Review of Home Battery Install with Solar PVs

February 22nd, 2017

Last year we installed a battery to help power our home

We were interested to review how this works from the perspectives of: energy usage, and cost benefits.

Image of home battery with garden view

Batteries, and renewables are very topical at the moment with energy prices, base load power and blackouts in the news, and debate around the requirements for installing batteries in and around your home.

The debate is tending to become an embarrassing game of political football which no-one wins. 

It should not be framed as: sun and wind, versus coal and gas. 

To work for the best interests of all Australians, we believe any debate should be around how the existing grid, power system and utilities can transition smoothly to the reality (ie here already) of an industry which progressively mixes all of the above.  And how we can provide stability to make best advantage of the employment, research and investment opportunities which will continue to evolve.

But back to the battery…

We believe the battery and PV system we’ve installed will pay for itself inside the warranty period of the system. 

We also believe this will improve for new purchasers.  Even since we installed our system last year, the price of a storage system per kWh has dropped significantly.

Further, we get a warm green glow

We know that, irrespective of politic will – we are doing what we can, within the means we have available to us, do stand up for what we believe in.  You can, too.

We are happy to update the following over time as we learn more about how the battery performs and how we perform with it.

Background:

  1. We installed a 5kW PV solar array, including a 6.4kWh battery system with inverter in 2016.
  2. We work partly from home, have a plug in hybrid (6kWh electric) car we need to charge, and use gas for cooking and some heating.
  3. Our average daily use WITH the car is around 20kWh (varies with time of year)
  4. Assuming average daily exports of solar to the grid around 20kWh (varies 15-30kWh to date)
  5. 10 year warranty on battery etc.
  6. The fun (nerdy) phone app shows us we’ve saved around 10,000 light bulbs being powered for 1 day (or 1200 kg of CO2 emissions saved) for the 4 months we’ve had the system now.

Base costs before battery and PVs

  • Charge for electricity is assumed at around 23c / kWh
  • So cost around $3.2 / day CONSUMPTION
  • In addition around 50km driving per day with petrol price assumed at $1.30/litre and say around 8 litres per 100km, so $5.20 petrol per day.

With the battery and PV’s this converts to:

  • No cost for energy used, day or night.
  • Sale of extra energy back to the grid around 20kwh per day (approx.) at 8c/kWh = $1.60/day
  • Saved petrol use above up to the first 50km driven each day
  • So saves $5.20 petrol but spends 6kWh x 8c =$0.48 / day on charging car.
  • So $4.70 saved in fuel for car per day.

So the net difference is in this simplistic summary:

  1. Save on electricity we used to buy: $3.20/day
  2. Save on petrol we used to buy: $4.70/day
  3. Save on energy sold back to the grid: $1.60/day

TOTAL SAVINGS PER DAY = $9.50 per day.

This equates to saving around $3,467 per year (assuming same habits on weekends etc)  Or over $17,000 in 5 years. 

This is more than what the entire system, including PV’s cost us… and all within half the warranty period.

So this means that the systems original cost is paid for in under 5 years, by the savings made.

Screenshot of software app illustrating energy generated, self-consumed and drawn from grid for the month of February to date.

NOTE How you live makes a difference.

IN this case we have chosen to be different to many people… But you can make the same choices if they are right for you:

  • The electric car we use makes a big difference to this payback period – ie about half the costs we save on a daily basis are petrol costs.  We feel this also significantly improves the environmental benefits of the system (reducing fossil fuel use further)  We’d catch public transport more but… there IS none where we live.  But that’s another story.
  • We haven’t included the COST of the electric car here.  We were buying a car anyway, found this one second hand and so did not pay a premium for it beyond what we might have chosen for a car with a sunroof, or with a good speaker system.  It’s just that we made a choice we believed in.

 This review is ignoring

  • the ongoing costs of connection to the grid which in theory could be avoided if we did not need the grid.  This would make our savings greater – so the system would pay for itself more quickly. 
  • Our daily electricity use does NOT require the grid for electricity – however we’ll need to review that again after winter.  (noting that we’ll likely stay connected anyway into the future as the community needs the grid just like it needs public transport or roads or swimming pools we might not use – and we are happy to play a fair role in maintaining that)
  • The 50c rebate which some people receive for their existing solar PV generation when exported to the grid
  • etc

In summary:

This is a very simplistic look at how the costs and benefits balance for us, and gives a very rough idea on the difference the system can make.  We would expect this to vary over winter as we may have assumed too high an average export to the grid OR too low an average consumption.

The benefits in our case will be greater if we had higher average daily use – and the more this use is loaded towards day time usage while the sun is shining and PV’s are generating their power… as we would then use more of the PVs energy (“free”) versus paying 23c/kWh to buy someone else’s power.

 

To be Continued.