diy solar

diy solar

Off grid greenhouse

K

Knotrusty

New Member
Joined
Feb 12, 2021
Messages
15
Hello. First time posting. Just retired from the Navy and have been working on isolating my 3,000 sq ft greenhouse from the grid. Located in San Diego, CA. I have the last twelve months of power bill but that includes a well pump that won't be part of this system. Also I would like to oversize the system for future expansion. My neighbor gifted me 17 250 w panels and micro inverters. I've been watching all the videos and am comfortable using a 12/24 or 48 volt system. Having an issue with sizing the system. Here is the info over the last twelve months of power consumption with the well attached.
Avg daily kwh = 4.2
Highest peak hour 5.3
Avg Monthly 253 kwh
(again these numbers include the well 3hp pump that will not be attached to the system)
In the greenhouse I have:
1 - security camera - 24 hrs
wifi - 24 hrs
10 100 watt bulbs - 4 hrs/day winter only
6 exhaust vents .26 amps ( runs off a thermastat approx 3 hrs only on very hot days)
2 exhaust fans 5 amp ( runs off a thermastat approx 1.5 hrs only on very hot days)
That's about it. I rarely run a heater in the winter and maybe a few other lights etc to hatch chickens.
I have no space restrictions and wish to oversize the system.
Anyone out there that can help me size my system. Any solar panels I don't use for the greenhouse I will add to the solar array for the house. I think our area states 5 hours of sunlight but I think we get more. Not real worried about loss of days since it's the greenhouse.
Thanks in advance.
 
Micro inverters are normally for grid-tie. Some models e.g. newer IQ7 or later from Enphase do have the option to interact with battery inverters.

If you can connect to grid, backfeed from PV when the sun shines and draw power from grid when it doesn't, that is best.

To design off-grid, you need to estimate what power the well pump drew and subtract from total.

"Avg daily kwh = 4.2" I think you meant average daily kW. That is, 100 kWh/day divide by 24 hours per day equals 4 kW average load.

[edit] did you really mean on an average day, 4.2 kWh consumed? May not include well pump. This figure is close to my sum below.

Greenhouse, 10, 100W bulbs 4 hours/day winter.
So you're not illuminating it for growing.
Are those 100W incandescent bulbs? If so, replace with LED.
10 x 100W x 4 hours = 4kWh/day, only needed in winter.

Exhaust fans 0.26 amps. Now you're mixing amps in the watts equation. I'll assume 120V, so 30W each. 180W total, 3 hours so 550Wh/day in the summer.
Exhaust fan 5A x 120V = 600W x 1.5 hour = 900Wh x 2 units = 1800 Wh/day in summer.

1800 Wh + 550 Wh = 2500 Wh summer
4000 Wh in winter (reduce to 600 Wh by switching to LED)

WiFi, security camera, assume 50W? So 1200 Wh/day?

Now you need 3700 Wh in the summer, 1800 Wh in the winter.
5 hours effective sun in summer, 2 hours winter.
About 1000W of PV. A bit more for inverter inefficiency and idle current.
Get an inverter that has "sleep" mode, wakes up occasionally to produce AC and see if any loads present. That way only the couple hours of fan uses inverter.
Wire security system to run off 12V battery rather than A/C.

AGM battery 12V 200 Ah should be sufficient.
 
OK so the micro inverters won't be used off grid.
That's correct the 4.2 is peak kw
Switching to LED lighting is a great idea. Thank you.

So stick with 12v
4-5 250 watt panels
AGM 12v 200ah battery ( would a lithium 12v 100ah battery be comparable )
1000/12 = 83.33 amps charge controller ?
and a 2000 w inverter for expansion.

Thanks again.
 
Lithium can be used, offers more deep cycles.
AGM can last up to 10 years if shallow/infrequently cycled. Check the charts for brand you consider. Here's mine, see last page, 350 to 5000 cycles:


AGM is simple, maintenance free. Just need charger that manages it properly. FLA is cheaper and longer lasting (if quality) but needs watering and sometimes equalization.
Commercial lithium used to cost as much per amp-hour of cycle life as AGM. DIY today is less cash up front than quality AGM, at least for larger capacity system.
I choose AGM for KISS of small bank.

Yes, about 80A SCC. So long as MPPT, OK if not quite big enough, it ignores excess PV. If PV in multiple series strings (or individual panels) that are then paralleled, can aim at morning and afternoon sun, reducing peak to 0.7 as much (due to reduced area facing sun). Fewer amps but more hours, less than 60A peak.
As battery voltage rises, same watts is less current.

Pay attention to maximum allowed charge current of the battery. Some AGM (and especially gel) may want 0.05C or 0.1C. My batteries like at least 0.2C. If you have 60A into 200 Ah, that's 0.3C
You can use a bigger battery. You can use a smaller charge controller but "over paneled" so charge current remains max for longer.

Why off-grid?
Batteries cost more than grid power. Only DIY lithium is cheaper at this time. Except with those, you can't save money by using PV + batteries to either disconnect from the grid or shift time of use.

Batteries are cheaper than extending grid to a remote property.

PV is cheaper than grid.

Most cost-effective system is usually grid-tie net metering. Issue is if rules require you to switch to a disadvantageous rate schedule.
In that case, grid-tie with zero export may be better. Or off-grid with charging from grid. Less battery needed if you don't have to store for times without sunlight.
 
Thank you very much. I'll start collecting materials and get her built. I will reach back out when complete.

Your help is greatly appreciated.
 
Knotrusty said:
I'll start collecting materials and get her built. I will reach back out when complete.
Click to expand...
I strongly recommend checking back in when you select an SCC or have it narrowed down to a few models.
This is a critical piece and should be run by the group here BEFORE you actually buy (mistakes in this area are frequent and costly).
 
 
Battery is 100 Ah, so two in series gives you 24V, 100 Ah.

Look for documentation showing number of cycles lifespan vs. depth of discharge. I didn't spot it on that page.

Inverter includes PV charger. Other guys here are familiar with that brand.

Do your PV panels have microinverters hardwired? Or connected by MC cables you can disconnect? What specs for the PV panels?
Need to determine what series/parallel arrangement matches PV input of of inverter.

Select a fuse rated at least the maximum continuous current of inverter. Should have an interrupt rating (at 24V or higher) of at least 4000A, which is what battery can probably deliver. Class T is one of the best, but others are sufficient for this application.
 
Yes the micro inverters can be unplugged. The panels are rated at 29.8V and 8.39 Amps 250W. With the output voltage of 29.8 do I need to wire the panels in series ?

The battery link takes you to the 100 AH battery; But if you look under the price they have an option for the 200 AH battery. If I placed two in series that would give me 24v 200 AH.

 
Half the price of SunXtender 200 Ah 12V.

www.solar-electric.com

Sun Xtender PVX-2120L AGM Sealed Battery

Sun Xtender PVX-2120L AGM Sealed Battery
www.solar-electric.com www.solar-electric.com

Would be good to find cycle life vs. DoD. May be similar price per kWh life. Evaluate based on your planned usage. You may want 3500 cycles for 10 years life.


Inverter PV spec:
  • Max. PV Array Open Circuit voltage: 145V DC
  • PV Array MPPT voltage range: 30-115V DC
Need to get Voc spec of PV panels. That is then adjusted for record cold temperature (might increase 15%)
Probably 40V, so 3 in series for 120V nominal, 138V max on cold day fits inverter spec.
Vmp 29.8V, so 2 in series or 3 in series works.

You could wire 3s2p, for 1500W array, 3s3p for 2250W, 2s2p for 1000W, 2s3p for 1500W.
If only two strings in parallel, ns2p, no fuses required. If 3 or more in parallel, each gets a fuse.
 
Here is the data on the solar panels:

I'd like to oversize the array. You stated 3 in series. Can I use 4 or more in series ?

You've really enabled me to move this forward.
My plan is to purchase one 3000w Growatt
2 12v 200 ah Renogy AGM's wired in series.
and #____of my solar panels wired in series

Sound about right ? Thanks again!
 

Attachments

  • IMG_4675.pdf
    14.1 MB · Views: 5
Open circuit voltage 37.6V (At 25 degrees C)
3 in series would be 113V, OK with GroWatt.
4 in series would be 150V, exceeds 145V GroWatt limit even before weather gets cold.

No, can't use 4 in series. You can use 2 or 3 in series.

So 2s4p, 3s3p, etc.
You can generally add more in parallel. If some of the series strings have different orientation (e.g. one string of panels aimed at 9:00 AM sun, another at noon, another at 3:00 PM, that reduces peak current but extends hours of production, more watt-hours gathered and less or no "clipping" of maximum.

The inverter has modes to prioritize charging fro PV or from grid. If you can extend utility power to the greenhouse, that will avoid cycling batteries at night except in times of power failure. That would give longer battery life.
 
Sounds like I will start out with 3 in series. That will give us a recharge time of 3.2 hours

I have never used series and parallel together. I'll have to do more research on that.
 
OK I did a little research and I like the 3s2p array design. That will give me approx 1500 w array. 113 volts which works with the Growatt and the 2 200 AH AGM's providing 2400 w usable should manage my loads. Battery recharge rate of 1.6 hours. The growatt will also allow me to add batteries if required.
 
Knotrusty said:
OK I did a little research and I like the 3s2p array design. That will give me approx 1500 w array. 113 volts which works with the Growatt and the 2 200 AH AGM's providing 2400 w usable should manage my loads. Battery recharge rate of 1.6 hours. The growatt will also allow me to add batteries if required.
Click to expand...

1.6 hours - Charge rate of 0.6 is most likely too high for the battery. So long as you can program a lower charge current and let it take longer.
Is that 2, 6V 200 Ah AGM for 2400 Wh? if 2, 12V 200 Ah for 4800W then may be OK with SunXtender. But I set mine for about 0.2C
They're fine for delivering high current, but should charge more slowly. And have temperature probe to ensure they don't get too hot.
 
Review the GroWatt's manual, see if you can program a max battery charge rate.
That's what I did with SMA. My PV array could deliver > 0.5C, but I've set 85A charge current for my 405 Ah battery.

Probably with a hybrid, it can do that. Which is good because you can size PV array to carry loads and have small battery.
 
Thank you. I'll get into the manual and let you know what I learn about the charge rate.
 
You must log in or register to reply here.

Similar threads

C
Canada: Greenhouse Build - need review of schematics before purchasing components (please & thanks)
Replies
4
Views
197
crunchykooka
C
B
Looking to power a small hydroponic greenhouse.
2
Replies
25
Views
1K
Supervstech
Supervstech
G
Multiplus OFF / Help tweaking a few settings or diagnosing an issue
Replies
2
Views
155
gcap
G
O
Help me understand what went wrong .
Replies
11
Views
781
outboard1196
O
wattmatters
Grid Outage Stats
2 3
Replies
44
Views
2K
TK1979
TK1979
Back
Top