Isolated Diesel Grids –Renewable Integration

Marc Mueller-Stoffels, PhD

Hybrid-Diesel Power Generation

Diesel-only cost: between 0.35 and 1+ $/kWhWind in rural AK

Average $10,700/kW Large, commercial wind farms: < $3000/kW

PV in rural AKWe don’t really know the cost yetTarget: $5000/kW – makes it commercially viable in many places (@ avoided fuel cost)

NoteDiesel generators: (relatively) low initial investment, but then…RE sources: high initial investment, but then…

Customer RequirementsRural AK sees large variability in demand

Mostly high winter loadsBut, in some places, industry drives high summer demand

Power has to be of decent qualityOutages are always unacceptable

Especially at 50 below

Diesel PowerhouseGenerally:

Provides prime power (forms the grid, i.e., one diesel is always on)Provides electricity AND heatDiesels have sweet spot, outside this, efficiency suffers

Usually pretty well ‘dialed-in’ 100+ years of operation

Cost break-downFuel cost Cost of operationInvestment

Integration of RE – Basic Rules

Operational envelope of diesel generatorsNever under-load diesels (20 to 40%) Do not risk overload (>110%) [keep spinning reserve]Sudden large load swings should be avoided

Without control of RE resourceOnly small amounts of RE power can be allowedExample: distributed PV can quickly become detrimental

Hybrid-Grid Control: Source Management

Curtail RE source to remain in operational envelopeSpinning reserve:

Largest sudden load rise, or amount of RE on grid, which ever is bigger

Hybrid-Grid Control: Load Management

Loads that are controlled by the utility do not require spinning reserve

Examples: Pumps, electric heaters, cooling equipment

Allows operation with less or smaller diesel generatorsMaximizes RE power use

Diesel-off -- Game Changer?

Affordable Energy Storage< 0.10 $/kWh

Need to replace diesel by power-electronics as prime moverDiesel-off mode

Additional 30% fuel savingsReduced O&M costPermanent diesel-off – cheaper diesel packages

And the value of RE power?Displaced Fuel

Not a linear function, but direct savingsReduced O&M on diesels

‘Small’ maintenance can be scheduled based on gallons of fuel used

HedgingVolatile fossil fuel prices are a direct riskRE power can hedge against variation (usually fixed cost)

Questions?

Marc Mueller-Stoffels, PhDResearch Assistant ProfessorAlaska Center for Energy and PowerUniversity of Alaska Fairbanksmmuellerstoffels@alaska.edu