Overlanding Energy and Water Provision Planner

Introduction

Overlanding rewards good judgment long before the tires touch dirt. Once you leave towns, campgrounds, and easy hookups behind, two basic questions start driving nearly every gear decision: how much water do you need to carry, and can your electrical system keep up with your daily loads? This planner answers those questions in one place so you can make realistic choices about storage, payload, solar sizing, and battery autonomy before a trip becomes a field problem.

The tool is deliberately practical. It does not try to simulate every hour of sun angle, every refrigerator compressor cycle, or every change in weather. Instead, it uses daily averages to show the big picture: your trip's water demand, the effect of a planned refill, how much usable battery energy you actually have, how much energy your solar array may produce on an average day, and whether you are operating with a daily surplus or a daily deficit. That makes it especially useful during route planning, vehicle build decisions, and quick what-if checks when you are comparing different setups.

Because the calculator combines hydration logistics with power logistics, it mirrors the way real trips work. Water is heavy, bulky, and non-negotiable. Electricity is lighter to store, but easier to underestimate because several small loads add up quickly. Looking at both together helps you avoid a common planning mistake: building a comfortable-looking system on paper that is actually short on either cargo capacity, daily energy, or both.

How to use

Start with the trip basics. Enter the number of days, the number of people, and the amount of water each person will realistically drink each day. Then add shared cooking and cleaning water. Those two water inputs are kept separate on purpose. Personal drinking needs scale with group size, while dishwashing, meal prep, and simple camp hygiene are often partly shared. If you expect to refill at a town, faucet, cache, or reliable treated source, enter that amount in the resupply field so the starting carry estimate reflects your plan.

Next, fill in the energy section with a daily average rather than a best-case number. The base electrical load should include everything except the fridge and heater if you want those broken out separately. Typical items here are cabin lights, fans, device charging, a water pump, camera batteries, laptops, Starlink or radio gear, and any inverter-backed electronics. Then add the fridge's average daily consumption and the electrical draw of your night heater if you use one. Finally, enter solar wattage, average peak sun hours, battery capacity in amp-hours at 12V, usable depth of discharge, and overall charging efficiency.

After you press Calculate, read the result area first for a short summary, then use the table to inspect each number in detail. If the water figure seems too large to carry safely, you probably need a more dependable resupply plan, a lower daily water assumption, or more storage containers. If the energy balance is negative, the battery can only cover that shortfall for so long. In that case, the planner helps you see whether the better fix is more solar, lower loads, a second charging source, or simply a more conservative route plan with fewer stationary days.

Water planning model

Water demand is split into two buckets. The first is personal hydration, which scales with the number of travelers. The second is shared cooking and cleaning, which covers the daily camp uses that do not belong to any one person alone. That could include meal preparation, washing dishes, hand cleaning, brushing teeth, a little sponge-bath water, or rinsing dusty gear. Separating these numbers makes the estimate easier to reason about when your group size changes.

The calculator multiplies those daily needs across the trip and then subtracts any planned mid-trip refill. The result is the amount you should be ready to carry from the start. In other words, it is a starting logistics number, not just an abstract total demand number. That matters because water affects both safety and vehicle setup: tank volume, jerry can count, payload, rack placement, and axle loading all become real constraints long before the math looks extreme on paper.

Water formulas

Total trip water requirement (before resupply):

Where:

• d = trip length in days
• p = number of people
• w = daily water per person in liters per day
• c = shared cooking and cleaning water in liters per day

Starting water to carry (after resupply):

If you want a quick weight check, water is roughly 1 kilogram per liter, or about 2.2 pounds per liter. So 40 liters is roughly 40 kilograms before container weight. That is why many otherwise comfortable-looking plans become unrealistic when the route has no dependable refill. The weight is not a side note; it is part of the decision.

Electrical planning model (solar + battery)

The energy side of the planner works the same way conceptually: daily use versus daily replenishment. Your loads consume energy. Solar replaces some or all of that energy. The battery sits between the two and gives you autonomy when production and consumption do not match perfectly. The calculator estimates daily solar generation, total daily demand, and the usable share of the battery bank so you can see whether the system is truly sustainable or merely surviving for a short time.

Loads: what daily electrical load means

The form includes three energy load fields so you can keep the estimate organized.

• Daily Electrical Load (Wh): use this for everything except the fridge and heater if you want them itemized. Examples include lights, fan use, communication gear, charging devices, camera batteries, a water pump, a laptop, or inverter-backed accessories.
• 12V Fridge Daily Consumption (Wh): enter an average daily number. Fridge draw varies a lot with ambient temperature, ventilation, thermostat setting, how warm the contents are, and how often the lid or door is opened.
• Night Heater Load (Wh): this usually means the electrical consumption of a diesel heater's fan and control electronics. Fuel energy is separate. Resistive electric cabin heat is usually impractical from a modest vehicle battery bank.

The planner adds those daily loads together:

This split is helpful because fridge and heater numbers are often the least intuitive. Many travelers guess the base loads fairly well, but a warm-weather fridge or a cold-weather heater can dominate the budget if the estimate is too optimistic.

Solar production: peak sun hours and efficiency

Solar array output is modeled as a daily average using panel wattage, peak sun hours, and a charging efficiency factor. Peak sun hours are not literal daylight hours. They are an equivalent full-sun energy measure that helps convert panel rating into daily watt-hours. Charging efficiency accounts for real-world losses from wiring, controller conversion, panel temperature, battery acceptance, dust, and less-than-perfect conditions.

In formula form:

Many real rigs see something like 60% to 90% of the idealized nameplate output depending on season, roof layout, and shade. A conservative efficiency input is usually more useful than a hopeful one. If you plan to camp under trees, drive dusty roads, or leave the vehicle parked at poor angles, be especially careful not to overestimate solar.

Battery usable energy

The calculator interprets battery capacity as nominal 12V storage and converts amp-hours into usable watt-hours based on the depth of discharge you are willing to use in practice.

This is a planning approximation rather than an electrochemical simulation. Lithium batteries often tolerate a higher routine depth of discharge than AGM or other lead-acid types, but the right value still depends on how you want to balance autonomy, battery lifespan, and winter performance.

Daily net energy (surplus or deficit)

Daily balance is the simplest but most important output in the entire energy model:

If E_net > 0, the system has an average daily surplus and should recover battery energy over time. If E_net < 0, the system is running a daily deficit and the battery is being spent down to cover the gap. That does not always mean the trip is impossible, but it does mean the clock is already ticking unless you have another charging source such as alternator charging, a generator, shore power at some stops, or a plan to reduce loads.

How to interpret your results

Water results

The water result represents the amount you should plan to carry at the start after subtracting your planned resupply. If that number feels too large for your rig, that reaction is useful information, not failure. It means your route assumptions and storage assumptions are out of step. You can respond by reducing daily use, increasing container capacity, adding a treatment plan around known sources, or shortening the gap between resupply points.

Energy results

The solar production result is an average daily energy harvest, not a promise for every day. Total daily load is the amount you expect to consume. The daily surplus or deficit shows whether your system trends upward or downward over time. If the balance is negative, the battery autonomy estimate tells you how long the stored energy can cover the shortfall before you hit the chosen depth-of-discharge limit.

A practical rule of thumb is worth remembering: solar solves an ongoing daily deficit, while battery capacity solves short-term autonomy. Extra battery alone does not fix a system that regularly consumes more energy than it makes. It simply gives you more time before the problem becomes visible. That distinction helps prevent expensive build decisions that feel reassuring but do not actually improve long-trip sustainability.

Worked example

Suppose you are planning a 7-day trip for 2 people. Each person drinks 4.5 liters per day, shared cooking and cleaning uses 6 liters per day, and there is no mid-trip water refill. The water side is straightforward:

W = 7 × (2 × 4.5 + 6) = 7 × 15 = 105 L

That is roughly 105 kilograms, or about 231 pounds, before container weight. For many vehicles, that is a serious payload and packaging consideration. It is exactly the kind of number that can push you toward a better resupply plan rather than simply adding more jugs.

Now assume the energy system uses a 200 W solar array, receives 5.5 peak sun hours per day, and operates at 90% charging efficiency. Daily base loads are 1800 Wh, the fridge averages 600 Wh, and the heater uses 400 Wh. The battery bank is 200 Ah at 12V with 80% usable depth of discharge.

Loads: L_total = 1800 + 600 + 400 = 2800 Wh/day

Solar: E_solar = 200 × 5.5 × 0.9 = 990 Wh/day

Net: E_net = 990 − 2800 = -1810 Wh/day

Usable battery: E_batt_usable = 200 × 12 × 0.8 = 1920 Wh

If the real trip matches those averages and there is no other charging source, the battery would only cover about 1920 / 1810 ≈ 1.1 days of deficit. That does not mean the vehicle is badly built; it simply means the planned loads and generation are mismatched for the trip length. You would either need much more solar, much lower loads, more frequent driving with alternator charging, or a shorter interval between power replenishment opportunities.

Quick comparison: common build strategies

Assumptions and limitations

• Water needs vary widely with heat, altitude, exertion, illness, and food choices. Treat the water estimate as a baseline and add a safety reserve for real conditions.
• Resupply is treated as dependable. In reality, a spring can be dry, a faucet can be shut off, a river can be contaminated, or access can be blocked. If resupply is uncertain, plan additional carry or backup treatment options.
• Solar wattage is a nameplate number. Real production falls with heat, dust, partial shade, poor angle, and seasonal sun differences. The efficiency field is a simple way to reflect that.
• Sun hours are averages, not guarantees. A cloudy week can turn a balanced setup into a deficit quickly.
• Battery energy is estimated at nominal 12V. Actual usable energy depends on battery chemistry, voltage profile, temperature, and monitoring accuracy.
• Depth of discharge is a planning choice. Going deeper more often can shorten battery life, especially with lead-acid systems.
• User load estimates matter. Fridges and heaters are especially variable. Measured watt-hour data from a shunt or meter is better than guesswork.
• No hour-by-hour simulation is included. The calculator does not model inverter surge loads, charging taper near full, or time-of-day mismatches between load peaks and solar production.
• This is a planning aid, not a safety substitute. For remote travel, carry extra water, maintain margin for critical electronics, and adapt the plan to route-specific hazards.

Practical tips to improve accuracy

If you want the calculator to be more than a rough estimate, feed it better inputs. Log a normal day at home or on a local overnight trip. Measure your fridge for at least 24 hours in realistic temperatures. Note how much water the group actually uses when cooking, washing dishes, and handling basic hygiene. If you know your rig is often parked in shade, enter more conservative sun hours or a lower charging efficiency. These small adjustments usually matter more than adding another decimal place to the output.

It also helps to test the plan in reverse. Once you see a result, ask what would break it. Would two cloudy days matter? Would an extra passenger meaningfully change water weight? Would a colder-than-expected night heater load become the dominant energy problem? Good planning is not just entering likely numbers. It is checking whether the system still works when one assumption turns out worse than expected.