Design inputs guide

What each field on the site design form actually does — moved here so the design screen itself stays scannable. Follow the "What's this?" link next to any field to jump straight to its entry below.

Site & load

1Latitude: Drives the seasonal solar curve. Negative for southern hemisphere.
2Longitude: No engine uses this — it only places the pin on the map below.
3Location map: OpenStreetMap — no API key or billing required. Moves live as latitude/longitude change above.
4Outage starts at: Drives the 24-hour supply chart. A night outage needs more from the battery than the same length spanning midday.
5Short interruptions: Drives supercapacitor sizing, not battery.

Solar & weather

6Solar should carry: 0 disables solar entirely. Ignored below if a fixed array size is set.
7System losses: Inverter, wiring, soiling, temperature.
8Fixed solar array: For a brownfield site with an already-installed array — a given fact, not a target to size. Battery, generator and diesel are all sized around exactly this much solar; the target % above is ignored for sizing but the real coverage this array actually achieves is still shown for comparison.
9Poor-weather days to ride out: Increases battery so a cloudy spell needs no extra generator.

Battery

10Cap battery at: Reduces capex. Does NOT change annual fuel — that is a daily energy balance independent of battery size. A smaller battery only reduces buffering margin during the outage.
11Max cycles per day (cycle-life ceiling): The hard limit storage may never cross, derived from the chemistry's rated cycles divided by its warranty years (or a supplier's separate practical cap, whichever is lower). Storage is sized UP if needed to stay within it — never down past it. The actual binding number and which limit currently applies are shown live on the 'Battery cycles/day' result card, so they are not repeated here.
12Chemistry: Sets depth of discharge, round-trip efficiency and rated cycles from typical figures for the chosen chemistry. Replace with your supplier's actual datasheet figures once known — the typical numbers are a starting point for a conversation, not a substitute for one.

Cycle charging

13How cycle charging works: The generator does not just follow the load — once triggered, it runs oversized so the surplus recharges the battery, and keeps running until the battery is genuinely full, then shuts off completely. Fewer, longer, more efficiently-loaded runs, not frequent starts at partial load.
14Charging rate: The LESSER of the storage bank's own real charge-rate limit and the rectifier's remaining capacity after serving the load — both are genuine, independent ceilings.

Supercapacitor

15Cost: 0 disables supercapacitors.

Generator & fuel

16Generator size: Real generators come in discrete standard sizes, not an arbitrary continuous rating. Choose the nearest standard size at or above the computed minimum, or enter an existing site's real installed size — an undersized choice is flagged as a real overload risk, not silently accepted.
17Fuel absorption band: Fuel movement we absorb before the tariff adjusts. Only the excess passes through.
18Generator starts at: Battery discharged to this level triggers the generator.
19Generator stops at: Battery recharged to this level shuts the generator off.

Rectifier

20Why a separate rectifier: A real, separate bottleneck between the generator or grid and the DC bus feeding the load and battery — its own rated capacity can limit charging even when the generator has spare capacity. 0 cost keeps this folded into balance of system, matching the previous behaviour exactly.
21Rectifier cost: 0 keeps rectifier cost inside balance of system, unseparated.
22Fixed rectifier size: For an existing site's real, already-installed rectifier. This engine sizes only to the bare minimum needed to serve the continuous load — it does not attempt to derive a battery-recharge-speed figure, since there is no universal rule for how fast an operator wants a battery recharged; the generator start/stop thresholds control that instead.

Landed cost

23Price on landed cost: Treats the equipment prices above as EX-FACTORY and adds freight, insurance, duty, clearing and delivery. The gap is routinely 20-40%.
24FX to reporting currency: 1 if supplier prices are already in the reporting currency.
25Sites in this shipment: Freight and clearing are spread across the shipment; delivery and installation are per site.

Costs & commercial

26Balance of system: Rectifier, cabling, civils, install.

Technology comparison

27Technology comparison prices: Current market prices for the two chemistries in the comparison below, independent of whichever technology is actually chosen above — lets a supercapacitor-first design still be checked against real lithium and VRLA prices.

Total cost of ownership

28Why air-con capex/load: VRLA and lithium both genuinely need active cooling in their enclosure to reach rated life — a real cost, and real additional load the generator/rectifier must also serve. Supercapacitors need none of this; the TCO comparison applies these figures only to the chemistries that actually need them.
29Air-con default load: Default 1.7 kW reflects a real DC aircon unit's typical draw (30-40 A at 48V DC).

Charts

3024-hour supply mode: No battery charge/discharge rate limit is modelled — only energy capacity. A single continuous outage block is assumed, starting at the hour set on the left; real load-shedding schedules can be split differently.
31Battery cycling (DG status / SoC / current): Same representative day as the dispatch chart. Voltage is replaced with state of charge — a real battery's terminal-voltage swing IS its SoC swing. Current is charge/discharge POWER at an assumed 48V DC nominal bus (standard for this class of site) — an approximation, not a measured value; only DG status is a direct, unconverted simulation output.
32Annual site performance: The full year's hours accounted for exactly once across grid, solar, battery and generator — run for all 12 months, not just the worst-case month the other charts use.
33Generator hours by month: Estimated hours the generator runs each month across the year — peaks where solar is weakest and the outage falls outside daylight.
34Capex by scenario — solar and outage duration: Two comparisons in one chart. Solar bars: same load, same outage — only the solar target changes; removing solar shifts cost onto battery and, often, diesel. Outage-duration bars: same load, same solar target — only how many hours per day the grid is unavailable changes. The 'With solar' bar is this site's real current configuration — the same design shown everywhere else on this page.
35Chemistry — cost per year: Cost per year to own the storage bank alone, given the site's real cycles/year — the ranking that matters, since a cheap bank that fails early is not actually cheap.
36Power flow: Same representative day as the charts above. DG, battery and solar power are real simulation outputs. Rectifier power is APPROXIMATE — grid/generator power serving the load plus any battery charging that hour, per this site's own topology (grid and generator route through the rectifier, solar and battery discharge do not). Exact for a fully off-grid, no-solar site; can slightly overstate when solar and the generator are both active in the same hour, since the simulation does not separate which source is doing the charging.

Improving the return

37How this panel works: The main page shows one live headline (does this design meet your target IRR) plus the Target IRR field itself — everything below is the general explanation of HOW the diagnosis works, moved here so the design screen stays scannable. Three levers usually explain most of the gap: (1) Solar headroom — if the solar target is below 100%, solar has no fuel cost and no cycling limit, so raising it improves return for the whole term; try the 'Maximise solar use' objective and compare lifetime cost against the current design. (2) Diesel is usually the largest recurring cost — a site's annual fuel bill compounds over the full term, often exceeding the hardware cost itself; raising the solar target above 0% displaces diesel directly, and unlike storage it keeps paying every year of the term. (3) The tariff floor — an all-in rate at or below the floor cost loses money regardless of how the site is built; check the required tariff against what the customer will actually pay before assuming a design problem. Each specific number in the live panel is computed directly from your current design's real inputs, not a generic estimate — changing one input changes the others, so re-run the design rather than assuming the improvements listed there simply add up.

Recommended design KPIs

38Levelised cost: Per kWh — the floor under any tariff. No price below this ever pays the design back, at any term.
39Proposed price: Per kWh, for the shortest achievable payback shown next to it — this is the rate actually quoted, expressed as a percentage above the levelised-cost floor so it's clear how much margin is built in.
40Payback: The shortest payback achievable at the proposed price above. If this shows a dash, no price on the curve pays the design back at all — see the recommendations further down the page for what to change.
41Battery / main storage: Installed capacity, built from whole modules — module count and its real capex used to be shown here directly; both are still visible on the Technology comparison table this card links to.
42Solar: Array size required to meet the solar target. Its real capex is shown on the Technology comparison table this card links to.
43Short-interruption bank: A supercapacitor pool separate from the main storage above, sized only for brief grid blips — not the full outage. Shows "none" when there's no short-duration duty to cover, which is expected on many sites, not a gap.
44Generator: Real kVA required. Its daily runtime is shown on the DG hours/day card below, not repeated here.
45Battery autonomy: How many hours the battery alone can cover, compared against the site's actual daily outage length.
46Annual diesel: Litres per year. The real cost and who pays for it (customer or operator) are shown on the Diesel-by-month chart this card links to.
47Fuel savings: Percentage saved against a diesel-only baseline (this exact site's own generator, running continuously with no storage or solar), computed from the real hourly cycle-charging dispatch simulation — not the day-level balance the Annual diesel card above uses. That balance can't see battery-driven fuel savings at all on a no-solar site, so this card deliberately reads from a different, more detailed engine.
48ROI: NPV as a percentage of capex, at the shortest-achievable-payback rate shown in the tariff table below.
49IRR: Pre-tax internal rate of return, at the same shortest-achievable-payback rate the ROI card above uses.
50DG hours/day: The day-level energy balance's own figure — energy needed divided by the generator's real output. The hourly dispatch simulation below can show a slightly different number for the same design: it can only start and stop the generator on the hour, so it rounds up, while this card's figure sits closer to what actually happens. A warning badge appears on the card itself only when the two genuinely diverge by a meaningful margin.
51DG hours savings: Percentage saved against the same diesel-only baseline the Fuel savings card uses (generator running all 24 h/day, every day), on generator run-hours instead of litres — sourced from the same real hourly dispatch simulation, not the DG hours/day card's day-level balance above.
52Battery cycles/day: In equivalent full cycles (EFC) — the basis suppliers actually rate cycle life on. Compared against this design's own cycle-life ceiling (derived from the chemistry's rated cycles and warranty, or a supplier's own tighter cap) — a warning badge appears only when the design is currently over that limit.
53DG cycles/day: Generator STARTS per day — a genuinely different count from battery cycles above. "1 (continuous)" means the generator runs the whole representative day without ever cycling off, not that it started once and stopped.