Grid-tie VS Off grid

[Nicodemus]

Might be help full.
www.naturalnews.com/036194_solar_system_grid-tie_power_grid.html

[orly152]

Wow, learned something new. So, the bottom line is that grid-tie is less expensive and when the grid goes down you won't have any energy cause it shuts down automatically. That alone, defeats the purpose for me to own such a system.

Then the off-grid system is the most expensive to have because of the batteries life span. However, if I could afford the system I would prefer the off-grid for the simple reason that you will still have power during a major outage. The off-grid system looks to be more logical to have for a shtf or teotwawki scenario.

Thanks for sharing that info

[tjwilhelm]

I didn't read the link on the OP. It may have mentioned this: It's possible to do BOTH. It's called a bimodal system. You can have stand alone, critical loads AND you can sell back to the utility via a net-metering agreement. This is even more expensive and more complex than a stand-alone system; BUT, it gives you the best of both worlds.

[Deleted]

TJ, Do you think it would be possible to set up something that would run certain items (like my deep well) as well as a certain set of items in the house and have that off grid and runing while part of the house is still on grid? Maybe have the off grid part made so one could slowly expand it to cover more and more of the place as one can afford to expand? If so, how would you suggest one do it?

Also...I believe one time, a world ago, you posted about how to make the stuff for charging batteries...the acid or something I think it was. My memory bites sometimes...if that was you, can you repost that for us? Please?

[tjwilhelm]

Yes, you can do that, Dink! The loads you would power from the independent power system are referred to as your "critical loads." You need to set up a critical load panel (breaker box) to feed these loads, separate from the house's main panel.

Unfortunately, I don't have any of my old posts from STF. I'd have to recreate them.

I'll start shooting photos and making a few how-to posts...but give me a few weeks!

[Deleted]

You are AWESOME!!! Thank you so much!!

When you get time, some day...maybe we can figure out wehat I would need and how I would need to det it up so I can do it myself...$$$ is an issue, the more I can do myself the better off I will be.

THANK YOU!!

[olebama]

TJ, I saved some info from ST. I don't know if this would be of any use to Dink.

OK...Here goes...Part One...System-design assumptions and written description of system:

[ ] - I'm assuming you will want the ability to charge small electronics like cell phones, Ipods, etc. I'm also assuming, for each small device, you will have either a 12VDC (with cigar-lighter plug) charging cord, a 120vac charging cord, and/or a USB charging cord. Because there are 12VDC-to-USB adapters, and 12VDC-to-120vac inverters, I would configure this system as a stand-alone/battery-based solar-PV system with a nominal system voltage of 12VDC.

[ ] - You stated above, "(I) am considering something larger and that can handle laptops and other items similar." This criteria will primarily define the minimum size of the inverter and of the primary 12VDC battery at the core of the system. It can impact the size of the PV module; but not as strictly as the inverter and main battery. I just looked at the transformer on my laptop's power cord...here's what it says: Input = 100-240vac, 1,500mA. At an input voltage of 120vac (from the inverter's output), I'd need a minimum of (120vac x 1.5A =) 180Watts of inverter power. To be sure I have enough head room, I'd be looking at an inverter rated for at least 200-to-300 Watts, with a 12VDC input and a 120vac output.

[ ] - Now, I'm gonna pull a number out of my hind end (a reasonable number) just to give a target to shoot at...I'm going to assume that you will need 200 Watts of inverter power for up to 6 hours at a time in between sessions of fully charging the main system battery. 200W x 6hrs = 1200W-hrs. At a nominal 12VDC, this = 100 Amp-hours of accessible battery storage. I'd also like to limit the main system battery's "depth of discharge" to 70%. This means the actual storage rating of the 12VDC main system battery needs to be = 100A-hrs/70% = 143 Amp-hours. On the cheap but effective end, you could use two Durcell, 6VDC golfcart batteries, connected in series for 12VDC. At Sam's Club, these cost about $78.00, each...$160.00 for the main system battery.

[ ] - The system battery is the core/heart of the system. The battery should out-feed to a quality cigar-lighter socket; AND, it should be properly fused and have a means to disconnect/open this AC side of the system! Overcurrent protection and disconnect means are vital/critical needs! The (yet to be sized and selected) solar-PV module will feed into the battery via a properly sized PV "charge controller" with built-in blocking diode. Again, in this 12VDC side of the system, disconnect means and overcurrent protection are also critical needs.

[ ] - In a nutshell, this describes the system...PV module to overcurrent protection an disconnect means...to "charge controller"...to battery...to overcurrent protection an disconnect means...to 12VDC socket. Either a 12VDC load, a 12VDC-to-USB adapter, or a 12VDC inverter can be plugged into the 12VDC socket. Any (small enough) 120vac load (a laptop, etc.) can be plugged into the inverter's output.

[ ] - PV module, charge controller, wiring, fusing, and switchgear all need to be properly sized and spec'd. That will be Part Two, maybe written over the weekend.

[olebama]

Here is the rest of it. I never saw where you completed part 3.

As I sit here keying in this post, I'm thinking this will need to be, at least, a three-part epistle, instead of just two. So-o-o...Here is Part Two of at least three parts:

Part One primarily discussed the battery-inverter system that would be suitable for operating (or charging) your laptop for a 6-hour run. Part Two is about using solar-PV to re-charge that main system battery.

Two key factors effect how long it will take to re-charge the system battery: applied current and amount of time the current is applied each day. The amount of charging current is primarily determined by the size of the solar-PV module (or array). The amount of time the current is applied each day is determined by geographic location, season of the year, local climatic conditions, and the immediate "solar window" (are there shading issues?).

In the Part One example, we removed 100 Amp-hours from a 143 Amp-hour system-battery pack. To re-charge the system battery, we need to put back in the 100 Amp-hours we removed, plus another 10 Amp-hours to make up for internal losses...110 Amp-hours, total.

Just as an example, let's use the 45Watt PV kit from Harbor Freight. This solar-PV kit spits out about 3 amps at "peak sun." This means you need to give the 45W PV "array" good, "peak sun" for 37 hours...110 Amp-hours/3 Amps = 36.67 hours.

Now let's assume this PV kit is sitting in Kentucky, in the Summer. Those Kentucky folk get an average of 6 Peak Sun Hours per day, in the Summer. Therefore it would take them almost a week to recharge the system battery, in the summer, with the 45W solar kit...37 hours of Peak Sun / 6 Peak Sun Hours per day = 6.2 days.

If these Kentucky folk had 90Watts of PV, they could recharge in 3.1 days. If they had 180Watts of PV, they could recharge in about 1.5 days...in the SUMMER, that is. In the winter, they only average 3.6 Peak Sun Hours per day...that's only 60% of the sun that's available in the summer. This means the winter charge times would be about 10 days with 45Watts of PV, 5 days with 90Watts, and 2.5 days with 180Watts.

Another key point, if you only operate/charge the laptop for 3 hours, instead of 6, you'll only use 50 Amp-hours, and only need to put 55 Amp-hours back in.

Does this all make sense to ya? Can you see why these 40W to 45W PV kits are relatively inadequate for something as large as a laptop? Can you see how their advertising is a bit dishonest, while their prices are too high for what they're selling to you?

Here's an example of a 90W, crystalline, nominal-12VDC, 25-year warranty, solar-PV module for $200.00...$2.22/Watt: www.wholesalesolar.com/products.folder/module-folder/Astronergy/CHSM-5409M.html

Compare this to 45Watts of a lower quality module for $120.00 (if you could find it that cheap)...$2.67/Watt.

Part Three, coming soon...

[Deleted]

Thank you much Bama!!

[olebama]

You are very welcome. Again, I never saw part three, so I don't have that.

[tjwilhelm]

Sorry, I hadn't written part 3, and then STF went belly up. I'll put some more stuff together over the next few weeks.

[hunter63]

Jun 21, 2012 17:11:57 GMT -7 tjwilhelm said:

Sorry, I hadn't written part 3, and then STF went belly up. I'll put some more stuff together over the next few weeks.

That would be cool.......considered a grid tied system, kinda had to convince my Co-op (that didn't figure they had to do it as their sales were under a certain amount.)

Then they let it slip that my neighbor up on the ridge from me was already grid tied,,,,,first one.....they kinda eased up.

I even contacted Home Power Magazine, so the sent the co-op a complimentary subscription, (nice of them).

Anyway I contacted the neighbor, and he gave me a tour....was off grid in a hay bale house, with water collection system, and composting sawdust toilets, wood heat.

Is or was running at the time 1700 watts system, that could be stand alone with battery bank.....monitor checks battery charge and turns on the charger when needing to top off....... outage on power line end has a cut off,.... automatically cust the grid off line, so as to not endanger lineman if grid goes down ,,,then runs only needed loads off battery/collectors...till power goes back on.

System was about $35 K when I saw it 3 years ago.

I decided to do a power/energy audit, and spend my money on windows, insulation and so on, then start in on the solar grid tied system later on.

I really only need electric for the deep well pump, (have gen set)
and fridge,...really don't need that...but like my beer cold.
Most everything else is primitive, candles, wood stove etc.

[tjwilhelm]

Good move, Hunter! Energy conservation is always your best bang for the buck. Shouldn't spend a dime on a whole house solar-PV system until the loads are as small as possible.

[hunter63]

Before spending any money on gear....do the enegery audit.

Didn't take long tfor me to shift gears......

Much cheaper, more bang for the buck, to conservive that to manufacture energy

[missj]

I have my energy audit this friday from 9:30am- 1:30 pm. It costs $500 but the state of Oregon pays for it if they find I can save 30+% on my energy costs.

I am pretty confident I will get that $500 back since my windows are basically 1970s trailer park windows....and that is just the windows.... I don't have to agree to the contractor's deal to get my $500 back, just have to prove a 30% potential savings....

I'm getting cold feet on buying a big solar system.

for the money, I feel like a big pile of food, ammo, and a couple solar panels connected to some 12v batteries would be better used in a SHTF scenario....