Two Lines. One Goal.

The RioSol Transmission and SunZia Transmission lines are the largest parallel energy delivery projects ever conceived in the United States. Throughout their development by SouthWestern Power Group, the two lines have been co-developed in their planning, permitting, and are even parallel in their routes. While they have a shared history, each transmission line serves a unique purpose toward a singular goal.


Flexible AC energy delivery

RioSol is a High Voltage Alternating Current (HVAC) line as compared to SunZia which is High Voltage Direct Current (HVDC). Alternating Current, or AC, is the most prominently used interstate transmission technology in the United States power grid. Homes and businesses utilize AC Power, and therefore AC transmission such as RioSol allows for economical interconnection of both electrical generation and electrical users at any point of the transmission line.


Efficient point-to-point DC transmission

SunZia a is High Voltage Direct Current (HVDC) transmission line, in contrast to High Voltage Alternating Current (HVAC) of RioSol. DC transmission is an emerging technology in the United States that excels at delivering significant energy over long distances (500+ miles) with low real power loss. DC is ideal for point-to-point energy transmission.

Shared Route. Distinct Purpose.

Rio Sol & Sun Zia Comparison

Eastern Terminus
Torrance County, NM (Planned)
Torrance County, NM
Western Terminus
Pinal County, AZ (Planned)
Pinal County, AZ
Approximate Distance
550 Miles
550 Miles
Predominant Structures Type
Lattice Towers
Lattice Towers
Maximum Tower Height
199 ft
199 ft
Type of Conductor

A Shared Development

RioSol Transmission and SunZia was conceived and developed by SouthWestern Power Group (SWPG), together along a shared route as they were known as Line 1 and Line 2. As their unique purposes emerged, each line gained their own identity and construction timeline. SunZia line 1 was sold to Pattern Energy who now fully owns it. 




Operation Begins

SWPG expects to complete construction and start operation of RioSol (Line 2).


Construction Starts

SWPG expects to start full construction of RioSol (Line 2).

Operation Begins

Pattern Energy expects to complete construction and start operation of Line 1.


$2.4 Billion Economic Benefit Report Published

RioSol will create $2.4 billion economic impact and generate 2,626 jobs. Read more about the report.


NMRETA development partner

SWPG and NMRETA sign a join-development agreement for RioSol line. 

Construction Begins

Pattern Energy expects to start full construction of Line 1.


Amended Federal Record of Decision

The Department of the Interior’s Bureau of Land Management announced a Record of Decision.


Line 2 renamed RioSol

SWPG renames Line 2 RioSol.

Line 1 Sold to Pattern

SWPG sells SunZia Line 1 to Pattern Energy.


Revised Draft EIS Issue

BLM issues the Draft EIS for the re-routed Project.


NMRETA development partner

SunZia and NMRETA sign a joint-development agreement.


Federal Permit is re-opened

SWPG submits an amended SF-299 to the BLM to re-start federal permitting for the re-routed portion of the Project.


Line 2 remains HVAC
Line 1 changes to HVDC

SWPG and Pattern Energy agree to change the technical basis for Line 1 from HVAC to HVDC with 3,000 MW of capacity. Line 2 will now be HVAC with 1,500 MW of capacity.


SWPG and US Military agree on re-route

SWPG and the Dept of Defense agree to re-route a portion of the line in NM that avoids the Northern Call-Up area, north of WSMR.


SWPG selects Anchor Tenant

SWPG selects Pattern Energy as anchor tenant for Line 1.


Arizona State Permit is granted

The Arizona Corporation Commission approves a Certificate of Environmental Compatibility for the Project.


Federal Permit is granted

The BLM issues the Record of Decision for the Project


FERC approves SunZia cost recovery

FERC approves SWPG request for negotiated rate authority of Line 1.


Joint Development Agreement signed

SWPG and 4 other companies signed a joint development agreement for the SunZia Southwest Transmission Project.

Federal Permitting Starts for Two HVAC Lines

The SWPG submits an SF-299 to the BLM to commence federal environmental permitting under NEPA.


Start of Project Development

SouthWestern Power Group (SWPG) started planning the development of an interstate transmission project between AZ and NM consisting of two, single-circuit 500kV transmission lines and associated substations.