Sizing tool
Off grid solar sizing tool: size your system in five minutes.
Pick what the property has to run, tell us roughly where it is, and see the solar array, battery, inverter and generator that would carry it through a Central Victorian winter. Free, no login, and the result shows straight away.
Built for bush blocks, new builds and farms in regional Victoria by the team that installs them. It sizes the way we do, winter first, so the number you see is the number we would start a design from.
What does the place need to run?
Tick what you’ve got and rough numbers are filled in for you, adjust any of them. Or skip the lot and type a daily figure.
Fridge
Compressor cycles on and off, about 8 run-hours a day.
Chest freezer
Similar duty cycle to the fridge.
LED lighting
A whole house of LEDs, evening use.
Washing machine
Cold wash, a hot wash roughly triples it.
Dishwasher
Mostly the heating element.
TV & entertainment
Telly, sound and the bits on standby.
Laptop & office
Computer, monitor, router, printer.
House water pump
Pressure pump, short bursts, big start-up.
Bore / dam pump
Garden and stock water. Run it in the middle of the day.
Workshop tools
Saws, compressors, welders, one at a time.
Big-ticket extras
Heating & cooling (heat pump)
Reverse-cycle split. Winter heating is the load that matters.
Heat pump hot water
Timed to run in the solar window.
EV charging
About 40 km of driving a day. Charge from the sun, midday.
Something we missed?
Got three-phase gear?
Big bore pumps, workshop machinery, welders. Three-phase off-grid is a bigger build, flick this on and we’ll size a three-phase inverter bank for it.
Daily energy
0.0 kWh
Peak demand
~0.0 kW
the most it draws at once
How we size
The method, in plain words.
Written out so you can check our working, and so anyone quoting the tool quotes the method with it.
Winter sun for Central Victoria. A north facing panel here makes about 1.9 kWh per kW of panels on an average June day, against 6.3 in January. June is the number that sizes everything. Northern Victoria gets about 8 percent more, the High Country about 5 percent less, Gippsland about 8 percent less.
Array. Your daily load, divided by June's sun hours and a whole of system efficiency of 82 percent, then 25 percent on top. Panels are the cheap part of an off grid system and every extra night of battery is the expensive part, so we go solar heavy and keep the battery lean.
Battery. The nights of autonomy you choose (one or two is normal) times your daily load, divided by a 90 percent depth of discharge for lithium. The check is that a winter night's use fits in usable storage with margin.
Inverter. Sized from your peak demand, with surge headroom for motors: pumps, compressors and the fridge all draw about three times their running load for a moment at start up. Three phase loads move the whole design to a three phase inverter bank.
Generator. Where you want one, it is sized at 1.25 times the inverter so it can run the house and charge the battery at the same time. Its job is the darkest week of each winter month, when a run of overcast days makes about 65 percent of the monthly average.
What the tool does not do. It does not see your shading, your cable runs or your roof pitch, and it does not price anything. A quote comes after a site visit.
For builders, architects and agents
Put the sizing tool on your own site.
One line of code. Your visitors size a system on your page and the result carries the Trentham Energy name. No account, no cost.
<iframe src="https://trentham.energy/off-grid/sizing-tool/embed" width="100%" height="900" title="Off grid solar sizing tool by Trentham Energy" loading="lazy" style="border:0"></iframe>About the tool
Three things people ask.
- Is the result a quote?
- No. It is the system size we would start a design from. The price depends on the site, so it comes after a visit.
- Do I have to give my email?
- No. The result shows without it. Your email is only needed to send you the report or to book a call.
- Does it work outside Victoria?
- The sun figures are Victorian. Pick Somewhere else and it uses the Central Victoria baseline, which is conservative for most of mainland Australia.
Like what the numbers say?
A sizing gets you in the ballpark. A real design is built on your actual usage and the site itself. Send us the property details and we take it from there.