Wind, storage and back-up system designer

Peak demand, wind and back-up power / energy usage and storage capacity calculator

For the specification and design of renewable energy electricity generation systems which successfully smooth intermittent wind generation to serve customer demand, 24 hours a day, 7 days a week and 52 weeks a year.

Adopting the recommendation derived from scientific computer modelling, the tables offer rows of previously successful modelled system configurations – row A, a configuration with no back-up power and rows B to H offering alternative ratios of wind power to back-up power.

Columns consist of adjustable power and energy values in proportion to fixed multiplier factors.

The wind power generation Capacity Factor (C.F.) percentage can be adjusted too.

The recommended energy storage capacity is about 90% of one day’s average wind energy generation.

The Wind, storage and back-up system designer is hosted separately on the Scottish Scientist website. You must click to open the web-page.

Open the Wind, storage and back-up system designer (in a new page)
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7 thoughts on “Wind, storage and back-up system designer”

  1. Noting the story in “CLIMATE ACTION. In Partnership with UN Environment”
    CLIMATE ACTION
    In Partnership with UN Environment
    100% renewable energy fuelled micro-grid successfully operated in 24h test in Illinois
    http://www.climateactionprogramme.org/news/100-renewable-energy-fuelled-micro-grid-successfully-operated-in-24h-test-i

    I made the following comments …

    Well what’s needed is a system design that provides power on demand, reliably 24 hours a day, 7 days a week and 52 weeks a year. To achieve that without diesel back-up generators, I would recommend –

    store energy capacity = 1.5 days x peak demand power
    annual maximum wind (+ solar) power = 7 x peak demand power

    (assuming I only know the system’s peak demand power) –

    So for this Ameren micro-grid where I assume “the 50kW onsite microgrid which powers an American research facility” means that the peak demand power is 50kW, I would therefore recommend
    (see Grid Watch Demand Focus Table http://scottish.scienceontheweb.net/Wind%20power%20storage%20back-up%20calculator.htm?peak=50&units=kW#grid )

    storage energy = 1.5 days x 50kW = 36 hours x 50kW = 1800 kWh
    (whereas all the Ameren system has is “500kWh” which is too little by a factor of 3.6)

    annual maximum wind (+ solar) power = 7 x 50kW = 350 kW
    (whereas all the Ameren system has is “250kW” which is too little by a factor of 1.4)

    By “too little” I mean too little for 24/7/52 operation, even though the Ameren system worked perfectly well in the test conditions of that particular 24 hours. Clearly wind and solar power have days of plenty and days of shortage. My recommendations tell you how to design a system that works even on the days of shortage – for those dark days of winter when there’s not much wind blowing either – that’s when your system design gets its ultimate test.

    However, my above recommendation assumes that the system’s average power demand is about 60% (30kW) of peak power – (50kW), with an average daily energy usage of about 24 hours x 30kW = 720kWh and a higher maximum daily energy usage.

    If the average power used is significantly lower than 30kW and in particular if the maximum daily energy usage is significantly lower than 720kWh then it may well be that not so much storage or wind+solar generation is required.

    Supposing although a micro-grid had a peak demand power of 50kW its maximum daily energy usage never was as much as 720kWh but was a lot less.

    Let’s assume that the average power was, say, only about 10kW and their average daily usage only 24 hours x 10kW = 240kWh, but their maximum daily energy usage in any one day was a maximum of 482kWh.

    Then all that would be needed would be
    store energy capacity = 2.4 x maximum daily energy usage
    max wind (+ solar) power = 0.4666 per hour x max daily energy usage

    (See Off-grid daily usage Focus Table http://scottish.scienceontheweb.net/Wind%20power%20storage%20back-up%20calculator.htm?usage=482&units=kW#off )

    energy storage – 2.4 x 482kWh = 1157 kWh and
    annual maximum wind (+solar) power = 0.4666 per hour x 482kWh = 225 kW

    which is still a factor of 2.3 times more energy storage than the Ameren microgrid has (500kWh) but is exactly the wind+solar power they have.

    So it all really depends on what the maximum daily energy usage of the system is. Peak power demand doesn’t completely specify a system’s generation and storage requirements because both peak power and maximum daily energy usage are important design considerations.

    Likewise, a 50kW micro-grid which always runs flat out at 50kW (peak demand power was also the average power) and therefore had a maximum daily energy usage of 24 x 50kW = 1200kWh would have a greater energy storage and generation requirement.
    (See Off-grid daily usage Focus Table http://scottish.scienceontheweb.net/Wind%20power%20storage%20back-up%20calculator.htm?usage=1200&units=kW#off )

    In this case more energy storage 2880 kWh and maximum wind+solar power 560 kW would be required.

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  2. V interesting. Have you integrated the possibility of over capacity/storage electrolysed hydrogen being used in fuel cell vehicles or as a supplement to domestic gas supply (not allowed in the uk at present but can be done up to 15%)? The reason I say this is that this would permit sufficient over capacity to mean you could have a 7/24/52 guaranteed electricity supply without waste as surplus could be stored or used elsewhere.
    Also what would the impact be of domestic micro-generation? Has anyone done a study as the demand on the grid appears to be going down due to this and other techno?

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    1. For configuration rows A to E, one can easily calculate the average daily surplus of wind energy by subtracting the value in the “Daily Usage” column from the value in the “Wind energy per day” column.
      In terms of percentages of the Daily Usage = 100%, those surpluses are row A = 169%, row B = 111%, row C = 54%, row D = 27%, row E = 4%.
      As I noted on this page https://scottishscientist.wordpress.com/2015/03/08/scotland-electricity-generation-my-plan-for-2020/ in dozens of references to “hydrogen”, those surpluses are available for “wind farm on-site power-to-gas and gas-to-power”. Gas-to-power may be hydrogen fuel-cell or gas turbine generator. See – https://en.wikipedia.org/wiki/Power-to-gas
      For demand on the grid going down due to domestic solar micro-generation etc. see https://en.wikipedia.org/wiki/Duck_curve

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  3. Perhaps it’s worth factoring in local inter-seasonal heat storage. In the UK about half of energy use and CO2 emissions come from heating demand. Whilst it is extremely difficult and expensive to store electricity, low grade heat can be stored underground, affordably, for months. Perhaps it would make sense for all of the UK to use excess windpower electricity for heat storage in local heat stores and to make use of all the Scottish pumped hydro capacity for electricity for uses other than heating even if that means greatly increasing interconnector capacity between England and Scotland. https://en.wikipedia.org/wiki/Seasonal_thermal_energy_storage

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    1. You are welcome to post a comment about heating, thermal energy storage and how the UK’s options for investing in various technologies might effect electricity demand by posting in reply to my comment which begins “Using electricity and renewable energy hydrogen for heating …” in my post Scotland Electricity Generation – my plan for 2020.

      In this “Wind, storage and back-up designer” topic, comments are invited about how to use my webpage calculator to design grid configuration capacities for wind power (and other intermittent generators), primary energy storage and back-up dispatchable power in order to meet the grid’s customer power demand.

      Those capacities and peak power demand are considered in this topic as scalar quantities – a certain number of watts, or watt-hours. Please note that it is “off topic” in the “Wind, storage and back-up system designer” comments to second-guess grid customers as to what it might, or might not, “make sense” for them to use their electricity, whether for heating or for anything else. In electricity supply, as in retailing generally, the customer is always right.

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  4. Admittedly, the King Island Advanced Hybrid Power Station was up and running in 2014 before I had got this blog’s socks on in 2015.

    Also, I do like the King Island’s real time display on their website.

    But as Roger Andrew’s post on Energy Matters in January –“A first look at the King Island, Tasmania, Renewable Energy Integration Project”

    – explained “the project is not capable of supplying King Island with much more than 60% renewable electricity”.

    Using these 2 data items only from Roger’s post –

    * “Its annual electricity consumption is on the order of 13 GWh.”
    * “The capacity factor of the wind farm was an impressive 39%.”

    and dividing 13GWh by 365 days to calculate a daily usage of 35617 kWh

    I can use my “Wind, storage and back-up system designer” web-page with this link to generate a “Off-grid daily usage Focus Table”, whose rows A to H recommend different system configurations that can meet the 100% renewable energy aim, providing that the back-up power is renewable too – bio-diesel, hydrogen from power-to-gas-to-power or biomass etc.

    The table’s rows recommend energy storage capacity in the range 12 to 86 MWh – much more than their puny 1.5MWh battery.

    King Island seems to have enough to build a pumped hydro scheme of a suitable size.

    To source most of their energy from the wind, they would need a Row E or above configuration – at least 4 MW of wind power, in which case they can make do with only 1MW of back-up power.

    To manage with just the wind turbines and energy storage – without any other back-up power – they’d need a Row A configuration more than 10 MW of wind turbines, 86 MWh storage and then they could use the plentiful surplus power for electrolysis of water to make hydrogen fuel gas (to power their new hydrogen fuel-cell vehicles – or whatever).

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  5. Fair Isle renewable energy electricity scheme

    BBC: “The glory of 24-hour power finally reaches Fair Isle”

    It looks like the Fair Isle electricity scheme now has more than enough generation capacity for 100% renewable energy operation, though the system is somewhat imbalanced in terms of more power generation than they strictly need but not really enough energy storage to make the best use of all the intermittent power available.

    Assuming –
    * daily usage of 500kWh
    * capacity factor 52%
    – the “Off-grid daily usage Focus Table” is generated by this link

    Wind Turbines – 180 kW

    They’ve installed 3 x 60kW = 180 kW and that’s more wind power than my table recommends even for a Row A configuration (108kW).

    So they can easily meet their present electricity usage needs even with only 2 out of 3 wind turbines in operation – 2 x 60 kW = 120 kW.

    Having a redundant wind turbine will allow for maintenance and repairs on any one turbine while the other two turbines are operating. Smart.

    Solar PV Panels – 50 kW

    The 50 kW solar array looks surplus to requirements but I suppose that freak flat calm sunny day may happen once in a blue moon and justify the expenditure.

    Electric batteries – 500 kWh

    They would have been able to generate more energy reliably if they had instead spent more (or more efficiently if pumped hydro is an option there) on more primary energy storage (500kWh is only enough for a Row E configuration) or perhaps considered adding secondary energy storage such as power to gas.

    My guess is that once they figure out how much more intermittent power they’ve got they may invest in electric heaters and heat their homes using electricity when the wind is up instead of relying always, as I presume they do now, on some kind of fossil fuel heating.

    This is the link that generates the “Wind Generation Capacity Focus Table” for 180kW wind power and capacity factor 52%.

    This suggests that with 4 times more energy storage – 2000 kWh – they could supply 4 times more power reliably with the same wind turbines, or even more depending on how much back-up power they have.

    Good job! 🙂

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