Off Grid Solar Queanbeyan

Hi Everyone

I have three quotes from a couple of different suppliers/installers, and I am curious as to others thoughts on which system I should go for.

We are just east of the ACT in NSW, just south of Queanbeyan. Temperatures range between -5 and 40.

Both companies quoted based on average daily demand of 17.5kWh. I work from home, computer, monitor and internet mainly. We generally don’t watch much tv at night, and only have a few lights (low energy led fluorescent) on at any given time. Heating is with fireplace, hot water (including kettle) are gas. Cooking is all gas.

Quote 1 - $48k

  • 24x REC 325W N-Peak Monocrystalline (BF) Solar Panels (7.8 kWp)
  • Victron Quattro 48/8000/110-100/100 Inverter/Charger (7kVA cont. delivery)
  • Fronius Primo-6.0-1 Solar Inverter (includes Adapt mounting & off-grid programming)
  • Victron Color Control GX System Display
  • 2x BYD B-Box 13.8 LV PRO (IP20) - High Performance & Expandable Lithium-ion (LFP) Battery Unit (27.6kWh: 100% ‘usable’)
  • NO Generator

Quote 2 - $54k

  • 24x REC 325W N-Peak Monocrystalline (BF) Solar Panels (7.8 kWp)
  • Selectronic SP PRO SPMC482-AU Inverter/Charger (7.5kVA cont. delivery)
  • Fronius Primo-6.0-1 Solar Inverter (includes Adapt mounting & off-grid programming)
  • Selectronic Ethernet Adaptor (005081) for ‘Quick View’ Desktop Monitoring over LAN
  • 6x PowerPlus: High Performance 48V Rack Mounted L-ion (LFP) Batteries incl. 800/600/990 IP21 8 module Cabinet (19.8kWh: 100% ‘usable’)
  • NO Generator

Quote 3 - $45k

  • 22x Suntech 325 watt solar panels (7150 watt array)
  • Selectronic SP Pro SPMC 482-AU 7.5kW inverter charger
  • Fronius Primo 6.0-1 Selectronic certified string inverter
  • Selectronic Ethernet Adaptor (005081) for ‘Quick View’ Desktop Monitoring over LAN
  • 24x Hoppecke 6 OPzV 750 batteries 847Ah @ C100 (40.65kWh of storage @ C100 48V)
  • Honda EU70is generator with remote start & battery charger

The big differences I see are the lead acid vs lithium ion batteries, and the inclusion of the generator with the lead acid quote. So this would mean another $6k-$8k(?) for a generator for the lithium ion options.

Thoughts are very welcome.

Thanks, Steve

Solar Power Canberra

Hi Steve,

Interested to know why have the companies quoted based on the 17.5kWh value? By your description of the household appliances this should be much lower, I would estimate about 8 to 9kWh. Did either company do a load table with you?

All the quotes are quite good but option 2 is the best in my opinion followed by option 3. I’m not a huge fan of BYD batteries for off-grid due to low temperature disconnection issues. Here’s some information about the best off-grid batteries

The biggest benefits of Lithium batteries is the high efficiency and you can add more capacity in the future if required. Lead-acid is fixed size while lithium systems are modular. Since you are using gas for cooking etc, you may decide to convert to electric in the future which means more storage capacity is required. (although all of these systems are large enough to support electric cooking appliances)


Thanks Jason

Yes we did a load table with the first company and then applied it to the 2nd.

17.5kWh is similar to what we have with our current electricity bills so we thought that it was pretty close.

We included some bigger ticket items that we probably won’t be installing, and looking at the table again the total would make more sense if it was PEAK daily demand as opposed to AVERAGE, as the table is adding up all the appliance totals as if everything was being used at the same time… maybe it’s just the title?

Appreciate the comments about the batteries, expandability of the system was something we were thinking about just recently.

Thanks, Steve

Sounds like the load table might be a little misleading. The peak demand (kW) is different to the peak consumption (kWh). Peak demand is the maximum load on the inverter and battery system when all appliances are operating (the inverters quoted are all very capable, so no problem here).

The average daily consumption (kWh) is determined by how long the appliances are running, this usually differs from summer and winter depending on how you heat your home and hot water. Electric heating hot water alone usually account for 30% of your energy consumption which is why heating during the day using solar is a good choice. The 17.5kWh figure quoted is pretty high but is typical for a 3-bedroom off-grid home with typical appliances and electric cooking.

Also here’s a useful article comparing lead-acid and lithium batteries…

Proper design of an off-grid system is far different than grid tied… you have to design to get:

  • enough ‘new’ energy from your PV to re-charge batteries and supply average daytime energy on the shortest day of the year at your location, which is probably what… 4 hours? if your actual daily consumption has averaged 18 kwhr, you’d size your PV at least to 18/4 = 4.5kw to generate daily use at the very least, plus a little to ‘catch up’ and re-charge batteries if you had drained them from a cloudy day… so, probably a 6kw to 9 kw of PV is not unreasonable depending weather… i.e. how many ‘partially sunny’ days do you get?

  • battery chemistry/capacity is a huge differentiator. Flooded Lead-acid will be the cheapest, then AGM, then Li will be the most expensive. tradeoffs are amount of maintenance, and longevity. Longevity of ANY chemistry is affected by depth of discharge, even Lithium, don’t let them tell you it is not. lead battery capacity should be at LEAST 2x your average daily use, preferably 3x. The goal is to rarely take the batteries below 50% DOD for best life; firing up a generator at 60% is recommended. Lithium packs should not be taken below 70% if you want to maximize cycle life, going to generator no lower than 80% would be recommended. The key to lithium is a very good battery management system that is capable of keeping all cells ‘in balance’ at the end of the charge cycle to prevent any cell from going over voltage.

  • ANY offgrid system needs a generator… what if you have more than 2 days without sun, or a mech failure of charge controller or inverter! That also leads to checking out your Designer/Installers… how many off-grid systems have they designed, installed, and maintained? what is their emergency response policy if you have a problem? Do they stock spare parts?