Whist producing electricity with solar photovoltaics (PV) emits no pollution, produces no greenhouse gases, and uses no finite fossil fuel resources, it also “takes energy to save energy”. In other words, what is the “green” cost we must pay in the manufac ture of this technology to create emissions free energy over the long haul. We call this “energy payback” - how long does a solar system need to operate to recover the embodied energy including the generation of CO2 that went into the initial manufacture of the system.

Comparison of the embodied energy of three different systems:

• 6.6kW monocrystalline solar panels (say 18 typical panels); grid-connected, no batteries = 26,720kWh of embodied energy
• (2) 6.6kW monocrystalline, grid-connected, with a lithium battery, rated power storage capacity of 10kWh = 31,320 kWh of embodied energy

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• (3) Off-grid 6.6kW monocrystalline, with a lead-acid battery, rated power storage capacity of 35kWh = 38,020kWh of embodied energy.

So, the energy payback period relates to “repaying” the embodied energy required to produce the system, which once paid back all further generation is counted as positive for the environment. Forward estimates utilising Renew Magazine’s Sunulator https://renew.org.au/resources/sunulator/, (with additional information from Dutch researcher Erik Alsema https://www.nrel.gov/docs/fy99osti/24619.pdf) annual generation of a north-facing 6.6kW solar system across in different Australian locations amounts to approximately 8,745kWh in a southern State up to 11,385kWh in the northern more sunny Australian locations. Thus, a system without batteries has an energy payback period ranging from 2.4 to 3 years.. A system that includes 10kHh of lithium battery power storage (grid connected) means longer embodied energy payback, ranging from 2.7 to 3.5 years. With an expected 25 year solar panel lifespan this leads to at least 20 years of free from the sun energy. Note: you may still have some ongoing on -grid energy bills with either of these systems, particularly without any battery power storage.

Finally, if we install a completely off-grid system with 35kWh of lead-acid battery power storage you’d be looking at a payback period of 3.5 to 4.5 years. If you have long periods of heavy clouds or a spike in household power usage that necessitates the use of the back-up generator – this would also add to your “carbon debt” but overall you would still enjoy a couple of decades of completely green energy (along with the financial benefit of never having a power bill to pay). We at Pavilion Off-Grid Homes say - regardless of what level of off-grid you choose - over the lifetime of the system you will have paid back the embodied energy (“carbon debt”) in manufacture within one to four years of ownership - then emit minimal or no CO2 emissions ongoing... and, you will be enjoying massive savings on your power bill from day one.