12, 24 or 48V System?

Starting your off grid lifestyle opens a realm of possibilities, and at the heart of this lies a pivotal decision: the voltage of your power system. The choice between 12, 24, and 48 volts is not just a technical matter; it’s a crucial element that shapes the efficiency and flexibility of your off grid setup.

I’d love to give you a straightforward answer here, but it really depends on these things;

When deciding on a system voltage you need to take into consideration all of these things, and in some use cases, all three voltages may be suitable for your build. In this case, your selection may be decided on the space available and any future proofing required.

Our first step is to know what size system we need, luckily there’s a detailed post on sizing your system here.

Basing a system just on price may lead you to be disappointed when you find you’ve run out of power during the night, or worse, find that the cheaper, but larger system, now won’t fit in the space you’ve allocated.

So before you consider pricing, it’s important to know the basics of your requirements, mainly;

• Inverter size
• Battery bank size
• Solar Array size

With that in mind let’s jump straight to our calculations…

This table shows the limits of where each of the system voltages becomes more expensive than the following option.

For example; Our 12V calculations showed it remained the cheapest option to buy until the inverter size hit 1500 Watts, the battery was sized over 5 kWh’s and the solar array was larger than 500W.

Want to see the calculations behind these figures? Jump to them below

Take a look at each tab to see some of the benefits and considerations of each system voltage.

Table 1. A shorter bar means a cheaper system. Highlight over the individual segments of the bars to see individual component pricing.

This tiny system would be perfect for a small van, it will power lights and small power units up to 500W at a time, such as a WiFi router, or phone and laptop charging. Any water heating (e.g. a kettle) would need to be done using gas. It would also struggle with any electrical kitchen appliances.

Here you can see that the 12V and 24V options are the cheapest, and at this power, there are no issues with the battery being underpowered for the demands of the inverter. With the small amount of solar generation, and using Victron 12V panels, we can also spec a much lower solar charger, in this case a SmartSolar 100/20, without any power clipping.

It’s worth mentioning that 12V systems struggle with larger solar panels and arrays, you’ll need to size up the solar charger considerably compared to 24V and 48V systems ,which you’ll see in the larger systems. Victron’s solar charger calculator is invaluable here.

Table 2. A shorter bar means a cheaper system. Highlight over the individual segments of the bars to see individual component pricing.

This system is great for a higher-powered, larger van. If you’re a van lifer, this would give you ample power for living and working in a van, with a bit of battery-to-battery charging now and then to top up the solar.

You could also run a small tiny home with this setup, with some additional costs, however, if you’re looking to run a few kitchen appliances at the same time, the next system would be a better choice.

The standout here is the 24V system, thanks mainly to the remarkable 24V 280Ah Fogstar Drift battery, which actually provides 7 kWh’s!

At this size the 12V system is becoming more expensive due to running multiple batteries and associated cabling, busbars and fusing, not to mention the larger solar charger needed to avoid clipping the incoming solar power.

Meanwhile, this inverter size is covered by the EasySolar-II 3kVA, in both 24V and 48V variants, which removes the need for separate solar chargers and GX controllers. This also makes both options a cheaper alternative than the 12V system.

Table 3. A shorter bar means a cheaper system. Highlight over the individual segments of the bars to see individual component pricing.

Ideal for a tiny home setup, this pricing also includes the equipment required to make a safe permanent installation. Take a look at our detailed explainer on electrical safety.

This system would run most of your daily living, you would still need to be careful when running multiple appliances together though. (For example; a kettle, toaster and microwave, would max out the inverter power).

At this size of system, 12V is becoming more complex and expensive, to produce the same amount of power as the other systems. Two 12V Multiplus-II are running in parallel, and four Fogstar Drift batteries are in parallel to supply sufficient discharge rate and capacity. On top of that, there is the extra cost of larger diameter cabling, and a DC busbar, as well as battery isolators and fusing.

The cheapest voltage for a system of this size is 24V, closely followed by 48V. There’s a few reasons we’d choose the 48V system here, even though it’s a little more expensive;

• It’s cheaper to upgrade; you can easily add another rack-mounted US5000 to this system without any other components.
• Extra room on the solar charger if you need to increase the capacity.
• If you need to upgrade the inverter power output in the future, the cost of an additional MultiPlus-II is the same as a 24V inverter, but you’ll save on smaller diameter cabling and fusing.

Table 4. A shorter bar means a cheaper system. Highlight over the individual segments of the bars to see individual component pricing.

With increasing inverter power the price of battery banks for the 12 and 24V systems, that will discharge at a rate suitable to 8 kW is now becoming unfeasible. The benefits of the higher voltage of the 48V system are evident here, we’re able to spec a couple of rack-mounted Pylontech US5000s that have ample output for an 8 kW inverter. Not only that but at these power demands the 12 and 24 V systems need a cable diameter which is expensive, unwieldy and difficult to install.

Offgrid Western recommends a 48V system for most off grid homes, due to the greater number of options for inverters available and LiFePO4 batteries that have industry leading warranties. As well as simpler installation, and greatly reduced cost at higher power demand.

First some basics;

In essence, the larger the cross-sectional area of the cable, the lower the electrical resistance it presents to the current. This lower resistance translates to less energy loss as heat and more efficient power transfer.

Ohms Law states that the electric current through a conductor between two points is directly proportional to the voltage across the two points

Where;

Voltage = current × resistance

Combining Ohm’s Law with the Power Equation we get;

power = current × voltage.

Where:

• $P$ is power in watts (W),
• I is current in amperes (A), and
• V is voltage in volts (V).

So we can see that an increase in Voltage means a reduction in current to maintain the same amount of power.

Voltage Drop

Voltage drop is the reduction in electrical potential along the path of current flow. In DC circuits, this drop occurs due to the inherent resistance in conductors. Every conductor (cable), no matter how efficient, presents resistance to the flow of current. As electrons traverse the cable, some of their energy transforms into heat, causing a decrease in voltage.

Voltage drop intensifies with the length of the conductor. Longer cables translate to more resistance and, consequently, a more significant voltage drop. Higher currents also exacerbate voltage drop. Inverters drawing substantial current (more power) contribute to a more pronounced drop along the cable.

Why is it important?

• Performance: Many electrical devices, especially sensitive electronics, operate optimally within a specific voltage range. Excessive voltage drop can lead to these devices not functioning correctly or efficiently. If a 3kW Inverter has been installed on a 12V system and the supply cables are only 25 mm², very soon you’ll be seeing low voltage alarms and power cuts.
• Energy Efficiency: Voltage drop results in the dissipation of electrical energy as heat in the conductors. This is essentially wasted energy, reducing the overall efficiency of the system.
• Battery Health: In off grid systems, where batteries store energy for later use, voltage drop can affect the charging and discharging cycles. Proper voltage regulation is essential for maintaining the health and longevity of battery banks, more on this later.
• Lighting: If you’re using 12V DC lighting, voltage drop can lead to dimming or uneven illumination. Maintaining consistent voltage ensures proper lighting performance.
• Heating Issues: Most importantly, high resistance and voltage drop can lead to overheating in conductors, posing safety risks and potential damage to the insulation or surrounding materials.

It comes down to cost…

A higher-power 12V system (1000 W+) will result in a large and expensive DC cable.

By shifting to 24V the DC cable diameter is halved.

Going to a 48V system means the cable diameter is a quarter that of the 12V system.

Accessible DC cable comes in sizes up to 120 mm² which will set you back £20.34 a meter! Meanwhile, a 35 mm² comes in at a more reasonable £6.37 a meter.

You can see why we use 48V systems for our off grid home kits, in fact, there’s a few arguments for using 48V in smaller systems such as vans and boats. And we’ll get to a big one next..

Table showing DC cable pricing and some system examples. Pricing correct as of December 2023.

Wiring batteries in series or parallel is a common practice to create battery banks with different voltage levels.

Let’s explore how this is done:

Wiring Batteries in Series:

Objective: To increase the voltage while keeping capacity (ampere-hours, Ah) the same.

Equation: The total voltage (V_total) is the sum of the individual battery voltages.

V_total = V₁+V₂+…+Vₙ

Connection:

1. Connect the positive terminal of the first battery (V₁) to the negative terminal of the second battery (V₂).
2. Repeat this series connection until the last battery.

Result: The voltage adds up while the capacity remains the same.

Discharge Rate: Let’s explore how series and parallel connections affect the discharge rate of a battery bank;

In a series circuit, the current (discharge rate) is the same for all components. Therefore, each battery in a series contributes to the overall discharge rate, and the discharge rate of the battery bank is the same as that of an individual battery.

I_total = I₁ = I₂ = … = Iₙ

Wiring Batteries in Parallel:

Objective: To increase capacity while keeping voltage the same.

Equation: The total capacity (C_total) is the sum of the individual battery capacities.

C_total= C₁+C₂+…+Cₙ

Connection:

1. Connect all positive terminals.
2. Connect all negative terminals.

Result: The voltage remains the same while the capacity adds up.

Discharge Rate: In a parallel circuit, the total current (discharge rate) is the sum of the currents through each branch. As each battery in parallel contributes its discharge rate, the overall discharge rate of the battery bank increases.

Creating a 24V or 48V Battery Bank:

See our explainer on using the Lynx Distributor as a high-integrity busbar for battery banks.

Series-Parallel Combination:

1. Wire two sets of 12V batteries in series.
2. Connect these series-connected sets in parallel.

V_total= 12.8 +12.8 = 25.6 V

C_total= 280 +280 = 560 Ah

Creating a 48V Battery Bank:

Series-Parallel Combination:

1. Wire four sets of 12V batteries in series.
2. Connect these series-connected sets in parallel.

V_total= 12.8 +12.8 +12.8 + 12.8 = 51.2 V

Cₜ_total= 280 +280 + 280 + 280 = 1120 Ah

Note:

• Voltage Increases in Series: Adding the voltage of each battery.
• Capacity Increases in Parallel: Adding the capacity of each battery.

This flexibility allows the design of battery banks tailored to specific voltage and capacity requirements.

Thanks for getting this far, hopefully, you’ve now got more of an understanding of the benefits and considerations for each of the system voltages. And can now use this knowledge when designing your off-grid system, whether it’s a camper van, tiny home or your family home!

If this has just made you more confused or reaffirmed your belief that you’d like to have a system designed, get in touch for a bespoke quote or take a look at our pre-made kits that have all the calculations taken care of, including;

• A full, easy-to-follow wiring diagram.
• Commissioning manual for setting up your system.
• Pre-made quality cabling.
• A full solar array, with an MCS-approved mounting system, bespoke to your requirements.