1-Family Residential Solar System / Maximum Size

[saladhawks]

The utility that I currently work for has an approval process for 1-Family Residential Solar Systems that limits the installed capacity to the average annual energy consumption for the previous 2 years of electric billing history.

I have recently "rejected" several such Residential Solar System applications, as the installed capacity was around 2-to-3 times the average annual energy consumption. Before trying to change my utility's approval process, I wanted to check for any "case histories" where allowing Residential Solar Systems with a capacity 2-to-3 times larger than annual energy consumption directly led to problems.

Note that the 1-Family Residential Solar Systems that I am refering to are all less than 10 KW capacity and are connected to the utility 120/240V, 1-phase, 3-wire secondary distribuiton system.

 

[DanDel]

It sounds like your company doesn't want any power coming back to the grid from these sources. This seems to be un-typical from what I've seen. I can't imagine any problems from this type of installation, unless they are worried about the individual residential service drop capacity.

 

[dpc]

I don't see why there would be a limit for technical reasons. Does this limit have something to do with who is paying for the systems?

I would think you would also have to consider the peak demand periods - just using average kW would be pretty limiting, since power demand goes way down at night.

 

[TLCPA]

I'm having trouble understanding your company's requirements. How are you comparing capacity (kW) to energy (kWh). If I am an average 500kWh per month customer, that is an average annual energy consumption of 6000kWh. To produce 6000kWh per year of photovoltaic (PV) energy I need to install about 2.74kW of PV.

 

[bacon4life]

Are they required to pay retail rates for the power? If so, I would not be supprised the utility would not want to subsidize residential solar applications. Still, it is hard to imagine any technical basis for the limit.

 

[TLCPA]

And if you include (in)efficiency you need a 3.5kW(DC @ STC) of PV modules.

 

[waross]

I can understand that a utility may want to limit the amount of energy returned to the grid. A large uncontrolled input may put the utility in a potential liability position in regards to available fault currents. But
I cannot see the utility restricting the size of an installation as the more capacity you have, the more time that you will be able to supply all of your own needs with less than full sunlight available.
Some suggestions;
1> Limit the size of the amount of energy backfed into the grid but not the size of the solar array.
2> Develop a requirement for a protection and control package for customers wanting to install systems up to the size of capacity of the service. A part of this package may be an amended tariff to allow demand charges on the account.
You may have a customer using very little or no power from the grid but with the ability to demand full load current from the utility with no notice should their solar equipment fail. The standard justifications for demand charges apply.
3> Customers wanting to install larger systems than this would be subject to a full engineering review of plans and protection packages on an individual project basis.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[stevenal]

I share TLCPA's confusion regarding the comparison of two different units. You may also wish to check your utility's policy against applicable law, since the solar energy lobby has been successful. (Google "net metering").

Does the "installed capacity" take latitude and panel alignment into account, as well as efficiency of conversion?

 

[saladhawks]

In reviewing this issue a little more, I think this capacity limitation may be related to the existing net metering policy for 1-Family Residential Solar Systems at the utility I currently work for. Specifically, at the end of each calendar year, the customer electric meter at each 1-Family Residential Solar Systems is "zeroed" out. Thus, if a 1-Family Residential Solar Systems was generating significantly more energy than it was consuming, they would not be getting credit for this generated energy. Sounds like another disgrunted customer call the utility is trying to avoid.

 

[stevenal]

That puts the calculation back on the customer, so you do not need to reject any plans. Is extra capacity worth the added cost? Customer will need to consider all the above plus hours of sunlight and number of cloudy/rainy days.

 

[davidbeach]

The utility I work for has the same zeroing out policy (per state rules) and we leave it up to the customer to not over install. Nobody will ever hit it just right on a regular basis, but how close they come is up to their calculations and isn't our concern.

 

[DanDel]

It's certainly not for too much fault current; the typical PV unit has a fault current maybe 2-3% higher than it's rated FLA.
Also, most of these installations require the meter be changed to a 'net' meter design, anyway.

 

[itsmoked]

I agree with the net metering aspect stated above many times. Let them provide all they want as the utility doesn't pay them for more than they use.

Now I think that is actually foolish of the utilities because they can mine their users for that valuable solar energy and credits if they instead did the standard net metering then continued to pay the customer a wholesale price above that. Many people with too much money would still put up vastly oversized solar arrays to "help the environment" as long as they could make some small amount, and not look like a sucker. Don't forget that the utility can still change "transmission charges" even if the customer net generated gobs of extra power.

It's interesting how the utilities are stuck in an ancient business model. I wish they'd get some entrepreneurial thoughts going.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[stevenal]

Keith,

The Oregon PUC requires the investor owned utilities to donate the avoided cost of excess generation to low income energy assistance. Greenies can save the environment and help their fellow man while reducing or eliminating their energy bill. Are they suckers?

Publicly owned utilities have the option of paying the customer-generator for the avoided cost as you suggest.

 

[davidbeach]

My company falls under those mandatory Oregon PUC rules that stevenal gets take or leave.

 

[stevenal]

Not much freedom here, still got rules from the board. My point is that no utility I know of is free to either stick to or unstick themselves from ancient models as Keith suggests. We are all highly regulated. In all cases the rules come about after opportunity for public input. Got a suggestion? Get involved.

 

[itsmoked]

Yeah, I can appreciate that. Good points too.

As to your first response, if the greenies understood that they were helping the poor to cover some of their bills they probably wouldn't feel like 'total' suckers.

It would still be better to pay them something to entice larger installs. I would expect large solar capacity in areas with heavy A/C loads would be a huge benefit to those utilities. Especially since the generation would be in step with their heaviest demands and nicely distributed too.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[saladhawks]

In continuing to review this topic, my only significant technical concern at this point involves the reactive power requirements of common residential Line Commutated Solar System Inverters. My notes indicate that common residential Line Commutated Solar System Inverters may require reactive power between 10 to 40% of the Inverter rating. Thus, as more-and-more residential solar systems are installed, the power factor at the utility sub will begin to be impacted.