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projects/power/energy-conservation-tidal-solar-storage.md

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+# 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.