Charging in future environment of excess solar power

Which Spectrum issue was that in? You'd know if your solar generation was "going to waste" because it would show up as a drop in your online generation log (you do have one, right?) But I don't see how the utility could "spill" your grid-fed solar power. It has to go somewhere, and if not used, would create heat in something. As I understand it, the grid operator has to modulate the power production of those sources they control - carbon-based ESCOs, for the most part, though I imagine they could also require wind farms to feather their blades to drop capacity, or tell hydro facilities to spill water. This is one reason utilities don't like residential power producers, they can't control them.

 

Hopefully one of our CA solar experts will chime in, but I suppose it depends on your specific situation (rate agreements). What makes solar pay out tends to be the ability to sell your excess power to the grid for a decent price.

 

Yes, at least here in the Netherlands, for now it is like that. They always give solar energy production priority and adapt the carbon-based production. You can see it as follows. The solar energy production you provide makes that they save some fossile resources (gas or coal or oil) and keep it in their storage for the times when it will be needed. So, these stored fossile resources form a buffer or energy storage capacity. This system can work as long as at least part of our energy production is carbon-based.

Charging when you can use your own solar power is quite satisfactory to do. I also often try to do that. An advantage is that electricity transportation losses are avoided, which can be up to 30%. When you charge in the night, usually the electricity comes from far, so then such losses apply.

However, there are also some limitations or drawbacks. For example, when you charge on the middle of the day and the car is in the sun for the whole afternoon with full battery, this affects battery life in a negative manner. So, then better charge as late as possible in the afternoon. Still better, if you don't need the car very early in the morning, you can charge from the (early) morning sun.

 

Not in California. Utilities are only required to buy back your excess power (totaled over a whole year) at wholesale rates; roughly 3-4¢/kWh.
In the instantaneous realm, you get credited at retail rates, though. So in effect, I can bank kWh during the daytime or in summer, and get them back at night or in the winter for no cost.

I can't find the Spectrum article the OP mentions, but I don't think the electricity ever goes to waste - there's nowhere for it to go TO! It would have to be dissipated as energy somehow. More likely, I think it can just cause electricity spot prices to drop, possibly even (briefly) to negative - meaning the utilities will pay somebody else to take their excess electricity. So even if we generate more than we use in California, there's probably somebody stuck in the clouds of Washington or Oregon that would be willing to buy our excess, if the price is right.

There's certainly a limit to that, of course. I did find some other Spectrum articles on similar topics - like how a large number of solar inverters in Hawaii were recently upgraded to help stabilize the grid. Most inverters today will just drop off if the grid seems unstable, but now theirs will help to restore stability.

In the long run, things will probably have to get smarter; plug your car in at night, and tell it "be charged by 8 AM". Or plug it in at work, and tell it "be charged by 5 PM"; let the grid decide when to schedule your car's charging to even out the load. Maybe even borrow some charge from your car for a little while and return it later. A friend of mine is working for a startup to make flywheel power storage for utility companies - the idea being that they will spin up the flywheel any time there's an excess of power (or prices are very low), and draw from the flywheel when demand peaks. There are tons of different solutions to storing energy - from pumping water uphill to storing molten salt (typically, from a solar thermal power plant)... I even heard of a suggestion to use refrigerated warehouses for energy storage or load balancing - when there's excess power, cool the warehouse from 0°F to -10°F, then when power demand is peaking, let the warehouse slowly warm up (or even recover energy from the temperature difference between inside and out).

 

....OK but that sounds like effectively getting good credit for the solar produced.

 

This "problem" has been suddenly thrust into the public domain by (surprise!) electric utilities with minimal infrastructure investments over the past 30 years. I've been reading that Australia has areas where no new solar installations are allowed. My friend from Hawaii reports that interconnections there are no longer allowed, or require years of waiting time.

The technical issue for utilities is being able to deal with huge swings in generation when clouds go by, causing alternate demand and surplus, and confounding traditional generating stations.

Silly me, I thought having too much electric generation from renewable sources was a good thing. Who'd have thunk it's now a "problem?"

 

In places like California, using excess /peak renewable energy to run energy intensive desalinization plants would be a good use.

 

Great idea. Actually, for those who have seen that solar plant near the CA/NV border off I-15, the technology isn't generating as much power as projected. This particular solar plant does not use photovoltaics; rather, they have thousands of mirrors on gimbals, controlled by computer, that direct sunlight to a tower where the redirected, reflected energy heats water into steam that turns turbines to generate power.

With slight modification, heating sea water to boil and running it through distillation tubing would seem to be a better use for this technology. One major problem, of course, is that reliable and intense sunlight can only be had miles from the shore of the California coast due to coastal clouding and marine layers.

 

I think that excessive solar power is elusive. All of solar produced power gets consumed by the grid - not that its' a bad thing. Solar power, rather than fossil fuel generated power is a step in the right direction. Getting to store solar in off-peak hours to be used in high-peak hours is the challenge - both storage and affordability.

DBCassidy

 

Alternatively, using technology to allow the large power generators to dynamically allocate during daylight hours.

 

The energy in an electric grid must be in balance meaning that all power generated must be consumed or stored at each instant. The load must be followed with generation. Solar can be considered base load generation. Typically Nuclear generation and Hydro are also base load generation along with wind.

Fossil fired generation, especially gas turbines are used to load follow and rise and lower as needed. Plant design limits how easily and efficiently a power plant can load follow. Some Hydro, like pumped storage or lake controlled Hydro can also load follow. The transmission system also plays are role because specific load pockets may create constraints both into the area and out.

So to answer your question it depends. In some systems the instantaneous price will give an indication if there really is an excess of generation because the price can fall to zero indicating there is too much generation at the moment. In general most systems peak load and cost during the day and really don't benefit by you charging your car during the day.

 

It's called the "duck curve".

Read about it here:

https://www.caiso.com/Documents/FlexibleResourcesHelpRenewables_FastFacts.pdf



The world is full of problems but we really do need more problems like this one. Right now this is really only a concern for a few days in spring and fall when afternoon energy use is modest and solar generation is significant but in the next few years it will become a bigger "problem".

What to do:

1. Direct grid energy storage. The grid has very little energy storage today. This will change. Someone mentioned flywheels. Large stationary utility-grade battery packs are actually becoming cost effective. California has already ordered 1.3 GW of grid energy storage by 2020-2024. Texas is considering 3-5 GW for their grid. This is mainly about grid reliability but also can help smooth the transitions between peak solar and fossil generation.

2. Indirect energy storage. Introduce off-peak time of use rates in the afternoon.... EV workplace charging. Somebody mentioned running desalination plants at peak solar generation. Maybe even hydrogen electrolysis for fuel cell vehicles.

I think we need more plugin cars to absorb that renewable energy....

 

The folks who keep the grid stable under continually changing conditions were thinking about the general problem long before I entered engineering school back in the 70s. Renewables such as solar and wind just expand an existing problem, a hard one that had no solid analytical solution when I heard about it.

Pumped hydro storage between reservoirs seems quite reasonable. Many folks don't realize that hydro on rivers is severely constrained by fish habitats, shoreline erosion, navigation, and recreational safety. The machines are quite capable of load following -- when I was in school, we were told the Grand Coulee machines could be spun up from a dead stop, energized, synchronized, locked in, and opened up to full power, in 60 seconds. But nowadays, that would kill a bunch of fish nests, wash away another section of road bank, drown a few kids playing along the river, and run some river shipping backwards.

 

The problem here in PG&E land that they mentioned was that they have a lot of older natural gas fired generators that take a long time to cycle, so it just isn't practical to turn them on and off on a daily basis. They do have some newer "peaker" plants that can be fired up to handle peak load, but they tend to be small supplemental plants. With solar in the mix, what they see is a peak in demand in the evening when people get home from work, after the sun has set, taking the solar panels offline.

 

Tesla's new home battery would also go a long way towards dealing with the duck curve. This also has the benefit of not needing electric grid infrastructure upgrading.

Most everyone who can afford solar could also afford to lease or own one of these batteries. Even a few hours of stored energy to use in the late afternoon to early evening would solve the problem. Plus this energy would be considered "peak" for those on certain rate plans and could pay for itself.

The batteries have apparently already been leased to customers of SolarCity, a renewable energy firm chaired by Tesla CEO Elon Musk, as part of a small pilot program. Customers were asked to finance a $1,500 down payment followed by $15 monthly payments for 10 years. That puts the overall cost of a 10-year lease at $3,300, or $27.50 per month.​

Tesla's home batteries may be leased, rather than sold​

 

In much of south O.C. the utility is So Cal Edison ... but the surrounding utility companies (LA & San Diego) are very similar. We often over-generate beyond our monthly grid draw. Our surplus is calculated the same way our grid draw is calculated ..... Tiers 1, 2, 3, or 4.
HOWEVER ... at the end of the "true-up" year, all surplus is paid at the 2.9¢ per kWh wholesale rate.
For example ... we may have in one given month surplus calculated for our Tier1 .... then Tier 2 ... then even Tier 3 - which is appx 30¢/kWh. For that month, the total surplus may be 1,000kWh's - which would credit us $200 ... or if we'd use that, we'd pay $200. But at the end of the true-up year - they'd write us a check for $29. Funny thing is, SCE is lobbying hard to NOT have to pay for ANY surplus ... and many states are already not paying for any surplus.
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There is one utility energy storage mechanism I would like to understand the tradeoffs better. That mechanism would be electrolysis of water into H2 and O2 during oversupply and then use fuel cell electricity generation at peak times. There have been drastic improvements in electrolysis efficiencies (MIT work) and fuel cells are widely understood. The conversions are direct and the infrastructure could be fairly minimal. Yet the devil is in the details and I have not encountered an in-depth look at the tradeoffs.

 

1st it takes a lot of electricity - much of which is non-renewables. And water? Cali is in a serious drought.
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