how does solar tie into your house?

Discussion in 'General Electronics Chat' started by jdraughn, Mar 28, 2009.

  1. jdraughn

    Thread Starter Active Member

    Jan 30, 2009
    In a grid tie solar electric system power from the solar panels are ran through an inverter that syncs the output frequency with the grids ac.

    I am having trouble understanding how the power is added. Is is basically like a parallel dc circuit, but AC? Is there some diodes or something that stops the grid power from trying to go back up the inverter and into the panels? I don't really understand how a device in the house "knows" to use the power from the solar panel system FIRST, and then take what remains from the grid.

    I was wondering if it would even be possible to make a system that ties into your house electricity, but not the grid. That way any power you make will can go go into powering your house, and anything else needed comes from the grid. If you are making more then you need, normally that extra power goes into the grid, meaning you need a special meter that is capable of running backwards. I was wondering how feasible it would be to do the same thing, but instead of running your meter backwards, any excess would simply be wasted.

    There are programs available through the electric company where if you consume electricity during peak hours, you pay a lot more, but the power you consume off peak costs a little less. it just so happens that a solar panel does most of it's generating during the peak hours.

    I wanted to try and save money on my electric bill by starting out with a basic system of just a few watts. 100, 200 or 500 watts or so. I realize that is hardly nothing, but more then anything it's the principle. I am really interested in solar electricity and consider it a hobby. usually you don't expect to make money with a hobby, you spend money to have fun. I realize that even though I may be saving a few cents on my bill, I will be spending hundreds of times what im saving in the costs of the hardware - but thats ok cause im having fun.

    I have a very basic knowledge of electrical circuits but I am still having a hard time understanding the concept of using your solar panels first, then remainder from the grid.
  2. hgmjr

    Retired Moderator

    Jan 28, 2005
    To grid-tie any locally generated power, I understand that one has to install a grid-tie unit between the power source and the mains power service. There are what are called Net Power-meters that when installed will allow the power generated locally to be factored into your overall power usage and thus if you generate more than you use, the meter will keep track of the excess generated power.

    Here is one link to a fairly brief discussion of on the topic.

  3. Mike2545

    Senior Member

    Mar 26, 2009
    You could put up some solar panels with a bank of batteries that are tied directly to lights or some other equipment in your house, so if the batteries are charged you could utilize solar energy instead of the grid power.

    Solar electricity is expensive, the pay back in northwest Ohio at current electric rates is about 25-30 years. Solar water heating is more efficient and less costly, you will not be able to do space heating with a simple solar water heater but you can make all/most of the hot water a house will need,and pay back is around 5-10 years.

    We have done a project that involves both PV and solar water heating. You can see the results here:

  4. thingmaker3

    Retired Moderator

    May 16, 2005
    A "detented" meter will not run backward. A "non-detented" meter will indeed run backward. Some jurisdictions require two meters. Buy-back programs vary by location. PGE, for example will allow detented meters. Power we generate is deducted directly from our use if we generate less than we use. If there is a net excess, PGE will buy the extra power for a little over 2 cents per kilowatt-hour. (They sell to us for almost 9 cents per.) Jurisdictions requiring dual metering are not nearly as good a deal for the consumer.

    Grid tie inverters (also called "utility interactive inverters") are connected to the service entrance. (Or they can be connected to distribution panels in big installations.) Make sure you have appropriately rated disconnects on both sides of the inverter!

    They do indeed work in parallel with the grid. The electronics in an inverter use the grid's power to "commutate" the inverter switching. It works sort of like a driven oscillator or a phase-locked loop. Sort of. And yes, the switches in the inverter do isolate grid power from DC input.

    For an inverter which will keep the house powerd on a sunny day when the grid goes down, one needs a "bimodal inverter." These incorporate an automatic transfer switch, and will isolate themselves from the grid in the event of grid outage. During such an outage, they will self-commutate. They cost more, of course. Always insure the panel fed by a bimodal inverter is rated for at least 120% of the inverter output. (This won't typically be a problem in residential applications.)

    One can buy PV modules with grid-tie inverters on the module itself.

    Please comply with all applicable codes (electrical, structural, other) when installing PV systems.
  5. italo

    New Member

    Nov 20, 2005
    First of all no power company will not allow anyone to tie to the grid even if you can generate megawatts. the grid in the U.S.A. is a big tie and guess what they buy and sell from each other not every day but continiuosly because the power is there either comming or leaving from all sources Is it possible to sell yes only if the power company agree to buy from you the surplus.. YOU MAY use solar power,wind whatever if you are disconneted from the grid. suppose you system gets a massive short how are they know where the short is and how can it be disconnect.
  6. thingmaker3

    Retired Moderator

    May 16, 2005
    Italo, try living in the REAL WORLD for a change. At least read a book or run an internet search before posting your idle speculations!:mad:

    There is a huge industry supporting distributed generation. Every power company in America has a department devoted to assisting business owners and home owners in this area. There are thousands of grid tie inverters already online.

    Your idle speculations are simply wrong. Again.:mad: