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

[Home Guy]

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:

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.

According to this document:

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?

[Mark]

=A0We 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

[vaughn]

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

[trader4]

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.

[Home Guy]

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).

[Tom P]

Up front - you should in any case arrange for your building insurance to 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.

[Tom P]

------------------

The bark may be worse than the bite. The company who did my PV installation also did the entire beaurocratic paperchase for me. They sent me a whole pile of application forms to fill in, and I sent them all back with a limited power of attorney to let them get on with it.

I can understand that the grid operators need to know how many PV installations there are and how they are all connected.

[krw]

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

[daestrom]

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.

[m II]

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

[krw]

There is still a peter being robbed at the government's insistence, dope.

[Vaughn]

Well, we've degenerated to name-calling. I don't expect we'll see much more useful discussion from this thread.

Vaughn

[krw]

I can't help it if you don't like facts. harry *is* a dope.

[m II]

Please be informed that the Josepi clown has been forging my username for a few weeks now. His provider is doing nothing to stop the forgeries.

Check the headers when in doubt. It's times like these I wonder about the maturity levels of some, no doubt very ill, people.

mike

[m II]

Please be informed that the Josepi clown has been forging my username for a few weeks now. His provider is doing nothing to stop the forgeries.

Check the headers when in doubt. It's times like these I wonder about the maturity levels of some, no doubt very ill, people.

mike

[Kurt Ullman]

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.

[daestrom]

Got some numbers/calculations to support that? Is that including the next door neighbors with their PV installation?

daestrom

[Bruce Richmond]

Actually you can and do as I understand it. To pump power into the grid you supply a slightly higher voltage than what is in the line. When spread over all the loads on the grid the change in voltage is next to nothing. If enough inputs are made by others the voltage will rise, and it is allowed to so long as it stays within a certain range. If it is going to go too high it is up to the utility to reduce the input at sources they control.

[Han]

Bruce Richmond wrote in news: [e-mail]:

I have no idea how it works exactly, but here in North Jersey PSE&G has been putting up solar panels on their (I think) utility poles. Each one is maximum 200 Watts at 110V, feeding directly into the grid the poles carry. This is a link + picture in another town not too far away (1 line): or:

[David Nebenzahl]

On 4/4/2011 6:16 AM Home Guy spake thus:

and

Are you sure about that first statement? Pardon me if I misunderstand what you wrote, but don't you only get paid for the *net current* leaving your meter? If you're generating 5KW but "sucking" 6KW into your AC, etc., then you have a 1KW net draw, so you're not gonna get paid anything, correct?

That second statement is correct: you can't "push" electrons into the grid. But it doesn't matter *how* your inverters are working; it's a basic law of physics.