Energy storage: sizing and sales part 2

Monday, July 26, 2021
Veli Markovic

What did we cover in the last presentation?

In part 1 of this two part series on grid renewable energy battery storage systems, we looked at the psychological drivers that play a role in what a customer actually wants out of a battery storage system.

We asked systematic questions that included:

  • What are the psychological drivers when it comes to purchasing energy storage? 
  • What if there is an existing solar system? 
  • What other pertinent information do I need to know?

In part 2 we look at usage patterns, load consumption profiles, battery selection and finish with a simple step by step guide.

Energy Storage: usage

Usage patterns:

  • Let’s say the majority of energy is used outside of solar production hours
  • These hours correspond to the peak tariff rate
  • In other words solar cannot “directly” address these loads

Energy Storage: actual load

As before we are assuming the customer has existing solar:

  • The load outside of production hours is 10 kWh
  • Let’s assume a battery charging efficiency of 85%
  • So from the energy storage we will need approximately 12 kWh = 10 kWh/0.85

We have to select the storage chemistry and in this case it will be LiFePO4 and will design for a maximum DOD ( Depth of Discharge) of 80%, 20% remaining.

So will need:

  • 12 kWh/0.8 = 15 kWh of total storage
  • But what if the customer wants some backup if the grid fails?
  • Can’t predict when the grid fails so the question is how much energy buffer do we require?

So will need:

  • 14 kWh  ( 12 Kwh for loads + 2 kWh for backup)
  • 14 kWh/0.8 = 17. 5 kWh
  • Let’s say we select a 48 volt system
  • So you will need a 364 Ah bank @ 48 volts.
  • Will select a 400 Ah system, 400Ah x 48v = 19.2 kWh

Series parallel

Battery brand largest cell is 200 Ah @ 12 volts so will need to:

  • Parallel and series to achieve 400 Ah @ 48 volts
  • Will need 4 x 200 Ah cells in series paralleled to another 4 x 200 Ah in series
  • Total of 8 x 200 Ah 12 volt cells

Let’s say now we have a different  battery brand and its largest cell was 400 Ah @ 12 volts:

  • Still need to series the batteries to achieve 400 Ah @ 48 volts.
  • Don’t have to parallel
  • Will need 4 x 400 Ah cells in series 
  • Total of 4 x 400 Ah @ 12 volt cells

*Obviously the 400 Ah cells would be heavier to deal with compared to 200 Ah cells

What about the existing solar?

  • Assume customer has 5 kW system in Melbourne, Australia
  • Have 10 kWh of load outside solar production hours
  • During actual solar production hours have around 4 - 5 kWh of load

In winter time the solar may not be enough. The rest of the year is probably OK and it will be definitely fine during summer.

Tariff optimisation

Can the system you have selected achieve tariff optimization? In other words can you program the inverter to charge from the grid if advantageous and is the price discrepancy between tariffs enough to justify this functionality?

The main factors

With energy storage systems on the grid there are three main factors:

  • Storage capacity
  • Solar input contribution
  • Grid input contribution

In addition,  inverter charger functionality and the ability to determine what input is used and when comes at a cost and is this cost justified?

With standard grid connect systems, the solar services the loads during daylight hours, cost saving at $X/kWh and if there are no loads or loads fully serviced, excess goes to the grid but at what value? 

About $0.07/kWh.

It’s all about energy management or resource management strategies that can effectively be implemented.

Energy Storage: sales step by step

  1. How did you find out about us? Internet or referred, other
  2. Do you have an existing solar system? Yes or No
  3. What are the roof details? Near Maps, Google etc
  4. Do you work away from home? Yes or N
  5. What is your tariff arrangement? Flat, peak off peak
  6. What is your average daily load?
  7. What % of energy is consumed during daylight hours compared to after dark?
  8. Is there a suitable garage or similar available to install the equipment in? Y or N
  9. Is grid disruption a problem in your area and do you want battery backup? Y or N
  10. Can I send you out an Authority to Act doc so I can collect the interval data? Y or N

Next steps

Send out preliminary costing to the customer and if customer says yes, analyse the consumption data after receiving from retailer then organise a site visit and design and  submit formal proposal.


As energy storage is such a complicated area it is incredibly important to understand a customer’s motivation when it comes to energy storage. What they actually want as compared to need is all tempered by the financial commitment they are willing to undertake.

In this second part of the series we have looked at battery selection, load consumption profile and then asked a series of questions to determine a range of responses. 

If you’d like to see more of what Greenwood Solutions get up to in the real world of renewable energy, solar, battery storage and grid protection check out the following pages:

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About the author

Veli Markovic

CEC Designer
Veli has nearly two decades of experience in the renewable industry. He is passionate about providing people with valuable education and is highly regarded throughout the industry as an educator and operator.
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