Off-grid project - some technical Qs

Hey guys,

I have searched many forums for answers to my questions and I think this forum will be it :D

I am designing an portable off-grid hybrid generator (Solar & Wind).
It is supposed to be stationed in the desert (high temps, very wide temp range between day and night, lots of dust).

The configuration is as follows:

- 18 Panels of UniSolar PVL-144 (weight nothing, no glass - highly durable and work well in high temps and lower light conditions(covered in dust)).
- 1 Tangarie 2.25Kw VAWT.
- around 1000AH @ 24V battery bank AGM deep cycle (concorde/trojan).

This is the basic system, and this is where my questions are just rising all the time.

Q. which configuration give more yield?
Should I go with AC coupling configuration? Means I will connect the solar panels to SMA sunnyboy and the wind turbine to Windy Boy and have Sunny Island as mini-grid?
Or should I connect the panels on dc side with sunny island chargers (MPPT) and the turbine on the AC side and have the Sunny ISland manage the grid and charging?
The consumer draws 700W per hour 24 hours a day... I think that the second configuration yields more power at lower light conditions where the SunnyBoy would pass the limit to start generating energy - Is this correct?

Q. Connecting the turbine on dc side to yield power at low wind conditions:
Is there any charge controller that I can connect 0-600DC from the turbine so I can connect it to the dc side(meaning it will sync with sunny island)? Will this mess with the Sunny Island chargers if they won't be synced? Having 2 different chargers not sync on the same battery bank.

Q. How do I determine the threshold where the inverter/charge controller starts producing energy?

Meaning I see a charge controller have "optimal MPPT range 25V-60V", "max input voltage 140VDC", "Max input current 40A", "Max Pv power 1250W" - What is the parameters for starting the harvest the energy from the panels?

Q. Which AGM batteries would be best from your experience?
As you may noticed I chose AGM because they don't spill anything while this system is on the move and they have good characteristic for off-grid applications.

Which company is better out of Trojan and Concorde? Better performance, pricing and guarantee.

Comments and improvements are welcomed! :cool:

Comments

  • peterakopeterako Posts: 144Solar Expert ✭✭✭✭✭
    Re: Off-grid project - some technical Qs

    Hi there,

    If you want to make it portable, then leaf out the vawt wind turbine. And spend the money on more panels. Around 800 lbs is not portable plus you will not have the energy that you want.

    Also 700 Watt per hour 24 hours a day is a lot for 24V 1000AH. you are below the 70% from the energy whitin 24H. one day of heavy clouds and your system is down.

    You dit not inform about any backup generator????

    Greetings from Greece
  • System2System2 Posts: 6,290 admin
    Re: Off-grid project - some technical Qs

    Hi,

    Thanks for the quick reply.

    Portable meaning it can be towed(Max 2 Tons). - And the turbine mast is folding into half of the height and then turned horizontally to allow the unit to be highly portable...same for the solar - they fold into a third of the deployed size.

    I have used the turbine exactly for those days when there is no sun (meaning there is high probability of wind - storm, night etc..) - The array from the solar panels is already too big(by physical size) and I can increase it by 3 more modules - no more than that - it is already a big "sail". :blush:

    There is a backup generator, however, the client terms is that the system will have an hourly uptime of 70% per year.

    About the battery bank I might increase it a little to 1200AH...It is planned to by cycled down to 40% before the generator starts and 60% for the generator to turn off and the system to go on batteries again.
  • tallgirltallgirl Posts: 413Solar Expert ✭✭✭✭✭✭
    Re: Off-grid project - some technical Qs

    What Peterako was saying is that your system's loads are just too big. 700 watts, 24 hours a day, is an incredibly large load. Adding three more solar panels, or 200 more amp-hours isn't going to fix that problem.

    You have to reduce the 700 watt load. 18 x 144 watts per panel is 2,592 watts -- assuming the sun is shining directly and perfectly on the panels. 24 hours x 700 watts is 16,800 watt-hours before conversion losses are added in. Assuming 65% efficiency (it will very likely be less for you) for a battery backed system, you'd need 25,850 watt-hours per day from the wind and sun.
  • BB.BB. Posts: 25,034Super Moderators admin
    Re: Off-grid project - some technical Qs
    omerk wrote: »
    - 18 Panels of UniSolar PVL-144 (weight nothing, no glass - highly durable and work well in high temps and lower light conditions(covered in dust)).
    - 1 Tangarie 2.25Kw VAWT.
    - around 1000AH @ 24V battery bank AGM deep cycle (concorde/trojan).
    I understand the low weight of the UniSolar panels--however, they are probably 1/2 the efficiency of standard crystalline panels. Physically, you are going too need 2x the structure to hold the UniSolar panels vs crystalline--Do they really save you anything in the end? Granted, they are less likely to be broken (no glass).

    Regarding dust covered operation--both sets of panels produce power based on the amount of solar radiation hitting the cells... Cover either with 50% dust, both will lose 50% of their power output. I would suggest that you setup up 1 each UniSolar vs Crystalline solar and confirm actual structural support requirements and output characteristics.

    I would check any wind turbine and how well it is sealed against dust. Wind turbines tend to be less than reliable anyway--and dust will be a killer for both types.

    I am not sure I would go with a VAWT at all... Wind turbines need lots of non-turbulent air and, ideally that would work much better if mounted, at the very least, on 60' minimum tower (get into higher altitude prevailing winds). A VAWT mounted near the ground simply will not be in the wind anyay--And VAWT's in general have very poor history of measured power production and reliability.

    Concord (as I recall) is one of the few vendors that claim their batteries operate well when discharged to 20% state of charge--Since you need "light weight"--I would check their batteries out closely.
    Q. which configuration give more yield?
    Should I go with AC coupling configuration? Means I will connect the solar panels to SMA sunnyboy and the wind turbine to Windy Boy and have Sunny Island as mini-grid?
    Or should I connect the panels on dc side with sunny island chargers (MPPT) and the turbine on the AC side and have the Sunny ISland manage the grid and charging?
    The consumer draws 700W per hour 24 hours a day... I think that the second configuration yields more power at lower light conditions where the SunnyBoy would pass the limit to start generating energy - Is this correct?
    You have conversion losses anyway you look at it. If your heart is set the wind turbine -- I would contact Midnite Solar directly. They are in Beta with their new MPPT type solar/wind charge controller ("Classic" model). May offer substantial increase in wind turbine power collection through MPPT function for wind.

    700 watts 24x7--Is this for something like a Cell/Sat station in Afghanistan?
    Q. Connecting the turbine on dc side to yield power at low wind conditions:
    Is there any charge controller that I can connect 0-600DC from the turbine so I can connect it to the dc side(meaning it will sync with sunny island)? Will this mess with the Sunny Island chargers if they won't be synced? Having 2 different chargers not sync on the same battery bank.
    Yes, you can put two (or more) unsynced controllers on one battery bank.
    I don't know of an MPPT charge controller that can take 0-600 VDC wind turbine output... Midnite may take up to 250 VDC...
    Q. How do I determine the threshold where the inverter/charge controller starts producing energy?
    Meaning I see a charge controller have "optimal MPPT range 25V-60V", "max input voltage 140VDC", "Max input current 40A", "Max Pv power 1250W" - What is the parameters for starting the harvest the energy from the panels?

    Solar panels will produced a voltage > Vmp in fairly dim light... However, realistically, it takes direct sun (something that throws a shadow) or bright overcast to produce useful energy.

    The typical MPPT charge controller only has the capability to down convert voltage--So, when you see a range of 25-140 VDC (typically for a battery charge controller)--The minimum Vmp of the panel should be:
    • Vmp>= Vbatt-charging + ~2 volts for controller/wiring drop
    So, for various battery banks (note, I used ~14.5 volts for AGM, other flooded cell may require 15.-15.5 volts for equalization):
    • Vmp >= 14.5 volts + 2 = ~16.5 volts for a "12 volt bank"
    • Vmp >= 29 volts + 2 = ~31 volts for a "24 volt bank"
    • Vmp >= 58 volts + 2 = ~60 volts for a "48 volt bank"
    Q. Which AGM batteries would be best from your experience?
    As you may noticed I chose AGM because they don't spill anything while this system is on the move and they have good characteristic for off-grid applications.

    Which company is better out of Trojan and Concorde? Better performance, pricing and guarantee.

    I would suggest Concord as a good start--they claim the widest rated cycling range (20-80% State of Charge). Also, if I recall correctly, you can really stuff the current down them when needed (say a large genset to recharge back to 80% state of charge).
    Comments and improvements are welcomed! :cool:

    A few observations... Wind Turbines of any type, and VAWT specifically, have very poor history of power generation. An interesting set of data here done in Netherlands of small wind:

    Small windpower a scam ? Survey says SO

    What ever type wind system you choose--Elevation is critical. A small turbine up high is most likely going to perform much better than a large turbine down low. For example--some rules of thumb for wind distribution:
    Ground Drag
    The avoidance of ground drag will increase performance dramatically. Up to a considerable height, the least expensive way to increase your power output from a wind turbine is to increase tower height.

    A generally recognised 'rule of thumb' is that wind speed increases as the 1/7th power of the height above ground. The following curve illustrates this theoretical increase in wind speed with increasing height above ground:
    [see website for chart]
    As an example in the use of this curve, if a windspeed of 15 kph were measured at 2 metres above the surface, the windspeed at 20 metres height can be predicted from the curve.

    At 2 metres height, the 1/7th power is 1.104, and at 20 metres it is 1.534. Dividing 15 kph by 1.104 and then multiplying by 1.534 yields the predicted windspeed of 20.8 kph at 20 metres.
    However, the energy in the wind, and therefore wind generator output, is proportional to the cube of the windspeed. So, in this example, by increasing the tower height from 2 metres to 20 metres increases the wind-turbine output by 2.67 times.
    [see website for chart]

    Next, if it has to be light, easy to tow, etc... If this is a temporary installation--a fuel driving genset is difficult to beat--or at least should be a standard to compare alternative solutions with... For example:
    • Honda eu2000i genset running at 700 watts will give ~5.45 kWhrs per gallon of fuel
    • 2 tons of fuel = 4,000 lbs and 6 lbs per gallons (gasoline) = ~670 gallons
    • 670 gallons * 5.45 kWhrs/gallon = 3,650 kWhrs of power
    • 3,650 kWhrs / 0.700 watt load = 5,200 hours = 217 days
    Granted, a Honda euX000i is not the correct geset for this application--just using for fuel calculations (relatively fuel efficient at this load level).

    If this is a long term installation (multi-year) then solar and batteries can make economic sense. And then a fixed installation with rigid glass solar panels would seem to make sense too.

    But, light and mobile, with low(er) up front costs--an appropriately sized prime mover genset pair is going to be difficult to beat.

    I would suggest sizing the system based on solar+fuel genset... And you can add wind as an experiment (site by site, vendor by vendor performance testing). At this point, there are probably only a few reliable wind turbine vendors out there--and I am not sure that any of them are VAWT manufacturers.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • stephendvstephendv Posts: 1,571Solar Expert
    Re: Off-grid project - some technical Qs
    omerk wrote: »
    Q. which configuration give more yield?
    Should I go with AC coupling configuration? Means I will connect the solar panels to SMA sunnyboy and the wind turbine to Windy Boy and have Sunny Island as mini-grid?

    AC coupling works out slightly more efficient only if you consume more than 60% of the generated power directly, without it going into the battery. As soon as you start putting that power into the battery you hit the double conversion losses that Bill mentioned.
    There's an excel sheet comparing the efficiency of AC vs DC coupling over here:
    http://www.casanogaldelasbrujas.com/blog/2009/05/13/sma-sunny-island-ac-coupling/
    omerk wrote: »
    Or should I connect the panels on dc side with sunny island chargers (MPPT) and the turbine on the AC side and have the Sunny ISland manage the grid and charging?

    DC charging will give the you best charging efficiency, but I wouldn't bother with the SMA charger, it's max 40A and is laughably expensive compared to other MPPT chargers on the market. Morningstar, outback, xantrex all have MPPT chargers will almost double the capacity for half the price.
    omerk wrote: »
    The consumer draws 700W per hour 24 hours a day... I think that the second configuration yields more power at lower light conditions where the SunnyBoy would pass the limit to start generating energy - Is this correct?

    Not sure what you mean here? Check the speadsheet on the link I posted, you can tweak the variables to compare efficiencies, if this is what you're referring to.
    omerk wrote: »
    Q. Connecting the turbine on dc side to yield power at low wind conditions:
    Is there any charge controller that I can connect 0-600DC from the turbine so I can connect it to the dc side(meaning it will sync with sunny island)? Will this mess with the Sunny Island chargers if they won't be synced? Having 2 different chargers not sync on the same battery bank.

    If you connect any DC charging source (non-SMA) or DC load with a sunny island then you need the additional current shunt from SMA, this will let the sunny island know what's going into and out of the battery so that it can keep track of the state of charge.
  • System2System2 Posts: 6,290 admin
    Re: Off-grid project - some technical Qs

    Hi,

    Thanks for all the replies...I'll try to not miss something...
    BB. wrote: »
    I understand the low weight of the UniSolar panels--however, they are probably 1/2 the efficiency of standard crystalline panels. Physically, you are going too need 2x the structure to hold the UniSolar panels vs crystalline--Do they really save you anything in the end? Granted, they are less likely to be broken (no glass).

    High durability is a necessity so I can't have the panels being broken when the truck comes and lifts the structure or from rocks etc... other than that I have seen that Uni-solar being the most efficient out of the amorphous thin film also have triple pass diode which helps it achieve good yields in clouded and if the panel is covered in some section it doesn't render the whole panel useless only the cells which are covered...and at high temp the amorphous technology has the advantage.

    02_02_05img05.jpg
    BB. wrote: »
    I am not sure I would go with a VAWT at all... Wind turbines need lots of non-turbulent air and, ideally that would work much better if mounted, at the very least, on 60' minimum tower (get into higher altitude prevailing winds). A VAWT mounted near the ground simply will not be in the wind anyay--And VAWT's in general have very poor history of measured power production and reliability.

    The Vawt is placed at around 6 meters height... the best you can get from portable structure, at this high vawt is better than hawt since we have done testing in the field and the hawt don't switch direction fast enough and they can't harvest the gust wind because of that. About reliability, this is an important issue yet to be tested, we chose a company(Tangarie) that has installed in various climates (Ocean bouy, Antarctica, Northern Africa)...however good point mentioned here.
    BB. wrote: »
    You have conversion losses anyway you look at it. If your heart is set the wind turbine -- I would contact Midnite Solar directly. They are in Beta with their new MPPT type solar/wind charge controller ("Classic" model). May offer substantial increase in wind turbine power collection through MPPT function for wind.

    Thanks! I will check the additional companies, it is just that SMA has very good representative in my country and the rest have mediocre representative who don't understand much of what they are saying.

    Is SMA that bad? Or just plain expensive?
    BB. wrote: »
    700 watts 24x7--Is this for something like a Cell/Sat station in Afghanistan?

    Bingo...it planned to be for that application, therefore no fuel around...and can't rely on one energy source (sun)...the structure is moved every few months, it sits on a base like this:

    20flatrack.gif

    So pricing is less of an issue, I need the best products to have the best solution for all round any weather - that's why I chose Uni-Solar and that is why there is 2 power sources (wind and sun) - there is a backup generator but it should work more than 20% of the time...

    After checking with Concorde they have mil-std batteries and have higher capacity than Trojan so I think I will go with their AGMs.

    Q. If I leave the SMA Sunny Island as the "manager" of the grid between the battery bank and the device and the generator and have 2 other (un-synced) charge controllers (one from solar, one from wind) all charging the batteries it is ok? It doesn't do anything to the batteries?

    If I understood correctly from stephendv all I need is a current shunt from SMA for each charge controller?
  • BB.BB. Posts: 25,034Super Moderators admin
    Re: Off-grid project - some technical Qs

    Omerk,

    From what little I know--SMA should be a good supplier (expensive, but solid designs).

    Looking at the 50 meter wind maps of Afghanistan (PDF), only in the western edge of the country do you have significant areas of good or better winds.

    I really have a question about your VAWT and 6 meter tall mounting... I looked at the vendor website (www.tangarie.com ?) and did not see any ratings...

    The following are giant guesses about your wind installation using data from multiple sites...

    The swept areas of the Tangarie are not that large, and depending on which model you are thinking of using--say the middle model Gale 5--Even in the Class 4 or better areas from the Afghan wind map (maybe 10-20% of the country)--call it 7 m/s at 50 meters--or around 4.7 m/s at a 7 meter hub hight for the VAWT would generate less than 2.6 kWhrs per month per sqft:
    • 21.52 sqft [for Gale 5] * 2.643 kWhrs per month per sqft (at 4.92 m/s) = 56.9 kWhrs per month
    • 56,900 Whrs per month * 1/30 days per month * 1/24 hours per day = 79 watts average (based on HAWT turbine efficiencies)
    An near ideal Gale 5 wind turbine at 6 meters in the windiest western region of Afghanistan would generate around 10% of your average load of 700 watts...

    To be honest, it hardly seems like it is worth packing a 1,000 lbs of wind turbine and tower for that small amount of power.

    Have you actually characterized the Tangarie?

    Turbulence near ground level kills any turbine's output. I have not seen any studies that show that VAWT are significantly better than HAWT in turbulance--and in fact, on a swept area calculation Savonius drag type turbines (which the Tangarie appears to be) are even much less efficient than the HAWT bladed estimates I used above (at best only 1/2 as efficient based on sq.units)... So a Gale 5 may produce only 5% of your average needed power. Plus wind is usually highly seasonal--where as solar is more spread out through the year.

    On the other hand, Afghanistan is great for solar.

    Regarding Charging the AGM's--You probably cannot charge with too much current into the Concord AGMs (you will damage your cabling first--the Concords have been reported to take up a C*4 rate--full charge in 15 minutes?--you need to verify).

    The bigger issue with all AGM's is they are very sensitive to over charging (if you over charge, they will vent hydrogen / electrolyte and fail soon after). So, your charge controllers should all have remote battery temperature sensors (typically mounted to the positive post of the battery). As lead acid batteries heat up, their charging voltage drops. Will be very important in the wind ranging temperatures of a high desert.

    Another question--your battery bank is 1,000 AH at 24 volts? For a 700 watt 24x7 load that is not very much battery bank. Assuming a maximum discharge of 80%:
    • 1,000 AH * 24 volts * 0.80 max discharge * 1/700 watts = 27.4 hours of storage
    While you can do that--it will probably require much more genset run time. Wind tends to be highly variable and there will be days when the sun is not out... The longer you can run on battery bank, the more chance you will have to "catch up" with solar (or wind) on the following day or so... But, you are limited in weight--so more batteries are probably out of the question (normally, we recommend ~3 days of no sun and 50% maximum discharge for longer life--but battery life/replacement costs are less of a worry for your operation).

    However, if it was a choice between another 1,000 lbs of battery vs a 1,000 lbs of wind generator--I would take the batteries. Each Gale 5 is probably, on average, saving you 5 gallons (~30 lbs) of fuel a month. Get rid of a 1,000 lbs of wind turbine and add 150 gallons of fuel (real rough estimates assuming fuel efficient gas or diesel genset).

    Sorry for the meandering reply... Lots of issues.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • halfcrazyhalfcrazy Posts: 714Solar Expert ✭✭✭
    Re: Off-grid project - some technical Qs

    I assume this is a government contract you are competing for? How far along are you? I assume there are still many competitors at this stage if memory serves correctly you would have a complete design and possibly a prototype by the time it is down to the single digits of company's competing?

    I will say The standard Hawt probably wont hold up there but there are a couple company's producing a turbine that will but They may be direct competitors of yours not sure.

    The Vawt will be an issue they will not hold up and the turbulent wind is worse I would vote for a toughened Hawt any day
  • stephendvstephendv Posts: 1,571Solar Expert
    Re: Off-grid project - some technical Qs
    omerk wrote: »
    If I understood correctly from stephendv all I need is a current shunt from SMA for each charge controller?

    You just need 1 current shunt in total, doesn't matter how many charge controllers you have.
    There's nothing wrong with the SMA charge controllers except the price - they're big solidly built units and they integrate seamlessly with the sunny island. To give you an idea of costs, with a 24V battery and 2.6kW of solar, you'd need 3 of them for 120A max (approximate retail price of 2400 euro for 3). You could get 2 x outbacks FM60 for a little over 1000 euros.
  • westbranchwestbranch Posts: 4,176Solar Expert ✭✭✭✭
    Re: Off-grid project - some technical Qs

    Omerk, since you are dealing with a Mil contract you may want to look at SAFT NIFE batteries, they are primarily a Military, Space, heavy industry maker of 'wet ' NiCd batteries, very tough and resilient and tolerate overcharging well..

    http://www.norwatt.es/pdf/Saft/bb_data.pdf

    see the bottom for contact offices...

    HTH
    Eric
     
    CL 647 asleep  24V 900Ah C&D AGM
    CL29032 FW 2079/ 2073/ 2054 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,Omnicharge 3024,
    Linksys Wet54g WiFi Bridge, ASUS RTN10 router, Hughes1100 Sat Modem
     Eu3000i & 1000i Gens, 1680W & E-Panel/WBjr to come,
    West Chilcotin, BC, Canada



  • BB.BB. Posts: 25,034Super Moderators admin
    Re: Off-grid project - some technical Qs

    Omerk,

    The numbers below are just wild guesses--you will have to plug in your numbers based on actual hardware, measured performance values, configurations, and such. The numbers I gave are "good enough" for back of the envelope calculations though.

    Also, at one point you said 2 tons maximum, and the drawing shows 20 metric tons--Not sure which value you are aiming at.

    Again, look at the wind turbine's true performance vs weight vs fuel "displaced"... They like to say that the turbine starts to generate at 4.25mph for the G-5... 5mph wind (2.24 m/s) only contains 0.246 watts per sq.ft. (for an "good" HAWT).. Or:
    • 21.52 sqft [for Gale 5] * 0.246 kWhrs per month per sqft (at 2.24 m/s) = 5.29 kWhrs per month
    • 5,290 Whrs per month * 1/30 days per month * 1/24 hours per day = 7 watts average (based on HAWT turbine efficiencies)
    That is enough to power a night light (7 watts). And for a HAWT, at best you will get ~0.45 of 7 watts or 3.3 watts average power (at "cut-in" speed)... Pretty much worthless to your application.

    You need a good blowing wind, without turbulence (kills available energy by a whole bunch).

    Using 1,000 lbs for turbine kit estimated weight, and 40 watts for average production (based on swept area, 7 meter height, and 50% derating for HAWT to VAWT effective swept area conversion, and 5.5 kWhrs per gallon for a generic fuel efficient genset, 1,000 lbs for Wind Turbine + Tower Hardware, and 6 lb per gallon for fuel):
    • 1,000 lbs of fuel * 1/5 lbs per gallon * 5.5 kWhrs per gallon = 1,100 kWhrs of "electricity"
    • 1,100 kWhrs from fuel * 1/(40 watts for VAWT * 24 hours * 1kW/1,000 watts) = 1,056 days or 2.9 years of equivalent fuel weight
    lb for lb (or kg per kg) of wind turbine weight vs fuel weight, the break even point would be ~2.9 years assuming my VAWT calculations are anywhere near accurate... The wind turbine would appear to be more of an anchor than a valuable addition to your power capacity.

    I am not sure why you cannot get fuel to the power station when you will be moving it every few months... Assuming a reasonably efficient genset sized for your loads--you should be able to get ~5.5 kWhrs per gallon of fuel (diesel can be much better if you can find a small/efficient diesel genset)...
    • 0.7kWhrs * 24 hours * 30 days * 4 months * 1/5.5 kWHrs per gallon = 366 gallons of fuel (2,200 lbs or 1 metric ton of fuel).
    If you add batteries and an inverter (0.90 efficient battery, 0.80 eff battery charger, 0.85% efficient inverter:
    • 0.9*0.8*0.85= 0.61 "extra losses" for energy storage/time offset
    Or, you will need ~64% more fuel for the "privilege" of using a genset + batteries (Hybrid genset power plant).

    So--a simple calculation to compare running a genset at lower power (700 watts) and efficiency (generators operating at less than 50% load have the approximately the same fuel flow whether running a 50% load or a 1% load). So--if you your "prime mover" genset is a 7kW unit and you are using 0.7 kW of power (no batteries)--your fuel flow per kWhr will be roughly (assume ~5.5 kWhrs per gallon):
    • 1/0.50 fuel flow * 0.10 elec. load * 5.5 kWhrs per gallon * 1.1 kWhrs per gallon
    So, you get an overall efficiency of ~20% if genset is operated at 10% rated electrical load (assuming 50% minimum fuel flow). And would need 1/20% or 4x the amount of fuel to operate a 7kW genset 24x7 with a 700 watt load.

    If you throw a battery bank that can take 50%-100% of 7kW genset output (DC battery charger type?) you would have ~64% end to end fuel efficiency (and diesels should probably be operated at 60-75% minimum load for long/reliable service life)... So, your fuel load for 4 months of "Hybrid use" (genset + batteries) would be:
    • 366 gallons (~2.2 metric tons) * 1/0.64 = 572 gallons (~3.4 metric tons of fuel per 4 month deployment)
    In the end--it would seem that the total deployed weight of a 4 month fuel supply plus fuel efficient 700 Watt genset would be way less than a solar + wind + battery system. And, you need genset plus fuel anyway for backup power--it is just the amount of fuel you are discussing here.

    If you cannot get a fuel efficent ~700-1,400 watt genset that meets your needs--Then the option would be to add batteries and inverter to make a hybrid system that uses a 7kW or larger genset (which are more common in the US anyway--don't know about Israel). You will pay a fuel and weight penalty with the hybrid option--but depending on actual operating points and fuel flow requirements for the diesel genset, you may end up with saving weight and fuel with a hybrid system.

    Also, I would wonder about the 700 watt power requirement of the cell/sat site... I would guess that a fair amount of that is for Air Conditioning. You might work on sizing the system to run solar power for the average electronics package load and size the genset to run the A/C loads (presumably only needed in hot / daytime weather). The batteries/inverters can be smaller and the genset operated at its fuel efficient load point with A/C loads.

    Lastly, if you decide on a diesel hybrid system--then you can add the solar + charge controller as an option for fuel consumption reduction. Hybrid power plant will operate just fine either way--but the addition of solar (and wind if you have it) will just reduce the average fuel burn.

    It is a very interesting project.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Off-grid project - some technical Qs

    Hey all,

    Thanks for the replies I am studying them and I will get in reply very soon.

    Just a quick note on the calculation for the wind energy, it is based on a weibull distribution.
    We takes the average measured wind for each hour of the day(in chosen area) we input this to a program which calculates the weibull distribution for that hour and sums up the energy for the hour(using specific power curve for the turbine) - adding 24 hours and you get daily production.

    Since turbulent wind is exactly what VAWT is made for you could expect to have yields closer to the calculations we made.

    More about weibull - http://en.wikipedia.org/wiki/Weibull_distribution
    Anyways I will get some time in the weekend to write a good post.
  • russruss Posts: 593Solar Expert
    Re: Off-grid project - some technical Qs

    İf İ was Taliban İ would love to see a thing like this setup. Very easy to disturb - only a couple of rounds from the distance and then run! The bad guy is off free and the unit is out of business.

    İ suppose everyone here knows about weibull distribution. İt is generally used as a fancy way to dress up and confuse a discussion about potential output. İ have seen many sites where they use it for just that purpose. Unfortunately a turkey is still a turkey - even if you call it a weibull approved turkey.

    The lawn ornament your looking at for a turbine? Not proven in any way shape anywhere!

    UniSolar - İ haven't read much positive about them but there are a million stories about their problems on the net both technical and economic.
  • BB.BB. Posts: 25,034Super Moderators admin
    Re: Off-grid project - some technical Qs

    From a DEC 2004 Home Power Magazine article (PDF)--Writer's point of view agrees with my observations of VAWT design issues (note: author is an engineer with ARE--a HAWT manufacturer):
    Advantages & Disadvantages

    Some VAWT enthusiasts make strong claims of superiority for these machines. Many feel that ignoring this type of design is some kind of a conspiracy. Let’s examine the specific issues in more detail.

    Yawing. VAWT supporters are quick to point out that a VAWT is always pointing into the wind and does not need to reorient (or yaw) like a HAWT when the wind changes direction. This point is valid, but the value of this advantage
    is often overstated.

    It is true that a VAWT does not need a tail and that yawing in turbulent winds does create wear and tear on HAWTs, especially two-bladed ones. But under most conditions, properly sited wind generators do not see lots of rapid wind direction shifts (thirty-plus degrees). Wind direction usually shifts more slowly, and HAWTs will typically follow the changes smoothly. If a site experiences rapid and frequent changes in wind direction, don’t place any wind generator there! Turbulent winds are very hard on any wind generator—HAWT or VAWT.

    Speed Control. Offsetting the VAWT advantage of not needing to yaw is the fact that controlling the output of a VAWT is difficult. You can’t have it yaw out of the wind to reduce output, like a side-furling HAWT. This can be a serious problem...

    Fatigue. Another equally serious disadvantage for VAWTs is fatigue. If fatigue is a problem for the HAWT, it is the archenemy of the VAWT. There are two reasons for this. One is that during part of its revolution, a VAWT blade has lift on one side of the blade and then no lift, then lift on the other side, then no lift. This cycle is repeated in every revolution that the machine makes. The other source of fatigue occurs because for part of each rotation, the blade is operating in the turbulence downwind created by the upwind blade(s), and usually a tube or tower in the center...

    We have already seen the fatigue issue with wind turbines in general and of the few (one) VAWT tested at the NREL (Note: just the "mechanical issues" are typed below):

    NREL Mariah Power (Windspire) Tests (VAWT)
    NREL Report Itself (PDF)
    5/9/08 Two screws were found missing at the top of the turbine where the ring attaches to the airfoil. The tower base bolts/nuts were retightened/loosened and marked to show alignment.

    ...

    6/23/08 The testing team found two loose bolts at the tower base. The nuts were retightened and remarked, and a small adjustment was made to vertical.

    7/21/08 Routine inspection found a noise emanating from the turbine, a broken washer, loose nuts, and movement in the base tower plate.

    7/28/08 While the leading edge tape was being replaced (due to detachment), a broken weld was found at the top of the turbine and another crack was observed on a different weld. Initially, the welding was done in two spots per airfoil side.

    The airfoils also slid out of the struts that are supposed to clamp them. This may have caused the broken weld. The turbine was visibly wobbling and was tilted down.

    8/7/08 The manufacturer was on-site to replace the airfoils and struts. This is a change that will be required for all production machines. The tower base bolts were replaced with bolts with set screws to keep bolts from loosening. The weld was improved to a continuous weld.

    8/18/08 The magnetic bearing was replaced. The initial magnetic bearings did not have a dust cover and were susceptible to iron dust getting into the magnetic air gap, which can stop operation of the turbine.

    10/14/08 Mariah informed us that: “the welding of the top shaft has not been stress relieved properly and has a heat affected zone that has reduced strength and fatigue life below the design.” Based on the findings from an accelerated life test conducted at the Mariah facility, Mariah requested that the testing team stop and/or lower the turbine in winds above 40 mph until a fix could be implemented, The fix is not expected until January 2009.

    The testing team complied with Mariah’s request. However, they decided to terminate duration testing because the turbine did not meet the operation requirements. The testing team decided to continue power performance and noise testing.

    10/21/08 The testing team confirmed that the turbine does not shut down in high winds.

    10/30/08 The testing team found three loose nuts at the base of the tower. The nuts were tightened per Mariah’s direction.

    11/18/09 Two out of three airfoils slid down through the struts. In the picture, the black markings show where the airfoils used to be.

    12/16/08
    During the noise testing, a clanging sound emanated from the turbine. The
    testing team found two broken welds at the top of the turbine. The turbine was shut down until further notice. This photo shows one of the broken welds that caused the airfoil to separate from its end plate. However, the airfoil did not completely separate as it did in the previous occurrence.

    1/4/09 During the noise testing, a clanging sound emanated from the turbine. The testing team found two broken welds at the top of the turbine. The turbine was shut down until further notice. This photo shows one of the broken welds that caused the airfoil to separate from its end plate. However, the airfoil did not completely separate as it did in the previous occurrence.
    At least these folks believed in their product enough to take it to an independent lab and let the results be published... Few others have done this.

    I am not saying that Mariah was better or worse than any other VAWT--Just the mechanical/fatigue issues from any turbulence (and general issues with VAWT mechanical fundamentals) are real and do require a lot of work to resolve. Since turbulence is much worse near the ground--that only makes the problems worse.

    Remember that turbulence is not only wind changing directions--it also consists of a "rolling" 3 dimensional vortex--a vortex which "contains energy" but is not harvest-able by any VAWT or HAWT.

    My two cents--Always interested in reading information with another point of view.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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