Where the energy comes from: a sign test for on-board harvesting
Put a solar panel, a turbine and a regenerative damper on the same vehicle and three different things happen to the energy balance. Two of them add. One of them subtracts, and it subtracts no matter how good the hardware gets. The useful question is therefore not how much does this harvester yield but what sign does its contribution have — and that question can be settled on paper, before anything is built.
Three classes
Class A — external or ambient. The source draws energy that is present in the environment and that the vehicle was not going to spend. Photovoltaic conversion is the clean case: the photons arrive whether the vehicle moves or not. Thermoelectric conversion of waste heat, piezoelectric conversion of road-induced vibration and radio-frequency capture sit here too. The energy balance is unambiguously positive; the only open questions are magnitude, mass and cost.
Class B — recovered. The source recovers energy the vehicle is already committed to losing. Regenerative braking is the definitive case: that kinetic energy is going to be dissipated as heat in the friction brakes, and recovering a fraction of it is strictly better than recovering none. Regenerative suspension dampers are the same argument applied to energy already being dissipated in the damper. The balance is positive, bounded by the fraction of the loss that is accessible.
Class C — parasitic. The source draws its input from the vehicle's own forward motion during propulsion. A turbine facing the airstream and a generator on a driven wheel are both in this class. The balance is negative during propulsion, and no improvement in harvester efficiency changes the sign.
Why Class C is negative, derived rather than asserted
This one is worth working through, because the conclusion is counter-intuitive to anyone who has watched a turbine spin on a moving vehicle and inferred that something is being had for nothing.
The relative-wind argument. A vehicle moving at speed v through still air experiences relative wind of exactly v. There is no external wind field — the apparent wind is the vehicle's motion. A turbine placed in that stream extracts momentum from the air, and by Newton's third law the air exerts an equal and opposite force on the turbine, which is to say additional drag on the vehicle, transmitted through its mounting.
The power the drivetrain must supply to overcome that additional drag is
and the power the turbine can deliver to the electrical system is
where Literature C_p cannot exceed the Betz coefficient of 16/27 ≈ 0.593 — a bound that follows from momentum conservation across an actuator disc and applies to any turbine of any design [1] — and η_mech and η_elec are each strictly less than unity.
Derived The force that produces P_elec is the same force that produces P_drag. The turbine's electrical output is therefore a fraction of the additional propulsion energy the drivetrain must supply — the product of two efficiencies below one and a coefficient below 0.6. Add the parasitic drag of the turbine housing itself, which produces no output at all, and the deficit widens.
The result does not depend on the turbine being poor. A perfect turbine at the Betz limit with lossless mechanical and electrical conversion would break even at best, and no such turbine exists. This is not a manufacturing problem awaiting a better product. It is a conservation result.
The driven-wheel case is the same argument without the air. A generator on a wheel that the drivetrain is turning takes its input torque from the drivetrain. The energy is routed motor → wheel → generator → converter → battery, and every arrow is lossy.
The two exceptions, stated precisely
Class C hardware becomes legitimate under two specific conditions, and they are worth stating because they are the design guidance the taxonomy yields.
A non-driven, free-rolling wheel taps vehicle kinetic energy the same way regenerative braking does. If the vehicle is decelerating or coasting, that kinetic energy is being dissipated anyway. This is Class B behaviour and it is legitimate.
A generator or turbine engaged only during coast-down or braking is likewise physically analogous to regenerative braking, and avoids the steady-state drag penalty entirely. A clutched or electrically de-excited turbine that free-wheels during propulsion and loads only during deceleration is a Class B device wearing Class C hardware.
Both exceptions share one feature, and it is the whole of the rule: the harvester is active only when the vehicle is shedding energy, never when it is spending it.
Applying the test
| Source | Class | Consequence for a claim |
|---|---|---|
| Photovoltaic | A — external | Net-positive. Yield is set by area, module efficiency and insolation. |
| Thermoelectric, from waste heat | A — external | Net-positive. Yield is set by temperature differential and module area. |
| Piezoelectric, from road vibration or panel oscillation | A — external | Net-positive in sign; magnitude is the open question. |
| Radio-frequency capture | A — external | Net-positive in sign; magnitude is very small. |
| Regenerative braking | B — recovered | Net-positive. Mature and industry-standard. |
| Regenerative suspension | B — recovered | Net-positive. Demonstrated in published prototypes. |
| Wind turbine, active during propulsion | C — parasitic | Net-negative. Not to be presented as a range benefit. |
| Driven-wheel generator, active during propulsion | C — parasitic | Net-negative. Not to be presented as a range benefit. |
| Either of the above, active only on coast-down or braking | B — recovered | Net-positive; the qualifying condition must be stated. |
What this means for a claim set, including mine
Patent claims that recite a list of alternative energy sources are drafted broadly on purpose, and that is ordinary practice: a Markush group reciting a source type does not assert that the source is commercially attractive, only that the claimed system can accept it. The two are different statements and the law treats them differently.
A technical or commercial document is held to the stricter standard. One that presents every recited source as a contributor to range is making a claim the physics does not support, however carefully the underlying claim was drafted. So the taxonomy exists to make that distinction deliberately rather than by omission — and it applies to my own documents first. Where a specification of mine lists sources, the sign test above governs what may be said about them in a datasheet, a deck or a conversation with an engineer.
Magnitude: the one source with a firm number
Fixing the sign is not the same as knowing the size, and the honest answer differs sharply by source. Photovoltaic is the case where the arithmetic is unambiguous:
Derived At the AM1.5G reference irradiance of 1,000 W·m−2 [2] and commercial silicon module efficiencies of roughly 15–22 %, peak output density is of the order of 150–220 W·m−2. That is a peak figure at a reference condition, not an average over a duty cycle, and it must be multiplied by real insolation, angle and shading before it becomes an energy yield. The other Class A sources are positive in sign but far smaller, and radio-frequency capture is smaller again.
Why the architecture is the invention, not the sources
None of these sources is novel on its own. Regenerative braking is standard on every modern electric vehicle, solar roofs are in series production, and regenerative dampers are published. Saying otherwise would be easy to disprove and would not survive an examiner, let alone a diligence team.
The contribution claimed in the OMNIA Drive family is narrower and more defensible: the system-level integration — a unified, simultaneous, state-of-charge-aware multi-source control method, so that several inputs of different character and different availability can be accepted at once without the pack arbitrating badly between them. The family runs from PCT/IB2016/055563, priority 25 September 2015, and is granted in three jurisdictions — India IN 477613 (6 December 2023), United States US 11,117,476 B2 (14 September 2021) and Japan JP 7,109,623 (21 July 2022, running from a divisional, which is ordinary practice). Named, not counted, so that each can be looked up in a public register in an afternoon.
The sign test is what makes that architecture claim safe to make. A controller that accepts Class A and Class B inputs is adding energy to the vehicle. Whether it should also accept a Class C input, and under what gating condition, is a design decision the taxonomy answers rather than leaves open.
References
[1] Betz, A. (1920). Das Maximum der theoretisch möglichen Ausnützung des Windes durch Windmotoren. Zeitschrift für das gesamte Turbinenwesen, 26, 307–309. The actuator-disc bound of 16/27 used above.
[2] ASTM G173-03 and IEC 60904-3, AM1.5G reference spectral irradiance, 1,000 W·m−2. The reference condition used in the photovoltaic derivation.
[3] US 11,117,476 B2, granted 14 September 2021.
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