Solar Power, EVs And The Duck Curve – How Are All 3 Related?

APR 29 2014 BY MARK HOVIS 50

Duck curve


This year Duke Energy has made the move toward eliminating net metering for PV solar generators. They have stated that solar generators do not carry their fair share of maintenance of utility infrastructure, which is true but only part of the story. In a recent Greentech Media article, Jeff St. John gives his explanation of the strain the Duck Curve, a graphic that illustrates the shape of net demand on the California electric grid given the impact of renewable generation. Richard Lowenthal , CTO of ChargePoint rebutted that the good news is that California has discovered that the Duck Curve is good for EVs (electric vehicles), and EVs are good for the Duck.

At first, utilities complained that EVs would be bad for the grid and could potentially cause it to crash. That was of course until they realized just what a cash cow EVs will be. For the most part, EV owners can charge at night in a market that has been non-existent to utilities in the past. Most EVs are programmable to delay the charge to a preset time even if the grid is not smart enough to control it. This part is easy to understand. The revelation is that the combination of solar and workplace EV charging is even better for peak load when done between 10:00 AM and 3:00 PM.

A Typical EV Requires About 13 kWh of Power On Any Given Day

A Typical EV Requires About 13 kWh of Power On Any Given Day

A Glimpse into the future

The US national average daily commute is 39 miles. A typical EV requires 13 kWh of electricity (under a $1.50 for many) for that commute which takes about 3 hours at a typical 220V level 2 charging station or 8 hours on a standard 110V outlet. Calculate your eGallon rate here.

The modern EV driver will start their day by driving to work on electricity between 6:00 AM and 9:00 AM. The ideal charging time will be between the hours of 10:00 AM and 3:00 PM to parallel future solar production hours, so solar power will offset this additional load on the grid. The EV plugs in but does not begin to charge until 10:00 AM when solar power kicks in to add the balance to the grid during these hours.  The added benefit is to fill the belly of the duck with extra load.


Vehicle to Grid in action

The EV driver leaves work between 3:00 PM and 6:00 PM. They plug in once again at home but do not start their charge until after peak hours ending around 9:00 PM and 10:00 PM. As battery life cycles improve, future V2G (Vehicle to Grid) technology, shown here and currently in use in Japan , the head of the duck is flattened even more with the EV giving back its excess energy to the grid at the most critical time for peak usage.

Now typically when power consumption drops around 10:00 PM the EV will add more revenue to the utility in a time sector that was previously low on consumption. The cycle starts over the next day.



The real cost to your power bill

Peak load determines how utilities size facilities for  generation and transmission. This has a lot more to do with your cost of electricity than maintaining the lines for transmission themselves. Without building to handle peak loads of the grid, blackouts will occur. Richard Lowenthal   states that California fuel cost  accounts for less than 5 percent of the cost of electricity, it is important to use the big costs of transmission and generation efficiently. This entails finding a delicate balance between building and maintaining no more infrastructure than is needed and encouraging customers to use every kilowatt-hour that is generated. So the flatter the curve is, the more efficient the grid is. A flattened duck means that consumers pay the lowest possible price for electricity.

What happened in California?

Richard Lowenthal further states since California has made such spectacular progress with solar generation, they now have no afternoon peak at all; the sun is brightly shining and generating electricity at just the time that the air conditioners need it.  The result is a glut of power at 2 p.m. and a reduced load after dark. So why do we care what is happening in California? California is clearly ahead of the curve in the raw number of EVs and solar installations. While every utility has their unique issues with transmission , generation, and potential solar radiation, it is worth analyzing the issues that have occurred in California.  We care because it is a glimpse into the future of what the combination of solar power and EVs can do toward lowering the number one cause to higher energy,  and that is lowering peak demand.

Why would we penalize good behavior?

EVs and solar go hand-in-hand. They are coming simply because the technology is the better mouse trap in both cases. The question is will we build incentives to reduce the real rising cost of electricity, which is the need to add  to generation and transmission to handle new peak loads? Embracing these technologies that reduce peak loads reduces costs for all electric customers. We need the infrastructure to charge vehicles during the day at workplaces and garages.  For our future load profile, we want plenty of daytime charging opportunities combined with solar power between the hours of 10:00 AM and 3:00 PM. This is the most credible path to lower electrical cost for all consumers.

What is the Alternative?

Studies have shown that one in three EV owners power their EV via solar with an increasing number considering the natural combination. Currently the most amicable relationship between solar providers and the utility companies is net metering. It is a basic concept where the power company buys and sells to solar generators at the same rate. This will always be the best practice for solar generators though until you consider the duck (peak load), not so for utilities. So what happens if utilities and politicians fight against net metering and other renewable credits? Remember now that one in three EV drivers are also solar adopters. If adopters of both of these technologies are penalized then they will most likely have no desire to help the grid and use their EV, or old EV battery, or future solar storage devices for their solar arrays.

How far away is a real battery storage solution?

google solar

Google Cloud Data Center in North Carolina

Residential solar and EVs are coming and so is battery storage. By now, most of you are aware of the modern day Edison and Henry Ford of our time, Elon Musk. Recently Mr. Musk has released plans to build a 5 billion dollar US based Giga battery plant capable of producing batteries equal to the current global output of all lithium batteries. The plant will serve two purposes. First it will supply batteries to Tesla Motors 2017-18 Model E sedan. Second, it will produce battery storage devices for residential solar at a fraction of today’s prices and we know when. Between 2017-2018. That is less than five years out.


The best solution for solar generators will always be a symbiotic relationship with utilities.  If we choose to penalize solar installations however, then the real disruption will occur when PV residential solar/EV owners elect to use their own storage opposed to paying penalties to the utility companies.

As an engineer and a current user of both of these technologies, I really wonder if the utilities have thought this through? If the solar/EV owners elect for battery storage, then the current utility argument that cost will be spread to all consumers has just gotten worse. Ask your current utility/politician to stay on point and answer the question to what is the number one cause of raising your power bill. The answer is, and always will be dealing with duck (peak demand). If the combination of EVs and solar can reduce peak demand by filling the belly and flattening the head of the duck, should utilities and politicians not support the solutions that benefit everyone?

The problem is pretty straight forward. The scenarios are good for everyone except the utilities. The solution controls peak demand for now, but is a long term loss of revenue for utilities and their investors as renewables expand. So the decision has been made by utilities to fight to slow the expansion. The problem is that the solar/EV genie is out of the bottle, and though battery storage is less desirable than a continued partnership with utilities,  battery storage may soon become more viable. The utilities are making a stand that it is not in their interest to host a future business model with a loss of revenue. Given the stand off,  it is likely solar/EV adopters will choose their independent path in the very near future. 

PVWatts calculator is a useful tool to analyse how much energy can be produced in your area. The benefits of solar vary by region and is not the solution to all energy needs, but clearly the combination of solar and EVs can have a positive, not negative impact on the duck.

Categories: Battery Tech, General

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50 Comments on "Solar Power, EVs And The Duck Curve – How Are All 3 Related?"

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I don’t see ‘potential overgeneration’ until the belly drops below zero. And even then, that is not a problem, that is a benefit. We should direct our excess generation up to Washington and Oregon such that they can use less hydropower during the day. And then when the sun drops down, they can open up the valves and create more hydropower in the evening.

Wind is also counter-cyclical to solar PV . . . it tends to generate more power when the sun is not shining.

You are assuming Washington and Oregon not only have reservoirs to build up water during the belly (it takes a lot more water than you think, and overly fluctuating levels aren’t cool for wildlife), but also that they oversized the generators to be able to generate more power than the average water flow allows.

Wind’s variation is far larger than its average counter-cyclical behavior, so if you had enough to counter the belly, then you’ve got much bigger problems.

Er, first, that ‘duck curve’ chart very odd-looking: compare its 2014 line with what is currently the case in California:
Not at all the same thing. Quite the opposite actually.

Indeed, the very GreentechMedia article linked above actually heavily questions this chart.

Last but not least, let’s also take a look at who’s now using this IMHO false premise to push for more public/daytime EV charging: Richard Lowenthal, who happens to be the CTO of… ChargePoint.


Wow, they really have 4.4 GW pumping out of solar right now? What region does this chart cover?

As to your “IMHO”, I beg to differ: looking down the road, we *do* want more and more solar, and eventually there’ll be net over-generation. EVs are a very easy way to capture that over-generation, and potentially (with vehicle-to-grid) release it back in 7-9 PM as the article suggests.

Yeah, between the the California Renewable Portfolio Standard and the massive growth in roof-top solar, California is really starting to pump out a lot of solar.

And it will continue to grow. I wish I had another house to install solar on.

Note that the CAISO web page only includes utility scale solar PV, net-metered solar (about 2GW worth right now) shows up as a reduction in demand.


Thanks for an excellent article.

As to the campaign to make solar the villain, this campaign seems to be DOA. It might make an impression on a stupid/corrupt politician or regulator here or there in the near future, but the public isn’t buying it. Rather, it prefers to buy more solar 🙂

Also, there are enough pro-renewable utilities around – in the US and around the world – and this too helps expose the hollowness and crassness of the “solar is a free-rider” campaign.

The anti-solar people succeeded in Oklahoma.

I pay ~$5/month for distribution fees plus the utility sells my excess electricity to my neighbors at peak day-time rates while paying me back with cheap excess power they have at night, so it is not like they are not making any money off my solar PV system despite net-metering.

Stop with the nonsense of your electricity being worth so much.

Utilities would make that sale even if you didn’t generated that electricity, and they would pay ~5c/kWh wholesale for a centralized plant to generate it. Your electricity is not worth more than that.

Net metering costs them 13-36c/kWh in revenue, but only saves them ~5c/kWh in costs (possibly less). This can’t last.

You can be in denial all you want, but the utilities WILL raise rates on people without solar if they can’t ditch net metering. The tier system is there to encourage conservation and give poorer, smaller households a break, not to represent the true cost of providing electricity.

No. They pay more than 5 cents/KWH at peak daytime. And they have to pay for transmission whereas I deliver the power right to my neighbor that uses it.

And yes, they do lose revenue from me since I no longer buy. Welcome to the free market, utilities! But they also don’t have to generate that power I use.

So between the arbitrage profit they make off my electricity and the $5/month I pay for distribution, I’m not a net negative like they portray.

They really don’t pay much more than 5c/kWh. Take a look at 2013’s wholesale data for Northern CA: No, they don’t save transmission costs. They need all those lines anyway. First of all, your solar isn’t going to help when there’s dark clouds or in the evening, so the wires need the same capacity and maintenance. Secondly, when everyone is working during the daytime and solar penetration goes up, there is less electricity consumption in residential areas, and your solar electricity is actually flowing out to commercial and industrial areas using those same lines. Your power is worth only 5c/kWh. Face the facts and accept it. You know what else happens in the free market? Prices go up when volume goes down but capacity cannot (your solar does not help with the duck’s head, especially during a cloudy week). Utilities will suffer minimally. Your neighbors will suffer much more. Fair pricing would be you paying a fixed cost for the grid, unless you want to go off grid entirely. Now, if you paid for your share of storage to shift your peak production from the duck’s belly to its head, then I’d say net metering is fair. I assume… Read more »

Yeah, the Duck graph is unduly pessimistic. It is being used to try to help strangle solar.

Solar definitely has a coincident effect, but the grid is not there for someone to use as a battery, and otherwise pay nothing (assuming they use ~3x more than their roof space). I’d be fine if the market dictated they get taking out a peak wholesale hour-ahead rate, but where I think net metering proponents are going to have their hands full is failing to see that utilities add value for their back-up function. The most enduring price regime will have regard for the market value of that service.

In MA, they’re trying to kill virtual net metering, in exchange for raising the ~4% name plate cap.

I use less than 1/3 of my roof space and I generate much more electricity than I need for both my house and my electric car. Granted I live in California. But solar really works.

Solar PV people do value the grid but the utilities bash the value of solar PV. The utilities sell the excess solar to my neighbors at peak day time rates and then repay me with cheap excess power at night. So the collect on that arbitrage. They also collect $5/month from me.

Maybe someday the utilities will need to be taken over by the government and they’ll just keep some reserve natural gas stations around to provide power when there is not enough wind/solar/geothermal/nuclear/hydropower/etc.


I don’t know where you are located, but 1,000-2,000 kwh/month customers, in detached homes are fairly common. It has a lot to do with HVAC, and climates. To support that demand on a standard 1,500-3,000+ square foot structure takes a good amount of space.

Northern California, 6KW system, ~1600 square-foot house. I’ve had the system up for 6 months now and I’ve got 1.6MWH of extra energy so far. I can easily expand the system to 8KW if I add another EV.

And if you are using 2000KWH per month then your house is crap. People need to design houses better with orientation, awnings, insulation, wind coverings, heating/cooling zones, weather stripping, attic ventilation, whole house fans, etc. That’s like all the people who buy massive SUVs and then whine about gasoline prices. You dug your own grave.

I have no idea why everyone thinks LIon batteries are the answer to solar storage. Lions are good for low weight per watt. Taking an average lead-acid battery against the power needed to replace a 24kwh leaf, I find $3100 (Rolls battery) in total. The key is WEIGHT. Last time I checked, nobody cares how much they weigh in a fixed, house solar application.

PG&E and others are pushing hard to eliminate net metering based on their fixed asset costs. Nobody in business wants to buy for the same price they sell at, they want to mark it up.

As that model gains traction, not only do new users install batteries to store their own fusion power and not take the markdown, but the solar installers start calling their old installed customers to see if they might be interested in keeping a bit of their power on premises. Its already happening. The power companies are pushing back against installations that involve storage.

Carried out to the end, we will see the power companies stating they have the right to charge a fixed fee for users who exit the grid. Then you will know we have reached the end game.

“I have no idea why everyone thinks LIon batteries are the answer to solar storage.”

I used to think this but I’m starting to change my view. For one, the prices of Li-Ions are coming down heavily. If they are down in the $200/KWH range, they are not far from Lead-acid. And Lead-acid batteries to go bad much faster, they can’t handle as many discharge cycles. There is also the Peukert effect in lead-acid batteries.

So if the price drops enough, Li-Ions are better than lead-acid because they’ll last longer and require less maintenance. It also helps a lot that they are less toxic.

I try and watch this, too, and often find economies described in the per mwh stored/sold values. There, I’ve seen commentary that $200/mwh is about the current market for power, where storage can work. This assumes some kind of margin above a cheap overnight rate (~$10-30).

$200/MWh has got to be in rare circumstances, not every day. You can look up hourly wholesale prices and generally price variation is minimal.

Here’s a sample from yesterday for New England:

There’s a roughly $30/MWh price differential between the low and the peak. I assume the daytime price can get as low as the overnight price if solar has good penetration.

Right, $200 isn’t an easy rate to find, but New England could have used some batteries during Q1, if true. To your point, back during Q1, the overnight price held higher than $30. So, it is difficult to state a market price where it works without establishing what the spread is.

If the duck curve is such a problem then SCE should change their TOU schedule. Sounds like the afternoon now has a surplus so TOU rates should not be high at Solar peak output.

What happens when the hockey stick hits the duck curve?

You get the Mighty Ducks?

Its great when solar can contribute to peak shaving, although of course it would be very handy to enable this by having much more widespread installation of solar panels in workplace carparks, which additionally could provide shelter from the fierce summer sun and cool the vehicles, including the battery, passively as well as actively.

California should not be confounded with the US as a whole though.
The load patterns in New England, for instance, with its harsh winters as well as hot summers, are very different, with much higher demand when solar is at a minimum.

So solar is not a magic bullet, and should be deployed in association with other sources and with respect to the climate and demand in that region.

The cheapest way to store electricity is pumped hydro storage.

So if California or for that reason the whole coast has enough places and water to build pumped storage, all this discussion of storage batteries loses all sesnse right away.

There are a number of countries which have enough of the right geology to just forget about this battery application.

I live an hour north of Duke Energy’s Keowee / Jocassee / Bad Creek pumped storage complex. Jocassee’s generators can do +/- (generation/absorption) 610 MW, Bad Creek’s can do +/- 1065 MW. They can make a total swing of 2 x (610+1065) = 3350 MW, equal to the output of three big nukes, in minutes. For my region, the whole “duck curve” argument rings pretty hollow.

That is how wind and solar should store their power. That bad creek storage complex is ingenious.

The are not taking into account all the coffee makers and espresso machines kicking in at the belly of the Duck. The solution would be to drink more Java 😉

Also folks, notice the word “potential overgeneration”. It’s just a model.

Anyone else envision a future where our PV charges a spear EV battery during the day that we can swap out into the EV when needed? The battery can power the house at night or when PV is not producing enough.