What to do with extra power

OffGridRoryOffGridRory Solar Expert Posts: 26
Hello again everyone,

I've been using my system with (2) Evergreen ES 205 panels, Tristar MPPT-45 Charge Controller, Samlex 1500w pure sinewave inverter, and (4) 110Ah AGM batteries... I LOVE IT!

The "problem" I'm having is this... I only use about 50Ah of my power on a given night... It ususally works out to about 12% of my battery bank, which is perfectly fine with me since this should significantly extend the life of my batteries, but during the day this means that by about 10:30 AM my batteries are topped off and the charge controller has gone into float mode... Essentially during the 4 hours of the day that I'm getting up to 412W of power I have nothing to do with it... I HATE waste as I know many of you do since we're all like-minded in this community...

I'm hoping for some advice/ideas on what I can do with this extra power during the day... I've already hooked up a 12v fan that I plan on using on sunny hot days in the summer, but the maximum of 4 Amps it uses on HI is only scratching the surface of the 25+Amps of extra power...

Advice/ideas please :)

Rory

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: What to do with extra power

    That's the other off-grid dilemma: what do you do when the batteries are full and the sun is still shining?

    Two broad categories: load shifting and diversion loads.

    So you can run the dishwasher, microwave, vacuum cleaner, power tools, water pump ... or big screen TV. :D

    Or you can elect to send surplus power to a tank-type water heater, or a secondary "spare" battery bank for those days when the sun refuses to shine. With some systems this can be set-up automatically (Outback's AUX control). Otherwise ... pick whatever you need to run and turn it on.

    This is why I don't advise people to plan for a three day battery bank.
  • Ralph DayRalph Day Solar Expert Posts: 871 ✭✭✭
    Re: What to do with extra power

    Rory,
    Winter...oil radiator electric heater. Summer...dehumidifier. Any season...water distiller for batteries.

    Ralph
  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    Re: What to do with extra power

    I setup a diversion load ( water heater coils ) and controller for my solar setup. I put an average of 40-50% of the daily gross wattage into the diversion loads.
  • OffGridRoryOffGridRory Solar Expert Posts: 26
    Re: What to do with extra power

    Thank you for your suggestions so far, I definately like the dehumidifier suggestion for summer! Here in Maine it gets quite humid near the coast... I've read lots about diversion loads... People rigging up their excess power from windmills and solar panels to go to a DC heating coil in a water tank or for a space heater type element, but when I read about it there is always an assumed knowledge base... Unfortunately I lack in that assumed area... How does one set up a diversion load from the components I already have? Do I need to buy some other controller that senses when the batteries are topped off and then sends the power to the desired diversion load? Also, I only have about 410W of panel (Usually in the neighborhood of 28A peak), so is that enough for a conventional diversion load element?
  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    Re: What to do with extra power

    Yes, more than likely you will need another controller.

    I am using a Xantrex C60 controller + two 12VDC 300 watt heater elements in a old 40 Gallon water heater.
  • VicVic Solar Expert Posts: 2,810 ✭✭✭✭
    Re: What to do with extra power

    Currently, I manually skim excess power when in Asorb and Float, by Microwaving something, or running a 120 Vac heater, or a window A/C or two. Unfortunately, this is a manual system.

    The better current crop of MPPT CCs have one, or in the case of the Midnite Classic, two Aux Output (s), which, generally can be programmed to give a signal output for a relay when the charge mode is Float. If memory serves, the Xantrex XW SCC is the exception. It has no such Aux mode, and I was told by the Xantrex Product Manager for this product, that the XW SCC would never have such a (useless) function ... this might have changed.

    For me, an Aux output during some protion of Asorb, and in Float would still need a prioritizing processor which would assign the highest priority load to take the XS power. This will be a project for later ... much later. Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • XRingerXRinger Solar Expert Posts: 508 ✭✭✭
    Re: What to do with extra power

    I have a similar with my back-up power supply. After it goes into Float in the morning,
    all the juice from the 500w tracking array is pretty much wasted.

    When the weather forecast says there is little chance of basement flooding and/or grid failure,
    I use the backup to power the loads that are on the three backed-up circuits.
    Right now, it's mostly my PC.. Not really a suitable load for skimming off the top of the 500w of PV out back..

    So, I'm thinking of using the wasted power to help heat and cool my home when it's sunny.
    My Sanyo mini-split is has been using about 480watts (220vac) most of today.
    And it might be nice to take it off-grid for 4 or 5 hours on sunny days.. :cool:
  • OffGridRoryOffGridRory Solar Expert Posts: 26
    Re: What to do with extra power

    I've also been "skimming" my excess power by running a fan, watching TV, and plugging in every rechargable device I have that may be below 90% charged in an attempt to take up the extra power when I'm in absorb and float, but I think I'm going to purchase a dehumidifier for the summer months to take the stickyness out of the air, and as suggested get a 400w oil radiator for the winter months since this appears to be about the only "effecient" heating option that will not go over my maximum output from the panels... I look forward to looking into running a diversion load in the future... I guess I'll need a new controller for that one though since my Tristar MPPT 45 does not have that option... I like the idea of having one or two backup batteries as well...

    I will almost certainly have the need to charge some more AGM batteries for my electric trolling motor for my canoe during the summer months when fishing season is here... Is it possible to just use an AC charger that a typical On-Grid house would use to charge these batteries or is there a better way that is not expensive? I'm sure they're not very efficient since my 12v would get converted into 120 via the inverter then back into 12v for the battery though... The idea would be that I could use these batteries in the summer for my playing around, and in the winter could sit aside my permanant battery bank and could be hooked up to a cheap modified sinewave inverter as emergency power in the winter during several dark days... Anyone have any suggestions for doing something like this?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: What to do with extra power

    For charging AGM's regular automotive chargers aren't a good choice. They tend to be made as cheaply as possible: just enough to push a FLA back up to where it will start the car. No multi-stage and no variable set points.

    So you could buy an expensive 3 or 4 stage charger like an Iota. Or you could concoct some sort of secondary charge controller circuit to switch panel output to. Gets a bit messy that way. And with no automatic function on the 'main' controller you'll still be flipping switches. Bluesky for one has a controller capable of charging two separate batteries, but I don't think the parameters can be mixed.

    Certainly someone around here knows! :D
  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    Re: What to do with extra power

    Just to show how much the diversion/dump load is getting.


    160.2 AHs @ 13.5 VDC = 2162.7 watts
  • bmetbmet Solar Expert Posts: 630 ✭✭
    Re: What to do with extra power

    What about this echo-charger?

    The manual describes it as a voltage-follower, and even though it is meant to work with Xantrex products, the manual also states that is can be use with ANY DC charging source. Wouldn't that include a charge controller? I recently put in a small power pack into my workshop, how nice it would be to get a second battery for extended circumstances.
    For charging AGM's regular automotive chargers aren't a good choice. They tend to be made as cheaply as possible: just enough to push a FLA back up to where it will start the car. No multi-stage and no variable set points.

    So you could buy an expensive 3 or 4 stage charger like an Iota. Or you could concoct some sort of secondary charge controller circuit to switch panel output to. Gets a bit messy that way. And with no automatic function on the 'main' controller you'll still be flipping switches. Bluesky for one has a controller capable of charging two separate batteries, but I don't think the parameters can be mixed.

    Certainly someone around here knows! :D
  • azrcazrc Solar Expert Posts: 43
    Re: What to do with extra power

    Stupid question...I understand the point of the diversion load on wind to prevent over speed on a turbine, but what's the point of a diversion with solar? Why not just OC the panels?

    Thanks
  • BB.BB. Super Moderators Posts: 26,666 admin
    Re: What to do with extra power

    A solar pv Diversion Load is really an opportunity load.

    Instead of wasting solar pv array energy after the batteries are full, turn on a water pump, electric heater, etc. to use the "free electricity".

    Solar panels do not need a dump or diversion load for safety reasons (a wind turbine can overspeed and self district with no electrical load--typically a battery bank and electric heater to dump excess electrical energy).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • techntrektechntrek Solar Expert Posts: 1,366 ✭✭✭
    Re: What to do with extra power
    ...and as suggested get a 400w oil radiator for the winter months since this appears to be about the only "effecient" heating option that will not go over my maximum output from the panels...

    Actually the most efficient would be a mini-split set on "low" so it stays below 300 watts.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • XRingerXRinger Solar Expert Posts: 508 ✭✭✭
    Re: What to do with extra power
    techntrek wrote: »
    Actually the most efficient would be a mini-split set on "low" so it stays below 300 watts.

    I've heard the smaller units work down that low. My 24,000 BTU Sanyo
    is using 480w right now (it's 37F outdoors now).
    As it gets cooler out, it stays on all the time. During the day it's off and on,
    as the house gets above the (21C) setpoint.
  • techntrektechntrek Solar Expert Posts: 1,366 ✭✭✭
    Re: What to do with extra power

    Yes, I'm talking about the 9000 BTU units. http://forum.solar-electric.com/showthread.php?t=5104
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • MisterBMisterB Solar Expert Posts: 156 ✭✭✭✭✭
    Re: What to do with extra power

    Here is what I have: I replaced my old statpower modified sine wave inverter with a new Samlex pure sine inverter and I did a bit of creative recycling with the old inverter and an equally old Trace C30--the original one, the "Quad Function Voltage Controller". The voltage controller powers on the inverter when a preset voltage is reached and turns it off at another preset voltage. At the moment I have a small AC fridge with almost no surge connected to the inverter. Through the inverter it draws about 6.5 amps off the battery which is only 26% of what the panels can put out without even taking the wind turbine into account so I have it turn on at a fairly low voltage--13.2 and turn off at at 12.8 volts. On a sunny day, the fridge is on by 9am or earlier if the wind has been blowing at night. On exceptionally windy nights, it will turn on at night. Using the inverter gives me a lot of flexibility to add loads as power goes up in the summer. With more loads, I will raise the turn on voltage. With this controller the max is 30 amps or 360 watts which is all I have to divert but I could easily have it control an external relay if I put more panels up and had more watts to divert. The only issue I have is that this is a really old inverter and it has a very noisy modified sine wave that generates RF and audio frequency noise.
  • TenMileTenMile Solar Expert Posts: 62 ✭✭
    Re: What to do with extra power

    How about a solar powered / wood heated hybrid hot tub?

    Take one of these: http://www.alumitubs.com/productinfo.htm

    Add one of these diversion heating elements: http://www.survivalunlimited.com/diversionloads.htm

    Figure out a way to have a hot tub without electrocuting yourself and you've got a great system!
  • raydiasraydias Solar Expert Posts: 68 ✭✭✭✭
    Re: What to do with extra power

    Ken - what temps do you get in your 40 gal diversion water heater with the 2x300 watt heater elements and do you have any diagrams or pics to share. This is what i am looking at doing for my parents as well.
  • mr.radonmr.radon Solar Expert Posts: 158 ✭✭✭✭✭
    Re: What to do with extra power

    I recall a set up where a homeowner used excess energy to pump water into an elevated cistern.
    Use the extra energy to pump the water UP into the cistern, then when you need the water, allow the water to backflow through a small water generator. Store it as potential energy.
  • OffGridRoryOffGridRory Solar Expert Posts: 26
    Re: What to do with extra power

    Yes, I like the idea of using the extra power to turn on a water pump which will feed a rather large cistern... I've often thought about using the energy stored as a large battery bank via a water turbine of some sort and simply having the water run out of it when the house uses it and when you want to accellerate the energy output on extended darkness days just run the water a little more (assuming there is pleanty of stored water) Of course, like most things, I'm sure its not done for a reason (or several)

    I've recently done a lot of research on this site into the water pumping and it appears that like many other things, I need to look into this further as having a large storage tank appears to be the best way to go. I figure I can help solve two problems with a large enough cistern... Have something productive to do with extra power (pump hundreds of gallons of water into the cistern) and have lots of water in storage (hopefully elevated) for future consumption.

    I've ordered a 400W oil filled radiator for now, I figure during these spring days when its not necessary to burn wood to heat my house, but will get a little chilly without some form of heat, I will turn this thing on for about 4 hours a day. This will take care of my excess power for the spring, fall, and winter. Once I've finished my active solar air heating project this will hopefully be all I need to keep my house warm for many days of the year... During the summer I plan on finding some form of dehumidifier that has a 400W or less power consumption to help keep the house cool during the sticky months here in Maine.

    My girlfriend rather liked the hottub idea but I had to tell her that this was probably outside my abilities right now... I had visions of either administering unwanted electrical shocks to us or burning the flesh off my legs with the wood heat...

    Thank you all for your thoughts/ideas! Lets keep them coming as it seems everyone has their own unique solutions to this "problem".
  • techntrektechntrek Solar Expert Posts: 1,366 ✭✭✭
    Re: What to do with extra power

    If you get the mini-split you'll have 2-3 times more heat than 400 watts. That oil-filled radiator will put out 400 watts, period. Plus it will take care of your air conditioning problem. Look at the link on page 2.

    Only problem with making electricity from stored water is you will loose water pressure in the deal (no such thing as free energy). You could end up with a nice water-based battery but a shower that dribbles out of the faucet.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    Re: What to do with extra power
    raydias wrote: »
    Ken - what temps do you get in your 40 gal diversion water heater with the 2x300 watt heater elements and do you have any diagrams or pics to share. This is what i am looking at doing for my parents as well.

    I really don't take note on temp gain. It is so variable day-day. The highest was 90 Deg. F. We are getting snow next couple day. But next sunny day will try to take note. Will make up a ruff drawing for you this weekend.

    Can post AHs and est. wattage. to dump load.
  • SUNBURNEDSUNBURNED Registered Users Posts: 7
    Re: What to do with extra power

    So, I bought the Prostar-30 that has the load output. Having read this post do I hook up that load right to the inverter or how are you running the devices off of the dump load hook up?
  • XRingerXRinger Solar Expert Posts: 508 ✭✭✭
    Re: What to do with extra power
    SUNBURNED wrote: »
    So, I bought the Prostar-30 that has the load output. Having read this post do I hook up that load right to the inverter or how are you running the devices off of the dump load hook up?

    I'm far from being an expert on charge controllers, so I my 2 cents might be wrong.


    Depending on the voltage (12 or 24), you should be able to draw 15 or 30 amps from
    those load terminals. If your inverter doesn't use that many amps, (at that voltage)
    you should be able to connect it directly load output terminals.

    If your inverter load is large, you could use the Load Output to control a relay
    that connects the battery(s) to the inverter. (fuse the bank-to-load line).

    I have a low stand-by draw(70ma) on my inverter,
    so I could leave my inverter connected to my battery bank all the time,
    and I could use that 'dump load' voltage to switch on an SSR (solid-state relay).

    The SSR would connect the 120vac from my inverter to my loads..
    (I wonder how that config would work with a grid-tied inverter?)
  • bobdogbobdog Solar Expert Posts: 191 ✭✭✭✭✭
    Re: What to do with extra power

    from the Morningstar web site:

    We do not recommend wiring inverters to the load terminals of our products because of current in-rush on start up. Inverters typically have large amounts of input capacitance (for input filtering). When power is first applied, these capacitors can draw very large currents in the 100's of amps, albeit for a short period of time. These current surges can stress our power transistors and will trip our short circuit protections. The inverter may start eventually after several attempts to reconnect from the short circuit condition, but this mode of operation is not normal.

    For this reason, we do not recommend wiring inverters directly. Many inverters have their own LVD circuitry and will not allow the battery to discharge too low. However, if the customer requires load control and LVD functionality, they can switch the inverter through a relay wired in series between the battery and inverter. The relay is switched by the load terminals of the controller.
  • bobdogbobdog Solar Expert Posts: 191 ✭✭✭✭✭
    Re: What to do with extra power

    Also from the Morningstar web site:

    What is the purpose of the "Load" connection?
    The Load connection allows the user to wire DC devices such as fans, bulbs, or communication equipment directly to the controller. This allows the controller to disconnect the loads if necessary for protection of the controller, battery, or the loads themselves. This connection is optional.
  • XRingerXRinger Solar Expert Posts: 508 ✭✭✭
    Re: What to do with extra power

    "current in-rush on start up"..

    I've seen this on inverters, and on my TS-45 charge controller.
    The caps look like a dead short initially.

    I wonder if a better design would be to have a smaller relay (or FET),
    working with the high current load control switch.

    The smaller relay would switch in 10 or 30 seconds Before the main switch,
    but the smaller relay wouldn't handle any load per-say, but would have a series
    resistor (1k 10w?) to allow the input caps to charge in a controlled manner, avoiding the inrush..?.

    Inrush Insurance? :p

    In manual mode, I've connected a battery bank to an inverter by
    first charging the input caps up. Used a large 50 ohm resistor in series,
    for a few seconds. It worked.
  • BB.BB. Super Moderators Posts: 26,666 admin
    Re: What to do with extra power

    Yea, "hot plugging" circuit packs and larger power supplies always played heck with the power systems...

    Putting a precharge circuit can be very helpful (like you did)... Also, for AC systems, we would put a NTC Resistor (Negative Temperature Coefficient) in the input power circuit--When the NTC was cold, it had high resistance, as the current flowed through to charge the input caps, the resistor would heat up and drop its series resistance--Of course, on an AC Grid system, the losses are pretty small--For a DC power system with high currents, much more of an issue.

    Of course, if somebody cycle power very quickly or there was a power hit, the NTC was already hot and therefore the when power was reapplied--the high surge current was back.

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