First post. building a hybrid system.

Dforster67

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Found the forum through Ampster on another solar forum. This one seems a little more active.

I’ve been mulling over building a system for years. Finally ordered my panels and most my equipment from renvu, it’s showing up a little at a time. I’ve installed my critical loads panel and have it all working with a 30 amp temp breaker for now. Working on trenching running wires, ground mounting 14 380w panels comes next.
Plan to buy or build a lithium battery for backup at some point.

I’ve setup off grid hobby systems before so have a little experience. I’m sure I’ll have questions as I go.
Thanks!
 

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Dzl

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Welcome to the forum!
 

Dforster67

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Well the skybox install is coming along good. I turned it on about a week or so ago after I finally got the last of my mounting hardware from renvu (what a mess they are).
Anyway, I’ve got my 5.3 kw of panels producing on the skybox using a no export mode until I hopefully get an agreement going with the POCo. I am wasting a lot of production because I can’t sell or charge batteries yet. Still waiting on my cells. I imagine I should be producing 30kwh/day but am only able to consume about 6-7kwh. Am happy to report though that I can produce and use up to 5.33kw with my 5.3kw of panels and 5kw inverter. Was surprised the skybox allowed me to use more than 5kw.
I have room for 2 more panels. I was only planning on 14 to max out the skybox. But i don’t want to waste the space on the racking (was a lot of work for those 3 posts)!! And panels are cheap. It would give me more morning and evening and cloudy production while likely clipping off some mid day.

Here’s a few pics of the install
 

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Hedges

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I see your array depends on bending strength of the uprights. Which is OK if they are strong enough.
Triangles (trusses) would be much stronger.

If you can control loads to be enabled when there is surplus power, that would let you use more power prior to net metering, but also work better for battery operation when grid is down.

PV is cheap (especially used/surplus), plan to add more.

I started with pole mounts, then added legs and made large arrays.
 

Dforster67

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I see your array depends on bending strength of the uprights. Which is OK if they are strong enough.
Triangles (trusses) would be much stronger.

If you can control loads to be enabled when there is surplus power, that would let you use more power prior to net metering, but also work better for battery operation when grid is down.

PV is cheap (especially used/surplus), plan to add more.

I started with pole mounts, then added legs and made large
I see your array depends on bending strength of the uprights. Which is OK if they are strong enough.
Triangles (trusses) would be much stronger.

If you can control loads to be enabled when there is surplus power, that would let you use more power prior to net metering, but also work better for battery operation when grid is down.

PV is cheap (especially used/surplus), plan to add more.

I started with pole mounts, then added legs and made large arrays.
hopefully these pre engineered unirac systems are strong enough. I followed the install requirements and then some. I used about twice as much concrete and rebar as they spec.
Definitely will be adding at least 2 more panels. And with 1 more bay I could add another 8 for about $200 in extra racking. I would ac couple that array.
Sometimes I turn on the heater during the day to use up some excess energy, but that’s not very practical long term. I’ve thought about storing hot or cold water to use later on for heating and cooling. But is that kind of setup even any cheaper than a few kWh of diy battery banks?? Probably not. Just waiting on the cells is the only issue now.
 

Hedges

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Should be good for the wind loading according to their engineering.
Didn't realize Unirac had a design with their own posts. Mine used pipes.
The sloped portions could be extended to double size but would need additional footings to support them.

I like multiple orientations of panels. That reduces peak production, provides more hours. Same electronics handles more kWh, better matches consumption, less cycling of batteries.

Water is cheaper than lithium, but equipment is needed to handle it. I just calculated that 80 gallons of water heated from 50F to 160F would take 13kWh. Of course in winter when you want heat there will be less PV production. I think DIY LiFePO4 battery of that capacity would cost $2000. Cost per gallon of a tank should go down as capacity goes up, at least if not pressurized.

Maybe my math was off - this calculator says 21 kWh


Cold can be stored in chilled water or ice. Efficiency of refrigeration system is reduced making 0 degrees C vs. the air conditioning temperature you want. Water is easy to transfer heat out of, but once turned to ice that insulates the tubes and reduces rate of heat transfer.
 

Dforster67

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Yeah they do have their own posts. 13’ long C piles. It is a turnkey mounting solution. A lot of work to install. When I ordered them I figured I’d just hand dig a 12” post hole and set them in 3’ of concrete. Nope! Either have to be pounded 6’ down with a pile driver or set in 6’ deep 24” piers or a combination of footing and 12” deep piers. Or something close to that.
I’ve thought about chilling water and using hot water for heat. Hot water heaters are cheap. But then I’d need to integrate a coil into my hvac, etc. maybe someday.
 

Hedges

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Yeah they do have their own posts. 13’ long C piles. It is a turnkey mounting solution. A lot of work to install. When I ordered them I figured I’d just hand dig a 12” post hole and set them in 3’ of concrete. Nope! Either have to be pounded 6’ down with a pile driver or set in 6’ deep 24” piers or a combination of footing and 12” deep piers. Or something close to that.
I’ve thought about chilling water and using hot water for heat. Hot water heaters are cheap. But then I’d need to integrate a coil into my hvac, etc. maybe someday.

That's the thing about pole mounts.
I got three mounts for 8 (120W) panels. That was to feed one 2500W inverter 18 years ago.
It was supposed to use a 6" pipe in a large concrete footing.

I had existing concrete, so welded a bracket I could bolt for the base and clamped other pipes at angles, something of a teepee.

Later after installing a Unirac ULA mount (all 2" pipes), I extended the pole mounts with more uprights and rails similar to the ULA.
Some were also bolted to the concrete, others were over dirt so I drove 2" pipes in 30". Each array is twice as long and twice as wide as originally.
Not perfect and some settling, but it has served for over 15 years.

I think your hand-dug postholes would serve to support extensions.

I have net metering so I store energy in the accounting of the utility bill.
Time of use rates have changed to where 4:00 PM to 9:00 PM is now peak (instead of Noon to 6:00 PM), not as great deal.
I added some panels facing West, but storing heat to use late afternoon would help. Maybe a hot-water tank with fins and fan?
Time-shifting cooling is more difficult.

Add-ons to the refrigerant plumbing of an A/C and heat pump would ideally let us store heat or cold for later use.
 

GXMnow

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The 4pm to 9pm peak time of use rate is a bit of a pain, but it does help justify buying some battery.
 

Dforster67

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That's the thing about pole mounts.
I got three mounts for 8 (120W) panels. That was to feed one 2500W inverter 18 years ago.
It was supposed to use a 6" pipe in a large concrete footing.

I had existing concrete, so welded a bracket I could bolt for the base and clamped other pipes at angles, something of a teepee.

Later after installing a Unirac ULA mount (all 2" pipes), I extended the pole mounts with more uprights and rails similar to the ULA.
Some were also bolted to the concrete, others were over dirt so I drove 2" pipes in 30". Each array is twice as long and twice as wide as originally.
Not perfect and some settling, but it has served for over 15 years.

I think your hand-dug postholes would serve to support extensions.

I have net metering so I store energy in the accounting of the utility bill.
Time of use rates have changed to where 4:00 PM to 9:00 PM is now peak (instead of Noon to 6:00 PM), not as great deal.
I added some panels facing West, but storing heat to use late afternoon would help. Maybe a hot-water tank with fins and fan?
Time-shifting cooling is more difficult.

Add-ons to the refrigerant plumbing of an A/C and heat pump would ideally let us store heat or cold for later use.
We do have net metering available. I just haven’t signed up for it yet. I am working with the poco engineer now. They seem to have gotten more friendly to solar. We don’t have any variable rates. Our rates are fairly cheap around 12 cents. But will only have about $5k in my setup after tax credits. Not counting batteries. So payback will be around 5 years I think.
I’ll look into mounting the next array facing East I think. Or maybe do a tracking system to help with morning and evening loads. Those seem to be higher for us.
 

Hedges

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I think you will find that trackers cost more $$ per extra kWh produced than just adding more panels.
Multiple strings of different orientations paralleled on a single MPPT deliver about 2% less than on their own MPPT.

If your rates don't vary with time of day, and if you get credit equal to what you pay, that is a 100% efficient battery.
You may have a fixed monthly fee for it.

Our time of use rates have changed. There is a request to charge us something like $10/month/kW peak of PV. Also to credit us wholesale $0.04 while charging us retail $0.40/kWh (or some similar prices).

$5k is around what I figure it would cost me to put in 5kW of grid tie today. About $0.50/watt for panels and inverter, $1.00/watt with electrical and mounting included. What I put in 17 years ago cost me $8.00/watt up front and received $4.00/watt rebate.
Today, I estimate GT PV at $0.05/kWh amortized over 10 years, or $0.03/kWh amortized over 20 years and assuming one inverter replacement. But maybe only 20% of inverters fail outside the warranty period in that time if of high quality.
 

Dforster67

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I think you will find that trackers cost more $$ per extra kWh produced than just adding more panels.
Multiple strings of different orientations paralleled on a single MPPT deliver about 2% less than on their own MPPT.

If your rates don't vary with time of day, and if you get credit equal to what you pay, that is a 100% efficient battery.
You may have a fixed monthly fee for it.

Our time of use rates have changed. There is a request to charge us something like $10/month/kW peak of PV. Also to credit us wholesale $0.04 while charging us retail $0.40/kWh (or some similar prices).

$5k is around what I figure it would cost me to put in 5kW of grid tie today. About $0.50/watt for panels and inverter, $1.00/watt with electrical and mounting included. What I put in 17 years ago cost me $8.00/watt up front and received $4.00/watt rebate.
Today, I estimate GT PV at $0.05/kWh amortized over 10 years, or $0.03/kWh amortized over 20 years and assuming one inverter replacement. But maybe only 20% of inverters fail outside the warranty period in that time if of high quality.
Yeah tracking systems are pricey. I’d probably design my own. They look simple but probably aren’t!
Another drawback of our net metering plans is that our credits expire month to month. And they don’t pay us for our over production. It would be nice to set up something that would defer the excess production at the end of the month to some of that other storage we’ve been discussing, heat or cool water or batteries, etc.
 

Hedges

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Monthly true-up, not annual like mine. Bummer you can't save electric credits for winter heating. But still a better deal than buying a battery.

Commercial trackers are mostly single-axis. That wouldn't be so hard to build. But having East-West rotation and suitable tilt south for your latitude requires more structure plus counterweights, and the panels have to be spread apart. Unless you have a South facing slope.

I thought about trackers initially (when PV panels cost 20x as much). I did fixed orientation toward 2:00 PM sun to maximize value of power produced. Now I'm doing additional due West for peak rates, and extra South East facing panels to backfeed more Wh within the peak W limit (3 KWh in the morning pays for 1 kWh used late afternoon, but PV panels are far cheaper than utility rates.)
 

Dforster67

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Monthly true-up, not annual like mine. Bummer you can't save electric credits for winter heating. But still a better deal than buying a battery.

Commercial trackers are mostly single-axis. That wouldn't be so hard to build. But having East-West rotation and suitable tilt south for your latitude requires more structure plus counterweights, and the panels have to be spread apart. Unless you have a South facing slope.

I thought about trackers initially (when PV panels cost 20x as much). I did fixed orientation toward 2:00 PM sun to maximize value of power produced. Now I'm doing additional due West for peak rates, and extra South East facing panels to backfeed more Wh within the peak W limit (3 KWh in the morning pays for 1 kWh used late afternoon, but PV panels are far cheaper than utility rates.)
So in the winter we use very little electric. Maybe less than 10-20kwh/day, because I heat with wood and geothermal and also have propane floor heat, which expensive and temporary until I figure out a way to heat my floor with solar or geo.

Anyway, I did start using the net metering. It is working well so far, i'm pretty far ahead of them producing about 20-30kwh/day and only using about 15kwh because its nice out and no heat or cooling required. Still have to figure out the insurance thing or the Poco will likely cut me off. My state farm agent can't figure out how to add the Poco on as an additional insured.

I also have a smaller 5kwh lifepo4 battery bank getting ready to setup. That will give us a days or half a day's backup in case of outage.

I'll let this 5.3kw system ride for a while and see where we are mid summer. Then I may look at adding that AC coupled array. I could easily add about 3kw of ac coupled array to my shop roof which faces slightly west of south. That would take care of a lot of afternoon/evening AC use.

Goal is to eventually drop the grid as batteries come down more and I prove to the family that it is doable! It costs me $456/year just to be connected to this darn Coop here, even if I buy zero energy from them. That would finance a some nice battery banks over 10 years.
 

Dforster67

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Well I installed the battery pack. BMS seemed to be bad (other post about that), so I just set the inverter to net metering with backup and hooked the battery directly up to the inverter w/o a BMS for now, until I get a replacement. I did take some advice and turn down the absorb voltage on the inverter to keep the cells well below any voltage limits, just until I get a working BMS. With these settings the battery stays undercharged and the net metering/backup setting will not use the battery much at all, only during power outages. Hopefully this is safe w/o a BMS for the time being. I did let them charge up to 100% (54v) and rechecked all cells and they were all the same at 3.33.

Also added my final two panels, have a total of 16 now. Had planned on 14 but I had room on the racks for 16 and it would have been a shame to just cut off the extra racking. Even though I am 1kw over my inverter capacity, it will allow more production in mornings and evenings and cloudy days. although it may clip off some production. For basically another $300 it was worth it I think.

I do have some questions PoCo related. When I login it is still showing I am using 11kwh a day a couple days and nothing shows up for a couple other days, and I am not using anything since May1 when they installed the net meter according to the inverter, I have produced more than I've used. In fact the meter reads less than 0, it rolled backwards to 99,984 or something like that. I guess I'll see my billed usage at the end of the month.



bms.jpg
 

Batronca

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Looking good,My brother will buy a skybox next month and I will Install with him. I may need your help .I already have 29.2 kWh battery and 20 PV 315w
 

Dforster67

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Feb 2, 2021
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Looking good,My brother will buy a skybox next month and I will Install with him. I may need your help .I already have 29.2 kWh battery and 20 PV 315w

Be happy to help. I have limited experience but have setup my skybox with a ground mount 6kw array pretty much by myself. Of course I did have the help of forum members here and over at Outback. The hardest part of my whole install was the ground mount system. I used unirac C pile and would not use those again.
 

Batronca

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Thanks, I don’t have a big land as you have, so I do a root top, I did all in one inverter last year, 5.5 kw with 20kwh battery, it working good. I don’t know much at outback skybox. I may have some question to set up to play with it.
the advantage of a skybox is you can build a big battery bank
 
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