Off-Grid Power FAQ

Start with your loads, not the solar panels or other shiny box. Tell us what you want to run and for how long, and we work backwards to generation and storage from there.

Watts is power (how hard the load pulls at a point in time); amp-hours is the unit for a quantity of energy; it is used do measure a battery's stored capacity. Confusing the two - or amps with amp-hours - is the single most common mistake we see on chat.

Size it to your largest simultaneous load plus surge headroom. A kettle, microwave or toaster pulls far more than people expect, so a load that might look physically small on paper can still overload the inverter. Surging behaviour in your load will cause the power on startup to be many multiple times a loads nominal amount. This gets into a complex area we will need to consult with you on. I can give you one extreme example, water pumps, we usually factor in a surge rating of 7 times its nominal value, so for an example a 500w water pump will surge up to 3500w momentarily and the inverter needs to handle that without over loading.

Pure sine for anything with a motor, compressor, digital clock or sensitive electronics - fridges, microwaves, power tools, CPAP. Modified sine only suits simple resistive loads, and honestly, we steer everyone to pure sine wave, modified sine was a temporary trend 20 years ago when electronics was very expensive to produce, so still seen occasional around still.

Lithium is lighter and cycles more, but it's dearer up front, hates being charged at low temperatures, and needs charging voltages and a BMS matched to it, treat them wrong and they can catch fire or explode. For a shed, batch or boat that isn't weight-critical, lead-carbon often wins on total cost, compatibility, safety and robustness.

The best voltage is 14.6V absorption and about 13.5-13.8V float at 25°C, with temperature compensation. Else the range 14.4V - 14.6V absorption is ok. That's higher and more staged than a plain alternator delivers, which is exactly why house batteries chronically undercharge off an alternator.

PWM controllers act as a simple regulator and trim off excess voltage from the solar panels and pass through the same current supplied just as a lower voltage, the power from the excess voltage is lost.MPPT solar chargers commonly contain a power converter, this power converter will convert all the power available at one voltage into a different voltage with minimal conversion losses. This means panel voltage in excess of your battery charging voltage is not lost and can be observed as increased current going into the batteries from the solar controller vs the current supplied by the solar panels.

Depending on panel voltage vs battery voltage the efficiency gain from MPPT over PWM is commonly 15-30%.

It takes the roughly 14.0-14.1V a plain alternator puts out and converts it into the correct staged charging profile your house battery actually needs. Without it, a straight alternator connection chronically undercharges the house bank of batteries if it is the predominant charger.

People usually spec cable only by maximum current. The other main criterion is resistance and the resulting voltage drop - and also crucially knowing how voltage-sensitive the two things it connects are. Some links barely care about losses; others need much thicker, lower-resistance cable.

Use our Voltage Drop calculator, which will tell you what voltage drop and cable size you need to be in the green, depending on how voltage sensitive your application is: https://waveinverter.co.nz/calculators/dc-voltage-drop/

Classic alternator undercharging: ~14.0-14.1V can't complete the staged charge a deep-cycle needs. A DC-DC charger or a proper multi-stage mains/solar charge fixes this. Observe by measuring with a multimeter that the correct absorption voltage for your battery type is being applied to the battery for an extended time.