Mini-grid 1 MW ?'s

SystemSystem Posts: 2,511 admin
Hello all,
I'm new to the site, great site by the way!
I have a potential client who is interested in having a mini-grid for a mining complex up here in Alaska and wants to know if we can install a wind farm in the 1MW range and have his diesel generators hooked up as well. Now wait for it....
He would like some sort of load shifting capability as in have the gensets run full time then when the wind kicks up enough to offset the current load there would be a load shift and the gensets would idle down while the wind took over.
Anyone ever heard of such an animal or maybe point me in the right direction?




  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Mini-grid 1 MW ?'s

    My guess is that anything is possible if you have enough money! My guess is that it is out of the expertise here, but let's see what happens when you run it up the pole. My only suggestion is to contact some of the commercial wind farm folks, especially the engineers. I don't know of any technical reason why you can't have a wind turbine and a diesel to phase together, but I sure don't know how.


    PS Welcome to the forum. There are some pretty smart folks here.
  • System2System2 Posts: 6,290 admin
    Re: Mini-grid 1 MW ?'s

    Thanks icarus,
    I felt that I needed to get in the trenches so to speak and see what people were talking about with RE issues etc.
    I feel I owe it to my customers to be as informed as possible and help them make the best possible choice without getting burned. I know it sounds corny and scripted, but I would feel terrible selling something somebody can't utilize properly. Lots of money involved and my reputation and the company's on the line.
    Thanks for the warm reception and I hope I can contribute here as well.

    Kindest Regards,


    Alaskan Wind Industries
  • BB.BB. Super Moderators, Administrators Posts: 32,019 admin
    Re: Mini-grid 1 MW ?'s

    There are two reasonable storage methods right now... Battery and Pumped storage (Hydro).

    Both are going to be fairly capital intensive and can be made bi-directional.

    Smaller Diesel installations in Africa have been made "Hybrid". Basically, use Batteries 18 hours a day, and 6 hours a day (evening) crank of the genset and run at >50% load powering the evening loads and recharging the battery banks. Once the evening loads fall off and the batteries are charged--turn off the diesel and let the batteries carry the lighter/variable loads for the rest of the cycle.

    The fuel savings is based on running the genset always in its optimal range--and the batteries when the genset would be under 50% capacity and using fuel just to keep it turning and supplying a few loads.

    With large battery banks--you certainly have options. Traditional Lead Acid, and non-traditional technologies (like molten sodium batteries).

    Hook up with the Department of Energy and/or local state agencies--and see if you can swing a research grant in there too.

    Wind--that is a difficult subject. Many times, it is unpredictable and so you need the rest of the grid to operate as if wind is not present (and that may be true--Wind runs from 2%-30% or so of its name plate rating). Big wind turbines will be better than a bunch of small turbines--but you still will need a pretty suphisticated method of storing the engergy.

    For our "small home and off-grid system"--typical systems are designed to store 3 day of load down to 50% discharge level (lead acid batteries do not like to be deeply cycled below 50%).

    If your wind is highly variable--it may not be economic to expect to offset a bunch of your diesel usage unless you have a bunch of opportunistic loads (hydro storage, water pumping, process loads, etc.).

    Diesel (and other fuel based power sources) probably cost around $1 of capital per installed watt. And off-grid solar/wind/battery storage system may cost you (in very rough numbers) $10-$20 per watt...

    Of course, you have no fuel costs with the RE equipment--but you still have maintenance costs and repairs (and limited life).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Mini-grid 1 MW ?'s

    Have a chat with the chaps at SMA they have some experience with village electrification (up to 68kW) - but I've not heard of a 1MW system. Their AC connected off-grid kit uses the mini-grid frequency to control the output of their inverters. So all AC generation sources sync to the mini-grid frequency that the Sunny Island controls. When the sunny island detects too much production it increases the grid frequency. All the connected SMA inverters (windy boy or sunny boy), then throttle back their output based on the frequency.
    If you want to parallel generators then these will also have to synchronize to an existing frequency - if they can do this, and they can throttle back their output based on the grid frequency, then I suspect the system would be sorted.

    So it would work something like this:
    - Windy boy inverters for all the turbines, configured in off-grid mode
    - SMA Sunny Island battery inverters, just to control the grid frequency, they'll need a small 48V battery to power them, but in this design they won't be providing any power from the batteries.
    - Diesel generators that can synchronise and connect to the mini-grid. They would NOT be connected to the gen-input on the Sunny Island, but instead connect directly to the AC output. The key control component here is that the generators will throttle their output based on the grid frequency.
    - You can also control loads by using frequency dependent relays, these are called "Distributed Intelligent Load Controllers". They'll turn on or off based on frequency and or voltage thresholds.

    For example, you'd then configure the sunny island to operate between 49Hz and 52Hz (if you buy a US version, these will be different). Then configure the diesel generators to throttle back at 50.5, 51 and 51.5Hz (for example), then configure the windy boys to throttle back between 50hz and 52hz. So as too much power becomes available when the wind starts blowing, the windy boys will push out more power, then sunny island will detect this and raise the grid frequency, the diesel gensets will detect the raised frequency and throttle back their output first, if there is still too much power going in, the frequency would rise even more, till it reaches the upper limit of 52Hz where the windy boys would stop putting any power into the mini-grid.

    Although I've described the inverters as responding in an on-off fashion here, it's actually a linear scale based on the frequency shift. E.g. at 50Hz the windy boys produce 100% output, at 52Hz they produce 0% and at 51hz: 50%; so there's a linear scale in between the two extremes.

    That's the theory anyway! The SMA engineers will probably be able to give you more practical advise.
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Mini-grid 1 MW ?'s

    Understanding that I am over my head, but

    Why couldn't you run a small diesel to provide the frequency to simulate the grid with the load coming from the wind genny(s). The inverter(s) would "see" the grid from the small diesel. The biggest single problem that I see is matching the loads, as the wind power changes. How quickly can and idling diesel pick up the load that may be dropped as the wind slacks, or vise versa?

    Clearly you would need some sort of buffer. Figuring out how to do it without a battery is the trick!

    Interesting idea.

  • mike95490mike95490 Solar Expert Posts: 9,363 ✭✭✭✭✭
    Re: Mini-grid 1 MW ?'s

    You can't idle the diesel. It has to keep spinning at 50-60hz

    Diesels also need to run at least 50-90% load, or they "slobber" un burned fuel.

    Wind is just too variable, state wide grids are finding they have to keep 90% conventional generation going, because the wind keeps changing .
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

  • peakbaggerpeakbagger Solar Expert Posts: 341 ✭✭✭
    Re: Mini-grid 1 MW ?'s

    For a system this size you need to bring out the big guns. Give the folks at my former employer, Northern Power a call. They supply "wind diesel" solutions for villages in Alaska that are off grid and have to haul diesel in for gensets. There are a couple of somewhat larger installations that have been running for a few years. They have a 500 KW wind turbine set up for cold weather climates (enclosed Nacelle and tower) plus they use a permanent magnet generator so no gearboxes to maintain. They were working on a self erecting option that doesnt require a large crane to install, but not sure if it went commercial. The turbine isnt cheap but it is quite robust and built for nasty weather conditions. I think a rough cost was 500K installed. As mentioned,these arent cheap but the payback is there compared to trucking in Diesel and living without a standard turbine when it breaks down in the middle of the winter.

    They design and build power electronics that coordinate between the wind turbine and the gensets. As mentioned, diesels want to run at or near full load, so a load analysis and load management is going to be critical to making a system that will work reliably. I expect that rather than one big diesel, you may end up with several smaller units. Northern used to supply remote power for very remote sites (but critical use) like Antartica and Siberia, so this would not be their first system.

    They also have some interesting patents on mini grids and actually operated one in an industrial park in VT for awhile.

    They got caught up with some Wall Street "sharks" a few years ago and went bankrupt, but some new folks took the wind side private and they seem to have gotten backup to speed. They usually would retrofit into existing Diesel systems and I am not sure if they care to do the whole project like they may have used to since the reorganization, but I expect that that would be your preference to be an integrator working with an experienced OEM.

    I still have a few contacts, but best shot is go right to their website. A heads up is that you need an accurate wind profile in hand before they can do much for you. NRG systems makes assessment towers.

    If you have any hot springs near the site, PM me, for an alternative (yes folks Alaska does have some hot springs)
  • System2System2 Posts: 6,290 admin
    Re: Mini-grid 1 MW ?'s

    I have been researching this very issue, yes you can store Wind & solar in a Fly wheel storage system ( Similar to UPS), your Generators would run more efficient, as no catch load variation, or Higher Fuel demand. We are also about to move into manufacture of of a Faraday Amplifier to reduce Fuel input / Co2 , increase Kwhr out put. Currently working on Mine power solution for The Australian mining industry. Happy to share my Knowledge.
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Mini-grid 1 MW ?'s


    FYI (in case you hadn't noticed): You just necroposted on a dead thread from over a year ago. :D Nothing wrong with that, but I wouldn't hold my breath for an answer.
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