DEC 03

DC to AC to DC.
Why not straight to DC?

It's a good opportunity to cut out middlemen, especially when you're effectively doing a round-trip conversion.

It would be great to see houses with separate DC circuits and AC circuits. Imagine a standardized DC outlet (different from the current 2 or 3 prong AC outlet) on the wall next to your current AC outlet. Plug DC into DC, and AC into AC.

Much of the power supply is used to regulate and condition the voltage, so though some of the loss would be saved most would still exist.

Still a cool concept though.

low voltage dc is easy, however you need to pick a standard voltage. 12v? 3v? 4.5v? 24v? 6v? just off the top of my head i've got all of those in my house. a "dc outlet" could have half a dozen of the female receptacles that your phone or laptop wallwart supplies and you plug a male to male cord in, but unless you can standardize on one low voltage, there will still be conversion loss.

the reason ac won out in the current war was safety, voltage drop, and transmission range. low voltage DC is great for some lighting, but not as useful for many other things. you can't send DC more than a few miles w/o a sub station, and it's a lot more dangerous to send over distance

use stock 12v DC for built in lighting with LED and MR16s, doorbells, and home control, and convert to AC for table lamps, and other appliances, sell back to the grid on AC. you'll get the efficiency gains but still be able to deal with higher power consumption appliances (hair dryer, microwave, washer, computers) and sell back to the grid in a useful fashion.

ac is a must to have a grid, and a significant ammount of appliances will need to run on it, so the standard there is a good thing to keep around.

Collecting heat through solar thermal collectors and then producing electricity through a steam turbine can, in some turbines, produce AC directly without need for an inverter.

Regardless of the method of generation used, the electricity will still need to be converted.

In house solar:
Generated Voltage DC converted to in house DC.
No matter what, the generated voltage will need to be 'conditioned' or 'complimented with outside power'. The panels won't generate exactly what you want in house in all likelihood.

Outside DC:
Say you turned the grid to DC. What Metis says is mostly true. However, today we can also perform DC/DC conversion. The grid could be made of a DC backbone so it would be DC-DC-DC. Still two conversions and it would most likely be less efficient than AC-AC-AC-DC. Those grid AC transformers are something like 99% efficient. Ac-DC are generally 87-92%.

Just like tesla wanted.

I'm really glad a group is looking into this option. I've explored it myself. An issue I ran into is high power devices.

If an air conditioner pulls a few amps, there is a surprising amount of energy lost just from the tiny resistance of the DC power wire within the home. I have not done all the math but it could negate the power savings from removing inverters and regulators and such.

The grid should definitely stay AC. DC is really only a good option for local supply (i.e. within a home)

if you want to be efficient you have to keep the grid on AC power. there are very few things in the home that use AC instead of DC, but all the necessary AC/DC conversions happen where they need it and in exactly the way they need it.

making everything DC would necessitate huge size wiring for simple household electronics, don't mention the fridge, computer, plasma tv, PS3 etc.

forget conversion losses, the real killer (besides DC safety concerns) is wire resistance. there isn't enough copper in the world to feed American homes in DC.

High voltage DC does not require larger conductors than AC - However it becomes just as unsafe as high voltage AC. Low voltage AC is safe too.
The nice thing about AC is that you can (reasonably) efficiently convert voltage to avoid transmission losses - that's why we can string 11,000 Volt power lines from the power station into neighbourhoods. All the methods of converting DC voltages require power regulators that have a limited current capability, and get very expensive at high power levels.

We have an off-grid DC cabin here in Texas. No air conditioning and no refrigerator, but everything we have is 12vDC except for propane heat and campstove. It's like an RV without wheels or a yacht nowhere near water. Lighting, fans, and anything that can plug into a cigarette lighter (battery charger, laptop, radio, dvd player, lots of stuff. The whole solar powered set up cost less than $800.

Reading some of the comments I believe they are technically incorrect about DC. The main advantage to AC and the reason why it was used in the past is the ease with which it can be stepped up to higher and down to lower voltages, this aids in transmission and distribution. DC can be transmitted more effectively than AC as their are no losses associated with AC such as the skin effect. The problem with DC is that large solid state switching is required to transform the voltages but this is no longer a problem for modern power equipment and many DC transmission systems are in use today - There's one major 300MW Approx. DC transmission system not far from me which spans at least 100km.

DC is good, but AC can be carried further on wires, with less loss of power. I see DC only in locat production.use applications, not as Tesla wanted, but
yet Tesla's work has a place in todays world.

This question may sound very basic, but I am in interested in starting a small scale solar panel setup: solar panel -> regulator-> battery-> inverter-> electrical appliance. I was hoping to take the battery and the inverter out of this equation and switch to solar panel -> regulator-> electrical appliance.

The problem is I don't know anything about DC usage except to make sure to use 12V for 12V appliances etc. Is there anywhere that I can learn more about the basics of hooking up my appliances? As soon as I get this straightened out, I will buy 12V DC appliances such as water hearter and AA battery chargers.

Any help would be appreciated.
Thank you!

Rohan

Rohanjcp,
It would not be very wise to attempt to run an electric water heater that heats to 140 degrees with solar or wind. It is possible (but expensive). I would use the suns rays directly! Look up batch solar water heater. I am having issues myself finding dc converter instructions to create my own. Can't really afford 200 dollars on a radio shack laptop converter. I will use the ac inverter that I have sparingly. Current(amps) is the enemy of low voltage. Current requires large wires(due to heat) Simple equation Volts*Amps=Watts. Hope this helps. Conrad

Stop with the "dc can't" crud as well! Direct Current is very good at doing everything Alternating Current does. As the name suggests (Direct Current) it does not change direction. And all points taken, run back and forth across the floor from room to room picking up stuff and see how tired you get, THEN get a basket and pick up the same amount of stuff in a SINGLE fluid motion. I AM a direct man but I do not have the intention to spark a flame so nothing I said should be taken personally.

As the (GRD) great republican depression squeezes the current "American Dream" lifestyle, and some discomfort is beginning to show, demands are changing, downsizing is popular, frugal living found on websites, and bigger "land yachts for cars" and SUV's are disappearing so fast GM is going broke! Better diets are being demanded, and better, less hormone and antibiotic saturated meats are now in demand! Soon, growth hormones in milk will be examined and we will, by many small steps, modify diets to more healthy ones. The McMansions, now foreclosed and rotting away were a call to awaken Americans to demand saner, better designed, more economical to heat and maintain, housing! The GRD driven by shortening, expensive supplies of oil (OPEC cutting back to boost prices as we speak), is causing a re-evaluation of the efficiencies of our lifestyle, and forcing truths we don't like to face on us! In the end, each home will have solar powered LED lighting systems installed, totally independent of grid power, and probably a D.C. low volt system. Homes will also have other power systems, probably grid - powered, but not using large high current induction motors, which will no longer required in the new solar powered fridges (once the cat is out of the bag! they can be found in African outpost hospitals today, and work fine thank you, and no thanks to the shylocks who hide then from the American people). Microwave cooking using lower power D.C. to furnish enough heat to brow and cook most meals is possible, reducing the large 220 volt A.C. cooking load to the grid, but we must, and we will be forced to, by economics, to adapt to. Heating will be largely solar, passive, and geothermal, we won't like the changes, they will be a hardship on us but again, economic forces and realities of a post GRD world will make them more amenable! We simply will have adapted newer technologies to do away with the high amperage A.C. loads that now serve us! Every home will have a greenhouse, compost, and use the Swedish developed dry toilet composting system to save our lakes and waterways, and we will only have to work part-time or as occasional in the only industries not sent off shore, to live a respectable comfortable albeit frugal new "American Dream" with more time off than ever before, and lots to do in it.

"Solar panels and fuel cells produce DC electricity; the inverters which turn it into grid-worthy AC inevitably lose some of that electricity in the process." So we should change based on that? Solar panels and fuel cells are about the only method of power production to produce DC. Windmills, hydroelectric, nuclear, and just about every other method of energy production (that produces evergy from magnetic fields) produce AC. Converting that to DC would introduce more losses. Not to mention how much more inefficient transmission is.

People also shouldn't forget that even when you convert from AC to DC you still need to convert to the correct DC voltage. In items with large transformers this is done with a highly inefficient linear voltage regulator. So the DC/DC conversion is already being made, but every device has to have its own converter, which is usually thrown out with the electronics. This would allow the process to happen only once per needed voltage.

It is not completely right to say that most methods of power production yield ac power. Windmill produce ac power with a different frequency than the one required from the grid, so it needs to be rectified into dc in order to be useful. Other examples are microturbines that produce high frequency ac that has to be rectified in order to use it. So dc actually saves conversion stages and improves generation efficiency.

Utility grade solar cells produce around 400V DC, so the use of 12V pc's is not an option in that case without 400VDC-AC-12VDC in the pc to get the correct voltage- which has substantial losses.
Also, does anyone understand that a low voltage +12V DC circuit (What PC's run on) would require substantially heavy gauge or multiple runs of conductors in order to deliver a useful amount of power to a load device?
Consider a typical pc power supply: 300Watts
Consider amps at 12V: 25A
Consider an office with 10 PC's
The amps then are: 250A
This would require 4/0A or 2/0C conductor (Very Large)
Consider first the carbon footprint/environmental impact of the mining of copper or aluminum and production of your cable. I'm sure you will find it more beneficial to use the 120/240Vrms to +12V DC power supply in each computer, despite the marginal losses.

You can probably pay for a DC-DC converter from the copper recycle return from that transformer on the street, so the local grid could easily be 400 VDC. That happens to be the voltage produced by Power Factor Correction boost converters. With a 400V DC grid even a single solar panel could be cost effective at selling power to the grid. With an AC grid to initial cost of selling power to the grid is prohibitive.

You can probably pay for a DC-DC converter from the copper recycle return from that transformer on the street, so the local grid could easily be 400 VDC.