How this tool works
The DIY Power System Designer is an integrated planning workbench for small off-grid, backup, mobile, workshop, laboratory, and experimental electrical systems. One load table feeds the battery, inverter, solar, and charge-controller calculations so assumptions stay synchronized.
Phase 4 uses transparent first-principles energy and power budgeting rather than a black-box product selector. It distinguishes daily energy from instantaneous power, keeps AC surge sizing separate from battery autonomy, and now adds hourly dispatch so timing-related deficits become visible.
The hourly simulator repeats each load schedule across the selected number of days, models a normalized PV-production window, enforces inverter/controller/battery-current limits, and tracks state of charge, unserved energy, and curtailment. A separate PV String + MPPT module checks temperature-adjusted Voc/Vmp and controller input/output limits.
Measured Profile Import can replace the synthetic load and/or solar curves with timestamped CSV data. Sub-hour power samples are held to the next timestamp and integrated into hourly bins so energy is preserved; measured irradiance can also be converted into modeled PV power from the installed array rating and an explicit derate factor.
Phase 4 now also includes a battery-realism screen for retained capacity, temperature capacity factor, Peukert/rate effects, and charge/discharge C-rate limits, plus a hybrid-source dispatcher for optional grid/shore support and SOC-controlled generator operation with a first-pass fuel estimate.
Long-Term / Seasonal Simulation extends that same hourly hybrid dispatcher to 7, 30, or 365 days. Jan-Dec load and PV multipliers shape synthetic profiles, while monthly summaries expose energy balance, minimum SOC, grid/generator dependence, generator fuel/run time, battery throughput, curtailed PV, loss-of-load hours, and service percentage.
Reliability + Lifecycle re-runs a standardized 365-day seasonal dispatch for every project year while applying explicit battery cycle/calendar fade, PV degradation, optional load growth, and generator run-hour maintenance/replacement thresholds. The result is a scenario projection of annual service, renewable contribution, grid/fuel use, replacements, maintenance, and cumulative entered cost rather than a lifetime guarantee.
The DC Distribution + Protection module maps the synchronized inverter, PV-controller, DC-load, and charger currents onto a simple battery/DC-bus one-line architecture. It screens manufacturer busbar/disconnect current ratings, branch voltage drop, configurable current density, and nominal fuse/breaker planning targets while keeping actual conductor ampacity, fault current, interrupt rating, and time-current coordination outside the model.
The Architecture Comparison module holds the same energy, inverter, PV, module, BMS-current, and conductor-path assumptions constant while comparing 12 V, 24 V, 48 V, and a configurable higher-voltage DC bus. It exposes the inverse current relationship, I²R cable-loss scaling, series/parallel battery-module geometry, charge current, bus-current basis, protection planning target, and first conductor meeting the entered voltage-drop/current-density screens.
The Equipment + Project BOM module turns the synchronized engineering outputs into datasheet-selection filters for battery modules, inverter, MPPT controller, PV modules, busbar, main disconnect, and main protective device. User-entered manufacturer/model ratings are screened against the calculated requirements, then combined with branch conductors/protection/disconnects into an exportable CSV/JSON project BOM. Product data is intentionally user-entered rather than embedded as a live vendor catalog.
Engineering Handoff transfers bounded, typed operating points to compatible Neutron STEM Lab workbenches. The inverter branch can populate DC wire sizing, the inverter power-stage operating point can populate the MOSFET loss/thermal tool, and battery/SOC/current-limit context can accompany a control-system model without inferring missing plant dynamics.
Engineering Project Report consolidates the synchronized sizing, storage, inverter, PV string, distribution, equipment, seasonal reliability, lifecycle, and BOM results into a browser-local planning record. It separates modeled pass/review/fail screens from mandatory external engineering review so the export cannot be mistaken for a stamped design or code-compliance certificate.
The DC wiring module estimates voltage drop, conductor loss, and a configurable current-density screen. It deliberately does not label the result as code-compliant ampacity.
Core equations
E_daily = Σ(P_load · quantity · hours/day · duty cycle)E_battery,nominal = E_daily · autonomy · (1 + reserve) / (DoD · η_discharge)C_bank,Ah = E_battery,nominal / V_bankP_inverter,continuous = P_AC,running · (1 + margin)I_DC,inverter ≈ P_AC / (V_bank · η_inverter)P_PV,min = E_daily / (PSH · derate · η_charge)I_controller ≈ P_array · η_controller / V_bankSOC[k+1] = SOC[k] + E_charge[k]/E_nominal − E_discharge[k]/E_nominalC_effective ≈ C_rated · f_age · f_temperature · min[1,(I_ref/I_load)^(k_Peukert−1)]I_max ≈ C_Ah · C-rate_limitI_branch,design = I_continuous · continuous-current factorI_bus,basis = max(ΣI_load, ΣI_charge) · bus continuous-current factorFor equal power: I_DC ≈ P/(V_bus · η), so doubling bus voltage approximately halves currentFor a fixed conductor path: P_cable = I²R, so halving current reduces cable loss to roughly one quarterV_oc,cold = N_s · V_oc,STC · [1 + α_Voc(T_min − 25°C)]V_mp,hot = N_s · V_mp,STC · [1 + α_Vmp(T_cell,max − 25°C)]t_runtime = V_bank · Ah · DoD · η / P_loadΔV_DC = 2 I L R_conductor
Method and assumptions
The workbench first converts every load into running power, average active power, and daily watt-hours. That shared load summary is then passed into independent battery, inverter, and solar sizing functions so one edit propagates through the complete design.
Battery sizing divides the required delivered energy by usable depth of discharge and discharge efficiency, then maps the resulting nominal energy to a simple series/parallel module model. The actual module-derived bank voltage is shown so a mismatch with the target voltage is visible.
PV sizing first computes the array needed to replace daily energy under the entered peak-sun-hours and derating assumptions, adds a user-controlled design margin, rounds up to whole panels, and estimates charge-controller output current.
Hourly dispatch converts each load schedule into 24 one-hour bins, converts AC demand to DC-bus demand through inverter efficiency, distributes the daily PV energy across the selected solar window, and then applies direct PV supply, battery charge/discharge limits, usable-SOC floor, charge/discharge efficiency, inverter rating, unserved-demand accounting, and PV curtailment.
Battery Realism begins with the installed amp-hour capacity, applies explicit aging and temperature capacity multipliers, then applies a conservative Peukert/rate-capacity factor based on the entered exponent and reference discharge rate. It separately converts entered C-rate limits into maximum continuous charge/discharge current screens.
Hybrid dispatch reuses the same hourly load/PV/battery state. Grid/shore support can be preferred or held as a backup below an SOC threshold. Generator operation uses start/stop SOC hysteresis plus minimum run time, source/charger power limits, battery charge/discharge current limits, and a linear no-load-to-full-load fuel-rate estimate.
Long-term seasonal simulation constructs a calendar-aligned hourly series from the same daily load/PV bases, applies Jan-Dec multipliers to synthetic values, runs the unchanged hybrid dispatch logic for up to 365 days, then aggregates load, utilized PV, grid/generator energy, generator fuel/runtime, minimum SOC, battery throughput, curtailed energy, and loss-of-load metrics by month.
PV string design evaluates series/parallel candidates using first-order Voc/Vmp temperature coefficients. A candidate passes only if cold Voc is below the controller absolute maximum, hot/cold Vmp remain within the MPPT window, 1.25 × parallel Isc remains within the entered PV input-current limit, and estimated controller output current remains within its rating.
DC cable sizing derives AWG conductor area from the geometric gauge relationship, applies copper or aluminum resistivity with a first-order temperature correction, then calculates full-loop voltage drop and I²R loss.
DC distribution derives four synchronized branch-current models from the rest of the workbench: battery-to-inverter, PV-controller-to-bus, aggregate DC loads, and the larger enabled AC charging path. Each branch applies a user-selected continuous-current factor, cable drop/current-density screens, a rounded nominal protection planning target, and entered disconnect rating. The busbar screen uses the larger aggregate load-direction or charge-direction current multiplied by a separate bus continuous-current factor.
Architecture Comparison recomputes battery series/parallel geometry, inverter/DC-load current, PV charge current, bus current, fixed-conductor voltage drop/I²R loss, and an automatic conductor screen for each candidate voltage while keeping system power and energy assumptions unchanged. The highlighted candidate is only the lowest-current option within the user-entered preferred voltage ceiling that passes the modeled BMS-current and cable recommendation screens.
Equipment screening derives a compact set of minimum/range checks from the synchronized battery, inverter, PV-string, and distribution results. Battery module candidates are converted into a whole-module series/parallel bank; inverter and controller candidates are checked against voltage/current/power windows; PV changes are flagged for string revalidation; and busbar/disconnect/protection candidates are screened against DC voltage/current targets. The BOM preserves pass/review/fail status and user-entered cost without treating a candidate as certified.
Cross-workbench handoff uses a versioned neutron-engineering-handoff envelope containing source provenance, an explicit target tool and engineering intent, and a bounded typed payload. Destination tools validate the envelope and apply only fields they explicitly support; unsupported context remains informational.
Assumptions
- Daily load energy uses user-entered operating hours and duty cycle. The hourly dispatch model treats duty cycle as average power within each load's scheduled operating window and uses one-hour time steps rather than minute-by-minute switching.
- Battery nominal energy is reduced by user-selected usable depth of discharge and discharge-path efficiency. Chemistry presets are planning defaults, not battery-manufacturer limits.
- Battery Realism applies user-entered retained-capacity and temperature multipliers and a conservative Peukert/rate-capacity screen. It does not infer hidden manufacturer curves.
- Hybrid dispatch treats grid/shore and generator sources as bounded AC inputs feeding the same DC-bus-equivalent hourly model through user-entered charger efficiencies. It is an energy/power model rather than a transfer-switch electrical model.
- Seasonal simulation uses a non-leap 365-day calendar and twelve user-entered monthly multipliers. Synthetic load/PV profiles are scaled by the active calendar month; imported measurements are preserved unless the user explicitly enables scenario scaling of measured data.
- Lifecycle projection standardizes each modeled project year to a 365-day dispatch. Battery capacity fade is derived from equivalent full cycles plus a user-entered calendar-fade scenario; replacement resets battery age/cycle counters for the following year. Generator maintenance and replacement are run-hour threshold events.
- PV energy uses peak-sun-hours with a single derate factor when synthetic solar mode is selected. Measured Profile Import can instead use measured PV power or measured irradiance; irradiance conversion still uses the installed array rating and an explicit user-entered derate rather than a full module-temperature/weather model.
- Imported power samples are treated as piecewise-constant until the next timestamp and are energy-preserving resampled into one-hour bins. The last sample uses the median source interval, and large gaps are flagged for review.
- Inverter surge sizing conservatively sums configured AC starting surges; real equipment may have non-coincident or differently shaped inrush events.
- DC cable calculations use bulk conductor resistivity and a complete source-to-load-to-source loop.
- Architecture Comparison treats 12 V, 24 V, 48 V, and the configurable higher-voltage value as nominal bus classes. Actual bank voltage is derived from whole battery modules and may differ from the class label.
- Engineering handoffs transfer only quantities explicitly represented by both source and destination. Device switching parameters, plant dynamics, PID gains, conductor ampacity, and protection coordination are not inferred from unrelated source values.
