Hello, i have questions

[fatjay]

Hello, i have many plans for solar and power. I have an engineering background and am pretty handy. I just built my garage, and had the trusses engineered to take 6000lb of solar panels, but I want to start small first.

First, I'm going to build a trellis off my back porch that I want to hold 15 200w panels, 3 rows of 5, with the potential to add another 2 rows later. I want to tie it into the panel with a grid tie inverter. Then I have roof space with room for another 25 panels down the line. My question is, if there is no grid power, ie the power goes out, does the inverter shut off and stop providing power?

Second question is finding a grid tie inverter that is ~50a 220v, 2 110v 180 degree's out of phase, or roughly 10kw, so I can grow the porch panel array over time. This would go in my basement, but I also want a second one to go in the garage eventually when I put the panels on the roof of the garage.

Third, I also want to add a bank of batteries, I want the solar panels to charge the batteries, but don't want the batteries to supply power to the inverter unless the grid goes down. I realize that 10kw power flow is considerable from a battery, so I'm not sure what technology I want to go with or it's capacity, it's changing rapidly and I haven't kept up.

Forth, I want to build it myself, and I don't want it online. There's 2 reasons for this. Cost is a big one, but also the ability to change whatever I want to suit my needs without having to go with proprietary equipment. I want the ability to mix and match.

I can build and wire anything. I'm well versed in dc and ac power. I can run cable and build buildings, structures, and towers. I have all the equipment and tools necessary to do so as well.

Here's my current brain logic, if I'm wrong please correct me: Are panels wired in series or parallel? I'm guessing series, so that would make 10 200w panels producing 12v wired in series would be 120v dc at 16.6a, fed into an inverter. But a 10kw inverter I'm looking at says max input 500v dc. With 200w panels producing 12v, I would need 50 panels to produce 10kw, but that would be 600v dc.

Also, where are some good places to buy affordable inverters? From what I'm looking at 200w panels seem to be hovering around $100. But 320w panels are coming down a bit. Can I mix and match in series? It's just dc voltage, that shouldn't be a problem right?

Edit: I just realized I can do panels in series and in parallel. So 5 panels in parallel makes 1000w and 12v, then in series with 4 other sets of 5 wired in parallel makes 48v instead of 20 panels in series making 240v. I think.

 

[400bird]

Hello, i have many plans for solar and power. I have an engineering background and am pretty handy. I just built my garage, and had the trusses engineered to take 6000lb of solar panels, but I want to start small first.

Wow, that's a huge load of panels. My 370 watt panels weigh less than 60 lbs each. So, you're designed for over 100 of these residential sized panels.

First, I'm going to build a trellis off my back porch that I want to hold 15 200w panels, 3 rows of 5, with the potential to add another 2 rows later.

Why the small panels? Are you buying used or new?

I want to tie it into the panel with a grid tie inverter. Then I have roof space with room for another 25 panels down the line. My question is, if there is no grid power, ie the power goes out, does the inverter shut off and stop providing power?

That's the way a standard grid tie inverter functions. Shut down when the grid is down to protect lineman working to restore power.

Second question is finding a grid tie inverter that is ~50a 220v, 2 110v 180 degree's out of phase, or roughly 10kw, so I can grow the porch panel array over time. This would go in my basement, but I also want a second one to go in the garage eventually when I put the panels on the roof of the garage.

Most, if not all grid tie inverters are not split phase. They produce just 240vac, no neutral or 110/120 volt output.

Third, I also want to add a bank of batteries, I want the solar panels to charge the batteries, but don't want the batteries to supply power to the inverter unless the grid goes down.

Are you looking to add the batteries now? Or is this a down the line eventual thing?

There's more details to it than I think you see at the moment. But to power loads when the grid goes down, you must disconnect from the grid. Some inverters have built in transfer relays to do this some people/systems use external transfer switches.

The batteries would always be connect (and supplying power) to the inverter, but it's your programming of the inverter that would mean the inverter doesn't support loads from battery power when the grid is up.

I realize that 10kw power flow is considerable from a battery, so I'm not sure what technology I want to go with or it's capacity, it's changing rapidly and I haven't kept up.

Forth, I want to build it myself, and I don't want it online. There's 2 reasons for this. Cost is a big one, but also the ability to change whatever I want to suit my needs without having to go with proprietary equipment. I want the ability to mix and match.

Build it yourself, as in solder stuff on the board of the inverter?

I can build and wire anything. I'm well versed in dc and ac power. I can run cable and build buildings, structures, and towers. I have all the equipment and tools necessary to do so as well.

Here's my current brain logic, if I'm wrong please correct me: Are panels wired in series or parallel?

Yes, both. But I see below you found that out.

I'm guessing series, so that would make 10 200w panels producing 12v wired in series would be 120v dc at 16.6a, fed into an inverter.

12 volt panels are just marketing, 12 volt panels often produce 19 volts open circuit. When doing spec calculations, you need to use VOC.

But a 10kw inverter I'm looking at says max input 500v dc. With 200w panels producing 12v, I would need 50 panels to produce 10kw, but that would be 600v dc.

You'd need to use multiple strings. I wouldn't do it with 12v panels. But you also need to factor in the max current and number of MPPT inputs on the inverter.

Also, where are some good places to buy affordable inverters? From what I'm looking at 200w panels seem to be hovering around $100.

Where are you finding those deals? $0.50/watt is pretty low unless these are used panels.

But 320w panels are coming down a bit. Can I mix and match in series? It's just dc voltage, that shouldn't be a problem right?

Edit: I just realized I can do panels in series and in parallel. So 5 panels in parallel makes 1000w and 12v, then in series with 4 other sets of 5 wired in parallel makes 48v instead of 20 panels in series making 240v. I think.

Panels are wired in series strings first. Then each string is paralleled at a combiner box. This makes for less roof top connections.

 

[Hedges]

Some inverters are batteries optional. They can backfeed the grid, and provide backup power given enough sunshine.
Some (e.g. SMA Sunny Boy) are grid tied, do not work with batteries (except AC coupled batteries), but can provide 120V 2000W backup given sunshine.

You can mix and match panels to some extent, multiple strings of similar voltage. Also mix and match grid-tied inverters.
If you want battery backup, best to plan up front. Some all in one can be stacked for more power. Some inverters work well for AC coupling (I have SMA battery and PV inverters for my system.)

"4 other sets of 5 wired in parallel makes 48v"
Those would be nominal voltages. More like 18Vmp, 22Voc per panel, so 88V for the 4s string under nominal conditions. A bit over 100V in extreme cold.
I designed most of mine around 600Voc max, now have 3-phase inverters good for 1000V. But also some DC coupled charge controllers 145V max.

 

[fatjay]

I don't think i'm looking to add batteries now, but I want the ability to add them down the line.

That's interesting that a 12v panel has closer to 19v, that's considerable and may change design.

Grid tie is the way to go from what I understand. I use a lot of electricity, my bill is consistently $400-500 and I have about the lowest price of electricity in the country at 11c/kwh. I understand back feeding and net metering, but this first system I don't plan to have generate more than I consume at any given time, so that wouldn't come into play. I just want to put a dent on how much I'm pulling from the grid during peak production times. My monthly consumption is about 4k kwh, or 133kwh per day, or 5.5kw per hour, or if my math is correct, I'm pulling about 50 amps from my panel at any given time. And I don't use considerably more during the day than at night, other than when my wife is using the oven.

I went to a different costco than I normally do and they had 200w panels for $100. I feel like i regularly see them pop up on amazon or other sites. I was thinking 200w as it was the lowest price per watt that I'd seen. However I've been seeing some other higher wattage panels coming down in price. Is the brand as important? I see a lot of off brands. Is there a technology to avoid?

 

[400bird]

Even if you're just looking to put a dent in your bill, you likely still need an agreement with the power company and permits (both depending on your location)

Read the spec sheet for any proposed panels, it will list voltage and current (VOC, Isc, Vmp, Imp) at a minimum, if not look at other brands.
I just checked Costco online, they don't have any bare panels, so I can't pull the spec sheet.

At 50 amp constant draw, adding a battery back up would be a huge requirement without load shedding. That's pretty substantial, are you mining? That's a lot of juice.

From an overall cost perspective, you might be best off with a standard grid tie inverter for now, then later adding or changing to a battery inverter. The expense of a battery capable, UL listed, inverter (so you can pass inspection) is a significant increase over a simple grid tie inverter of micro inverters.

Don't forget the cost of racking. With the smaller 200 watt panels, significantly more racking is required when compared to the larger residential panels.

 

[Hedges]

Assuming net metering is available, grid-tie is the way to go.
I estimate material cost at $1/W, and $0.025/kWh amortized over 20 years. Prices are up a bit lately due to demand and supply chain. If rooftop, "Rapid Shut Down" probably required, another box per panel maybe $50 each boosts cost if using a string inverter. Microinverter provides compliance without extra hardware but costs more than string.

Paying for labor and getting a turnkey installation, more like $2 to $4/W, so $0.05 to $0.10/kWh.

Then there is the tax credit, and any state incentives. But with your utility rate of $0.11/kWh, PV isn't as compelling an investment as for people in other markets. Also realize net-metering may go away, and a "photon tax" could be implemented (in California there was an attempt to charge consumers net money for power exported to the grid, and charge for rooftop PV consumed without export.)

The best you can hope for is 5 year break-even if DIY labor is free, or as long as 20 year break even for turnkey. In the latter case, better to invest your money elsewhere.

$500/month / $0.11/kWh = 4545 kWh/month.
Assuming 6 hours effective sun (more in summer, less in winter, net metering lets you store power through accounting),
4545 kWh/month / 30 days/month / 6 hours/day = 25 kW PV system needed.
$25,000 hardware (maybe $30k)
20% efficient panels, 200 W/m^2, 126m^2 or 1360 square feet of panels.

Note that commercial or large residential panels in the 300 to 500W range are more practical. Consider also used, take-down from commercial systems, for lower prices.

Quality is important. There are several degradation mechanisms for PV panels, some related to humidity, high temperatures, and high voltage. Some arrays produce well for 20+ years, some degrade badly in 5 years. Accelerated testing (increased stress in a lab environment) is performed to evaluate them, and there is a company that publishes reports. What we see for free is only the names that faired well; anonymized regarding poor performers.

Without net metering, ordinarily GT PV would produce more than consumption at some instants in time and therefore backfeed, so zero-export with current transformers would be needed. An always-on load (like GT PV connected after the switch of a pump) might never backfeed, unless an overtemperature switch shut motor off.

Here is a 25kW system:

Finally, the start of my 25kw Ground Mount grid-tie system

@MarkSolar Would you use T-Posts to hold up the snow fence or something else? I've not really had to deal with fencing much. With the price of that, it may be worth it to just throw it up for a bit and then tear it down. I'd use the tall verticals on the high side of the ground mount to attach...

diysolarforum.com

 

[Mattb4]

... I understand back feeding and net metering, but this first system I don't plan to have generate more than I consume at any given time, so that wouldn't come into play. ...

Actually it does come into play and you will need an interconnect agreement with your utility. It does not matter if you have zero export if your system is in parallel with the grid.

 

[Hedges]

If your continuous load is crypto miners or anything else with a DC bus, then you would have the option of using SCC to convert PV to DC feeding that. Designed correctly, all PV would be used to supply the bus, but if that came up short and voltage sagged, SMPS powered by grid would take up the slack. Likely not trivial to accomplish - the SMPS I've seen that are designed for parallel operation share power by delivering current proportional to voltage droop. More easily done with a CV supply that doesn't object when output voltage is held above setpoint. If your system had a 48V intermediate bus from which DC/DC were fed, should be easier to implement than if individual AC powered PCs with SMPS supplying motherboard voltages.

 

[fatjay]

No crypto, just a small datacenter in the basement to do work.

Any suggestions on where i could buy or look at pricing for used panels from commercial systems?

In the next couple years, i anticipate that 11c/kwh increasing. I don't think that's going to be that way forever with the way things are going. Additionally, I lose power a lot, and am on backup generator for days or weeks at a time. I have a 10kw 220v backup generator wired directly into the panel with interlock. But when I'm on generator, that thing is working hard and sucking fuel. A lighter load would mean less fuel consumption and less refueling. It could also provide the grid power so the grid tie inverter functions.

 

[Hedges]

Here's a panel liquidator many people are happy with:

Solar Panels | SanTan Solar

www.santansolar.com

eBay and Craigslist will have ads from vendors like him, also installers with leftovers from jobs.

Can your datacenter run from a 48V battery? If so, you could do PV to SCC, and draw from grid only when that drops low.
An on-line UPS might also let you blend in DC as priority source.

 

[Ampster]

I just built my garage, and had the trusses engineered to take 6000lb of solar panels, but I want to start small first.

Uplift is the biggest load to be concerned about. Panels only weigh 50 lbs at the most and are 12 square feet so that is 3 or 4 lbs per square feet.

First, I'm going to build a trellis off my back porch that I want to hold 15 200w panels, 3 rows of 5, with the potential to add another 2 rows later. I want to tie it into the panel with a grid tie inverter. Then I have roof space with room for another 25 panels down the line. My question is, if there is no grid power, ie the power goes out, does the inverter shut off and stop providing power?

The cost per kW goes down for larger panels. You could do 3000 Watts with only ten 300 Watt panels or eight 400 Watt panels. The racking will cost less per panel if you go larger panels. My first system ten years ago used 270 Watt pamels and I replaced them on the same racking with 325 Watt panels and got a whole lot more production.

 

[fatjay]

I didn't think about wind getting under the panels on the garage roof. But i have hurricane ties on the trusses, trusses are 16" OC, plywood on that, then 13' steel panels ontop, the roof is 1100sq ft and I was planning on basically filling it eventually. But I wanted a smaller scale system on the back porch roof that I'll be building just to learn exactly what is involved and what I need to do.

These blemished panels are pretty cheap, $45 for 250w. Are the blemishes visual only? Or do they reduce efficiency, or shorten the life of the panel?

 

[Hedges]

Would worry about blemishes and split backsheets reducing life. Or having electrical leakage to chassis. But if you buy for $0.12 to $0.20/W, maybe that is OK.
Racking and labor is worth something too, so I preferred premium quality. Don't want to have to change pitch of array to replace in a few years.
Look at W/m^2; higher efficiency panels around 200W/m^2 will save you on everything else. compare to 140W/m^2.
Panels are getting to be a smaller portion of system cost (especially for battery backup system.)

 

[Ampster]

I didn't think about wind getting under the panels on the garage roof.

If you are pulling a permit, uplift most likely is the calculation often seen in calcs for the racking. Depth, size and spacing of fasteners we're listed in my permit application. I also needed to use the expected wind velocity in my local.