Low voltage application for alternative home power

Hi Folks,

I'm running solar in my home, and am tied to the grid to back-feed energy I don't use. This works great for balancing costs, but still a slave to the grid. If I lose power, I'm still out. What standards are available for high-efficiency low-voltage applications for wiring a home?

I'd like to efficiently be able to power some of my standard home appliances with minimal loss. I was considering 48v AC, similar to that of PoE, low voltage lighting, and HVAC thermostats. I wasn't sure if there are already available standards for this. I was even considering a more conservative approach and just wiring up a single panel to a small battery array to just charge portable devices from laptops down to cell. I'm already doing this for external perimeter lighting quite efficiently but with a single car battery and 20w cell.

One of the reasons for high voltage in your home is better efficiency. Higher voltage needs fewer amps to produce the same wattage. Its much easier to pump more volts through a wire, than it is amps.

If you wanted to cut back from 110 volts to 48, you would need to rewire the house with wire that could support 2.5 times more current than it does now. All your switches, outlets, and breakers would have to be upgraded from 20 amp to 50 amp. All appliances would have to be redesigned for low voltage. Just try finding microwave that runs on 48v. Or a toaster. Or a hair dryer.

Its much easier, economical, and practical to just convert up the voltage from your system to the house's voltage. That has to be done for the sell back anyway.

Drunkskunk said:

One of the reasons for high voltage in your home is better efficiency. Higher voltage needs fewer amps to produce the same wattage. Its much easier to pump more volts through a wire, than it is amps.
y.

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Its a common mistake, you don't pump volts.
Ohms law says, Power(Watts) =Volts (potential) x Amps (current)

If yow want to power a 100watt load and you have a 100volt battery you will need 1 amp of current to flow.
The only thing limiting this is loss in the wires, switches etc. if the wire is too small it will get hot and limit the amount of current which can flow to your load. As you increase the wire size the losses will decrease. So thicker wire will reduce loss and improve efficiently.

If you can't increase the wire size you can also reduce the Amps (current) flowing in your wire.
To maintain 100 watts to your load Ohms Law says Power = Volts x Amps so if you have a 200volt battery you will only need
0.5 amps to flow. So higher Voltage will reduce loss and increase efficientcy.

Supersleeper said:

Hi Folks,

I'm running solar in my home, and am tied to the grid to back-feed energy I don't use. This works great for balancing costs, but still a slave to the grid. If I lose power, I'm still out. What standards are available for high-efficiency low-voltage applications for wiring a home?

I'd like to efficiently be able to power some of my standard home appliances with minimal loss. I was considering 48v AC, similar to that of PoE, low voltage lighting, and HVAC thermostats. I wasn't sure if there are already available standards for this. I was even considering a more conservative approach and just wiring up a single panel to a small battery array to just charge portable devices from laptops down to cell. I'm already doing this for external perimeter lighting quite efficiently but with a single car battery and 20w cell.

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You might want to look and see if your inverter has a battery backup option. And if not consider upgrading the unit, as many modern grid tie capable inverters do have the option. When power is lost they operate as a off grid solar system till the AC comes back. And you wont need a full size house battery if all you want to do is ride out the occasional hiccup on the local distribution network.

As for dual wiring a house, i have seen it done on 2 off grid systems i have direct experience living with. In both cases it was only due to the fact that power inverters built in the mid 90s (may have been older) pulled a huge amount of power on the DC side just being on. In both cases the homes were duel wired with 120VAC and 12VDC. The 12V system was used almost exclusively for lighting in both cases. And if i built a system now using a modern charge controller and inverter i simply wouldn't bother with the 12V system now since inverters have become much more efficient running at partial loads.

i wonder if you could wire the house up at 48V lifepo4 or 56V DC and see if stuff like the tv and radio would work and maybe you could find pumps and refrigerator to run on 56V DC. then use DC converter locally for the led lighting. not sure if a microwave would run on DC power so that would be the biggy. cooking, and heating, and water heating backup after solar hot water with gas is the best solution if you don't use wood.

dnmun said:

i wonder if you could wire the house up at 48V lifepo4 or 56V DC and see if stuff like the tv and radio would work and maybe you could find pumps and refrigerator to run on 56V DC. then use DC converter locally for the led lighting. not sure if a microwave would run on DC power so that would be the biggy. cooking, and heating, and water heating backup after solar hot water with gas is the best solution if you don't use wood.

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It's not a new idea. 60 to 80 years ago farms and stations would run 32volts systems using slow reving engines and wind generators to charge a bank of 16 x 2volt lead acid cells. Power was mostly used for lighting but things like 32 volt motors and power tools were used to run workshops. The common make was Dunlite in Australia.
Many old boys still talk about living on 32 volts.
during the 90s I worked for a solar company and many remote systems were 24volts and we would supply 24vdc appliances and lighting to reduce the cost of a power system when solar was $20 per watt and a dollar was worth twice what it is today.

Now days with cheap solar less than $2 per watt and cheap inverters it's probably not worth messing around with DC systems other than motor homes and caravans.