GridTie vs OffGrid (setup variations)

quique
quique Solar Expert Posts: 259 ✭✭
First off, let me just say that my experience started using Trace Inverters to charge battery bank from the grid for backup power during blackouts which were very common in the 90s. The inverter would keep the batteries nice and charged and if Grid power ever went out, it would automatically kick in by pulling juice from the BBank.

Then i started getting into solar because my dad got a couple of solar panels, CController and BBank for a remote home in the mountains. That system is all DC though...nice but expensive to get appliances for and very hard to do so in Honduras.

Then we ordered some solar panels with my dad and he set up his, and i set up mine. My setup is what i call OffGrid but with a Manual Switch although it has an ATS from Iota. My setup is 2 panels, soon to become 4...the lines run into a CC and then into a BBank. From there lines run off into an inverter which has a power cord for if it should be used like my dads inverter, to charge the BBank from the Grid, but i keep it unplugged. The inverter feeds into the ATS and the ATS is fed by a line from the MainBreakerPanel, MBP and it also feeds into an AuxBreaker Panel, ABP.

The way i run it right now is that when the power goes out, i go to the inverter and flip the Power button. This goes to the ATS, finds there is no alternate power source and therefore feeds the ATS, which lights up the ABP.

I know its not the best setup in the world, but i dont like using up my batteries that much because i also like to keep them for blackouts which are still common. So ive gone over some videos on the net, bought a course which was no good but i did pick up a few things from it and im looking at the big picture now b/w GridTie vs OffGrid.

I understand OffGrid is when your house basically lives off of your solar/generator source if you have one. (A generator is not an option im interested in for my setup). There is no incoming Grid power at all. Therefore you use a generator for some things which are too energy demanding. However im interested in reducing my energy consumption as much as possible and just using the Grid for the most vital situations. For example ive got a solar water heater (passive) which takes out my need for hot water. Ive got plenty of sun to dry my clothes so i have no need for clothes dryer. We have a gas stove which elminates the need for an electric one. And im getting a solar A/C which will reduce energy consumption supposedly. So Im looking at only needing heavy power surges for A/C units, although these are expendible, but my fridge is a must.

So then i ran into some videos of GridTie Inverters which you plug into the wall and actually put energy back into your grid, or you can also use them, i guess, to power up an ABP and whatever is left over you can pump back into the grid.

So first im wondering if what i have is really an OffGrid Inverter or a GridTie Inverter. Its a no brand name one, i couldnt tell you, they sell them down here. But i would basically want to know, am i better off going with a GridTie setup where i use the PVArray to load my BBank via my CController and then the GridInverter to use up my solar juice constantly during the day and feed the remaining energy to the Grid? The thing is Im not sure my grid can take power back into it. Im not in the US, so i dont know how i would know that.

I guess, ideally i would like to feed energy from my solar panels into the grid for power savings but i would also like to make sure i have charged batteries for power outs?

Normally during the day, when nobody is home (only the fridge is running and maybe 1 hr washing machine), the BBank should charge. If there is not enough sunlight, the inverter should do the rest. Then when i get home at night, id like to use up my leftover energy in order to save some more money and then when i run out, at nighttime when there is no sun available, id like the grid to kick in and leave my batteries fully charged (which normally takes what? 2-3hours?) and then maybe thatll be from 6-8pm. So i can have power at night in case i need anything during the night?

Does this make sense?

Comments

  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: GridTie vs OffGrid (setup variations)

    Was the Trace unit you used to charge battery a DR or SW series?

    A grid tied inverter syncronizes to grid and runs in parallel with it just like the power company's generators do.

    For the old SW series and new XW series the inverter is syncronized to grid and a relay closes to conect inverter in parallel with grid. The output is always connected to inverter so when power goes out, the input relay from grid just opens allowing the inverter to supply AC sinewave power.

    These are called hybrid grid tied systems or battery based grid tied systems. They are bi-directional inverters where with a slight modification to inverter voltage level can charge battery or push power to grid.

    A grid tie only (no batteries) inverter requires grid to be present to syncronize to. It pushes current to the grid based on available solar power production. In this aspect it is like a current source. When grid goes down it disconnects and no power is used from PV array. Some folks get surprised when they find out that all the money they spent on PV system and their power goes out when grid goes down.

    Battery cost and maintenance is significant but does provide power backup on a hybrid based grid tied system.
  • quique
    quique Solar Expert Posts: 259 ✭✭
    Re: GridTie vs OffGrid (setup variations)

    Ok wait. I saw that a grid-tie inverter can be used to just put energy from the solar-charged BBank into the home and any leftover into the grid. So it can be used to power your home at the same time it moves leftover into the grid?

    GridTie Only sounds 'not very useful' because of that part of the grid going down and you having no power as backup. I guess it works if your netting your power meter usage against what you produce during the day, but thats still kinda silly to me.

    My dads Trace uint is DR UBS something or other.

    So my confusion is between the GridTie Hybrid (with batteries) and the OffGrid. Not confused as to what they are, but rather as to what the best option for me would be. Like i said, normally we all leave the house at 730am, the only power really needed to run is the refrigerator for 24 hours straight. We come back home at 530pm and we use basically lights, fans and TV and cable modem. Some nights we use the A/C for which i would definitely need grid power since a generator is not an option. All through the night we use fans and the AC and the fridge. Of these, fans can run off a BB i think, but AC and fridge would probably be better off running from the grid. So at this point i would need the grid back!

    Or i setup an extra ABP for just the fridge and the ACs which are always connected to the grid? But then if i have extra power during the day, which i will, i wont be able to use it for the fridge, so no, this is no good. I need the hybrid grid tie system to use the PVA during the day to power the fridge and then if anything is left in the BBank use it for fans and lights at night. When the BBank is depleted at night, the grid must kick in to power the fridge and fans and ACs.

    I guess ACs can definitely be on a separate 100%Grid circuit since i dont ever plan to have enough batteries or a large enough inverter to run an AC on solar :) Even with the solar ACs i plan to get, they only provide a 30% reduction in power (nominally) so i dont expect to drain my bbank on that!

    So based on this, i guess i could just leave my inverter turned on, during the day, since the only thing consuming power would be the fridge, the BBank would feed the fridge only. If the sun is not enough, the ATS should switch automatically to grid power. The problem is that i would have a depleted battery bank! And if i plug in my inverter to the wall, to a grid fed socket, the grid would be charging my BBank all the time, not the PVA, because obviously the voltage coming from the grid is greater than the one from the BBank, right?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: GridTie vs OffGrid (setup variations)
    quique wrote: »
    Ok wait. I saw that a grid-tie inverter can be used to just put energy from the solar-charged BBank into the home and any leftover into the grid. So it can be used to power your home at the same time it moves leftover into the grid?
    A pure grid tied inverter just feeds AC power back into the home's wiring.
    Any loads in the house will draw from the inverter and/or the utility. Any excess power from the GT inverter not used in the home, typically, turns the utility meter backwards (different utilities have different meters and billing requirements).

    What ever the loads are (lights, AC battery charger, etc.) does not matter--AC load is AC load.
    GridTie Only sounds 'not very useful' because of that part of the grid going down and you having no power as backup. I guess it works if your netting your power meter usage against what you produce during the day, but thats still kinda silly to me.
    For me, Grid Tied generates, very roughly, 4x as much power as the equivalent off-grid system when costs/battery replacement is distributed over 20 years.

    Plus, I get to "store" up to 1 year worth of power with my utility for $5.50 per month (and I can start negative and make it up later in the year with summer power generation).

    For me, I kept looking at a Hybrid GT system (Like the Xantrex XW system)--But given that we get maybe 1-3 hours of outage every few years (my last 5+ day electrical power outage was over 50 years ago)--It just did not make any sense to spend $1,000's per year (additional system costs, battery replacement costs,) just to ride through those few hours.

    Instead, I purchased a quiet, fuel efficient Honda eu2000i genset (plus manual transfer switch wired into the home) and store about 20 gallons of fuel+stabilizer (plus a siphon+fuel in our vehicles if we need more)... Realistically, that will keep my food cold for at 10-20 days. Plus the generator+fuel is portable in case we have to leave (earthquakes are probably our "end of the world" event).

    No one right answer, everyone makes their own choices.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: GridTie vs OffGrid (setup variations)

    The DR series was a modified sinewave inverter. Not a grid tied inverter system.