# 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 1. **Direct use first** - Shift flexible loads into solar hours: - dishwasher - washing - EV charging if relevant - pumps/pool/workshop loads - appliance scheduling 2. **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. 3. **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 4. **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.