I have a solar setup running around my ranch, and have a need to set up some smart switches and sensors.
Why is everything 110 or 220v? Does anyone know of anything besides Shelly that will work as a switch on a 12v dc system without an inverter? Same for sensors?
An esp8266 or esp32 connected to a relay and powered by esphome.
May I ask why this particular exclusion?
They work very well with home assistant.
No real reason except I already know about them. Was hoping to find new stuff that I hadn’t considered.
It’s mind blowing that 12v isn’t a bigger deal for smart stuff. It seems eith solar diy getting bigger these kind of go hand in hand!
Possibly because there are so many diy options, which don’t need certification, with parts off the shelf.
The device @system suggested here is very nice and should work with a input from 5V up to 36V. Beside it could switch a load on/off it could also pwm/dim it 
Low voltage (under 70V according to the National Electric Code) are unregulated. No certification required. But, yes, it’s much easier to simply work with existing appliances.
We are probably decades from the low-voltage house. For example, LED lights would be tremendously more efficient (and cheaper) if they didn’t each have a 110VAC to 12VDC power supply in them. But the NEC which is used as the reference for local building codes will require inefficient 110V lighting for many years to come.
Luckily the world is a little big bigger than the united states of america 
Some humans (even in the US) just go ahead and create facts - like @DrZzs 
with low voltage lightning
The NEC is formally adopted by 12 other countries, mostly Latin America. The EU codes are mostly copied from the NEC. Only Australia has remarkably restrictive standards.
You still have to build the house with wiring and switches for line voltage lighting per the electrical code.
Today there is no standard fixture for low-voltage lighting. You can’t go into Home Depot and buy a 12V LED light. It’s still all DIY. Same as our smarthomes- there is no standard. You can’t call an electrician because your smart home hub is acting up. It’s all DIY. If you try to sell your home as a smart home with Home Assistant and Alexa, chances are your realtor is going to recommend that you remove the devices.
I don’t think 12v is a good choice due to voltage loss. We lived on a 36,000 acre “ranch” in .AU back in the 60’s and 70’s with a 32 volt lighting plant with a battery bank comprising 16 x 2 v batteries and generator driven by petrol engine. We had basic appliances like iron, kitchen mixer and portable evaporative air conditioner. Today, assuming its more than a weekender I think I would use a 48V battery bank so there was a pathway to 240v/110v via an inverter.
I totally agree. I use inverters and go 110v near the home. But in the remote areas, all I have are cameras, wifi repeaters, and flood lights. No reason to run inverters there, it’s just wasteful when a 12v deep cycle and a solar panel gives everything I need.
I have suggested esphome, which uses wifi infrastructure, but LoRa may give better range 
DC currents have some issues with longer distances, but there are a lot of 12V and 24V devices available.
You just have to look for devices for boats, cars and RVs.
Thanks for the link to some useful looking devices! On the AliExpress page linked from one of the above, I also saw this device. Any thoughts?
My interest is in 12VDC for boats and RVs. I agree that it’s not ideal for home use, due to the voltage drop over any distance. In the US, there used to be a lot of 12VAC outdoor lighting systems available, but with the advent of LEDs and solar those seem to be less popular. You still needed a transformer to drive the 12V side, but at least with AC you didn’t have the voltage drops you get with DC, and so the wiring could be smaller for the same load.
If have a couple of these but not a real fan I must admit. The esp01s just has like 
usable GPIO’s which makes extending it close to impossible. Also if you want to use it for 12VDC it might be better to go with a FET solution and no mechanical relay which (in theory) wears out faster (beside creating noise when switched 
)
Which proves my point.
The home is still entirely line-voltage, regardless how you deliver it. Not every one lives on a city-sized property and in the average home the voltage loss from 12V throughout the house would be negligible using commonly available 14 gauge wire.
The problem with getting there (a low-voltage house) is that there are no “off the shelf” 12V LED lights and no standard fixture or socket. Coupled with the fact that most communities have an electrical code that requires line voltage wiring. (The Amish can get a religious exception to the construction requirements).
I think the voltage drop would still be an issue for many homes. Remember that the distance to the fixture has to be measured both ways, to and from (the + and - wires.) For 14 gauge wire running 5 Amps you would get a 10% voltage drop after 65 feet (almost 20 meters.) Adding both wires, that means about 38 feet (10 meters.) When you consider that most wiring doesn’t go in a straight line, that would be a bit limiting.
The problem is that home systems were designed for incandescent lights, along with all the other appliances we use. We could easily switch to LED lighting. There are lots of marine and RV fixtures we could use. The problem is you would be designing, installing and maintaining two electrical wiring systems. I wouldn’t be surprised to see this start to evolve in that direction. But you’re on your own until the manufacturers, designers, standards and building codes catch up.
This would be at least a decade or two in the future. At least.
I I were designing low-voltage fixtures, I would use an LM1117-5 inside and run the LEDs at 5V. This way a couple of volts drop on the 12V bus would be irrelevant. The LN1117-5 is a lot cheaper and cooler than the 110V power supplies in every fixture today.
Using a linear regultor from 12 V to 5 V mens that you get
Power in = 12 V * I where I is the current of the LEDs
Power out = 5 V * I, same I above
Power efficiency Pout/Pin = 5/12 or 41.7 %
Any switch mode power supply in common use has 80-90 % efficiency. Even a capacitive dropper in a cheap LED bulb does better than that.
The LM1117-5 is a low drop output type serial voltage regulator. This means that is can regulate the output with an input voltage that is only a little more than 1 V. But feeding it with 12 V does make it low drop. The voltage drop over it will always be 12-5 = 7 V. And the power lost as heat will be 7 V multiplied by the current in Amps. It will get hot. And your electricity bill will be high. Not a good idea.
This is sadly true. 