12 KiB
12 KiB
Energy Conservation / Local Power Project
Date: 2026-05-25 Context: Michael is exploring practical local-first energy resilience: tidal/current capture in NSW coastal inlets, especially Wagonga Inlet/Narooma, then broader household solar and storage strategy.
Core framing
- Solar generation is comparatively mature and cheap at household scale.
- The hard problem is storage, especially storing enough usable energy for high-demand household loads and multi-day/seasonal mismatch.
- Tidal/current energy is attractive because it is predictable and locally visible in coastal inlets, but usable power depends on current velocity, not just total water volume.
- Best near-term path is not “replace grid with one magic system”, but layered resilience:
- use solar directly when available
- store heat as heat where possible
- store premium electricity in batteries
- keep grid/generator as rare backup unless full off-grid is explicitly worth the cost
Tidal/current turbine exploration
Initial question
Michael observed that NSW coastal inlets move huge volumes of water daily and wondered whether tidal propellers/turbines could capture useful power, using Wagonga Inlet as a local example.
Existing Australian work found
Key project: AUSTEn / Tidal Energy in Australia
- Led by University of Tasmania / Australian Maritime College with CSIRO, University of Queensland, ARENA and industry partners including MAKO, Sabella, and SIMEC Atlantis.
- Produced national tidal resource modelling at ~500 m resolution.
- Focused field/case studies at Banks Strait TAS and Clarence Strait NT.
- Found Australia’s strongest tidal stream opportunities mostly in northern Australia, plus Banks Strait TAS and Port Phillip Heads VIC.
- Even promising Australian sites commonly show max tidal velocities around ~2–2.8 m/s, whereas many international commercial projects prefer nearer ~4 m/s.
- Australian tidal energy remains mostly research/demonstration scale; no large commercial tidal farm currently operating domestically.
Other examples:
- MAKO tidal turbines: Australian small turbine work/trials including Tamar River TAS, Gladstone Port QLD, Singapore and overseas activity.
- Tidal Turbine Reef feasibility study: WA concept around One Arm Point / King Sound conditions.
- International comparison: MeyGen in Scotland demonstrates tidal stream can work at commercial/demonstration array scale, but in stronger-current sites than typical NSW inlets.
Main physical constraints for NSW inlets
- Velocity cube law: available power scales with current velocity cubed.
- 1 m/s = baseline
- 2 m/s = 8× power
- 3 m/s = 27× power
- 4 m/s = 64× power
- Large tidal prism does not automatically mean useful turbine power if the flow is spread across too large a section or too slow.
- Tidal generation is intermittent through the cycle: flood peak, slack high, ebb peak, slack low.
- NSW inlets are sediment machines: shoaling, scour, storm response, bar movement, training-wall effects.
- Turbine frames/fences could change local flow, causing scour holes, shoaling, altered navigation depths, bank erosion or changed flushing.
- Best current is often in the navigable channel, creating boat-safety and approval conflicts.
- Marine ecology concerns: fish strike, rays/seals/dolphins/turtles depending site, noise/vibration, cable EMF, benthic disturbance, altered flushing/salinity/sediment.
- Maintenance is harsh: salt, biofouling, weed, fishing line, flood debris, logs, storm access, corrosion.
- Economics must compete with very cheap solar and batteries.
Small turbine concept
Michael asked whether 10 m turbines are necessary or whether 0.5–1 m turbines could be deployed in strings across/along fast channel sections.
Conclusion:
- Small turbines are the more plausible direction for Wagonga-style inlets.
- Concept should look less like an underwater wind farm and more like modular, guarded, removable tidal cartridges.
- Avoid spanning the main boat lane initially.
- Prefer mounting near existing structures where possible:
- training walls
- wharf piles
- bridge-adjacent structures
- edge-flow zones outside marked navigation channel
- Design requirements:
- removable/lift-out frames
- guarded rotors
- storm/flood retrieval
- low-cost serviceability
- local battery/load nearby
- minimal seabed works if possible
Rough 1 m turbine power at useful efficiency:
| Current speed | Approx output per 1 m turbine |
|---|---|
| 0.8 m/s | ~70 W |
| 1.0 m/s | ~140 W |
| 1.2 m/s | ~240 W |
| 1.5 m/s | ~475 W |
| 2.0 m/s | ~1.1 kW |
| 2.5 m/s | ~2.2 kW |
A 0.5 m turbine has roughly one-quarter the swept area, so roughly one-quarter the power.
Interpretation:
- If sites reliably hit ~1.5–2 m/s, small turbine strings become technically interesting.
- If most sites are <1 m/s, the concept becomes mostly demo/education unless hardware is extremely cheap.
Wagonga Inlet data found
Public NSW estuary data:
- Estuary volume: ~39,101 ML
- Average depth: ~5.7 m
- Tidal prism measured 1986:
- ebb: ~6,340 ML
- flood: ~6,640 ML
- Local tidal range:
- ebb entry: ~1.49 m
- flood entry: ~1.24 m
- Entrance is open/trained.
- Downstream channel often described around ~3–5 m below MSL, with shallower shoals upstream.
- Flood Data Portal has TUFLOW model input/output for Wagonga/Kianga/Dalmeny, but outputs are large (~1 GB) and flood-focused rather than a simple normal-tide current table.
- Public searches did not uncover a clean ADCP/current-speed dataset for normal tidal currents in Wagonga.
Back-calculated estimate from ebb prism:
- 6,340 ML = 6.34 million m³ over roughly half-tide (~6.2 h).
- Average exchange flow: ~284 m³/s.
- Estimated sinusoidal peak tidal flow: ~445 m³/s.
Estimated peak speed depends on channel cross-sectional area:
| Flow cross-section | Estimated peak speed |
|---|---|
| 150 m² | ~3.0 m/s / 5.8 knots |
| 200 m² | ~2.2 m/s / 4.3 knots |
| 250 m² | ~1.8 m/s / 3.5 knots |
| 300 m² | ~1.5 m/s / 2.9 knots |
| 400 m² | ~1.1 m/s / 2.2 knots |
| 500 m² | ~0.9 m/s / 1.7 knots |
Working estimate:
- Fast entrance/channel sections of Wagonga are plausibly ~1–2+ m/s on stronger tides, with local faster jets possible near constrictions, walls, bridge/channel features, and ebb-bar conditions.
- This is not enough for design; it is enough to justify measurement.
Measurement path
Need current mapping before turbine design.
Best instrument: ADCP — Acoustic Doppler Current Profiler
- Uses angled acoustic beams and Doppler shift from particles/bubbles/sediment in the water.
- Measures current speed/direction at multiple depths, giving a vertical profile.
- Can be:
- bottom-mounted looking upward for days/weeks
- boat-mounted looking downward during transects
- side-mounted from wharf/bridge/pile
For Wagonga, useful survey points:
- Narooma bridge area
- downstream training wall edges
- entrance channel
- flood-tide delta edge
- spring vs neap tide comparison
- surface/mid-depth/near-bed velocity profiles
Cheaper first-pass option: calibrated propeller/impeller current meter.
- A small free-spinning rotor can estimate current speed from RPM.
- Use Hall sensor / optical sensor / encoder / small generator frequency.
- Must be calibrated by towing at known GPS speeds in calm water.
- Best for finding promising spots, not for final engineering/approval.
- Avoid loading it as a generator during measurement, because electrical load changes RPM and corrupts speed estimates.
Solar and battery/storage discussion
Michael’s situation
- Household has ~20 kW rooftop solar.
- Often produces more than household uses during peak days/weeks/seasons.
- No battery yet.
- Concern: cannot find a battery system large enough / economical enough to store all excess.
- Specific pain loads:
- hot water
- cooking
- other high-power/high-energy thermal loads
- Rest of household load seems manageable.
Core conclusion
- Household solar generation is mostly solved.
- Storage is the limiting problem.
- Batteries are good for same-day/overnight shifting and resilience.
- Batteries are poor/economically awkward for storing all surplus, multi-week deficits, seasonal mismatch, or repeated large thermal loads.
- Chasing “store all excess solar” is likely the wrong target.
- Better target: maximise useful self-consumption and resilience without overbuilding storage that sits idle much of the year.
Recommended hierarchy
-
Direct use first
- Shift flexible loads into solar hours:
- dishwasher
- washing
- EV charging if relevant
- pumps/pool/workshop loads
- appliance scheduling
- Shift flexible loads into solar hours:
-
Store heat as heat
- Hot water is a cheap thermal battery.
- Prefer:
- heat pump hot water
- solar diverter to hot water tank
- larger hot water tank
- controlled daytime heating
- Thermal storage is much cheaper per stored kWh than lithium for hot water.
-
Battery for premium electricity
- Use battery for loads that truly need electricity:
- fridge/freezer
- lights
- computers/network
- pumps
- security/comms
- short cooking bursts
- overnight baseload
- outage backup
- Use battery for loads that truly need electricity:
-
Grid/generator as rare backup
- 90–95% self-powered is much cheaper than 100%.
- The last 5–10% is where system cost explodes.
Battery sizing thoughts
- Practical sweet spot for a 20 kW solar household may be roughly 20–40 kWh battery, depending actual load profile.
- For serious resilience, maybe 50–60 kWh, but only with a specific goal and inverter/load analysis.
- Beyond that, caution: large batteries can be expensive and underutilised for much of the year.
Cooking
- Cooking is high power but not always huge total energy.
- Induction can pull hard, but often for short durations.
- Design issue is both:
- battery capacity (kWh: how long)
- inverter power/surge (kW: how hard)
- A household can cook from battery/solar, but making it feel normal requires adequate inverter capacity and careful load management.
System philosophy
Do not store all solar surplus as electricity.
Better overall design:
- 20 kW solar remains core generation.
- Add battery sized for overnight/resilience, not full seasonal capture.
- Convert hot water to controlled solar/heat-pump thermal storage.
- Shift flexible loads into solar windows.
- Retain grid/export/backup for the economically ugly edge cases.
Working phrase:
Use solar directly, store heat cheaply, store electricity selectively, and only buy enough battery to cover expensive/important overnight and outage loads.
Open questions / next research steps
Tidal/Wagonga
- Can actual normal-tide current data be obtained from:
- NSW/Eurobodalla hydrodynamic studies
- Flood Data Portal TUFLOW outputs
- Marine Rescue / local navigation records
- council coastal management planners
- universities / consultants
- Is there a practical ADCP hire/service path locally?
- Could a low-cost impeller logger be built and calibrated for initial site reconnaissance?
- Which edge/structure locations are fastest while avoiding the marked navigation channel?
Household solar/storage
- Pull actual household interval data if available:
- solar generation by 5/15/30 min interval
- import/export
- hot water load timing
- cooking peaks
- winter vs summer profiles
- Model battery sizes: 13.5, 20, 30, 40, 60 kWh.
- Model hot water options:
- heat pump hot water
- resistive diverter
- larger tank
- controlled relay/timer
- Identify practical inverter requirements for cooking/backup circuits.
- Decide whether goal is cost saving, blackout resilience, grid independence, or technical sovereignty; sizing changes depending priority.