Is DIY Off-Grid Advisor free to use?

Yes. The Scout plan is completely free — no credit card required. You can create builds, run the load calculator, use all the standalone tools, and join the community at no cost.

What off-grid systems does it support?

DIY Off-Grid Advisor supports vans, caravans, RVs, 4WDs, boats, cabins, sheds, and remote properties. It handles 12V, 24V, and 48V systems.

How does the Component Wizard work?

You enter your loads (appliances and usage hours), your location (for real sun hours), and your system type. The wizard then recommends the right battery bank, solar panels, MPPT controller, inverter, and DC-DC charger — all sized for your exact setup. It also generates a wiring diagram and PDF report.

Do I need electrical experience to use it?

No. The platform includes a full beginner-friendly knowledge base — Electrical 101, How-To guides, Troubleshooting, and a Glossary — so you can learn as you build. The tools are designed to guide you step by step.

What's the difference between monocrystalline and polycrystalline panels?

Monocrystalline panels are more efficient (20–23%) and perform better in low light and high temperatures. Polycrystalline panels are slightly cheaper but less efficient (15–17%). For most off-grid applications where space is limited (van roof, cabin roof), monocrystalline is the better choice. The price difference has narrowed significantly — mono is now the default.

How much does shading affect solar output?

Dramatically. A single shaded cell in a series string can reduce the entire string's output by 50–80%, because current is limited by the weakest cell. Even partial shading from a vent, antenna, or tree branch at certain times of day can significantly reduce daily yield. Map your shading carefully before finalising panel placement.

What angle should I mount my solar panels at?

For fixed installations, the optimal tilt angle equals your latitude. In Australia (latitude 25–45°S), 30–35° is a good starting point. For van and RV roofs, flat mounting is common — you lose some efficiency but gain simplicity and wind resistance. Flat panels in a good location still produce excellent results.

Can I mix different solar panels?

In parallel: yes, but only if they have the same Vmp (within ~10%). In series: only if they have the same Isc. Mixing panels in series is generally not recommended — the weakest panel limits the whole string. If you must mix, keep different panels in separate strings and combine at the MPPT.

What is NOCT and why does it matter?

NOCT (Nominal Operating Cell Temperature) is the cell temperature under more realistic conditions than STC — 800W/m², 20°C ambient, 1m/s wind. Typical NOCT is 45–50°C. At NOCT, a panel produces about 85–90% of its STC rating. This is a more realistic estimate of real-world output than the headline wattage.

How long do LiFePO4 batteries last?

Quality LiFePO4 batteries are rated for 2,000–5,000+ charge cycles at 80% DoD. At one cycle per day, that's 5–14 years. In practice, most off-grid systems don't cycle daily, so the calendar life (typically 10+ years) becomes the limiting factor. This is 5–10× longer than AGM lead-acid.

Can I charge LiFePO4 with a standard lead-acid charger?

No — not safely. Lead-acid chargers use different voltage profiles and may apply equalization charges that will damage lithium cells. You need a charger with a LiFePO4 profile (absorption voltage ~3.65V/cell, no equalization). Most modern MPPT controllers and inverter-chargers have a LiFePO4 setting.

How many batteries do I need?

Calculate: (Daily Wh × Days of autonomy) ÷ DoD ÷ System voltage = Ah required. Example: (2000Wh × 2 days) ÷ 0.80 ÷ 24V = 208Ah. Round up to the next available size — in this case, 2× 100Ah 24V batteries (or 4× 12V 100Ah in 2S2P configuration).

Can I mix old and new batteries?

No — never mix batteries of different ages, capacities, or chemistries in the same bank. The weaker battery will limit the whole bank's performance and will be stressed by the stronger batteries. If you need to expand capacity, replace the entire bank with matched batteries.

What is a BMS and do I need one?

A Battery Management System (BMS) monitors and protects individual cells in a lithium battery pack. It prevents overcharging, over-discharging, over-current, and charging in freezing temperatures. All quality LiFePO4 batteries have a built-in BMS — if a battery doesn't have one, don't buy it. Lead-acid batteries don't need a BMS.

Should I store my battery at full charge?

For LiFePO4, no. Long-term storage at 100% SoC accelerates calendar aging. Store at 50–60% SoC if the battery will sit unused for more than a few weeks. For lead-acid, the opposite is true — store fully charged and top up monthly to prevent sulfation.

What size inverter do I need?

Add up the wattage of all AC appliances you might run simultaneously. Add 20% headroom. That's your minimum inverter size. Remember: motors (fridges, pumps, power tools) surge to 3–6× their running wattage at startup — your inverter's surge rating must handle the highest single-load surge.

Pure sine wave vs modified sine wave — does it matter?

Yes, significantly. Modified sine wave inverters are cheaper but can damage sensitive electronics, cause motors to run hot, make transformers buzz, and won't work with some appliances at all. Pure sine wave is the only safe choice for laptops, TVs, medical equipment, and any appliance with a motor. Always buy pure sine wave.

What is an inverter-charger and do I need one?

An inverter-charger combines a pure sine wave inverter, a multi-stage battery charger, and an AC transfer switch in one unit. When shore power (campsite hookup or generator) is available, it charges the battery and passes AC to your loads simultaneously. For full-time van life or cabin use, an inverter-charger is the right choice.

How far should the inverter be from the battery?

As close as possible — ideally within 1 metre. The DC cable between battery and inverter carries very high current (a 3000W inverter at 24V draws 125A). Every extra metre of cable adds resistance and voltage drop. Use the shortest, thickest cable you can practically run.

How do I choose the right cable size?

Use our Wire Calculator — enter the circuit current, cable length, and system voltage, and it calculates the correct cable size for less than 3% voltage drop. As a rough guide: for 12V systems, use at least 6mm² (AWG 10) for runs over 2m at 20A+. Always err on the side of larger cable.

Where should I put the main fuse?

As close to the battery positive terminal as possible — within 300mm (12 inches) is the standard. The fuse protects the cable from the battery to the first distribution point. If there's a fault anywhere in the system, the fuse must clear before the cable can ignite.

What type of fuse should I use for a LiFePO4 battery?

Class T fuse — mandatory for LiFePO4. LiFePO4 batteries can deliver thousands of amps in a fault condition. ANL fuses are too slow — the cable can burn before the fuse clears. Class T fuses clear in microseconds and are the only safe choice for lithium battery terminals.

Can I use automotive wire for solar panel cables?

No. Solar panel string wiring requires UV-resistant, double-insulated PV cable (PV1-F in EU/AU/NZ, USE-2 in US). Standard automotive wire is not rated for outdoor UV exposure or the voltages involved in PV strings. Using the wrong cable is a fire risk and may void your insurance.

What is voltage drop and why does it matter?

Voltage drop is the loss of voltage along a cable due to its resistance. A 12V fridge that needs 12V but only receives 11.4V (5% drop) will run inefficiently and may not start. Aim for less than 3% voltage drop on any circuit. Use our Wire Calculator to check every run.

Can I charge my leisure battery from my vehicle alternator?

Yes, but use a DC-DC charger (B2B charger) — not a VSR (voltage sensitive relay). Modern vehicles have smart alternators that vary output voltage, making VSRs unreliable. A DC-DC charger works with any alternator, provides a proper charge profile for LiFePO4, and limits current to protect the alternator.

How long does it take to charge from solar?

Depends on your array size, battery capacity, and sun hours. A 400W array in 5 peak sun hours produces ~1600Wh per day (accounting for losses). A 200Ah 12V battery (2400Wh) would take about 1.5 days of good sun to charge from empty. In practice, you're topping up daily rather than charging from empty.

Can I use a generator to charge my battery?

Yes — through an inverter-charger. The inverter-charger's AC input connects to the generator, and it charges the battery at its rated charge current. Size the generator to at least 1.5× the inverter-charger's AC input rating. A Honda EU22i (2200W) is a popular choice for systems up to 3000W inverter-chargers.

What is shore power and how does it work?

Shore power is AC power from a campsite hookup, marina, or building. An inverter-charger connects to shore power via its AC input, charges the battery, and passes AC through to your loads simultaneously. When shore power is disconnected, it automatically switches to inverter mode. The switchover is typically less than 20ms.

Do I need a battery monitor?

Yes — especially with LiFePO4. Unlike lead-acid, lithium batteries have a very flat voltage curve, so you can't tell SoC from voltage alone. A shunt-based monitor (Victron BMV-712 or SmartShunt) tracks every amp in and out and gives you an accurate SoC percentage. It's one of the most important components in the system.

What is the Victron VRM portal?

VRM (Victron Remote Monitoring) is a free cloud portal that displays real-time and historical data from Victron GX devices (Cerbo GX, Venus GX). You can see battery SoC, solar production, load consumption, and system history from any browser or the VRM app. It's free and requires a Cerbo GX or similar GX device.

How do I know if my system is working correctly?

A battery monitor showing SoC trending upward during the day and stable or slowly declining at night is the key indicator. Check that your MPPT is producing expected power (compare to panel wattage × sun hours). Verify battery voltage is reaching absorption voltage during charging. Any significant deviation from expected values warrants investigation.

Do I need a permit to install solar panels?

In Australia, solar PV installations on fixed structures (cabins, sheds) require a licensed electrician and may require council approval. On vehicles (vans, caravans), DC systems are generally DIY-permissible. In the US, requirements vary by state and county. Always check with your local authority before starting work.

What electrical standard applies to my van or caravan in Australia?

AS/NZS 3001.2 covers electrical installations in caravans, motorhomes, and transportable structures. DC systems under 50V are generally DIY-permissible. Any 240V AC work must be done by a licensed electrician. The standard requires RCD protection on all AC circuits.

Do I need an RCD on my inverter output?

Yes — in Australia and most of Europe, all AC circuits from an inverter must be protected by an RCD (Residual Current Device). In the US, a GFCI (Ground Fault Circuit Interrupter) is required. This is a safety requirement, not optional. Most quality inverter-chargers have built-in RCD/GFCI protection.

How much does a basic van solar system cost?

A basic weekend van system (200Ah LiFePO4, 400W solar, 2000W inverter, MPPT, DC-DC charger, battery monitor) typically costs $2,000–3,500 AUD / $1,400–2,500 USD for quality components. Budget brands can reduce this by 30–40% but with reduced reliability and warranty support.

Is LiFePO4 worth the extra cost over AGM?

Almost always yes, when you factor in lifetime cost. LiFePO4 lasts 5–10× longer, has 2× the usable capacity (80% vs 50% DoD), charges faster, and weighs half as much. A 100Ah LiFePO4 effectively replaces a 200Ah AGM. Over 5 years, the total cost of ownership is typically lower for LiFePO4.

What's the most cost-effective way to expand an existing system?

Add more solar first — it's the cheapest way to increase daily energy input. Then add battery capacity if you need more autonomy. Upgrading the inverter or MPPT is usually the last step. Never add batteries of a different age or chemistry to an existing bank — replace the whole bank.

Are cheap solar panels worth buying?

For panels, mid-tier brands (Renogy, Rich Solar, Victron) offer good value. Ultra-cheap no-name panels often have inflated wattage ratings and poor temperature coefficients. For MPPT controllers and inverters, quality matters more — cheap controllers can damage batteries, and cheap inverters can fail under load. Victron is the gold standard; Renogy and REDARC offer good mid-tier options.

My MPPT is showing less output than expected — what should I check first?

Start with shading — even a small shadow on one cell can cut a series string's output by 50–80%. Then check cable sizing from panels to MPPT (voltage drop reduces harvest). Clean the panels — dust and bird droppings are a common culprit. Finally, check that the MPPT's battery voltage setting matches your actual battery voltage. A 12V-configured MPPT on a 24V bank will stop charging at 14.6V, leaving the battery at ~50% SoC.

My battery isn't reaching 100% SoC — what's wrong?

The most common cause is the wrong absorption voltage in your charger settings. Even 0.2V too low means the battery never fully charges. Check your battery manufacturer's spec sheet and verify every charging source (MPPT, DC-DC charger, inverter-charger) is set to the correct absorption voltage. For LiFePO4 12V: typically 14.2–14.6V. Also check for parasitic loads — something drawing power continuously will prevent the battery from catching up.

My inverter keeps shutting down under load — what's causing it?

The most common cause is voltage sag — the battery voltage drops below the inverter's low-voltage cutoff under load. This is usually caused by undersized DC cables between battery and inverter (high resistance = high voltage drop at high current), or a battery that can't supply the peak current (AGM at 0.2C can only deliver 20A from a 100Ah battery). Measure voltage at the inverter DC terminals under load — if it's dropping below 11V (12V system), the cable or battery is the issue.

My battery monitor is showing incorrect SoC — how do I fix it?

First, verify the shunt is the only path for all negative current — any device connected directly to the battery negative (bypassing the shunt) will cause drift. Second, check the battery capacity setting matches your actual bank. Third, perform a full charge cycle to let the monitor synchronise to 100%. For LiFePO4, set the 'charged voltage' threshold to 13.2V (12V system) and tail current to 4% of capacity. If the monitor never synchronises, the charged voltage threshold may be set too high.

My DC-DC charger isn't charging when the engine is running — why?

Most DC-DC chargers require alternator voltage above ~13.2V to activate. Modern smart alternators can output as low as 11.5V at times — the charger may not trigger. Check input voltage at the charger with a multimeter while the engine is running. If it's below 13V, the alternator is in economy mode. Some chargers require a D+ (ignition) signal wire to know the engine is running — check if this is connected. Also check the input fuse on the start battery side.

My BMS keeps tripping — what should I check?

Connect a Bluetooth BMS app (if available) to see which protection triggered — this tells you exactly what to fix. Common causes: over-current from inverter surge (BMS rating too low for the load), cell imbalance (one cell hitting HVC before the others), low temperature charge protection (correct behaviour below 0°C — don't bypass it), or a loose connection causing a voltage spike. If the BMS trips on discharge, the load is exceeding the BMS continuous current rating.

I have a hot connection — what does that mean and what should I do?

A hot connection means high resistance at that point — the connection is doing work it shouldn't be. Causes: loose terminal bolt (re-torque to spec), poor crimp (remake the lug), corroded contact (clean with contact cleaner and re-torque), or undersized cable (replace with correct gauge). A connection more than 10°C above ambient under load needs attention. Left unchecked, it will get worse — resistance increases as the metal oxidises from heat, creating a thermal runaway that can ignite insulation.

Off-Grid Solar FAQ — 72 Questions Answered

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6 questions in Getting Started

Where do I start when designing an off-grid solar system?

Start with your loads — what do you want to power, and for how long each day?

Getting Started

What's the difference between 12V and 24V systems?

Both voltages deliver the same power — the difference is in current.

Getting Started

How do I calculate how much solar I need?

1) Add up your daily energy use in Watt-hours (Wh).

Getting Started

Can I build an off-grid system myself?

Yes — DC systems under 50V are generally DIY-permissible in most regions.

Getting Started

What's the most common mistake beginners make?

Undersizing the battery bank.

Getting Started

What tools do I need to install an off-grid system?

Essential: a quality multimeter, cable crimping tool with the right dies for your lug sizes, wire strippers, torque w…

Getting Started

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Frequently Asked Questions

Where do I start when designing an off-grid solar system?

What's the difference between 12V and 24V systems?

How do I calculate how much solar I need?

Can I build an off-grid system myself?

What's the most common mistake beginners make?

What tools do I need to install an off-grid system?