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Plug-N-Play inverted power generation into the grid....  RSS feed

 
pollinator
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I realize this may have issues with safety and servicing, but I was wondering if anyone routinely uses their home power generation implemented in the following way (see diagram below).  In some respects, this modularity would be quite practical for certain settings.  Additional comments are welcomed.  Thanks!

Edit--Is the 300W limit in this diagram only due to the capacity of the inverter?  If the circuit into which the inverted power was a 20 amp circuit, could one us a ~2000W inverter (GTI) and relevant power source?
PlugNPlay.JPG
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pollinator
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While I'm sure there are a few people doing that....

First off, it's illegal.  Well, it violates electrical code.  You probably wouldn't get arrested for it, but you could get fined.

Second problem, if you have a new modern digital meter or "smart meter" that setup will likely INCREASE your electric bill.  The reason is that modern meters measure power flow through them, but don't care which way it flows.  In order to get credit for energy sent to the grid, you need a meter designed specifically to act as a "net-meter".  The power company will only install a 'net-meter' after your installation is inspected and approved.  Obviously they will never approve a setup like the one you describe.
 
John Weiland
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Peter VanDerWal wrote:.....modern meters measure power flow through them, but don't care which way it flows.  In order to get credit for energy sent to the grid, you need a meter designed specifically to act as a "net-meter".  The power company will only install a 'net-meter' after your installation is inspected and approved.  Obviously they will never approve a setup like the one you describe.



Hi Peter......understood and thank you.  Although the clip below is from a neighboring rural electrical cooperative, I suspect our own would be using similar set-ups and adhering to the Minnesota PUC rules for intertie.  Do you feel that the meter to which they are referring below is the "net-meter" that you mentioned above....i.e., subtracting off user-generated power instead of adding to the total flow-through?  I guess what I'm thinking right now is to sit down with the coop expert on interties and seeing what exactly *would* be acceptable to them, although I may need to double-check with the PUC that their demands aren't being too stringent.  Thanks again!
MeteringMVC.JPG
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Peter VanDerWal
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Yes, the meter described is the type I was talking about, one that can measure the amount of energy AND the direction its flowing (into or out of the residence).

For the NEC installation requirements, this is a really good guide:
https://nccleantech.ncsu.edu/wp-content/uploads/PV-NEC-V-193.pdf

However, it's a bit dated.  They update the National Electric Code every three years and there have been a few significant changes in the last two updates.   While most of the changes were in the structure of the code to make it easier to understand and more appropriate for solar PV specifically, there have been a few changes to requirements, labeling, etc.

I used the above guide when I installed my Solar array in 2010 and had no problems with the inspections.  Well except one of the inspectors apparently didn't know anything about NEC requirements for low voltage DC wiring & outlets so I had to explain it to him.

You should find out which version of the code is used in your area.  Some places automatically adopt the latest version, other places review the new code before adopting it, which can result in them using a version that is 1-2 years behind the current version.

After reading the above try reading the following to see how the requirements changed:
http://solarprofessional.com/articles/design-installation/nec-2017-updates-for-pv-systems#.WrfFk4jwZPY
http://solarprofessional.com/articles/design-installation/practical-application-of-nec-2017#.WrfFlIjwZPY
 
John Weiland
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Thank you for your excellent response and useful links, Peter, I hope to read through those at my earliest convenience.  As I was pondering the possibility of grid intertie last night, I found the following *Coop-Specific* (i.e., just at our own coop's website) verbiage regarding a "Distributed Energy Grid Access Charge" that the Rural Coops have been granted the right to levy by the state PUC:

"The Distributed Generation (DG) Grid Access Charge is $2.86/KW of nameplate capacity of the DG
system above the first 3.5KW of nameplate capacity. The DG Grid Access Charge will not exceed the
cooperative’s fixed costs to serve the member based on the year end Form 7 report and there will be a
cap of $45/month for each DG system.
**For example a 10KW DG system would be billed a monthly DG Grid Access Charge of $18.59/month.
10KW nameplate capacity system – first 3.5KW of nameplate capacity=6.5KW and 6.5KW times
$2.86/KW = $18.59.
The cooperative is given the authority to recover the costs of service through MN State Statute
216B.164, Subd. 3: Purchases; small facilities."  [end quoted text]

I guess I find it a bit dismaying that they are able to charge based on the *rated* generating capacity of the system, whereas their payback is based on the actual *generated* flow-back power.  If they simply adopted the "reduced-rate payback" model for power generated by the home-owner, wouldn't this be more fair than being a net-metering state and than add on a fixed connection charge that seems to be overly-taxing?  What if I (hypothetically) get no sun or no wind?....Aren't I still paying the grid access charge anyway according to this language?  (And of course, I'm already paying an 'access charge' of sorts since the coop will charge a monthly service fee irrespective of my use of their own power.)  Maybe this is just the ins and outs of grid intertie that all home generators of power have had to deal with before and I'm just experiencing newbie frustrations...(?)

 
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John Weiland wrote:
Edit--Is the 300W limit in this diagram only due to the capacity of the inverter?  If the circuit into which the inverted power was a 20 amp circuit, could one us a ~2000W inverter (GTI) and relevant power source?



John, yes the capacity of the inverter is the limit. You could possibly place 4 or more panels (or panel watts) on it and it would still only insert near nameplate, but it would ride full capacity more often and for a longer duration The other limit is in the input side materials and arrangement and it varies as to how many amps and volts is capacity.

We do this with grid tie inverters and charge controllers and with reasonable pv module prices, 25% or more oversize on the array size is usually doable equipment wise and benificial.

For the ac intertie circuit, any amps up to the utility's policy limit and utility service conductor max acceptable currrent is the confines. Usually we stay below 20kw inverter nameplate on residential installs. There are several reasons and may change on locality. The main reason for 20kw is service entrance equipment and service conductors. Unless you have a 200a- 400a service already and are lightly loaded or otherwise have headroom on  the mains bus rating.

Many times interties are about 40 amps. We  regularly build 60a and 70a 240v inverter ac circuits. Sometimes a line side intertie is best because there is insufficient room for more current on the load side without a mains service panel change.

A good way to meet code with a lower budget and without optimizers or microinverters is to wall mount the array overtop or adjacent to the service entrance and place an integrated ac/dc disconnect string inverter right there. It avoids requirement of additional remote disconnect/ rapid shutdown equipment and wiring, $600-$1000 or more. Few homes have the right orientation to do this, ground mounts are generally more cost and the differences of these will need to be evaluated for every project, same tact, mount the inverter at the array.

A string inverter is usually going to be the cost effective type in $/watt.

Microinverter, optimizer and ground mounted systems will also meet rapid shutdown requirements, it is when an array is building mounted (exception for structure purpose to house and support the system) and you need to be able to disconnect the array from the ground that the wallet comes out.

Usually the electrical will be straight forward with these systems, a snatch of wire and conduit (or no conduit is a possible with microinverters) pass through enclosure, disconnect, breaker, done.

If your equipment is grouped well, expenses are lower all around the integration.

The missouri inverter not sure if it is listed, but it could be plugged in as long as it has a dedicated inlet and differentiated plug type with disconnecting means appropriately located. Ventilated outdoor enclosures are available, but the cost and labor involved may promote a better and hardwired inverter or micros.

I have seen the plug and plays work.... most are only 500 or 600w so, the output is absorbed by loads before double billing as long as standing loads are higher.
 
frank li
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John Weiland wrote:Thank you for your excellent response and useful links, Peter, I hope to read through those at my earliest convenience.  As I was pondering the possibility of grid intertie last night, I found the following *Coop-Specific* (i.e., just at our own coop's website) verbiage regarding a "Distributed Energy Grid Access Charge" that the Rural Coops have been granted the right to levy by the state PUC:

"The Distributed Generation (DG) Grid Access Charge is $2.86/KW of nameplate capacity of the DG
system above the first 3.5KW of nameplate capacity. The DG Grid Access Charge will not exceed the
cooperative’s fixed costs to serve the member based on the year end Form 7 report and there will be a
cap of $45/month for each DG system.
**For example a 10KW DG system would be billed a monthly DG Grid Access Charge of $18.59/month.
10KW nameplate capacity system – first 3.5KW of nameplate capacity=6.5KW and 6.5KW times
$2.86/KW = $18.59.
The cooperative is given the authority to recover the costs of service through MN State Statute
216B.164, Subd. 3: Purchases; small facilities."  [end quoted text]

I guess I find it a bit dismaying that they are able to charge based on the *rated* generating capacity of the system, whereas their payback is based on the actual *generated* flow-back power.  If they simply adopted the "reduced-rate payback" model for power generated by the home-owner, wouldn't this be more fair than being a net-metering state and than add on a fixed connection charge that seems to be overly-taxing?  What if I (hypothetically) get no sun or no wind?....Aren't I still paying the grid access charge anyway according to this language?  (And of course, I'm already paying an 'access charge' of sorts since the coop will charge a monthly service fee irrespective of my use of their own power.)  Maybe this is just the ins and outs of grid intertie that all home generators of power have had to deal with before and I'm just experiencing newbie frustrations...(?)



This is as good a reason as any to have an inverter and controller that can use the utility line as a backup and insert nothing! Long duration heavy loads, loads higher than inverter max output and strings of cloudy days are no longer a tax on your battery and the system can be sized smaller and the major equipment hub is there for transition to offgrid, expansion and meaningful battery backup for a day or two are in place.

$20 was near our total usage per month! More people contact me with the desire to have this arrangement, its a good thing where the roadblocks are being put in place to discourage or profit on our choice to adopt renewables at home. They take the money and buy solar and wind capacity to lower cost of operation! I would keep my money and do the same, im sure they paid million to experts for that conclusion and are waiting as looong as possible to implement it, gradually just ahead of and our awareness of it.
 
Peter VanDerWal
pollinator
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John Weiland wrote:
"The Distributed Generation (DG) Grid Access Charge is $2.86/KW of nameplate capacity of the DG
system above the first 3.5KW of nameplate capacity.



For what it's worth, my current array has a nameplate capacity of 2.8 kW, up until recently I was producing approximately 2,000 kWh per year more than I used.  Last summer I bought a Chevy Volt and it looks like charging it will use up all my surplus plus another 200-300kwh per year, so I'm going to add another panel, which would put my nameplate capacity at around 3 kW.

My house is 100% electric, electric stove, electric dryer, electric water heater, etc.

Granted I live in a very sunny location, but still I'd think that staying below the 3.5k kW nameplate capacity shouldn't be too difficult as long as your home is moderately efficient.  Even if you needed to use a 5KW system, that is less than $5 a month for grid access, I'd consider that a good deal.

My power coop is phasing in a grid access charge for their solar customers, but it's a flat rate fee and in 3 years, when it's fully phased in, it will be $50 a month.  At that point I will only be saving about $5 a month over not having any solar at all, so I plan to disconnect and go off grid when that happens.
 
Peter VanDerWal
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frank li wrote:[
good way to meet code with a lower budget and without optimizers or microinverters is to wall mount the array overtop or adjacent to the service entrance and place an integrated ac/dc disconnect string inverter right there. It avoids requirement of additional remote disconnect/ rapid shutdown equipment and wiring, $600-$1000 or more. 



I don't understand what you mean here.  All grid-tie inverters include rapid shutdown capabilities when grid power goes away, so regardless of where you mount them there is no additional cost.

If the power company wants the capability to do remote shut down, that is usually built into THEIR equipment (meter or transformers) and THEY bear the cost not the consumer.  Even if the consumer had to pay for it, the requirement would exist regardless of where you located your inverter.
 
John Weiland
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Peter VanDerWal wrote:Even if you needed to use a 5KW system, that is less than $5 a month for grid access, I'd consider that a good deal.

My power coop is phasing in a grid access charge for their solar customers, but it's a flat rate fee and in 3 years, when it's fully phased in, it will be $50 a month.  At that point I will only be saving about $5 a month over not having any solar at all, so I plan to disconnect and go off grid when that happens.



frank li wrote:
I have seen the plug and plays work.... most are only 500 or 600w so, the output is absorbed by loads before double billing as long as standing loads are higher.



Thanks for the additional input here.  Yes, it had escaped me the first time that if I were to implement a 3.5 KW system, then my monthly access fee might be zero, correct?.....they are only hitting up systems of greater size for the access fee if I'm thinking about this correctly now.  Since we have a transfer switch at the power pole that allows us to disconnect the mains from the power company when I'm switching to a generator, I've also toyed with the idea (since I'm on-site a LOT MORE these days in retirement) of assembling the infrastructure that both of you have described that may also allow me to power the house at times with the mains from the power coop disconnected during those times.  We too have a well-pump, an electric range, electric water heater, oil-burner furnace (winter) and low-wattage window A/C for when necessary (summer), and with only two quite power conservative inhabitants of the house, pretty low power use in general.....so clearly the idea in the previous sentence would have to be attempted only when heavy loads were turned off. We already do this naturally when powering the house from a 7 kW generator---breakers for the stove, water heater, etc. are switched off so there is no risk of accidentally turning them on to create extra load.....but we do NEED the well pump to run for watering the animals in their stalls, etc.  Nevertheless, a flip of the transfer switch and all of the loads could come online again as soon as their breakers are re-set.

But I'm liking where this discussion is going especially as we've arrived at the time when I've been interested in finally getting the first modules installed.  (....tariff or no tariff!)  And as we are in a great area and micro-location for wind, I have not ruled that out as a complement.  Thanks again and hope addition comments come in on this.....
 
frank li
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Peter VanDerWal wrote:

frank li wrote:[
good way to meet code with a lower budget and without optimizers or microinverters is to wall mount the array overtop or adjacent to the service entrance and place an integrated ac/dc disconnect string inverter right there. It avoids requirement of additional remote disconnect/ rapid shutdown equipment and wiring, $600-$1000 or more. 



I don't understand what you mean here.  All grid-tie inverters include rapid shutdown capabilities when grid power goes away, so regardless of where you mount them there is no additional cost.

If the power company wants the capability to do remote shut down, that is usually built into THEIR equipment (meter or transformers) and THEY bear the cost not the consumer.  Even if the consumer had to pay for it, the requirement would exist regardless of where you located your inverter.



Peter, it has to do with cutting power at the array. For building mounted arrays code now requires photovoltaic array disconnects to be actuated from the main systems safety disconnect and the disconnection must be within 10' of the array or within 5 feet if it is inside the building, under the roof-deck, for instance.

Obviously, microinverters, roof mounted string inverters, and optimizer systems can accomplish it without remote (remote from the array) disconnects or additional rapid shutdown equipment, the dc power not leaving the areas described around the array.

As a fireman or in other scenarios, the idea is that there are no live conductors in the roofing, attic, walls, etc., that they might need to rake through or cut through and spray water all over while making puddles to stand around fighting fire in!

Same for all battery systems now... battery disconnects, pv disconnects at the array and inverter output circuits have to be rapid shutdown capable and labeled so.

Not so, if you have all equipment mounted outside of the building as i described in the wallmount situation or in its own purpose built building. Then you only need a safety or main system disconnect located where it can be found preferably grouped right in the same area as the meter, generator service entranc and its disconnect ( and or utility service entrance to the building ), but signs can work.

I use disconnects that are rated to contain ac and dc wiring and accessories like breakers. The disconnecting combiners can cut several strings of microinverters or, the way i use them most is to disconnect everything with one lever, the pv, generator and battery inverter ac output to the property or building electrical system at offgrid cabins and other battery based system installs, like grid tie with battery backup.

2017 had alot of changes so i have to reference it, but most of this is from NEC 2014.

 
Peter VanDerWal
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Ah, I see.  Apparently I need to do a more in depth reading of the recent code before I change my array over to off-grid.   Although, if I do it soon it might not matter, my county is still following the 2011 NEC.

Thanks.
 
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