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Going off-grid questions

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JoergK.

New Member
Joined
Nov 5, 2022
Messages
21
Location
Vauxhall, Alberta, Canada
Hello,

I live in Alberta and have sufficient PV production to generate my yearly usage.

Here my details:

2010 House and farm shop that uses ~30,000 kWh/year, 2,800 kWh/month winter purchased, 1,200 kWh/month summer purchase - 208VAC 3ph, 200 Amp main panel
2011 Irrigation pump & pivot using 3,300 kWh/month May to September - 480 VAC 3ph, 100 Amp main panels.

Each system has 20 kWh PV panels with micro inverters. Both systems are within 100m (330').

My annual production is 10% higher than my usage and I can shuffle between the two services. So far, so good, but I am paying still CAD6,000 for distribution & Transmission. This is CAD60,000 over 10 years and it probably goes higher rather than going down.

Could I build sufficient storage to bundle all DC energy together and go to two inverters delivering 208VAC and 480VAC when I need it?

Dumb thought? Or possible task?

Cheers, JoergK.
 
No matter how many panels you have and how much storage you have (within reason), you will eventually run out of storage. What happens then?
In Vauxhall Alberta, your winter power generation is a little better than ⅓ of your summer generation. Summing your irrigation and non-irrigation, you're still seasonally out of balance. So even with "enough" battery capacity to get your through storms and such, your seasonal imbalance already dictates a need for more than 10% margin. Using PVWatts your 40kW of panels will generate about 20kWh in December (assuming a 45° tilt). That's a 40% shortfall. Even with essentially infinite storage you will need to increase the system by 16kW. But you can't buy infinite storage, so you will need even more than that unless you are willing to run a generator to make up the difference (or remain grid-tied).

Sizing an off-grid system is much harder than sizing a grid-tied one. You have to decide how much generator time you are willing to accept and how to balance costs between batteries and panels.

And that irrigation pump is going to be a real challenge. From the stats, it's presumably a multi-HP pump. The starting surge is going to be a real killer for an inverter.
 
Irrigation pump is 480v 3ph can be powered by VFD that can be fed directly from DC solar array. Adjusting motor speed will inherently adjust panel maximum power point and the whole thing can be turned into MPPT with a micro controller. No need for batteries. Irrigation pump energy and power demand coincides with optimal seasonal solar production.
 
AntronX said:
Irrigation pump is 480v 3ph can be powered by VFD that can be fed directly from DC solar array. Adjusting motor speed will inherently adjust panel maximum power point and the whole thing can be turned into MPPT with a micro controller. No need for batteries. Irrigation pump energy and power demand coincides with optimal seasonal solar production.
Click to expand...
This approach will isolate those panels from the system that powers his house and charges his batteries, necessitating manual switching if he wants to benefit from them
 
Hello again,

I didn't have much time this week to answer.

My winter production is round 1/2 of summer, but when I take the irrigation on to the yard, I produce in winter month what I need. My production is 23% higher than my usage, after going over all numbers more accurate then before.

I entered this in to a DC to AC converter and it gave me this for the Pivot at max. output volume and 40 psi at the pump. The VFD shows a draw of 34 Amps when I lower the pressure to 34 psi, but then my irrigation volume per acres is lower.

AC Voltage480VAC
AC Amperage40Amps AC
Wattage19200Watts
DC Voltage 48 V
DC Amperage441.60 Amps DCPer hour

My yard main panel has EKM metering and the Amps run normally below 60, just a few spikes up to 80amps and I suspect that this is the air compressor and lathe, both with 8hp without VFD and I am going to change both to VFD's anyway. The DC to AC converter gave me this:

AC Voltage208VAC
AC Amperage60Amps AC
Wattage24960Watts
DC Voltage 48 V
DC Amperage574.08 Amps DCPer hour
​
If I take ten 12VDC deep cycle batteries with 300Ah for CAD1300 each, I have 3000 Ah for CAD13000.

I feel the eye of the needle would be avoiding spikes and trying to get a stable 'average' usage', one thing we normally with a grid connection don't think about.

I guess I see this all to easy.

So, please be gentle with me, I am just trying.

Cheers, JoergK.
 
Those are big loads, but having the pumping only during good solar time of year, and then the benefit of both arrays to just run the house for the off season seems like an efficient set up.
I don't recommend anything but LiFePO4 (Lithium-Iron-Phosphate) these days, since useable watt-hours cost is clearly lower than Lead-Acid. (remember you can only use 40-50% of the L-A energy, while LFP you can use 80-90%.
The one thing to consider is the temperature in the room the batteries will be stored - you need possitive temps (above 0 Celsius) for charging and best for discharging too. {LFP like the temps people like}

Not sure if you run twin utility meters or not or if AB has Time of Use rates (ToU): in my set up, with the house and business side by side on two lots, I was able to ditch the Commerical meter off the shop, altogether, and keep the lower cost residential meter on the house next door.
Like your set up, My shop runs all year on solar, and the house benefits from the 'excess' solar from mid Jan - late October each year.
I bite the bullet and pay utility rates for Late Oct-Nov-Dec-early Jan each year for the house, but by building a large ESS, I only use off-peak power at the lowest cost per kWh, and the house runs off batteries during on-peak ToU all winter.
 
@AntronX 'What brand/model is your VFD?' Lenze ESV303-4T- it serves the pivot pressure with one set-point and the yard sprinkler systems with two other set-points.

Our meters are by-directional. no ToU.

Batteries can be located indoors, does the room need special ventilation?

We probably change over top geothermal this summer. I finally found a driller that does installed, finished wells with 1" loops for CAD15/ft. A big difference to the CAD60 for only drilling from several years ago, just a a site comment.

Back to the off grid thoughts, what type of inverters would one use then?

Run all users over 10 amp then directly with DC from the battery bank to VFD's? All VFD's I looked at are AC 3ph input.
 
Yard Meter:
RRO Energy @.224610/kWh $587.74
Energy Generation Credit $116.12
Admin $8.00
Transmission $152.52
Small Capacity Distribution $154.76
Operation Round Up $0.72
AMI Ride $3.50

Irrigation Meter (no Small Capacity Distribution for Nov. to April, double for May to October )
RRO Energy @.224610/kWh $4.04
Energy Generation Credit $267.51
Transmission $1.05

$0.224610/kWh is just for the power and I didn't contract my power since I produce more in 12 month then I buy, so it benefits me. I could lock five years in for $0.0944/kWh for five years.
 
Ok, in that case stay grid tied the way you have it now. To avoid drawing power from the grid you can install power limiter controller for your VFD that will automatically reduce motor power when there is not enough sun to power your pump completely from solar. You can also add more grid tie solar to your pump solar system which would be cheapest option compared to batteries. Panels are really cheap now.
 
Yes AntronX, this would mean turning the irrigation off at night or during low sunshine activity, correct. This would not be an option.

Remember, I would have over 10 years about CAD60,000 to invest from not having to pay for the T&D. If the system works longer then 10 years I am well ahead and it should.

Our province de-regulated the energy sector about 20 years ago. At the moment premier had a good idea, but didn't see the ingenuity of the sector to split all entities (generation, transmission and distribution) up and make money where ever they can outside the actual kWh price.

All other Canadian provinces & territories still operate as crow organizations where you pay one price for power plus a general account fee. I have been pushing for probably 15 years to be able to lock all three parts in for five years with no avail.
 
It's a noble idea, but I don't think you would be happy off-grid with that large of loads, unless you had a really good backup generator. $60,000 sounds like a lot, but that's not all that much for battery capacity. Do consider that they have a lifetime too, so it's not a one and done purchase.

Keep doing the calculations, and see if batteries get cheaper. If you are going for it, at least make sure you go in eyes wide open. Maybe there is a middle ground?

Good luck with whichever road you take!
 
​
If I take ten 12VDC deep cycle batteries with 300Ah for CAD1300 each, I have 3000 Ah for CAD13000
Click to expand...

Just a quick math check on this. 300 amp hours at 12v is not the same as 300 amp hours at 48v. In your $13,000 CAD example, that is only 3,000 amp hours x 12 volts or 36,000 total watts. Now consider around a 50% max draw for lead-acid and you are down to 18,000 watts. There may be cheaper lithium options in that range.

Consider lead acid doesn't last very long.

Consider that if you don't have time to tinker, this could be a major headache for you.

Not trying to talk you out of anything. Just making sure to present the reality of a very large draw setup like you have. It would require inverters that can handle the draw if you are no longer grid tied to take the surges. It's really a huge operation. Not like a simple residential setup at all.
 
Lead-Acid allow max 40- 50% depth of discharge, and maybe three to five years of cycling.
LFP allow 80-90% depth of discharge and 10+ years of cycling.
 
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