150 W, no central battery
The panel feeds the charging Distributor directly. Lights, radio, fans, phones and power banks carry their own small batteries. The household buys storage only in the appliances that need it.
Upgrade path · additive by design
150 W → 300 W → storage and refrigeration.
The emerging upgrade path keeps every useful part of the entry system. Start with one nominal-12 V 150 W panel and no central battery. Add a second identical panel in parallel for 300 W of daytime capacity. Later, reconnect the same two panels in series and add an inexpensive 24 V solar charger plus a 25.6 V / 50 Ah LiFePO₄ battery. The original Distributor and portable appliances remain in service.
150 Wworking batteryless entry target
300 Wsecond panel added 1S2P, still batteryless
1.28 kWh25.6 V × 50 Ah first shared battery
Refrigerationthe first major load that strongly rewards shared storage
Make every upgrade additive.
The design goal is simple: no household should have to throw away the first panel, Distributor, lights, radio, fan or charging hardware in order to climb to the next rung. The first 150 W system should remain useful at 300 W, and the 300 W system should become the front end of a battery-backed 24 V system with only a wiring change and added hardware.
300 W, still no central battery
Add a second identical 150 W panel in parallel (1S2P). Voltage stays in the same nominal-12 V PV range while available current and daily energy roughly double. Add more Distributor channels or near-plug-in modules as useful loads grow.
300 W + 24 V shared storage
Reconnect the same two panels in series (2S1P), feed a low-cost 24 V solar charger, and add a 25.6 V / 50 Ah LiFePO₄ battery. The battery bus can then feed the original Distributor, refrigeration and other 24 V loads.
One pair of panels, two useful configurations.
The intermediate batteryless 300 W stage matters. A household can gain substantially more daytime charging and direct-use energy before it can afford a central battery. When storage finally makes sense, changing the same two panels from parallel to series is a trivial field operation compared with replacing equipment.
Stage 1 — one panel
1 × 150 W PVnominal-12 V panel
→
Raw PV busprotected, field-serviceable
→
Distributor5 V USB + regulated 12 V
→
Battery-in-appliance loadslights · radio · fans · phone · power banks
Stage 2 — add a second panel, still no central battery
2 × 150 W PV · 1S2Psame operating voltage, roughly twice the current
→
20–25 A-class raw PV trunkdesigned from the start for the second panel
→
Main + add-on distributorsparallel taps, no on-site soldering
→
More daytime loadscharging · fans · pumps · tools · thermal loads
Stage 3 — same two panels, now with a 24 V battery
2 × 150 W PV · 2S1Prewired from parallel to series
→
24 V solar chargerlow-cost buck charger matched to panel string and LFP battery
↔
25.6 V / 50 Ah LiFePO₄1.28 kWh nominal shared storage
→
24 V household busDistributor · refrigerator · future DC loads
Compatibility requirement. Future Distributor revisions should tolerate the fully charged 24 V LiFePO₄ bus comfortably; 50 V-rated input capacitors and appropriately rated protection parts are preferred. The present prototypes still require bench qualification before this becomes a field specification.
After light and air movement, refrigeration is a major prize.
Lighting changes the evening. Fans change comfort in hot climates. Refrigeration changes food storage, shopping frequency, medicine storage and the household's daily rhythm. It is also the point where a shared battery starts to earn its cost much more clearly than it does for small portable loads.
300 W gives useful daily margin
At 5 peak-sun-hours, 300 W represents about 1.5 kWh/day gross solar energy before system losses. That is enough to contemplate an efficient small DC compressor refrigerator while still leaving energy for the original low-power services.
24 V × 50 Ah = 1.28 kWh nominal
A shared LiFePO₄ battery of this size can carry a modest refrigerator through the night and buffer cloud transients, while also feeding the original Distributor from a stable DC bus.
Efficient DC refrigeration
A working design target is roughly 0.3–0.5 kWh/day for a small efficient 12/24 V compressor refrigerator. Hot-climate performance, insulation, door opening and real household use still need field measurement.
The refrigerator should not force an inverter. A 12/24 V compressor refrigerator can run directly from the DC system, avoiding inverter standby and conversion losses. AC can remain an optional later capability rather than becoming mandatory at the refrigeration step.
What the stages are intended to support.
These are working design envelopes, not prescribed bundles. Efficient appliances and actual household behavior matter more than nameplate wattage.
| Stage | Generation / storage | Natural loads | Design intent |
|---|---|---|---|
| 1 · Entry | 150 W PV; appliance batteries only | Reading/task lights, phone, radio, small fans, power banks | Useful electricity with the minimum central hardware. |
| 2 · Expanded batteryless | 300 W PV, 1S2P; appliance batteries only | More charging capacity, more/larger fans, tool batteries, pumps and other daytime-direct loads | Double the solar resource without forcing a central battery purchase. |
| 3 · Shared storage | 300 W PV, 2S1P; 25.6 V 50 Ah LFP | Everything above plus efficient small DC refrigeration and other 24 V loads | Introduce shared storage only when a load such as refrigeration makes it valuable. |
Where this rung stands.
This is a working architecture, not yet a field-tested product. Its purpose is to ensure that the entry design does not paint a household into a corner.
Working principles
- Make 150 W the current entry-panel design target under evaluation.
- Design the raw PV bus from the start for a second identical panel.
- Use 1S2P for the 300 W batteryless stage.
- When the 24 V battery is added, change the same panels to 2S1P rather than replacing them.
- Keep the original Distributor and battery-in-appliance loads useful after the shared battery arrives.
- Prefer efficient DC refrigeration; add an inverter only when a later appliance actually requires AC.
Still to demonstrate
- Actual 150 W and 300 W household energy capture under real African conditions.
- Best low-cost 24 V LiFePO₄ solar charger and its real efficiency/protection behavior.
- Distributor operation and component lifetime from a 24 V LFP battery bus.
- Actual refrigerator consumption in hot households.
- Battery cycle life, service model and upgrade financing at project-scale prices.
Documentation note: All panel, battery, energy and cost figures here are project working assumptions. Exact MTF tier assignment also depends on availability, reliability, quality, affordability and safety.