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Home Forums General Discussion tie panels directly to inverter?

This topic contains 5 replies, has 4 voices, and was last updated by  ytmtnman 7 years, 1 month ago.

Viewing 6 posts - 1 through 6 (of 6 total)
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  • #36694

    turbodog1
    Member

    Have you ever heard of tying your panels directly to an inverter? I just spent a lot of money on a decent charge controller. Did I waste money? http://cgi.ebay.com/NEW-GRID-TIE-INVERTER-600-WATTS-SOLAR-WIND-/220634595834?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item335ed8c1fa

    Thanks

    #40839

    elnav
    Member

    No you did not.

    #40840

    elnav
    Member

    The kind of advertising illustrated in the link provided by Turbodog is deceptive and close to being deliberately misleading. In fact some countries would deem this kind of advertising a breaking laws.

    My first exposire to grid tie inverters was back in 1978 Since then I have worked for a power utility companyand befoer I became an independent consulting / designer I worked for Xantrex who is now among the big players in alternative and off grid power systems.

    The above is only to point out I have a nodding acqquaintance with these kinds of products.

    The advertised inverters have a wide voltage range making them suitable for for direct connection to a large solar panel. However fat lot of good it does you after sundown. One of the principal uses of solar arrays is generating sufficient power to be able to store eeenergy after the sun sets. for that you need batteries.

    Thanks to US government program funding ‘grid-tie’ has abecome a magical marrketing word. It implies everything yet delivers little.

    What they do not tell you is that by law all grid-tie installations must have safety interconnects and one of the safety features being that the grid-tie system shuts down if the grid goes down. So when the grid is not working neither is your grid tie solar panel + inverter system. Ooops!

    The whold concept is intended to get private individuals to pump extra energy into the grid during peak demand for air conditioning then useand pay for grid power during dark time. The whole point being this relieves the utility company from having to build additional capacity. Oh yes I almost forgot to mention the ‘buy-back’ details. In every case I have looked at

    The rate at which a consumer buys electrical power is greater than the rate the utility pays back for any power sent to the utility grid. So who is the winner here?

    Should you desire to take advantage of your grid-tie generated power when storms take out the grid you still need batteries. Now you are back to a conventional system that needs a good controller to prevent frying the batteries with an over charge.

    Looking at the prices on the linked website they are two to three time what I expect to pay full retail for ordinary inverters of same capacity and these work at night as well as daytime assuming you have battery.

    A totally seperate issie has to do with the practicality of running a 250 watt inverter to feed the grid with ‘surplus’ power. In the first place a legal grid tie system has to be able to sense grid voltage and synchronize to it. In order for power to flow to the grid the inverter voltage must be slightly higher than the grid voltage. This requires a sophisticated regulator. the AC power must be in phase and this part of the cccircuit is what is often used to detect whether or not the grid is running or ddown ddue to storm damage.

    AS a safety precaution grid-tie system ( whatever their capacity) must disconnect from the grid during an outage. I will tell you the cost of such a disconnect switch that is utility approved, cost way more than the inverter. It has to be installed by a licenced installer and inspected by the utility. Guess how much that cost?

    If the inverter only provides one kilowatt of power how much of it will be surplus for selling back to the utility.

    A 500 watt solar panel array is expensive. not much point in getting an inverter bigger than that so I question the cost benefit ratio of this kind if setup. Maybe some poeple like the warm fuzzy feeling they get from buying so called ‘green’ products. Maybe its similar to the warm fuzzy feeing the retailers of these status products get.

    #40842

    WestTexasLawrence
    Participant

    This is an OFF GRID forum…so I assumed there would be no grid tie discussion

    because typically a remote rural retreat that’s off grid is not grid accessable.

    From a technical standpoint, solar panel arrays should feed a charge controller

    that in turn feeds a battery bank with about 3 times as much amp hour capacity

    as your highest possible usage.

    I recommend bussing 12 or 24 volts DC directly from the battery bank to point of

    service inverters for appliances that just HAVE to have AC voltage. Use large

    cross section conductors for the DC buss to the inverter, and 10 guage wire

    from the inverter to the appliance on the AC side.

    But, I also recommend buying RV ammonia absorption refrigerator/freezers that will run off 12 volts DC or propane. 12 volt DC microwave ovens are available,

    but are expensive…so are the refrigerators. So, I recommend searching for

    people who salvage RV appliances and resell them to off grid dwellers for a

    fraction of what they originally cost. Example: I have several refrigerator/freezers that all work. The least I’ve paid for one is zero dollars…picked it up off the side of the road where it had been dumped. Bought another one at a garage sale for $20. On the high end, I bought a full size refrigerator/freezer (ammonia absorption) for $150 cash. That refrigerator

    retails for $1600. The smaller ones are still around $800.

    So, start there with savings for your off grid effort. A microwave oven might cost $1300 new…you can pick one up for $180.

    Then ditch the incandescent lights and go with LED and CFL lights everywhere.

    Run DC voltage direct from the batteries wherever possible through a dedicated,

    isolated, circuit breaker protected circuit.

    I have several sources for such lighting and appliances. Buy new lighting, but

    buy used RV refrigerators. Depending on where your off grid retreat will be,

    you want to choose either refrigerated air conditioning or evaporative air conditioning. There are several (besides me) individuals who convert 120 VAC

    evaporative air conditioners to DC operation, for a price. I make those conversions cheaper than a new evaporative AC powered air conditioner.

    I recommend Amorphous silicon solar panels whenever possible because they produce some voltage in low light conditions, when its cloudy or snow covered, or there are shadows from trees,etc. The monocrystalline and polycrystalline panels cut off completely in such conditions. Amorphous panels are also cheaper

    because it is older technology…but they are less efficient and it takes more

    real estate to produce the same output as the mono and poly panels.

    WestTexasLawrence

    #40849

    elnav
    Member

    West Texas Lawre wrote: I also recommend buying RV ammonia absorption refrigerator/freezers that will run off 12 volts DC or propane.

    It has been my experience with these units that the DC power option is really for holding cold not suitable for chilling down a fridge with warm content like. I used to do electrical maintenance and service for a fleet operator. On hot days the drivers would always come in complaining the Frideg must have quit because it was not cold enough. Naturally they parked and plugged in When I got the service note I would go on board and find the units working fine on 120V AC. Switching to DC, it would remain cold.

    Finally when I compared the wattage of the respective heaters I realized the

    dc only put out half as much as the AC heater element. Later on I discovered the propane heater delivered some 5000 BTU of heat. Way more than the electric heater elements.

    This means the propane fridges are most effective on propane, less so but close on 120V AC and least effective for chilling on 12V DC.

    Delving further into failure modes it turns out the DC side failed first to work followed by the 120V AC and lastly by propane PROVIDED you kept the propane burners cleand and serviced.

    What I have not found is a fridge built to use sunshine to heat the expansion section that has to be heated. Seems some mirrors to reflect the sun’s energy onto the heat pipe would really work well.

    Has anyone seen such a critter?

    #40989

    ytmtnman
    Member

    Remember you can insulate your fridge!

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