Winter could pose solar farm 'ramping' snag for power grid

NYS winters could pose solar farm 'ramping' snag for power grid
From left, Jackson Siff ’19, Jeff Sward and Jiajun Gu, both doctoral candidates, examined ramping on the electric grid and land parcels for solar farms. Credit: Cornell University

By adding utility-scale solar farms throughout New York state, summer electricity demand from conventional sources could be reduced by up to 9.6% in some places.

But Cornell engineers caution that upstate winters tell a different tale. With low around midday in the winter, combined with solar-electricity production, New York's could face volatile swings of "ramping—which is how power system operators describe quick increases or decreases in demand.

"It's a very surprising finding," said senior author Max Zhang, Cornell associate professor at Cornell's Sibley School of Mechanical and Aerospace Engineering. "When are you going to have maximum ramping take place in New York? It's not going to be in the summer when the is the highest and the needs are more balanced. It turns out to be in the winter."

Said Zhang, a fellow at Cornell's Atkinson Center for a Sustainable Future: "When you have several days of sunshine in a row during winter, that causes the largest ramping on the power system in New York state."

The new paper, "Strategic Planning for Utility-Scale Solar Photovoltaic Development—Historical Peak Events Revisited," was published May 15 in Applied Energy. In addition to Zhang, co-authors are Cornell doctoral candidates Jeff Sward and Jiajun Gu, and Jackson Siff '19.

The energy industry's ramping dilemma—due to spikes in net load, which is the total electric demand minus renewable electricity generation—creates a so-called "duck curve." When people wake up and prepare for the day, it takes energy to run the house—and that becomes the morning peak. Since solar reaches peak production in the middle of the day, the net load lags.

When people get home from work in the evening, energy demands create a second peak. Thus, with a peak, a large lag and a second peak that slowly diminishes in the evening, the graphic curve of net load resembles a duck.

Ramping makes the grid less efficient, because system operators then must employ natural gas or other carbon methods to keep up with demand, Sward said. "This paper can inform regional development trends and could lead to the improvement of electricity transmission from upstate to downstate," he said.

"The increasing ramping requirement will be a challenge in pursuing our renewable energy target," said Zhang, "but it can be met with flexible resources, both in the supply and demand sides, as well as energy storage."

As part of the paper, Siff worked with David Kay, senior extension associate in development sociology, with Cornell's Community and Regional Development Institute to conduct spatial analysis of New York state land parcels in order to identify places where utility-scale could work best.


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More information: Jeffrey A. Sward et al, Strategic planning for utility-scale solar photovoltaic development – Historical peak events revisited, Applied Energy (2019). DOI: 10.1016/j.apenergy.2019.04.178
Provided by Cornell University
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May 29, 2019
Are those people generally COMPLETELY STUPID?
Have they generally considered even for one moment having some off-the-grid energy storage as being the OBVIOUS solution to that?
Have any of them ever heard of this thing called a "battery"?
I am relieved that the above article at least just once mentions "energy storage" albeit not as the OBVIOUS solution.

May 29, 2019
Are those people generally COMPLETELY STUPID?
Have they generally considered even for one moment having some off-the-grid energy storage as being the OBVIOUS solution to that?
Have any of them ever heard of this thing called a "battery"?
I am relieved that the above article at least just once mentions "energy storage" albeit not as the OBVIOUS solution.

May 29, 2019
Or they could support people to switch to electrical heating instead of gas/oil fired heaters. That would balance the load in winter easily.

It's a switchover that has to occur at some point in any case.

May 29, 2019
This comment has been removed by a moderator.

May 29, 2019
Batteries would make financial sense only if the utilities could rent the battery storage for the relatively short period of the day and year that it was needed -from say EV owners.
As efficiency in mini-split heat pumps approaches 5:1 over electric resistance heating adding a moderately sized mini-split to any home or business make a lot of sense but more often than not this efficiency is lost when the heating load is incorrectly calculated and a way oversized unit is installed in an attempt to cover the coldest day of the year so that the system runs at idling speed most of the time. Maximum efficiency is only achieved when running at full capacity. The solution is to install cheap resistance heaters for the few very cold days.

May 29, 2019
Ramping makes the grid less efficient, because system operators then must employ natural gas or other carbon methods to keep up with demand


That's an incomplete description. Ramping makes the grid less efficient because the net demand varies fast, so fast generators are needed - the fast generators are smaller once-through units like gas turbines or even marine type diesel generators that are built on land, just to absorb the rapid variability of renewables.

off-the-grid energy storage as being the OBVIOUS solution to that?


What is OBVIOUS isn't necessarily ECONOMICAL. Batteries are wildly expensive, and the required sizes for grid balancing applications outstrips the supply, making it even more expensive because the prices go up when you start building them in the required amounts.

May 29, 2019
-from say EV owners.


1) There are only a miniscule number EVs around, and the situation won't be any different for at least a decade to come.

2) The owners need to get a high price for the electricity in order to justify losing capacity for grid reserve, and the additional wear (shorter lifespan) for the batteries.

3) Even if you count all the cars in the US as EVs, it still won't make a very large battery.

May 29, 2019
For example, if you reserve 10 kWh off the top of the battery of every EV, and you have a million EVs, then you have 10 GWh of batteries - assuming absolutely everyone has their car plugged in to a suitable V2G charger during the time you need it.

Take all the cars in the US and apply the calculation. You get about 2.5 TWh of enegy storage, which is enough to back the US for up to 4 hours on average demand.

What you need is about 10 times more to begin to deal with the long term seasonal deficit/excess of renewable energy that happen on a monthly timescale. If all the cars were EVs, and they were always connected to the grid, it would just about deal with the one winter day when solar power comes in excess, but not the next day, and definitely not the next week.


May 29, 2019
The reason why the vehicles need to be plugged in all the time is because you want the other generation capacity to run at a steady rate (avoid ramping it) , and you want to discharge the reserve for the next peak.

So you capture 4 hours of peak solar output, and then you spend the next 20 hours discharging it at a steady rate, in order to capture the same peak again the next day. This only works if there's a charging cable connected to the car at all times - which won't be the case.

In fact, the cars will be least likely to be plugged in right during the midday peak in the first place, because that's when most of the traffic happens and people are parked at work, or at shops, etc. where they can't use the V2G system.

May 31, 2019
So that leaves us with pumped storage hydro or compressed hydrogen or molten salt or ammonia generation? Seems like there are plenty of energy intensive long term projects that could absorb a variable power excess and serve us well in the near or distant future.

California is contemplating reducing or cutting power to remote areas to minimize forest fires. Now that's a disruption and if folks learn to deal with it we may learn that the load is more flexible than we all assume.

Jun 01, 2019
So that leaves us with pumped storage hydro or compressed hydrogen or molten salt or ammonia generation? Seems like there are plenty of energy intensive long term projects that could absorb a variable power excess and serve us well in the near or distant future.


There's many ways to skin a cat. Problem is, you first got to catch and kill it.

Nobody wants to spend any money on these schemes, because they are all unproven and tend to be very very expensive - except for pumped hydro which is just very very expensive and politically inconvenient thanks to the greenies.

Now that's a disruption and if folks learn to deal with it we may learn that the load is more flexible than we all assume.


Of course folks will learn to deal with it - they have to. It's just that reducing the electric grid to 3rd world level of operation with rolling blackouts and randomly available power isn't doing any favors to the economy or people's quality of life.

Jun 02, 2019
Or they could support people to switch to electrical heating instead of gas/oil fired heaters. That would balance the load in winter easily.

It's a switchover that has to occur at some point in any case.


Not necessarily. The reason why they're not using electricity already is because it's too expensive. Natural gas costs a fraction of the price of installing electric heaters and storage boilers and paying for electricity. Likewise, the cost of domestic solar power and the subsidy structure means that it's not reasonable to use your own renewable energy - so instead of heating a water boiler for later use, people send the power off to the grid and cause the duckbill problem.

If solar energy was to be used for domestic heating, the most cost-effective way would be to use direct solar heating - not electricity - because it achieves many times the efficiency at a lower cost. See Drake Landing in Canada which does exactly this, producing 97% of the yearly heating energy.

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