Solar panel question - PeachParts Mercedes-Benz Forum

davidmash · #1 06-10-2021, 06:40 PM

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?

Dubyagee · #2 06-10-2021, 07:00 PM

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.

davidmash · #3 06-10-2021, 09:12 PM

Quote:

Originally Posted by Dubyagee

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.

sloride · #4 06-11-2021, 10:12 AM

Quote:

Originally Posted by davidmash

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.

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.

davidmash · #5 06-11-2021, 12:13 PM

Quote:

Originally Posted by sloride

Not sure what you mean by 1:1 net metering. I don't think it, I know it for a fact. 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.

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.

sloride · #6 06-12-2021, 07:25 AM

Quote:

Originally Posted by davidmash

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.

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.

ah-kay · #7 06-10-2021, 09:16 PM

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.

davidmash · #8 06-10-2021, 09:26 PM

Quote:

Originally Posted by ah-kay

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?

ah-kay · #9 06-10-2021, 10:40 PM

Quote:

Originally Posted by davidmash

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.

davidmash · #10 06-11-2021, 12:07 AM

Quote:

Originally Posted by ah-kay

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.

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?

Mxfrank · #11 06-11-2021, 12:11 AM

Quote:

Originally Posted by davidmash

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?

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.

davidmash · #12 06-11-2021, 12:23 AM

Quote:

Originally Posted by Mxfrank

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.

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?

Mxfrank · #13 06-11-2021, 10:20 PM

Quote:

Originally Posted by davidmash

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?

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.

Dubyagee · #14 06-10-2021, 10:57 PM

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

davidmash · #15 06-11-2021, 12:19 AM

Quote:

Originally Posted by Dubyagee

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

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.