Modern inverters and efficient walwarts (thank you EU) will be more efficient than 12v DC because of the power lost to the cables for anything but trivial loads.
The problem is some squared math functions which come and bite you. Your 12V DC system will pull 10 times the current as a 120V AC system. That's going to mean bigger wire. But then the kicker comes in, each volt you drop means 10 times the energy loss because 11/12 is a lot worse than 119/120, so you'll have even bigger wire. My 24V system with the batteries in a shed has $900 of copper wire between there and the house.
Then consider that all your loads probably already have a voltage converter in them, either an AC-DC external converter or something internal. Most of them won't take 11-14VDC inputs with spikes on it, so you'll need DC-DC converters on them anyway, so you aren't saving the conversion losses on the device end.
In summary, with modern high efficiency inverters you will probably find that your dollar is better spent on solar panels and batteries than masses of copper wire. If I were starting in 2018 I would not have run the DC lines.
From your experience it sounds like I should do the math carefully before spending any money.
Have you had to replace your batteries yet? I’d assume batteries are a recurring (if with a long period) expense, while wire is a one-time cost. Does the downward trend in battery prices still kill any consideration in that direction?
I’m on my third set of lead acid batteries. I got 8 years out of the last ones and 7 from the first. This is on the long end of lead acid battery life. Capacity was down at the end for both, but I limped along. These are my last lead acid batteries. In 6 years I’m sure I will use something lithium based. The location is remote, requires small boats and hand carrying and the batteries are about 1000 pounds. A lithium replacement system will weigh a fraction of that, last longer, and won’t rupture and spill acid all over the place when I accidentally freeze them in the winter while the cabin is inaccessible and in telemetry only mode. (I’m two for two on this, both sets I’ve misjudged just how small their capacity had become and not gotten into emergency power conservation mode fast enough.)
DC-DC converters don't have the hellacious design constraints that AC inverters have.
If an AC inverter doesn't provide a sine wave, some equipment will fail. Making the sine wave is a serious burden, drives up the cost, and doesn't make efficiency any easier. In my case the DC cables are a few feet long.
It might have been cheaper, but my conduit is full and won't handle the extra size. I trenched and buried that in the rock years before I learned to always oversize any conduit, especially ones that I have to trench and bury.
Modern inverters and efficient walwarts (thank you EU) will be more efficient than 12v DC because of the power lost to the cables for anything but trivial loads.
The problem is some squared math functions which come and bite you. Your 12V DC system will pull 10 times the current as a 120V AC system. That's going to mean bigger wire. But then the kicker comes in, each volt you drop means 10 times the energy loss because 11/12 is a lot worse than 119/120, so you'll have even bigger wire. My 24V system with the batteries in a shed has $900 of copper wire between there and the house.
Then consider that all your loads probably already have a voltage converter in them, either an AC-DC external converter or something internal. Most of them won't take 11-14VDC inputs with spikes on it, so you'll need DC-DC converters on them anyway, so you aren't saving the conversion losses on the device end.
In summary, with modern high efficiency inverters you will probably find that your dollar is better spent on solar panels and batteries than masses of copper wire. If I were starting in 2018 I would not have run the DC lines.