Feeding solar power back into municipal grid: Issues and finger-pointing

Page 1 of 9  
We have a residential energy program here in Ontario (Canada) that I really don't agree with (called the Micro-Fit program) where the electricity from roof-mounted solar panels is purchased by the provincial power authority (OPA) at something like 80 cents per kw-hour (a crazy-high fee that will have to be subsidized by somebody - ie the general population, taxpayers, etc).
I believe all the details for this can be found here:
http://microfit.powerauthority.on.ca /
A neighbor of mine had a free evaluation done on his home to see how many panels situated on his roof would generate how much electricity.
The problem he's facing is that two different levels of power distribution (the city-owned municipal owned and operated company, and the provincial or regional power supplier or distributor that either supplies the electricity to our city or owns the high and medium-voltage lines and sub-stations where the electricity is stepped down) are pointing the finger at each other by stating that there is a capacity problem caused by the other as the reason why his solar panel installation (which he hasn't yet contracted to be installed) can't be connected to the grid.
It's my impression that any electricy that he'd be generating would essentially be 2-phase 208 volts (ie - identical to the service that enters our homes) and this electricity would simply be inserted or wired in parallel through a meter to his existing electrical service. I don't see how the capacity (or lack thereof) of the sub-station serving our corner of the city plays any role as to whether or not our local grid can accept and utilize the estimated 5 or 6 kw that his panels are likely to put out at maximum.
This issue has recently come up as indicated by this:
----------------- The OPA is proposing that all new microFIT applications submitted on or after December 8, 2010, would need an offer to connect from their local distribution company before the OPA issues a microFIT conditional offer of contract. The proposed rule change can be viewed here.
http://microfit.powerauthority.on.ca/Program-updates/2010-December-8-microFIT-Connection-Rule.php ------------------
According to this document:
http://microfit.powerauthority.on.ca/pdf/microFIT-Program-Overview.pdf
Page 18 shows the most likely connection scheme - which is to connect the Microfit PV project to the grid on the customer's side of his load meter (ie - "behind the meter" - the load meter that is).
My basic thesis here is that I think any argument about the capacity of the "grid" (where-ever or what-ever the "grid" is) being at or near capacity and thus the application for eligibility to get the green light for approval is bogus. We are talking about installations that can't generate more than 10 kw - and more likely would only generate 5 or 6 kw on a mid-summer day, with the bulk of that energy being consumed by the home owner's own AC unit (I'm sure) with little or none to spare to be injected back into the neighborhood grid.
Comments?
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
 We are talking about installations that can't

agreed, this is actually a bureaucratic economics or business problem and they are trying to call it a technical problem.
It isn't a technical problem.
Mark
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I would certainly be tempted by that deal. That's better than the long-term return of the stock market. There are, however, other factors. I would need to be convinced that the panels 1) would likely survive a hurricane and 2) their installation would not damage my roofing system.
Vaughn
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 04/04/2011 01:36 PM, vaughn wrote:

be extended to include cover for the panels. Why? Because if it does blow away in a gale or catch fire or whatever and they don't know about it, in the worst case the insurance could refuse to pay for the damage. The additional insurance for my roof panels costs here (Germany) €88 per year. There are cheaper offers but I preferred to use the same company for all the building related insurance to avoid any finger pointing problems in the event of a claim. It is possible that the insurer might demand that the roof structure be checked by a surveyor before you start work. As far as any damage to the roof during installation, a reputable installation/roofing company should in any case have professional liability insurance.
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

As long as the government can rob peter to pay you.

Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

There is still a peter being robbed at the government's insistence, dope.
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Well, we've degenerated to name-calling. I don't expect we'll see much more useful discussion from this thread.
Vaughn
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I can't help it if you don't like facts. harry *is* a dope.
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

After you have some experience with the group, Grasshopper, you will discern that calling Harry a dope is a statement of fact and not name-calling. In fact, dope is letting him off easy.
--
"Even I realized that money was to politicians what the ecalyptus tree is to
koala bears: food, water, shelter and something to crap on."
  Click to see the full signature.
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It can equally well come and go provided the distribution system that is there can handle it. It seems to me that if you have a distribution system that is already at 100% of it's capacity, then strange as it may sound, adding more generating capacity and putting it onto that part of the system could exceed it's capacity. Now it would seem unlikely that taken together all the solar panels in that particular problem distribution system could be generating a net addition to the system during peak demand. In other words, if it's 100F at 3PM, what would happen? Would everyone with solar have their AC on and be either taking power from the grid or at least not giving it back? Or because of being paid 80C a kwh to generate electricity, will people be putting in large systems and leaving their AC off? If the latter, then it would seem to me that taken together enough solar panel systems could put more power into the distribution system than it could handle. Certainly given the small penetration of solar, you would not think a few more would really matter, but at some point, they do start to add up.
It's also possible that just like with national electric codes there are some codes or rules that apply to electric utilities that say in essence you can't ever allow more than X generating capacity to be connected to a grid with certain characteristics, regardless of where it comes from. Could have been put in place before anyone thought of small solar generators....
Now is that the real reason behind what's going on? Don't know, but it's certainly theoretically possible.

Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
" snipped-for-privacy@optonline.net" wrote:

Under the terms of the Ontario Microfit program, you (the home owner) with a (typical) 3kw to 6kw solar array, will be paid 80 cents /kwh for 20 years. The going rate for buying electricity in this market at the residential level is (when you factor in all the various transmission and delivery costs) about 15 cents / kwh.
You are paid 80 cents / kwh for *any* electricity leaving your array (a billing meter is installed right after your invertors). It doesn't matter if your own home (AC unit, etc) will suck 100% of that solar energy with none of it going back into the grid. In fact, it's probable that on that hot summer day that your home will still be pulling energy from the municipal grid - just not as much because of the contribution from your own panels.

There has been some mention of a PF (power factor) issue when it comes to these panels.
But still - you can't push more electricity onto a network than the load is asking for (given that your invertors are functioning correctly I guess).
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 4/4/2011 9:16 AM, Home Guy wrote:

One issue that utilities worry about is the available fault current. The breaker main in a typical home might be able to safely interrupt as much as 10 kA. The current of a dead short in your home is a function of the sources feeding it. If the total is less than 10 kA, the breaker opens and everyone's safe. If the sources could feed more than 10 kA, the breaker may fuse/melt and the fault will continue to draw current and your house burns down.
So when adding new sub-station equipment and generating units, they have to calculate the available fault currents and make sure it's still under the breaker/protection equipment capabilities.
All that being said, I can't honestly think a small grid-tie PV installation would make enough of a difference to be a problem. Worst case is your neighbor has a fault and the combined current from the utility and your PV setup exceeds his breaker's interrupting capacity.
But a good EE could sharpen his pencil once and do the calcs and probably find there is a wide margin between what the pole transformer can supply to a fault and what your PV system would supply. They're probably just to worried about their liability to bother.
daestrom P.S. Maybe if every household in a whole development had such a microFIT installation? I'd have to see the numbers though to believe it.
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"daestrom" wrote in message One issue that utilities worry about is the available fault current. The breaker main in a typical home might be able to safely interrupt as much as 10 kA. The current of a dead short in your home is a function of the sources feeding it. If the total is less than 10 kA, the breaker opens and everyone's safe. If the sources could feed more than 10 kA, the breaker may fuse/melt and the fault will continue to draw current and your house burns down.
So when adding new sub-station equipment and generating units, they have to calculate the available fault currents and make sure it's still under the breaker/protection equipment capabilities.
All that being said, I can't honestly think a small grid-tie PV installation would make enough of a difference to be a problem. Worst case is your neighbor has a fault and the combined current from the utility and your PV setup exceeds his breaker's interrupting capacity.
But a good EE could sharpen his pencil once and do the calcs and probably find there is a wide margin between what the pole transformer can supply to a fault and what your PV system would supply. They're probably just to worried about their liability to bother.
daestrom P.S. Maybe if every household in a whole development had such a microFIT installation? I'd have to see the numbers though to believe it.
-----------------
The fault capacity of a household main breaker or fuses is not an issue, unless very old technology, like you. One hundred feet of twisted triplex supply cable limits faults to well within the fault tolerances.
On a commercial installation or multiple dwelling installation this can be a problem with main breakers / meters bolted to a huge supply bus or less than 10 feet of conductors but the fault capability spec. requirements are typically increased to accommodate the huge fault levels available.
mike
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 4/6/2011 19:31 PM, m II wrote:

Got some numbers/calculations to support that? Is that including the next door neighbors with their PV installation?
daestrom
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"daestrom" wrote in message
On 4/6/2011 19:31 PM, m II wrote:

Got some numbers/calculations to support that? Is that including the next door neighbors with their PV installation?
daestrom
-------------------
Sure! Basic Ohms lawa and a wire resistance table
http://en.wikipedia.org/wiki/American_wire_gauge
A 200 ampere service running 240 Vac and only considering the straight resistance of copper (many use AL outside conductors these days). and considering the street transformer as an infinite current supply (0 Ohms impedance)
The chart shows we would use 2/0 copper (assuming solid copper, but it won't be)
In a 100 feet of overhead run to a house, down the stack and through the meter to the main panel, where the fuses or breakers are, not considering the impedance of the overcurrent devices (that allegedly cannot handle a fault this big) we come up a with a minimum copper resistance of
200 feet (has to return) x 0.07793 x 10^-3 Ohms / foot (oh look ...your old units too) = 0.015586 Ohms
Using 240 Vac as the fault supply (it won't be under a faulted condition) the max fault current would be
240 Vac / 0.015586 Ohms = 15.4 kA.
Now we haven’t figured in any of the other impedances (very generous) and any approved O/C device in a panel these days is rated at 100kA. The old "code" fuses were 10kA and no amount of lowering the impedance of the grid source using a PV generator attempting make it lower than 0 Ohms impedance is going to increase that fault current. In real life this fault current would be below 5kA after connection impedances, transformer winding impedance, primary impedance, ferrous openings, smaller conductors used by the utility that uses free air rating on smaller conductors, etc.. etc...
Engineering people do not worry about fault currents at residential services unless special circumstances apply, like within a few feet of a commercial busbar splitter without enough wire in between. Then they know how to close their eyes and say "Nobody told me."
Mike
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 4/10/2011 22:12 PM, m II wrote:

Only problem with that is that many home service panels use breakers with an AIR of only 10kA, not 100kA. (my old house, built in 2000 was 10kA, and my new one, built in 2010 is also 10kA, both perfectly correct by code)
Here's are some modern service panels that come with 10k AIR breakers. http://static.schneider-electric.us/assets/DIGEST/load-centers.pdf
And how many homes in the utilities service area are even up to current code? I'd bet many homes in many service areas have only 10kA AIR.
The utility that is being ultra-conservative may have to consider that older homes in their service area may not even support this.
Can you just imagine the hue and cry when some homeowners are told they have to spend a couple hundred bucks to upgrade their service panel because of changes in the utility's distribution?
daestrom
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"daestrom" wrote in message Only problem with that is that many home service panels use breakers with an AIR of only 10kA, not 100kA. (my old house, built in 2000 was 10kA, and my new one, built in 2010 is also 10kA, both perfectly correct by code)
Here's are some modern service panels that come with 10k AIR breakers. http://static.schneider-electric.us/assets/DIGEST/load-centers.pdf
And how many homes in the utilities service area are even up to current code? I'd bet many homes in many service areas have only 10kA AIR.
The utility that is being ultra-conservative may have to consider that older homes in their service area may not even support this.
Can you just imagine the hue and cry when some homeowners are told they have to spend a couple hundred bucks to upgrade their service panel because of changes in the utility's distribution?
daestrom
-----------
Well that situation would be unfortunate and impossible to regulate as `legal, not conforming`
This is not a problem here as 10kA hasn`t been passed for many years. I believe any Canuck panels have to to have the class `R`or rejection fuse holders so that only the nasty electricians can force an old `code` fuse into the holder. The 100kA fuses have been promoted for a few decades with the seriousness getting more severe in later years. I thought they were actually not allowed, here, anymore. This may be incorrect. More research would be required to verify.
Either way the 10kA doesn't take much more impedance to drop it down with a few added factors mentioned in my previous text. Most of our service feeds are (ACSR) aluminum conductor, steel reinforced, and present higher impedances. I don`t see some small cogen circuit at the end of a few hundred feet of grid (mine plus yours) being a fault capacity concern in a residenial environment.
Having said that I guy up the street is just finishing installing 200kW or more of PV panels. Wait until they produce nothing all winter as they were snowed in most of last winter being at a low slope. The hook up wasn't`t completed so he won`t find out until next winter...LOL See how much harmonic crap we get on the street when they go online.
mike
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1
On 11-04-11 07:45 PM, m II wrote:
nothing
-----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux)
iQEcBAEBAgAGBQJNo7PoAAoJEJXfKw5kUPt7+DwIAKqPxACmq2yuve0Jswhf4hQa 1bw47CtFB8qDx9ZlKF3OgpIwcbyIh7duLfAcQQPbw+tcVnT/hx7jeyj3ETlip0Og kk6/M41PNvaMfllzZdlDJ6lCg7MQ/kbsj6tPAuzy36SG4ly/wMgF6K/WpBT4bZuX cKuG1FV/Btwf9r0h+vJ6JiF5LMax0MogqNZWJ8H19H6mDNolbEutP/b0g9F6ELXH U/rokl7TDf/Viw7xLqhLtDDTifTPsXkyVFHG91GncyA7QGP/mSHz8U97Mp03BFno VX29hu/MHRjxnEY7SkAXOC49rvSHpEJVvCE4v188y2D8XYLGdXrgBrYtc//VSbI=bxJh -----END PGP SIGNATURE-----
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
harry wrote:

Our regional and municipal electricity distributors are not pointing the finger at the capability or specs of residential service panels or neighborhood distribution / stepdown transformers as the reason why they won't let small-scale (less than 10kw) roof-top PV systems to connect to the grid.
They are saying that the local sub-station doesn't have the "capability" to allow for a handful (or perhaps even a single) small-scale PV systems to be hooked up and they would need to "upgrade" the sub-station in some way.
For more about this, see here:
http://www.greenpowertalk.org/archive/index.php/t-13885.html
And less relevant, here:
http://www.canadianenergylaw.com/2010/06/articles/electricity/metering-discrepancy-first-major-snag-in-the-rollout-of-fit-and-microfit-projects /
All the arguments put forward here about why homeowner-operated PV systems (with nameplate rating under 10kw) are not being allowed to connect to the grid through their own bi-directional revenue meter have not addressed the issue as to how the connection of such a PV system can possibly affect or influence the operation of the regional municipal sub-station supplying power (at 20 kv?) to the neighborhood in question. The sub-station is "insulated" from direct exposure to any individual home by at least 1 step-down distribution transformer (in our case, a ground-mounted distribution transformer supplying maybe 20 homes - our electrical service runs underground - not on poles in our neighborhood).
There may not yet even be a single residential PV system that's been connected to the grid for the area being served by the sub-station in question.
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 4/11/2011 4:31 PM, daestrom wrote:

This is a fatal flaw in your argument. Transformers are not infinite sources. A utility transformer might supply a fault current 20x the rated current (for a "5% impedance" transformer). (While a transformer will supply a fault current larger than the rated current that is not likely with PV. PV is basically a constant current source.)

Using a real transformer houses will have far less available fault current.

Cite where 100kA is required.

I agree that is very likely. One reason is that a higher rating is not necessary.
(SquareD, if I remember right, has a rating of 20kA downstream from both the main and branch circuit breaker.)
I doubt many Canadian house panels have fuse protection, or are different from US panels with circuit breaker protection rated around 10kA.

The interrupt rating required goes up with the service current rating. For a house, the utility is not likely to have over 10,000kA available fault current. The transformers become too large, many houses are supplied with longer wires and higher resistance losses, and the system is much less safe.
I believe it would take a rather massive amount of PV installations to cause a problem. The PV installations would all have to be on the secondary of the same utility transformer. The transformer is then not likely to support the PV current back to the grid. If the fault current is 20x the transformer full load current, and the PV current is equal to the transformer full load current, the PV supply would increase the fault current by about 5% (assuming the inverter doesn't shut down). If there were too many PV installations the utility could put fewer houses on a transformer. Seems like a problem that is not that hard to handle for the utility, at least until PV generation becomes rather common.
--
bud--

Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.