Off Grid System Staged Upgrade ??

[Gord Greer]

Hi Rob and all, thanks for letting me join your forum. I've been spending many enjoyable hours reading and learning from the many interesting threads here.

I'm starting to plan / engineer a major solar upgrade (in stages), to an off grid cottage for a close friend. The cottage is co-owned by three people, I'm just a close friend who spends many wonderful hours on Lake Ontario and helping out with the technical stuff as no one else has any technical ability.

History / background:
The cottage is a two storey 3 bedroom (more like a home) on lake Ontario owner built in the 70's. It is mostly passive solar design, large south facing windows with large amount of interior stone mass, rarely goes below freezing in the winter. It has always been off grid as running in power would currently be in the $80K range and its mostly only used in the summer, although with the current mild winters it's used on some weekends. Driveway access in about 1.6km, difficult to walk in if you can't drive.
Heating is wood stove with propane for the stove/oven, hot water, fridge and BBQ. Electrical is 24vdc, two PV panels & battery bank. Lights are 24vdc LED's with a 24vdc servo motor running a double acting piston pump for water, both running directly off the batteries. The only 120vac supply is a 300 watt 12vdc inverter running off 1/2 the battery bank and is moved every so often to different cells to avoid unbalance, I know this is not ideal. The 120vac supplies the on demand hot water heater, cell phone charging and a radio. Everything currently works fine for the current cottage use.
Details of current equipment are shown at the end.

Why is an upgrade planned:

The batteries are getting to the end of their life and will have to be replaced in the next few years. Propane is a problem as delivery is not an option due to access. So we have 4 - 100lbs tanks, a manifold regulator system runs 3 tanks for the house and one for backup when we take the 3 tanks into town to be refilled. Problem is we are all over 65yrs and lugging the tanks into town for filling is not something we want to do in the future. Also the fridge is acting up and may need to be replaced soon, so would like to go electric 120vac off a new inverter. This would reduce the amount of propane used and also let us run a vacuum once in a while.

Options looking for input:

A) Staged to spread out the cost as 2 or 3 owners don't want to spend money
- Add 4 more PV panels, 24vdc 3500 watt inverter, & fridge 120vac
- Use the existing batteries till next upgrade, probably LiOn when the price is a little cheaper, 24vdc bank. Continue to run pump and lights directly off batteries.
- Use any excess power in the winter to run a dump load directly off the charge controller to a water tank with dc elements, keeping the battery room warm and maybe the cottage above freezing.
- I'm tending towards this option right now, but I have flip flopped several times.

B) Expensive all at once batteries and etc. etc.
- In this scenario my initial thought is a 48vdc bank would be the desired choice but many current LiOn banks BMS don't like 48 volts. Also this would require the pump and LED lights to all change, probably to 120vac.
- This determines the inverter choice 24 or 48 volts, don't want to change it again later.

Current System:

- PV array: 2 - Canadian Solar CS6P-260P currently wired parallel, want to change to series
Pmax 260 W, Vmp 30.4V, Imp 8.56A
Voc 37.5V, Isc 9.12A
- Charge Controller: Outback Power Flex 60
- Batteries: 12 - Gould 2V telephone backup approx 25 yrs old
I think they are FCT-25, 180AH and about 250lbs ea.
- Water heater: On demand propane direct vent Eccotemp i12 120vac
- Water pump: 24Vdc servo motor
- Lights: 24Vdc LED's
- Backup generator: Honda 2500W basic contractor

Staged Upgrade, my current thoughts, subject to change:

- Add 4 PV panels, two parallel strings of 3 in series, (2 new with 1 exist)
voltage wouldn't be a problem, but need to match the current so the existing panel does not drag down the string too much, not sure which one of your Hanwha or LG panels would be a good match. Otherwise adding another charge controller increases the cost.
- Add inverter, Outback Power VFXR3524
- Add OutBack Mate3 for programming, hopefully wouldn't need a hub, just swap between Flex60 controller and VFXR inverter, probably leave hooked to inverter most time.
- Add Fridge: 28 inch 14 cubic ft, Energyguide 336Kwh per year

The above should easily handle the current load but would like to run the inverter on search mode to reduce the 30 watts it normally draws on idle. On search I believe the fridge would have to be a mechanical thermostat as electronic circuits, relays & defrost cycles would get all messed up on intermittent power.

Sorry for the long first post, but as we are in lockdown again I have too much time to think and plan these things. Looking for brainstorming ideas from those of you who have been there done that. In the long term it can get expensive if you start down the wrong path and have to change course and equipment later.
thanks for any input you can provide
Gord

[Rob Beckers]

Hi Gord,

You mention the current system is set up as 24V, with two 60-cell panels in parallel. I don't know if the batteries are lead-acid or another chemistry (Nickel-Cadmium was popular for telephone backups systems, and they lasted nearly forever), but for lead-acid it takes 72 solar cells in series to get the Voltage high enough to reliably charge a 24V bank. With 60 cells, on a hot day the panel Voltage is just a bit too low to fully charge the batteries, on a cold (battery) day the batteries need a higher Voltage than the panels can provide. That's why 12V battery charging panels have 36 cells in them, and run at about 18 Volt (at 25 Centigrade), the head-room is needed since flooded lead-acid requires around 15 Volt for absorb, and nearly 16 volt to equalize them. That goes up for cold batteries, while solar Voltage goes down when panels get warm.

Anyway, just wanted to mention that. Since you got 25 years out of them it worked out for you! I got to run now, will get back with more later!

-RoB-

[Gord Greer]

Hi Rob,
Thanks for taking a look at this situation.

Yes they are lead acid batteries, picture below. Short story is one owner got 16 of these, used, for just hauling them away. No one else would take it on as they weigh close to 300 lbs ea. The original system was 32 volts (16 - 2v cells) with a wind generator, no controls and no dump load. So the batteries were not treated well in their early life, at the time no one knew how to care for them, before my time.

https://www.greenpowertalk.org/attachment.php?attachmentid=1464&stc=1&d=1617467900

Over the years they lost a few batteries, I think one froze and a couple had a cracked case probably damage from the original move. When I met the owners a battery had just leaked, took out alot of the pine floor and a couple of joists. We had to assemble an engine hoist in the room to get the batteries off the rack, rebuild the floor and joists. Note we had a SS pan made for under the rack to prevent damage from a future failure.

So at this point it is 24 volts (12 - 2v cells) and I agree the two panels parallel aren't really enough which is why I planned to change them to series and let the Flex - 60 charge controller deal with it. My thinking is that would also help with harvesting a little more power in the early morning and late afternoon. Will do that this spring, now I can get up on the second storey roof. Also planning to modify the Unistrut mounts so they can be around 30 deg summer and maybe 80 deg in winter. This year they were snow covered for weeks at a time and not safe to try and clean them in winter.

The more I read on the various threads here, in particular your experience 6yrs ago with the 8Kw PV and the Surrette battery problems. The more I think long term the owners will need a LiOn bank system, as none of them have any technical knowledge nor are they interested, just flip the switch and have it work.

I see the most urgent problem as battery charging and as they only have PV for that, I'm urging they buy an inverter/charger now which can be fed from the Honda 2500W generator for top ups as needed. Their original charger is an old farm charger 36V brute force from the 50 - 60's, only useful as a boat anchor now.

I'm reading you like the MagnaSine inverters, good bang for the buck, I'm leaning that way also. They cheaper than the OutBacks and programmers are cheaper. My original thought was Outback because the CC is a Fex-60 and I could use the same programmer for both, but the Mate3 is over $600 itself.

Gotta go for now, finishing up new laundry room renovation for a friend, LED lights today, then done.

Gord

[Rob Beckers]

Hi Gord,

Flooded lead-acid batteries can work well, but I've over the years changed my mind on the "off-grid living is nearly the same as being on the grid" thing. People living off-grid need to be much more aware where energy is going, and with lead-acid batteries they need to stay on top of their state. It's easy to correct a little sulphating when you catch it early on, it's near impossible if it's left to fester over a winter and you get to spring with batteries that suddenly are only half-capacity at best. Some take to this naturally, some are such Luddites that they can't or won't wrap their head around it (mostly an attitude thing IMO). The latter are much better off living on the grid, so others take care of their energy needs, or possibly with lithium-ion batteries, though that too comes with its own potential for issues.

Anyway, back to your story...
The fridge you mention would likely clock in around 1 kWh/day (the yellow tags "lie" a little, and over time fridges get less efficient), and an inverter would use up 0.5 kWh/day to keep it running. Those would be your largest energy users. The rest is no much right now (going by what you describe), but people have a tendency to add more over time. So, a rough number would be 2.5 - 4 kWh/day as a reasonable number.

Every kW of solar PV facing south, at a reasonable tilt-angle, without shade, would produce around 2.66 kWh per average between spring and fall in our general area. That puts your solar PV needs at 950 - 1500 Watt for spring-through-fall use (panels will do half that in winter, if you can keep the snow off and put them at a steep angle).

In current 345 Watt-or-so panels that translates to 3 - 5 panels (roughly). Adding 4 more panels to the existing 2 sounds like a reasonable plane. The existing 60A charge controller can handle the total just fine, with some occasional clipping (assuming a 24V battery bank).

You can add any higher-Wattage 60-cell panel to the existing two 60-cell panels in series. The net-effect is that the new panel will be limited to the current of the existing panels, so you loose a little. You can combine that string with any other string of 3 panels that are 60-cell, they all run at just about the same Voltage regardless of brand/Wattage.

How well this works with your existing batteries after you add a larger load (fridge) is a bit of a guess. The batteries have to be able to get the system through the night, and possibly through some cloudy days. Having more solar PV helps, but it's not the entire story if there's little battery capacity to store the energy, or get you through the dark times. If it was for winter as well I would suggest looking harder at replacing batteries, in this case you might be OK for spring-through-fall. Not many very dark days in that time.

Regarding lithium-ion batteries and winter: If the cottage is not used I would suggest either taking the batteries away (less chance of theft) or making it so there are no loads, everything is shut down. Lithium-ion batteries won't charge below freezing, the BMS won't let you, and in case of deep discharges (snow on panels) the BMS will switch the battery off. That likely means it will stay off until someone comes around in spring to "jump start" it, so you might as well plan for shutting things down in fall.

-RoB-

[Gord Greer]

Hi Rob,

Yes I have definitely come to the same conclusion that lead acid battery banks are not plug and play, or just flip the switch. They do require diligent monitoring / tracking records and manual ongoing intervention to avoid their easy ruination. So I will be pushing hard for a LiOn battery bank solution, but hopefully that can be put off for a year maybe two, time will tell.

I agree the addition of 4 - 60 cell panels should provide enough Kwh's, as long as they don't think they can now plug in anything they want. I was hoping the inverter could run in search mode to reduce consumption but not counting on that as the fridge may not like it, certainly not if it has electronic controls. Would try to find one that has electro - mechanical controls.

I had a look at the panel watts and connections for the old and new combinations. Total individual watts at normal operating 800W/m2 would be 1410W of course that would require the 4 new panels be on a separate string with another new CC. Using the existing Flex-60 with two strings my first thought was they should be balanced, ie 1 old & 2 new in each string, which would yield 1262W, reduced due to old panel current limit. Then looked at 2 old & 1 new, in parallel with 3 new, the old sting is a little lower voltage and thus the limit, but total comes out a little higher at 1296W. So I think I have a handle on that and it uses the current Charge Controller to its fullest, any additional future panels would have their own CC.
spreadsheet attached with calculations.

The busy times are July thru mid Sept where the fridge would be running continuously with occasional water pump and LEDs. During this time when not inhabited all AC (except fridge) and DC loads are shut off. This avoids the disaster of a leak and pumping 5,000 gals of cistern water onto the floor in the second floor bathroom. Stuff happens, twice in last 8yrs, hot water tank and then pressure tank. Luckily we were having lunch in the kitchen when both events happened, so could quickly react.

In the winter its the occasional weekend with just the water pump and LED's. The fridge becomes an old fashioned ice box with ice from the lake or we just use the entrance airlock which stays in the 40's F range.

With respect to inverters do you favor the MagnaSine's for this type of application. I thought your MS4024-U or would there be any pro or con for the MS4024PAE 120/240, although I don't see any 240V split phase loads in the future. Also for programming would the ME RC50 handle everything we would need.

Thanks again Rob for your helpful insights into the design of this little project.

Gord