Solar system planner · Free · No upload
Plan your off-grid solar system, then play with it.
Drag appliances and equipment onto a live workspace, or start from a ready-made kit, and watch your off-grid system run: current flows through the wires, the battery fills and empties, inverters trip and fuses blow when something is wrong. A score lists strengths, weaknesses and mismatches with one-click fixes. It runs in your browser and nothing is uploaded.
- Off-grid & portable
- Panels · battery · inverter
- Cables & fuses
- Battery life
What fkSolar can do
Pick appliances, not parts
More than 40 typical appliances with watts, hours per day and motor start-up surge: lights, TVs, laptops, fridges, pumps, washing machines, tools. Every number is editable.
From a camper van to a large home
Start from a kit (a field hut, a water pump, a small home, four air conditioners) or build from nothing. Systems can have several inverters, several charge controllers and an all-in-one inverter, up to about 30 kW on a 12, 24 or 48 V battery.
Sized with real equipment
Real panel sizes with series and parallel layout, an MPPT or PWM charge controller, a pure sine inverter and a 12, 24 or 48 V battery bank.
Surge and idle aware
Starting surge of pumps, fridges and washing machines, plus the inverter’s own idle draw, are included. They are the usual reasons small systems fail.
A live workspace, like the electronics lab
Every part sits on one schematic and every appliance has its own switch. Run the clock at up to 3 hours per second, add clouds or take the sun away, and watch current flow through the wires, the meters and the battery. Appliances switch off when the battery is empty, inverters trip when overloaded and fuses blow.
Cables and fuses
Copper cable size for each run from current and voltage drop, in mm² and AWG, with a fuse rating for each run.
Compatibility check and score
Swap any part and get a 0–100 score. It lists strengths, weaknesses and mismatches such as wrong voltages, missing fuses, thin cables and undersized inverters, each with a one-click fix, and every point lost is named.
Share, print and learn
Copy a link that contains your whole design, print or save a report as PDF, and work through guided experiments such as why a pump trips an inverter or how to survive three cloudy days.
Private by design
The planner runs in your browser. Your projects are saved in this browser only and are never sent to a server.
How to use fkSolar in 5 steps
Start from a kit or an empty canvas
Press “Start planning”, then pick a ready-made kit, or drag appliances and equipment from the left onto the canvas. Tap any part to change its size, wiring or settings.
Read the score
Open Checks to see the 0–100 score, what costs points and what is right. Apply a suggested fix with one tap, or let Auto-size rebuild the whole system from your appliances.
Run it
Watch the day go by. Flick appliances on and off, speed up time, add clouds or take the sun away, and see the voltage, current and battery level, and what trips or blows.
Stress-test it
Open Tests to run a sunny, cloudy or rainy week, see the biggest appliances running together, and how long each part should last.
Save and compare
Undo and redo any change, save projects in this browser, and compare designs by their score.
What people use it for
A cabin, van, boat or shed
Work out how much solar and battery you need before you spend money on equipment.
Backup power for the essentials
Check that the fridge, lights, router and phones can run through a day or two without sun.
Learning how solar systems fit together
See why the voltage, current and surge of each part must match the next one.
Your files stay on your device
fkSolar runs entirely in your browser. Your projects and settings are saved in this browser only, so you can come back later, and are never sent to our servers.
These pages use anonymous page-view analytics (Google Analytics); the contents of your files are never part of that data. Read more about privacy.
Browser support
Good to know
- fkSolar covers off-grid systems with one DC battery bank and single-phase AC (up to about 30 kW and 48 V). Grid-tied (on-grid), hybrid and three-phase systems are not covered; a grid-tied system without a battery does not power your home during an outage. The simulation is a simple model, not a forecast, and fuse and cable failures are simplified for learning.
- Equipment numbers are typical values, not data for a specific brand. Always check the datasheet of what you buy.
- Panel tilt, shading, temperature extremes and AC distribution wiring are not modelled in detail.
- The result is an estimate for planning and learning, not an electrical design or an installation guide.
- fkSolar is an early release, and features may be added or changed.
Frequently asked questions
Is fkSolar free?
Yes. It is free, with no sign-up and no login.
How do I share my design?
Press Share to copy a link. The link holds the whole design, so nothing is stored on a server, and anyone who opens it sees your system and can change their own copy. Report gives a printable page you can save as PDF.
Are my appliance list and settings uploaded?
No. Everything is calculated in your browser. Your projects are stored in this browser only so you can return to them.
What kinds of solar systems does it cover?
Off-grid systems from a 12 V camper van to a large single-phase home (about 30 kW at most): panels, charge controllers, a battery bank and one or more inverters, including all-in-one inverters. On-grid and hybrid systems are not covered.
Should I buy a power station or build a system?
If your daily use is small (roughly under 1 kWh) and you have no big motor or heating loads, an all-in-one power station is simpler and safer. For larger loads, separate components give the right size and room to grow. Build both on the workspace and compare their scores.
Why does a fridge or water pump need a bigger inverter?
Motors and compressors draw several times their running power for a second or two when they start. The inverter must handle that surge, not only the running watts.
Why is my battery bigger than my daily energy use?
Batteries should not be emptied fully. Lead-acid is best kept near 50% depth of discharge and LiFePO4 around 80%, so the bank must be larger than the energy you take from it. A reserve of cloudy days adds to that.
How is the score calculated?
The score starts at 100 in five weighted groups: safety 30%, compatibility 25%, capacity and balance 25%, longevity 12% and efficiency 8%. Each problem found subtracts named points, and you can open any group to see exactly what cost points. Any critical problem caps the score below 60 until it is fixed.
Can I try switching appliances on together?
Yes. On the workspace every appliance has its own switch. Turn on one, two, three or all of them while the clock runs, and see the total power, the inverter load, whether a motor start-up trips the inverter, and how long the battery lasts. The Tests tab also shows the worst cases with the 1, 2, 3, 4 and all biggest loads on at once.
What happens when the battery runs out?
The inverter cuts off at low battery, so the appliances switch off, just like the real thing. They come back when the sun has charged the battery above 15%. If a motor or heavy load overloads the inverter it trips until you reset it, and a fuse that carries too much current blows until you replace it.
How accurate is it?
It uses standard engineering rules and typical equipment values, so it is good for planning and comparing options. Real results depend on your exact equipment, shade, temperature and wiring.
Can I build my system straight from the result?
Use it to plan and learn. Batteries and DC wiring can start fires, so have the final design checked by a qualified electrician and follow your local electrical code.
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