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

live4soccer7

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Ok. I have been wanting to do this for years now since I have moved into my current location which I will be until I physically can't be here anymore. I have some things planned.

Location: Spokane, WA 99022 (Eastern WA)

I am still deciding on a source for panels and exactly which panel I would like, but I have been working on some of the details and will begin pulling the trigger on purchases before long.

I would like any input/advice as this will be my first time installing and working with solar.

My area is quite open as far as sun and potential blockages with that only happening early in the morning and late in the evening. I will be going with a string inverter setup.

I'll probably go with the SMA Sunny Boy Inverters. I can currently get them for about $1360 for the 7.7kw configuration. I will need 4 of these. I am open to alternative inverters if anyone has input. I will run two strings into each inverter (I believe the can accept 3 different strings). I did some calculations based on a 320w panel with temperature taken into consideration and it had an optimal string size of 9-11 panels.

Is it best to be on the upper end of that spectrum if the physical configuration allows? I would think that as the panels age then the voltage would drop a little bit, so being on the upper end would probably be better. Doing stings of 10-11 depending on the requirements.

Ideally, I would like a ground mount system that I could have two tilts for a summer and winter tilt. Anyone that has a ground mount system, have you found this to be worth it? There is quite a swing in the sun's location where I am between winter and summer, so I would think that this could increase output by a decent amount by just changing it for summer and winter months.

I am considering the UniRac GFT racking system. Based on their building application online it should be about $6k for the ground mount infrastructure plus installation. I can rent an augur to set the posts and pour concrete. I'd imagine that will probably run about $1500 with concrete. I suppose, I could look into getting a post driver attachment for the skidsteer and that would save concrete and maybe cheaper and easier if I don't run into rock. Again, I am open to suggestions on the racking system. I know iron ridge is popular, but I talked to a local solar dealer and they said the pipe is unbelievable expensive right now for the main support. I'm not sure that the UniRac GFT system is meant to "tilt" after installation and setup. I'm kind of thinking no. GFT (Ground Fixed Tilt). This system is what my local rep referred me to and said it is getting a lot of good feedback. I'm not sure I want to go with something home made on this as it would take a lot of time and I don't quite know what the local permitting will need for my county.

On to the Panels. This is where I get hung up. I can get panels from bluesunpv (china supplier) for about $11k and also get the wiring and MC4 connectors for an additional $1400. They are 455W panels (57-58 panels), which would mean I could get away with a smaller ground mount configuration and save some money there as well (about $1500). Otherwise I can go with something available locally around the 320W range Hanwha Q-Cell G5 315W for about $14k (80 panels). I'm kind of at a loss on panel selection due to pricing. I can make the calculations etc.... That isn't a problem.

Component location logistics - I would think that it would be best to have the inverters closer to the grid tie meter as opposed to closer to the panels. The array will be roughly 300 feet away from the meter. I can get the inverters within about 40' or so of the meter for my ideal location. I suppose I could get them closer, but if not necessary then I'd like to keep them at that 40' location. Is my thinking correct on this?

Array Orientation - I have attached a photo to show where I want to put the array. Location information:
Height:741mSet Lat/Lon
Lat:N 47°33'0.61''47.55017°
Lng:W 117°38'58.49''-117.64958°
UTM:11T 451125 5266510
TZ: America/Los_Angeles DST PDT

The field as you go east has a gradual incline and then there is a larger hill across the road. II plan to have a shop in the eastern portion of the field and I believe it won't shad the panels at all or for too long in the morning due to the hill that is further east anyways that I can not control. The big building to the south does not block the sun in the winter. Only do the buildings to the west block the sun in the very end of the evening. I think I have picked the ideal location given these things. Again, open to suggestions.

My next question is the orientation of the actual array. Everyone always says to point your panels south, which is exactly perpendicular to the driveway. Is there a more scientific way to calculate this based on my actual lat and long? Same goes for the optimal tilt on the panels if I were to only use a single angle all year.

solar.PNG


Incentives: 26% Federal Tax Credit and WA Sales tax exemption on solar components/installation/systems

I did just find this information:
To optimize overall production year-round, tilt your panels at your latitude. To lean toward more production in the summer, tilt your panels at your latitude minus 10-15°. To lean toward more production in the winter, tilt your panels at your latitude plus 10-15°.
 
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MPRanger

Beefield, GA 30461
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Awesome introduction and description! Thank you. Rainy cloudy Washington. SEvGeorgia here and I wonder if my 6KW rooftop out performs you in some instances. Going to double 6 to 12 soon. We here are legally limited to 10. Residential customers can’t push more than 10 back on the grid, commercial agriculture can push 20. Do you have such limits?
 

Supervstech

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Awesome introduction and description! Thank you. Rainy cloudy Washington. SEvGeorgia here and I wonder if my 6KW rooftop out performs you in some instances. Going to double 6 to 12 soon. We here are legally limited to 10. Residential customers can’t push more than 10 back on the grid, commercial agriculture can push 20. Do you have such limits?
Nah, eastern WA isn’t like Seattle, the mountains shield most of the rain west. I lived there in the 70’s and miss it dearly… had a huge place in Cheney… our house had an old windmill to pull water from the aquifer, and the guy meant came out to test flow limits, and with 80HP couldn’t get any drop in level… they approved our use of the meltwater… couldn’t imagine running off solar at the depths they needed, I recall it was around 800’? Not sure… we also had a creek flowing through the place… man it was beautiful…
 

live4soccer7

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Awesome introduction and description! Thank you. Rainy cloudy Washington. SEvGeorgia here and I wonder if my 6KW rooftop out performs you in some instances. Going to double 6 to 12 soon. We here are legally limited to 10. Residential customers can’t push more than 10 back on the grid, commercial agriculture can push 20. Do you have such limits?

I'm in eastern washington. It is quite a bit different than western washington. Not even close to as much rain and clouds. I just spoke with a local installer and I'm not even limited to 25kw if our transformer that feeds the house can handle more. It feeds two homes, so I should actually be able to build an even larger system. I'm going to have our power company out and install the grid tie meter and I'll have them tell me what the transformer is as well. If I can build larger and afford to do it now then I will do that.
 

live4soccer7

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Nah, eastern WA isn’t like Seattle, the mountains shield most of the rain west. I lived there in the 70’s and miss it dearly… had a huge place in Cheney… our house had an old windmill to pull water from the aquifer, and the guy meant came out to test flow limits, and with 80HP couldn’t get any drop in level… they approved our use of the meltwater… couldn’t imagine running off solar at the depths they needed, I recall it was around 800’? Not sure… we also had a creek flowing through the place… man it was beautiful…
That's really cool! I'm over near Medical Lake area, so very close.
 

wattmatters

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My next question is the orientation of the actual array. Everyone always says to point your panels south, which is exactly perpendicular to the driveway. Is there a more scientific way to calculate this based on my actual lat and long? Same goes for the optimal tilt on the panels if I were to only use a single angle all year.
There are various sites to help estimate production from a solar PV system, e.g.:

If I were constructing a ground mount array with option to align them in any way I wanted then I would be wanting to know what sort of power production profile I can best take advantage of.

Generating the most total energy doesn't mean the energy is generated when you need it most.

This is where splitting the orientation of the array can be helpful - some east, some south, some west (or a variation such as SE + SW) and you can adjust the number of panels in each azimuth depending on the power output profile you prefer for the day.

Splitting the array directions means the total output will be lower but the output curve for the day will be wider and provide more power at the start and end of the day. e.g. my NW array has about an hour's lag behind my NE array (I'm southern hemisphere hence north orientation). So the NE brings power up earlier and NW supplies power later. Mine is roof mount so I just take the space that's available and it's 3/4 NE and 1/4 NW but if I had my preference I'd flip that the other way as here late day production is more useful for summertime cooling.

Similar principle for the tilt of arrays. The tilt for highest overall production may not provide the best seasonal profile of energy output for your needs. Optimising tilt for Winter output will cost you Summer output but it will reduce the output differential between seasons. Obviously having the ability to tilt an array between seasons provides best of both worlds but comes with construction challenges. It needs to be very secure.

Have a play with PVwatts and put in a range of array tilt and azimuth options to see both the overall impact of production by month but also look at the simulated hourly production for a typical weather year.
 

live4soccer7

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There are various sites to help estimate production from a solar PV system, e.g.:

If I were constructing a ground mount array with option to align them in any way I wanted then I would be wanting to know what sort of power production profile I can best take advantage of.

Generating the most total energy doesn't mean the energy is generated when you need it most.

This is where splitting the orientation of the array can be helpful - some east, some south, some west (or a variation such as SE + SW) and you can adjust the number of panels in each azimuth depending on the power output profile you prefer for the day.

Splitting the array directions means the total output will be lower but the output curve for the day will be wider and provide more power at the start and end of the day. e.g. my NW array has about an hour's lag behind my NE array (I'm southern hemisphere hence north orientation). So the NE brings power up earlier and NW supplies power later. Mine is roof mount so I just take the space that's available and it's 3/4 NE and 1/4 NW but if I had my preference I'd flip that the other way as here late day production is more useful for summertime cooling.

Similar principle for the tilt of arrays. The tilt for highest overall production may not provide the best seasonal profile of energy output for your needs. Optimising tilt for Winter output will cost you Summer output but it will reduce the output differential between seasons. Obviously having the ability to tilt an array between seasons provides best of both worlds but comes with construction challenges. It needs to be very secure.

Have a play with PVwatts and put in a range of array tilt and azimuth options to see both the overall impact of production by month but also look at the simulated hourly production for a typical weather year.
I appreciate the reply and will definitely take a look at PVwatts. Since it is grid tied, I don't think it really matters what time of day the power is generated and the most generated power overall is what would be important. Please correct me if I'm wrong.
 

wattmatters

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I appreciate the reply and will definitely take a look at PVwatts. Since it is grid tied, I don't think it really matters what time of day the power is generated and the most generated power overall is what would be important. Please correct me if I'm wrong.
Assuming you have no restriction on the power you are permitted to feed back to the grid, that's correct.

Here in Australia there are limits on how much power may be fed back to the grid. e.g. I have a 3kW per phase limit, so my system (3-phase) is limited to a maximum export of 9kW. If required my system will throttle production to remain within export limits. Split azimuth arrays reduce the chance of peak production being curtailed due to export limits as they flatten out the production curve across the day.

The other consideration is the tariff structure where you live.

If your export and import tariffs per kWh are about the same then it doesn't matter, the grid effectively acts like a big financial battery, you get feed in credits in the daytime and you draw back on those credits at night time. And bills are pretty much in proportion to your import-export energy balance.

But where we are the grid feed in tariff is considerably lower than the grid import tariff, so it is far more valuable to self consume solar PV (and hence replace imports) than it is to export the energy. The tariff ratio is about 2.5 to 1. This is when having a wider spread of energy production over the course of a day is more useful as it reduces grid imports, increases self consumption and results in better financial outcomes even though the total energy production is lower. Put another way, we need to export 2.5kWh to cover for 1kWh of import costs.

So it very much depends on individual circumstances for each household.
 

live4soccer7

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My current known cap to feed the grid is 25kw. If the transformer that feeds my neighbor's house and mine can allow more then I can build a larger system.
 

live4soccer7

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No tarrifs really. If I over produce then I get credited toward the next month and it just keeps rolling. Once a year my credits will reset. The name of the game is to simply produce as much power as possible and when it it produced does not matter.
 

Hedges

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I have a similar plan, but at the time had a choice and selected time-of-use. Power Noon to 6:00 PM was valued higher and I made sure I was a net exporter. Now, time of use is mandatory, and peak is 4:00 PM to 9:00 PM so more difficult to get more kWh in credit than what I produce.

You can over-panel your inverters to about 150% of rated wattage by having multiple PV strings with different orientations. That brings peak production down to what the inverter can handle, but extends hours of operation.

Get yourself two or four Sunny Islands (check eBay and Craigslist) to make a grid-backup system. With four, they can pass through 26 kW. If only two you would only put half your PV on them, the others straight on grid. (if 100% off grid, two Sunny Island could manage all of them; internal relay is the limit.)

Panels - check out SanTan Solar. Limited quantities of new warrantied panels, large quantities of used panels.
Probably worthwhile to get the more efficient panels that produce closer to 200W/m^2.

 

live4soccer7

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I have a similar plan, but at the time had a choice and selected time-of-use. Power Noon to 6:00 PM was valued higher and I made sure I was a net exporter. Now, time of use is mandatory, and peak is 4:00 PM to 9:00 PM so more difficult to get more kWh in credit than what I produce.

You can over-panel your inverters to about 150% of rated wattage by having multiple PV strings with different orientations. That brings peak production down to what the inverter can handle, but extends hours of operation.

Get yourself two or four Sunny Islands (check eBay and Craigslist) to make a grid-backup system. With four, they can pass through 26 kW. If only two you would only put half your PV on them, the others straight on grid. (if 100% off grid, two Sunny Island could manage all of them; internal relay is the limit.)

Panels - check out SanTan Solar. Limited quantities of new warrantied panels, large quantities of used panels.
Probably worthwhile to get the more efficient panels that produce closer to 200W/m^2.

Any recommendations on brand? I currently won't be using any kind of battery backup, but would like to keep that option open for down the road.

I can get the Q-CELL Hanwha 315W panels for $150USD each here locally from a company.
I've also been quoted from BlueSUNPV for their 455W Panel at about $180. I'm just not sure how I feel about bluesun solar. I have confirmed with them that they make TALESUN panels, which is the "brand" they use for resale/distributors. The bluesun panels are definitely the more economical way to go, but they have some not so great reviews on facebook and a lot of the good ones seem like they could be fake.

I'm also considering going with the fronius controller now as I have about a 350 foot run for each array/string back to the inverter and the Fronius allows a higher string voltage, so I might be able to use less strings and will have less inverters as well. Fronius makes up to 15.5k and Sunny boy has a max of 7.7k. If I can settle on some items, I'm actually thinking of going larger, more like 30-45kw.
 
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MPRanger

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Will uses, as do I, the Sense monitor I believe. This is a great tool for planning based on your needs and time of day sources.
 

live4soccer7

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Will uses, as do I, the Sense monitor I believe. This is a great tool for planning based on your needs and time of day sources.
With the way my grid tie works, time of day is irrelevant. I know how much power I use and it will not go down. With the federal solar incentive and WA's sale tax exemption for solar, it is wisest IMO to go as large as I can afford and am allowed to by the utility company. I'll use the power. If not all of it in the first year or two, I will increase my consumption as well as the years come.
 

live4soccer7

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I just got the go ahead from the Utility company to design whatever sized system I want (above 25kw). The individual I spoke with said he didn't see an issue with going larger in my scenario. I'll have to submit an application once I get details figured out for them to approve it.
 

Hedges

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Any recommendations on brand? I currently won't be using any kind of battery backup, but would like to keep that option open for down the road.

I bought SunPower (E20, not P17 series) after searching the topic. No one questioned their quality, only whether worth the premium.

Various panels have different degradation modes. Backsheets that fall apart are a visible one. Tedlar is a premium backsheet, possibly some others are good.

"Potential Induced Degradation" occurs with some (P-type vs. N-type) silicon panels if negative grounded so all cells higher voltage than grounded frame, other type if positive grounded. Some panels are supposed to be highly resistant, others degrade more rapidly (when dust and water make an electrode across glass surface.) SunPower discovered this when their panels were negative grounded so used a model of SMA inverter which allowed selection of negative or positive grounding. Their newer panels are supposed to be highly resistant. My plan for the future is to positive ground Sunpower, negative ground others.

Most newer inverters including Sunny Boy 7.7 are transformerless, so half the panels will be above ground and half below ground. At least that means half as much voltage. But make sure to select panels highly resistant to "PID"

 
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