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Old 10-10-11, 09:37 PM   #11
S-F
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Yes there is power loss in the inverter. That being said, do you know how much batteries will cost? Enough batteries to run lights for a house for the night, much less an AC unit? Can you get DC AC units? I imagine not.

Off the grid is cool and I'd do it if I were a bazillionaire, but alas I'm not. Honestly an off the grid system would probably cost 1/2 as much as my house.

I know a fellow who recently built an off the grid house for a rich guy. The guy wanted spray foam for insulation entirely. It cost $60K for insulation alone. I don't know what the power get up cost but I was told that the cost of the insulation was nothing in comparison.


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Old 10-10-11, 10:16 PM   #12
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Quote:
Originally Posted by d3vi1d06 View Post
i just know that an inverter wastes current to produce AC...
DC cant be that dangerous... my phone hasnt blown up on me, but if i touch an AC outlet, i get fried... ive put my tongue on a 9v battery, got a little tingle, yet it can power a flashlight for hours. ive always thought of DC being more efficient... if it wasnt, then why doesnt RVers use an inverter for their appliances, including a stove... All DC appliances on a RV or Boat. Why? AC wastes too much power in its inversion from DC.
DC at low voltages is less dangerous however it loses a lot when you try to send it long distances. A 12V system would lose a lot of it's energy with regular 14/2 wiring on a long run so you go with thicker wires. The copper costs alone eventually make it cheaper to switch to a higher voltage system. That's why on most whole house systems you see 36V or 48V. touch your tongue to the leads of a 48V battery bank and you're dead.

You do waste power converting to AC but it's trivial to deal with cost wise compared to going 100% DC. The major reason boats and RV's are all DC is because they have to have a DC battery on them and then it saves them money to not do an inverter to make 110V for a few lights and fans. I don't know of any RV that tries to run more then that off of the 12V system. All appliances are gas and things like the AC and microwave work off of an inverter and usually only when a generator is running.
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Old 10-10-11, 11:40 PM   #13
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Some of the most efficient solar electric systems you can install use micro inverters on the back of the solar panels to convert the low voltage DC to high voltage AC, the higher the voltage the less line loss you have and the smaller the wire has to be, and with AC power you can use a transformer to bump the voltage up even higher to go longer distances, like is done with high tension power lines, there are losses in transformers too but there is greater losses in low voltage wiring.
RV's use DC wiring because, like has already been stated, it's cheap and RV's are small so the wire runs are short, but the light at the far end of the RV is going to be dimmer then the light close to the battery.
My electric car runs off 48v DC and if you touch the two ends of the pack with bare hands it will not kill you but you will feel it and you can get burned if you are not careful, I'd like to have 72v in my car but that is boardering on what can kill you.
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Old 10-27-11, 03:55 PM   #14
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It's not the voltage that can kill you but the high amperage thats unsafe
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Old 10-28-11, 09:55 AM   #15
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I will echo the earlier post that suggests you focus on reducing consumption first. 45 kWh/day is a LOT of solar, and a lot of $$$. It's almost always easier and cheaper to reduce that load than it is to increase production.
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Old 10-28-11, 01:16 PM   #16
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It's almost always easier and cheaper to reduce that load than it is to increase production.
PaleMelanesian speaks the truth! But if you really consider where we are in the grand scheme of things, 'almost always' may not belong in that sentence any more.


This is a prediction graph generated by a computer in the early 70's. It is from a book called 'Limits To Growth'.

The book has attracted a legion of critics and deniers since it was printed. But the irony of it all is that we are pretty much on track, regarding it's predictions.

It takes a bit of study to soak it all in.

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Old 10-28-11, 08:14 PM   #17
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great chart AC. They don't chart education which I would suggest might change the results for industrial and service output forecasts. ever the optimist.

@d3vi1d06
To go back to your original post. Why go to an all DC household? Why not have a separate part of the house DC. Low voltage DC is perfect for LED lighting. Yet AC offers all the benefits of mass produced highly efficient appliances, esp. fridges.
How do you control DC though. I can't help you there. You mentioned rectifiers. Anybody? It's a question I share. Can you run a 3volt/.5 amp device on a 12 volt/1200 amp battery or do you have to damp it down and how?
** btw. you've been in the house for a bit, what is your daily electric consumption? I can't believe it would be 45kwh.
** S-F Batteries aren't that expensive. A modest 1kw system can run on 6 L16 batteries and that, I would think, would power a households' lights and tv/internet/computers. Maybe even an AC fridge off an inverter. You might want to double it and run your heat and (if nec.) well pumps. That's $5 to 7K diy?
DC to AC inverters are up to 97% efficient now. If you have 3.6 kw daily input off a 1kw system and you lose 100 watts it's not a big deal.
** Ryland:that just made me laugh. Hands across the waters.
Also, old news? AC current alternates. So apparently there's a 1/10 millionth of a second pause between alternations. And, I've heard, the human brain sends muscle response signals at 1/100 millionths of a second. Hence, you can pull your contact (ie. drop the live wire) by sending a signal to your muscle and with AC, message received. DC just overwhelms the signal paths and you can't let go. With sufficient amperage the last thought you will have will be, "oh, so that's what my eyeballs boiling in my skull smells like."
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Old 10-28-11, 09:41 PM   #18
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Default JumboCarbonitefootprintious ?

Quote:
Originally Posted by d3vi1d06 View Post
i just know that an inverter wastes current to produce AC...
~~~~
AC wastes too much power in its inversion from DC.

If you are really using "roughly 45kw avg a day", that comes out to 1350 kWh a month!

That's like you are continuously burning 1,875 watts, 24 hours a day, 7 days a week..

Please tell me what kind of appliances you have plugged in, to burn power at that rate.

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