Home solar: exporting to grid and the "duck curve"

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kingdragonfly

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#237762 17-Jun-2018 11:45

Large scale what if home users export solar into grid? Also a video that talks about solutions, such as using electric cars to store power for home use.

https://en.wikipedia.org/wiki/Duck_curve

"In commercial-scale electricity generation, the duck curve is a graph of power production over the course of a day that shows the timing imbalance between peak demand and renewable energy production.

In many energy markets the peak demand occurs after sunset, when solar power is no longer available. In locations where a substantial amount of solar electric capacity has been installed, the amount of power that must be generated from sources other than solar or wind displays a rapid increase around sunset and peaks in the mid-evening hours, producing a graph that resembles the silhouette of a duck.

Without any form of energy storage, after times of high solar generation generating companies must rapidly increase power output around the time of sunset to compensate for the loss of solar generation, a major concern for grid operators where there is rapid growth of photovoltaics.

Storage can fix these issues if it can be implemented ... However, cost is a major limiting factor for energy storage as each technique is expensive to produce at scale and comparatively not energy dense compared to liquid fossil fuels."

"Vox ducked the issue"

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#2039109 17-Jun-2018 13:38

This is what time of day rates will solve. At the moment there is no incentive for people to shift their usage, so they will just keep using it how they feel.

Richard rich.ms

Aredwood

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#2039304 17-Jun-2018 22:49

Thanks for posting this. As whenever I say that large scale solar won't work, people just can't see the economics of the situation. Mainly that peak capacity has to be paid for somehow.

That duck curve has been present in NZ long before solar was widely available. And solar will just make it far worse.

I would like to see capacity based charges for power, combined with time of use plans. This will make off peak per unit costs really cheap. And in turn encourage tasks that are done with fossil fuels to instead be done with renewable electricity.

elbrownos

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#2039401 18-Jun-2018 09:04

Aredwood:

That duck curve has been present in NZ long before solar was widely available. And solar will just make it far worse.

How can you have a duck curve without solar?

neb

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#2040090 18-Jun-2018 22:11

richms:
This is what time of day rates will solve. At the moment there is no incentive for people to shift their usage, so they will just keep using it how they feel.

Time of day rates won't solve it for the vast majority of people, who are bound by work schedules. They come home, they cook dinner, they heat their house, they maybe have a shower, all of which uses a lot of power, and they can't change any of that no matter what the time of day rates do.

neb

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#2040091 18-Jun-2018 22:13

elbrownos:
Aredwood:

That duck curve has been present in NZ long before solar was widely available. And solar will just make it far worse.

How can you have a duck curve without solar?

That's simple, you get a witch and weigh her. If the duck curve weighs the same as the witch, it's a duck curve, and you get to burn it.

pdh

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#2040136 19-Jun-2018 03:10

It's not just solar that can make a curve look like a duck - it's the power consumption pattern in the community.
If it looks like a duck... then I guess it's a duck curve.

Power usage in NZ (and especially) Auckland has (for 50+ years) spiked in early morning and again in evening - as workers rise to prepare for the day, and get home to cook tea. We're not very industrialised - and we don't use much chilling (air conditioning) - so daytime power use is pretty low. Likewise, night heating isn't huge. As an engineer who's worked on power systems in other parts of the world, that's my take on why Auckland power curves (pre-Solar) look much more Duck-like than (let's say) California.

So, NZ Power Authorities need to hit their peak outputs near sun-up and after sun-down. Adding lots of Solar (ie: day-time production) is going to make the rises & falls in the baseline generation curves steeper - as California is discovering. Well, their politicians are discovering it - it's not rocket science ;-)

What's needed is a way to store the surplus day-time (solar) energy. Simple (but expensive) are batteries - eg: Tesla Power Walls. Cheaper, but not terribly efficient is to pump water back up behind Hydro damns - or store compressed air in vast caverns (Sweden). Many ways, none of them is great. As an example, last year Tesla's 'giant' battery facility in S. Australia cost about 50 M$A and can hold up Melbourne for 10 minutes (Tesla 129 MWh, Melbourne 6500 GWH annual).

That looks to me like about 1$A per person, per minute of storage. Anybody - please check my math... I'm still full of non-fun post-op drugs ;-(

So, there are no magic bullets in storage – until Elon’s built 5 more Giga Factories and we’ve all invested (individually – or societally) in about 2000 $NZ per person in batteries.

Just hope they last longer than the one in your cellphone.

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pdh

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#2040137 19-Jun-2018 05:05

Neb said:
Time of day rates won't solve it … and they can't change any of that no matter what … rates do.

Well, it does actually turn out to be very cost-effective to use pricing schemes to motivate consumers to change their consumption habits. Done all round the world – and here, for years.

In the early '80s, I was involved in upgrading many of the old NZ Power Authorities' ripple-control plants, which performed a very crude neighbourhood-wide power-deferral, by turning off hot water cylinders. This was, and for all I know still is, very commonly done here to reduce peak power requirements.

A HWC is just a mechanical battery – you put heat in when you can and take it out when you want.

There are many options for deferring power consumption – hot water, space heating, your dishwasher, clothes dryer, freezer & fridge. They all have some ability to provide their service ‘in time’ by using electricity at some other time of day.

You just have to be motivated to spend the time &/or $$ to make it possible.

I saw my first ‘Night Heat’ unit at my Uncle’s house in N England 60 years ago. Stores electrical heat into a big block of fire bricks and blows it out all day, the following day (if it’s asked to). Perfect device for storing energy in a non-electrical way.

Here in Auckland, I built a house in ’93 with lots of concrete slab – which slab I heated extensively from 11 pm to 6 am – when power was at a significant discount. That heat bank lasted all day. Obviously a few others started using cheap night power, because about 12 years later, when I lost two 7-day time switches to a power surge – my annual savings were no longer worth the $400 to replace them and I went back onto a blended day/night power rate.

In my calcs for a new house (second build in 25 years), my annual power consumption is roughly 1/3 for HW, 1/3 for heating and 1/3 for everything else (server, TV, toaster, jug, oven & other appliances). Lighting is now trivial (all LED).

So you can defer – pretty substantially and pretty cheaply – about 2/3 of your residential power consumption (HW & space heating) – plus other odds & sods. If you’re motivated…

Either you spend some effort + money to do it – or you pay (though higher KWh costs) for someone else to save it on your behalf. It’s a zero-sum game, the way we’re engineering energy nowadays.

tdgeek

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#2040150 19-Jun-2018 07:19

I agree, there is a lot of available time shifting. If you have solar PV, HW runs only in sun hours. Timers on fridge and freezer so they only run in sun hours. Winter, pre heat house during the day, Summer, pre cool during the day. Dishwasher and laundry, set on timers to run one after the other (if both used in one day, or stagger by day). Roast or slow cook meal? Run those for 8 hours to capture about half from solar. If you have solar HW as I have, you can remove a lot of HW from PV

The issue that @aredwood often mentions is lines fees. I gather much of these is built into kWh rates? So if solar was widespread, there would be a need to up the lines fees?

tdgeek

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#2040152 19-Jun-2018 07:42

Side issue (as some here will have PV) Is it difficult installing panels on a concrete tile roof?

Aredwood

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#2040174 19-Jun-2018 08:29

On the low user plans in Auckland. The lines fees are more than 10c per unit. And are by far the most expensive input cost that makes up your total per unit cost of electricity.

Because they make the cost of electricity so expensive. People respond by reducing their power consumption, and by getting solar installed. And the biggie - converting to gas. I'm a plumber and gasfitter by trade, And I have installed countless numbers of gas hot water heaters and gas cookers over the years. But only rarely has someone asked me to install an electric hot water cylinder to replace a gas water heater, or disconnect a gas cooker to allow an electric cooker to be installed. It's extra money for me, but really bad for the environment, considering how much extra carbon emissions you get from gas hot water compared to off peak heated electric hot water. But gas hot water saves people money compared to electric hot water. So they will keep on phoning me and I will keep on giving them what they want.

These reductions in power usage at a household level result in less lines fees paid, but hardly any reduction in operating costs to the lines company. As the network capacity required is based on peak demand. Not the total demand. Yet because we bill by total demand instead of peak demand, there is no incentive to time shift or reduce peak consumption Vs off peak consumption. So lines companies are stuck with falling revenues per household, but static or rising costs. So every year without fail, they have to increase their prices.

What needs to happen? Simple - we need a system of collecting lines fees that is not a per unit surcharge. Simplest option- A large fixed daily charge. This could be around $4 - $5 per day. Which might sound expensive, but your per unit cost would then be around half of its current price, and could easily be lower again.

Or capacity based charges. Smart meters can be programmed to limit capacity. So unlike what happened in the Turangi area, exceeding your capacity won't result in a bill shock. And would give the option of different capacity levels for peak and offpeak.

If we don't do anything. We will have forever increasing power costs, along with those who can afford to. Spending lots of money on switching grid power usage to gas or alternative systems like solar. While the poor will bear the brunt of most of the increased costs.

So yes - widespread solar would mean more expensive lines fees and therefore grid power under the current system. And having a non per unit fee means of collecting lines fees would also mean no need for any more so called solar taxes. And could potentially allow the return of net metered solar pricing plans.

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#2040181 19-Jun-2018 08:48

tdgeek:

Side issue (as some here will have PV) Is it difficult installing panels on a concrete tile roof?

Its all relative, but I don't believe concrete tiles are difficult to install panels on. It doesn't really matter.

I like the idea of storing the extra power in your electric car battery, but how does that work if your car is it work during the daylight hours. Maybe you run multiple batteries and swap them. So we need a modular battery system (come on EU, regulate this like usb chargers) then the extra cost of batteries get absorbed in the vehicle purchase.

A breakthrough in battery technology - lowering prices - would be the nicest development.

And we use additional renewable energy sources. Wind, Tidal, Geothermal, Hydro.

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tdgeek

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#2040186 19-Jun-2018 08:59

Dairyxox:

tdgeek:

Side issue (as some here will have PV) Is it difficult installing panels on a concrete tile roof?

Its all relative, but I don't believe concrete tiles are difficult to install panels on. It doesn't really matter.

I like the idea of storing the extra power in your electric car battery, but how does that work if your car is it work during the daylight hours. Maybe you run multiple batteries and swap them. So we need a modular battery system (come on EU, regulate this like usb chargers) then the extra cost of batteries get absorbed in the vehicle purchase.

A breakthrough in battery technology - lowering prices - would be the nicest development.

And we use additional renewable energy sources. Wind, Tidal, Geothermal, Hydro.

I read up on the car storage issue. In short, not all support that, you may need extra wiring in the home, but the kicker is, these car batteries are designed for infrequent charging, as compared to daily charging or movement or power. It will degrade them sooner. Unless that changes, its not really an option. Its ok for charge, drive 200km, recharge etc, but not for charge, use in home, charge, drive the next day, use in home, charge that night etc

elbrownos

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#2040187 19-Jun-2018 08:59

pdh:

It's not just solar that can make a curve look like a duck - it's the power consumption pattern in the community.
If it looks like a duck... then I guess it's a duck curve.

The duck curve is total load less solar and wind power.

It's the sun's path across the sky that makes it look like a duck.

If there's no solar then it won't look anything like a duck, hence it's not a duck curve.

MikeAqua

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#2040266 19-Jun-2018 09:56

Storing energy - the HWC as mentioned is an obvious candidate. I guess a second (much larger) HWC could power a hydronic heating system, but that's getting expensive. Is it possible to get water to air heat pumps?

What about over-cooling the freezer during the day. The it has less work to do later on. Probably minor.

Night-store heaters used to be a thing in NZ in the 1970s (my parents had one). But that was more about creating an environment for consumption of electricity: Convert people to electric heating, get them to pay for two meters, and reduce the pricing differential over time. My parents replaced ours with a log burner after a about 5 or 6 years.

Washing you can do during the day, but then no-one is at home to hang it out on the clothesline, so it has to wait until the next day, by which time it's a bit musty. You can do washing overnight, provided the noise doesn't disturb sleep and then hang it out in the morning.

Cooking - only in the oven or slow cooker and it's never a great idea to leave cooking un-supervised.

We wouldn't heat our house during a sunny day in winter as it gets very warm just from the sun. Any additional heating would make it uncomfortable.

Mike

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#2040300 19-Jun-2018 10:26

Aredwood: On the low user plans in Auckland. The lines fees are more than 10c per unit. And are by far the most expensive input cost that makes up your total per unit cost of electricity.

[snip]

What needs to happen? Simple - we need a system of collecting lines fees that is not a per unit surcharge. Simplest option- A large fixed daily charge. This could be around $4 - $5 per day. Which might sound expensive, but your per unit cost would then be around half of its current price, and could easily be lower again.

[snip]

This has been tried before (in the 1980s IIRC), but the Green Party led an attack on it because it badly disadvantaged poor people who had to pay the same $100/month as rich people; and because it removed most of (they said 'any') incentive to use less power since the marginal cost of usage was so low.

The problem is that they are right, but also wrong: from a lines company point-of-view, it costs pretty much exactly the same to supply your property if you use 5,000kwh/yr or 150,000kwh/yr.
So we end up with a situation where fixed costs are being collected from variable price elements, thereby giving dodgy price signals to the market and producing perverse outcomes.

I don't know what the 'right' answer is, it's a Hard Problem.

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