With a DC system power generation needs to be very close to your dwelling. What if this isn't possible? There are many scenarios for this - wind on the top of the ridge but you can't get a house built there, or perhaps you have an underground dwelling. There may be sunlight for photovoltaics in a meadow some distance (maybe there will be some sunlight, as several of the Mayan events did not include loss of sunlight), or the stream where you have your power generator is not where you want to live because of possible flooding. You can get around this by using 4 gauge wire, or 2 gauge wire. Priced this stuff lately? Its expensive. The other method is to use 6-10 gauge wire to boost the voltage to 160 volts or multiple modules wired in series, and then using a switching transformer (Todd Engineering makes one for $84-250) to lower the voltage to 12 volts to charge your batteries.
Offered by Michael.
Keep in mind that DC power attenuates if you run it longer than a distance of 30 feet due to the built in capacitance and inductance of the medium you are conducting it with. AC power can be propagated for much longer distances with very little attenuation. There is a tradeoff. If indeed you lose power with AC to DC and DC to AC conversions, it might only be a small fraction compared with using DC over long distances.
Offered by Kurt.
If your going to use large DC consuming devices you should probably reconsider your no AC decision. Low voltage DC is actually more difficult to use in large quantities. The wiring of low voltage, high current DC devices is critical to prevent power loss and fires. When you factor in the cost of heavy gauge wires, connectors and the other necessary components of your pure DC system you may find the cost surprisingly high. When I chose to go with AC as a major part of my electricity plan I simplified many other plans and devices. The vast supply of inexpensive but high quality AC powered equipment far exceeds the amount of DC equipment available at what I consider affordable prices.
Offered by Ray.