watts on a shoestring, will this work?

green_fieldgreen_field Registered Users Posts: 7
Greetings!

My first posting here, and wanted to say, what an information rich forum! I've done a bit of perusing since discovering this board and have gained some very useful insights and ideas. I wonder if I could bounce a couple off you folks and see what you think?

I've been off the grid for eight years, have my very last "on-grid" power bill framed up on the wall. I love thumbing my nose at blizzards and ice storms, it's great being in control of your own power system.

The wife and I've also learned to seriously economize on power usage, and live comfortably on the power that my city cousin would pay a whopping $4/month for. He think's I'm crazy, and could be right, but I don't miss that power bill of his one little bit.

We currently share a solar/wind system built by myself and my neighbor, with my neighbor, who's an old friend and business partner. The hardware is situated on his side of the hill. I’m a computer guy, he’s into electronics, so he’s handled such as this up to now, but his grandkids are keeping him busier these days, so I’d like to tackle a new project on my own.

Power needs over there have grown the last few years, while mine have decreased, so, if possible, I'd like to rearrange things a bit, and just provide my own, and let him have all of what’s coming from the system over there. We will maintain that 110V line between our places for a backup for us, (and us for him, if need be.)

I'm working on a fixed budget (tighter than I enjoy), so am trying to cobble together a temporary system that’ll cover our modest needs til I get all the preferable components together.

I currently have a small system that can cover about half of what I'd like to do. A pair of 90W Photowatt crystalline, running through a Morningstar controller into a pair of 12V deep cycle marines in parallel. A nearby lightening strike this spring took out our true sinewave inverter, so we’re making do on a 175 watt MSW til I get something better. This provides enough for lights, fan, and nightlights. (stepping on the cat's no fun for either of us!)

Last summer, some Amish friends wanted to buy a palette of Kaneka 60W amorphous panels, but didn’t need all of them, so I traded for five of them. They’re 48V nominal, specs say they’ll put out up to 60V when new, then drop back a bit, after ya wear the shine off, I guess. I’ll have a 40’ run out to my panels, so the 48V appealed to me, hoped it’d be less lossy.

I don’t have a 48V controller, or bank of batteries to work with, yet, those are yet to come. I do have a 48V Chinese true-sine inverter, however. I also have six matched T105’s, with cabling to set up a bank at 12V. They are old, coming up on their seven year life expectation, but I believe they’ve enough life yet to bother with. They have not been used their full lifetime, in that they sat unused (but kept charged), for the last four years. They are the original batteries for the system over the hill.

I’ve pondered assorted (affordable) options that would allow me to put these 48V panels into service, and might have one that would work, what do you think?

In my readings on the net, I’ve found several pieces in which the author indicated that you could put an inverter directly on solar panels, (without a controller) to provide 110V at whatever capacity the panels could support, while the sun shines, of course. Do you folks concur with this, in essence? Or am I going to fry my inverter doing that?

I ask because what I’m wondering is this: Could I take the 48V, 500W inverter I have, and hang it off these 48V panels to provide daylight 110V household power needs, typically 120W or less? And secondarily, could I also hang a 2-amp trickle charger off that inverter to put a charge on that bank of six T105’s at 12V for my evening needs?

Specs say each panel outputs about one amp, and I’m inclined to use all five panels.

I realize that this setup probably dribbles juice all over the place, but our needs are modest, and I have everything but the 2 amp trickle charger on hand now.

If I hook up what I’ve described, am I gonna let the smoke out of that inverter?

Thanks for any suggestions,
Howard

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,697 admin
    Re: watts on a shoestring, will this work?

    It is a tough call how to save money...

    If your power needs continue to stay small, you probably would be better off staying at 12 volt battery bank and a nice 300 watt TSW from MorningStar. It also has "search mode" and a remote inhibit (12 volt signal voltage) switch (allow you to save inverter losses when you have no AC loads)--It is a very nice 12 volt inverter with many of the features you don't see until you are paying lots more money.

    With your 48 volt panels, you could also support a 24 volt battery bank very nicely (probably a good idea if your charging power and/or load power exceed ~1,200 watts).

    However, to run a 12 or 24 volt battery bank from your 48 volt panels--you are pretty much limited to using a MPPT type charge controller (or else, you will lose 50% to nearly 75% of their output charging a 24 or 12 volt battery bank with a PWM charge controller). Also, usually, a 48 volt panel does not have high enough voltage to charge a 48 volt battery bank (need ~70+ volts Vmp into a pwm controller to charge a 48 volt bank).

    And, if you put two 48 volt panels in series, you are looking at $600+ solar charge controllers.

    Some charge controllers to look at (from smaller to larger, note they have different input/output requirements--you will need to decide on your battery bank/solar array as you review panels):
    And there are larger controllers too from other manufacturers.

    Running the Vmp-array voltage higher than "12 volts" (really ~Vmp=17.5 volts or so), is a great idea. It will allow you to use much less copper for the panel to charge controller run (and support higher array power later on--if you need "more power").

    In the end, as you know, know your loads and conserve. Then work backwards to your battery bank sizing... Lastly, size your solar array, inverter, generator AC charger, etc. to the battery bank needs. And try to do this on paper first before spending more money (we are all pretty cheap here).

    It sounds like you have been doing well so far. Probably not much I can add regarding long battery life.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: watts on a shoestring, will this work?
    In my readings on the net, I’ve found several pieces in which the author indicated that you could put an inverter directly on solar panels, (without a controller) to provide 110V at whatever capacity the panels could support, while the sun shines, of course. Do you folks concur with this, in essence? Or am I going to fry my inverter doing that?

    Absolute bloody nonsense. No off-grid inverter can function without batteries. Panel varies in Voltage and current according to the amount of sun falling on it and the amount of load applied.

    How about starting by determining your daily Watt hour needs and maximum Watts at any one time?
    In the long run you're better off determining your power needs and obtaining the right equipment to supply it. Cobbling together a make-shift system out of whatever you can find is heartache and headache and a drain on the bank account. If you do have those numbers then maybe some of your equipment can be utilized to supply those needs.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: watts on a shoestring, will this work?
    Absolute bloody nonsense. No off-grid inverter can function without batteries. Panel varies in Voltage and current according to the amount of sun falling on it and the amount of load applied.

    Attention "green_field":
    I realize that you may have a hard time picking out the truth in the various things you read on solar power etc, but you can be sure of this - - Cariboocoot WILL NEVER, knowingly steer you, or anyone else wrong. What he said re the off-grid inverter without batteries, is dead on and I couldn't have said it better. Obviously there are people out there who either have no idea what they're talking about on such things, or are deliberately trying to screw people over and have a good laugh over it.
    You've come to the right place to get answers. Good luck with your projects.
  • green_fieldgreen_field Registered Users Posts: 7
    Re: watts on a shoestring, will this work?

    Wow, Cariboocoot, "absolute bloody nonsense"? shoots that idea down in smokey flames!! ok, I believe you, since Wayne vouches for ya! :)

    thanks for your opinion. In case you're interested, one of my sources suggesting hanging an inverter directly off PV panels was a rather detailed pdf entitled:

    "MAINTENANCE AND OPERATION OF STAND-ALONE PHOTOVOLTAIC SYSTEMS"
    Naval Facilities Engineering Command, Southern Division Photovoltaics Review Committee, Department of Defense and Sandia Nat'l Laboratories’ Design Assistance Center

    I found it under the section describing basic system configurations. They illustrated an inverter hanging off solar panels, powering a 110v water pump.

    It was dated December, 1991. Do inverters now work substantially differently than they did 20 years ago? I wasn't aware of any big changes, but I'm not well versed in inverter tech. I'm betting you folks are, thus my posting. So, ok, I'm content, and will look elsewhere for strategies.

    And I like BB's suggestions, and will consider each. Just need to get a lot richer.

    I've observed that some of you folks aim towards high efficiency in all things. Nothing wrong with that, but I have this hardware on hand, and very few bucks to spare. If I can put something together with what I have on hand, I need to do so. I'm here fishin' for affordable suggestions to do so.

    Our average daily usage has been measured at about 1.5 KWhrs. That was measured over a year's time, using a digital meter similar to the Killawatt on my line from over the hill. The number is on the high side of actual, as I ran the generator over the hill numerous times when higher amperage was required than the batteries over there could deliver. That generator power was brought over and metered along with the solar/wind power, so I'd estimate that my day to day ordinary use was more like 1.2 KWhrs per day. (I have a small generator for this side of the hill that will serve a similar purpose.)

    The 500 or so Whrs that we use while sleeping (if it's hot and we're running our fan), can be provided by the small system now operational, and is seasonal, summer only. So I'd like to use the additional five amorphous panels to provide the rest of the watt hrs I need during the day.

    So, that 700-800 Whrs is what I'd like to provide for myself with my 300W of panels at 48V. This *is* a realistic ambition, isn't it? My location gets full sun during solar prime time.
  • SevenSeven Solar Expert Posts: 292 ✭✭
    Re: watts on a shoestring, will this work?

    I have read about water pumping straight from panels, but there are pumps made to do that. You will not be able to power normal ac loads like that.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: watts on a shoestring, will this work?

    300 Watts of panel might just barely make that low figure. You can check out your year-round numbers using the PV Watts program: http://www.nrel.gov/rredc/pvwatts/

    The short-cut Icarus Formula (using default sun hours) says 300 W * 4 = 1200 Watt hours / 2 =
    600 Watt hours AC. That's not encouraging, but it does give you an idea of how much you may have to add or make up with a generator. Most people under-estimate their loads (I'd go with the 1.2 kW hour figure myself) and over-estimate their sun.

    Don't know what kind of inverter was being used to power a 110 VAC pump without batteries, but it sounds like somebody was playing games with a grid-tie unit. They do output without batteries, but need a grid (or other 60 Hz signal source) to synch to. Since motors too can accept a varying input, you could rig such a unit up. But it's not any sure solution for off-grid use. Some people try setting up a small battery-based inverter to act as a synch signal source for their larger GT set-up, but that meets with varying degrees of success.

    Try the PV Watts program and see what you could expect.
  • BB.BB. Super Moderators, Administrators Posts: 29,697 admin
    Re: watts on a shoestring, will this work?

    Actually, it is always dangerous to say something "...can't be done" because there will always be somebody somewhere that will prove you (or me) wrong.

    It sounds like the solar panel to AC pump is really a VFD (Variable Frequency Drive) implementation (or at least, that is how it would be done today).

    Yes, a VFD is a form of inverter (takes DC and converts it to 2/3 phase AC).

    However, motor/pumping loads are sort of special... With a VFD, you can design it to run the motor (power, rpm, etc.) to take 100% of solar panel output and run run the pump at less than 100% power.

    The advantage of powering AC pumps with VFD's is that you don't have brushes (which have very limited life) and you can efficiently control the pump (soft start, less than 100% rated RPM for lower flow rates, etc.). Also they can power induction motors (typical AC motors) or Permanent Magnet Motors (something like 15% or so more efficient than induction motors).

    Or, you can use regular DC motors and use a Linear Current Booster which take the high voltage/relatively low current from a solar panel (morning/evenings) and convert it to lower voltage/higher current needed to run the DC motor at lower power.

    I have seen a few stand-alone Solar Panel to AC Motor VFD controllers--but they do not seem to be popular (at least looking with Google).

    It appears that it is more common to have the VFD integrated with the pump (Grundfos, and possibly others)...

    You will not find off-the-shelf inverters to run TV's, washing machines, and other devices from solar->AC Inverter->AC load.... Solar panels have no surge, and standard inverters have no energy storage. So to have a constant power device (computer, TV, etc.) with steady power, you would either need over-sized solar panels plus special wide input voltage AC inverters (to support fixed power AC loads like TV, radio, computer) through the middle of the day, birds flying overhead, clouds, etc... Or you will need significant energy storage (typically the lead acid battery) to keep steady power to the loads.

    In general, we choose energy storage (still for the most part, lead acid batteries), so we can have stable power to run our various electrical loads.

    In special cases, like water pumping, where you can pump during the day only, solar panel->pump systems can be really nice. Cheaper to install and less to maintain (no storage batteries). Of course, if you need water pressure for your home (kitchen, bathroom), you may end up with a solar only pump to cistern, and a small battery powered pump (AC or DC) for water pressure for 24x7 usage.

    Anyway, how I see what is out there and how I would answer your question in detail.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: watts on a shoestring, will this work?

    Hmm. Let me read that original premise again.
    In my readings on the net, I’ve found several pieces in which the author indicated that you could put an inverter directly on solar panels, (without a controller) to provide 110V at whatever capacity the panels could support, while the sun shines, of course. Do you folks concur with this, in essence? Or am I going to fry my inverter doing that?

    Yes; that's what I thought it said. Big difference between panels powering "a type of inverter" (VFD) to run a water pump and running an off-grid inverter sans batteries. The latter premise is still a bunch of absolute bloody nonsense. But I wouldn't doubt there's someone out there on the Misinformation Super Highway deliberately leading people to believe it. Why just yesterday I saw a site that told me how expensive commercial panels are and said I could make my own "from $2.95 per Watt" which of course would be much cheaper.

    Except that Kyocera 135's are about $2.50/Watt, with a warranty, and there's no assembly required. :roll:
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