I read a fascinating article on renewable energy the other day. Well worth a read; the author, Judith Curry, is highly qualified.
In essence - most of us in the UK point our solar panels south in order to maximise PV generation, rather than west to better match the late afternoon / evening demand. The mismatch between solar generation and demand creates this demand curve, which the National Grid is forced to deal with:
As you can see, our panels generate peak output around the middle of the day, but ramp down just as the evening demand ramps up, creating a "mega ramp".
Take the graphic with a pinch of salt, because (1) it was created in 2013, when the actual curve was shown by the slightly less dramatic blue line (I haven't found a more up-to-date graphic to say if the brown estimate lines are actually what we're experiencing now), and (2) it shows the load for sunny and presumably more PV-equipped California!
The article does touch on the tools that utility companies can use to try and regulate demand, to an extent... but I can certainly see how adding more and more south-facing panels may not be great for our infrastructure.
I have a SolarEdge inverter which tells me how many lorries' worth of CO2 I've saved and how many trees I've "planted". However... if I (and everyone else) generate 5kWh between 11am-3pm, will some power plant somewhere actually generate 5kWh less? The article suggests that one "coping mechanism" is that traditional power plants can be required to stay online, so that they are ready to jump in during the big ramp. Are they actually burning any less coal?
As I mentioned, that chart is based on data for California. Does anyone know what the situation is like here in the UK, or how our National Grid copes with the load? Do we have a duck curve? To what extent do we store energy in this country? Adoption of solar isn't especially high here, but the feed-in-tariff degression is encouraging more and more people to put up solar panels, mostly south-facing, and mostly exporting the majority of their peak demand... Are all these new solar panels actually benefiting the environment, or just causing pain for the grid while costing the energy suppliers money?
Are solar panels actually that "green"?
Re: California Duck Curve - in the UK?
On a closely-related note, see Trystan's recent blog post, Understanding zero carbon energy systems: Energy storage (part 1) - Trystan / OEM team, if you're reading this, I'd be interested to hear your thoughts!
Re: California Duck Curve - in the UK?
To add to this "duck curve" many of us run excess PV diverters and each morning as the sun comes up, every last bit of PV is used to heat our DHW during the AM mini-peak rather than easing the load on the grid, which then reaches temperture just in time for the peak generation and low use period.
Perhaps when power storage solutions improve sub-stations can be kitted out to act as local powerbanks charged during high generation to take the edge off the PM peak, the remote locations of the substations would heavily reduce the strain on the main grid and allow for a slower reaction to demand peaks so powerstations can go into a low gen mode.
Some time ago there were some posts on a pilot storage solution involving strategic geographic positioning of mobile battery trailers, I wonder how that panned out?
Paul
Re: California Duck Curve - in the UK?
We have very similarly shaped graphs in SE Queensland. This one is from one particular 11kV feeder on the same day over 4 consecutive years. By 2014 they had about 40 11kV feeders that actually dip below 0, i.e. run backwards in the middle of the day. I'd imagine there are even more that do that now. Those two late evening mini-peaks are them turning back on the remotely controlled loads (hotwater, pool-pumps etc) after the real peak has subsided.
You can also see PV has done nothing to alleviate peak load, which is what they have to build their network for. Although it has put a big hole in overall consumption. Fixed network costs used to be built into the kWH unit price but that model is starting to strain as more and more people buy way fewer kWH, but still expect to be able suck as many amps as they want come 6pm. That's the so-called "death spiral". Here they're moving towards much higher daily fixed-charges that you pay just to be connected to the grid, whether you use it or not. So the next stage of the death spiral is to get some batteries and get off the grid altogether, although I don't think that's cost effective... yet.