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Project identity
Location
Solar panels
Battery bank
System parameters
Load
Watts
min
Wh
No loads added yet. Add your first load below.
Total daily energy
0 Wh
Peak simultaneous demand
0 W
Add a load
— Wh/day
—
—
—
panels
Total required
—
kW
Array capacity
—
batteries
Total required
—
kWh
Usable bank
Monthly peak sun hours
Design month (worst case)
Other months
Wiring configuration
Panel strings—
Battery wiring—
Peak sun hours—
Daily generation—
Design month—
System losses
Wiring & connections−3%
Temperature derating—
Dust & soiling−3%
MPPT / charge controller−3%
Battery round-trip−5%
Inverter—
Total derate—
System summary
Daily load—
Energy with losses—
Battery chemistry—
Depth of discharge—
Days of autonomy—
System voltage—
Loads breakdown
Help & User Guide
SolarPal · by DEC Group
★ Quick start
SolarPal sizes a solar power system in three steps. Complete them in order — each step unlocks the next.
1
Enter site information
Name your project, enter GPS coordinates, choose panel direction and battery type.
2
Add your electrical loads
List every device that will run on the system — its power draw and how many minutes per day it runs.
3
Compute & review results
SolarPal calculates panels, batteries, wiring, and losses. Share or export a full system report.
1 Site information fields
Project identity
Site name
A short label for this project in your projects list (e.g. "Cabin A" or "Farm Workshop").
Description
Optional notes — location, owner, purpose. Appears on the exported report.
System type
Off-grid — no utility connection; batteries supply all power when panels aren’t generating. Grid-tied — excess power may be sold back to the utility. Hybrid — grid connection plus battery backup for outages.
Location
Latitude & Longitude
Enter in decimal degrees (e.g. 45.5017, −73.5673 for Montréal). These drive all solar calculations — sunrise time, day length, sun angle, and peak sun hours by month. Tap Use my GPS location to fill automatically.
Elevation (metres)
Height above sea level. Higher elevations receive slightly more solar irradiance due to a thinner atmosphere. Filled automatically when using GPS.
Solar panels
Panel direction (azimuth)
The compass direction the panels face. South (180°) is optimal in the northern hemisphere. East or West orientations reduce output by 15–25% but may suit your roof shape.
Tilt angle (°)
Angle of the panels from horizontal (0° = flat, 90° = vertical). A tilt equal to your latitude balances summer and winter output. At 45°N, a 45° tilt is a good starting point.
Panel capacity (W)
Rated peak power of a single panel in watts — found on the panel label or datasheet (e.g. 400 W). SolarPal uses this to calculate how many panels are needed.
Panel Voc (V)
Open-circuit voltage of a single panel at 25°C (STC). Used to determine series string count and to verify the MPPT controller max input voltage is not exceeded in cold weather.
Battery bank
Chemistry
Flooded lead-acid (FLA) — lowest cost, requires water top-up and ventilation, excellent cold tolerance to −25°C, 50% DoD.
AGM (sealed) — maintenance-free, no off-gassing, slightly better cold performance, 60% DoD.
Gel — sealed, vibration-resistant, sensitive to overcharging, 60% DoD.
LiFePO4 lithium — highest cycle life, lightest weight, 80% DoD, but must NOT be charged below 0°C without a BMS low-temperature cutoff.
AGM (sealed) — maintenance-free, no off-gassing, slightly better cold performance, 60% DoD.
Gel — sealed, vibration-resistant, sensitive to overcharging, 60% DoD.
LiFePO4 lithium — highest cycle life, lightest weight, 80% DoD, but must NOT be charged below 0°C without a BMS low-temperature cutoff.
Capacity (Ah)
Amp-hours per battery at the C20 rate (20-hour discharge). Found on the battery label. Do not use the CCA figure — that is for starter batteries, not deep-cycle storage.
Battery voltage (V)
Nominal voltage of a single battery unit (2V, 6V, 12V, etc.). Multiple batteries are wired in series to reach the system voltage.
System voltage (V)
12V — small systems; high current on long runs. 24V — medium systems. 48V — recommended above ~1 kW; lower current means thinner wire and less heat loss.
Days of autonomy
Days the battery bank must power loads without any solar input (e.g. during a cloudy stretch). 3 days is a common off-grid target. Cold climates or critical systems may warrant 4–5 days.
System parameters
Safety factor (%)
Oversizing margin added to panel and battery counts to account for real-world variation, aging, and future growth. 25% is the recommended default. Use 10% for tight budgets; 35–50% for critical or remote sites.
Inverter efficiency (%)
DC-to-AC conversion efficiency of your inverter. Most pure-sine inverters run at 90–97%. Enter 100% for DC-only systems.
2 System loads
Enter every device that will draw power from the system. SolarPal totals them to determine how much energy your system must generate and store each day.
Load entry fields
Name
A short label for the device (e.g. “Refrigerator”, “LED lighting”, “Water pump”).
Description (optional)
Extra detail — model number, circuit, or location. Appears in the results breakdown and exported report.
Power & unit
The device’s rated power draw. Select the unit: W for most appliances, kW for large loads like pumps or heaters, mW for sensors and small electronics. SolarPal converts all entries to watts internally.
Duration (min/day)
How many minutes per day the device runs. Maximum 1440 (= 24 h × 60 min). A refrigerator compressor typically runs 360–480 min/day; a water pump may only run 30–60 min.
💡
Finding power draw: Check the device label or manual for watts (W). If you only see amps and volts, multiply them: W = A × V. For AC devices showing VA (volt-amps), multiply by the power factor (typically 0.8–0.9).
💡
Live preview: The Wh/day figure updates as you type — it shows the daily energy for that one load. The sum of all loads drives your battery and panel sizing.
⚠️
Include standby loads: Phone chargers, routers, security cameras, and appliances on standby can add 10–20% to daily energy use. Don’t leave them out.
3 Understanding your results
Solar array
Total panels required
Minimum panels needed to meet daily energy demand in the worst-case month at your location, after applying all system losses and the safety factor.
Array capacity (kW)
Total rated peak power of all panels combined. Actual output varies with sun angle, temperature, and shading.
Battery bank
Total batteries required
Number of battery units needed for your autonomy days, accounting for the chemistry’s DoD limit and cold-weather derating.
Usable bank (kWh)
Total capacity multiplied by the DoD limit. This is the energy available during cloudy periods.
Sun chart
Monthly peak sun hours
Peak sun hours (PSH) = equivalent hours of full-strength (1000 W/m²) sunshine per day, adjusted for your latitude, tilt, and azimuth. The red bar is the design month (least sun) — which drives panel count. A system sized for the worst month has surplus capacity in all other months.
Wiring configuration
Panel strings (e.g. 2S × 3P)
S = panels wired in series (voltages add). P = strings wired in parallel (currents add). 2S × 3P means 3 strings of 2 panels = 6 panels total.
Battery wiring (e.g. 4S × 2P)
4S = 4 × 12V batteries in series = 48V. × 2P = two strings in parallel = double the Ah. Always wire series first, then parallel. Fuse each parallel string independently.
System losses explained
What each loss means
Wiring & connections −3% — resistance losses in DC cables and terminals.
Temperature derating — panels lose efficiency as they heat. Cooler climates (>40°N) −4%; tropics up to −8%.
Dust & soiling −3% — dirt, snow, and debris. Clean panels regularly.
MPPT / charge controller −3% — power conversion losses in the maximum power point tracker.
Battery round-trip −5% — heat losses during charge and discharge cycles.
Inverter — DC-to-AC conversion loss based on your inverter efficiency setting.
The total derate is applied to your daily load to calculate how much the array must actually produce.
Temperature derating — panels lose efficiency as they heat. Cooler climates (>40°N) −4%; tropics up to −8%.
Dust & soiling −3% — dirt, snow, and debris. Clean panels regularly.
MPPT / charge controller −3% — power conversion losses in the maximum power point tracker.
Battery round-trip −5% — heat losses during charge and discharge cycles.
Inverter — DC-to-AC conversion loss based on your inverter efficiency setting.
The total derate is applied to your daily load to calculate how much the array must actually produce.
? Frequently asked questions
Why does my panel count seem high?
SolarPal sizes for your worst-case month and includes a safety factor — both intentional. If the count seems too high, verify your daily load total is realistic, or reduce the safety factor or days of autonomy in Step 1.
What is the “design month”?
The calendar month with the fewest peak sun hours at your location. For most northern hemisphere sites it’s December. SolarPal calculates all 12 months and uses the lowest to size the system — so it’s never underpowered.
Can I use SolarPal for a grid-tied system?
Yes — select “Grid-tied” or “Hybrid” as system type. Calculations are the same; the type appears on your project card and exported report. For actual grid interconnection you will also need utility approval (e.g. Hydro-Québec’s net-metering programme).
Why FLA or AGM for cold climates?
FLA and AGM batteries can safely charge and discharge to −25°C when fully charged. LiFePO4 must NOT be charged below 0°C without a BMS low-temperature cutoff — charging below freezing causes permanent lithium plating damage. In an unheated enclosure in a cold climate, FLA or AGM is the safer default.
Is my project data saved automatically?
Yes — SolarPal saves all projects to your device’s local storage automatically. Nothing is sent to any server. If you clear browser data or the app cache, projects will be lost. Use the Export button on the results screen to keep a permanent copy.
How do I install SolarPal on my phone?
iPhone (Safari): Open the app URL → tap the Share button → “Add to Home Screen” → Add. Opens full-screen like a native app.
Android (Chrome): Open the app URL → tap the ⋮ menu → “Install app” or “Add to Home screen” → Install.
Android (Chrome): Open the app URL → tap the ⋮ menu → “Install app” or “Add to Home screen” → Install.
Is the output suitable for a permit application?
SolarPal is a design aid. For a regulated installation (any permanent structure in Canada or the US), a licensed electrician or engineer must prepare drawings and obtain permits. The exported report is a useful starting point for those conversations.
✉ Contact & support
Questions, bug reports, or commercial licensing enquiries:
Email
info@decgroup.proWebsite
decgroup.pro
SolarPal
Version 1.0 · Free for personal use
About
SolarPal is a solar power calculator for designing off-grid and grid-tied residential solar systems. It computes panel counts, battery banks, wiring configurations, and system losses using real astronomical solar calculations.
Developed by DEC Group Inc. · decgroup.pro
Copyright
© 2025 DEC Group Inc. All rights reserved.
The SolarPal name, DEC Group name, logo, and associated marks are trademarks of DEC Group Inc.
License agreement
Free for Personal Use
This software is provided free of charge for personal, non-commercial use only under the following terms:
✓Personal, non-commercial use is permitted at no cost
✓You may install SolarPal on any device you personally own
✓You may share the unmodified application files freely
✗Commercial use, resale, or distribution for profit requires a written licence from DEC Group Inc.
✗Modification, reverse engineering, or derivative works are not permitted without written consent
✗Removal or alteration of copyright notices or branding is not permitted
THIS SOFTWARE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. DEC GROUP INC. SHALL NOT BE LIABLE FOR ANY DAMAGES ARISING FROM USE OF THIS SOFTWARE. OUTPUT IS A DESIGN AID ONLY — CONSULT A LICENSED ELECTRICAL ENGINEER FOR ALL REGULATED INSTALLATIONS.
For commercial licensing enquiries: decgroup.pro
Solar calculation method
Peak sun hours are derived from real astronomical formulas: solar declination by day-of-year, sunrise hour angle from latitude + declination, surface irradiance adjusted for panel tilt and azimuth. System derate applies wiring, temperature, dust, MPPT, battery round-trip, and inverter losses. All project data is stored locally on your device — nothing is transmitted to any server.