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More Green Building News
Electricity generated on the rooftops of buildings in the U.S. has the potential to hit 39% of current electricity sales, nearly double the amount that was estimated in 2008.
在报告中，国家可再生能源实验室表示，装备所有合适的屋顶的“技术潜力”为1,118千兆瓦的能力，每年都有1,432泰国特拉瓦数。这与八年前的分析相比，与664 GW和800 TWH相比。
The authors of the study said that previous estimates “lacked a rigorous foundation in geospatial data and statistical analysis.” This time, researchers said that they used light detection and ranging (LiDAR) data and other sophisticated tools to calculate the suitability for PV of rooftops in 128 cities around the country, collectively representing 23% of all U.S. buildings. The results were extrapolated to cover the entire continental U.S.
The PV potential was greater in some states than in others. California, for example, has the greatest potential to offset electricity, according to the report: 74% of all the electricity sold by state utilities in 2013. Percentages also were very high, 55% or more, in several New England states; they had a lower solar potential, but also lower per-capita consumption. Florida and Michigan also had better-than-average potential.
Even Washington State, with the lowest solar resource in the country, could generate 27% of its electricity with rooftop PV systems.
Researchers developed two statistical models, one for buildings under 5,000 square feet in size, and the other for medium and large buildings. Only about 26% of the small buildings were considered suitable for PV, but the huge number of buildings in this size class gave them the greatest technical potential — 739 GW of capacity and 926 TWh of electricity annually.
Modules are getting more efficient
marketpl代表的混合技术ace, the analysis assumes that PV modules have an efficiency of 16%. If a module efficiency of 20% is used instead — an efficiency that “premium systems” are now capable of delivering — each of the technical potential estimates would go up by 25% over the values in the report, the authors said.
“此外，我们的结果仅估算了现有合适的屋顶平面的潜力，并且他们不考虑地面安装PV的巨大潜力，”该报告增加。“城市地区PV的实际生成可以通过在不太合适的屋顶区域安装系统，在檐篷上安装PV，例如停车场，或将光伏集成到建筑物外观上的开放空间上安装PV。”
The estimates represent “technical potential,” smaller than the total “resource potential” but greater than the “economic potential,” which in turn is bigger than the “market potential.” The report defines it this way: “Technical potential, which is the topic of this report, estimates how much of that total resource could actually be captured, given physically available area and technology performance without considering economics.”
The technical potential does not, for example, take into account what would be required to get all the PV-generated electricity to end users.
“In practice, the integration of a significant quantity of rooftop PV into the national portfolio of generation capacity would require a flexible grid, supporting infrastructure, and a suite of enabling technologies,” the authors said.
即便如此，报告说，屋顶提供“太阳能发电的大型未开发的未开发区域，现场分布式发电可能会降低与电力传输和分配相关的成本和损失。”
3 Comments
潜力，“合适的屋顶”，PPA
Potential PPA customers need to be aware--you are not the winner in the PPA agreement, due to the following, and due to other considerations not even mentioned below.
The article references "suitable roofs" in relation to solar potential. Not sure, but maybe these studies
甚至不考虑添加的，虽然通常在阴影和北方屋顶上的潜在效率低下。
By direct observation, I have seen a LOT of PV, installed by Solar City and other PPA providers, that is installed on northern facing roofs and even heavily shaded roofs. They seem not to care where they put PV--they just care about the placement of their sign out in the front yard.. The certain conclusion is that the PPA providers are making tons of money in the bargain with their customers, regardless of how poorly the panels will perform, while customers save none or little..
PV适当的位置
I agree with Sonny that a number of big PV installers put PV on residential rooves where little, if any, direct sun shines.
I have two neighbors who recently had PV installed on their houses.
一个阵列面向西南，直接阳光3-4小时/天。
The other array faces due west and is blocked by trees 25' higher than the roof on both the south and west sides. In July, it gets 2 hours of direct sun. From September - May, it gets no direct sun.
What a waste of money from both the homeowner and utility customers (who subsidize these based on the capacity, not actual production).
由于我的房子也被阴影，我去了附图中所示的路线。它沿着太阳，每5分钟调整每5分钟才能捕获每件最后一次瓦特。在上周只有一天（不是新英格兰的年度最长的日光），我得到了123千瓦时。在过去的一年里，我的制作了大约23,000千瓦时。
In most locations TPO PPAs are compensated on production.
Sonny, C.B.:
Where are these gross mis-installs?
Most state regulators have it set up where the output is net metered, and the solar company charges the homeowner for power use at a lower than retail fixed rate up to the amount of power that is produced.
The financial risk of low production is primarily on the third party solar company, not the homeowner, though the benefits to the homeowner may be lower than advertised. Poor installation siting would only make sense for the solar company if the up-front subsidies were so rich that it didn't much matter if the system underperformed, which is at least theoretically possible. If the system underperforms it may mean less lower-cost power for the homeowner, but it's not a direct cost.
In some states there are incentives based on capacity, but those usually stipulate a maximum shading factor/minimum output to qualify. In MA there was once a program set up that paid a $/installed-watt-DC, but stipulated site factors of no less than 70% of the theoretical maximum insolation based on shading & pitch (where my house fails). But by FAR the biggest subsidy in this state has been SREC production credit payments.
Assuming reasonable site factors, the other way to get bitten in a PPA is the annual escalation clauses. I've seen a lot of marketing BS that shows your "savings" relative to a 5% or 6% annual grid-power inflation rate (which simply can't happen), starting at a heavily discounted per kwh rate that escalates "only" 3% per year. The broad 30 year trend on electricity pricing relative to core inflation is sligthly downward, not upward, and CERTAINLY not 5-6%, and as PV and wind power costs fall there is continued downward pressure on electricity rates. The Federal Reserve targets ~2% core inflation, but has been well behind that for years, and it won't take more than a decade at a contracted 3% annual escalator on a PPA for some people to be paying MORE than grid-retail for the remainder of the contract period. Taking a lesser initial discount below retail and NO annual price increase is more likely to pay off over time, since core inflation will be making it effectively cheap every year, staying ahead of the long term electricity price deflation. See:
http://inflationdata.com/articles/wp-content/uploads/2012/07/Inflation-Adjusted-Electricity.jpg
http://inflationdata.com/articles/inflation-adjusted-prices/electricity-price-inflation-rate/
The new NREL study knows the pitch and shading factors on each roof area, from lidar distance measurements and other satellite data (including weather averages). It is explicitly NOT counting off-pitch or shaded roof areas.
在年度电力的39％中，峰值输出可能超过许多高峰时段的载荷的100％，因此在技术上可行的同时，在较智能的载荷浸泡之前，它不会在该程度上建立到那程度上IT电网感知热水器或电动车充电器等），但随着屋顶光伏的价格保持不断地落在其20％+学习曲线上，这将由公用事业法规抑制而不是促进而建立的分布式发电。这将通过州的州，公用事业效用变化很大。
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