Wouldn't it be more efficient to simply drive all our electronics equipment directly off DC? Almost all electronics devices now days run off 5VDC (USB) or 12VDC, Solar panels put out 12VDC, all those conversions seem like a waste of energy. What if you just run our big appliances off 120VAC and run all our small stuff off of Solar directly along with a battery back up. It seems like if a new wiring standard were developed that had both AC and DC distribution it would greatly reduce the cost of installing Solar. In fact, I believe it would be possible to put a DC bias on top of the AC (similar to the way old time phone lines work). Just a thought, rather than shrinking the inverter, think outside the box and get rid of the inverter all together.
There are a few reasons for not using DC until the last metre or so.
First of all, you want to avoid having multiple wiring systems in one building. Wiring a building for 110V alone is expensive enough (both initially and later during maintenance). In the vast majority of situations, you are going to have to pick one or the other.
So: AC or DC? Either way, you need to be able to run high power appliances (e.g. a 2000W kettle), and to keep losses in your cables low you need to use as high a voltage as possible, which will keep the required current as low as possible. So either way, in a realistic scenario, you need to retain the high voltages (110/230V) that we currently use.
When you require high power / high voltages, AC is a better solution. It is easier to switch (your kettle switch will burn out much more quickly while trying to interrupt a high current DC supply than it will interrupting an AC supply that crosses 0V 100 times per second). Overload devices work more reliably with AC for the same reason (which makes your house less likely to burn down). AC also makes it much easier to transform voltage levels - you just use an inductor or two. DC requires relatively complex electronics. DC distribution is also more complicated since the the distribution network and everything attached to it has parasitic (or deliberate) inductance and changes in load produce voltage spikes
There's nothing to stop you from installing a DC system in your house, but I think you would find it significantly less practical than you had imagined
Minor nitpick: relatively few quality solar panels generate
12Vdc. Most generate around 40V
This is something that always caught my imagination: using DC for the last mile.
I don't understand electricity well, but it seems that electronic components require regulated DC, and producing that requires an AC somewhere in the transforming circuit. Is that correct?
In a sense, you're right. Although it's perhaps not the style of AC you were thinking of. Inside every DC-DC conversion circuit there's one or more energy storage elements charging and discharging repeatedly. This internal waveform is AC. It's not sinewave AC, but it's technically alternating current.
No, you can generate 'regulated' DC from another DC source (see for example buck converters or more generally any DC-DC converter).
Regulated really just means clean DC which stays at the same voltage and doesn't contain a lot of noise. Not all devices require a regulated supply. A drill, torch or heater will happily run on a noisy supply. Your iPhone will not.
You are right. I remember more details now. The problem occurs when you want to make regulated DC from a lower voltage DC supply. Step-down is easy.
For example, my battery is 12V, but my laptop needs 19V. AFAIK, you can't get regulated 19V supply from the 12v battery without a transformer (or maybe something equivalent).
Step-up is easy too. That's what boost converters (http://en.wikipedia.org/wiki/Boost_converter) are for. Most single-cell LED flashlights contain tiny boost converters to increase the 1.5v coming from the battery to above the drop voltage of the LED.
