Risks of Going Solar

On February 22, 2016, Catherine Wolfram posted the blog Risks of Going Solar on the Energy Institute at Haas blog, part of the University of California Berkeley.  I posted the following, which I am adding to my blog.

Of the various regulatory Risks of Going Solar, Catherine Wolfram identifies two biggies, reducing the size of the net metering interval and shifting the rate design to include a smaller energy charge and a greater fixed charge.  But the risk of these two can be much larger than Dr. Wolfram suggests.  Reducing the size of the net metering interval exposes rooftop solar customers to the possibility of negative prices, while cost re-classification could result in (greater) demand charges instead of greater monthly customer charges.

In “Renewable Electric Power—Too Much of a Good Thing: Looking At ERCOT,” Dialogue, United States Association for Energy Economics, 2009 August,[1] I point out that a surplus of wind in West Texas forced the wholesale price for electricity below zero for about 25% of the pricing periods during that April, at least in West Texas.

Transmission constraints generally kept these negative prices from spreading to the rest of Texas.  Negative prices did spread to other parts of the state for just less than 1% of the rating periods.  As Dr. Wolfram well pointed out, these pricing periods are sometimes as short as 15 minutes (as they were in West Texas at the time), though are often one hour.

Many ISO do not seem to allow prices to go negative.  In West Texas, the combination of transmission constraints and the various credits[2] given to wind led to negative prices.  I believe that similar combinations elsewhere will force ISOs to allow negative prices in their dispatch programs.

I have long seen the need for utilities outside the footprint of an ISO to implement real time “value of solar” prices that are similarly negative.  Hawaii seems to be ripe for such negative solar prices.  Utilities outside the footprint of an ISO can implement “value of solar” prices using a Walrasian auction, as is discussed in many of my articles.

I actually disagree with the concept of a separate price for “value of solar.”  If we are to use prices to influence generation, there shouldn’t be a separate price for solar versus other spot generation imbalances.  A different price for unscheduled versus scheduled generation, yes, but not a separate price for just solar.

There will often be many prices during any pricing interval.  For instance, a single 15 minute period may be part of a 24×7 contracted delivery of power with one price and part of a 16×5 contracted deliveries with another price.  A third price might be applicable to variances.  Variances would include both solar that is dumped into the system and hiccups in the 24×7 or 16×5 deliveries, whether the hiccup is positive or negative.

Utility rate making often includes the concept of cost classification, where costs are identified as energy related, customer related, and demand related.  In the context of Risks of Going Solar, customer related and demand related are combined into the concept of a fixed charge.

The discussed increase in the monthly charge is only one way to reduce the energy charge.  The other way, and I believe a better way, to decrease the energy charge is to increase the demand charge, or to implement a demand charge when there is not a demand charge in place.

Customer charges impose greater burdens on small, often lower income, residential customers, while demand charges tend to protect these smaller customers, as is discussed in

  • “Curing the Death Spiral,” with Lori Cifuentes (Tampa Electric Company), Public Utilities Fortnightly, 2014 August;[3]
  • “Demand a Better Utility Charge During Era of Renewables: Getting Renewable Incentives Correct With Residential Demand Charges,” Dialogue, United States Association for Energy Economics, 2015 January;[4] and,
  • “Fairly Pricing Net Intervals While Keeping The Utility Financially Healthy,” 48th Annual Frontiers of Power Conference, cosponsored by The Engineering Energy Laboratory and The School of Electrical and Computer Engineering, Oklahoma State University, Stillwater, Oklahoma, 2015 October 26-27.[5]

Thus, as we see a continued growth in solar, I see a growing need for finer pricing intervals and a growing need for demand charges.  Fortunately, the huge growth in interval meters allow these better rate designs.  We just need to political will to implement something other than a monthly charge for energy.

[1] http://livelyutility.com/documents/USAEE-ERCOT%20Aug%2009.pdf

[2] such as production tax credits and renewable energy credits

[3] https://www.fortnightly.com/fortnightly/2014/08/curing-death-spiral?authkey=54d8da5efd3f76661023d122f3e538b4b3db8c8d5bf97a65bc58a3dd55bb8672

[4] http://dialog.usaee.org/index.php/volume-23-number-1-2015/271-lively

[5] A copy is available on my website, www.LivelyUtility.com.

Billing Tweaks Don’t Make Net Metering Good Policy

Severin Borenstein published a blog on 2016 January 4 with the title of “Billing Tweaks Don’t Make Net Metering Good Policy.”  The entry reminded me of a presentation I had made in October at Oklahoma State, so I added the following comment to Severin’s Haas Blog.

Net Metering can be Good Policy for the recovery of some costs incurred by a utility in serving its customers, such as the cost billed to it by its ISO supplier.  But for the rest of the costs incurred by the utility, such as the cost of wires and meters, a demand charge and a monthly customer charge are more appropriate.

For the cost billed by the ISO supplier, the metering periods need to be aligned, an issue that is current before FERC in Settlement Intervals and Shortage Pricing in Markets Operated by Regional Transmission Organizations and Independent System Operators, FERC Docket No. RM15-24-000.  If the ISO is billing the utility based on fifteen minute intervals, it might be good policy for the utility to bill the retail consumer for those ISO costs on fifteen minute intervals using net metered amounts during those fifteen minute intervals.

This net metering paradigm seems to be only appropriate for the charges coming to the utility from the ISO, as I discussed in “Fairly Pricing Net Intervals While Keeping The Utility Financially Healthy,” 48th Annual Frontiers of Power Conference, cosponsored by The Engineering Energy Laboratory and The School of Electrical and Computer Engineering, Oklahoma State University, Stillwater, Oklahoma, 2015 October 26-27.  A shorter version of this paper was published in Dialogue, United States Association for Energy Economics, 2015 September 1.  The full paper is on my web site  in the library under Conference Papers.

The majority of the cost incurred by an increasing number of utilities are incurred for wires.  A much better way to recover the cost of wires is a demand charge.  When the customer wants to have access to a specific amount of power, the customer can contract for wires access in that amount, which would be billed monthly based on contract demand.  Customers with poorer information about their power requirements can rely on a demand charge based on the interval with the highest net metered amount, generally fifteen minutes or an hour, though I have seen the interval being an entire summer month.  Customers who exceed their contract demand would pay for the excess demand through a multiple of the demand charge.

There are a few appropriate demand metrics, such as the customer maximum demand or more exotic demands such as the contribution to the distribution system peak or the peak on a subsection of the distribution system, all as discussed in the above paper.  We are still several years away from real time pricing of the distribution system, as I discussed in “Dynamic Pricing: Using Smart Meters to Solve Electric Vehicles Related Distribution Overloads,” Metering International, Issue 3, 2010.

Net Metering–Morphing Customers Who Self Generate

The U.S. Public Utilities Regulatory Policy Act of 1978 started a flood of non-utility generation, initially a few very large cogeneration plants and recently a large number of small roof top solar generation.[1]  The rapid growth in the number of small roof top solar generators requires the electric industry to develop a pricing plan that is fair to traditional customers as well as to the hybrid customers, those still connected to the grid but with some self generation.

Electric utilities support their pricing decisions with class cost of service studies  (CCOSS).  The CCOSS allocates the utility’s revenue requirement[2] to groups of customers, called classes.  Classes of customers are claimed to be homogeneous, such as being of a similar size, but more often as having similar load patterns.

Some costs in a CCOSS are allocated based on the number of customers, perhaps weighted by the cost of meters and services.  Fuel costs are allocated based on energy through the meter, though often weighted by the losses incurred to reach the  meter.  A large portion of the costs are allocated based on demand, the amount of energy used by the class during the times of maximum stress on the utility, or at times of maximum stress upon portions of the utility, such as on the generation, the transmission, distribution.  Utilities are concerned about recovering these demand related costs as customers morph from being a full requirements customer to being hybrid customers.

Electric utilities have long alleged that the homogeneity of residential load patterns allowed the utility to use energy meters, often called watt-hour meters, to determine how much each residential customer should pay each month.  The logic is that the allocation process brought costs into the rate class based on the customer’s demand.  Further, homogeneity means that the amount of energy through the meter is proportional to the customer’s demand.  The utility could collect roughly the right amount of money from each residential customer by charging residential customers based on their energy consumption[3] instead of charging residential customers based on the demand.

Charging customers based on energy allowed utilities to reduce substantially the cost of owning and reading meters without significantly distorting how the revenue to cost ratio from each customer.  At least until roof top solar substantially reduced the amount of energy that goes through the meter without necessarily reducing the customer demand.  Thus, with roof top solar, the revenue collected from the customer goes down greatly while the costs brought in by the customer demand goes down only slightly.

The growth in roof top solar coincides with the growth of Advanced Metering Infrastructure (AMI).  AMI often includes automatic meter reading and interval metering .  Automatic meter reading generally means replacing the person walking door to door with equipment.  The carrying cost of the equipment is often less than the cost of the human meter reader, allowing AMI to pay for itself.  Interval metering means collecting the amount of energy delivered during small time intervals, generally one hour (24×7), though sometimes on an intra-hour basis.  These interval readings are the demands in the CCOSS.

The intra-hour meter readings made possible by AMI would allow electric utilities to charge all residential customers based on their maximum demands, the determinant used in CCOSS to allocate costs to customer classes.  No longer would the utility have to rely on homogeneity assumptions in regard to residential customers.  The demand charge permitted by AMI would reduce the disparity between the lower revenue to cost ratio for residential customers with roof top solar relative to the revenue to cost ratio of standard residential customers.



[1] See

[2] the amount of money the utility needs to collect each year to continue functioning

[3] with a very inexpensive watt-hour meter