East-west oriented systems the future of flat roof PV?

Interest in installing PV Systems on east-west roofs is increasing.

Although south-oriented modules produce more energy, east-west (WE) can generate substantial earnings since they adapt better to load profile, especially in residential PV systems. From the perspective of grid operators, WE systems are preferred because the energy is fed-in more evenly throughout the day.

By making the peak “flat”, the inverter used for the system can be smaller and cheaper because the device doesn’t need to adapt to few minutes of operation during the peak. In WE systems inverter is loaded uniformly throughout all the day which and that is more efficient.

What’s more, as GreenTechMedia says, WE installation increases possible number of panels installed by 20-50%. More land can be used for photovoltaics with WE oriented modules (70%). South-oriented panels fill only 30% of the land due to inter-row spacing to prevent shadowing.

Up to now it was assumed that WE- oriented modules require separate inverters for each orientation or at least more than one MPP tracker, otherwise mismatch losses would be significant due to various irradiation level exposure.

A report titled Efficient East-West Orientated PV Systems with One MPP Tracker [1] examined WE-oriented system with one inverter and 1 MPP. Arrays of c-Si and thin-film panels were compared. Normally, installation of single inverter would make us expect large mismatch losses. But, as report says, as much as current differences are large, the MPP voltages are almost identical; therefore minimal mismatch losses can be observed (0,1%). Those losses are also compensated by more efficient inverter performance.

Mismatch losses will depend on inclination angle and technology used, for example, the higher the inclination, the higher mismatching losses. It was also confirm that low temperature and good panel ventilation are important factors for WE systems.

The energy losses are highest on a sunny day because the lower the irradiation differences between the east and west strings, the lower the deviation of the DC voltages. It’s easy to notice that WE installation make more sense for sites with a lot of diffused irradiation.

Panels installed on flat roof towards south are favorable for users with high energy demand. This demand will be also higher in wintertime around 12 o’clock. If we have a closer look to daily load profile, it can be observed that WE-oriented panels can produce up to 49% in peak demand hours than south-oriented ones (according to Pecan Street Research).

What’s more, an additional research made on pilot PV system in Aachen in Germany [2] has shown that WE panels produce only 10-20 % less energy than south-faced panels with the inclination of 35 degrees.

While adapting the best PV system for your customers, it is worthy to spend more time on load profile analysis and building characteristics. Sometimes, PV systems that are oriented towards east and west can be more favourable than the systems we are used to see. Check different configurations in EasySolr app. 

[1] Efficient East-West Oriented PV Systems With One MPP Tracker, Dipl.-Ing.(FH) Dietmar Staudacher FRONIUS International GmbH Froniusplatz 1, A – 4600 Wels

[2] Evaluating the Impact of PV Module Orientation on Grid Operation, Eckehard Tröster
Jan David Schmidt, 
Lisbon, 13th November 2012, 
2nd International Workshop on Integration of Solar Power into Power Systems