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

# 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.