Linear Programming Model

Prepaid Electricity Scheduling

Optimal operating hours for household appliances under a fixed prepaid wallet. The model maximises the Priority Service Factor by solving a fractional knapsack linear program with a greedy method.

Input Data

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Appliance Priority Factor Average Power (kW) Cost per Hour ($) Cost for Full Period ($) Actions
Presets

Optimal Schedule

Appliance hours allocated in order of Priority Service Factor per dollar.

Rank Appliance Priority Factor Power (kW) Cost per Hour ($) Hours Cost Allocated ($) Status

Budget Sensitivity

The optimal schedule is piecewise linear in the wallet balance. Markers show the balance at which each appliance starts to receive hours.

Priority Service Factor against Wallet Balance

Optimal schedule against the unrationed baseline, in which every appliance runs simultaneously until the balance is exhausted.

Allocated Hours against Wallet Balance

Cumulative hours by appliance. Appliances are funded strictly in ranking order, so only one appliance is partly served at any balance.

Budget Thresholds

Cumulative cost of serving the appliances ranked above each appliance for the full period.

Rank Appliance PSF per Dollar Cost for Full Period ($) Cumulative Threshold ($)

Method

The service factor of appliance k is the fraction of the planning period for which it is enabled, SFk = sk / H. The Priority Service Factor is the priority-weighted sum of the service factors, and the decision problem is

maximise    PSF = Σ μk sk / H
subject to  Σ λ Pk sk ≤ Z
            0 ≤ sk ≤ H

Each hour of appliance k costs wk = λPk and adds bk = μk / H to the objective. Because fractional hours are permitted, the problem is a fractional knapsack and the greedy order by rk = bk / wk is optimal. The application ranks the appliances, funds each one for the full period while the balance allows it, and gives the remaining balance to the first appliance that cannot be funded completely.

The unrationed baseline assumes that all appliances run simultaneously until the balance is exhausted, so each appliance runs for min(H, Z / (λ ΣP)) hours.