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

Forums › Home Workshop DIY › Home solar: exporting to grid and the "duck curve"

1 | 2 | 3

341 posts

Ultimate Geek

#2040342 19-Jun-2018 12:00

Duck Curve – Eating Crow here…

Teach me to check my terms – even if I do think I remember their meaning.

As the Auckland curve does have that vaguely waterfowl look – bumps for tail-feathers & head with a trough in the back. Check out Transpower’s curve for Auckland yesterday 2018-06-19. Twin humps.

But the South Island curve is essentially flat.

So the nature of the community’s power usage does shape the curve – although solar will (almost) always exacerbate it as (you so rightly point out, the sun rises & falls predictably. Not so predictable is its contribution.

That’s the obvious downside of the major Renewables (Solar/Wind/Wave) and makes them a (practical if not political) liability for any Grid. Without copious energy storage, or more or less aggressive deferral of consumption, you have to provide 100% backup of the grid’s maximum consumption from non-renewable power stations for the inevitable day or even hour when it’s dark & still. Even our NZ hydro needs a coal/gas backup plan for that 10 year drought.

That’s where Melbourne’s 10 minute Tesla parachute is really useful, it lets them kick something into life, when the lights flicker.

The more energy storage we can afford, the more honestly useful our Renewable power becomes.

Hammerer

2476 posts

Uber Geek

Lifetime subscriber

#2040343 19-Jun-2018 12:00

elbrownos:

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.

If the graph looks like a duck then it is a duck.

The term "duck curve" or "duck chart" is generic and applies to any graph that looks like a the curve of a ducks neck, e.g. https://en.wikipedia.org/wiki/Duck_curve

The California duck chart is a specific application of the term that does relate to solar generation. In many discussions "duck curve" is now a shorthand for the solar generation issue just like solar is a shorthand for "solar generation" but the presence of solar generation is not the definitive requirement to apply the term.

pdh

341 posts

Ultimate Geek

#2040347 19-Jun-2018 12:06

Thanks Hammerer - I guess I can spit out a few of those dark feathers.

Hammerer

2476 posts

Uber Geek

Lifetime subscriber

#2040361 19-Jun-2018 12:29

pdh:

Thanks Hammerer - I guess I can spit out a few of those dark feathers.

Impressive - you beat me too it by seconds and included a graph. I had a NZ graph ready to go from yesterday's stats but was going to drop it into another post more focused on the NZ situation.

tripper1000

1617 posts

Uber Geek

#2040504 19-Jun-2018 14:37

PolicyGuy: 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.

It wouldn't be the first time the Greens stuffed something up through lack of good science.

It isn't true that it costs the lines companies the same irrespective of use volume - the system has to be geared to cope with peak load, so it depends on weather the load is constant or cyclic/spiking.

The lines need continually upgrading to cope with increasing peak loads (I'm talking not just local but national grid level as well) but the flat rate per unit charges don't bill the usage/users that contribute to this peak loading.

The present electricity charges are not right - if you time you hot water to heat off peak, you are not contributing to the problem and driving the need for lines upgrades (quite the reverse), but you are effectively charged an upgrade levy, and subsidise the people/usage that is driving the need for upgrades, encouraging more undesirable consumption. So the current billing system is making the problem worse.

kotuku4

483 posts

Ultimate Geek

ID Verified

Lifetime subscriber

#2040522 19-Jun-2018 15:01

F@*k the DUCK curve!

When installed PV I was allowed to install up to a 10kW residential system, now this seems to be limited to 5kW to reduce export. I have just under 5kW.

The export buy back rate was intially 25 cents and has dropped to around 7 cents now, so there is far less incentive to export.

With hot water diverter, washing during the day, etc there is little export in winter.

I am investigating battery storage to make even more use of self generation, and can see an EV in future. All nice, feel good stuff. But with rather long payback period.

pdh

341 posts

Ultimate Geek

#2040569 19-Jun-2018 15:18

kotuku4:

I was allowed to install up to a 10kW residential system, now this seems to be limited to 5kW

Was this restriction from Vector, your Power Supplier or the Solar Installer ?

I assume that this was the portion you were allowed to grid tie ?

If you were to add extra panels to run directly into HWC or battery banks - that would be outside the scope of those doing the 'allowing' ?

Equinox IT

Cloud spending continues to surge globally, but most organisations haven’t made the changes necessary to maximise the value and cost-efficiency benefits of their cloud investments. Download the whitepaper From Overspend to Advantage now.

kotuku4

483 posts

Ultimate Geek

ID Verified

Lifetime subscriber

#2040582 19-Jun-2018 15:49

"Was this restriction from Vector, your Power Supplier or the Solar Installer ?

I assume that this was the portion you were allowed to grid tie ?

If you were to add extra panels to run directly into HWC or battery banks - that would be outside the scope of those doing the 'allowing' ?"

I had Andrew from Sunshine Solar Blenheim around last weeks to adjust tempurature probe on hot water cylinder for power diverter, and he is to send me some information on battery controller and battery modules, a 4kW storage installed for $9000. Not sure it would ever pay back as I have such low power bills now, mostly fixed charges.

He metioned the 5kw limit in place now for grid tied, could be Marlborough Lines limit. And I can see the point, in my case the house is on a single pole 63 amp supply. I have a 4.9kW of panels and a 4.6 kW inverter.

Yes could install more panels and battery storage etc, to limit the export to approx 5kW.

kotuku4

483 posts

Ultimate Geek

ID Verified

Lifetime subscriber

#2040588 19-Jun-2018 15:54

kotuku4:

F@*k the DUCK curve!

I am investigating battery storage to make even more use of self generation, and can see an EV in future. All nice, feel good stuff. But with rather long payback period.

My point is we are not California, there are ways to use more self generated power, and in the south island this is not an issue. I think we should be more positive about our renewable power generation and use electricity wisely and move away from gas, oil and coal.

kingdragonfly

11190 posts

Uber Geek

Subscriber

#2040635 19-Jun-2018 16:52

kotuku4: I had Andrew from Sunshine Solar Blenheim around last weeks to adjust tempurature probe on hot water cylinder for power diverter, and he is to send me some information on battery controller and battery modules, a 4kW storage installed for $9000. Not sure it would ever pay back as I have such low power bills now, mostly fixed charges.

You might want to make sure it can disconnect from the grid in a power outage.

https://www.worldsolar.co.nz/blog/power-outages-and-solar

"...However, should the power go out, your solar system’s inverters are automatically shut off, to prevent surges that endanger power line repair workers. That means your home gets no access to the extra energy stored in the grid.

This is not the case with a system, that features Emergency Power Supply (EPS) capability. In a system like that, the battery remains in a constant state of charge. In the event of an outage, the grid is bypassed and power is drawn from the battery.

That means if the power goes out in your area, your lights will stay on. Depending on the battery’s capacity, by being careful with consumption, you might be able to meet your most important power needs at home for several days."

MikeAqua

7779 posts

Uber Geek

#2040637 19-Jun-2018 16:54

kotuku4:

My point is we are not California, there are ways to use more self generated power, and in the south island this is not an issue. I think we should be more positive about our renewable power generation and use electricity wisely and move away from gas, oil and coal.

We are in the South Island (Nelson) and would struggle to directly use a lot of self generated solar power. The house heats so well passively on sunny days that it's difficult to see us using solar for additional heating. Water heating to a high cylinder temperature would be about it.

Batteries would change the game considerably in winter - they could power a heat pump at night. In summer not so much we just open the doors and use insect screens

Mike

neb

11294 posts

Uber Geek

Trusted

Lifetime subscriber

#2040674 19-Jun-2018 18:00

pdh:
Well, it does actually turn out to be very cost-effective to use pricing schemes to motivate consumers to change their consumption habits.

That only applies to the sorts of people who read this forum: Hardcore geeks, technically knowledgeable, plenty of disposable income, and with the time and resources to make the necessary changes and deal with e.g. a load of washing being ready at 4am. Try asking the person at the supermarket checkout, or petrol station, or coming over to fix your leaky tap, whether they've got the time and motivation and finances to do this sort of thing. Look at the most basic no-brainer energy-saving measure possible, properly insulating your home. That only happened because the government made it mandatory for landlords and free for everyone else. Apart from the major energy-burners, which can't be changed because they're dictated by work schedules, how are you going to convince people to change their energy usage without e.g. giving everyone a free washing machine/dryer (because people won't be up at 4am to hang out the washing, so it'll need to deal with drying as well) with a built-in automatic off-peak timer?

neb

11294 posts

Uber Geek

Trusted

Lifetime subscriber

#2040676 19-Jun-2018 18:02

Hammerer:
If the graph looks like a duck then it is a duck.

Unless it looks like a dick and not a duck.

Aredwood

3885 posts

Uber Geek

#2040762 19-Jun-2018 21:02

PolicyGuy:
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.

Actually poor people are more disadvantaged by the current system of low fixed costs and high per unit costs. Reason - The marginal cost of using extra power is really expensive. So we end up with children freezing in cold houses, because the parents can't afford 25c+ per unit of power, so they can't switch on any heaters. Despite late night power being really cheap on the wholesale market, plenty of available lines capacity late at night, and that power being close to fully renewables.

Note also that poorer households tend to have more people in them on average than richer households. As poorer people need to split the cost of the rent. So even if the fixed fees are say $5 per day, it would tend to be split over more people. So the per person cost will still be affordable. And more people in the house typically means higher total power usage, so the household often won't qualify for the low user rates and the subsidies that go with them. Even if the power usage per person in that house is still quite low.

Rich people are easily able to afford to get solar installed, convert to gas, get a heatpump to replace electric resistance heaters. Poor people in rental properties can't do those things. So they get hit the hardest by high per unit rates.

elpenguino

3421 posts

Uber Geek

#2040785 19-Jun-2018 22:27

kingdragonfly: 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.

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"

We're never going to see network size battery storage solutions and that's because the energy required by a whole country (or city) is so ginormous it simply isn't practical. Using annualised NZ consumption as a starting point we need 4 GWhr capacity to run NZ for 1 hour.

The way I see it, wide spread PV usage has a future when grid connected in a place like NZ where hydro forms so much of the base load capacity.

Every Whr generated with PV saves water which can be used after dark. Hydro can be brought online within minutes so it complements other renewables like wind very well.

I can't see domestic battery being practical or economic for quite a while (or ever?) due to the capital outlay and the regular replacement costs but if you're connected to the grid, that can be your battery.

Most of the posters in this thread are just like chimpanzees on MDMA, full of feelings of bonhomie, joy, and optimism. Fred99 8/4/21

1 | 2 | 3