Installing photovoltaic power on roofs facing east and west has such a big impact on the power generation of the system! (Experimental data included)

As we all know, when installing a photovoltaic system on a roof, the orientation of the components has a great impact on the power generation of the system. Taking the northern hemisphere as an example, photovoltaic components should be installed facing south as much as possible, so that they can receive the most solar energy. However, in actual applications, due to the limitations of building layout conditions and scene area, photovoltaic components are often not all installed in the best orientation, especially in household photovoltaics, where photovoltaic components are also installed on roofs facing east and west.

So, how much impact does installing photovoltaics on the east-west slope have on power generation?

The “short board effect” in multi-directional roofs

In traditional string inverter systems, since the components are connected in series, they are often affected by the "short board effect". When a string of components is distributed on roofs facing multiple directions, the reduced power generation efficiency of one side of the components will affect the power generation of the entire string of components, and thus affect the power generation output of photovoltaic components on multiple roofs.

However, in the face of the multi-orientation of the house, we can adopt a micro-inverter system to solve this problem. The micro-inverter system adopts a component-level input design and has an independent maximum power point tracking (MPPT) function, which can completely eliminate the "short board effect" and ensure that each component operates independently. Even if the components are installed on roofs with different orientations, the output of each component can be optimized so that the power generation of components on different roofs does not affect each other, reducing the power generation loss caused by multiple orientations.

Experimental simulation shows that the power generation differs by nearly 15%

Through the PVsyst simulation experiment, we conducted a study on the rooftop photovoltaic system in Zhejiang, China in the northern hemisphere. In the experiment, we installed 20 570W photovoltaic modules on the east and west roofs, set the inclination angle to 15 degrees, and the total system capacity was 22.8kW. The experiment selected two different types of inverters and compared the power generation difference between the string inverter system and the micro inverter system under the same conditions. In the power generation data of a certain day in winter, we obtained the following simulation results:

Simulation 1

The system is equipped with a 20kW string inverter

The power generation on the east slope is 30.19 degrees, the power generation on the west slope is 31.14 degrees, the total power generation is 61.33 degrees, and the power generation curves of the east and west slopes are basically completely overlapped.

Simulation 2

The system is equipped with 10 APSON micro-inverters DS3D

The power generation of the east slope is 35.57 degrees, the power generation of the west slope is 36.29 degrees, and the total power generation is 71.86 degrees. Comparing the power generation curves of the east and west slopes, we can see that the power generation of the east slope is significantly better than that of the west slope in the morning, and the power generation of the west slope is significantly better than that of the east slope in the afternoon.

Through the above simulation experiment results, we can know that the east slope and west slope components in the string inverter system generate less power throughout the day than the micro inverter system. The main reason is that in the morning, the sun rises from the east, the east slope components receive strong solar radiation, and the west slope components receive weak solar radiation. Among them, due to the "short board effect" in the string inverter system , the power generation of the east slope components is limited by the power generation of the west slope components with weak irradiance. In the evening, on the contrary, the power generation of the west slope components is limited by the power generation of the east slope components with weak irradiance, and the power generation of the east and west slope components is always consistent; the micro inverter system has a component-level MPPT function, and each component operates independently. In the morning, the east slope components receive more solar radiation and generate more power than the west slope components. In the afternoon, on the contrary, the west slope components generate more power than the east slope components. The east and west slope components always output at the optimal power point and operate independently.

In summary, through data calculation, it is concluded that in this experiment, the string inverter system generates 10.53 degrees less electricity than the micro inverter system, a difference of 14.7% . Due to the east-west slope orientation, the 22.8kW photovoltaic system loses as much as 10 degrees of power in one day. If the time length is set to one year, the power loss is about 3,800 degrees, which will seriously affect the system's power generation and revenue.

Actual cases to verify simulation results

In the case of "APS Sunshine Family", a sun shed installation case located in Taizhou, Zhejiang, has a system capacity of 27.36kW, using a total of 12 APS Technology DS3D micro inverters and 48 570W modules , evenly arranged on two roofs facing east (36 degrees east-south, module inclination angle 9 degrees) and west (36 degrees west-northwest, module inclination angle 7 degrees).

Through APpower EMA intelligent operation and maintenance system, we obtained the power generation data of the project on January 4. The total power generation on that day was 100.35 kWh, of which the Dongpo module generated 52.92 kWh and the Xipo module generated 47.43 kWh . By observing the module power interface, we can see that in the morning: the power generation of the Dongpo module is significantly greater than that of the Xipo module, and vice versa in the afternoon.

Through the background data, we know that before 12:00 in the morning, the east slope components of the system generated a total of 28.8 degrees of electricity, and the west slope components generated a total of 21.34 degrees of electricity; after 12:00 until the sun sets, the east slope components generated a total of 24.12 degrees of electricity, and the west slope components generated a total of 26.09 degrees of electricity. Due to solar irradiation and component-level MPPT function, the east slope components generated 7.46 degrees more electricity than the west slope components in the morning, and the west slope components generated 1.97 degrees more electricity than the east slope components in the afternoon. If a string system is used, the power generation will be limited by the roof with low irradiance, so the power generation for the whole day is about (21.34+24.12)*2=90.92 degrees. It is 9.43 degrees less than the actual power generation of the micro-inverter system of 100.35 degrees, which is about 9.4% less. (*Affected by factors such as actual solar irradiation, the difference in power generation between the east and west slopes of the micro-inverter system is different in the morning and afternoon)

Through the above simulation experiments and actual case verification, we can see that the power generation loss caused by the east-west slope components in actual installation cannot be underestimated, which seriously affects the power station revenue. For such roofs, choosing micro inverters is an effective solution that can maximize the use of solar energy resources, reduce the power generation loss caused by multiple orientations, and improve the overall performance and economic benefits of the system.