Utilities Feeling Rooftop Solar Heat Start Fighting Back

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If you wonder why America’s utilities are rattled by the explosive growth in rooftop solar — and are pushing back — William Walker has a story for you.

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solarix

Re: Utilities Feeling Rooftop Solar Heat Start Fighting Back

Utilities are going to have to modify their business strategies, and solar inverters need to help stabilize the grid.
How about incorporate batteries or super-caps to deal with transients or at least limit backfeeding the grid when grid voltage is surging?

BB.

Re: Utilities Feeling Rooftop Solar Heat Start Fighting Back

Notice that the utility is balking at 9% of their load being supplied by solar (if I read the article correctly)... 10% was my SWAG at which point utilities were going to hit off on the solar switch for fast track installs.

The whole system is designed based on central power generation and distributed loads. With distributed power, a few percent of power sources is not going to affect much--But when the number gets larger (10%), it turns the entire engineering (and economic) model on its head. The normal power engineering assumptions simply do not apply anymore.

From an engineering/control theory point of view, GT solar does not stabilize the grid but actually makes it unstable.

It is a reasonable set of questions that the utility (and the regulators) need to answer. Sooner or later things will have to change. It cannot continue forever at current solar adoption rates.

-Bill

mike95490

Re: Utilities Feeling Rooftop Solar Heat Start Fighting Back

BB. wrote: »

......From an engineering/control theory point of view, GT solar does not stabilize the grid but actually makes it unstable....

Huh ? Sunny afternoon, loads skyrocket, generators and transmission lines maxed out, and you think that distributed rooftop PV generation will further destabilize a rickety system ? I only see it helping, by barely reducing the demand on the grid.

solar_dave

Re: Utilities Feeling Rooftop Solar Heat Start Fighting Back

mike95490 wrote: »

Huh ? Sunny afternoon, loads skyrocket, generators and transmission lines maxed out, and you think that distributed rooftop PV generation will further destabilize a rickety system ? I only see it helping, by barely reducing the demand on the grid.

The issue is that on a partly cloudy days the power output is all over the place, you go from pushing to the grid to adding load to the grid. No local buffer is really the issue.

BB.

Re: Utilities Feeling Rooftop Solar Heat Start Fighting Back

Yep--Loads are all very small to microscopic (from the grid point of view). "On average", the loads the utility sees are pretty stable.

Solar, to have net zero kill-a-watts, my house has to generate in ~6 hours what is uses (on average) in 24 hours. That means that my average load is around 300-500 watts, and my average solar generation is 2-3 kWatts. I went from an "average load" to a "open loop" generator that is ~4x or more larger than my historical loads. And when a front moves through, my generator will dramatically reduce it output. Much more than my loads would ever have changed. And my drop is multiplied by all the solar systems around me feeding the grid too.

And my loads, would cycle at a few hundred watts on and off (fridge, lights, TV, computers) and a few larger loads that I don't use that much (microwave, air compressor). But we get a small front moving through (a band of clouds a few miles wide and a 100 miles long, and my solar will drop by several kilowatts.

The "cheap plants" for a utility are the base load types (coal, nuclear, etc.). It can take 24 hours (or more) to turn one of those "on or off". In California, we have been building natural gas peaker plants all around SF Bay Area (and probably much of the state) to manage the growth and changing loads (and suck up all that "cheap natural gas" while dropping the use of coal). These guys can get going in something like 5 minutes (at least supporting loads--high efficiency probably takes more--just guessing).

Another good peaker is hydro--But big hydro (utility size) is getting a bad reputation for rivers and fish. And some dams are coming down now.

And, utilities, in general, do not have loads that they can turn on and off (water pumping for dams and irrigation can be used)--But it is not a lot.

There have been times when the wind is blowing and utilities guessed wrong on base loads where retail customers had a negative charge for power of a few cents per kWH (at least in the past decade--Don't know if presently it has happened).

In the last few years, we have had wind farms in the north west that had to pay the utility to take their power (utilities had no transmission capacity to export power to other regions where it, perhaps, could have been used). The only reason the wind turbines kept running was because their tax credits and subsidies were still higher than the cost to pay the utility to take the power.

If everyone wanted to feed Solar/Wind/Hydro/etc. into the grid and it was near the actual loads--It would probably change the entire model of a utility... Instead of just burning fuel (splitting atoms, etc.), they now would have to have control over large numbers of loads (your A/C, heating, electric water heater, stoves, etc.) so they could better match loads to generation.

And the utilities would have to figure out how to store/buffer power for short term needs (minutes to hours?)--Back to the experiments with flywheels, various large battery technologies, compressed air into old salt mines, pumped hydro, etc...

Many of the "cost effective" technologies today are geographically located (mountains/valleys/dams, salt mines, etc.). Something that can be used "anywhere" is going to be batteries, thermal, or something we may not have thought of yet.

In California, the peak solar (commercial solar?) is ~3,000 MW (for today, Dec 31), the load variation for most of the state of California is from 21,000 to 29,000 MW (morning minimum, 7pm peak). Add another 3-6 MW for GT (a SWAG)--And the variation in solar generation (roughly) equals the entire min/max load for the state.

http://www.caiso.com/Pages/TodaysOutlook.aspx#SupplyandDemand

This stuff is not easy to manage.

-Bill