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For the distances being discussed, say a maximum of 500 feet from top to bottom, there is very little difference between AC and DC transmission losses. It is mainly a question of volts and amps. AC does have the advantage of lower cost disconnects and fusing compared to DC. It could be worth a look at it. A detailed look at what the actual AC and DC loads in the house and the cabins needs to be done before any real planning on one system vs another, IMO.
Totally agree and even longer distances than 500 feet. Much better to keep all the electronics and batteries close to the house and run DC the distance. Run the DC at 300 to 400DC mppt and live the good life!
Well, voltage drop is voltage drop, AC or DC
Thank you for the reply, Dave. And yes, Don, Dave seems to really know his stuff. I am glad I asked my questions during one of Dave's "very active" phases. : - )It seems to me, though, that having the long run be DC between the panels and the controller and batteries would be better regarding the drop. The voltage drop will happen there, but the controller will then correct it to the proper charging voltage for the batteries, and full converted AC voltage will be available at the house.If The AC was converted at the panels then sent the 300-400 feet to the house, the voltage drop would mean that AC house voltage would be lower.The drop still happens, but the house voltage is good. If converted at the panels house voltage is reduced.
What should be considered is overall "power" (wattage drop), vs only voltage (given a load - there is no current without a load of some sort).AC is always used to transmit power over long distances because it is easy to step down (decrease voltage, increase current capacity) and up with a transformer. DC is not so easy (transformers don't work on DC). Most of the "step down" and "step up" conversions for DC create more loss than the transmission line itself. You can convert AC into DC fairly simply with a rectifier, but the opposite isn't as simple or efficient. So once you have DC, you better off leaving it as DC as well as at the same voltage. As far as transmission loss goes it is about voltage vs. current. Higher voltage and less current is always better (given the same total wattage). It can be explained mathematically with ohms law, and there are plenty of sources out there if you're curious about the equations. What makes you think that we do not consider overall power offgrid? What makes you think we are stepping up DC offgrid?what makes you think that AC is always used over long distance? What is long distance to you?What makes you think transmission loss is only about voltage and current?You make good points but the word always is wrong because there are"always" other strategies that you may not be considering.The bottom line - If you increase the voltage, and therefore drop the current you end up with less overall resistance and therefor power loss (because calculating resistance is based on the relationship of voltage and current). Since it is easier to step down AC voltage, you're better off leaving it as AC for as far as you need until you convert it to DC. Once power makes it to it's destination as AC, you can step the voltage down with a transformer, then convert it to DC via a rectifier (if DC is your end goal).I'll qualify this by saying I'm not exactly sure what we're doing with the panels, but this is what I know about line transmission. I understand that you do not understand the solar panels --Dave
What makes you think that we do not consider overall power offgrid? What makes you think we are stepping up DC offgrid?what makes you think that AC is always used over long distance? What is long distance to you?What makes you think transmission loss is only about voltage and current?You make good points but the word always is off because there are"always" other strategies that you may not be considering.[/color]
...Not to mention the fact that I like the idea of the batteries and inverter in place at the cabin and not 325 feet away...
Unless one of the batteries shorts out and catches on fire.
Hey Glen,I have your phone number you left a few weeks ago. Glad you are back in the county!The problem with forklift batteries is they are too heavy to easily move around. Someone like you no problem.The other problem they have for Offgrid is they are designed to be deeply cycled and charged for 16 hours or so. They work an 8 hour shift and charge for 16. People do use them offgrid but they really need to know what they are doing or they end up with problems long term.I pretty much use the 2V 1,100 AH L16 and get 10 years or 5 if the client does not follow the rules.With the newest battery technology hanging on the wall, like the Samsung Lithium Ion NMC cells there are some nice things ahead if they can make them safe enough for your home.