Off-Grid Power for NZ Homes
Going off-grid isn't about buying the biggest solar array or the biggest battery or thinking about what size battery I need to power this size inverter, it's about balance. The battery is a temporary buffer between what you generate and what you consume. A system that gets through a New Zealand winter must have zero weak points. Just one part of the system which is insufficient will cause the whole system to fail, and those points are everywhere. Design is done by David Jade, MSc (Energy Technology), and we supply every part: pure sine wave inverters, AGM and lead-carbon deep-cycle batteries, solar panels, MPPT charge controllers, cabling and steel ground-mount racking made to AS/NZS 1170.2.
The single biggest mistake in off-grid design is sizing for summer. NZ winters cut solar generation sharply as we are at a reasonably high latitude, so we size primarily from your winter daily consumption in kilowatt-hours, so the predictable runs of bad weather we have every year doesn't leave you dark. Where a load is heavy or seasonal or where the generation is inconsistent, a generator charging through a good charger is often cheaper than oversizing the battery bank to cover the worst week of the year.
Battery choice matters for cost and for safety. Lithium is lighter and cycles more, but it's costlier up front, hates being charged at low temperatures, and needs charging voltages and a BMS matched to it, treat it wrong and it can catch fire. For a house, shed or bach that isn't weight-critical, a well-sized lead-carbon bank usually wins on total cost, compatibility and safety, which is why AGM and lead-carbon are our first pick for in-home installs. We do carry lithium for the jobs where the weight saving matters.
Easiest thing is to contact us with a list of what you run and for how long, and we'll assess and design the system for you. More answers in our Solar & MPPT FAQ and our Batteries FAQ.
Common questions
How much solar and battery do I need to go off-grid in NZ?
Start from your winter daily energy use in kilowatt-hours, not summer, because winter is the season that most limits you. Size the solar array to replace that daily use on an average winter day. Do not make the mistake of thinking it's a simple calculation, such as I need 1-3 days of storage I can run off if there is no generation. That is a simplistic model made by people with a poor understanding of how energy systems work. There's a lot of complexity in the options, so the easiest thing is to send us a list of your appliances and we'll give you a firm figure.
Can I run a heat pump off-grid?
Yes, but it has to be designed in from the start, not added later. A modern inverter heat pump is efficient, but its start-up surge and its sustained draw through a winter evening need a pure sine wave inverter and a battery bank sized for it, and the solar to put that energy back the next day. Talk to us before you buy the heat pump so it will be possible for the whole system to be sufficient for it.
How many days of battery autonomy should I plan for in NZ?
Again, not quite the right question to ask, but often bandied about by people in industry with a limited understanding of energy systems. If considering battery autonomy, the result could be anywhere from half a day to 7 days. It's not a simple figure to choose and apply to your design requirements. There are many technical and subjective factors which influence this area and that question framed that way is a tell that you are talking to the wrong people.
Should I use lithium or AGM for a home off-grid system?
Both work. AGM and lead-carbon are forgiving, sealed, cost effective and happy in a cold shed or under the house, and lead-carbon tolerates partial-state-of-charge cycling far better than standard AGM. Lithium gives more usable capacity and less weight where it can be sited and charged properly. In a house the weight rarely matters, so lead-carbon usually wins on total cost to benefit.
Do I need a backup generator?
Often, yes, as a method to deal with variability in generation and consumption rather than the main supply. A right-sized generator charging the bank through a good charger is usually cheaper than oversizing solar and storage to cover the worst winter week, and periods of higher-than-usual consumption. Wind is the other option worth a look, it's strongest in winter when solar is weakest.