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Thread: Making biodiesel while maximising PV usage

  1. #1
    Join Date
    Mar 2013
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    Sydney, NSW
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    195

    Making biodiesel while maximising PV usage

    Hi all,

    Question: Is there any cheap and safe ways to adjust the input power to my 2.4kW heating element and 2 kW mixer motor to match the output of my solar PV system, which is usually between 1kW and 1.2 kW between 10am & 2pm most days?

    I have a 1.5 kW solar PV system and no battery storage. Where possible, I try to maximise the use of that PV system to minimise import of electricity from the grid and minimising export of the PV to the grid (as I only get 6c/kWh feed-in tariff). My main driver is similar to that for using biodiesel - to lower my dependence on fossil fuels on a budget.

    This involves setting my washing machine and dishwasher to go off via a timer as close to the middle of the day as possible. As it is only a 1.5 kW system and most of the time either side of midday I am lucky to get 1.2 kW out of it, I stagger the appliances. If it is a cloudy day, I try to wait until the sun is out, within reason.

    I also apply the same principle to making biodiesel.

    The problem is, the electrical demand on my 2 biggest electricity users are nearly double what the PV system can produce at any one point. My oil heater is 10 amp / 2.4 kW and my mixer motor is (if I remember correctly) about 2 kW.

    I have sort-of built a thermostatic controller for my oil heater from bits from eBay (I bought the controller and put it in an IP-rated box with Australian GPO and 3-pin flex plug). As much as I don't like to walk away from it, I feel fairly confident living it unattended for up to 2hrs while I'm doing other things at home.

    I am not an electrical engineer but understand a bit about motors resistive elements and wiring, but was wondering if there is anyone who knows a bit more who could advise on varying the input power for both the heating element and the motor to more closely match the PV output. The solution would have to have a low capital cost and not damage the equipment to be worthwhile.

    Correct me if I'm wrong on any of this, but my understanding is that the resistive load of the heating element is relatively easy to control. Similar to a halogen light dimmer, but it would need to handle a lot bigger load. Since Power = Voltage x Current (amps). Is it just a case of using something like a variac or autotransformer that steps the voltage down? How low can you go?

    With the motor, I understand 3-phase motors are easy and safe to control with variable speed drives (VSD) that lower the input frequency to as low as 15 Hz to slow the motor. Going too far will move the impeller speed out of the efficient pump curve and not move any fluid. There are similar motor controllers available for single-phase motors (especially pool pumps), but I'm not sure on how they work, but maybe that lowering of voltage is involved like with a step-down transformer? I have heard there is risk of lowering voltage too far burning the motor out and also slowing it so far as the direct-driven cooling fan on the back cannot provide enough air flow to cool it.
    3DB
    1995 Holden (Isuzu) Rodeo 2.8TD 4X4 - B100 since April 2013
    1976 Mercedes 300D Turbo 'The Coal Grenade' - B100 since May 2016
    (@thirddegreeburns on Instagram)

  2. #2
    Join Date
    Dec 2006
    Location
    Townsville, North Queensland
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    616

    Re: Making biodiesel while maximising PV usage

    If your worried about how much power you will use cooking up a batch of biodiesel, why not buy a diesel generator and run it on biodiesel?

    Then you will also have a backup for when there are blackouts.

  3. #3
    Join Date
    Jan 2008
    Location
    Sydney
    Posts
    828

    Re: Making biodiesel while maximising PV usage

    The element one is easy and done more simply than messing with resistors (which are just going to use the same amount of power and dissipate it as heat). Get some lower powered elements - the best ones are the cheap oil column heaters - you will find they have two elements in there - a low and a high - the one i have is 600w on low and 1500w on high (2nd element is 900w) - wire them so you can have them come on in any combo (and get a 2nd one if you want ultimate flexibility) - i saw heaters at bunninbs the other day for $39 each in this config (obviously did not see their elements but it is a logical guess). The only problem is the mounting of these as they typically screw in but with quite a fine pitch thread - in my case i use them in my bio drying drum, so i just cut a tight hole and threaded them into the plastic (two layers) by hand and then surrounded them with Sikaflex - it has lasted two years so far.

    As for the motor - i personally would swap it out for a DC motor and a Gear pump - easy to find 500w or larger DC motors , run it directly from your solar (or if they are the grid tied type) then run it from a 240v to 12/24/36v transformer (will lose some efficiency this way)

    Having said all that - do you not have a smart meter with time of day billing ? Our power at night between 10PM and 7AM only costs 14c/kwh - i would just keep it simple and do it at night and use you solar during the day for other time shifted load - dishwasher, washing machine, etc

    Craig
    Holden Suburban K2500 1998 6.5L Turbo GM engine
    210,000KMs (90,000 on new crate motor)

    Currently 2 tanks in and working - 90 litre BIO tank and main tank of 160L WVO

    30 plate FPHE in Engine bay and Helton Dual coil in rear
    Walbro FRB-5 pusher pumps x 2

    50,000KM on Veg and 10,000Km on B100

  4. #4
    Join Date
    Sep 2005
    Location
    WA
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    Re: Making biodiesel while maximising PV usage

    3DB,
    You could operate the heating element on DC direct from the solar panels. The downside of this is that you will need to have an electrician make the connections (you can run the cable though). It depends on the DC voltage of your panels, My 6 panel system runs at 180 VDC. This will reduce the power output of your element from 2.5KW to about 1.5KW. As this is more than the array can deliver, the heat output will be even lower. Possibly as low as 1KW.
    Your only mains power contribution would be for the pump.
    How does that sound?
    I am only heating the oil up to 40C and pumping longer (pump is hugely cheaper to run than heating element) and running the pump for 3 hours instead of 1 hour. My pump is a 450W unit which has a thermal cutout.
    Life is a journey, with problems to solve, lessons to learn, but most of all, experiences to enjoy.

    Current Vehicles in stable:
    '85 Mercedes Benz W123 300CD Turbodiesel single tank using 95% used cooking oil and 5% to 10% misfuel (where someone had filled diesel vehicle with petrol).
    '06 Musso Sports Crew Cab. Running on used cooking oil with 5% to 10% misfuel.
    Toyota Camry Hybrid - (Wife's Car)

    Previous Vehicles:
    '90 Mazda Capella. (2000 - 2003) My first Fatmobile. Converted to fun on veggie oil with a 2 tank setup. Died when supercharger stuck at max boost for weeks. Stretched head bolts.
    '80 Mercedes 300D. 2 tank conversion [Sold]
    '84 Mercedes 300D. 1 tank, no conversion. Replaced engine with rebuilt OM617A turbodiesel engine. Finally had good power. Donor for current Fatmobile coupe. (body parted out and carcass sold for scrap.)
    '99 Mercedes W202 C250 Turbodiesel (my darling Wife's car)[sold]
    '98 Mercedes W202 C250 Turbodiesel (my car)[sold]
    Parts Car C220 1993 All body panels, headlights, interior engine and ECU available.


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  5. #5
    Join Date
    Mar 2013
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    Sydney, NSW
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    Re: Making biodiesel while maximising PV usage

    Thanks everyone.

    Running the element on DC is a compelling argument. The distance between my existing DC circuit breaker (upstream of the inverter) on the main switchboard to my reactor tank is only about 5m, so limited cabling required. All I would need is another DC breaker and some spare twin & earth and I could DIY it I reckon. To operate I would just need to isolate the main DC breaker, then isolate the AC on the inverter side, then open the new DC breaker and then the old DC and it should be running. I could probably still use my thermostatic controller. Might just check that the 10amp AC-rated gear can handle whatever my max DC voltage would be though. I'm told the arcing from DC is much heavier at the same voltage.

    Craig - the oil heater thing is interesting too. I will pick up the next one I see by the side of the road and open it up.

    Qwarla - I would love a 4 kVA diesel genset. My neighbours who are less than 2m from my boundary on either side, less so. Also the reliability of the grid power here is amazing. We've had one blackout that I know of in the 6 years we've been here. But a generator would be handy when the revolution / apocalypse comes.
    3DB
    1995 Holden (Isuzu) Rodeo 2.8TD 4X4 - B100 since April 2013
    1976 Mercedes 300D Turbo 'The Coal Grenade' - B100 since May 2016
    (@thirddegreeburns on Instagram)

  6. #6
    Join Date
    Sep 2005
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    WA
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    Re: Making biodiesel while maximising PV usage

    If you plan to use a contactor (relay) to switch the DC, then use multiple contacts in series as this significantly reduces arcing at the contacts. eg use a 4 pole changeover contactor with 2 poles each for + and -.
    The contacts which close when operated should be for the heater element and the rest contacts for the inverter.
    Installed after the solar panel Circuit Breaker.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	Solar system direct DC heating.png 
Views:	19 
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ID:	2243  
    Life is a journey, with problems to solve, lessons to learn, but most of all, experiences to enjoy.

    Current Vehicles in stable:
    '85 Mercedes Benz W123 300CD Turbodiesel single tank using 95% used cooking oil and 5% to 10% misfuel (where someone had filled diesel vehicle with petrol).
    '06 Musso Sports Crew Cab. Running on used cooking oil with 5% to 10% misfuel.
    Toyota Camry Hybrid - (Wife's Car)

    Previous Vehicles:
    '90 Mazda Capella. (2000 - 2003) My first Fatmobile. Converted to fun on veggie oil with a 2 tank setup. Died when supercharger stuck at max boost for weeks. Stretched head bolts.
    '80 Mercedes 300D. 2 tank conversion [Sold]
    '84 Mercedes 300D. 1 tank, no conversion. Replaced engine with rebuilt OM617A turbodiesel engine. Finally had good power. Donor for current Fatmobile coupe. (body parted out and carcass sold for scrap.)
    '99 Mercedes W202 C250 Turbodiesel (my darling Wife's car)[sold]
    '98 Mercedes W202 C250 Turbodiesel (my car)[sold]
    Parts Car C220 1993 All body panels, headlights, interior engine and ECU available.


    Searching the Biofuels Forum using Google
    Adding images and/or documents to your posts


  7. #7
    Join Date
    Mar 2013
    Location
    Sydney, NSW
    Posts
    195

    Re: Making biodiesel while maximising PV usage

    Thanks, Tony - that's great.

    I am kicking myself a bit now as I had 2, brand-new, spare 4-pole DC breakers that I sold on eBay for basically nothing 6 months ago. Should have kept at least 1! My place is so cluttered with stuff that 'might come in handy one day' that I have had to become a bit more ruthless. Sure enough, as soon as you get rid of something, you need it shortly after.
    3DB
    1995 Holden (Isuzu) Rodeo 2.8TD 4X4 - B100 since April 2013
    1976 Mercedes 300D Turbo 'The Coal Grenade' - B100 since May 2016
    (@thirddegreeburns on Instagram)

  8. #8
    Join Date
    Sep 2005
    Location
    WA
    Posts
    4,095

    Re: Making biodiesel while maximising PV usage

    3DB
    With my diagram you don't need another DC breaker, although it would provide greater isolation from the Solar panels.
    Life is a journey, with problems to solve, lessons to learn, but most of all, experiences to enjoy.

    Current Vehicles in stable:
    '85 Mercedes Benz W123 300CD Turbodiesel single tank using 95% used cooking oil and 5% to 10% misfuel (where someone had filled diesel vehicle with petrol).
    '06 Musso Sports Crew Cab. Running on used cooking oil with 5% to 10% misfuel.
    Toyota Camry Hybrid - (Wife's Car)

    Previous Vehicles:
    '90 Mazda Capella. (2000 - 2003) My first Fatmobile. Converted to fun on veggie oil with a 2 tank setup. Died when supercharger stuck at max boost for weeks. Stretched head bolts.
    '80 Mercedes 300D. 2 tank conversion [Sold]
    '84 Mercedes 300D. 1 tank, no conversion. Replaced engine with rebuilt OM617A turbodiesel engine. Finally had good power. Donor for current Fatmobile coupe. (body parted out and carcass sold for scrap.)
    '99 Mercedes W202 C250 Turbodiesel (my darling Wife's car)[sold]
    '98 Mercedes W202 C250 Turbodiesel (my car)[sold]
    Parts Car C220 1993 All body panels, headlights, interior engine and ECU available.


    Searching the Biofuels Forum using Google
    Adding images and/or documents to your posts


  9. #9
    Join Date
    Feb 2006
    Location
    Sydney, Dili
    Posts
    53

    Re: Making biodiesel while maximising PV usage

    Won't tapping into the very high voltage ( 3-400 v ) coming from the solar cause the inverter to shut down if the voltage it sees becomes below it's operating range ? I forget how Mr. Ohm would put it - voltage drop ?
    What would a higher voltage do to the immersion heater ?

    I suggest using a solar diverter that sends any solar generation not used by the house to your heater rather than feeding the excess to the grid . It may not be much sometimes , but start the heating well in advance of doing a batch ( days before this time of year if clouds ). No need to change to a lower wattage element.
    I use a Solarmiser to heat my domestic hot water (1.5kw solar system ). It's like having a battery , it stores energy You consume the power you make but are not using instead of selling it for 10c/kWh - and paying triple for ( coal) power from grid.
    The small gadget is simple to install and cost only $250 . And you could switch it to heat water when not needed for bio-making.
    Heating at off-peak tariff with a timer would save cost as a quick-fix .

    The Solarmiser ( or other devices like it ) will not run an inductive load like the mix motor , however. But your 2kW mixer run at shoulder tariff would cost around 50cents for a batch .
    Last edited by timorcoco; 7th June 2017 at 12:38 AM.

  10. #10
    Join Date
    Sep 2005
    Location
    WA
    Posts
    4,095

    Re: Making biodiesel while maximising PV usage

    Solar diverter is a good option. Again, the DC working voltage of the array will be a factor. My example was for a 6 panel system with a Vmp of 30V per panel, making 180VDC.
    Solar arrays of up to 250VDC should work fine with a heating element with a power rating at or below the solar array rating.
    In fact the element will work at higher voltages but its life will be shorter due to the higher power caused by the higher array voltage (the element gets even hotter than at 250VDC).
    The trick will be to match the array to the element rating.
    My preference would be to have the array voltage (or power) less than the element rating. eg a 2KW 250VDC array output voltage will drop when trying to supply a 2.5KW element, sue to the lower resistance of the element than a 2KW element.
    Every installation configuration would need to be assessed individually against the element rating.
    Life is a journey, with problems to solve, lessons to learn, but most of all, experiences to enjoy.

    Current Vehicles in stable:
    '85 Mercedes Benz W123 300CD Turbodiesel single tank using 95% used cooking oil and 5% to 10% misfuel (where someone had filled diesel vehicle with petrol).
    '06 Musso Sports Crew Cab. Running on used cooking oil with 5% to 10% misfuel.
    Toyota Camry Hybrid - (Wife's Car)

    Previous Vehicles:
    '90 Mazda Capella. (2000 - 2003) My first Fatmobile. Converted to fun on veggie oil with a 2 tank setup. Died when supercharger stuck at max boost for weeks. Stretched head bolts.
    '80 Mercedes 300D. 2 tank conversion [Sold]
    '84 Mercedes 300D. 1 tank, no conversion. Replaced engine with rebuilt OM617A turbodiesel engine. Finally had good power. Donor for current Fatmobile coupe. (body parted out and carcass sold for scrap.)
    '99 Mercedes W202 C250 Turbodiesel (my darling Wife's car)[sold]
    '98 Mercedes W202 C250 Turbodiesel (my car)[sold]
    Parts Car C220 1993 All body panels, headlights, interior engine and ECU available.


    Searching the Biofuels Forum using Google
    Adding images and/or documents to your posts


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