A Proposal for
Solar Sun Safe

Two questions dominate this product: the thermal envelope inside the enclosure under UAE 50°C ambient conditions, and the solar energy budget against realistic daily guest usage. These are not separate questions. They are coupled, and answering them in isolation produces the wrong answer.

Solar yield drives the daily energy available. Daily energy available, against the session profile and charging output spec, drives the battery capacity required to buffer the gap between peak demand and average solar input. Battery capacity drives cell count, cell count drives pack physical volume, and pack volume drives the heat dissipation problem inside a sealed IPX rated enclosure under direct sun in 50°C ambient. Battery cell temperature drives charging behaviour, and at high cell temperatures LiFePO4 cells must derate or stop charging entirely. The Qi wireless charging coil adds five to ten watts of waste heat inside the box on every session. The electronics add further dissipation. The thermal envelope then feeds back into the battery chemistry and capacity decision.

The brief correctly identifies LiFePO4 as the right chemistry for this product class. It has a wider operating temperature envelope than Li-ion or LiPo, which is what makes the UAE deployment plausible at all. The remaining open questions, namely 10Ah versus 15Ah capacity, single panel versus multi panel solar layout, and the venting strategy that maintains IPX5 or IPX6 ingress protection, are exactly the decisions Phase 1 is structured to answer.

Our working position going into Phase 1 is that the product is technically feasible in UAE conditions, but achieving it requires the energy budget and the thermal strategy to be designed together as one workstream rather than as two separate engineering exercises. This is the Phase 1 Deliverable 3 central workstream.

Phase 1 will also include a steady state CFD spot check on the worst case Dubai scenario as a gate review item, covering 50 degrees C ambient, lid at solar saturation, and USB-C plus Qi both at peak load simultaneously. This is not a full CFD programme. It is a targeted check on the lithium cell temperature risk under the highest simultaneous load combination, sufficient to validate the thermal strategy and provide confidence before committing to the enclosure architecture. Full CFD validation with boundary conditions based on the production enclosure geometry sits in Phase 2.

Working from a primary lid panel of approximately 320 x 240 mm in monocrystalline ETFE technology, with an effective active area of around 0.07 m squared after frame and mounting losses, and a peak panel output of approximately 14 to 15 watts under standard test conditions, the indicative daily energy production by market, allowing for tilt, partial shading, real world derating, and MPPT efficiency, is in the following range:

UAE panel surface temperatures in Dubai summer can reach 60 to 75 degrees C, reducing panel output by approximately 10 to 18 percent against standard test condition ratings. A lower temperature coefficient panel specification is recommended for the UAE SKU. Phase 1 will model the combined primary lid plus optional auxiliary panel arrangement using PVGIS 5.3 simulations for each named target city as a Deliverable 3 output.

Optional auxiliary panels on the front and side faces add total solar harvesting area, but at non optimal tilt angles and with greater shading exposure from the lounger geometry. Realistic uplift from auxiliary panels is in the 20 to 40 percent range over the primary panel alone, depending on placement and exposure.

Against a target of two to five guest sessions per day, with each session delivering up to 18 to 20 watt USB Power Delivery output and 10 watt Qi wireless charging, the daily energy draw at the output side is in the range of 60 to 150 Wh depending on session duration and device charging behaviour. Adding standby losses, MPPT and BMS overhead, and the LoRa radio duty cycle, the realistic total daily demand is 80 to 180 Wh.

Set against the annual average solar yield above, the energy balance is tighter than a summer peak calculation suggests. In UAE conditions the system runs well across the year. In southern Europe in summer it runs cleanly. In the UK, the annual average yield (15 to 35 Wh/day) is well below the daily demand on a multi session day, meaning the battery is the primary energy buffer and multi day cloud cover will exhaust a lightly sized pack. This is the primary driver of our battery sizing position.

Our preliminary recommendation is a target pack capacity in the range of 130 to 180 Wh depending on the regional SKU, with a UK variant at approximately 150 Wh and a southern Europe and UAE variant at approximately 130 Wh. Standardising at 160 Wh across all SKUs is an option and simplifies supply chain at modest cost premium. Pack architecture should be kept below 192 Wh at 12.8 V nominal (approximately 15Ah) to manage IATA shipping classification, which steps up materially above that threshold. Phase 1 will confirm the final pack specification against the PVGIS energy model and the thermal envelope.

Maintaining the IPX5 or IPX6 target while managing internal temperature in 50°C UAE ambient is the harder of the two coupled problems. Our working position going into Phase 1 is a combined strategy of:

Phase 1 delivers the first principles thermal and energy budget model, including the steady state CFD spot check, that quantifies the temperature rise expected inside the electronics compartment under the worst case UAE deployment against this strategy. Full thermocouple instrumented validation testing sits in Phase 2 once the enclosure geometry is locked.

The product is a connected hardware system, not just a safe with charging. The full stack covers a LoRa node inside each unit, a venue gateway managing all units on site over LoRa with cloud connectivity over WiFi or 4G, a cloud backend handling device management and over the air firmware updates, a payment integration handling the guest QR code session purchase and the venue revenue share split, a guest facing mobile experience for QR scanning and session management, and a venue facing portal for the hotel to monitor and reconcile usage.

These workstreams are delivered through specialist external partners selected and managed by Shield Works as prime contractor on the founders' behalf. Shield Works directly delivers the hardware engineering, the LoRa hardware module selection and integration, the PCBA architecture, the certification programme, and the manufacturing. The firmware development, gateway architecture, cloud backend, payment integration, and app development are routed through named specialist IoT partners contracted under the Shield Works programme management.

The founders deal with one commercial counterparty and one point of accountability. The partner network sits behind that counterparty. This is the model Shield Works runs across the connected product category and it removes the single vendor dependency risk that has caused other clients in this space to lose product momentum at the worst time.

Phase 1 identifies the named partners for each workstream, validates their capability against this specific product, and provides indicative pricing for each as a discrete line item in the development budget.

One accountability point that must be agreed before Phase 2 proceeds: the system integration owner role. Shield Works will publish the system interface specification as a Phase 1 deliverable, defining the hardware to firmware boundary, the unit to gateway communication protocol, and the integration test requirements. The system architect and integration owner role, responsible for ensuring the firmware, gateway, backend, and hardware layers work as a coherent system through to pilot, is held by the founders by default. If the founders wish Shield Works to hold that role on their behalf, this can be contracted separately as part of the Phase 2 engagement. This boundary must be explicit before partner contracts are signed.

Working from the architecture in the brief, the components specified, and the partner stack required, our preliminary working range for the ex factory unit cost at scale, on the assumption of qualified mass production manufacture in the Shield Works facility, is:

Approximately £85 to £110 per unit at 20,000 units per year. Approximately £130 to £170 per unit at 1,000 units. Approximately £250 to £350 per unit at pilot quantities of 20 to 30 units.

These numbers reflect the realistic cost build of a LiFePO4 battery pack, integrated solar with MPPT, electronic lock and keypad, Qi coil and USB-C PD power electronics, LoRa module, outdoor rated injection moulded enclosure with IPX5 or IPX6 detail, and the assembly and test burden of a connected, certified product. Pilot unit pricing excludes NRE. NRE (tooling, jig manufacture, and first build setup costs) will be itemised separately inside the Phase 1 Development Roadmap.

On the founders' stated target of £50 per unit: we want to address this directly rather than leave it unchallenged. A fully specified Solar Sun Safe, carrying the battery pack, solar and MPPT, electronic lock, Qi coil, USB-C PD, LoRa module, outdoor enclosure, and the assembly and certification load, is not a £50 unit at 50,000 volumes. Our engineering view is that the realistic floor with this feature set is approximately £65 to £80 at 50,000 units per year, and approximately £55 to £70 at 100,000 units per year or above. Reaching £50 would require material de-specification, a level of factory margin compression that creates supply chain risk, or volumes well above the current commercial model. Phase 1 will produce the BOM-backed number that replaces this working position with a committed answer. We are flagging it now so the commercial model, session pricing, and venue revenue share can be built on the right foundation.

We are giving the founders these numbers up front rather than holding them for Phase 1, because the unit economics drive the venture's commercial model (the per session pricing, the revenue share with venues, and the unit payback period). Better to have the honest range now than to redesign the commercial model after Phase 1 delivers a different answer.

The founders' current raise target of approximately £75,000 covers what they have positioned as pilot stage. Our preliminary view of the realistic total development investment to get from current concept stage through to a working pilot run of 20 to 30 production representative units at a hotel is:

The ranges below are based on benchmarked category knowledge and represent the total programme investment including Shield Works programme management across all workstreams. They are not confirmed partner quotes. Phase 1 is the engagement that replaces these estimates with real supplier and partner pricing. The total investment range will be firmed into a committed phase by phase budget as a Phase 1 output.

The investment programme covers, indicatively:

We are flagging this range up front rather than finding it inside Phase 1. The delta against the founders' current £75,000 raise target is significant and material to how the venture is positioned to investors. There are real options inside the workstream list above to phase the spend, defer certain partner workstreams to a later round, or trim scope at the pilot stage. Phase 1 will firm this into a committed phase by phase budget with clear gates, identify where scope trade offs can move the number within the range, and give the founders a fundable roadmap to take to the next investor conversation.

Two commercial safeguards are built into the programme structure from Phase 1 onwards. No tooling commitment is made until DFX and a validation prototype build confirm manufacturability, system integration stability, and cost alignment against the target. Progression from Phase 1 into Phase 2 development is gated on agreement of the connected product partner stack selection, the indicative BOM and unit cost model, the certification pathway, and the overall development budget. Both gates protect the founders against premature spend, and protect us against scope drift on a programme that is moving from concept to manufacture.