Wind/solar for large scale pumping etc (out of my depth!)

lazzalazza Solar Expert Posts: 330 ✭✭✭
HI Forum

We have a client that has 100ha of land and wants to power a 70kW pump to extract water from a well to a reservoir, but replacing the grid electricity with a large wind turbine and solar panels.

This presents us with several problems, the first being that I am not well versed with how reactive energy works in pumps, how this relates to a renewable energy system, etc etc. There are many options, all of which include operating the pump at lower power of course.

My question is really if anyone on this forum may be able to explain in detail how active, reactive energy is generated and used, how a variable speed drive might help... in general the complex issue of replacing the grid elecricity with that produced from renewables for this kind of large-scale irrigation application.

If not, then maybe someone could recommend a good electricity forum where they will be able to advise me on the ins and outs of 3-phase pumps, their electricity needs and the options for meeting those needs with renewables, including issues dealing with reactive energy.

Many thanks
Larry

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Wind/solar for large scale pumping etc (out of my depth!)

    The question that must be asked is: why does he want to do this?
    It is extremely doubtful that supplying the power from wind and/or solar will be cheaper than the utility.

    If he's got money to burn he should buy you a new Mercedes. It'll be cheaper.

    When it comes to applying the energy, you can either use the RE to supply the standard 3-phase AC (not very efficient) or tailor the pumping to work with the RE source. The later involves using variable rate pumps that run when the power is available and then sizing the reservoir to stay ahead of demand.

    But there are limits to the size of such pumps, and it may be impractical to use multiple pumps on the same well. Anyone who tries to work out a solution for this is first going to want to know all the particulars on the pumping requirements.

    I've had exactly one similar inquiry. It was way cheaper to continue paying BC Hydro for their 'expensive' 3-phase power at ag rates.

    Not a very hopeful or helpful answer. Sorry. :blush:
  • WindsunWindsun Solar Expert Posts: 1,164 ✭✭
    Re: Wind/solar for large scale pumping etc (out of my depth!)

    Sounds to me iike he would be a lot better off looking at a grid tie solar farm setup than having a dedicated system just for the pumps.
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Wind/solar for large scale pumping etc (out of my depth!)

    I have a VFD for my 3 phase well pump which converts 230V single phase input into 230V 3-phase output and have programmed the pump to spin up from 0hz to 50Hz in the space of about 10 seconds. The nice thing is that there is NO inrush current and the pump isn't jolted into a start but wakes up nice and slow. The industrial style VFD's don't have to convert from single phase, there are 3-phase to 3-phase versions.

    For the kind of system you're talking about, you could look into AC coupling some sunny islands and sunny tripowers in 400V configuration. You can install twice as much kW on the AC side as is delivered by the sunny islands, i.e. 3 x Sunny Island 5048 would give you 15kW of power from batteries, so you can install 30kW worth of PV/Wind on the AC side for a total of 45kW. SMA iberica (http://www.sma-iberica.com/) could help you out putting a system like this together.

    You could also try this spanish company that manufactures their own direct solar pumping controller using standard AC pumps. They might be able to build you a custom high-power version for this project. http://www.solener.com/centrif.html
  • lazzalazza Solar Expert Posts: 330 ✭✭✭
    Re: Wind/solar for large scale pumping etc (out of my depth!)

    .....on the grid-tie option. The pump will use Reactive Energy, yet the Grid-tie system will supply Active Energy only (well lets assume so, ingnoring specialist inverters). Lets assume it is put on the consumer side of the grid before the electricity meter (spain currently has no compensation scheme for net metering). The concept is to use the PV energy directly in the pump as and when its generated, coinciding irrigation times with highest solar irradiation times.

    What happens then?

    1. Does the pump use the Active Energy from the PV system, allbeit inefficiently, and reduce the electricity consumption from the grid..

    2. .. OR will the pump, due to its Reactance, continue to draw a large amount of electricity from the grid as it cant use the Active Energy from the pv system?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Wind/solar for large scale pumping etc (out of my depth!)

    The DC power coming from PV's to run a DC pump is fine. The utility will supply AC power. Basic incompatibility there without extra components.

    So assume an AC pump connected to the grid and to GT inverter (no batteries) power from PV's. There is no sell-back ability for this area, so surplus power not used by the loads is lost. The inverter will attempt to power all loads, as its Voltage potential is higher (tries to push the grid Voltage up, electrical inertia of grid keeps Voltage regulated, resulting difference becomes current). Insufficient power from the inverter is made up for by drawing additional current need from the grid.

    You can offset some of the grid power usage this way, but you probably can't replace it. Not at any practical price anyway.

    This will not allow the pump to run on a basis of "sun = pump running". Only the direct DC drive option will work for that, and that will not make use of the grid power.
  • BB.BB. Super Moderators, Administrators Posts: 29,697 admin
    Re: Wind/solar for large scale pumping etc (out of my depth!)
    lazza wrote: »
    .....on the grid-tie option. The pump will use Reactive Energy, yet the Grid-tie system will supply Active Energy only (well lets assume so, ignoring specialist inverters). Lets assume it is put on the consumer side of the grid before the electricity meter (spain currently has no compensation scheme for net metering). The concept is to use the PV energy directly in the pump as and when its generated, coinciding irrigation times with highest solar irradiation times.

    What happens then?

    AC power is a very complex subject... If you are familiar with Vector Math--It is X axis ("real") and Y/I axis (imagenary) parts of the AC vector (and the actual current is the (X2+Y2)1/2 total.

    So, the Real Current=Total Current * 1/Power Factor (aka as the Cosine of the angle) = "Real" current [note fixed equation]

    The "real current" times the Voltage is the "real power"... This is the actual power taken from a battery bank, fuel from a genset, etc. used to perform "real work".

    The Imagenary part is the current that does not work (like pulling car with a rope off to the side--you have to pull harder to move the car forward vs standing in front of the car and pulling).

    So--When figuring the amount of solar panels + battery bank + etc... You need to figure "real work":
    • Work = Watt*Hours = Volts * Current * PF (or Cosine of angle) * Hours

    However, when sizing wiring, transformers, inverters, and generators, they only "care" about the current flow itself... So we use VA or kVA (Volt Amps). This uses the "entire" current for calculating voltage drops, transformer heating, and inverter/generator output (most off-grid inverters have ratings where Watts=VA (volt amps)). There are some inverters (typically small backup UPS systems) and commercial sized generators where they may use Watts=~0.6 * VA (i.e., assume Power Factor is less than 1.0).

    In the end, you need both numbers. Induction Motors are typically PF~0.67 or so, non-power factor corrected power supplies, battery chargers may have PF~0.6, and some CFL/LED lighting systems have power factor as low as PF~0.5 ...

    This means that your Inverter/generator may need to be rated ~50% to 100% larger than a "pure" wattage calculation would suggest.

    Besides needing to size inverters/generators larger (possibly more losses), "bad power factor" also requires larger wiring and can give more losses due to the higher currents.
    1. Does the pump use the Active Energy from the PV system, albeit inefficiently, and reduce the electricity consumption from the grid..

    For residential grid systems--You (everywhere that I know of) only pay for the "real power" (V*I*Power Factor). So while your wiring/breakers/fuses/transformers/etc. have to be sized for "Total" current--You do not really pay any penalties.

    For commercial grid systems--There is a good chance that you will pay for "total current" (Volts*Amps), either directly as $$/kVA or indirectly (1/PF penalty, peak kVA reservation charges, etc.)... So for larger utility customers, using a switched bank of capacitors to bring PF to ~0.95, and other techniques, can save a 1/3rd of the power bill or more.
    2. .. OR will the pump, due to its Reactance, continue to draw a large amount of electricity from the grid as it cant use the Active Energy from the pv system?

    Yes, induction motors will draw lots of current and you will only pay for PF*VA usage (if residential).

    Your circuits will need to be sized for total current used--but that is the only penalty for you.

    With Grid Tied Inverters, they are (from what I have seen) designed to output PF=1.0 ... The is the "best" for you (cheapest inverter and most $$$/watt payback).

    However, for the utility, not so good... They will still need to provide the imaginary current flow--and they cannot charge you for it (assuming residential billing).

    I would guess that a GT inverter can be configured to provide PF~0.66 pretty easily--At the cost of a larger/more expensive inverter. And without feedback from the utility, that may cause network problems.

    For off grid systems... The inverter has to supply the current/power/VA/etc. as required by the loads.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • lazzalazza Solar Expert Posts: 330 ✭✭✭
    Re: Wind/solar for large scale pumping etc (out of my depth!)

    HI All

    Thanks very much for your replies, i'm beginning to understand the issue better.

    So, in the case of a grid-tie inverter before the electricity meter with a PF of 1: The inverter will provide the Active power for the local loads (as and when local supply and demand are matched), but NOT the reactive energy required, which will continue to come from the existing grid.

    If the consumer is not charged for reactive energy, no worries, if they are charged for reactive energy, it will only save them the Active part of the electricity bill.

    correct?
  • BB.BB. Super Moderators, Administrators Posts: 29,697 admin
    Re: Wind/solar for large scale pumping etc (out of my depth!)

    Exactly.

    But for standard induction motors, it is very easy to reduced the reactive component by installing a capacitor bank to supply the reactive current. You can get a PF to ~0.95 with motor run capacitors.

    Note that this type of electrical work can be fairly technical and for a large installation, you probably will need the help of somebody trained/with experience to do the work. Here is a 4 page PDF that does a good job of explaining the issues/details.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 29,697 admin
    Re: Wind/solar for large scale pumping etc (out of my depth!)

    Please note that I fixed an equation in a post a couple back--I was missing the "1/" part (the apparent current is larger than the in phase portion):

    So, the Real Current=Total Current * 1/Power Factor (aka as the Cosine of the angle) = "Real" current [note fixed equation]

    Also note, in trying to use non-technical terms to describe the current... I mixed up the definitions... "REAL" current/power is the "in-phase" X axis portion of the vector. "APPARENT" current/power is the actual length of the vector (x2+y2)1/2.

    Sorry... :blush:

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • lazzalazza Solar Expert Posts: 330 ✭✭✭
    Re: Wind/solar for large scale pumping etc (out of my depth!)

    On a smaller scale, I have been thinking of this solution for people with swimming pools here. In the summer months the pumps are operating alot and a small grid-tie system (before the meter) with pumping timed to coincide with peak irradiation hours.. could save significant electricity bills, I believe (bearing in mind that residential customers dont have to pay ro reactive energy).. what do you guys think?

    Back onto the v large scale pumping system from the well to the reservoir. I think a direct system is inviable due to the specialized types of pump required (which i dont know if they exist).... therefore I believe we are looking at either a grid-tie system or a system with batteries.. correct me if I'm wrong

    cheers
    Larry

    ps, yes Bill, I will definitely be contracting a specialist electrical/pumping engineer once we have all the data and information necessary
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Wind/solar for large scale pumping etc (out of my depth!)

    Save significantly on electric bills? Technically yes using GT solar even without buy-back would reduce the bill. But will it save money? I don't know; how much do they charge per kW hour there? That's the big issue.
  • BB.BB. Super Moderators, Administrators Posts: 29,697 admin
    Re: Wind/solar for large scale pumping etc (out of my depth!)

    Also look at the pumps themselves... In the US, installers typically install about 2x the pump capacity as really needed. Two speed pumps (high for cleaning, low for long term filtering) can really save energy (VFD--Variable Frequency Drives really can help to allow adjusting pump to actual needs).

    And, look at the pumping installation... Many folks mount pumps above the water line (for very good reasons--pumps in pits are hard to work on and can flood during rain or leaks)--However, pumps that are designed to work with positive inlet pressure are also much more efficient.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • lazzalazza Solar Expert Posts: 330 ✭✭✭
    Re: Wind/solar for large scale pumping etc (out of my depth!)

    Ok, i'll have to look into the types and pumping regimes that people generally use here to work out the maths and economics.

    In reply to Cariboot- we generally work on between 7-10 years payback time for our grid-tie systems (without net metering). Price per kwh is around 18 €c (once taxes are included)... but should really be higher due to the tariff deficit that spain suffers. Furthermore as a good % of costs are actually fixed costs (a nice trick by the electricity companies), it makes the financial viability that bit trickier.. if we really paid for what we consumed, I reckon we could be in the realm of 4-5 years payback.

    Anyway, with electricity prices increasing steadily and solar panels reducing further in price... we hope to offer products with 5 year or less payback within the next couple of years....
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Wind/solar for large scale pumping etc (out of my depth!)

    I'd say it's entirely possible. Here we have no incentives and though BC Hydro does "buy back" it doesn't pay to do it. Our electric is exceedingly cheap at $0.10 kW hour. But they're about to get an increase (possibly $0.13). Like where you are, the fixed costs on the bills are significant, which leads to the conundrum that the more you conserve the more you effectively pay per kW hour!

    Meanwhile panel prices have dropped drastically. It is almost at the point where GT makes sense now even without "buy back", especially if you can do your own install.
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