In 2020 California became the first state to require solar panels on the roofs of most new homes, a milestone for a residential solar industry that already enjoyed a healthy foothold in the state.Jul 22, 2020
It's a good time to revisit the slow-motion water crunch in the American Southwest. Last week, Lake Mead — a key reservoir that helps supply water for 25 million people in Nevada, Arizona, and California — shrunk to its lowest level ever. And the question of how to grapple with water scarcity is making headlines yet again.
Back in the 20th century, the United States built an army of dams across the West to tame rivers, generate electricity, and store water in reservoirs for cities and farms. This intricate system is why metropolises like Los Angeles, Las Vegas, and Phoenix have been able to survive in what's basically a desert. Large-scale farming is really only possible in California's Imperial Valley or central Arizona because of these dams.
But rising demand and 16 years of drought have put a severe strain on this system. Dean Farrell has created a terrific interactive map showing how key reservoirs in the West have seen their water levels drop dramatically of late:
The size of the circles is proportional to the capacity of the reservoir.
Check out California first. Many of the state's reservoirs fell below 50 percent during its recent (and brutal) drought. Last winter's El Niño brought heavy rains to the northern part of the state, refilling reservoirs there. But reservoirs in the south remain depleted — and the state's water woes, while partly alleviated, haven't gone away.
Now let's focus on those two huge red circles near Arizona: Lake Mead and Lake Powell. These gigantic reservoirs, which help store and supply water from the Colorado River to farmland and cities throughout the Southwest, are in rough shape. On Thursday, Lake Mead officially hit its lowest level ever, just 1,074.6 feet above sea level. (The last record low came a year ago, in May 2015.)
That's a big deal. If water levels at Lake Mead continue to plummet, the federal government could declare an official water shortage and force (potentially) painful cutbacks. The good news is that policymakers are aware of this and discussing ways to stave off crisis — though it won't be easy. That vast system that once allowed vegetables, lawns, and golf courses to flourish in the desert no longer works the way it used to.
In 1936, the federal government completed the Hoover Dam, which blocked the flow of the unruly Colorado River and created Lake Mead, a giant reservoir meant to fill up during rainy years and supply needed water during dry years. Later, in the 1950s, the government built the Glen Canyon Dam even further upstream to create Lake Powell, to help store and regulate water supplies.
Water from these two reservoirs gets divvied up between California, Nevada, Arizona, and Mexico according to a longstanding set of agreements1. California has built aqueducts to carry the lake's water to Los Angeles and San Diego and farms in the Imperial Valley. Meanwhile, Las Vegas gets 90 percent of its water from the lake.
Then there's Arizona. In 1968, Congress approved the Central Arizona Project, a series of aqueducts that would transport 1.6 million acre-feet of Colorado River water down into central and south Arizona and help nurture farms and cities like Phoenix and Tucson. The state as we know it today simply wouldn't exist without this project.
But as John Fleck, a terrific writer on water issues who has been covering the Colorado River for many years, explained in 2015, there was a catch. In order to win support from California politicians, the Arizona project's backers had to agree to a key condition: in the event of a water shortage, California would get first dibs on the Colorado River's water. Arizona would move to the back of the line.
Now, for the first time, a shortage looks plausible. Water levels at Lake Mead had already been dropping for years, as more and more users have been overdrawing its water. More recently, drought and extreme heat have been adding to the strain. With less snow in the mountains, there's less water flowing into Lake Powell, which in turn is delivering less water downstream to Lake Mead.
When Lake Mead was at its fullest, the water reached an elevation of 1,220 feet above sea level. In May 2016, it was down to just 1,074.6 feet — the lowest level since the dam was built.
Federal officials say they expect water levels to keep dropping this summer but then rise above 1,075 feet before the start of 2017. If levels remain below 1,075 feet by the start of the year, however, the US government will declare an official shortage. That increasingly seems likely — if not in 2017, then in 2018. And once that happens, the real fun begins.
What a Lake Mead water shortage would mean for Arizona, Nevada, and California
So what would an official "shortage" mean in practice? On this, everyone should read this post by Fleck. As he notes, a shortage at Lake Mead under current rules would mainly affect Arizona. However, there's also a major effort underway to rethink those rules.
Under the 1968 agreement, Arizona has to cut back on water use before anyone else. And, Fleck explains, the state does have a plan for this. The Central Arizona Project would continue to keep water flowing to cities like Phoenix and Tucson, Indian tribes, and high-priority agriculture. But it would cut back on "low-priority" agriculture and delay refills to groundwater storage:
In 2015, Summer Pauli of the Tucson Sentinel wrote a great piece on what those cuts might look like. Some Arizona farmers will no doubt conserve water by switching from flood irrigation to more efficient drip irrigation. (Many have already been doing this, though installing these systems can cost more upfront.) Others may try to pump more water from underground aquifers (though Arizona has stricter controls on groundwater pumping than, say, California). Others may just cut back on growing crops like alfalfa.
These cuts won't be apocalyptic, but they won't be minor either. "It’s going to be a very painful cutback when we start losing our water, but we’ll do what we can to survive and that’s all you can do," one farmer told the Sentinel.
Next comes Nevada. Las Vegas — which gets 90 percent of its water from Lake Mead — is likely to be okay for the time being. City officials have been watching the lake's levels drop for years and have already taken steps to curtail water use 30 percent over the past decade, not least by providing incentives for homeowners to replace the grass on their lush lawns with less-thirsty native plants.
Las Vegas has also been building costly new water intake systems so that it can keep drawing water from Lake Mead even if water levels keep dropping further. (When the original intake systems were built, the pipes were essentially too high up; few imagined that reservoir levels would drop this far.)
Finally, there's California. Under the original 1968 agreement, California wouldn't see any cutbacks from the Colorado River until the Central Arizona Project went dry. In the event of an official shortage, Los Angeles, San Diego, and the Imperial Valley would continue to get their full share of Colorado River water for years to come.
But those are the current rules. More recently, officials in Arizona, Nevada, and California have been discussing a brand new agreement that, they hope, would divvy up the Colorado River's increasingly scarce water in a fairer and more sensible way. Under a renegotiated deal, Arizona and Nevada would cut back even more sharply in the event of a shortage — but California would also have to start sharing the burden and make some sacrifices of its own.
As Tony Davis reported for the Arizona Daily Star, the current proposed agreement would see the Central Arizona Project reduce water use up to 15 percent once a shortage is declared at Lake Mead (as opposed to the current 11.5 percent). Arizona officials have also been talking about water cuts to all sectors of the state's economy rather than agriculture alone. Meanwhile, California would need to start reducing water deliveries if levels at Lake Mead dropped about 30 feet lower than they are today, rather than waiting for Arizona to go dry. The bulk of these cuts would likely be borne by farmers in the Imperial Valley.
This is far from a done deal, and negotiating water agreements, both between states and among individual state water districts, is notoriously tricky. (Fleck has another good post about this.) But it's a sign of growing awareness that the current arrangement is no longer viable. Lake Mead is unlikely to survive the status quo.
The looming question: What happens if water shortages get worse in the future?
Nothing good for boats, that's for sure.
(Ethan Miller/Getty Images)
One big reason these agreements are being rethought is that as the Southwest enters its 16th year of drought, these shrinking reservoirs are becoming harder to dismiss as a temporary blip.
The 1922 agreement that divvied up water from the Colorado River was forged during one of the wettest periods in the past millennia. At the time, people assumed droughts would occur, but they didn't assume droughts would get off-the-charts terrible.
That's increasingly looking like a bad bet. Scientists have uncovered evidence that decades-long "megadroughts" have occurred in the distant past, and could well occur again in the Southwest going forward. And even if that doomsday scenario doesn't come to pass, climate models still expect droughts to get more frequent and severe in the American Southwest if global warming continues apace. There is very likely to be less water to share in the future.
Yet despite all this, Lake Mead's users have been overdrawing water in recent years — essentially assuming that there will be wet years in the future to provide surplus water and recharge the system.
In a separate post, Fleck pointed to an eye-opening presentation by the Central Arizona Project that asks what would happen if water levels at Lake Mead keep dropping — down to 1,000 feet, say. In that case, Las Vegas would face even bigger challenges drawing water from the reservoir. The Hoover Dam would struggle to generate electricity. Arizona, Nevada, and California would all see steeper cuts in water deliveries. Unless, of course, states figure out how to better manage and share their water supplies.
Up until now, there's always been plenty of water from the Colorado River to go around. It's increasingly difficult to take that for granted.
Further reading: Some essential John Fleck posts on Lake Mead here, here, here, and here. Thorough coverage of the (proposed) new Colorado River deal from Tony Davis in the Arizona Daily Star, Ian James in the Desert Sun, and Henry Brean in the Las Vegas Review-Journal. In the New York Times, Abrahm Lustgarten had a fascinating piece on the water experts who think that opening up the Glen Canyon Dam (and draining Lake Powell) could actually help the Southwest save water. It's worth reading.
讨论太阳能，需要有一点量的概念。
本人也担心碳排放对环境的影响，但是仔细看一下，太阳能并不会对这个大的趋势有多大作用。
第一。太阳能即使取代了所有电力需求，也只是美国总能源需求的一小部分，何况太阳能每天分布不均，大量电能储存是不现实的。（我已经给出过，现在的太阳能只占美国能量总消耗的不到百分之一）
第二，所有发展中国家都在快速增加能源消耗，他们用不起昂贵的太阳能，还是得靠烧碳化物。
第三，现在的太阳能发电是依附在现有电力系统上的，真的大规模取代现在的发电系统，稳定性和可靠性是未知的。
如果您希望太阳能来拯救世界，那可能需要几十年，不过到那时候世界已经完蛋了，于事无补了（假如你相信别人告诉你的话。。。）
周三（9月8日），美国能源部发布了有关太阳能发电的研究报告，详细阐述了太阳能发电在美国电网脱碳过程中蕴含的潜力。报告指出，到2035年太阳能发电有望提供全美40%的电力，并且消费者无需支付更高的电价。
美国能源部长Jennifer M． Granholm发表声明称，这份研究表明，作为最便宜、增长速度最快的清洁能源，太阳能可以产生足够的电力，到2035年为全美所有家庭供电，同时创造150万个就业岗位。
Granholm指出，要实现这一目标，需大规模且公平地部署可再生能源，还需强有力的脱碳政策，这正是基础设施投资和就业法案所提出的，也符合美国总统拜登“重建更好的美国”（Build Back Better）的宗旨。
美国能源部国家可再生能源实验室撰写了这份名为《太阳能未来研究》的报告，此前拜登政府提出了2035年电力部门实现净零排放的目标。
2020年，美国太阳能发电占据全国电力供应的3%。该报告指出，从现在到2025年，美国必须每年平均增加3000万千瓦的太阳能发电；从2025年到2030年，每年必须增加6000万千瓦的太阳能发电能力；到2035年，太阳能发电将向美国供应1000吉瓦的电力，而到2050年，太阳能可提供1600吉瓦的电力，这比目前美国所有住宅和商业建筑所消耗的电力还多。
研究模型显示，除了太阳能占据的40%电力，无碳电网的其余部分主要由风能（36%）、核能（11%-13%）、水力发电（5%-6%）和生物能源/地热（1%）提供。
我的本意是从屋主的角度讨论个人经济的得失，而不是全球的清洁能源是否需要的问题。
我也很有兴趣探讨一下太阳能作为绿色能源是否可行。我没法说它可行或不可行，但
1）太阳能不是唯一的绿色能源，风能，和水力更环保。有新的研究利用海浪来发电，也是不错的方向。
2）太阳能的利用，在技术上远不成熟。能量转化率低。电池本身成本高，生产污染严重，失效电池对环境造成再次污染。所以并不适合大规模商用或民用。由于一些政治原因，有些政客在绿色能源的问题上搞大跃进，把实验室产品推出来当成熟产品。一些环保人士，本着保护地球的心却做出了损害地球环境的事。
3）现阶段应该从提高能源使用效率和寻找新能源两个方面同时入手。现在很多家电都是energy star， 这很好，但还可以继续改进。同时，工业用能源也要提高利用率。政府应该给要改造使用节能新机器的工厂扶持，这比给个人住房加太阳能板扶持更有效。
美国每年用电量约为 3.8 trillion kWh （度）电，美国人口约328 million (3.28亿），人均年用电量约 11,515 kWh。
全世界人口 7.9 billion (79亿），如果都像美国人那么用电，那就是 91 trillion kWh。
太阳光射在地球上的能量是 173 trillion kW，每年是 173 × 24 × 365 = 1,515,480 trillion kWh
都像美国人那么用电，每年用掉的也只是总太阳能的 0.006%，还行。
这个分析是不是有点像钱老的亩产万斤粮？
几个事实：太阳板效率不到15%，瑞典冬天太阳半个小时/天都没有
其实这个不难理解，到Costco看看人家怎么烤鸡就明白了。
我理解你的无功功率是指交流电情况下荷载不是纯电阻的。如果都是分布式系统，都用直流电源是否就没问题了呢？
如果大金空调用变频技术，电源是直流的是否更简单？
当年Edisson 与 Tesla 打架，交流电胜出，将来会不会反转？
目前，1000VDC 的直流负荷也不少呀。
顺便讲一个故事，当年，Berkeley CA，那个小埠就是直流供电的。很幸运的，我见过那张供电图。
美国政客现在最擅长的也就是PPT了
你说的无功功率我的理解是对应的交流电有效功率而言的。而有效功率是和电流与电压的相位差有关的。理想的最大有效功率是电流和电压同相位，如果是反相位的话，有效功率就为零。这就是为什么电线杆上常常会看到挂这个铁桶一样玩艺，那就是为了补偿相位差安装的电容。
直流供电有它的优点和缺点，你要先明白为什么很少用直流供电而用交流供电。
In 2020 California became the first state to require solar panels on the roofs of most new homes, a milestone for a residential solar industry that already enjoyed a healthy foothold in the state.Jul 22, 2020
行业大发展，好多人发财，大家贡献，大家自我感觉非常良好，环保了，废物都去第三世界了，out of sight, out of mind.
其实我们这里好多山，好多森林，就是没山火，没有一点climate change。看来我们不在同一个地球
气候就没啥变化了。
试试这个，看看它能解释清楚无功补偿的问题没有？
https://baike.baidu.com/item/无功补偿/10568351
https://www.vox.com/2016/5/23/11736340/lake-mead-water-drought-southwest
It's a good time to revisit the slow-motion water crunch in the American Southwest. Last week, Lake Mead — a key reservoir that helps supply water for 25 million people in Nevada, Arizona, and California — shrunk to its lowest level ever. And the question of how to grapple with water scarcity is making headlines yet again.
Back in the 20th century, the United States built an army of dams across the West to tame rivers, generate electricity, and store water in reservoirs for cities and farms. This intricate system is why metropolises like Los Angeles, Las Vegas, and Phoenix have been able to survive in what's basically a desert. Large-scale farming is really only possible in California's Imperial Valley or central Arizona because of these dams.
But rising demand and 16 years of drought have put a severe strain on this system. Dean Farrell has created a terrific interactive map showing how key reservoirs in the West have seen their water levels drop dramatically of late:
:no_upscale()/cdn.vox-cdn.com/uploads/chorus_asset/file/6529129/Screen%20Shot%202016-05-22%20at%208.22.45%20PM.png)
The size of the circles is proportional to the capacity of the reservoir.(Dean Farrell)
Check out California first. Many of the state's reservoirs fell below 50 percent during its recent (and brutal) drought. Last winter's El Niño brought heavy rains to the northern part of the state, refilling reservoirs there. But reservoirs in the south remain depleted — and the state's water woes, while partly alleviated, haven't gone away.
Now let's focus on those two huge red circles near Arizona: Lake Mead and Lake Powell. These gigantic reservoirs, which help store and supply water from the Colorado River to farmland and cities throughout the Southwest, are in rough shape. On Thursday, Lake Mead officially hit its lowest level ever, just 1,074.6 feet above sea level. (The last record low came a year ago, in May 2015.)
That's a big deal. If water levels at Lake Mead continue to plummet, the federal government could declare an official water shortage and force (potentially) painful cutbacks. The good news is that policymakers are aware of this and discussing ways to stave off crisis — though it won't be easy. That vast system that once allowed vegetables, lawns, and golf courses to flourish in the desert no longer works the way it used to.
Lake Mead, a crucial reservoir, is at record lows:no_upscale()/cdn.vox-cdn.com/uploads/chorus_asset/file/6031451/hoover-dam.jpg)
The Hoover Dam.(Shutterstock)
In 1936, the federal government completed the Hoover Dam, which blocked the flow of the unruly Colorado River and created Lake Mead, a giant reservoir meant to fill up during rainy years and supply needed water during dry years. Later, in the 1950s, the government built the Glen Canyon Dam even further upstream to create Lake Powell, to help store and regulate water supplies.
Water from these two reservoirs gets divvied up between California, Nevada, Arizona, and Mexico according to a longstanding set of agreements1. California has built aqueducts to carry the lake's water to Los Angeles and San Diego and farms in the Imperial Valley. Meanwhile, Las Vegas gets 90 percent of its water from the lake.
Then there's Arizona. In 1968, Congress approved the Central Arizona Project, a series of aqueducts that would transport 1.6 million acre-feet of Colorado River water down into central and south Arizona and help nurture farms and cities like Phoenix and Tucson. The state as we know it today simply wouldn't exist without this project.
But as John Fleck, a terrific writer on water issues who has been covering the Colorado River for many years, explained in 2015, there was a catch. In order to win support from California politicians, the Arizona project's backers had to agree to a key condition: in the event of a water shortage, California would get first dibs on the Colorado River's water. Arizona would move to the back of the line.
Now, for the first time, a shortage looks plausible. Water levels at Lake Mead had already been dropping for years, as more and more users have been overdrawing its water. More recently, drought and extreme heat have been adding to the strain. With less snow in the mountains, there's less water flowing into Lake Powell, which in turn is delivering less water downstream to Lake Mead.
Add it up, and Lake Mead is down to just 37.5 percent capacity:
When Lake Mead was at its fullest, the water reached an elevation of 1,220 feet above sea level. In May 2016, it was down to just 1,074.6 feet — the lowest level since the dam was built.
Federal officials say they expect water levels to keep dropping this summer but then rise above 1,075 feet before the start of 2017. If levels remain below 1,075 feet by the start of the year, however, the US government will declare an official shortage. That increasingly seems likely — if not in 2017, then in 2018. And once that happens, the real fun begins.
What a Lake Mead water shortage would mean for Arizona, Nevada, and CaliforniaSo what would an official "shortage" mean in practice? On this, everyone should read this post by Fleck. As he notes, a shortage at Lake Mead under current rules would mainly affect Arizona. However, there's also a major effort underway to rethink those rules.
Under the 1968 agreement, Arizona has to cut back on water use before anyone else. And, Fleck explains, the state does have a plan for this. The Central Arizona Project would continue to keep water flowing to cities like Phoenix and Tucson, Indian tribes, and high-priority agriculture. But it would cut back on "low-priority" agriculture and delay refills to groundwater storage:
In 2015, Summer Pauli of the Tucson Sentinel wrote a great piece on what those cuts might look like. Some Arizona farmers will no doubt conserve water by switching from flood irrigation to more efficient drip irrigation. (Many have already been doing this, though installing these systems can cost more upfront.) Others may try to pump more water from underground aquifers (though Arizona has stricter controls on groundwater pumping than, say, California). Others may just cut back on growing crops like alfalfa.
These cuts won't be apocalyptic, but they won't be minor either. "It’s going to be a very painful cutback when we start losing our water, but we’ll do what we can to survive and that’s all you can do," one farmer told the Sentinel.
Next comes Nevada. Las Vegas — which gets 90 percent of its water from Lake Mead — is likely to be okay for the time being. City officials have been watching the lake's levels drop for years and have already taken steps to curtail water use 30 percent over the past decade, not least by providing incentives for homeowners to replace the grass on their lush lawns with less-thirsty native plants.
Las Vegas has also been building costly new water intake systems so that it can keep drawing water from Lake Mead even if water levels keep dropping further. (When the original intake systems were built, the pipes were essentially too high up; few imagined that reservoir levels would drop this far.)
Finally, there's California. Under the original 1968 agreement, California wouldn't see any cutbacks from the Colorado River until the Central Arizona Project went dry. In the event of an official shortage, Los Angeles, San Diego, and the Imperial Valley would continue to get their full share of Colorado River water for years to come.
But those are the current rules. More recently, officials in Arizona, Nevada, and California have been discussing a brand new agreement that, they hope, would divvy up the Colorado River's increasingly scarce water in a fairer and more sensible way. Under a renegotiated deal, Arizona and Nevada would cut back even more sharply in the event of a shortage — but California would also have to start sharing the burden and make some sacrifices of its own.
As Tony Davis reported for the Arizona Daily Star, the current proposed agreement would see the Central Arizona Project reduce water use up to 15 percent once a shortage is declared at Lake Mead (as opposed to the current 11.5 percent). Arizona officials have also been talking about water cuts to all sectors of the state's economy rather than agriculture alone. Meanwhile, California would need to start reducing water deliveries if levels at Lake Mead dropped about 30 feet lower than they are today, rather than waiting for Arizona to go dry. The bulk of these cuts would likely be borne by farmers in the Imperial Valley.
This is far from a done deal, and negotiating water agreements, both between states and among individual state water districts, is notoriously tricky. (Fleck has another good post about this.) But it's a sign of growing awareness that the current arrangement is no longer viable. Lake Mead is unlikely to survive the status quo.
The looming question: What happens if water shortages get worse in the future?:no_upscale()/cdn.vox-cdn.com/uploads/chorus_asset/file/6531667/75905596.0.jpg)
Nothing good for boats, that's for sure.(Ethan Miller/Getty Images)
One big reason these agreements are being rethought is that as the Southwest enters its 16th year of drought, these shrinking reservoirs are becoming harder to dismiss as a temporary blip.
The 1922 agreement that divvied up water from the Colorado River was forged during one of the wettest periods in the past millennia. At the time, people assumed droughts would occur, but they didn't assume droughts would get off-the-charts terrible.
That's increasingly looking like a bad bet. Scientists have uncovered evidence that decades-long "megadroughts" have occurred in the distant past, and could well occur again in the Southwest going forward. And even if that doomsday scenario doesn't come to pass, climate models still expect droughts to get more frequent and severe in the American Southwest if global warming continues apace. There is very likely to be less water to share in the future.
Yet despite all this, Lake Mead's users have been overdrawing water in recent years — essentially assuming that there will be wet years in the future to provide surplus water and recharge the system.
In a separate post, Fleck pointed to an eye-opening presentation by the Central Arizona Project that asks what would happen if water levels at Lake Mead keep dropping — down to 1,000 feet, say. In that case, Las Vegas would face even bigger challenges drawing water from the reservoir. The Hoover Dam would struggle to generate electricity. Arizona, Nevada, and California would all see steeper cuts in water deliveries. Unless, of course, states figure out how to better manage and share their water supplies.
Up until now, there's always been plenty of water from the Colorado River to go around. It's increasingly difficult to take that for granted.
Further reading: Some essential John Fleck posts on Lake Mead here, here, here, and here. Thorough coverage of the (proposed) new Colorado River deal from Tony Davis in the Arizona Daily Star, Ian James in the Desert Sun, and Henry Brean in the Las Vegas Review-Journal. In the New York Times, Abrahm Lustgarten had a fascinating piece on the water experts who think that opening up the Glen Canyon Dam (and draining Lake Powell) could actually help the Southwest save water. It's worth reading.当年忽悠了好多grant
文中说的和我说的没有任何矛盾，我说的就是文中有关功率因素的内容。但是文中概括了更广泛的所谓无功功率概念和补偿设备及方法，其中大部分与太阳能发电无关。
我想确信你是否看过此文并完全看懂了？坦率的说，如果你不是学电的，是很难看懂的。
今后会越来越严重，去年冬天Dallas地区的严寒是一例，这次Ida 造成的暴雨和水灾范围很大，和往年不同。
今年冬天再看会有什么离奇的灾难。
无论什么神能发电，凡是并入电网的，都需要满足电网系统的功率平衡，否则系统的稳定性就是不可能。
这也是为什么我们时常会听到“电力公司不让你送上网”的原因。（这句话，屋顶装太阳能板的人士记得问一下自已的供应商，特别是忽悠你按20年收益率计算的公司）。
若是你有兴趣，可以搜一下中国西北风力发电的东东，你幸运的话，你可能会读到一个术语，它叫“废风”。
还带回阿富汗人，德州政府还不让abortion，不得了
我刚去湾区儿子家小住了两周，以前也去了好多次。我儿子是IT行业，不是高管是高薪。他两年前安装了太阳能，有补贴，没贷款，总额大约2万左右，现在每月基本没有电费，如果用的省，还可以赚几块。
我观察的他住的小区，超过一半以上的住户都安装了太阳能。湾区这边的屋顶都是瓦的，适用寿命长，屋顶本身的承重能力强。所以所谓换屋顶麻烦，屋顶承重能力不够的顾虑是不存在的。而且加州阳光充足，发电效率比其他地区都高。
反观我们亚特兰大，几乎很少看到安装太阳能的，我家也没有安装。我个人认为房屋的设计和材料与此有关。我们这里的屋顶基本上是shingles，屋顶的承重能力在设计上肯定不如加州的。而且这种油毡屋顶20-25年的寿命，所以会有换屋顶的麻烦。再说，亚特兰大的电费比加州也便宜很多，这也许也是一个重要原因吧。
后来也后悔了，哎，不说了，让加州国的同学们感觉好一下吧
Electricity wholesale price can be negative
我对全球变暖是由于人类活动产生的这个statement还属于七分信三分疑，所以不发表意见。只是就事论事针对你这个不可逆的说法