Grid/solar Q?

Discussion in 'Off Grid Living' started by snowbyrd, Sep 8, 2012.


  1. snowbyrd

    snowbyrd Latet anguis in herba

    Can a solar array that is connected to the grid, power only the house. The panels go into a locked box then to three meters. Cut off switch is located there. The line is connected to the grid.
    The house is connected to the grid. How would one connect directly to the house with the solar?
    Just for info of course, never know when the power will go off for a LONG time.
     
  2. BTPost

    BTPost Old Fart Snow Monkey Moderator

    Solar Panels are DC devices.... There are some that have GridTie Inverters built-in, but they are RARE. so one would need to KNOW, just WHAT is in the Locked Box. If there is a Gridtied Inverter in the Box, then yes, what you say is possible, and no Batteries are required. It would all depend on just WHAT was inside the Locked Box..... YMMV....
     
  3. TnAndy

    TnAndy Senior Member Founding Member



    The short answer is : You can't.

    You have what is called a GRID TIE ONLY system. It ONLY works with the grid.


    The longer answer is:

    You don't have batteries in your system (unless you forgot to mention them).....you are using the grid as your 'battery'......feeding excess power to it when you have excess, and pulling power from it when your solar doesn't produce ( like rainy days, or a cloud passes over the panels, or at night, etc ).

    For the most part, you can't connect solar panels to a load without the buffer of a battery ( or the grid ).


    The even longer answer is:


    1. You'd have to change inverters ( one of those boxes ) to a hybrid type that has on AND off grid capability. ($2,000 to$5,000)

    2. You'd have to install one, or more, charge controllers to take care of your batteries. ($600each) ( I have 3 on my system )

    3. You'd have to install a decent sized battery bank......$1,000--to whatever you want to spend, depending on your loads, the number of panels you have, and how long you want power when the sun doesn't shine.
     
  4. npe1pas

    npe1pas Monkey+

    +1 on the above responses.

    ALL NEC compliant inverters will have an anti-islanding circuit built in. This circuit will keep the inverter from putting power onto the house circuit (and the grid) if the grid is down. This circuit is in place to keep your solar system from backfeeding onto the grid and killing someone working on the "de-energized" line.

    The "combo" inverter would include a transfer switch that would isolate the house, or portion of the house, circuit from the grid, allowing it to power that circuit without energizing the grid line. You mention wanting to have power while the grid is down so expect to purchase batteries and a charge controller.

    Costing is still running $9/watt for a simple grid tied system (no battery backup, no solar if the grid is down, based on our 2009 install), up to $12+/watt for a system with battery backup.
     
  5. OSI

    OSI Monkey+++ Founding Member

    You might want to just consider using surplus server UPS running deep cycle lead acid batteries in a ventilated area for critical items, for example in your garage to run the freezer. It is possible in an emergency to run jumper wires to individual circuits in your home power panel but how it would go depends a little on how it is set up. A lot of commercial business, hospitals and municipalities run 1KW and larger UPS systems and then discard them due to the high cost of replacement proprietary batteries vs the cost of just replacing the whole thing. The computer systems inside the UPS are set up to "learn" the capabilities and capacity of replacement batteries since it is assumed they could be getting improved technology batteries as replacement as time goes on. Most UPS will take your grid power and then charge two 12v batteries which are connected together inside, sometimes just held together with double sided foamy tape, and fairly easy to recognize positive and negative wires. Upon removing the old batteries (you can get some recycle/salvage value out them), you drill some holes in the case at a non-critical point (usually side or bottom) and splice in extended battery leads (thicker wires would not hurt either). Connect two conventional deep cycle 12v batteries in series, and viola, you now have a high capacity power system with a pure sine wave inverter that automatically charges off house power, then automatically stops charging when the batteries are full, and your grid tie system just happily goes on selling the surplus power to the power company during peak daytime hours.

    In a short term power outage, your UPS will take over and feed whatever devices are plugged into it (that's what they are intended to do, in addition to acting as a surge/brownout protection/prevention device. That will give you power for the life of your battery bank, within the capabilities of the UPS inverter (I suggest getting 1000 watt or bigger since you are getting used and cutting into it anyway, and the places that sell them used have them all for about the same price anyway).

    In a long term power outage, and this is important, you have to cut off your main breaker so that it is not connected to the grid. This should isolate your grid tie inverter which you have noticed has not been producing any power since the power went out. That is a feature known as "island protection" and a legal standard on grid tie inverters that prevents the backfeed from electrocuting a line worker who is trying to repair downed power lines. You have to fool the inverter into thinking that the power is back on, so you need to feed the line some live power somehow. Now here is a trick, you may not be able to figure out right away which of the two positives in your breaker box is feeding the grid from your array, but that is the one that you need to reactivate.

    The next step requires a three prong power cord that has been modified to have male plugs on both ends. It is critically important that you not fuck up the polarity on this. The white (negative) wire on the slightly larger left prong, the positive (black) wire on the right side slightly smaller prong.

    Again, with the main breaker in the OFF position, you plug one end into a small AC generator. You plug the other end into an outlet that is on the same leg of the electrical panel as the solar array power feed. As soon as the grid tie inverter senses power, it will turn on the array and feed that particular leg of the power system. That will most likely get half your power going. It depends a lot on how your particular system is set up, and whether or not your generator can tolerate the additional amperage going through its circuits.

    DO NOT turn the main breaker on while a generator is powering your home. The generator power will be cycling differently from the main power grid, and the grid tie inverter will have timed itself to the generator. If the two phases of power hit each other, you get some big sparks and hopefully it just trips the breaker, but it could possibly blow a transformer and the power company would figure out it is your fault sooner or later.

    What I am describing is an "improvised" method of getting power from a grid tie system in the event of a longer term power outage, but the short term solution (UPS systems modified with larger batteries for higher capacity) is pretty good for short to mid term. If you have the money, then there are professionally made kits for adding off grid capability to a grid tie system that an electrician can install, but some municipalities will require an electrical build/modify permit. The kits typically include another junction box, battery bank and or charge controllers, some protection breakers and wiring. Typically, they cost about half as much as your the current price of a solar array comparable to whatever you are using.

    Remember though, that is at current pricing, so if you have a five year old system that was $25K, current pricing might be closer to $7k to $9K, and then the battery/off grid system would be roughly in the $4K range, not $12K range.
     
  6. BTPost

    BTPost Old Fart Snow Monkey Moderator

    Just a NOTE, here......
    What you are describing above is called "A Suicide Cord" and it is called that for a REASON. It violates so many NEC Rules, that they can't be enumerated in a single Post. Using such a device is beyond "Stupid" and bordering on Negligent. Also should you use something like this, in your residence and have an incident, your Homeowners Insurance will NOT Pay Off, if they find such wiring inside, even if it wasn't the cause of the issue. If you are not familiar with common Residential electrical wiring, and systems, you are better off Hiring such modifications to your house electrical system to competent electrician. There are Monkeys here, that are Journeyman, and Master Electricians, that can help, dealing with such installations. .... YMMV.....
     
    chelloveck and TnAndy like this.
  7. TnAndy

    TnAndy Senior Member Founding Member

    What he said.....ahahahahaaaaaaaaaaa
     
  8. OSI

    OSI Monkey+++ Founding Member

    I might have misgivings about the load of power from a grid tie inverter going into a house without some sort of battery bank as a buffer, but the double ended power cord, on a 2KW or smaller generator running through an outdoor GFCI 20 amp outlet, that's pretty standard practice with a lot of people. I personally invested in the battery bank and have not even turned over my generator in years, but I know the method of use since it is one way to keep cold out of the house and not have the generator building up poison gas in the garage.

    Now if you guys hate me for double ended power cords, get a load of this:

    I get a call late one night from a Mexican guy, he needs to get power to his mobile kitchen trailer the same night, will give me a hundred bucks if I can pull it off. I needed a tank of gas for my van, so what the heck, I would be up to it. I get there, he has this big old catering trailer all there with a 230v power cord hanging out the back. Wants it plugged into the garage if possible. I check the garage, and the 220v dryer plug is dead, wires cut, no options there. Then on to the power box, oh that was dead too.

    So off to Home Depot, grab the fattest generator cord I can find with four prong ends, and a cable end to match the female side of it. Grab a couple heavy duty conventional three prong type power cords and try to talk the guy into a shorter generator cord, but he gets ticked about spending so much money on power cords. Oh well.

    So we get back to the burrito shop trailer in the yard that is waiting to go to its semi-permanent position, and its starting to get late. I break out some cable cutters and start splicing away. So off goes a couple feet out of the male end of the four wire generator cord. Female sides of the conventional cords go bye bye too. Inside, I check the color codes on the wires, and yep, its pretty conventional. White for the return, green ground, black positive, red positive. So I strip things back a bit, hook a black on the conventional cord to a black from the generator cord (220 type) tie all the greens together, then a red to a black, then uh oh, I only have enough return lines on the generator cord to go on one of the two conventional power cords. Lessee here think...ah yes, jumper wire, but that means a lot of stuff pumping through that one wire heading back. Eh, how about tying it into a green? Yeah, that's the ticket, it all goes back to the same bar on the power box anyway.

    So with another illegal as hell frankenpowercord, we go into experiment phase. If it fucks up, I don't get my $100, and that guy might have a problem with his landlord or power company while I scoot out of there hoping he forgets my name. Now with one end of the power cord plugged into the cord coming out of the trailer, the other goes to a Y with lots of good fresh clean electrical tape on it (and pretty carefully spliced connections), and two 25 foot ends with conventional three prong plugs. So into the house we go, looking to plug each end into a different room so as to make sure they are going into two different circuits off the guy's panel box.

    Badda bing, and mileage did not vary. All the gizmos and stuff in the kitchen trailer start working. No sparks, no blown fuses, no SWAT crew from the electric company, no pissed off landlord or insurance agent.

    So with a raggedy but quite spendable Bren Franklin in hand, we start to discuss his options on a somewhat more permanent outlet. Now there are so many different types of 220v power plugs out there it is staggering, but everyone knows how those regular three prong 120v outlets work right? Take a look at the side of one a little more carefully some time. There are little tabs on the sides that you can break off so that the upper and lower plugs will require separate feeds. If you get an outlet rated for 20 amps, break those little tabs off and then run a 20 amp wires from different breakers to each of those. IE, check that breaker panel, and use two breakers that are one on top of the other, just like as if you were using a 220v double breaker.

    So, in relatively conventional fashion, the power outlet looks pretty normal when installed, but the upper is on its own 20 amp breaker, and the lower is on its own 20 amp breaker. Use the frankenpowercord with two plugs on one end, and a 220v type receptacle on the other end, and you can power a 220v type item off those two outlets.

    Now going in the other direction (partially with the piece of 220v extension cord you had cut off to make the first frankenpowercord but you end up having to buy more male ends for the 120v sides), you now also have a way of backfeeding the house from your generator. Yeah the pros will hate you for using it, especially if you fuck up and leave the main breaker (the one leading to the power company grid) turned on when the generator kicks in, but if the place is isolated from the grid anyway, then it just means a different set of breakers in your panel just became your main once you have turned off and isolated out whatever other set of breakers had been serving as your main.
     
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