Off grid idea... Thoughts?

[Joeybags]

My entire house is LED. I want to use a 12v system.. Seems to be the most practical and cost effective.

I wanted to run each circuit on its own panels, MPPT controller, batteries and inverter.

I want to be able to run the circuit during the day and any extra power left to charge the batteries for night use.

Looking at a 40 amp MPPT controller , 6 x 250 watt panels in parallel, Full sine wave 1500watt continuous 3000 peak dc/ac inverter. 4 x 110a/h batteries in parallel. I want to do at least 1 circuit per..

Double this for a 220 circuit.

A 15 amp circuit has the maximum power output of 1725 watts. 20 Amp is 2300 watts. Rule of thumb is to never go more that 75% of max, so that's 1300 watts and 1725 watts respectfully.

I'm not aware of what each circuit does in terms of load, but I think I may have it covered..

6 x 250 watt panels = 1500 watts - (20% loss) = 1200 watts (usable)
If the demand is not that high, then I'm good. Some circuits will use less panels.. Such as my office lights.. I have 13 high-hats on a dedicated circuit. Did this before I went LED. The total draw is only 13 x 10.5 watts. So, 136.5 watts total but with a light output of 845 watts.. @ 2700k. A single 250 watt panel and 1 110 a/h battery and a 500 watt inverter will be used for that..

I'm confused on why 12v systems are not more mainstreamed. I've seen many successful 12v DIY off grid solutions that work awesome.

Joey

[Sunking]

Many many things wrong with your idea, not to mention throwing money away.

First LED lights do not use very much power. On the order of 6 watts per fixture. So if you only have six fixtures and all LED's turned on amounts to about 40 watts, and if left on 24 hours per day only uses 40 watts x 24 hours = 960 watt hours. Assuming you have a minimum 4 Sun Hour day only requires a 300 watt panel.

Second point if you are connected to the grid, taking anything off grid is just plain foolish.

12 volt system are not used in homes because 12 volts is for toys, RV's and Boats. 12 volt systems are extremely inefficient and waste a lot of power, and much more expensive to install.

[Mike90250]

......I'm confused on why 12v systems are not more mainstreamed. I've seen many successful 12v DIY off grid solutions that work awesome.Joey

1) wife's blow dryer

2) % Percent. When you have low voltage, a few % low, or high, becomes a Big deal Do your lights like 16v when you EQ the batteries? at 120V, a few % is nearly meaningless, 105v or 123V everything still works.

3) Loads If you just have a few lights, the ohmic copper loss is not bad, but when you get to higher power, then it starts eating away and voltages sag.

4) charge controller limits. Most major ones are 60A With a 48V system, 60A is 3Kw of power. At 12V it's 800w, and you might need 2 or 3 of them beasts.

[Joeybags]

1) wife's blow dryer

2) % Percent. When you have low voltage, a few % low, or high, becomes a Big deal Do your lights like 16v when you EQ the batteries? at 120V, a few % is nearly meaningless, 105v or 123V everything still works.

3) Loads If you just have a few lights, the ohmic copper loss is not bad, but when you get to higher power, then it starts eating away and voltages sag.

4) charge controller limits. Most major ones are 60A With a 48V system, 60A is 3Kw of power. At 12V it's 800w, and you might need 2 or 3 of them beasts.

To get to 48 volts @ 440 amp hours ill need 16 batteries for the same output.. How is this better?

[Sunking]

To get to 48 volts @ 440 amp hours ill need 16 batteries for the same output.. How is this better?

Simple you would not use 110 AH 12 volt batteries. You would use eight 6 volt 440 AH batteries wired in series.

With a 1500 panel system minimum battery voltage is 24 volts, 48 is even better.

The problem is you are stuck in a 12 volt box. Batteries come in 2, 4, 6, 8, 12, and 24 volts. You do not want to use parallel battery strings because you cannot equalize the resistances. That means the string with the lowest resistance does all the work weakening it and bringing the other parallel strings down with it. If you need 440 AH's, then buy 440 AH batteries. Highest voltage battery you can find at 440 AH is 6 volts. You will not find 12 volt 440 AH batteries and if you did would need a fork lift to move it around because it would weigh around 550 pounds.

[mschulz]

To get to 48 volts @ 440 amp hours ill need 16 batteries for the same output.. How is this better?

And remember, as your System voltage goes up, amp hours can go down:
example:

If you need 2000 watt hours / day.

2000w / 12 volt system = 166 amp battery bank
2000w / 24 volt system = 83 amp battery bank
2000w / 48 volt system = 41 amp battery bank

As Sunking said, as you go up in volts your system becomes more efficient, uses smaller wires, etc.

[Joeybags]

Simple you would not use 110 AH 12 volt batteries. You would use eight 6 volt 440 AH batteries wired in series.

With a 1500 panel system minimum battery voltage is 24 volts, 48 is even better.

The problem is you are stuck in a 12 volt box. Batteries come in 2, 4, 6, 8, 12, and 24 volts. You do not want to use parallel battery strings because you cannot equalize the resistances. That means the string with the lowest resistance does all the work weakening it and bringing the other parallel strings down with it. If you need 440 AH's, then buy 440 AH batteries. Highest voltage battery you can find at 440 AH is 6 volts. You will not find 12 volt 440 AH batteries and if you did would need a fork lift to move it around because it would weigh around 550 pounds.

I was going to connect the wires from the middle to even out the resistance. 5 batteries, connect the wires at the 3rd battery. no? Would make sense to me..

6v 440Ah batteries seems to be quit expensive. The most common seems to be Trojan 370Ah. I guess I'm not grasping the theory. But what the difference if the money is thrown at the 12v system vs 48v? The higher voltage the more expensive it becomes. 12v system is inefficient but cheaper with the same outcome, but a 48v system will cost more and be more efficient. However, in my eye's the lower cost makes it more practical and easier to build.
A 12v system just seems more practical vs 24 or 48v systems.. The battery costs is much lower.

If I were to invest that kind of money, I would just get a 8000 watt on-grid system and call it a day.

Again, I wanted a system that can sustain itself (at each breaker) during the day plus charge the batteries, and at night run on batteries.
Each circuit breaker would get its own bank of solar panels, charging cotroller...etc.. Since its low power (1300 Watts), I did not see the issues you are seeing..

[russ]

I did not see the issues you are seeing..

That is because you have no idea what you are doing. I suggest you read a lot of posts and ask more questions before spending money.

[paulcheung]

You get what you are pay for. Those 12 volt batteries are cheaper because they do not last long. When you buy a good bank of batteries, you get 3 to 7 years solid service depend on which you get and how you use them, those 12 volt batteries you get for $60 only can last you 1 year or less if you deep cycle them daily.

[mschulz]

If I were to invest that kind of money, I would just get a 8000 watt on-grid system and call it a day.

So you have grid power- Than absolutely you would do a grid tie. You are finally making sense of this. You only want/ need batteries when there is no grid.

[Sunking]

If I were to invest that kind of money, I would just get a 8000 watt on-grid system and call it a day.

That is the first smart thing you have said. Anything you take off grid is going to cost you about 10 times more than you can buy it from the power company for the rest of your life with constant battery replacement.

For example lets say you want to replace 1 Kwh per day with off grid, and you live in Kansas City. In KC electricity cost roughly 10 cents per Kwh so in 5 years the cost to buy the power is $183. Want off-grid solar battery to do that? Well it takes

Panel Wattage = 450 watts = $600
40 Amp MPPT Controller = $350
12 volt 400 AH battery = $700
Wiring, Inverter, materials = $500

Total = $2150

Now tell me which is less. $183 to the power company or $2150 to your solar/ battery dealer and in 3 years buy new batteries at even a higher cost.

You have battery cost all wrong. For the above system takes the same exact 4 12 volt batteries. In a 12 volt system they are wired in parallel, 48 all in series. (12 volts @ 400 AH, or 48 volts @ 100 AH are equal with 5 Kwh of capacity). Additionally if you were foolish enough to go with 12 volts you would need a 40 amp controler and some huge wires between panels/controllers/batteries. At 48 volt battery all you need is a 10 amp controller at 1/3 the cost and much smaller wiring. The 48 volt system is much less expensive to install and operate.

Look you need to stop because you really do not have a clue what is going on. It is just not me telling you this, everyone who has replied is telling you that you do not have a clue. You need to listen, or you are going to learn the old fashion way by loosing your money. Perhaps that is what it will take.

[Joeybags]

Electricity prices averaged 19.6 cents per kilowatt hour (kWh) in the New York-Northern New Jersey-Long Island area in April 2014

[pleppik]

Electricity prices averaged 19.6 cents per kilowatt hour (kWh) in the New York-Northern New Jersey-Long Island area in April 2014

That's expensive, but not nearly as expensive as battery storage. IANAE (I Am Not An Expert), but my understanding is that the cheapest off-grid battery storage will cost you around $0.50/kWh when you take into account the life expectancy of the batteries. That's under ideal conditions.

Since batteries are cycle-limited, every time you take power from the battery you are consuming part of the battery's life and it is costing you money just as surely as writing a check to the power company.

Maybe if you could get battery storage for $0.05/kWh it would be a different story. But that's still a ways in the future.

[ChrisOlson]

I've seen plenty of 12V systems in off-grid cabins, sailboats (up to 36-37 footers) and RV's. And it does work fine but you can't power large loads with a 12V system (at least not economically). I consider 12V to be OK as long as your peak load isn't much over 100 amps on the battery bank. Higher than that you should be looking at going to 24 or 48V.

For us off-gridders the most expensive thing we got (and have to periodically replace) is batteries. If you have utility power I don't really recommend playing around with an off-grid system because the batteries cost too much. We need them for off-grid power because without them we're kind of screwed. But if you can get utility power for 20 cents/kWh you pay less than JUST what our batteries cost us over the long term for every kWh we use. If you have a legitimate use for the batteries, like in a RV or sailing yacht or something, then fine. But I have seen countless "off-grid" systems that people have as a hobby thing in a utility connected home that get abandoned when the batteries go to hell.

And those little 110ah 12V batteries won't last much beyond one year being cycled every day. A real 5 kWh off-grid battery bank that can survive daily cycling for many years is going to cost you about $1,200. The reason us off-gridders don't buy them little off-the-shelf 110ah 12V batteries is because they are too expensive. They cost about double per kWh of lifetime storage that good ones cost.

Don't throw your money away.

If you do intend to put in a 12V off-grid system no matter what, you can get like Trojans at the low end for about $400 each for L-16 6V for $800 total cost. At the high end you can get the big 12V Rolls 12CS - this battery has about 400ah capacity at the 20hr rate and it is not too bad for weight - they are around 300 lbs full of electrolyte. The big Rolls also has individually replaceable cells in the event one would go tits up after a few years. The Rolls is around $1,200.

http://www.dcbattery.com/rollssurrette_12cs11ps.html

For cost/kWh, the little "marine" deep cycles (which are not real deep cycle batteries) will cost you the most because you'll go thru several sets of them in short order. They lose capacity very fast and will be down to only about 75% of their rated capacity after 50-60 cycles.

The Trojans will be in the middle and give you 5-7 years depending on cycle depth.

The big Rolls will cost you the least and give you 10+ years of service at 50% DoD cycling, and in that amount of time you're almost guaranteed to have to replace a cell or two to get 15 years of life from the battery. The cells are $212 (today's cost) plus shipping from Rolls Battery in Springhill, Nova Scotia.

[Mike90250]

For "first timers", a set of generic deep cycle batteries is a good set of "training wheels" to debug the system and your lifestyle. If you make a mistake, it's a $400 set of batteries you toasted, instead of a set of HUP cells. When it's all dialed in, then the top of the line cells make better cent$.