Where to put the solar panel

The following article was provided by Dr. Joshua Rhodes, a postdoctoral researcher at The Webber Energy Group and the Energy Institute at the University of Texas at Austin.

Recent issues concerning the orientation of solar panels have caused some controversy. The origin of the topic came from a report by Pecan Street Inc. The paper compares the actual amount of solar battery power that is actually put into use and finds that the panels installed westward tend to have better power output to meet the power demand during the summer peak season, which is different from the maximum annual output of electricity. Soon after, Greentech media published an article titled: Is the solar panel loaded in the wrong direction? The article was published on various publications including National Geographic and USA Today.

Recently, the "New York Times" and "Popular Science" even claimed that solar panels should be installed westward rather than southward to avoid unexpected consequences. However, each of the above articles considers only the westward or southward simplification. Just like the amount of sunshine in a region, different time and place, the answer to the question is not the same.

I recently published a paper in the Solar Energy journal that details my views on this issue. We assembled a generic solar panel model and calculated its output power at each possible orientation. We tried various directions (such as using 12 o'clock as the north pole and 6 o'clock as the south pole) and pitch ( From 0 degrees or lying on the ground to 45 degrees).

Then, we selected more than 1,000 regions across the United States to conduct simulation tests and calculate the results. By analyzing Typical Meteorological Year data, we can calculate the total amount of electricity generated when solar panels are installed in any direction in any area. Since our model calculates solar energy production in one hour in units of hours, it also makes sense to use the total electricity generation times multiplied by different electricity prices in different periods. Figure 1 shows an example of Texas Grid (the Electricity Reliability Council of Texas, hereinafter referred to as ERCOT) to illustrate that the placement of solar arrays will not only change the time for the storage of panels, but also affect the electricity market. The average selling price (ERCOT settlement point price, hereinafter referred to as ERCOT SPP).

Solar cell power lines that are arranged in the south (red line) and west (blue line) in the whole year and in the summer are compared with the average price in the electricity market (ERCOT SPP) in the same period.

The graph shows the average hourly output of the solar panels in each year (top) and summer (bottom) when each square meter of solar panels is facing south (red line) and west (blue line). The difference between the red line and the blue line shows that when the solar panels are placed in different directions, the time for generating electricity is also different. The east-facing electric power generation curve is shifted to the left from the west (red). The figure also shows the average ERCOT wholesale market price (indicated by the black line). During the year, about 14% of the electricity was produced by the solar panels in the west direction. However, in summer, this difference has only narrowed to 1%.

If we are to find out the best installation location of the solar panels throughout the year, multiply the output per hour by the hourly electricity price (black line), then we can get the orange curve, about (in the positive direction when the east is positive (clockwise) 219° or south-south west 39°, almost in the middle of the southwest. If you only consider the extremes, that is, the peak power output during the period from 3 pm to 7 pm, then it is most appropriate to place solar panels toward the west.

But in the final analysis, the orientation of solar panels is attributed to government incentives. At present, Texas's capacity compensation policy has prompted the installation of solar panels in the south. However, given the limited availability of solar energy on weekdays and the dilemma of the electricity market, the real concern in the utility sector is whether the panels installed in the west can best meet their peak demand.

The above experimental results apply only to Austin, Texas. Solar sources, local electricity prices, and local incentives in other regions are all different. Therefore, the answer to the question is very regional. With the increase of the penetration rate of solar energy, the local power grid department may have to rethink how to formulate energy rates and discounts so as to reduce the impact of solar panels on the power grid to some extent.