Technical and Economic Aspects of Gridconnected Solar Photovoltaics in Brazil - Implementing Environmental and Resource Management - page 49

Thanks to the wide range of products offered and their competitive prices, the
“SunnyBoy” line produced by the company SMA (SMA Solar Technology AG,
Niestetal, Germany) was deemed the best option in this case. In a comparison of
technical data for the most used SunnyBoy inverters (with AC output voltage
240V and 60Hz frequency, suitable for Brazil's electric grid), in terms of effi-
ciency and flexibility as well as specific cost, the best options are the ones of
higher capacity, that is 6000 W and 7000 W (Affordable Solar 2008).
Finally one type of solar module has to be chosen and the minimum number re-
quired to cover the established supply level determined. Then, taking into account
the type of preferred inverter, the optimal choice of: modules connected in series
in one array, the number of arrays, arrays connected in parallel to each inverter,
and total number of inverters, can be determined. Some commercial applications
(such as “GenAu” from SMA) to do this task exist in the market, but it is also pos-
sible with the assistance of a simple spreadsheet software, for example Microsoft
Excel.
6.3.3 Configuration Results
The first technology alternative considered was thin-film CIS (copper indium dise-
lenide) solar modules, specifically the model WS111007/75 manufactured by
Würth Solar, with 75 Wp of power per unit and an efficiency of about 10%. As-
suming that the inverter SB7000US (by SMA) could be used, and following the
steps outlined above, it was found that (from a theoretical minimum of 340) with
352 panels two good configurations could be obtained using four inverters. The
chosen one, in view of the layout on the roof, was connecting 11 units in series to
each array (disposed transversally) and 8 arrays in parallel (eight rows) to each in-
verter. The resulting configuration, with 352 solar modules and 4 inverters would
have an installed capacity of 26.4 kWp, requiring a total roof surface of 395 m 2
(about 18% of the roof's total), of which 257 m 2 for the panels and the rest for
spacing to avoid shading. The annual amount of electricity generated, considering
a global performance ratio of 75%, would be 34,415 kWh, meaning a surplus of
1,161 kWh above the building's needs, in spite of falling short in some months
(from January to March, and in June and July).
The second technology alternative considered was pc-Si (polycrystalline sili-
con) solar modules, specifically the model KC200GT manufactured by Kyocera,
with 200 Wp of power per unit and a theoretical 14.2% efficiency. Assuming
again the possibility of using the inverters SB7000US, and after all the dimension-
ing steps, it was found that already with 128 panels an optimal configuration could
be obtained using four inverters, connecting 16 units in series to each array (dis-
posed transversally) and two arrays in parallel (two rows) to each inverter. The re-
sulting configuration, with 128 solar modules and 4 inverters would have an in-
stalled capacity of 25.6 kWp, meaning a total roof surface of 278 m 2 required
(about 13% of the roof's total), of which 181 m 2 for the panels and the rest for
spacing to avoid shading. The annual amount of electricity generated, considering
a global performance ratio of 75%, would be 33,372 kWh, meaning only a surplus