By Rhys Coffin: Off-Grid Solar Designer, Power Station New Zealand. Updated October 2026. About the Author

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Looking for more? Check out this 10-minute read Beginner’s Guide to Off-Grid Solar

The starting point for sizing any off-grid solar system is how much energy your home is likely to use during a typical 24-hour period, particularly in winter.

The amount of electricity you use over a period of time is measured in kilowatt-hours (kWh).

Working out your total kWh usage over a full day is called a Load Evaluation.

It normally takes around 10 to 20 minutes to complete over the phone, where we talk about the appliances and other equipment you expect to use over the span of a day, particularly in winter.

Everyones uses power differently.

There’s no single answer as to how much power an off-the grid home might consume over 24-hours in winter, but in our experience 80% of households in New Zealand will use between 8–16 kWh per day.

According to the folks at Canstar, Kiwis who are connected to the grid in a family home with children might use between 16 kWh per day for a small family and up to 30 kWh per day for a larger family home.

With careful planning in the early stages of the house design and build, it’s possible to reduce your expected energy use. Reduced energy use means a smaller system and lower costs, but with the option to expand later, if needed.

If you want to understand more about off-grid sizing and the load evaluation, check out What is an Off-Grid Load Evaluation?

One of the most important things that determines the correct sizing of your off-grid system is how much power you will typically use at any one time.

This is not about the total electricity you might use over a 24-hour day (kWh). It’s about how many appliances and other pieces of equipment might be operating simultaneously (kW).

In a grid-connected home, we hardly notice it. Running two or three induction elements, the oven, microwave, heat pump and jug all at the same time is reasonably common.

But off-grid, we have to plan for both maximum simultaneous power use and total electricity consumption over 24 hours, because maximum simultaneous power use determines the size of your inverter or inverters.

And it’s not just about how much electricity a family might use today. We also need to consider what their ‘power-use profile’ might look like in 10 or 20 years.

This is where an experienced off-grid solar designer earns their keep.

Future Power Use

Something we’re also seeing increasingly in 2026 is off-grid customers wanting to move away from LPG for cooking and hot water because of the expense.

Why is this relevant?

Because as their electricity use increases, not only will they need more solar panels and battery storage, they also need to make sure their inverter can handle the increased simultaneous demand.

Adding more solar panels or battery storage later can be relatively straightforward if the system has been designed to accommodate expansion. Adding another inverter, or replacing one with a larger model, can be much more complicated, expensive or sometimes impractical.

That’s why we consider these possibilities during the initial design, even if the additional appliances or buildings are still several years away.

Talking to us early has very little to do with ‘getting a quote’. It’s actually about uncovering the important things that you may not know to ask about.

Knowing how many kWh you’ll use over 24 hours, and how many appliances you might run at the same time, is only part of the picture. We also need to understand when that energy is being used.

During daylight hours, your solar panels can power the house directly, reducing the amount of electricity you need to draw from your batteries.

Energy used overnight comes from energy stored in your batteries.

If you’re at home during the day, it makes sense to run your washing machine, dishwasher and other appliances while the sun is shining.

How much power you use during the day compared with overnight can influence how much battery storage you’ll need.

When it comes to sizing your off grid solar system and calculating how many solar panels you’ll need, here are some of the main factors that we consider:

The other factors are about YOU. We call this your ‘power use profile’ and in our experience, no family’s power-use profile is the same.

Lifestyle habits, changes in your situation over time, and how you consume power play a greater role than many people think.

Software can calculate how many north-facing solar panels you might need on your property in Waipukurau. But designing an off-grid system that works for your family, both now and in the future, requires more than a solar generation calculation.

We like to uncover these factors from our very first phone or video call.

Here’s one real example where unique factors about how your changing lifestyle can impact on the size of your panel array, and where you can get caught out:

Designing for your family and the future: A true story

A frustrated customer called about replacing a system only after 12 months of it being installed (not by Power Station). Their power use was expected to double from 7 kWh per day to 12-14 kWh per day after retiring their gas cooking (for induction hobs) and gas hot water (for a hot water heat pump).

The issue? The question about upgrading appliances or future power use wasn’t asked at the time their system was installed, and advice wasn’t given. The customer was unaware that the size of a solar array is linked to the size of the inverter.

Their existing inverter could accommodate a maximum of 6 kW of solar panels (about 14 × 430 W panels), leaving no room to expand the array when their electricity requirements increased.

The solution? Replace the inverter and associated components with a Power Station dual-inverter system, retain the existing 6 kW solar array and add 3 kW of panels. The battery bank also needed to be increased due to the higher electricity use.

Correctly sizing your off-grid system involves designing for today and planning for tomorrow.

inter is when an off-grid solar system faces its biggest challenges. It’s not just about shorter daylight hours, but what happens when you have several days of poor sunshine in a row.

When designing your system, we consider four things:

There’s no single correct system size for every off-grid household.

Two families living in similar-sized homes, even in the same part of New Zealand, can have quite different electricity requirements.

One might have gas cooking, a wood burner and relatively modest electrical loads. The other might have induction cooking, electric hot water, heat pumps, a workshop and plans to charge an electric vehicle.

The systems they need could be very different.

Our job is to understand those differences and recommend a system that suits your particular circumstances.

Sometimes that means explaining how a few changes to your plans could reduce the cost of your system. Other times it means recommending a larger inverter, additional battery storage or more solar panels to accommodate future requirements.

We’ll explain the reasons behind our recommendations, discuss the alternatives and help you understand the trade-offs.

If you’re considering going off-grid, we’d encourage you to get in touch while you’re still planning your project.

Our Free Off-Grid Solar Design Service is a good place to start. You can also explore our core Off-Grid Solar Systems Guide to see how we pair our Base Systems with custom battery and inverter sizing.

You don’t need completed house plans—an initial conversation is often enough to give you a realistic picture.”

An initial conversation is often enough to identify the important considerations and give you a realistic idea of what you’ll need.

Rhys has been part of the Power Station founding team since 2018. He is passionate about sharing knowledge, especially with people new to off-grid solar. He has personally been involved in designing and planning hundreds of off-grid solar systems throughout New Zealand including the Pacific region.

Contact: rhys@powerstation.nz