Solar panel question
 

I am looking into getting panels and a generator for power and back up. I was told something interesting by two f the sales reps and neither had the technical expertise to explain the reasoning for what they said and both agreed that it should be able to be done.

If you have solar panels and the power goes out, even though your solar system has the ability to power your house, it wont. The power your panels generate goes to the grid and the grid will power the house. If I were to get a system like the Tesla Wall, the same applies. Once the batteries exhaust themselves, the solar panels will not charge the batteries. Now, if I add a generator into the mix, the generator will charge the batteries.

The only thing that kind of makes sense is that the generator is AC and the solar panels are DC but, there is an inverter so that seems to indicate that this is possible. Besides, If I live off the grid, I can get solar panels, an inverter and power my house. So whats the deal? Is the power company some how getting their hands in the mix to prevent people from having an efficient system and cutting them out?

Any ideas?

The power companies will pay you pennies to use the excess energy you make and charge the going rate for it downstream. I would install a hybrid system. Panel power for heavy use items like HVAC and the rest on solar.

A 5k smart inverter system with a power wall would be more than enough to carry you through any two to three day outages. More if sunny out.

The difference with solar is you have to keep an eye on all power consumption. You would be amazed at how much power those phone chargers and small transformers consume.

Actually, Reliant and one other company will do 1:1 net metering. So any excess I produce on sunny days is put in a 'bank' and I use it 1:1 when I need to draw power.

According to Tesla, I would have to have 4 power walls to power my house for 5 days without power. Given how much power the 3T and 1.5T ac systems use, I do not see how they could last that long. My issue with the power walls is longevity. They are only guaranteed for 10 yrs which means they will likely fail shortly there after. Current price on a power wall is somewhere around $7k last I checked. If, worst case scenario, I have to replace 4 walls, that $28k out of pocket. Considering I have only lost power a handful of times over the last 20 yrs, spending that kind of money for backup power is not worth it for me.

They hybrid I am looking at is solar panels for day to day use and a 18kWh backup Generac for power failures. The only necessities are the AC, pool pump and fridge. The generator can handle that plus a few ancillary lights, ceiling fans and so forth.

They system I am considering guarantees 21 kWh a year. If I fail to produce that, the company will cut me a check for any shortage. Last year, I used a bit over 22 kWh for the year. So if that hold steady, my electric bill will be nearly zero and after the system is paid off, I will be saving about $2500 a yr in electric costs. More if/when utility prices go up.

I just do not understand why during a power failure, the power generated by the panels cannot power the house through the same switch the generator would. That does not make any sense to me.

Grid tied system will NOT power the house if the grid goes down. It is because the inverter doesn't see the grid and it will not invert the solar power.

You need a hybrid inverter if you want power during blackout. It works on solar, battery in that order. If the battery is out then it will use the grid or generator to recharge. It is kind of a reverse UPS.

Why do they not use a hybrid? Both salespeople said that their systems do not charge when power is down and every article I have read since says the same thing.

Is there some cost or legal impediment?

Grid tied system is always like that. They don't want to electrocute the technicians fixing the blackout. Solar panels never invert during blackout and put voltage on the wires. It is a design feature.

Bottom line is it will be very expensive to make a grid tied system to retrofit with battery.

Solar panel question
 

https://unboundsolar.com/2550157/outback-power/inverters/outback-power-gs8048a-01-inverter

This ties into the grid and solar. It draws from and and charges the batteries. Its stackable and is grid tied. You can set priorities depending on what you want. For example, pull from grid first and batteries second or reverse. You can charge the batteries anyway you want to and let this charge them from the grid as a last choice. It will not back feed a dead grid.

Install PDF

https://documents.unboundsolar.com/media/2550157_gsa_w_v_1616428321.pdf


https://uploads.tapatalk-cdn.com/202...b12001dfef.jpg

Keep your system off the grid. Flip the main fuse and engage your system for, as you say: for power and back up"

Perhaps I am not being clear. I can set up a whole home generator that when the power goes out, it will kick on, power my home and not put current into the grid. Why cant a solar panel use the same switch that a generator does?

I believe the issue is phase matching. The inverter output has to be perfectly in phase with the power line current, otherwise it's just injecting noise when it feeds power to the grid. So it senses grid phase and creates a matching waveform from battery power. No grid, no sine wave.

When the generator is on, a transfer switch has to be present, and that will disconnect the system from the grid. The system shouldn't be feeding power back to the generator, so the control system has to know which power source it's on and behave accordingly. And when switching back from generator to grid, it first needs to adjust the phasing. So a lot more sophistication and expense would be required.

20kwhr/yr seems way too low. I can use that in a month, without A/C.

From what I can tell, this does not change the fact that the solar panels will not supply power to either batteries or the home when the grid if off line.

There is no fuse to flip.

A kWh is not the same as a kWhr. I went through each bill and I used 22k kWh in the year. My current rate is about $.09kWh.

Are you saying that the panels produce a power that the Home cannot use but the generator does?

No grid, no power. It is to sync the incoming AC phase for grid tied system otherwise you can't feed power back to the grid. Grid tied solar with battery backup is more expensive and payback period is long.

Whatever you do, DON'T lease a system.

Definitely not going to lease.

Perhaps I am missing something but if a house that is not even tied to the main grid can have a solar system powering their home, why cant a house that is tied to the grid work the same way but have a switch that cuts off power to the grid when main power fails. They do it for a generator, why not for solar?

This sounds more like a legal issue than a technical one.

Not sure what you mean by 1:1 net metering. It sounds like you think the power company will buy your power for what they charge their customers. I highly doubt that will ever happen, not a good business plan. Maybe let you go to zero, but doubt that also.

It can be done but it is just more expensive. Grid tied inverter is cheap. You need a more expensive hybrid inverter to do what you want plus a automatic transfer switch. Any competent sale guy can explain all these to you.

Net metering is a gimmick. If you SIZE your grid tied system right and you use what you generate then it is perfect. So it is same as off grid. The power company pays you peanut for surplus generation, not retail price.

It does exactly that. It also can remote start a fuel based generator as needed. It is what you asked for.

It kills the grid power connection when the grid is down. It can switch to battery or gen power and you can program what power source is the priority for main power.

That is exactly what I mean and it is in the contract with the power company. They credit my excess energy at the same rate I buy it from them at. Assuming I do not use more then my panels produce over the course of a year, I will not pay a penny out of pocket for survey. The days I over produce will cover the days I under produce.

Maybe taking solar into account, or maybe as an average, but there's no way you use just 22kWh in a year.

Do you understand the difference between AC and DC? Your panels and your batteries produce DC power. The inverter converts that to 120V 60hz.If you were standalone solar, your inverter can use its own 60hz clock and it would be fine. But you tie into the grid, so the 60hz current produced by the inverter has to be exactly in phase with the power supplied by the grid. Otherwise, any power back fed would just be distortion and would end up dissipated as heat. So the inverter shuts down when it can't sense grid power. That's also a safety feature, so that your system isn't feeding back to the line when there is a blackout. Imagine how that would work if there are people working on the lines.

If you add a generator, the inverter should once again work, because the generator is producing 60hz current which can clock the inverter. There will be a transfer switch that isolates the house from the grid, so there is no phasing issue. At that point there's probably not much point in adding back the solar panels, because a) solar power can't back feed the generator and b) it won't have a material effect on generator fuel consumption.

Depending on the age of your system fuse = circuit breaker. Are you trying to say you do not have a main disconnect in the service box?

I doubt you will ever be paid for one bit from your panels at the rate they sell it for. Can you go to zero, maybe but I also doubt that will happen.

Again, let me make self clear, what you think you know is entirely irrelevant. The 1:1 metering is in the contract. I am not the only person in Texas to consider/have solar panels. The 1:1 metering is the only thing that makes the panels a viable option here.

Since you do not understand what net metering nos and you seem to have no inclination nto want to research it on your own (common theme with you) here is a net metering primer.

https://quickelectricity.com/2018-solar-panel-incentives-texas-net-metering-buyback-programs/

Green mountain offers 1:1 credit upto what you use.
https://www.greenmountainenergy.com/home-energy-solutions/renewable-rewards-perfect-match/

If I produce equal or more than I use over the course of a year, my bill will be zero.

Not sure what is so hard to understand.

Not sure if you think it is high or low but last year I used a bit over 23,000 kWh. The system I am being quoted will produce about 21,000 kWh a year so on avg, I'll be out a few bucks each year unless I fan reduce my consumption by 2,000 kWh. Might be able to shorten my pool run cycle during winter.

As for the rest, your understanding not solar is different than the sellers is.

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.

See above. The panels do not power my household, the grid does. I do not know enough about electricity but according to them, the solar power goes to the grid and I draw power from the grid at the same time. A house with solar that is tied to the grid is set up different than. House with solar off grid.

I would never consider a system that couldn't stand alone off grid. But unless you have 2 meters .... you might be able to disconnect from the grid and use your solar.

I am guessing I would void the warranty by altering it. Being tied to the grid is the only way solar makes sense because of the net metering. I need power at night and with out batteries, I would be losing money on the deal.

Plus I do not know enough about electricity to know what I would need to do to alter the system to power my house when the power is down.

The house draws power from the panels, if it is not enough then it draws power from the grid. Meter goes forward. Conversely, if the panels generate too much power then it is fed to the grid, meter goes backwards. You offset what you used prior, hence net-metering. If you generate too much, then power company will pay you but NOT at retail rate.

Grid tied system needs battery or generator during blackout. Grid tied system is cheap, but adding battery will be very expensive. Get a quote from your 'Sale person' for system with battery ( or generator ) backup and decide for yourself. If the sale guy cannot explain what had been posted so far then get a different company who can.

According to the people selling this stuff, not quite.

The panels do not power the house at all. They always send power to the grid. My house will only be powered by the grid.

You are correct about the net metering thing but here in TX it's 1:1. The rate they are selling is $.13 a kWh. I sell overage at $.13 and I buy at $.13. if I produce more then I use, I do not get surplus cash back but my electric bill will be zero.

The thing I don't get is that since the panels are sending power to the grid, why can't that post be diverted to my house when the power is out. There is a switch for the generator so that the grid does not get powered. Why not do the same for the solar?

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

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.

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

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.

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.

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.

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?

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.

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.

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

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:

https://www.peachparts.com/shopforum...n-ac-vs-dc.jpg

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:

https://www.peachparts.com/shopforum...tion-phase.jpg

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.

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

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.

A hybrid system seem like what you are wanting. There is a lot of posts in this forum about how they work. https://www.solarpaneltalk.com/forum

Better get that all set up before the big heat wave shuts things down

You are right. That is what I want but the cost is too prohibitive in my situation. A 15-20 break even point is not worth it.

I wish...best case is 3 months.

Just go buy one. Need me to ship one from here?