The perils of solar (did you know about all these problems?)

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By: SGN Staff

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Solar proponents claim that rooftop solar brings all sorts of benefits to utilities. Utilities counter that solar brings problems too. But unless you're an expert, you might not realize all the big-time challenges solar can pose to a utility once its penetration rate starts to climb.

 

So we arranged for two EnerNex experts to stop by with this eye-opening discussion of the technical challenges. Have you experienced any of these issues at your utility? Have you encountered other costs or problems not documented here? Use the Comment form to alert your fellow utility colleagues. - Jesse Berst

 

By Kay Stefferud and Bob Russ

 

California leads the nation in new solar installations adding over 400 MW in the first quarter of 2013. As California marches toward meeting its mandated Renewables Portfolio Strategy (RPS) target of 33% by 2020 and the Governor’s additional renewables mandate of 12GW, a number of challenges have arisen as PV and other renewables penetration rates have increased.

 

Projected capacity for California-wide customer-installed PV systems is projected to be over 3 GW by 2016. With SDG&E reporting a 3% monthly increase in solar capacity, PG&E reporting it has 25% of the nation’s customer owned rooftop solar systems, and SCE reporting greater than 100% solar penetration on some distribution lines, the impact of distributed energy resources (DER) clearly needs to be addressed. Protection schemes and real time operational procedures need be revised to accommodate rapidly increasing numbers of distributed energy resources.

 

The existing electric grid was designed and created to safely and reliably distribute power from a few concentrated power generation sources through highly monitored and controlled transmission lines to typically radial distributed loads. Distributed Generation (DG) puts new demands on the existing electric infrastructure by introducing electric generation sources distributed throughout the distribution grid.

 

Today’s power distribution networks have limited visibility, diagnostic, control and forecasting capabilities. Distribution grid operator’s visibility to distribution level PV is limited to either sites with integrated SCADA (generally larger > 1 MW), or assumptions based upon irradiance measurements at nearby locations. Operators are blind to locations with highly distributed PV and no communication or measurement of irradiance in close proximity. In addition, as penetration rates increase on distribution circuits, they introduce new challenges that range from reverse power flows, to inverter control loop feedback, to potential instability and sub-optimal performance. As solar PV systems proliferate, synergistic PV forecasting and control strategies can help not only integrate solar PV into the grid but can also help optimize local distribution grid performance.