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A company is proposing a pumped hydro system where they state on their website as “capable of producing up to 335 MW of electricity with around 8 hours storage”. The same company is proposing a battery proposal that is stated on website as “with capacity to dispatch up to 500 MW of power over a duration of up to 4 hours”.

  1. So does this mean the PH is producing less total power than the battery?
  2. If we add in the time factor does this mean to get MWh you simply divide the total storage by the number of hours that it produces for? This is very confusing to novices trying to work out the better option.
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    \$\begingroup\$ Please give us a link to the web site you mentioned. \$\endgroup\$
    – Elliot Alderson
    Commented Feb 4, 2023 at 20:46
  • \$\begingroup\$ what option are you trying to work out? \$\endgroup\$
    – jsotola
    Commented Feb 4, 2023 at 22:06
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    \$\begingroup\$ Define "better". The PH stores more energy, the battery provides higher power. But battery can be installed pretty much anywhere, while PH requires suitable local geography. The biggest operating expense will be the electricity you need to charge either system, so end-to-end efficiency should be an import part of "better", too. \$\endgroup\$
    – Dave Tweed
    Commented Feb 4, 2023 at 22:46
  • \$\begingroup\$ The sight is Energy Australia. Both PH and battery proposals are on the same site. energyaustralia.com.au/about-us/what-we-do/new-energy-projects/… \$\endgroup\$
    – CLC inquiry
    Commented Feb 5, 2023 at 0:20
  • \$\begingroup\$ We are trying to work out the relative benefits for the two options. Ideally something like - how many 500 MW batteries it would take to match the output of the PH system. \$\endgroup\$
    – CLC inquiry
    Commented Feb 5, 2023 at 0:22

2 Answers 2

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This question is about the relationship between energy and power.

The SI unit of energy is the joule (J).

Power is the rate of energy transfer. The SI unit of power is the watt (W). One watt = one joule per second.

Whilst the SI unit of energy is the joule, a common measure is the watt-hour (Wh.) This is the energy transferred by one watt for one hour, so equivalent to 3600 J.

With this background, we can see that the storage capacity of a system comes from power * duration, but we need to exercise care because sometimes we see peak power quoted with the duration quoted for a lower average power.

Q1. "Total Power" doesn't really make sense in this context. "Power" is a measure of energy transfer/consumption rate. The PH system can deliver 335 MW, whilst the battery system 500 MW. So the battery system can deliver almost 50% more power.

Q2. Assuming the power quoted can be sustained for the full duration, we can see the PH system has a capacity of 335 MW x 8 h=2680 MWh, whilst the battery system has a capacity of 500 MW x 4 hr=2000 MWh. So the PH system has around 25% more energy storage.

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    \$\begingroup\$ These are all good numbers but to make a choice between these options requires much more information mostly involving cost such as initial cost, maintenance costs, distribution costs, land acquisition costs, etc. \$\endgroup\$
    – Barry
    Commented Feb 4, 2023 at 23:05
  • \$\begingroup\$ 100% agree. I was just answering the question about energy and power. \$\endgroup\$
    – colintd
    Commented Feb 5, 2023 at 0:15
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does this mean the PH is producing less total power than the battery?

Less power, yes: 335 MW vs 500 MW.

"Total power" is meaningless. If you mean "energy", then that's different from power.

Energy:

  • Pumped Hydro: 335 MW * 8 hours = 2680 MWh
  • Battery: 500 MW * 4 hours = 2000 MWh

So, that pumped hydro project stores more energy than that battery.

does this mean to get MWh you simply divide the total storage by the number of hours that it produces for?

No. Energy = Power x Time = Watts x hours = Watt-hours

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