Inverters

Van Inverter Sizing Guide: Pure Sine, Surge Ratings & Real Costs

The inverter is the component van owners most reliably get wrong, and they get it wrong in both directions. Half buy a 3,000W unit to run a laptop and then wonder why their battery drains overnight with everything switched off. The other half buy a 600W unit, plug in a kettle, and trip it within four seconds. Correct van inverter sizing is not about buying the biggest number you can afford — it is about matching continuous rating, surge headroom and idle consumption to loads you have actually measured.

What an Inverter Actually Does — and What It Costs You

An inverter converts 12V or 24V DC from your battery into 230V AC mains. That conversion is not free. Quality inverters run at 88–93% efficiency under load, so every 100W your laptop draws pulls roughly 110W from the battery. Cheap units run at 78–85%, and the difference compounds across a full day of use.

The more important cost is idle draw — the power an inverter consumes simply by being switched on with nothing plugged in. This is the figure that quietly destroys van battery banks, and it scales with inverter size:

300–600W inverter: 4–8W idle
1,000–1,500W inverter: 8–15W idle
2,000–3,000W inverter: 15–30W idle
5,000W inverter: 30–50W idle

A 3,000W inverter left on continuously at 22W idle consumes 528Wh per day — more than a compressor fridge, and more than a 200W solar array generates in a British December. Buying an oversized inverter and leaving it powered is one of the most expensive mistakes in van electrics, and it is entirely invisible until you watch your state of charge fall overnight.

Every inverter should be switched off at the unit or via a remote panel when not actively in use. If you cannot be disciplined about that, size down.

Continuous Rating vs Surge Rating

Inverters carry two numbers. The continuous rating is what the unit will deliver indefinitely. The surge rating — usually 2× continuous for 3–10 seconds — covers the inrush current when a motor or compressor starts.

Resistive loads (kettles, toasters, hair dryers, heaters) draw their rated wattage instantly and hold it. A 1,200W kettle needs 1,200W continuous, full stop.

Inductive loads (fridges, pumps, power tools, microwaves) draw a starting surge far above their running figure:

Compressor fridge: 45W running, 150–250W surge
Water pump: 60W running, 180–300W surge
Microwave (800W rated output): 1,200–1,400W running, 1,800–2,200W surge
Angle grinder or circular saw: 800–1,200W running, 2,000–3,500W surge

Size the continuous rating to your largest simultaneous running load plus 25% headroom, then verify the surge rating covers your worst-case inrush. In most vans the continuous figure is set by a kettle or microwave, and the surge figure is set by a power tool.

Pure Sine Wave vs Modified Sine Wave

Modified sine wave inverters approximate mains AC with a stepped square wave. They cost 40–60% less than pure sine units and they will run a kettle, a filament bulb or a resistive heater perfectly well.

They will also, over time, damage or refuse to run a long list of things van dwellers actually own: laptop chargers with active power factor correction, CPAP machines, variable-speed power tools, induction hobs, modern TVs, battery chargers with switch-mode supplies, and most medical equipment. Motors run hotter and less efficiently on modified sine and fail earlier. Some devices simply buzz audibly and work at reduced performance until they don’t.

The verdict is straightforward: fit pure sine wave. The price gap on a 2,000W unit is roughly £120–200, and a single replaced laptop charger erases the saving. Modified sine is defensible only in a dedicated tool-only circuit, and even then barely.

Calculating the Right Size — Worked Example

List every 230V device and identify what genuinely runs at the same time. Van owners consistently overestimate simultaneity — you do not boil a kettle while microwaving and running a hair dryer.

A typical touring van:

Laptop and monitor: 90W
Phone/camera chargers: 40W
Kettle (occasional): 1,200W
Microwave (occasional): 1,300W running, 2,000W surge
Cordless tool charger: 90W

The largest realistic simultaneous load is the microwave at 1,300W plus background charging at 130W, totalling 1,430W. Add 25% headroom: 1,790W. The correct continuous rating is 2,000W, and the surge requirement of 2,000W is comfortably inside a 2,000W unit’s typical 4,000W surge capability.

Note what this calculation does not justify: a 3,000W inverter. The extra 1,000W of capacity you will never use costs you 8–12W of additional idle draw every hour it is switched on, plus heavier cable and a larger fuse.

If your van has no kettle and no microwave — many don’t, because both are brutally inefficient uses of stored battery — your largest load drops to around 200W and a 600W inverter is genuinely sufficient. Gas or induction on shore power handles cooking better than any inverter will.

12V or 24V: The Decision That Sets Everything Else

Inverter current draw on the DC side is the load divided by system voltage. A 2,000W load on a 12V system pulls approximately 185A after conversion losses. The same load on 24V pulls 93A.

That difference dictates cable, fusing and cost. 185A requires 50–70mm² cable and a 200A fuse; 93A needs 25–35mm² and a 100A fuse. Heavy DC cable is expensive, stiff, and difficult to route through a van.

The practical rule: any inverter above 2,000W belongs on a 24V system. Below 1,500W, 12V is simpler and keeps you compatible with the enormous range of 12V appliances, lighting and fridges. Between 1,500W and 2,000W either works, and the deciding factor is usually whether the rest of your system is already 12V.

Cable Sizing and Fusing — Where People Get Hurt

Inverter DC cables carry currents high enough to melt an undersized conductor in seconds. This is the single most dangerous part of a van electrical system and the part most often improvised.

Minimum cable cross-sections for a 1.5m run at 12V, keeping voltage drop under 2%:

600W inverter (≈55A): 16mm²
1,000W inverter (≈92A): 25mm²
1,500W inverter (≈138A): 35mm²
2,000W inverter (≈185A): 50mm²
3,000W inverter (≈275A): 70mm²

Keep the run as short as physically possible — mount the inverter within 1.5m of the battery bank. Every additional metre demands a larger conductor and wastes energy as heat.

Fit a Class T or MRBF fuse within 200mm of the battery positive terminal, rated at approximately 125% of the inverter’s maximum continuous DC current. Standard blade fuses are not rated for these currents and will not interrupt a fault safely. Use proper crimped and heat-shrunk lugs, torqued to the terminal manufacturer’s specification — a loose high-current connection generates heat, and heat in a van is a fire.

Standalone Inverter or Integrated Power Station?

A wired system — battery bank, separate inverter, separate charge controller, separate DC-to-DC charger — gives you the best cost per watt-hour at scale and full control over every component. It also demands correct high-current wiring, proper fusing, and enough confidence to do it safely.

An integrated power station puts battery, inverter, MPPT controller and AC charger in one certified box with no high-current DC wiring for you to get wrong. You pay a premium per watt-hour and you cannot upgrade individual parts, but the failure modes that injure people are engineered out.

For most van conversions the integrated route is the correct answer. The Bluetti AC200L delivers 2,400W continuous with 3,600W surge from 2,048Wh of LiFePO4 storage — which is precisely the 2,000W-class sizing the worked example above arrived at, with the cable and fusing already handled internally.

For higher-demand builds running induction cooking or workshop tools, the Bluetti Elite 400 provides 2,600W continuous with 3,900W surge from a 3,840Wh battery, covering many loads that would otherwise need a 24V wired system with heavy cable throughout.

Where a compact permanent installation matters more than peak output, the Bluetti Elite 300 sits between the two on both capacity and footprint.

Inverter-Chargers and Shore Power

An inverter-charger combines the inverter with a mains battery charger in one housing, switching automatically between the two. Plug into a campsite hookup and it charges the battery bank while passing 230V straight through to your sockets; unplug and it reverts to inverting from the battery without interrupting whatever is running.

The convenience is real, but so is the price — expect £400–900 for a 2,000W unit against £220–420 for a bare inverter plus £90–150 for a separate charger. The genuine advantages are automatic transfer switching, a single set of high-current cables rather than two, and proper charge profiles for lithium chemistry.

Buy an inverter-charger if you use campsite hookups more than a few times a month, or if your van is your permanent home and mains charging is a routine part of winter. For occasional hookup use, a separate mains charger left in a cupboard costs less and does the same job with one extra plug.

Three Inverter Configurations With Real Costs

Minimal — 600W pure sine, £90–160

Runs laptops, chargers, small tools and a TV. Idle draw 5–7W. Needs 16mm² cable and an 80A fuse. Suits vans that cook on gas and heat with diesel — which is to say, most efficient builds. This is a far more common correct answer than the market’s marketing would suggest.

Standard — 2,000W pure sine, £220–420

Adds kettle and microwave capability. Idle draw 15–20W, so switch it off between uses. Needs 50mm² cable and a 200A Class T fuse on 12V. This is the configuration most touring and full-time vans should target.

High output — 3,000W+ pure sine on 24V, £480–900

Supports induction hobs, air fryers and 110V power tools simultaneously. Idle draw 25–40W. Requires 24V architecture, 50mm² cable, and a battery bank capable of sustaining 130A+ discharge — typically 400Ah or more at 24V. Only justified if you genuinely cook by induction daily.

Four Mistakes That Cost Real Money

Sizing for a load you’ll use twice a year. A 3,000W inverter bought for an occasional heat gun costs you 300Wh a day in idle draw for the other 363 days. Rent or borrow for one-off jobs.

Leaving it switched on permanently. Fit a remote on/off panel where you can reach it. This single habit is worth more battery capacity than a second solar panel.

Undersizing cable to save money. The cable is not the place to economise. A 2,000W inverter on 25mm² cable will brown out under load, run hot, and eventually fail — usually the cable, sometimes the van.

Ignoring the battery’s discharge rating. A 2,000W load pulls 185A. Many budget lithium batteries limit continuous discharge to 100A, so the inverter shuts down under load regardless of its rating. Check the battery BMS discharge limit before choosing the inverter.

Verdict: Smaller Than You Think, Better Than You Planned

Correct van inverter sizing almost always lands lower than instinct suggests. Measure your real simultaneous loads, add 25%, buy pure sine, and spend the money you saved on cable and fusing rather than on unused capacity. For the majority of UK van builds the answer is a 2,000W pure sine unit on 12V with 50mm² cable and a 200A Class T fuse, switched off when idle — or an integrated 2,000W-class power station that removes the high-current wiring from the equation entirely.

The inverter you never notice is the correctly sized one. Oversizing announces itself every morning in your state of charge.

Affiliate disclosure: Van Power Lab earns commissions from Amazon Associates, Jackery, EcoFlow, Bluetti, Renogy, and Goal Zero. We only recommend products tested in real vans. Your purchase costs the same; we earn a small commission that helps us write more guides.

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Solar Systems

Solar Power Van Setup: Complete UK Sizing, Wiring & Cost Guide

Most van solar systems in the UK are sized using American numbers, and that is exactly why so many of them disappoint their owners every November. A solar power van setup that comfortably runs a fridge in Arizona will not keep the same fridge alive through a Yorkshire winter. This guide works from real UK irradiance figures, real component prices, and the honest maths behind panel sizing, charge controller selection, and wiring — so your system performs the way you expected when you paid for it.

What a Solar Power Van Setup Actually Delivers in the UK

A solar panel’s rated wattage is a laboratory figure measured at 1,000W/m² irradiance, 25°C cell temperature, and perfect perpendicular alignment. Your van roof never sees those conditions. In practice, a flat-mounted panel in the UK produces the following daily energy yield per 100W of rated capacity:

June–July: 380–450Wh per day per 100W
April–May and August–September: 250–330Wh per day per 100W
March and October: 140–190Wh per day per 100W
November–February: 40–90Wh per day per 100W

Read those winter figures again. A 400W array — a genuinely large van installation — generates roughly 160–360Wh on a December day. That is enough to run a compressor fridge and charge a phone, and nothing else. Anyone selling you a “year-round off-grid solar van setup” without mentioning a mains hookup or an alternator charger is selling you a summer system with a winter problem attached.

The honest planning rule for UK van life is simple: size your solar for spring and autumn, accept that summer will give you surplus, and plan a second charging source for December through February. That second source is normally a DC-to-DC alternator charger, which we cover in detail in the wiring section below.

Step One: Calculate Your Daily Consumption for a Solar Power Van Setup

Solar sizing starts with your load, not with how much roof space you have. Work in watt-hours per day. Multiply each device’s power draw by the hours it actually runs, not the hours it is switched on — a compressor fridge rated at 45W runs a duty cycle of roughly 35–45% in UK ambient temperatures, so it consumes around 400–480Wh per day, not 1,080Wh.

A realistic mid-range van load looks like this:

Compressor fridge (45W, 40% duty cycle): 430Wh
LED lighting (18W for 5 hours): 90Wh
Laptop charging (60W for 4 hours): 240Wh
Phone and tablet charging: 60Wh
Water pump, USB fans, extraction: 70Wh
Diesel heater (winter only, 30W running + 100W glow starts): 250–400Wh

That totals roughly 890Wh per day in summer and 1,290Wh per day in winter. Now apply the yield figures above. To generate 890Wh in April you need approximately 300W of panels. To generate 1,290Wh in December you would need around 2,000W of panels — which does not fit on a van roof and would be economic nonsense. This single calculation is the entire argument for a hybrid charging strategy.

Add 20% headroom to whatever figure you calculate. Every van owner adds devices in the first year, and a system running at 100% of design capacity has no margin for a cloudy week.

Panel Types: What Belongs on a Van Roof

Monocrystalline rigid panels

Monocrystalline rigid panels are the correct default for permanent van installations. They deliver 19–22% conversion efficiency, meaning more watts per square metre of roof — the constraint that actually matters on a van. Expect £0.60–£1.10 per watt, a 25-year output warranty from reputable manufacturers, and a service life that comfortably exceeds the van itself. A 200W monocrystalline panel measures roughly 1,580 × 800mm and weighs 11–13kg. Renogy and Photonic Universe rigid panels are the two brands most consistently fitted in UK conversions.

Polycrystalline rigid panels

Polycrystalline panels cost 10–15% less per watt but deliver 15–17% efficiency, requiring roughly 20% more roof area for the same output. On a house roof that trade is worth considering. On a van roof, where area is the binding constraint and the price difference amounts to £30–50 across a whole array, it is a false economy. Buy monocrystalline.

Flexible and semi-flexible panels

Flexible panels are heavily marketed for van conversions because they are light, low-profile, and can be bonded directly to a curved roof. The reality is less attractive. Semi-flexible panels typically deliver 16–18% efficiency, degrade faster than rigid panels because they cannot shed heat into an air gap, and commonly fail at the 3–5 year mark through delamination or micro-cracking. Warranties are frequently 2–5 years rather than 25.

Flexible panels earn their place in exactly two situations: a pop-top roof that cannot carry rigid mounting hardware, and a vehicle where total height is legally or practically critical. Everywhere else, rigid panels on a 25–40mm air gap will outlive them by a factor of four.

Portable folding panels

A folding panel is not a compromise — it is a genuinely different tool, and the best solar decision many van owners make. Because you can angle it directly at the sun and park in shade while the panel sits in sunlight, a portable panel routinely outperforms an equivalent roof-mounted panel by 30–50% in spring and autumn. The a 220W folding portable panel is the setup that suits this best: light enough for one person to reposition three times a day, which is where the extra yield comes from.

The trade-off is theft risk and the discipline of setting it up. For weekend and touring use, portable wins. For full-time living where the van is left unattended, roof-mounted wins. Many well-designed systems run both: a fixed array for baseline charging and a folding panel deployed when parked for several days.

Charge Controllers: MPPT Is Not Optional in the UK

The charge controller sits between your panels and your battery, regulating voltage and protecting the battery from overcharge. There are two technologies, and the choice matters more in the UK than almost anywhere else.

PWM (Pulse Width Modulation) controllers pull the panel voltage down to battery voltage, discarding the difference as lost potential. A 100W panel operating at 18V feeding a 12V battery through a PWM controller delivers roughly 12V × its current — losing 25–30% of available energy before it reaches the battery. PWM controllers cost £15–40.

MPPT (Maximum Power Point Tracking) controllers convert excess voltage into additional current, harvesting 93–97% of available panel output. Under bright summer sun the advantage over PWM is 10–15%. Under the low-light, overcast, partial-shade conditions that define British weather, the advantage widens to 25–40% because MPPT continues extracting usable power at irradiance levels where PWM effectively stalls. Quality MPPT controllers cost £70–200.

The payback maths is decisive. A £90 MPPT controller on a 300W array recovers roughly 90–120Wh more per day in shoulder seasons than a £25 PWM unit. Across a UK year that is 25–35kWh of additional harvested energy — the equivalent of adding 100W of panels for a quarter of the cost. Fit MPPT. There is no scenario in UK van life where PWM is the correct engineering choice.

Size the controller by array current, not by wattage alone. Divide total array watts by battery voltage and add 25% margin: a 400W array on a 12V system needs 400 ÷ 12 × 1.25 = 42A, so a 50A controller. Check the maximum open-circuit voltage rating too — cold weather raises panel voltage above its rated figure, and a controller destroyed by a frosty January morning is an expensive lesson.

Wiring, Fusing and Cable Sizing

More van solar systems underperform through bad wiring than through undersized panels. Voltage drop across a cable run is proportional to current and length and inversely proportional to cross-sectional area. Keep total drop under 3% from panel to controller and under 2% from controller to battery.

Practical minimums for a typical van installation:

Panel to controller (up to 5m, under 20A): 4mm² cable
Panel to controller (5–8m, or 20–30A): 6mm² cable
Controller to battery (under 1.5m, up to 40A): 10mm² cable
Controller to battery (under 1.5m, 40–60A): 16mm² cable

Fusing is a legal and safety requirement, not an optional extra. Fit a fuse or breaker within 200mm of the battery positive terminal, rated at 125% of the controller’s maximum output current. Fit a second fuse between array and controller if you run more than two panels in parallel. Use MC4 connectors for all roof-side connections, and crimp them with the correct tool — a solar system that fails in year two almost always fails at a badly crimped connector.

Wire panels in series where possible. Series wiring raises voltage and lowers current, which reduces cable losses and lets an MPPT controller start harvesting earlier in the morning and later in the evening. The exception is partial shading: series strings suffer badly when one panel is shaded, so if your roof has a vent, aerial or skylight casting shadows, wire in parallel or use panels with per-panel optimisers.

Roof Mounting Without Drilling Holes

Adhesive mounting brackets bonded with Sikaflex 252 or Dekalin hold rigid panels securely without a single roof penetration, and are now the standard approach for van conversions. Clean the roof with isopropyl alcohol, abrade the bonding area, apply primer where the manufacturer specifies it, and allow a full 48-hour cure before driving. Correctly bonded brackets exceed the pull-out strength of self-tapping screws into thin van steel.

Maintain a 25–40mm air gap under the panel. Panel output drops roughly 0.35–0.45% per degree above 25°C cell temperature; a panel bonded flat to a hot roof can lose 10–15% of its output on a summer afternoon purely through heat. The air gap costs nothing and pays back permanently.

Three Complete Solar Van Setups With Real Costs

Weekend build — 200W, £420–560

A single 200W monocrystalline panel, 20A MPPT controller, mounting brackets, cable and fusing. Generates 500–660Wh on a good spring day and 80–180Wh in December. Suits weekend use with a small fridge, lighting and device charging. Pair it with a portable power station rather than a wired leisure battery bank and you have a system you can move between vehicles.

Touring build — 400W, £860–1,180

Two 200W panels wired in series, a 40–50A MPPT controller, upgraded cabling and a DC-to-DC alternator charger. Generates 1,000–1,320Wh in April and 160–360Wh in December. This is the sweet spot for extended touring: enough for a fridge, heating controls, laptop work and lighting across three seasons. Feeding a lithium bank such as the Bluetti AC200L gives you 2,000Wh of storage with a built-in inverter, which removes most of the wiring complexity from the equation.

Full-time build — 600W, £1,600–2,400

Three 200W panels, a 60A MPPT controller, heavy-gauge wiring, alternator charging and a substantial battery bank. Generates 1,500–2,000Wh in April and 240–540Wh in December. A system of this scale supports full-time living including induction cooking and occasional power tools, provided storage capacity matches. The Bluetti Elite 200 V2 or a comparable 2,000Wh+ bank is the minimum sensible pairing — undersized storage wastes generation the moment the battery hits full at midday.

The Four Mistakes That Cost the Most Money

Undersizing storage relative to generation. A 600W array charging a 1,000Wh battery reaches full by 11am on a sunny June day and then produces nothing for the rest of the afternoon. Generation and storage must be balanced; as a rule, aim for battery capacity of roughly 3–4Wh per watt of installed panel.

Ignoring shading. A single roof vent shadow across one cell of a series string can cut array output by 40–70%. Survey your roof layout before committing to panel positions, and prefer parallel wiring or split strings where shading is unavoidable.

Buying a controller sized to today’s array. Almost everyone expands. A 30A controller bought to match a 300W array becomes landfill the moment you add a fourth panel. Buy the next size up — the cost difference is £30–50 and it buys you an upgrade path.

Treating solar as the only charging source. A DC-to-DC alternator charger costs £120–220 and delivers 20–50A whenever the engine runs. In a UK winter it will contribute more energy than your entire solar array. Budget for it from the start rather than fitting it in February as an emergency.

Verdict: Size for Spring, Plan for Winter

A solar power van setup that performs reliably in the UK follows three rules: calculate real consumption before buying anything, fit monocrystalline panels with an MPPT controller and correctly sized cable, and accept that solar alone will not carry you through December. Four hundred watts of well-installed panels, a 50A MPPT controller, 2,000Wh of lithium storage and an alternator charger is the configuration that solves the problem completely for around £2,000–2,800 all in.

Spend the money on the controller and the wiring rather than on extra panel wattage. A 300W array wired properly through a quality MPPT controller will out-harvest a 400W array wired through a PWM controller on undersized cable, every single day of the British year.

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Category: Van Electrical Build