Transmission costs
Energy transmission consumes energy due to electrical resistance. Around 10% of electrical energy we use here becomes heat energy while crossing a transmission line. Energy costs more because we bring it in from away.
Where could grid-scale solar work on the Mendocino Coast?
A solar developer approached Caspar Water Company interested in a lease on its field near Highway 1. We learned that interconnection capacity is a major obstacle for new solar developments. What does that tell us about site suitability? We learned that Mendocino Coastal zoning codes do not permit grid-scale solar in residential zones*.
*See below
The edge of the grid
If we want sustainable energy, we have to make it here.
The electric grid carries energy over transmission lines that separate major population centers. Our capacity to transmit energy to and from the coast is limited by the size of these lines. To bring a new solar utility online requires an interconnection agreement with PG&E. When the grid is capacity-constrained, transmission across that section is not permissible without upgrading the grid.
Legacy transmission lines
Coastal Mendocino is served by three aging transmission lines, designed before electric vehicles, residential heat pumps, and grid-scale solar. As energy usage grows, the coast will need new transmission lines or new local generation.
Backwards transmission restricted
PG&E's coastal power stations were not designed to feed power from the coast back into the grid. Energy generated here can't be sent away without first upgrading power stations.
Non-competitive market
According to Sonoma Clean Power, "The current grid was not planned with sufficient capacity to enable a competitive market." Because transmission capacity is limited, energy has to be generated locally.
Local generation
The local high-voltage grid connects our former industrial sites.
The Mendocino Coast is served by a local distribution grid of 12 kV power lines that links our towns. These lines were upgraded in the late 1940s when PG&E expanded service to a wider residential area and connected the local mills to phase out use of coal and kerosene. Locations with access to the 12 kV local distribution network are ideal sites for solar generation.
Generation limits
Connecting a new solar generation facility to the energy grid shifts the dynamics of the grid. Electricity follows the path of least resistance and goes to serve the nearest demand. The farther energy travels the greater the waste; physical grid capacity means that generation is limited by local demand.
Integration capacity
Before connecting a new generation facility to the grid, the utility company must perform an analysis of the capacity for new energy production. CPUC requires energy utilities to publish Integration Capacity Analysis (ICA) numbers for sections of the grid to assist solar developers in identifying candidate sites.
Power control
Published ICA numbers are based on a variety of factors indicating how much power can be safely introduced without overloading the system. There are actually two ICA numbers, one for general generation facilities and one for solar generation facilities.
Energy storage
The ICA number limits what a generation facility can produce at the peak, while sunshine limits energy generation to approximately 20% of the day in the Coastal zone. Adding battery storage enables a solar system to deliver energy around the clock. A site with 100 kW generation ICA and battery storage can support a 500 kW solar array.
Motivation
Why we made this site.
This site began as a question about land use. During the first attempt to develop solar on the Caspar Water Company site, the Mendocino County Planning Department discovered a discrepancy in its books. Section 20.376.015 of the County's Coastal Zoning Code lists off-site alternative energy facilities as a conditional use in Coastal Rural Residential zones and cites Ordinance 3857, adopted in May 1993. Certified LUP Policy 3.11-12 and section 20.320.020 omit Rural Residential from the categories allowing off-site facilities, creating an unresolved inconsistency. Coastal Commission staff report that it remains unclear whether the Rural Residential entry was ever certified.
The Department has to weigh the impact of changing its list of Coastal Civic Conditional Uses for Rural Residential districts. Otherwise, the Coastal Plan only permits solar development in Agricultural, Forest Land, Timber Production, Rangeland, and Industrial zones. We ask, what would be the impact of this change? Would the Mendocino Coast be suddenly covered with solar panels?
Energy has limits
What we learned about solar on the Mendocino Coast.
To develop a grid-scale solar facility on the Mendocino Coast requires more than a Conditional Use permit with correct zoning. Successful development requires at least 10 acres of undeveloped land, access to the local high-voltage grid, that the local distribution grid has capacity, and that there is sufficient demand for electricity nearby. As soon as one generation facility is installed in a location, capacity and demand constraints will prevent another facility from being built nearby.
Candidate analysis
How were the candidates identified?
The study starts with all Mendocino APNs with at least 10 acres followed by exclusion and elimination for various reasons:
- Sites more than 1 km from PG&E's 12 kV coastal distribution network.
- California prime, important, or unique farmland.
- Protected areas, including wetlands.
- Sites with improvement value above $10,000 per acre.
- Sections that slope more than 10 degrees.
- Open Space zoning.
Candidates were then ranked according to ICA number, distance from the distribution lines, and highway visibility.
Analysis
How many grid-scale solar generation facilities are there on the Mendocino Coast? How many could there be?
There are no grid-scale solar projects on the Mendocino Coast, despite there being over seventy candidate sites east of Highway 1 with AG/FL/TP/RL/I zoning and available interconnection capacity. There are 60 Rangeland, 7 Agricultural, 4 Forest Lands, 2 Timberland Production, and 1 Industrial parcel with compatible zoning.
Other candidate zoning categories east of Highway 1 with available interconnection capacity include 5 Rural Residential, 2 Remote Residential, 2 Public Facilities, and 5 in the Point Arena municipal zone.