BlockRate(Customers, TimestepsPerBillingPeriod, Rate_1, RateDenomUnit_1, UpperLimit_1, UpperLimitUnit_1, Rate_2, RateDenomUnit_2, UpperLimit_2, UpperLimitUnit_2, ..., Rate_N, RateDenomUnit_N)
Tiered water pricing policies are often touted as a means of promoting demand management. Water conservation practices are motivated by increasing unit costs on higher usage of water. The BlockRate function allows for the approximation of revenues generated by such a block rate pricing structure. There is no limit to the number of blocks.
Customers: The number of customers included in the demand site. Note: the block rate is calculated for the average customer use--actual rates will differ slightly, because some customers will use more than the average and some will use less, and the block rate structure is inherently non-linear. WEAP will take the total water used by the demand site and divide by the number of customers to derive the average usage per customer. The block rates will be applied to this average usage to get the average cost per customer. This average cost will then be multiplied by the number of customers to get the total customer cost.
TimestepsPerBillingPeriod: The length of the billing period, in timesteps. E.g., for quarterly billing and a monthly timestep, enter 3. WEAP will calculate the cost for each timestep, by dividing the block sizes by this number of timesteps. For example, instead of one bill every 3 months, there will be a bill every month, but each will be approximately 1/3 of the quarterly bill.
The following four parameters are repeated for each block, except for the final block, which includes only the first two parameters (because it has no upper limit).
Rate_i: The cost of water for block i, either a unit cost or a flat rate. See RateDenomUnit_i
RateDenomUnit_i: The denominator unit for Rate_i (e.g., "gallons," or "cubic meters"), or "flat" to indicate a fixed cost regardless of usage within this block. A flat rate, or "base rate," is often charged for the first block.
UpperLimit_i: The upper limit water volume for this block. This parameter is not included for the last block, because it has no upper limit.
UpperLimitUnit_i: The unit for the upper limit water volume. This parameter is not included for the last block, because it has no upper limit.
The 100,000 households in South City are billed every 6 months, using the following block structure:
Base charge of $29.20 per bill includes up to 20,000 gallons
20,000 - 30,000 gallons at $1.40/1000 gallons
30,000 - 50,000 gallons at $1.65/1000 gallons
50,000 - 70,000 gallons at $1.90/1000 gallons
70,000 - 90,000 gallons at $2.25/1000 gallons
Over 90,000 gallons at $2.60/1000 gallons
The following expression should be entered in the "Variable Benefit" data tab for South City:
BlockRate(100000, 6, 29.20, flat, 20000, gal, 0.00140, gal, 30000, gal, 0.00165, gal, 50000, gal, 0.00190, gal, 70000, gal, 0.00225, gal, 90000, gal, 0.00260, gal)
Note that WEAP calculates the cost for each month, but because the bill covers 6 months, WEAP will divide the size of each block by 6. Also, the flat rate would be divided evenly over each of the 6 months. If, for example, the average customer use in January was 4000 gallons, this would fall in the second block: 20,000 - 30,000 gallons for 6 months is equivalent to 3333 - 5000 gallons for 1 month. 4000 gallons would be charged a flat rate of $4.87 for the first 3333 gallons, and $0.0014/gallon for the next 667 gallons. The cost per customer = $29.20/6 + (4000 - 3333) * $0.0014 = $5.80, or a total cost for all customers of $580,047.