Many review papers on hybrid renewable energy systems point out DC-bus and AC-bus solutions as equally good options for an off-grid system but I would like to know whether the rural electrification scenario would favour one or the other. Requirements in rural regions include low cost, simplicity (fewer components decrease the risk of malfunction), relatively small system size (typically under 1 MW), ease of operation and maintenance, etc. Other aspects to consider are whether grid connection will arrive in the future, and the type of appliances commonly in use in developing areas.
Thank you in advance for your insights.
With AC systems the cost of varying the voltage/current ratio for a given power is simpler, you just need a transformer. DC systems need a DC to AC converter, a transformer and a rectifier. AC systems can be switched more easily as an AC switch is less difficult to make than a DC switch for the same peak voltage (it is self quenching and has a much less chance of striking a sustained arc). So for different linked systems in the rural area I would think AC would be cheaper. But it isn't necessarily the most cost effective as a DC system will operate at full rated voltage and current all the time while an AC system needs to be able to stand 1.414 times the stated 'RMS' voltage, so its insulation will need to be thicker and its switchgear rated at the higher voltage.
From economical, and major technical issues points of view, I prerfer 3-phase AC systems. In my opinion, minimization the use of electronic converters is a better situation from reliability, cost, and lifetime concerns. However, if the geographical area, scatter of the load subsystem is small, and significant percentage of the load operates using DC power, a DC system would be a good choice; however, the protection issues mentioned by Tony should be carefully considered.
I recommend that you start your design by extensively studying the load subsystem from various aspects such as, characteristics and types of the loads, sensitivity of the loads to harmonics, suitability of aerial or underground distribution systems, and availability of logistics and well-trained technical crews.
Thank you all for your helpful answers! I am indeed in the process of analysing typical loads and their susceptibility to power quality. Safety and cost clearly go hand-in-hand, which may pose problems in rural scenarios where little technical know-how is available.
You are welcome. Please don't hesitate to ask me for any support. Good luck with your study.
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