    That is great. I always wondered why they didn’t implement more solar solutions in areas where the sun rays are intense.

  7. I’ve looked at a number of Ausra’s presentations and documents, but don’t see any figures for water use and for water consumption per MWH generated. Some STE plant designs reportedly require water levels comparable to the largest water-using and water-consuming thermal power plants like nuclear power. Is the Ausra design a significant improvement in this regard?

  8. cce says:

    Would it make sense to colocate CSP and enhanced geothermal? Many of these areas have excellent geothermal potential.

    Solar follows demand during the day, and the geothermal could supply baseload using the same steam turbines.

    If you wanted to get really fancy, you might be able to use the spent hot water from the geothermal side to regulate the temperature of algae ponds (via some some kind of radiator system) before it is pumped back underground.

  9. Mark Shapiro says:

    Michael –

    Ausra uses dry-cooled generation, so the only water used is in the pipes making steam. This costs some efficiency, but makes it more suitable for desert installations, where insolation is highest and most reliable, and water is scarce.
    Source: the video on Ausra’s technology page and prior discussions at ClimateProgress.

  10. Doug Meyer says:

    “largely unused Federally-owned lands”, eh? Tell that to the plants and animals that have been living there a lot longer than any of us have been around.

    [JR: But not living there much longer if we don’t deploy hundreds of GWs of renewables ASAP.]

  11. Doug Meyer says:

    My purpose is only to leverage the term “environmentalism” out of the progressive arsenal. The public has been fooled into thinking you guys are environmentalists. We both know those plants and animals are doomed regardless, and their death will be on human hands. You guys want to save civilization, go ahead and try, but don’t tell me or anyone else you’re saving the emvironment. Thousands of square miles of desert ripped up in desperation prove my point.

    “Vanity, thy name is humanism.” -Edward Abbey

    [JR: I have no clue what your “purpose” is in posting here. I am not an environmentalist, as I have said many times. If have an alternative strategy for avoiding the end of human civilization as we know it — plus the extinction of the majority of species on land and sea — than what I have proposed on this blog, I’m eager to here it. Otherwise, your only purpose here is to sew confusion and promote outcomes that are far worse for all the planet’s species.]

  12. Mike D says:

    Actually Joe, a lot of these species would stand to benefit from climate change as aridland habitats expand. But that’s not the point. There needs to be concern about habitat corridors from the earliest stages of planning and development. No different than any other type of development. I firmly believe we can and must balance sustainable energy development and habitat conservation.

  13. Doug Meyer says:

    I often feel the global warming deniers actually understand the moral/environmental aspect better than the progressives, that’s why they deny. Proposing vast desert power plants while selling the idea that our problems are merely technological comes off as disingenouos, further separating the camps. A lot more public acknowledgement that these new power plants also mean a substantially humbled way of life for us might get progressives a lot more respect.

    [JR: Not! The deniers deny for many reasons, but I doubt any do so because they “understand the moral/environmental aspect better than the progressives.” That would make them outright evil.

    I take it you don’t actually read this blog, or else you’d know that your comments are quite offbase here. That said, calling “for a substantially humbled way of life for us” — an inevitable outcome of our current Ponzi scheme, as I’ve argued many times — would get progressives far LESS respect with the public and media. Try seeing how those who do that are viewed.]

  14. Doug Meyer says:

    No, Joe, they understand it very well and they don’t want to believe it, that we humans are responsible for biological destruction on a planetary scale (for many it would uphend their religious beliefs). What’s the first stage of grief? Denial. It’s who we are.

  15. Mike D says:

    Ridiculous. Global warming deniers are the same people who want to end the Endangered Species Act, sell off federal lands to oil companies, eradicate wolves, and advocate countless other environmental atrocities.

  16. Yuebing says:

    100 GW nameplate, trough solar thermal, how does this compare to (say a large 1.5 GW) nuclear plant at 90% availability?

  17. Rick says:

    a humbled life seems to be coming up no matter what. It’s pretty simple. Our excess and luxury come from cheap and abundant fossil fuel. Renewables are a whole new thing.

  18. Leland Palmer says:

    Nice to read Climate Progress after a couple of days of rolling in the irrelevant filth of the mainstream media. It’s like a cool wind of logic blowing through my hair.

    Wonderful news about the solar. Sounds like a lot of it. It’s been known for a long time, since the 1980’s of course, that CSP on this sort of scale was possile.

    Why not use biochar for backup fuel? Coal log pipelines could be constructed from forested or agricultural areas to carry pelletized biochar compressed into logs. Or, railroad transport could be used, as well. This would make these CSP baseload plants carbon neutral.

    Another possible carbon neutral energy transport medium is carbon monoxide derived from biomass, believe it or not. A old process known as COSORB, which was originally proposed to transport combustible gas from coal mines to power plants, could be updated and used to transport carbon monoxide hundreds of miles, without being worried about hydrogen embrittlement of pipelines.

    If you’re not worried about hydrogen embrittlement, and I believe there has been some progress in this in the past couple of decades, there is always hydrogen derived from biomass as a transport medium, for a carbon neutral backup fuel.

    Another possible backup for solar thermal is geothermal hot dry rock, called engineered geothermal these days, I think.

    And, of course, there is always the option of just adding more sensible heat storage on to CSP plants.

    Finally, there is the possibility of using phase change materials for increased heat storage. There has been work done on this in the past, but successful large scale heat storage by a phase change material (which would be melted, for example, absorbing heat as it melts, then would recrystallize and give off heat upon solidifying) has not yet been achieved, I think.

    Many technologies are possible to provide heat storage for solar themal power plants, or for subsequent storage of the electricity generated by such plants.

    Flywheel storage of electricity is another technology, proposed long ago, with a great deal of potential, which has not been developed for utility scale energy storage but which probably could be with effort and engineering development.

  19. BBHY says:

    I don’t think people realize how much of our money is wasted.

    We’ve spent a trillion dollars on the Iraq war, and we’re told we can’t afford clean energy. The US has more military spending than all the other countries combined. When Don Rumsfeld was Secretary of Defense, he owned 80 million shares of a defense contractor that was awarded a huge defense contract. The Wash Post, the NY Times, they all thought that this sort of obvious corruption was ok, and hardly even noticed.

    We spend much more on health care than any other country, our health care providers are much more profitable and they spend enormous amounts of money on lobbying. Yet our health care is ranked far below many other countries.

    We just spent enormous amounts of money bailing our financial institutions who lost enormous money investing trading toxics asserts that were fraudulently rated AAA.
    To get an idea of the mindset of these guys, the CEO of Merrill-Lynch bought a $35,000 toilet for his executive bathroom with his bailout money.

    We spent about $500 billion dollars on foreign oil last year alone, and that’s only going to go up. That’s money flowing out of the country that we don’t get to use to invest in renewable power, grid improvements, and alternative transportation. We can’t afford electric cars, but if we had them we could save $7 trillion over the next ten years. Huh?

    All of this waste and yet we are told over and over that we can’t afford clean energy. It’s complete nonsense. It took only two days to install solar panels on my roof and I cut my electric bill in half. Now I’ve got an electric car, and I’ve cut my fossil fuel usage by 70%.

    My life is exactly the same as before, I am NOT living a humbled life.

    The US has done basically nothing to move to clean energy and already we are told it’s too expensive.Shouldn’t we try a few simple steps first? Then we can evaluate how much it’s costing and how much it’s saving? Shouldn’t we try get our house in order and stop giving all our money away to the rich people running the defense, health care, financial, and oil industries?

  20. James Thomson the second says:

    [JR: I have no clue what your “purpose” is in posting here. I am not an environmentalist, …]

    I don’t understand this statement. If you are lobbying against climate changing CO2 emissions because they change the climate then you are an environmentalist. We all share the same environment, even if you only profess concern over it’s impact on US civilisation.

    [JR: Well, you might read some of the posts on this blog, starting here. I am a physicist and a technologist who studied physical oceanography at the Scripps Institution of Oceanography. I am not “lobbying against climate changing CO2 emissions because they change the climate.” I am working as hard as I can to avoid catastrophic impacts on humanity from GHG emissions. If you are suggesting that everybody should be an environmentalist, that is a different matter.]

    Bit worried about hybrid gas/solar. This approach addresses energy but not climate change. The acid test is whether such a solution leaves us with a clean energy system BEFORE all carbon has been extracted. This one does not aim to do that.

  21. “with a projected capacity to generate 97,000 megawatts of electricity” — equal to nearly 30% of the nation’s household electrical consumption.

    But how does that compare with the nation’s TOTAL electrical consumption, including industrial as well as household?

    [JR: Try Google!]

  22. James Thomson the second says:

    […I am working as hard as I can to avoid catastrophic impacts on humanity from GHG emissions.]

    That is a really strange position. I assume it must be because the term “environmentalist” comes with some unwelcome baggage – long-haired, unwashed people who break into coal fired power stations. That sort of stuff.

    The point I an trying to make is that curbing CO2 is all about the environment. Nothing else. You can’t see it, smell it and it’s not about to suffocate anyone, but CO2 threatens to become the biggest environmental disaster of all time.

    Joe -if you are not an environmentalist then no-one is. On the other hand, if you somehow deny your intetest is environmental then that makes me wonder if climate change is just a convenient vehicle for pushing other, unrelated agendas. I do hope not.

  23. CS: But how does that compare with the nation’s TOTAL electrical consumption, including industrial as well as household?

    [JR: Try Google!]

    From google, I learn that total US electrical generation capacity is about 1 million megawatts.

    Thus, the solar energy study areas can generate only about 10% of current total US electrical generation, and it is a bit misleading to state it as 30% of household electricity consumption, ignoring other consumption.

    [JR: It was their stat. But people typically write about electricity savings/generation in terms of American homes — this would provide enough power for about 30 million — and hence the percentage. Not misleading. Quite standard.]

    I think solar thermal can do better than that, and when they plan the transmission corridors, they should look at the best sites on private lands as well as on public lands.

    [JR: Of course it can, this is just solar plants currently proposed on U.S. lands.]

  24. James Thomson the second says:

    According to this source a relatively small area could power the whole of America.

  25. Leland Palmer says:

    The best way to get rid of the coal fired power plants, I am convinced, is to convert them to carbon negative bioenergy power plants, combining biochar fuel with enhanced efficiency via oxyfuel combustion and a topping cycle with deep injection of the resulting CO2.

    Some of these monster coal plants are in the desert, the “Navaho” plant located in Maracopa county, Arizona, for example, is located in an area of high sunshine.

    I have speculated that these plants could be converted to CSP, with biochar backup, with the biochar brought in through biochar log pipelines from elsewhere. Another backup possibility is to bring biomass energy to the site as carbon monoxide or hydrogen, via pipeline.

    It seems possible to bring steam to a central power plant from solar power towers, using very long steam lines buried inside insulated conduits. These lines could be constructed to have a certain amount of thermal mass, themselves, and so constitute sensible heat storage. So, you get heat storage and steam transmission capability in one retrofit. One cement that might be able to withstand the extreme conditions of these insulated conduits is a family of cementitious materials known as “geopolymers”. Another high temperature solution would be to simply construct these conduits of firebrick, insulate them with something like pumice, and fill them with rock, gravel, and sand, as sensible heat storage for the steam lines coming from an array of solar power towers surrounding the power plants.

    As solar production and biochar use is ramped up, coal consumption could be ramped down. As carbon storage or sequestration capacity is increased, the plant becomes increasingly carbon neutral, finally becoming carbon negative when completely converted to solar with biochar backup, enhanced sensible heat storage, enhanced thermal efficiency via oxyfuel combustion and a topping cycle, and deep injection of captured CO2.

    If we depend on the coal and utility industries, this will never happen, even though it might be technologically feasible. We need to seize the coal fired power plants, and massively convert them by fiat into carbon negative power plants. CSP could certainly help, for those power plants located in the desert, such as the Navaho plant in Arizona.

  26. Mike Roberts says:

    The comments here seem to remain focused on huge, centralized power generation, and large powerlines to carry the product to the consumption point. I live in a state (Wyoming) where wind power projects are seriously changing the landscape. Public lands in the southwest will be highly impacted by large solar installations. Millions of acres of solar collectors have a similar impact on the land as millions of acres of parking lots – it just feels better because of the green energy aspect.

    Why are we not looking elsewhere for siting options for solar energy? The nation’s hundred million rooftops could host solar PV collectors. The land under the roofs is already disturbed, and the visual impacts of the buildings on which they sit is already accepted. As a bonus, the power can be used near the generation point, meaning no new powerlines, with their hundreds or thousands of miles of land disturbance and visual impacts, would be needed.

    I’m no engineer or green energy expert, but it makes sense to me. The balance of the energy could come from all the cool technologies proposed by all those smarter than me who have commented here.