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Comment by mooism2 | Hacker News Reader

There are extra panels built into the site, so “when the plant is partially covered by clouds, the control system can actually call upon the portion of the panels that is not impacted” and recruit the extras there to make up the difference.

I don't understand. Why forego the extra power when there are no clouds?

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If I had to guess.

1) Maintenance - When not cloudy you can bring them on-line to cover the maintenance on other parts of the site.

2) They've designed for a fixed output under certain conditions so in effect they don't want to push more than 290MW but the extra panels help them not drop that too far.

3) Grid operators like plants this size to be capable of consistent output - similar to why some gas plants run with either one or the other turbine on but often not both (In the old days before successive governments trashed it the UK national grid aimed for an unused capacity overhead of 25%, this would cover maintenance, accidents, natural disasters etc, we are currently running with about 4% spare)

My only guess is that they are limited by the transmission lines.

Upstate NY has a lot of hydro and wind power, and actually produces more energy than it can export on a lot of days. The obvious answer is to build more high voltage transmission lines, but people are fighting them for two reasons: No one wants to live under the transmission lines, and when they build transmission lines next to your house your electricity gets more expensive because the cheap power being exported to the rest of the state.

I don't live quite upstate, but we already have a nuclear power plant; and our town supervisor is complaining about a plan to land a transmission line in the town not to far from it to export power from upstate to downstate (http://westpointproject.com/). The HVDC converter will buzz.

I imagine that this is just one of a number of uses of extra capacity. When we deploy servers, we don't like to run them at 100% for a number of reasons (extra capacity to handle spikes and failures, unpredictable behavior of components at full load, breathing room for planned maintenance, etc.). I bet a large-scale solar deployment is no different.

They are also in a better financial position if they can supply guaranteed power instead of variable power. If power fluctuates relative to the weather then energy traders get involved in your pricing and no one wants Goldman Sachs and Enron in their business.

The panels themselves are getting maximum sun and converting it into voltage no matter what. So the only thing you have to upgrade is the distribution wires, so they can handle the full panel output without being at capacity.

But I guess nobody wants to buy the highly-variable extra power. And it leaves them room to install storage in the future.

Shading can impact the power output of a string significantly. By dynamically reconfiguring the topology and effectively stringing together panels from various locations they can balance the power output in a nicer way.

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