Deciding between Grid Power vs. Solar - Island Property

LakeHouseLiving

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Hello All,

Newly registered member, looking for some input/system information to help determine pathway for power solution on our island property.

Backstory as to how we get where we are today:
We have an island property on a lake in New Hampshire. Small 1 room cabin, nothing large or fancy. Property was built circa 1980. At that time, it was connected to grid power via underwater power cable from the neighboring island property. Approximately 5-6 years ago, the neighboring property underwent extensive renovations when it changed ownership. They upgraded all their buildings/electrical service. At that time, the municipal power company deemed that the connection line from their property to ours was no longer up to code, and disconnected our service. Seemingly, even though we were not renovating/changing anything, it wasn't grandfathered, and we've been without power since.

This brings us to the question of both cost and convenience as we decide what path to take on restoring power to the property.
As we are now fully disconnected from the grid, we can effectively consider it "off-grid".

Considerations/usage plan:
  • We typically only use the property on weekends - possibly arriving late in the day Friday, leaving Sunday afternoon/evenings.
  • Property is Spring/Summer use only, not used in cool weather/winter.
  • As its an island property, and most of the entertainment comes from enjoying the water/swimming/boating, again we typically are only on property when the weather is nice (IE: Sunny weather).
  • No TV's/DVDs/Computers
  • Music is all Bluetooth speakers connected to phones - charged offsite before coming to the property
  • Propane grill is used for all cooking
  • Propane water heater is used for hot water/showers
  • Bathroom - as we are an island property, we do not have/cannot have a normal waste system like a storage tank/leach field. We have an Incinolet Toilet, which is one of the large power draws, to incinerate the solids.
  • Our electrical needs are "basic" in my opinion if I look at our total usage/needs - see chart below
  • The property is already fully wired with breaker panel from when it was grid connected
To restore grid power to the property is likely a $35-50k prospect between permitting, underwater cable, marine services to run the cable, electrical connects, etc.
The question/concern about moving to solar power is functional space/ability to size a system suitably for usage without having to "conservatively" use the systems we need.

Basic Information regarding system installation option/details
  • Azimuth Angle of 180* (East Facing)
  • Approximate Solar Radiation (May-September) - 5.62 hours/day
  • 39.8 degree tilt for roof mounted panels
Calculations for usage expectations:
Screen Shot 2022-06-19 at 12.14.38 PM.png

First, I'll say thank you, if you made it this far.

A working refrigerator and toilet are the essentials.
Too many years of hauling coolers and ice out to the island for a weekend... time to get back to being able to put things in a fridge.
The Incinolet toilet is critical, for the simple fact we don't want to have to keep emptying marine head tanks at the end of every weekend.
Obviously those 2 items are the primary power consumers.

Questions -
Am I correct in interpreting this to indicate that we would need ~3,000W system to run what we're looking at for consumption needs?
24v battery setup, if used with an appropriate inverter, can it be connected to the 120V wiring system that is present in the cabin already?
The refrigerator spec'd above (Link) is designed for either 12v or 24v - so can the electrical system be wired to allow 24V power to the fridge, and also provide power to the 120V system?

What I'm ultimately trying to identify is, if the conversion to utilize solar is going to cost for example ~$20k between Solar system, compatible refrigerator, battery bank... and grid power "only" costs us $30k, does it make "sense" to go through the work to install the solar setup. So really I'm trying to understand what size system we need, so I can begin to price out suitable solutions.

Average monthly electrical bill at the property prior to disconnect was $35, so monthly operational cost was not a concern...

Any insight/words of wisdom/guidance is appreciated.
-Chris
 

Bluedog225

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Welcome!

Good analysis. Have a look at the SOK 48 volt 100 amp hour server rack batteries. A stack of 4 will cost you around
$7,000 for 20,000 watts or so. No offense, but solar isn’t all that great up north. But panels are cheap. 50 cents per watt or so (maybe used). Lots of cheap all in one inverter units around.

The Will Prowse videos on Utube are very good.
 

12VoltInstalls

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No offense, but solar isn’t all that great up north. But panels are cheap. 50 cents per watt or so (maybe used). Lots of cheap all in one inverter units around.
I’m in Vermont. Yes, solar at these latitudes ain’t Arizona. But it’s doable. I’m off grid and I seem to not have gotten that memo.
I'm trying to understand what size system we need, so I can begin to price out suitable solutions.
Are you going to self-install? Cuz that can save 50% or more of cost…
Am I correct in interpreting this to indicate that we would need ~3,000W system to run what we're looking at for consumption needs?
That is a reasonable wildhat guess for panels if you don’t do this:
Azimuth Angle of 180* (East Facing)
That will compromise your power input a lot.
24v battery setup, if used with an appropriate inverter, can it be connected to the 120V wiring system that is present in the cabin already?
Yes, but I might go with 12V for a number of reasons. 3000W inverter is a lot more than I’d typically want to do with 12V but you don’t look like you’ll ever get there unless the toilet cycles while microwaving a tv dinner 😆
The refrigerator spec'd above (Link) is designed for either 12v or 24v - so can the electrical system be wired to allow 24V power to the fridge, and also provide power to the 120V system?
Yes. Because the DC is a separate system
If you have all the stuff to do the toilet it will run a 120V fridge just fine and save you $500-$700

Other than microwave surge a wildhat guess is that even a 2000W inverter would meet your needs on the minimalist side, but 3000-5000W of panels and appropriate SCC will take care of you. The batteries for overnight are the big expensive part of this
 

Bluedog225

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As an aside, what do you think of the incinolet? Never occured to me to run one off solar.
 

Supervstech

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Can you perform an actual load test? Since you do not have power, I'd guess not, but a propane generator is cheap, and a killawatt gadget isn't pricy either.
Fridge can run from the bank, and if all you need is power for lights and the toilet, if the toilet is a small demand, you won't be anywhere neat 30K...
A pair of 200Ah 24v rack mounts, a 24V3000W all in one 120V inverter, 2500W of panels and you should cover those loads easy. 5 to 10K depending on install...
Now, if it were me, I would ditch the propane water heater, install a heat pump electric tank, and upgrade the system to 240V, install a pair of LV6548 inverters, and 10K solar, get 4 100Ah 48V rack mounts, and be power free in the 20K range installed...

But perform a real usage list first. Much easier to plan the right amount of need from the beginning than to upgrade when you realize it's too small.
 

Don B. Cilly

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Indeed, you can rent (beg/borrow/etc. ;·) a small generator and actually measure your consumption.
It might be less that you estimated.
My microwave, for example, has 5 settings, from low to high power. I keep it on 3, it draws some 100W.
Actually, I would buy the generator. Some 2 kW, inverter, quiet. Good investment. Rainy days and all.
Me, I would not ditch the propane heater. They're great, IMHO.

I have a 70 sqm. (750 sqft) house, computers, fridge, microwave, washing machine (I run "cold" cycles), sawing machine, electronics lab, the lot.
5kW of batteries (24V), 1 kW of panels (nominal). I hardly ever use 20% of battery power.
I don't have an electric toilet, but if you run that when solar is charging...
-
 

Don B. Cilly

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Of course, solar is better at these latitudes. So maybe a few more panels.
But still... if you learn to manage your energy - not difficult, and quite gratifying, really - something like what I have, with a couple more panels, should do.
I have two batteries (LFP, 110 Ah each, 24V) ~€2000
Four panels (two good, two so-so) ~€600
Cheap AIO inverter/charger/SCC ~€400.
Cables, breakers, distribution panel, etc. ~€400.
2kW inverter generator ~€600
-
 

LakeHouseLiving

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That will compromise your power input a lot.
Yes, very valid point on panel orientation, I did the calculations and was disappointed to see what we'd be giving up by having the panels mounted facing east, but given orientation of the building on the property, roof mounted is really our only option. The property is pretty small, and clearing any trees to achieve a Southern facing panel array would be undesirable. I have to make an effort not to make this stand out and try to make it blend in.

We have a small 2200W Honda EU generator already. I have not yet wired a generator connect to the 120V house panel that is already in place, so measuring what the property would/does consume would be a bit of a challenge right now... I have thought about trying to run the incinolet off the generator, to see if the quoted consumption from incinolet is accurate or overstated(it's right at the permissable "max" for the Honda generator). I was at the property this weekend, and used the EU2200i generator to run the saw I needed. We had talked about building a concrete box to put the generator in to utilize that for power vs. solar, but even with it around the corner of the cottage, it's just too much noise when compared to the silence/quiet that normally exists without it running. While our neighbors aren't close, noise carries easily across the water, and I need to be considerate in that respect.

I would be self installing, my father in law is a master electrician, so someone would be looking over my shoulder to at least ensure I don't burn everything down the first time we flip the switch.

The Microwave we could easily get rid of.
The Incinolet & fridge are the critical units... along with the water pump to be able to take hot showers.
I did explore a propane fridge, but the cost of annual propane bottle fill ups if we installed a larger "immobile" tank on the property would in a few years equate to the solar investment.

As for perceptions on the Incinolet, unfortunately we haven't ever used it... It's sitting wrapped up, waiting for the power solution to come to fruition.

I appreciate the kind insight and recommendations.
As evidenced by original post - being somewhat ignorant - I have approached this from the standpoint that the panels need to generate sufficient power to provide all needs, and the batteries are just there for backup/surge support. From the above, it sounds like perhaps I should look at the batteries as also part of the power solution plan....

Thanks for the guidance/insight, much appreciated.
-Chris
 

Bluedog225

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Nice you are considerate of the neighbors. Generator noise is rotten.

I‘m thinking just plug the appliances into the generator using a watt meter deal. It will tell you consumption without messing with the house panel.

You do have the advantage of it being a weekend place. A couple of big, south facing panels you put out while gone and put away when in use could top off a few server rack batteries. They would have all week to charge. Might not be an eyesore.
 

E. Cho

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Did you read the Incinolet manual?

".... Electrical Preparation -
This appliance has a 20-amp plug and is meant to fit only into a 20-amp receptacle. (Fig. 4) If the outlet you intend to use for the INCINOLET is not the proper type, then change the receptacle. You must have a circuit suitable for 20 amps, headed by a 20-amp circuit breaker. Do not
attempt to defeat this safety feature by modifying the plug in any way. Power cord is 4 feet long. Extension cords should not be used with this appliance."

Drawing shows a special 20 amp receptacle for 120 or 240 volt use.

Also, it says that a "cycle" is 75 minutes as the factory default and ... "... Power Consumption -
One complete cycle uses about 1 1/2 to 2 kilowatt hours of electricity. Because you can use INCINOLET any time during the cycle, your “per use” cost is lower."

Would a 2Kw generator handle that AND other loads at the same time? If not, timing uses would need to be set up. Does your generator and or house wiring power set up already have the 20 amp service?
 

Supervstech

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Did you read the Incinolet manual?

".... Electrical Preparation -
This appliance has a 20-amp plug and is meant to fit only into a 20-amp receptacle. (Fig. 4) If the outlet you intend to use for the INCINOLET is not the proper type, then change the receptacle. You must have a circuit suitable for 20 amps, headed by a 20-amp circuit breaker. Do not
attempt to defeat this safety feature by modifying the plug in any way. Power cord is 4 feet long. Extension cords should not be used with this appliance."

Drawing shows a special 20 amp receptacle for 120 or 240 volt use.

Also, it says that a "cycle" is 75 minutes as the factory default and ... "... Power Consumption -
One complete cycle uses about 1 1/2 to 2 kilowatt hours of electricity. Because you can use INCINOLET any time during the cycle, your “per use” cost is lower."

Would a 2Kw generator handle that AND other loads at the same time? If not, timing uses would need to be set up. Does your generator and or house wiring power set up already have the 20 amp service?
A 20A receptacle appliance usually draws 1800W, but some can draw 2200, so it’s important to know the actual demand of the appliance.
 

12VoltInstalls

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Yes, very valid point on panel orientation, I did the calculations and was disappointed to see what we'd be giving up by having the panels mounted facing east, but given orientation of the building on the property, roof mounted is really our only option.
I would maybe use two arrays- your rooftop, and figure out a way to ground-mount for southern/south western exposure. (I actually can get 40-100-ish watts from my 400W array that faces SE when sun is SW and no longer on them merely by atmospheric reflection. For reasons not clear to me I once saw ~130W from them one afternoon. These are vertical mounted panels that seldom go over 350W because of that. East sun is low power already never mind the non-optimal angle.)
I’d find some way to get that south-facing power.
 

svetz

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Welcome to the forums Chris!

  • We typically only use the property on weekends - possibly arriving late in the day Friday, leaving Sunday afternoon/evenings.
Might be an opportunity to reduce the number of panels as they could charge up a battery slowly during the week. The nice thing about shorting the solar and having more storage is you'll average better for rainy days.

Let's run some numbers and see.

  • Azimuth Angle of 180* (East Facing)
From this, New Hamshire has an insolation of about 4 with east-facing panels in May.

Energy Usage
You didn't have the total and I was too lazy to add them up, but let's say it's 8 kWh/day, just modify the equations below for the actual values. You're there for two days so you need 16 Whs total per week. But inverters aren't 100% efficient, check your inverter's actual value but we'll assume it's 90%... so you really need 16 kWh / .9 = 18 kWhs

How Many Solar Panels?
With an insolation of 4, a 90% conversion efficiency, and 86% battery charging efficiency, you need a weekly charging of:
18 kWh usage per week / 7 days per week / .86 charging efficiency / insolation 4 ~= 740W array.
Three Q CELLS 360 Watt Mono Duo Cell Black G10+ would do that for $816 (not including shipping).

Battery Chemistry
Lithium is nice, but with your usage of 2 days per week over the spring-summer, 600 cycles via lead acid would last 11 years. So, sealed AGMs are the way to go if your back can handle moving them and they won't sink the island. ;-)

Lead-acid chemistry loses a lot of power when it's cold, so if it's always cold there this might not be the way to go.

Another bad thing about Lead-acid batteries is they don't like to be left for long periods with no charge, so if you leave the lights on over winter you'd lose your investment. Possibly a timer switch to disconnect the power after 48 hour-weekend to ensure no accidents?


How Many Batteries?
You need 18 kWhs of storage, but with lead lets keep the DoD at 50%, so you'd want 36 kWhs. At $380 per battery, a 24 Concorde Sun Xtender PVX-6480T, 2V, 648AH AGM Battery would get you 48V and 24x2x648 = 31 kWh for $9120 (not including shipping). That's 48V rather than 24V, but that's a lot of storage.

The Trojan SPRE gets over a 1000 cycles with 80% DoD and sells for about $500. So, 18 / .8 = 22.5 kWh. It's a 2.4 kWh battery, so that's ~$4700 if the datasheet is to be believed. Lithium is around $300 per kWh (less if you DIY your battery), so with an 80% DoD that's only $6800. LFP at 80% will last thousands of cycles, but they'll die from calendar agining long before your use-case consumes them.

UPDATE: Just noticed the SPREs are FLAs, so probably not the best to be left unattended for long periods.

That's a worst-case scenario. Three 360W panels with an insolation of 4 will generate 4 kWh on a nice day. So, if you want to assume you always get at least 50% power (cloudy days), you could say you'd generate 4 kWh over the weekend, so you'd only need 14 kWhs storage. With that assumption, you'd want 28 kWhs of storage at 50% DoD (or 17.5 at 80%), which would drop the storage costs a couple of thousand.

Inverter
Am I correct in interpreting this to indicate that we would need ~3,000W system to run what we're looking at for consumption needs?
From your table it looks like you need a 2 kW inverter, but bumping it to a 3k won't hurt and gives you margin for error.

A lot of folks like the all-in-one inverters, basically an inverter, charger, and mppt as they're simpler and cheaper. But you could go the other way if you're looking for high quality, for example, the Victron Energy Quattro 3000W 48V Inv/Charger 120VAC would set you back $2000 (not including shipping) and you'd need to get an MPPT matching your panels.

So, probably around $7k for this approach with the Trojans.

24v battery setup, if used with an appropriate inverter, can it be connected to the 120V wiring system that is present in the cabin already?
Sure. Disconnect the undersea cable, you don't want to lose power along it if there's any short in that system.

The refrigerator spec'd above (Link) is designed for either 12v or 24v - so can the electrical system be wired to allow 24V power to the fridge, and also provide power to the 120V system?
Sure, you can even go 48V and use a 24V step-down.
 
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sparrowhawk

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Just a few words of advice from a novice. Install a larger panel array, inverter and battery bank than you think you need. It's better to have it and not need it, than to need it and not have it. :)

When I originally sized and installed my system it worked well for it's original design function but I liked it so much I wanted more out of it. I had over paneled so I took advantage of it and doubled my battery bank and after that it works fantastic. The other thing I should have done was to go larger on my inverters. Not because I need more power but because there are many times where I'm using them at close to their max rating and since they are Chinese made it's likely to shorten their life. I would feel better if I had more head room with their ratings.
 

12VoltInstalls

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have approached this from the standpoint that the panels need to generate sufficient power to provide all needs, and the batteries are just there for backup/surge support. From the above, it sounds like perhaps I should look at the batteries as also part of the power solution plan....
Yes, batteries will make it better.
Solar @ time of demand isn’t always friendly.

What did you think of the Svetz plan? I thought it was pretty good. I might do a couple things differently.

I’m not a fan of AGM from what I’ve seen. I avoid them like the plague. YMMV
The Trojans are a good fla option but I’d be inclined to utilize LiFePo and leave them disconnected at 75% charged for the winter.
Install a larger panel array, inverter and battery bank
Since you know or will know your demand you can probably be secure with a battery calculation imho. Same with inverter.
Panels, however, I would do a few more somehow. Either four or probably six of them imho. This will be better later in your season.

The thing with lithium is if you stick with the smaller panel array they can recharge over several days with no harm. Lead acid batteries do not like to linger partly charged and are best to be recharged in half a day or less. The only weekend use gives them ample time to get to 100% over several days. I’d again be inclined to utilize 12V for the reasons I mentioned- but not only does that not ‘compute’ for everyone (maybe you) but also conducting 12V from the shed to the house may introduce enough voltage drop to make it undesirable.

The svetz plan is a good framework to either use directly or swap in other properly rated components as you wish and recall the math.

One thought I had is if you can find 25-cents/W used or surplus panels like some have sourced you conceivably could cover the entire shed roof. Actual harvest specs would stink because of sub-optimal placement but they’d do something
 

Rednecktek

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One thought I had is if you can find 25-cents/W used or surplus panels like some have sourced you conceivably could cover the entire shed roof. Actual harvest specs would stink because of sub-optimal placement but they’d do something
Maybe I missed it, but why only and east facing array? Is the building a single slope roof ALA lean-to or a pitched roof ALA regular house? Is there any reason you couldn't do an east AND a west array?

Lithium is nice, but with your usage of 2 days per week over the spring-summer, 600 cycles via lead acid would last 11 years. So, sealed AGMs are the way to go if your back can handle moving them and they won't sink the island. ;-)
I actually need to disagree with this one and argue in favor of LFP's for this project (Don't look so shocked, I'm chemistry-curious! 😝 ) and I say that because of 2 things:

1:
Property is Spring/Summer use only, not used in cool weather/winter.
There shouldn't be much worry about Charging in sub-freezing weather so that solves the cold-charging issues.

2:
At $380 per battery, a 24 Concorde Sun Xtender PVX-6480T, 2V, 648AH AGM Battery would get you 48V and 24x2x648 = 31 kWh for $9120
So 31Kwh for $9,120 to last him 3 days by the math in the Power Audit posted. That's 1300Ah of battery by your math. Ouch! Is the island big enough for that? :) Even making a 24v array out of those (12x cells @ 2v = 24v) would be $4560 for 320 usable Ah = 7680Wh or less than a single day with the microwave, just even without it, $9300 for 2 days. I think one of us is missing something in our math.

LFP's of the PowerQueen/Chins/Ampertime variety for a 24v 200Ah battery are about $1800ea for 2400Wh, or $9000 for 2 days. That's about the same money BUT only involves 10 cells (batteries) and a LOT less wiring connecting everything up. Physical space should be significantly less as well.

The Power Audit above, including the microwave, calls for 450Ah/day of battery, so 2 days would be 900Ah, rounding up to an even 1000Ah is 5 of the 200Ah variety batteries, assuming no power generation. You've got the Honda so you should always have at least enough to recharge the batteries, but 2 days is a healthy guess.

End result, AGM's and LFP's are pretty neck-and-neck for $/usable watt, but the LFP's will be easier to wire up, have a longer lifespan, take up less space, and will hold their charge a LOT better when you shut down and leave.
 
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svetz

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Setting the John to Burn on Wednesday
Just a thought, but can the incinerator run in batch mode, possibly on a timer? Perhaps run it on Saturday and then on Wednesday? If so, it decreases your weekend power needs a lot, reducing the cost of storage.

Even making a 24v array out of those (12x cells @ 2v = 24v) would be $4560 for 320 usable Ah = 7680Wh or less than a single day with the microwave, just even without it, $9300 for 2 days. I think one of us is missing something in our math.
As the original post says, 24 2V cells with 648 AH each is 24 x 2 x 648 = 31 kWh. At $380, 24 batteries is ~$9k. So, that math checks out, but it obviously not the full 36 kWh (I just went with the first 2V battery I saw to try to get a single bank).

The SPREs mentioned are half that, but FLAs. I know FLAs are better, but I've heard they're fiddly even with a water-kit (no personal experience with them).

LFP's of the PowerQueen/Chins/Ampertime variety for a 24v 200Ah battery are about $1800ea for 2400Wh, or $9000 for 2 days.
Let's see...From their energy usage, they need 18 kWh. At 80% DoD that's: 18 / .8 = 22.5 kWh.

At 24V 200 AH is 4.8 kWhs at $1800. 22.5 / 4.8 = ~5 batteries, at $1800 each that's $9000, so that does seem a better deal as LFP have less power losses overall and are fairly maintenance-free with higher efficiencies (although charging even once at sub-freezing can be the end of them, but a temperature cutoff can solve that).

Although now I'm thinking about it, with his use case he could probably go 100% DoD with LFP, lowering the price to four batteries or $7200. So, good idea!
 
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