随着太阳能开发人员扩展到新的州或地区，通常会出现一个新的太阳能设计问题：如何将内部办公室的设计实践映射到新的地点或地区？

从历史上看，设计选择专门基于项目的纬度。许多太阳能工程师认为，模块的倾斜度必须等于该位置的纬度，此外，根据冬至上的行的阴影计算了行间距（也受到位置纬度的显着影响）。

最近，随着较便宜的硬件和改进的软件工具，最佳设计正在发展。那么，工程师的最佳设计选择因位置而异？随着时间的流逝，情况发生了什么变化？

Historical design rules varied greatly by latitude

Historically, modules were tilted at or near the latitude of the project’s location. This would mean a 25° tilt in Miami, a 35° tilt in Raleigh, North Carolina and a 45° tilt in Seattle. This orientation optimizes for the sun angles throughout the year, pointing the modules as close as possible to the sun’s average position in the sky.

Then, the row spacing was typically defined based on a rule of not allowing inter-row shade on the winter solstice from 10 a.m. to 2 p.m. This created a double-whammy impact on row spacing. Not only are modules tilted more steeply at higher latitudes, but because the sun is lower in the horizon on the winter solstice in those northern locations, the shadows they cast are longer. As a result, the row spacing in northern latitudes was typically very large—in the example here, nearly 9’ in Seattle, compared to under 2’ in Miami.

These design rules are good for maintaining a high energy productivity per watt (specifically, optimizing kWh/kWp), but result in smaller systems when working on space-constrained rooftops. For example, the same rooftop that could support a 545-kWdc array in Miami would field just a 240-kWdc array in Seattle—a difference of over 55%! When modules were expensive, this was the right tradeoff to make. But as prices fell over time, the high-tilt approach made less and less sense.

Lower tilt with time-of-day spacing

With cheaper modules, a lower tilt becomes optimal: Squeeze more watts into a unit of area, sacrificing yield per peak-watt (kWh/kWp) to optimize total energy yield. Most systems were installed at relatively low tilts (typically 10 to 15°), yet the row spacing rule of avoiding shade on the winter solstice from 10 a.m. to 2 p.m. still persisted. This resulted in far greater harmonization between different systems.

While the sun angles on the winter solstice differ based on latitude, the net impact on row spacing is relatively modest (changing row spacing from ~1.2’ to ~1.6’), resulting in system sizes that are only about 10% different between Miami and Seattle.

现代方法：优化的行间距

Finally, as modern software tools enabled system designers to quickly evaluate different combinations of row spacing and tilt, the final stage of design has been built around iteration and optimization.

在这个世界上，从一个位置到另一个位置有多少可变性？如图5所示，对于大多数位置，最低的倾斜度是最好的。只有两个最北端的位置（斯波坎和波士顿），较高的倾斜度和更宽的间距是最佳的。考虑到北纬度的较低的太阳角，这是有道理的。

结果，迈阿密与西雅图的屋顶的规模只有14％。它们都以15°的倾斜度安装了，但不如我们认为进行此分析的那么重要。

The more things change, the more they stay the same

您可能会预料，随着行业从“经验法则”转变为定量优化，不同位置的最佳设计将根据每个站点的独特方面急剧差异。毕竟，不同的位置在天气模式，温度和太阳角度上具有巨大不同的位置。但是，相反，设计并没有太大变化，实际上，比基于纬度的倾斜的原始设计更加协调。

Certainly, any system engineer who truly wants to squeeze out every dollar of their project should ensure that the tilt and spacing are optimized—after all, a 20-minute analysis could improve a project’s margin by 3 to 5%. But all in all, optimized systems across the country are trending toward looking more similar than different.

Footnotes:

Tilt: We are only looking at a minimum of 5° tilt. While lower tilts are theoretically possible, they increase soiling losses because rain does not wash off the dirt and dust from the modules.

Costs: This optimization analysis is based on the default cost structure from NREL’s System Advisor Model. We’re using identical cost assumptions for each location to keep it an apples-to-apples analysis, since we’re trying to isolate the impact of irradiance and sun angles—but we certainly understand that labor, permitting and interconnection costs can vary, sometimes significantly, from state to state.