Running glass kiln (10kwh) off-grid?

tomas
tomas Registered Users Posts: 3
in Solar Beginners Corner #1
Hi guys,

I'm absolute newbie to solar (but I spent few days studying :) and I would like to know if it would be possible to run single (or even 3-phase) glass kiln totally off grid. The kiln I'm talking about would be something similar to this one (lower graded ones at the top of the list) - http://www.essexkilns.co.uk/glass-kilns-studio

I know that some people actually run such stuff on diesel generator but as the whole glass fusing cycle takes ~12 hours I'm thinking about some combined solution aka bank battery (fully charged by solar panels) and a diesel generator as a backup. The kiln takes max energy on the very beginning of the process when it warms up to 700-800C and then it just switch on for couple of minutes each 30 minutes or so to maintain the temperature on the same level.

Would it be possible to run such thing on something like 8/12 * 325A 12V AGM batteries connected in 2/3 groups on 48V + some sort of the inverter and get those batteries charged up with solar panels to minimise running time of the diesel generator?

To get on-grid would cost me ~$40k+ and I hope it would be possible to get the off-grid solution for less then $20k maybe but I'm really not sure if this is doable at all due to high peaks of power needed at the beginning.

Thanks a lot!
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #2
    Re: Running glass kiln (10kwh) off-grid?

    Spend the $40K!

    Just guessing but a PV battery system is going to hve to be huge,, (read EXPENSIVE!). Give us a better idea of the the a wattage draw of the klin is, I'm guessing huge.

    Just for comparison, I spend yesterday working on the wiring for a ceramics kiln. It draws nearly 14 kw, 56 amps at 240 vac. That would be 280 amps on 48 vdc (not counting inverter loses. To run this kiln through a cycle burns ~100kwh. To begin to power that you would need a PV system of ~80 kw along with a battery bank capable of delivering the kinds of currents you need to drive the heating elements. At $8/watt, that is a cool $64k, with a battery replacement cost to factor in, of perhaps ten years.

    How much power does your glass kiln draw peak, and what is the kwh/day calc?

    Tony

    PS, Welcome to the forum and fell free to ask as many questions as you have, as there are sine pretty smart folks here!

    It looks like the medium glass kilns draw 5-10 kw.

    PPS. http://www.skutt.com/glass/resources/ElecReq.php
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  • tomas
    tomas Registered Users Posts: 3
    #3
    Re: Running glass kiln (10kwh) off-grid?

    Hi Icarus,

    the current kiln is DYI made so I have no idea what parameters it does have (and I'm not electrician as well :) All I know is it's 3-phase and that it takes 10kwh for one cycle (yes 10kwh). Anyway, I'm aware it's quite hard to get 3-phase off-grid so I'm keen to buy/swap with some modern (and single-phase) kiln (something similar as http://www.essexkilns.co.uk/glass-kilns-studio, some of those smaller versions) - so I guess it would be 10kw max and the cycle will burn 10-15-ish kwh. Also I would need to burn stuff 30-ish times per year only.

    And btw I'm based in New Zealand and power cost's ~$0.3NZD here (~$0.25US).

    So do you think that even with that backup diesel which could run at the very beginning to cover the peak usage it's still better to get on-grid (the $40k will be the min price for getting there, it also can be $60-80k, I have no quote yet, I'm more doing a research before buying a block of land and I would love to get totally off-grid).

    Thanks.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #4
    Re: Running glass kiln (10kwh) off-grid?
    tomas wrote: »
    Hi Icarus,

    the current kiln is DYI made so I have no idea what parameters it does have (and I'm not electrician as well :) All I know is it's 3-phase and that it takes 10kwh for one cycle (yes 10kwh). Anyway, I'm aware it's quite hard to get 3-phase off-grid so I'm keen to buy/swap with some modern (and single-phase) kiln (something similar as http://www.essexkilns.co.uk/glass-kilns-studio, some of those smaller versions) - so I guess it would be 10kw max and the cycle will burn 10-15-ish kwh. Also I would need to burn stuff 30-ish times per year only.

    And btw I'm based in New Zealand and power cost's ~$0.3NZD here (~$0.25US).

    So do you think that even with that backup diesel which could run at the very beginning to cover the peak usage it's still better to get on-grid (the $40k will be the min price for getting there, it also can be $60-80k, I have no quote yet, I'm more doing a research before buying a block of land and I would love to get totally off-grid).

    Thanks.

    Three phase motors require three phase supplies because the timing relationship among the three phases, applied to the right set of motor coils, is what makes it spin.
    For resistance heating, as long as you have three pairs of wires coming from the heating elements rather than just three wires and no neutral, you will be able to drive them with a single phase supply although you may need a transformer to get all of the voltages correct.
    SMA SB 3000, old BP panels.
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #5
    Re: Running glass kiln (10kwh) off-grid?

    Off-grid 3 phase is supported by all the big inverter companies... but then you need to install 3 inverters which adds to the costs.
    If you could convert the system to single phase, that'll simplify things somewhat (or just run the heaters on single phase as inetdog suggests).

    You could then base the system on a reliable 1500rpm diesel generator which feeds a battery bank through an inverter/charger. Since you can rely on the diesel generator you can install a smaller battery bank, say 20kWh = 416Ah at 48V. The problem is going to be that every time those heaters come on they draw 10kW, even when they're just trying to maintain the temperature, so the inverters will have to be able to cope with 10kW peak draw. Since the inverters can cope with the peak, the generator doesn't have to and can be used to charge the batteries.
    The whole system can work without solar, but if you want to save on fuel then you can add as many panels as your budget allows. The usage cycle would be:
    - Turn on gen when you first fire up the kiln
    - Gen pushes 8kW and the inverters make up the deficit of 2kW from the batteries (not all inverters support this "generator boost" feature. Xantrex XW does, SMA sunny island only certain models and Victron multiplus)
    - After kiln reaches operating temperature the generator keeps running and starts charging the batteries until they reach 90% state of charge.
    - Throughout this process the solar augments battery charging with whatever it can

    All of the above can happen automatically based on the inverter's programming, except turning the generator on at the start of the day.

    EU prices for a system like the above would be:
    - 8kW 1500rpm perkins diesel: about 5000 Euros
    - 2 x Sunny Island 5048: 6000
    - 500Ah 48V forklift battery: 3000
    - 2kW solar panels: 2000
    - Charge controller: 600

    Total: 11,600 euros = NZ$ 17,996

    The only differences between the above system and the equivalent 3 phase system is that you'll need 3 inverters and a 3 phase gen. AFAIK, price of a 3 phase gen is the same or slightly cheaper than single phase. Since each inverters only has to handle a third of the power you're probably looking at something like:
    - 3 x Victron Multiplus 3kW = 6500 Euros, so only slightly more expensive than the same single phase system.

    The 2kW of solar is an arbitrary number, the more you put, the less you'll run the gen.
    The 90% state of charge trigger to stop the generator is also a slightly arbitrary number, you'll have to experiment with this to see whether your solar panels can finish the charge. Also, if the business only runs monday-friday, then you have the weekend to run a complete charge purely from the solar panels and you can stop the generator sooner, e.g. 80% state of charge during the week.

    For extra piece of mind, spring for a generator that can run the full peak load so that in case the inverters fail, you can always run directly off the gen.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,590 admin
    #6
    Re: Running glass kiln (10kwh) off-grid?

    One issue that can make or break the economics of a solar power system is how many days a year your system operates at full load (around 66-75% of daily available power)... If the system operates daily for around 9 months of the year or more--You are using most of the sunlight available.

    If you are only using your system 30 days per month--Then you are losing ~8 months worth of available power (batteries can only store around 1-3 days of solar energy cost effectively).

    A genset will only burn fuel when you need it to run. 10 kWH may be in the range of 5-10 liters of fuel per run.

    Although, it may use quite a bit more fuel if the kiln's duty cycle 10kW peak is only 10% of the time--means the genset is running "unloaded" 90% of the time--using fuel while not consuming power for the kiln, and diesels don't really like to run unloaded for extended periods of time). It would not be unusual (my guess) to see a genset use 2-5x more fuel because of the cyclic nature of your kiln.

    The positive side is the genset installation may be a lot cheaper than solar--And it does not consume any fuel when not running (setup a smaller solar system to run your shop/home on non-kiln days).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #7
    Re: Running glass kiln (10kwh) off-grid?
    BB. wrote: »
    The positive side is the genset installation may be a lot cheaper than solar--And it does not consume any fuel when not running (setup a smaller solar system to run your shop/home on non-kiln days).

    On the flipside, given that once the kiln reaches operating temp, the heaters only come on every now and then to maintain temp. With a pure generator instalation it'll be running at close to zero load in between the heaters coming on, which would waste fuel.
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  • tomas
    tomas Registered Users Posts: 3
    #8
    Re: Running glass kiln (10kwh) off-grid?

    Without the kiln I would use the system for powering the house (freezer/fridge/audio/power tools) and I would need a three-phase diesel gen for the occasional welding anyway - so it's not like I'm building something just for the kiln :-). So I guess from the comments its totally doable (and even not so expensive, but getting EURO prices in NZ is quite not realistice, I would say I need to double EURO prices to get the usual NZ price, that's the fee for living on island in middle of nowhere - http://www.sunpowerplus.co.nz/sunpowerplus%20Prices.html) and I just need to scale the gen/inverter for the kiln peaks.

    I thought that three-phase off grid systems would be much more expensive so I'm quite surprised I could actually go with 3*inverters and get 3-phase and use the same system for the welding jobs - would it be possible to somehow make the gen start automatically (let's say if the battery drops under 60% start the gen by some trigger and it will charge then up again and then switches off)?

    Thanks again guys.
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #9
    Re: Running glass kiln (10kwh) off-grid?
    tomas wrote: »
    would it be possible to somehow make the gen start automatically (let's say if the battery drops under 60% start the gen by some trigger and it will charge then up again and then switches off)?

    Yep, most inverter/chargers have auto-gen start. They all differ slightly in when they start it. Some just use low battery voltage, others use state of charge from a built in battery monitor. Some also offer the option of gen start based on load.
    The generator must have a remote start kit too, preferably 2-wire: wires connected = generator start, wires disconnected = generator stop.

    There was a chap on the forum a few months back who was using an Ausi made inverter which looked very good from its specs... forgot the name though! Victron could be an option to check because they cater to the marine market so usually have inverters available in most places.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #10
    Re: Running glass kiln (10kwh) off-grid?

    A diesel running near zero load is really hard ont he engine, and risks "wet stacking"

    T
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #11
    Re: Running glass kiln (10kwh) off-grid?
    icarus wrote: »
    A diesel running near zero load is really hard on the engine, and risks "wet stacking"

    T

    Very interesting. Had never heard of it. I'm sure I'm not alone in that, so here's a link describing Wet Stacking and the harm it can cause.
    http://www.plantengineering.com/industry-news/electrical-news/single-article/a-close-look-at-wet-stacking/e0b399904af236d9f863742ca8f03440.html
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #12
    Re: Running glass kiln (10kwh) off-grid?

    In short, in my understanding (and I am no expert!) a diesel that is running at speed, but with no real load, will use more fuel just to keep it running than it can use. This leads to unburned fuel, and cool exhaust which can plug up the exhaust, as well as damage the valves and the pistons in the engine.

    Unlike a truck engine for example, a diesel genny needs to run at a specific RPM (900/1800/3600 for 60 Hz) to maintain proper phase. A truck can idle down using less fuel, the genny needs to be kept up to speed. All in all a bad idea. In the old days, we ran the 5 kw Lister with a "normal" load of ~1 kw. It didn't like it much, lots of carbon. We then ran a 2 kw heater just to load it up more,, which was a bit of a problem in the genny shed, getting it pretty warm!

    Tony
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  • Ralph Day
    Ralph Day Solar Expert Posts: 1,020 ✭✭✭✭
    #13
    Re: Running glass kiln (10kwh) off-grid?
    icarus wrote: »
    We then ran a 2 kw heater just to load it up more,, which was a bit of a problem in the genny shed, getting it pretty warm!

    And we thought the climate was changing for other reasons!

    Wouldn't the heat be better used in the cabin, or was it too far/unavailable for an opportunistic load?

    Ralph
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #14
    Re: Running glass kiln (10kwh) off-grid?

    At the time, this was a summer use system,, so the last thing we needed was more heat! Should have run a window A/C unit!

    Tony
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