Going off grid- Talk to me about AC versus DC for appliances

[308AndyJ]

I am toying with the idea of building a small home on some family land but it does not have power. Luckily I have a family member who can provide solar panels at $0.70/watt.

I will be living by myself and my power needs are very small, but there are a few things I need to determine.

I want to know for the following things, if it is more cost effective to do AC or DC. By allocating as many things as possible to DC I can get by with a smaller inverter for cost savings. DC is also more efficient and does not occur as many loses as inverting power, correct?

-Lights
-Fans (box fan for the bedroom etc)
-Kitchen appliances


With lighting it would be simple to invert the power from my battery bank and run conventional ac lighting. By doing this though, I would be taking up space from my inverter and might need to step up to a bigger size (more$$) and I would also deal with the loss from inverting, right?


Fans-I have seen some ready made box fans and I have also seen people take a normal box fan and replace the ac motor with a dc one. The cost effectiveness would depend on the cost of a dc motor though I am guessing.

Kitchen appliances- This one seems the one most fitting for "just go AC" am I right?

[Sunking]

Run 48 volt battery with a inverter.

[Mike90250]

Run 48 volt battery with a inverter.

Exactly what I would say. 12V dc wire runs will cause 2 problems, needs large gauge wire ($$) and wide voltage variation between charge voltage 15.5V and night time voltage 12.5V Some gear will fault or fail at >14V.

[308AndyJ]

Exactly what I would say. 12V dc wire runs will cause 2 problems, needs large gauge wire ($$) and wide voltage variation between charge voltage 15.5V and night time voltage 12.5V Some gear will fault or fail at >14V.

My only concern is how expensive 48v inverters are. To give you an idea of the rest of my system, I will only be using about 2,500 kwh in a 24 hour period. It seems silly to spend $400 on a 48v inverter just to run lights, fans, and a blender. That same $400 could easily pay for the increased cost of wiring.

I do appreciate the comments though, perhaps I am missing a part of the equation?

[Sunking]

My only concern is how expensive 48v inverters are. To give you an idea of the rest of my system, I will only be using about 2,500 kwh in a 24 hour period

That is no small amount of power for OFF-Grid Battery system and well beyond a 12 volt system. Depending on you location you are looking at a 1200 to 2000 watt solar panel array. At 12 volt battery would require two very expensive 80 amp charge controllers and a 12 volt 1000 AH battery which does not exist.

At 48 volt battery you can use a less expensive 40 amp controller. Battery size does not change just the configuration of 48 volts @ 250 AH which is 8-6 volt 250 AH batteries wired in series. Lowest battery voltage you can use is 24 volts and that would require a 80 amp MPPT controller and a 24 volt 500 AH battery.

Forget 12 volt toys, you are well beyond what 12 volt can do.

[russ]

[QUOTE=308AndyJ;115786] I will only be using about 2,500 kwh in a 24 hour period. [QUOTE]

Most don't use that in a month - maybe you mean something different?

[inetdog]

[QUOTE=russ;115801][QUOTE=308AndyJ;115786] I will only be using about 2,500 kwh in a 24 hour period.

Most don't use that in a month - maybe you mean something different?

Like 2500Wh maybe? Or 2.5kWh? That would be a small amount of energy that could be provided pretty reliably by a 1500W PV system in most parts of the country.

[Sunking]

I assume he means 2500 wh/day which is still a huge number for off-grid.

[billvon]

My only concern is how expensive 48v inverters are. To give you an idea of the rest of my system, I will only be using about 2,500 kwh in a 24 hour period. It seems silly to spend $400 on a 48v inverter just to run lights, fans, and a blender. That same $400 could easily pay for the increased cost of wiring.

I wouldn't be so sure about that. Let's compare a circuit to run a blender and other random appliances. We'll make it a 15 amp (1800 watt) AC circuit run 100 feet. (Or 150 amps at 12 volts.) Now to Home Depot for pricing for the NEMA-legal wiring you need for those circuits:

100 feet 14 gauge Romex - $18.06
100 feet 1/0 THHN x2 - $438.00 (ignoring the ground wire; it will be cheap)

So you save $419.94 by going with AC wiring for just that one circuit.

If you are going to run 12 volts around your house best restrict it to a few LED lights, perhaps a cellphone charger or two. That will keep the wiring cheap and you can run the LED's all night without having to turn the inverter on.

[308AndyJ]

[QUOTE=inetdog;115804][QUOTE=russ;115801]

I will only be using about 2,500 kwh in a 24 hour period.
Like 2500Wh maybe? Or 2.5kWh? That would be a small amount of energy that could be provided pretty reliably by a 1500W PV system in most parts of the country.

This is correct, sorry for my typo, thanks for catching it. Here's more info about my situation.

For the good pricing of the panels I have to buy way more than I need a this point, I will be getting 7 panels at 220w each. My area gets 4.71 sun hours a day avg, for a total production of around 7,200 watts. My daily consumption will be around 2,500w so I'll be producing much more than I need. This will be good in a few ways one being the size of my battery bank can be smaller. If a cloudy day rolls around and I only get 2 sun hours, it's OK cause I'm still producing 3,000w.

About the length of the wiring which was brought up by someone let me say this. The building here is going to be very small, think Tiny House. The floor plan is very open, and the inside will be painted a bright color to help lighting go a little further. The max length of wire that'll be ran is probably closer to 50ft, though I do sincerely appreciate the math you provided and it shows very clearly how wiring can add up ($$$$)

The main consumption of electricity will be my chest freezer and my other chest freezer converted to a fridge via a Johnson thermostat control. I don't plan on AC or electric heating. I do have a computer that gets a couple hours of use each day. After dark I will have the lighting, and during the afternoon a simple box fan might see an hour or two of use in the hotter months. I will also have a toaster, small microwave, and blender. the big cooking appliances will all be avoided thanks to a wood stove.

[Sunking]

For the good pricing of the panels I have to buy way more than I need a this point, I will be getting 7 panels at 220w each. My area gets 4.71 sun hours a day avg, for a total production of around 7,200 watts.

Andy quit debating, you have no other choice than 24 or 48 volts. It would be foolish to even try 12 volts. Panel wattage is limited by the charge controller. The largest controller is 80 amps, and they cost about $700 to $880 each. Input wattage is limited to:

1000 watts @ 12 volt battery
2000 watts @ 24 volt battery
4000 watts @ 48 volt battery

You have 7 x 220 watts = 1540 watts. 12 volts is out of the question so give it up. Go 12 volts and there are no batteries that will work and will require two of those expensive 80 amp controllers. 12 volt is for RV and toys period. With 1540 watt input the smallest battery you can get away with is 24 volts @ 500 AH or 48 volts @ 250 AH. No such thing as a 12 volt 1000 AH battery. You are going to have to use either 6 volt 250 AH for a 48 volt system, or 6 volt 500 AH for 24 volt system. Get use to it and dig deep in your pockets.

One more thing. What size generator and LP tank size are you going to use? At a minimum you will need a 3 Kw genny and a 100 amp 24 volt charger for the genny. Plus a LPG tank.

One last mistake you made is used average Sun Hours. For off-grid you use December insolation or else you go dark in winter months.

[SunEagle]

[QUOTE=308AndyJ;115819][QUOTE=inetdog;115804]

This is correct, sorry for my typo, thanks for catching it. Here's more info about my situation.

For the good pricing of the panels I have to buy way more than I need a this point, I will be getting 7 panels at 220w each. My area gets 4.71 sun hours a day avg, for a total production of around 7,200 watts. My daily consumption will be around 2,500w so I'll be producing much more than I need. This will be good in a few ways one being the size of my battery bank can be smaller. If a cloudy day rolls around and I only get 2 sun hours, it's OK cause I'm still producing 3,000w.

About the length of the wiring which was brought up by someone let me say this. The building here is going to be very small, think Tiny House. The floor plan is very open, and the inside will be painted a bright color to help lighting go a little further. The max length of wire that'll be ran is probably closer to 50ft, though I do sincerely appreciate the math you provided and it shows very clearly how wiring can add up ($$$$)

The main consumption of electricity will be my chest freezer and my other chest freezer converted to a fridge via a Johnson thermostat control. I don't plan on AC or electric heating. I do have a computer that gets a couple hours of use each day. After dark I will have the lighting, and during the afternoon a simple box fan might see an hour or two of use in the hotter months. I will also have a toaster, small microwave, and blender. the big cooking appliances will all be avoided thanks to a wood stove.

Be careful. Your estimated usage of 2500wh per day may be low. That comes to an average load of 104 watts used every hour. Based on the loads of a freezer, fridge, toaster, microwave, blender, computer and lights I think you will see a much higher watt hour usage in a day. Even if some of those are only on for a few minutes like the toaster and microwave those appliances are probably more than 1000 watts each and will run up your watt hour usage pretty fast.

Underestimating your true electrical load usage is common for most people and will end up draining a battery bank very quickly.

[Mike90250]

If a cloudy day rolls around and I only get 2 sun hours, it's OK cause I'm still producing 3,000w.

i want panels like you have. When I have a cloudy day, my 3Kw of panels only gives about 200w production and I have to run a generator.

[billvon]

The main consumption of electricity will be my chest freezer and my other chest freezer converted to a fridge via a Johnson thermostat control. I don't plan on AC or electric heating. I do have a computer that gets a couple hours of use each day. After dark I will have the lighting, and during the afternoon a simple box fan might see an hour or two of use in the hotter months. I will also have a toaster, small microwave, and blender. the big cooking appliances will all be avoided thanks to a wood stove.

Based on those loads you absolutely, positively need a good inverter. And once you are doing that you might as well run 120V everywhere.

[Robert1234]

Buy an even number of panels unless you just want one as a spare for grins and giggles.