Solar and gas/diesel generator:

Hello.

I had written in this forum before about the Colombia project regarding a R.O. system and possibly using a wind/solar system.

Having just spoken with the national park where the system will be built, we have decided not to use a wind generator due to the size and possible problems with birds.

So now we are left with either using a combination of solar panels and a gas/diesel generator or just a gas/diesel generator.

Anyone have experience in using solar panels and a generator? I would love to hear your opinions. This forum has been very helpful.

Simon
p.s.
We need 24kW of energy per day so 1kW per hour.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 30,219 admin
    Re: Solar and gas/diesel generator:

    Simon,

    You might try and stick with one thread about the RO system in Coluombia... There are links to weather, your site, and other bits and pieces of information that you provided that would help size this system without having to go through multiple threads or asking the same questions over...

    Either go back to the "main" thread of yours--or transfer the basic information (power requirements, both instantaneous, and average, seasonal variations, etc.). Without the exact requirements (costs, both upfront and possible donations, and expected finacial reserves/ongoing costs down the road)--it would be difficult to craft an optimum system--when most of us probably don't have a clue to the delivered price of solar panels, fuel, parts, skilled labor, etc.

    Regarding the use of a generator/solar panels--Calculating the "true" costs (capital, maintenance, fuel, risks, fixed per year, variable per kWhr, etc.) would be the first place to start.

    Generally, with fuel costs, you will want the optimum use of fuel (best efficiency). Basically you have two choices (that I see). First choice would be to size the motor to run the RO 24 hours per day (say RO is a 1kW by 24 hour system, or 24 kW by 1 hour). Size the generator to 50-80% of the load would probably give you the best fuel burn.

    If, you need to run the RO 24 hours per day (1kW x 24 hours), but only want to run the generator a few hours per day, then you could size the generator to run at, say, 4 hours per day. That would suggest:

    Gen Size = (24 kWhrs per day / 4 hours)*1/0.8 batt eff*1/0.85 charge eff + 1kW RO load * 1/0.75 rated load = 9.8kW generator

    Notice that just adding batteries and a charger (if AC charger--a 48 VDC generator may save you some fuel/voltage conversion losses) give you an efficiency hit of Eff=0.8*0.85=68% or 32% loss (these are just SWAGS--use real numbers when you get specs).

    If you decide to use batteries, then 80-90% of the battery charge "energy" is during the "bulk" or "absorb" stage where you can run the generator near maximum efficiency (and power). As you go for the last bit of charge (and occasional equalization charging, etc.), the amount of current required is much less. And solar panels are a good use for this (quiet, efficient, lower power requirements). Run the generator in the morning, and around noon (or a bit before) put, roughly enough panels to run the 1 kW RO unit + the amount of power to finish charge the batteries. Again, using a SWAG:

    Panel Ratings=[{1kW+ (24kWhr/4hour solar charge)*10% daily batt usage final charge*1}/0.66 solar panel derating]=2.4 kW

    Anyway--This is how I would start to address the problem. Throw in the costs of fuel, fuel flow per kWhr generated, costs of generators (AC/DC), efficiencies of AC/DC, availability in Columbia of AC/DC/Diesel/Gas/other fuels, etc.

    For costs, also need to divide the Capital costs by lifetime (20-25 years for solar panels, 2,000-10,000 hours 500-1,500 hours for portable gas, 6,000-10,000 hours for 1,800 rpm gasoline, and upwards of 20,000-30,000 hours for diesel (range/guesstimate for total overhaul/replacement).

    Simon, I would like to see what you find and how you are looking at costs--it would be interesting to see what real numbers you are getting.

    -Bill

    By the way, 24kWhrs/day is a good deal of electricity. Just as a guess, you are looking at producing 1,600 gallons of water a day (24kWhr per day/0.015kWhr/gal) and that is 24kWhr/day * 30 days per month = 720 kWhrs per month. Here in California that is $70-$140 per month power bill.

    Fuel wise, running a 2kW Honda eu2000i generator (pretty efficient small consumer generator) 24 hours per day at 1kWhr will roughly use 1.1 gallons every 4 hours (up to 1,600 watts continuous):

    Gas=(1.1 g / 4 hours) * 24 h/d * 30 d/m = 198 gallons of gasoline per month.

    Here, that would be $3.40/gallon * 198 = $673 per month just for fuel (and a ~$900 generator that would need to be replaced every 2,000 hours or about 4x per year, at least).

    A small diesel might use about 1/2 the gallons per kWhr as the small Honda gasoline example above.

    Any way you cut this--you are talking about good sized capital costs, plus the ongoing operational costs.

    Problem would be to either find a small prime mover rated diesel generator (~2kW) and run it 24 hours per day, or run a larger one with batteries, or get a larger RO unit + 10kW or so prime mover genset and run it 4-8 hours per day (or what ever fraction your consumers/officials would allow).

    Without knowing more about your load's duty cycle and other requirements (and locally available resources)--I am not sure where to head with this.

    How much to run power lines and/or water lines from an appropriate source to the point of use. Does all water need to be "biologically pure" or could you pipe lots of "low-mineral content water" with local treatment (lower pressure RO and/or chemical treatment/filtering/etc.).

    You know the region--and I obviously don't--but I have seen 100 year old pipes run 20+ miles from a mountain spring for use in-town (gold/silver mining at the time).

    I used 1 gallon per day as a one step up from minimal fresh water per person per day. UN was using ~40 gallons per day of fresh water (really 40 liters per day per person) as a point for having a "civilized" amount of fresh water. Using RO to make 40 gallons per day per person sounds expensive. Piping (including water shed/cistern/storage) 40 gallons per day of non-salt water with local treatment for the 1/2-1 gpd per person use seems to a much better long term investment vs reliance on salt water desalination for folks trying to get one step up from a subsistence existence.

    Simon, I am not trying to second guess you--I really am interested in your reasoning based on what is available locally.

    -Bill

    PS: Fix a few small typos... :roll: and now updated/added a few numbers on generator life and fuel consumption...

    And for those interested, here is a 2005 Colombian project that uses locally produced bio-diesel at 1.30 Euro per gallon vs the landed cost of 5.50 Euro per gallon in a more remote village... Bio-Diesel production probably does not apply to the arid region that Simon is working with.

    http://www.scizerinm.org/biodiesel.html
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Solar and gas/diesel generator:

    Hi Bill,

    I started a NEW thread because I am not talking about a wind/sun system anymore. Now I am talking about a solar / generator system therefore I thought it would make sense to start a new thread.

    I will repost any information here so no one has to go back to the old thread regarding the wind/solar system:

    Insolation for ColOmbia (this link spells ColOmbia wrong too! Hehe!):
    http://www.apricus.com/html/insolation_levels_sth_am.htm

    The project description can be found at:
    http://www.aguayuda.org/Eng/Proj/Almendros.cfm

    And the RO filtration system is explained here:
    http://www.aguayuda.org/Eng/Sol/Fil.cfm

    I am still waiting on a quote of the water purification system that we are possibly going to buy therefore I can not give anymore technical details regarding the system besides the power consumption (24kW per day). Soon though, I promise.

    I will also answer all your questions by the weekend. I am hungry and it is time for dinner. : ) I hope you understand. Thanks for your input.

    Simon
  • BB.BB. Super Moderators, Administrators Posts: 30,219 admin
    Re: Solar and gas/diesel generator:

    Simon,

    It is OK either way to post a new thread or continue in the old--The systems change and morph as more information is gathered (and I am not a moderator--so you can safely ignore my two cents worth :| )

    Sorry about the ColOmbia (I knew that... yea sure...)--I guess you are not doing the system for Washington DC (District of Columbia--).

    Don't worry about not posting for a while. No information, can't really post anything.

    Take care,
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Solar and gas/diesel generator:

    Simon,

    With the hybrid wind power generator / PV energy system out and a hybrid fossil fuel generator / PV energy system in, here’s a possible solution to consider.

    Assumptions / Facts:

    5.63 kWh/m2/day average insolation (= 5.63 hours/day “full” Sun)
    24 kWh/day net energy requirement
    Desalinator can be run from 24 VDC

    Approach:

    A “hybrid” solution of battery-stored electro-chemical energy would be used to quietly power the desalinator at night, a generator would be used to power the desalinator in the morning and begin recharging the batteries, and a PV energy system would power the desalinator from late morning though the evening to finish recharging the battery bank and complete the 24 hour cycle.

    Assuming the desalinator will be quietly and reliably powered from the batteries alone for 12 hours per day (i.e., 6 PM to 6 AM), they’ll need to supply 1 kW x 12 hours = 12 kWh of energy. Limiting a 24 V battery bank to max discharge of 50%, the 24 V bank will need to be rated at (12 kWh / 50%) / 24 V = 1,000 Ah minimum.

    Considering the proposed 24/7 operation and the planned availability of both PV and generator energy sources, a battery bank as large as 24 V x 2,000 Ah – enough to power the desalinator without the PV array or the generator for 24 hours and without discharging the batteries below 50% SOC – should be considered. In a pinch, the fully charged battery bank could run the desalinator for 36 hours continuously before reaching a 25% SOC.

    Max’ing out two OutBack Power MX60 MPPT charge controllers, a combined 3,200 W STC PV array (1,600 W STC per controller) could be deployed for a 24 VDC system. Assuming 88% PV array operational efficiency, 97% wiring efficiency, and 97% controller efficiency, the system’s average gross energy production capacity would be 3,200 W (STC) x 88% x 97% x 97% x x 5.63 hrs/day = 14,900 Whr/day.

    Assuming the PV system runs the desalinator directly for 8 hours/day (i.e., 10 AM to 6 PM), 8 kWh of the gross PV energy production will be consumed directly by the desalinator. The remaining 6,900 Wh will be used to recharge the batteries. Assuming 80% battery efficiency, 6,900 W will replace 5.5 kWh of the 12 kWh battery energy used the night before.

    Mid-day power rate from the PV system would be ~2,650 W. With 1,000 W used to power the desalinator, ~1,650 W would be available to charge the batteries in bulk mode. At ~28 V, charge current would be ~59A, or just under 3% of the recommended 2,000 Ah battery bank capacity. With no other loads, that should be OK, but just.

    The generator will be required to supply the remaining 6.5 kWh (net; 8.13 kWh gross) required to recharge the batteries (12 kWh net - 5.5 kWh net from PV = 6.5 kWh net). It will also need to supply the 4 kWh of energy required to power the desalinator from 6 AM to 10 AM, for a total of 12.13 kWh at 24 VDC nominal.

    Assuming DC generator loading of 75% and fours hours of run time, the generator would need to be rated at (12.13 kWh / 75%) / 4 hours = ~4 kW. Using a big DC power supply/battery charger (~90% efficient) and an AC generator, you’ll need a generator rated at ~4.5 kW.

    Assuming 12.13 kWh over 4 hours at 24 V nominal, the current will be significant: ~126 A (up to ~6% of a 2,000 Ah bank; that’s OK). Also, note that some days will be cloudy and need more generator time, and others will be sunnier and therefore require less.

    You’d also need to experiment with a generator-to-PV array transition time (~10 AM). The basic goal would be to get the batteries through a complete absorb stage and into float stage just before the desalinator starts drawing power from the batteries. (~6 PM?)

    Note that the approach above discusses “a way” to meet your energy requirement, and it may need a bit of tinkering. It’s not the only way, and there are many variations to consider. One might be to use a smaller generator and charger, but run the generator for six hours per day instead of just four, with a couple of hours significant overlap with the PV system.

    Another possibility would to consider a 4,800 W (STC) PV array and three controllers. This approach would probably supply ~ 75% or so of the daily energy requirement.

    From a systems perspective, here's an incomplete list of other issues to consider:

    The PV array charging system will actually run as high as ~30 V on a daily basis. Will this be a problem for the desalinator’s “24 V” system?

    Maintenance: A maintenance protocol, especially for the generator and batteries, would need to be established and followed.

    Spares: A spare parts store would need to be created and maintained.

    Technicians: An operations and maintenance staff would need to be trained as well as equipped with tools.

    Security: The generator, batteries, PV modules and controllers may be tempting targets.

    Accessibility: How easy will it be to deliver the equipment?

    Fuel availability and quality for the generator?

    Transport / distribution / pumps: If the desalinator is operated near sea-level, how with the potable water be delivered to the “customers”?  If pumps are used for distribution, what will be their energy source?

    Pump all night? / storage: What will happen to the potable water that’s produced at night? How will it be stored? Pumped up into a community tank at night for gravity feed during the day?

    How will the batteries be recycled once their useful life is exahusted?

    Is this at all cost effective?


    HTH,
    Jim / crewzer
  • System2System2 Posts: 6,290 admin
    Re: Solar and gas/diesel generator:

    Excellent analysis Jim. To make a long story short, we are now looking for a small continuous generator for our system. We are ruling out wind and solar now. However, that does not mean we will not look at solar and wind in the future but for this project it does not make sense anymore. When we first heard about this project last year, we said using a generator would be the easiest solution but we really wanted to make the wind / solar idea work.

    For those that may be interested, I will update you on how our system ends up looking including what generator we decide on. The project starts in September.

    A special thank you to Niel, Jim and Bill.

    Simon
  • mike95490mike95490 Solar Expert Posts: 8,666 ✭✭✭✭✭
    Re: Solar and gas/diesel generator:
    szimmer wrote:
    Excellent analysis Jim. To make a long story short, we are now looking for a small continuous generator for our system. We are ruling out wind and solar now.

    How about bicycles ? Want a drink, spin the wheels. http://www.scienceshareware.com/bike_gen.htm

    Or maybe bicycle powered pump to lift the water high enough to self-pressurize to filter it? (80' tall, 8" pipe) RO does not need voltage, and runs off tap water pressure
    Stick a couple PV panels on top?

    You think motor fuel is pricey now in remote areas, wait a few more years. Get a good, low RPM diesel, and lots of oil filters and oil for it.
    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.BB. Super Moderators, Administrators Posts: 30,219 admin
    Re: Solar and gas/diesel generator:

    Mike,

    I believe that Simon needs to desalinate sea water... From what I have read, a sea water RO plant needs on the order of 850 PSI of pressure... That is a head of some 1,800 feet (just round numbers).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 8,666 ✭✭✭✭✭
    Re: Solar and gas/diesel generator: desalination

    Just 900 PSI ?

    Had any of the solar/thermal/still processes been considered ?
    http://globalcrisis.info/wateravailability.html#desaline
    best/easiest seemed to be the cement block greenhouse style, away from the baseball field.

    Brine disposal back into the ocean seems to be a fine way to be rid of it, unless a cottage industry can be set up to sell Sea Salt. http://www.celticseasalt.com/

    http://www.idrc.ca/en/ev-3178-201-1-DO_TOPIC.html
    http://www.technion.ac.il/rdl/Solar_Energy.html
    http://web.idrc.ca/en/ev-83031-201_830311-1-IDRC_ADM_INFO.html

    I hope you have already seen these sites, and are not trying to re-invent the wheel.
    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • System2System2 Posts: 6,290 admin
    Re: Solar and gas/diesel generator:

    hehe!

    I don't think the bike will work for this case, but I appreciate the creativity. :-)

    850psi is correct.

    I wish the water was from a river which would make the pressure necessary around 200-300psi. Big difference I know.

    Just as a side note, the going rate for one gallon of gas is $2.09 where the project is. Luckily (I think), Colombia has lots of oil and so does neighboring Venzuela. That should keep the gas prices relatively low for awhile.
    Also this location is not that remote, there is a major city just 20 minutes away. As for running water lines and power lines which was mentioned as a post earlier, the latter was attempted but unfortunately a storm destroyed the power lines. As for water lines (piping), that would be a logical step but not with the local government that exists there. Besides, the homes are not connected via pipes anyway. They will get water from a water tank which is connected to our water purification system.

    Have a great weekend.

    Simon
  • System2System2 Posts: 6,290 admin
    Re: Solar and gas/diesel generator:

    Yes, I have seen that. I am pretty sure I have seen everything that exists on the internet about RO systems, etc...

    The most impressive system I have seen is the following:

    http://www.spectrawatermakers.com/

    Search for Solar Cube. I can't create a link there because they are using frames! :oops:

    Interestingly enough, I think their system is a bit exaggerated. With only 6 panels and one small wind generator I don't know how they could produce so much water. There clark pump is impressive but not that amazing.

    We are not trying to reinvent the wheel, we have a filtration expert on our board who has his own filtration company and also a chemical engineer who has about 35 years of experience. Are only weakness was the RE side of it.

    I appreciate the interesting comments though.

    Simon
  • System2System2 Posts: 6,290 admin
    Re: Solar and gas/diesel generator:

    One last post, I promise.

    Stills are useless once you get past 100 people or so. They don't produce enough water in a day. But for less than 100 people, it is a great idea.

    Simon
  • mike95490mike95490 Solar Expert Posts: 8,666 ✭✭✭✭✭
    Re: Solar and gas/diesel generator:
    szimmer wrote:
    Search for Solar Cube. I can't create a link there because they are using frames! :oops:

    link http://www.spectrawatermakers.com/solarcube/index.html

    ve have vays !
    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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