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Normally, solar-powered homes have an inverter, which is a device that converts DC input voltage to AC. That AC is used to power electronic devices, which may use an adapter to convert back to DC, for example in the case of LEDs.

Wouldn't a DC-only setup without inverters or adapters be more efficient, assuming no AC devices?

What kind of efficiency gain might there be from stepping down 48VDC to 12VDC instead of doing the usual, three-step conversion from 48VDC to 110VAC to 12VDC?

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    \$\begingroup\$ People have done it. The difference isn't as big as you think — inverters are pretty efficient these days. And the higher voltage is more efficient to distribute throughout a house. I think we already have a question on the topic, but maybe it was some other site :) \$\endgroup\$
    – hobbs
    Sep 4 '21 at 5:48
  • \$\begingroup\$ The basic idea is OK. You do want to avoid conversions. But the grid tie inverters are over 95 percent efficient. Some of them can put out several kW with no fan. Small AC-DC converters (like for laptops) can be 90 percent efficient or so. In a grid-tie inverter system there is no conversion from 48 to 120. The PV string runs at a few hundred volts into the grid-tie inverter. The grid-tie inverter puts out 240 VAC. \$\endgroup\$
    – mkeith
    Sep 4 '21 at 5:50
  • \$\begingroup\$ Off-grid systems with batteries sometimes run at lower voltages like 48V. The 48 and lower Voltage inverters are not quite as efficient as the grid-tie inverters. So if you run a low-voltage system, you will pay a bit of an efficiency penalty for loads that DO need 120 VAC or 240 VAC. But I have often wondered if it would make sense to run houses off of high voltage DC (Like 350 - 400 V). This would facilitate having large battery packs and solar arrays. Also, 240 VAC rectified can make about 350 VDC. So it wouldn't be hard to supply 350 VDC from normal mains supply. \$\endgroup\$
    – mkeith
    Sep 4 '21 at 6:04
  • \$\begingroup\$ Convert all your appliances to 12v. Work out the current flow needed for each. Add suitable wiring to get that current to the ponts of use. Now think about the electrical losses and extra costs involved. Possible yes. Efficient? Smart? \$\endgroup\$
    – Solar Mike
    Sep 4 '21 at 6:06
  • \$\begingroup\$ Having a DC only supply to the house will prevent appliances that have AC motors such as fans, dishwashers etc that need an AC power supply from working. Also, you would need low voltage DC input chargers for your laptop, phone etc. So you would have to replace all your chargers. \$\endgroup\$ Sep 4 '21 at 15:38
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Every time you pass energy through a converter of some description, you lose some due to inefficiency. Maybe 5%, maybe 20%, it all depends on how well the converter was designed, which often (but not always) correlates with how much you paid for it.

Superficially then, a single converter setup is likely to be more efficient than a two converter setup.

However, a solar powered home is more than the converters. It will usually have battery storage, cables to distribute the power around, and things you want to power.

Cables are surprisingly expensive, and surprisingly inefficient at moving power around at low voltage. There's a good reason long distance power is moved at 100s of kV. In a house, the difference between 12 V, 48 V and 120 V distribution will show up in the cross sectional area of cables needed to move the power efficiently. Point of load conversion to 12 V from a higher voltage will often make sense, when all the losses are considered.

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  • \$\begingroup\$ I could in theory do the distribution at 48V, or whatever battery voltage, and convert to 12V at the point of load, as you say. Based on your answer I think the only way for me to know the efficiency delta is to do some testing with actual hardware. \$\endgroup\$ Sep 4 '21 at 12:23
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I have always supported the concept of pre-wiring homes for 48V for all peripheral DCDC converters, LED lighting and some appliances. The main reason I suspect that this hasn't caught on while telephone wires are almost extinct with so many cordless conveniences is the cost of extra AWG16 copper distribution wires. Even though appliances have reduced in power consumption over the decades, you still need fairly expensive copper to do all the house in addition to AC grid distribution.

The battery backup gives you automatic UPS functions for computers and lights and storage for Green power sources which is a positive contribution for consumers. (pun not intended)

Although if designed just for lightning and mobile chargers, wiring homes also with DC, I believe, will eventually occur. Each port must be current limited.

There are standards now for these common LED engines at a standard DC voltage and interface, but slow to gain popularity.

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