Solar panel question - Page 3 - PeachParts Mercedes-Benz Forum

ah-kay · #31 06-12-2021, 01:19 PM

No point beating a dead horse. Get another company who understands their stuffs.

davidmash · #32 06-12-2021, 02:35 PM

No horse. I know 4 other people who have solar from different companies. This is how they are designed to work.

I just want to know for my own sake. Curious.

Paulwho · #33 06-12-2021, 06:01 PM

duck duck a go go says it is easy,

https://www.sunnova.com/watts-up/add-battery-existing-solar

https://www.gogreensolar.com/pages/solar-battery-back-up-systems

davidmash · #34 06-12-2021, 07:45 PM

Batteries are to costly and their life span is not long enough for me to justify their expense.

Right now I am paying roughly $2300 a yr on electric. A battery/solar system is going to run $50-$60 thousand. Before financing cost, it would take over 20 yrs to hit the break even point and that at the low end of $50k.

I wish the federal subsides were higher to make the systems more affordable. I think anything we do to reduce fossil fuel use would be a good thing in the long run.

Dubyagee · #35 06-12-2021, 07:48 PM

If a solar sales guy says it doesnt power your house they are confused. It uses the grid as a battery. Whatever power the panels cannot make it takes from the grid. Whatever surplus the panels make goes back to the grid, running your meter in reverse. The inverter phase matches to the grids AC frequency.

A grid tied system shuts down when the grid fails. A hybrid can be set up to take over.

davidmash · #36 06-12-2021, 10:02 PM

Quote:

Originally Posted by Dubyagee

If a solar sales guy says it doesnt power your house they are confused. It uses the grid as a battery. Whatever power the panels cannot make it takes from the grid. Whatever surplus the panels make goes back to the grid, running your meter in reverse. The inverter phase matches to the grids AC frequency.

A grid tied system shuts down when the grid fails. A hybrid can be set up to take over.

No, they are not confused. I have spoken with 3 different companies and I know 4 people with solar. They have all confirmed that when the power is out, their panels will not power the house.

This may be a Texas thing but they have all confirmed that here, the solar panels do not supply any power to the house directly. All the power goes to the grid. The power I need I get from the grid. If I need less than I provide, I get credit to use when I produce less than I need.

I know that a hybrid can provide power when the grid is down. WHat I do not understand is if a home not tied to the grid can have power from solar and a house tied to the grid can have battery or Generator power when the grid is down without sending power to the grid, why cant the same cannot be done to let the panels power the house when the grid is down and just divert the power to the house.

The more I research the more I am convinced that it is a legal issue and not a technical issue.

Diseasel300 · #37 06-12-2021, 10:09 PM

The answer is extremely simple. The inverter requires a constant/steady power source to operate. It cannot be powered directly from the panels. In hybrid and fully isolated systems, the panels charge the battery, the battery powers the inverter, the inverter runs your home.

In a grid-tied system there is no battery. When you lose the grid, you lose your stable power source to power the inverter which is why it shuts down. Without having a hybrid system that has the battery bank, the panels CANNOT power the load (your home) directly. It is a technical issue, not a legal one.

Dubyagee · #38 06-12-2021, 10:24 PM

Like I said, grid tied uses the grid as a “battery”. Thats why it shuts off when the grid fails like a battery powered inverter would if the batteries failed.

Panels feeding an inverter without a battery would have voltages all over the map. The battery helps smooth out voltage variances. Like a capacitor.

When a grid tied system loses the grid it shuts down to protect the inverter and not back feed the grid. If there was a battery bank in between the panels and inverter and the inverter had an automatic transfer switching system it would keep power on until the batteries were drained. A larger group of panels would lengthen the battery time.

Its not a legality issue, its a financial one.

davidmash · #39 06-13-2021, 12:08 AM

Quote:

Originally Posted by Dubyagee

Like I said, grid tied uses the grid as a “battery”. Thats why it shuts off when the grid fails like a battery powered inverter would if the batteries failed.

Panels feeding an inverter without a battery would have voltages all over the map. The battery helps smooth out voltage variances. Like a capacitor.

When a grid tied system loses the grid it shuts down to protect the inverter and not back feed the grid. If there was a battery bank in between the panels and inverter and the inverter had an automatic transfer switching system it would keep power on until the batteries were drained. A larger group of panels would lengthen the battery time.

Its not a legality issue, its a financial one.

I misunderstood the first part. My apologies.

If I have a off the grid house with solar panels, I get power from the panels do I not? Assuming yes, why can that not be done on the grid and just have a switch, like they do for a house that has a generator, which cuts off power from the grid?

ah-kay · #40 06-13-2021, 01:18 AM

Quote:

Originally Posted by davidmash

I misunderstood the first part. My apologies.

If I have a off the grid house with solar panels, I get power from the panels do I not? Assuming yes, why can that not be done on the grid and just have a switch, like they do for a house that has a generator, which cuts off power from the grid?

Get a better engineer, not a sale person. The inverter for grid tied and off grid system is DIFFERENT. That is why you can't turn off the grid and 'turn on' your solar panels. The panels doesn't work like a generator. Enough said.

Diseasel300 · #41 06-13-2021, 08:53 AM

Quote:

Originally Posted by davidmash

I misunderstood the first part. My apologies.

If I have a off the grid house with solar panels, I get power from the panels do I not? Assuming yes, why can that not be done on the grid and just have a switch, like they do for a house that has a generator, which cuts off power from the grid?

You have misunderstood a lot. An off-grid home running solar panels has a huge battery bank. Your house is powered from the battery bank in this case. The solar panels are charging the batteries. You do not take power directly from the panels in any case at any time. Ever.

You also cannot have the solar panels operating in parallel with a generator. The inverter will cause the generator AVR to literally go crazy. The generator must have a load on it and the inverter does not understand that, if you back-feed the generator hard enough, you will cause the windings in it to fail. The grid-tie inverter is not designed to "share load" with a generator, it is designed to dump the maximum power it can back into the grid. Seen it happen many times by people who thought they were clever enough to trick the grid-tie system, it isn't pretty and the load in your home gets real unhappy when it does.

If you want a true backup system, you need a generator. Even off-grid solar systems have a backup generator for when the system is down for maintenance or on cloudy/snowy days when there isn't enough sun to keep the battery bank charged.

davidmash · #42 06-13-2021, 11:30 AM

That's why I am asking questions, because I don't understand. But that's for sharing.

Not asking why panels and generator can't be used in parallel, I'd be looking to use one or the other.

I did find what seems to be a very detailed explanation here.

https://arstechnica.com/civis/viewtopic.php?f=26&t=1402629

Mxfrank · #43 06-13-2021, 06:59 PM

Quote:

Originally Posted by davidmash

My solar panels (should I get them) do not power my house at all...ever. They send power directly to the grid and I buy power from the grid to power my house. No idea why or how this works and it makes no sense. At any rate, the phasing issue is not an issue since it does directly to the grid. When the power goes out, there is a switch to cut the feed to protect workers on the line. The generator would be needed to power the house.

I just do not understand why the solar cannot power my house like the generator does and if the grid goes down, a switch kicks in to kill power back to the grid.

Ok, let's begin by getting this clear: solar panels NEVER power the grid directly. The solar array is producing DC power...probably 48V DC. The power company supplies 120AC, 60hz current. compare:

Your inverter converts the DC power produced by your cells (or supplied by your batteries to 120VAC, 60hz, so that it's compatible with the grid and with all of your appliances. And in order to feed power back to the grid, it has to precisely match the phasing on the power line. If the power line and inverter current aren't precisely phase matched, then the power you are 'selling' back is just wasted as heat, and can damage equipment, both in the grid and in any customer equipment plugged into the grid. When there's a phase mismatch, the power trace looks like the top picture. When the inverter is operating correctly, it looks like the bottom:

The way the inverter creates the correct feed is by sensing line voltage, and synthesizing a matching output feed. No line voltage, no means of clocking the correct phase. In addition, shutting down the inverter when line voltage goes away is a critical safety factor: imagine that your system was supplying the entire grid in the event of a black out. Or if a worker is repairing a down line while you are pumping current into a line he expects to be unpowered

Now let's talk about the generator. You're never going to be on generator when the power grid is supplying power. So it's not concerned with phase matching. It doesn't require an inverter at all, and doesn't have to clock the power line feed. It supplies 60hz current by virtue of being a rotating machine, operating at a fixed RPM. So when the generator engages, it flips a switch, called a transfer switch, that disconnects the power line feed and isolates the house from the grid. To switch back, you usually turn the generator off manually and then reset the transfer switch, although there are automatic switches.

To do something similar with solar, you would need an inverter which can either supply its own clock when the grid was down, or sense the phase of the grid when line power was available. And when the grid was offline, it would need to isolate the house for safety. And then switching back to the grid would require several steps to achieve phase match. So there would be a whole lot more going on.

INSIDIOUS · #44 06-13-2021, 11:14 PM

Absolutely wonderful post ! I'll add ..if Dave wants to go power backup he should look at stand alone systems.

Quote:

Originally Posted by Mxfrank

Ok, let's begin by getting this clear: solar panels NEVER power the grid directly. The solar array is producing DC power...probably 48V DC. The power company supplies 120AC, 60hz current. compare:

Your inverter converts the DC power produced by your cells (or supplied by your batteries to 120VAC, 60hz, so that it's compatible with the grid and with all of your appliances. And in order to feed power back to the grid, it has to precisely match the phasing on the power line. If the power line and inverter current aren't precisely phase matched, then the power you are 'selling' back is just wasted as heat, and can damage equipment, both in the grid and in any customer equipment plugged into the grid. When there's a phase mismatch, the power trace looks like the top picture. When the inverter is operating correctly, it looks like the bottom:

The way the inverter creates the correct feed is by sensing line voltage, and synthesizing a matching output feed. No line voltage, no means of clocking the correct phase. In addition, shutting down the inverter when line voltage goes away is a critical safety factor: imagine that your system was supplying the entire grid in the event of a black out. Or if a worker is repairing a down line while you are pumping current into a line he expects to be unpowered

Now let's talk about the generator. You're never going to be on generator when the power grid is supplying power. So it's not concerned with phase matching. It doesn't require an inverter at all, and doesn't have to clock the power line feed. It supplies 60hz current by virtue of being a rotating machine, operating at a fixed RPM. So when the generator engages, it flips a switch, called a transfer switch, that disconnects the power line feed and isolates the house from the grid. To switch back, you usually turn the generator off manually and then reset the transfer switch, although there are automatic switches.

To do something similar with solar, you would need an inverter which can either supply its own clock when the grid was down, or sense the phase of the grid when line power was available. And when the grid was offline, it would need to isolate the house for safety. And then switching back to the grid would require several steps to achieve phase match. So there would be a whole lot more going on.

davidmash · #45 06-14-2021, 01:03 AM

Going with a generator.

Solar at this point for my situation is not worth it. A solar only would run $35k plus financing costs and it would take me 15 yrs to break even. A Tesla system is going to run over $50k and take 20 yrs to break even and that assume the batteries last double thief projected life span.

I'll wait to either solar comes down in price, subsidies go up and/or tech improves.