Costing and energy

The price schedule every design is costed from, the rules for turning a design into a bill of materials, and exactly which loads count against the daily energy allowance.

Two hard constraints govern every design in this course: $30,000 of new spend including a required 10 % contingency, and 5 kWh a day of process energy in the peak month. Both are pass or fail, and both are checked before the marking criteria are applied.

The price schedule

$30,000 is a costing allowance, not a market quotation. Assessment uses the schedule below whatever real prices are doing, so that every design in the cohort is costed on the same basis. Lines marked indicative come from a retail listing; lines marked course assumption were set by the course.

Where the schedule is weakest

• Storage per kilolitre. $130/kL holds at 22 to 30 kL, which is where the bill-of-materials rule buys. The real curve is U-shaped — roughly $200 to $260/kL at 5 to 10 kL, and about $157/kL at 46 kL — so the figure understates both very small and very large tanks.
• Aquaponics. $2,500 per 4 m² is optimistic: Australian kits want roughly $3,400 for about 2.7 m². Kept as decided, and flagged as sitting at the low end.
• Installed greywater diversion. The hardware prices check out; the installed figure rests on a search summary rather than a fetched supplier page. It is the weakest line here.
• Insect rearing unit. No Australian black soldier fly unit publishes a price. A mealworm three-tier system is about $160. The $300 figure is a course assumption with little behind it.
• Ultraviolet units. Australian retailers cite WaterMark, not NSF/ANSI 55 Class A. Do not write a Class A claim into a design you have not sourced.

Turning a design into a bill

These rules are course assumptions, published so that two people costing the same design get the same answer.

• New storage arrives in tanks of at most 25 kL, so the per-tank establishment charge scales with tank count.
• One first-flush diverter and leaf screen per 75 m² of connected roof.
• Two pumps: one for domestic supply, one to move tank water to the garden. Both are counted energy loads.
• The aquaponics line bundles tank, pump and aeration. A second 4 m² bed on the same system needs neither, so extra beds cost $1,800 — the bundle price less one pump line. This is the rule that stops a pump being paid for twice, and it was added after an earlier costing did exactly that.
• Drip irrigation covers the whole production area, because the model irrigates the whole production area.

Priced in the schedule, not drawn in the reference designs

No recipe parameter and no counted load implies these, so charging them to a threshold-setting design would inflate every threshold. You may choose them, and you pay for them from the same allowance.

• Greywater treatment system [S33]
• Household anaerobic digester
• Humidified mushroom fruiting chamber
• Fruit or nut tree, potted, each

Not priced by the schedule at all

Published so the allowance is not mistaken for a quotation. A real build carries these; this costing exercise does not.

• Garden establishment: soil improvement, mulch, seed and seedling stock
• Aquaculture tank heating or cooling hardware
• Labour beyond the lines marked installed
• Earthworks, slabs and access beyond the per-tank establishment line
• Council approval, plumbing certification and fitting of WaterMark-licensed devices
• Consumables and replacement: UV lamps, filter cartridges, imported fish feed, desludging

What the reference designs actually cost

Until September 2026 these designs were costed from five simplified prices with no establishment, treatment, irrigation or contingency lines, which produced totals of about $3,000, $14,100 and $22,000 to $25,000. Priced against the full schedule, the excellent design came to $33,704 to $39,545 — over the allowance at every one of the five sites.

Two recipe rows changed in response and nothing else: new-storage spend fell, because the monthly tank balance saturates well below what the old recipe bought, and the excellent design's added roof catchment fell from 25 % to 5 %, because it was the most expensive water lever per point of closure. The thresholds on the method page were recomputed.

At Darwin the excellent design clears the allowance by $2,280. That is inside the noise of a screening model priced from retail listings. The published claim is that the reference designs fit the allowance as this schedule prices them, not that a real build would cost this. Treat your own design as untested if it lands within a few thousand dollars of the cap.

One bill in full

Energy: what counts, and what you must declare

The allowance covers every load that runs the food, water and waste loop, reported as the peak-month average daily figure with the month named. General household appliances, the fridge, cooking, lighting, space conditioning and water heating for bathing and laundry are not counted: they belong to the proposed sequel on energy and shelter.

Uncertain loads are carried at their upper estimate. That rule applies to you and it applies to the reference designs, which declare 0.65 kWh/day for counted loads the screening model does not compute:

The systems the reference designs do not contain

Each of these brings its own counted loads, and the headroom above is what your additions have to fit inside. Their combined upper estimate is 1.65 kWh/day — more than Darwin has left at the competent design.

For scale: a four-person Australian household uses roughly 21 kWh a day of electricity in total. This allowance governs about a quarter of that, and only the quarter that runs the loop.