Design of photovoltaic water pumping system

mechatronixmechatronix Registered Users Posts: 5
Hi all. I'm new here. I am doing a project currently titled 'design of a photovoltaic water pumping system'. It can be used for applications like borehole water extraction or water irrigation. I am desperately looking for an appropriate book which deals with the subject. I have come across a book titled 'Le Pompage Photovoltaique' which is in French and I am having all the world's trouble in understanding it. I am looking for one written in English and which focusses on photovoltaic pumping. Can anyone help me please?

Comments

  • BB.BB. Super Moderators, Administrators Posts: 31,068 admin
    Re: Design of photovoltaic water pumping system

    Our host, NAWS, has some information on their website about pumping...

    One of their vendors, Grundfos, has a nice 40 page book on solar pumping:

    SQ Flex Complete Guide (40 pages)

    Here is one Article about choosing an inverter (if battery backup):

    Choosing an inverter for water pumping

    A lot of what goes into "picking" the right solar solution (panels, panels + batteries, panels + batteries + inverter, etc.) really depends on you designing the water pumping system to meet your needs...

    For example, you can power just about any reasonably sized AC Motor based pump + pressure storage tank from solar panels + batteries + inverter -- However, it will probably be one of the most expensive ways of doing it.

    Basically, a panel+battery+inverter system works out to be about 52% efficient at generating your electricity and you have the cost of battery replacement every 4-8 years or so. Plus AC induction motors are not the most efficient either (DC type solutions can be upwards of 20-30% more efficient).

    If you can pump just during daylight hours into a storage tank/pond--you can look at some solutions (such as Grundfos) which can connect directly to your solar array and adjust the pump speed (water volume output) based on the amount of sun that the panels are receiving throughout the day. Solar panels, without batteries and extra inverters, are about 77% efficient (based on name plate rating) and you don't have the battery maintenance/replacement issues either.

    Also, picking pumps that are efficient (no "Jet Pumps", look at DC Motor Pumps--electronic controlled, not brush motors). They may be more expensive, but they are so much more efficient and the supporting costs of your solar RE system will be much less (A simple Array+controller will produce electricity for ~1/10 the $$$/kWhr costs of a panel+controller+battery+inverter system over a twenty year period).

    I would guess you are not in the US (Mauritius?)--So, you will have to adjust your expectations to what is available in your area (unless you can find/convince a local distributor to carry the hardware to make efficient solar pumps)...

    There are other types of pumps available (above ground, in well, "Pump Jacks" (look like oil pumps), even compressed air based). You might be able to find an efficient pumping method available in your area--then find a motor/system that can efficiently retrofit it to solar.

    Here is one thread where solar conversion was discussed.

    Take a read through this Pump 101 type tutorial--it is geared more towards AC irrigation pumps.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mechatronixmechatronix Registered Users Posts: 5
    Re: Design of photovoltaic water pumping system

    Thank you for your help mate. That is really encouraging. By the way,yes, I live in Mauritius.

    Coming back to the topic,there are issues that are pertinent to the design like designing the system for autonomy(i.e providing power for the auxilliaries), hybrid systems and solar tracking which I am looking for. I have searched on Google for books but full view books are not available. Do you know about any links that focus on these topics related to PV pumping?
  • BB.BB. Super Moderators, Administrators Posts: 31,068 admin
    Re: Design of photovoltaic water pumping system

    I am not sure how I can help you--your questions are pretty general.

    Regarding solar trackers--try this thread with some discussions about a couple different solutions.

    In the US, and probably some other places, solar panels are getting pretty cheap and the extra costs and maintenance of solar trackers does not make sense for lots of us.

    However, there are people here that use trackers and are very happy with the results. Extending the operating hours to earlier in the morning/later in the evening can be a big help for some applications (such as longer hours for water pumping).

    I cannot find any solar data for Mauritius -- Just using the PV Watt Program for Harare Zimbabwe, (similar latitude--don't know about weather effects)... You can compare the amount of power collected between a fixed panel and a 2-axis tracking. Seems like you will collect ~20% more power with 2-axis tracking vs fixed array.

    Also, you can use ~77% derating for a system without batteries/inverter and ~52% derating for a system with batteries+inverters.

    Regarding the types of solar pumps... I am certainly no expert. Perhaps you can help by giving a bit more information on the typical type of well/pumping you will be doing (depth, well diameter, amount of water, special issues--sand, salt water, desalination, etc.).

    Depending on your needs and trade-offs--the price of just the Solar RE system (panels vs panels+controllers+batteries+inverters) can result in a range of 1:10 in pricing difference in 20 year costs of system.

    Some pumps will pretty much need to be designed for solar from the ground up (such as in well pumps). Others can be a standard off-the-self pump with just a DC Permanent Magnet Motor bolted on to the pump body (shallow well, surface water pumping, pump jack, etc.).

    If you have a lot of water to pump (10+ HP)--those are expensive and require a lot of solar panels to operate. Issues of high up-front costs (installing solar array), vs low up front costs (diesel motor pump/genset) with long term fuel costs--make the decisions less obvious.

    Do you have a prevailing wind that would lend itself to a classic wind mill pump (or other variations)?

    -Bill

    PS: If you don't have good data for solar irradiance--you can look at buying / building a logging Irradiance meter (I have not purachased anything from this site--but looks like an interesting solution).
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mechatronixmechatronix Registered Users Posts: 5
    Re: Design of photovoltaic water pumping system

    Thank you again for your help. About the last question, yes we have wind power available in Mauritius but only certain locations are apt for the installation of wind generators.

    For the PV pumping, I will have more info about the requirements in the coming days when I will meet a maintenance Engineer working for the Irrigationn Authority. Till now I have been reading the book which I told you was difficult for me to understand since it is in French.That is precisely why I was asking if you know about any book on PV pumping written in English. If I could get a free Engineering Translator software to download so that I can translate the text in English, that would help me to a a large extent. Otherwise, I will communicate to you any further info that I obtain later. I have been only understanding the concept so far.

    I read about solar tracking as a means to capture maximum solar energy and to maximise the efficiency.
    This can also help to make the system autonomous if more electrical energy is being obtained to be then used to power the auxilliaries.

    About battery and hybrid systems, there are certain issues that are not clear to me. Firstly, for a system to operate continuously and to be able to control the amount of water that we want to collect, we need a sytem with battery. This basically consists of the PV module, the charge controller, the battery and the inverter(for Ac pumps). Does this mean that we will have to wait for the battery to be charged to be able to pump water and during all this while the pump is inactive? Because from what I have read, batteries serve, as one of their purposes, to provide autonomy for 3- 5 days when the weather is cloudy for example.

    Secondly, consider this example. Say for example that during a cloudy week,on a particular day the battery is 70% charged. The next day(day 1), the weather is cloudy and the charge level drops to 40% to continue the pumping of water. Again, the next day( day 2), the same weather prevails and the charge drops to 15- 20%. On day 3, still the same cloudy weather. Now what happens? Almost no charge is available as it is not advisable to drain the battery completely or even if we use the 15- 20% charge , what happens the next day? Does the system not work until the minimum amount of solar energy reappears?
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Design of photovoltaic water pumping system
    Does this mean that we will have to wait for the battery to be charged to be able to pump water and during all this while the pump is inactive?

    Nope, you can pump as long as there is power available from the PV, doesn't matter what state the battery is in.
    Does the system not work until the minimum amount of solar energy reappears?
    Yeah, the system won't work until there's energy available - it's got to come from somewhere! What off-gridders in remote homes usually do is have a backup generator for these edge cases, but I think for water pumping you have a better option...

    I think you should start at the beginning here and first define exactly how much water you need and when you need it (and at what pressure?). This should be clearly defined on a monthly basis if the demand changes during the year. So once you have a demand laid out, then you can overlay your local weather conditions to find out how much sunlight you typically have for that demand period.
    Then you'll need to find out about the maximum amount of water you can pump from the water source and how long the water source takes to recover (to back the same level it was at before you started pumping).

    Then look at your weather data and demand data and see how the two correlate with each other. Does the sun shine when you need water? or is the demand highest exactly when you don't have that much sun?

    Next, if you can install a large water reservoir that will meet your water demand for a number of days then you don't need an expensive battery. You can effectively use the water tank as your battery. Pump it full when there's enough sun, and let it be drawn down when there isn't any. Guaranteed to be a lot cheaper than using batteries.
  • BB.BB. Super Moderators, Administrators Posts: 31,068 admin
    Re: Design of photovoltaic water pumping system

    Some other places to start reading:

    www.homepower.com (get a subscription and you can download past issues in PDF)

    Solar Book used by some as Class Text (TnAndy recommended)

    Here is a set of links to various websites regarding solar power from our host:

    NAWS Reference Links

    Kyocera has some nice catalogs/FAQ's to look through.

    Some other basic questions... Do you have utility power available but just want to reduce costs, "go green", control future costs (as fuel rises)? Grid Tied systems are the cheapest/most efficient way to generate electricity. However, you (typically) need approval from the utility (which many will not approve as this reduces their revenue).

    Adding batteries to a system makes it 2-10x more expensive to generate power. Batteries cost a lot of money, batteries need replacement every 4-8 years, and waste quite a bit of power (up to 20% losses charging batteries, another 15% or so losses for DC to AC inverter, etc.).

    Some systems can be configured to allow you to drive the pumps with commercial AC power / backup diesel genset directly.

    And even some pumps (like Grundfos) can run from either AC, battery DC, or Solar Panel DC power just fine.

    Generating power with solar is not cheap--And providing power with batteries 24x7 makes it very expensive.

    As Stephendv says... If you can use storage tanks/reservoirs as your "energy storage" (provide 24x7 water storage/pressure/flow)--it would be much cheaper than trying to do this with Off-Grid Solar.

    In the US, very roughly it costs us for power (simple cost+maintenance divided by power produced, assuming 20 year useful life, no fancy present value/future worth, tax breaks, etc.):

    $0.08-$0.30 per kWhr -- Utility Power (also simple solar panel+DC pump)
    $0.15-$0.35 per kWhr -- Grid Tied Solar (utility power + solar + inverter)
    $0.45-$0.75 per kWhr -- Hybrid Solar (GT + Off Grid backup)
    $1.00-$2.00+ per kWhr -- Off-Grid Battery Bank AC Power

    A lot of the answers depend on the scale of your system... If you are looking to irrigate a small field near a home--that can be done nicely with solar. If you are looking to run the water supply of a modern city with solar -- that is a huge undertaking with huge expenses.

    It may make economic sense--but will require a lot of detailed engineering and political will (even to get a power company to accept utility tied / GT solar) to implement such a system.

    There are many small pumps (less than 1 HP/1kW) that are designed to work with various flavors of solar systems... If you are asking about large pumping systems (>10kW)--you are going to need professional help to figure out what will work for you and optimize the designs.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Solar Expert Posts: 5,501 ✭✭✭✭✭
    Re: Design of photovoltaic water pumping system

    You could just hire a consultant and get specific design advice. Armchair solar water pumping over the Internet is not always the best way in some cases.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • mechatronixmechatronix Registered Users Posts: 5
    Re: Design of photovoltaic water pumping system

    Ok thank you all for your help. I will get further details about the requirements of my project and discuss the issues with you.
  • mechatronixmechatronix Registered Users Posts: 5
    Re: Design of photovoltaic water pumping system

    Hi all! Been quite long since I last posted. I was reading my Book about PV pumping that was given to me by my lecturer and which is written in French( which in fact took most of my time since I am used to the English language) and visited the links which you posted as well. Thank you, they were very helpful. My semester exams as well kept me busy but, I'm free now and can concentrate again on my project.The implementation project fell through due to lack of proper funding and now I'm doing a prototype for my project. So, Ive decided that I'll use a 12V, 80Wp solar panel to power a 12V DC centrifugal suction pump.Then, I'll add a 12V battery, shunt charge controller and a Max power point tracker( which can be a linear Current booster or a boost converter). These are the main components of the prototype apart from the wiring and other auxiliaries.Since I live in Mauritius and I have to finish it by March next year, I'm looking for an appropriate supplier for solar pump systems that can ship all I need rather quickly. All the major suppliers like Grundfos, Lorentz, Shurflo and Global Spec have their retails in countries quite far like India, China etc.....It will take about one month to ship from these places and it's too much delay.I am checking in South Africa and it's hard to find a reliable one. Just in case you have any info about it, let me know please.
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