Solar in an Off Grid Cabin in Maine

Speedunlimited · January 2016

I am new to this forum and certainly would like any advice/input from the rest of you.

My electrical needs would be:

Well pump

110V Atwood 20 Gal Hot Water Heater

Refrigator

LED Lights

Desktop Computer etc.

65in LED TV and associated Direct TV attachments

Wood Stove for heat with a blower

I am new to solar but I plan on this year finishing up a log cabin in Maine. To run power to the cabin would cost approximately 7k so I believe solar is the way to go. Most of my power consumption should be in the evenings. I have a 6250 generator as a backup if needed or to top off the batteries if needed as well.

From doing my research I have come up with a system which I believe will satisfy my current electrical power needs and will allow for some expansion if needed in the future however there are some questions that I do have. So for now here is the basic setup:

8 – 250Watt Poly Panels wired for 48V (KYOCERA or Canadian Solar) (Recommendations?) mounted on the ground (approximately 50ft run to house)?

DC Disconnect between panels and combiner box (Recommendations?)

From the combiner box go into an MPPT controller (Flexmax 80 AMP or MidNite Classic 250V-63Amp)

Into another DC Disconnect before it goes into 8 AGM Mighty Max 12V 200AH battery bank wired serial/parallel for 48V.

Into another DC Disconnect before going into a Magnum MS4448PAE 120/240 Volt Off Grid Inverter 60 Amp Charger. Out of the inverter into AC Disconnect before going into the 100 amp service panel.

At this point I’m not exactly sure of the wire sizes throughout the system before the service panel?

Can I use a 48V battery charger?

What type of DC and AC Disconnects/fuses should I use?

What I have mapped out looks right or am I missing something?

So I guess this is a good place to start.

softdown · January 2016

I'm not a solar consultant though I have three initial thoughts:
1) $7000 for grid electricity is very cheap. If the power company offer reliable, quality service....this option would likely save you plenty.
2) Heating your water with solar is generally not a good plan.
3) If you go with solar, would recommend a few more panels. Closer to 3 Kw.

Raj174 · January 2016

Speedunlimited,
I totally agree with softdown, grid power for 7000 dollars is the way to go if money is a concern. Also more reliable and less work and trouble. However if you want to do off grid, you will need to know which well pump, how much power it uses and for how long each day and then get an average. Do this for all the equipment and devices you want to power. It is difficult to size the system without it. The closer the estimate the better.
But a rough guess based on your list you might require 3000 watts of PV panels, 500 AH battery bank with your stated inverter and charge controller, costing over 10,000 dollars. It is close enough for a comparison with the grid connection option. By the way, grid power is about 10 time cheaper than battery based solar.

vtmaps · January 2016

Speedunlimited said:
Well pump
Refrigerator
110V Atwood 20 Gal Hot Water Heater
<snip>
Desktop Computer etc.
65in LED TV and associated Direct TV attachments
<snip>
From the combiner box go into an MPPT controller (Flexmax 80 AMP or MidNite Classic 250V-63Amp)

Into another DC Disconnect before it goes into 8 AGM Mighty Max 12V 200AH battery bank wired serial/parallel for 48V.

Welcome to the forum,

As per Softdown and Raj174, $7,000 for grid is a very good deal.

If you insist on being off grid, use a laptop (not desktop) computer. Do some research on the DirectTV... I seem to remember someone writing that it uses a lot of power and if you power it down it takes a long time to reprogram itself. Use propane for heating water.

Midnite makes some great controllers, but you should be using a Midnite Classic 150, not the Classic 250.

Why AGM batteries? Under most circumstances you will be better off with flooded lead acid batteries, especially as a first system. Always avoid parallel batteries, especially with AGM batteries. It is easier to avoid parallel batteries if you use flooded LA batteries because they come in larger sizes (per cell).

It's a bit premature to discuss fuses and wiring... you need to do more research on your electrical loads, and find ways to minimize them.

One more thing... the well pump. That may be a defining load for your system. That means you are designing the system around the needs of one large load. I have seen many systems that were double the size they would otherwise be, because of a well pump. It may be worthwhile to research ultra-efficient well pumps with low startup surges. They cost more, but if it lets you cut the system size in half, it may be worthwhile. If not for the pump, could you get by on 120 volts? If so, look into an 120 volt Outback inverter... they have low tare losses. My Outback 3500 watt inverter uses only 20 watts just being turned on... it doesn't sound like much (and for a big inverter it is not much), but that's as much energy per day (480 watthours) as my refrigerator uses!

In Maine, you will need a generator. Since you have one, use it to keep your system size down. If I wanted to be able to run a vacuum cleaner or table saw for an hour on batteries, I would have to more than double my battery bank. Doubling my battery bank means doubling my solar array (to be able to charge a larger bank). I would rather run the generator for an hour per week than double my system size.

--vtMaps

edit: by the way, look into Midnite's ePanels, they come designed for the inverter and controller of your choice and have all the breakers, busses, shunts, disconnects, bypasses, etc. that you will need.

softdown · January 2016

People like to say that off grid power costs "10 times" more. That should not be true. But I will attest that it costs at least twice as much...assuming you did everything right of course. People have paid exorbitant amount for installers to make an off grid system.....so there is that possibility.

I might say that off grid power costs 3-4 times more than grid power. IT is exciting. Good for some, not for others.

Then you have the possibility of a solar flare or an EMP pulse knocking out the grid. The solar flare threat is likely underestimated. Will off grid solar resist a solar flare? Who knows. Opinions vary greatly. How can we possibly know?

I am a believer in being prepared. I also realize that it is ridiculously expensive to be prepared for most threats. Every generation has thought it was the final generation.

ramloui · January 2016

Just to put things in perspective, my off grid system for my cabin is about half the size of what you are planning and it cost me about 8000$.

Going off grid means you are your own utility company and you are responsible for all maintenance and repairs. Mind you, there is a lot of "fun" to be had doing this yourself but it is not for everyone.

oil pan 4 · January 2016

Since I lived in maine for about 5 years total I know what its like. You better over panel and get a good backup generator. There was one year I remember it was over cast for 17 days straight. The sun would peak out from the clouds minutes before it set and some of the nights were clear almost as if to tease you.

Do not heat water with PV power, its the ultimate waste.

Unless you are on top of a mountain or on the shore of a lake then you should really think about putting the panels up high so trees don't block the panels during the winter, the sun is very low in the winter and sun hang time is very short, nights very long.

Low sun, over cast, I would try wiring the panels for the highest voltage the MPPT charge controller could handle. Normally, anywhere else I would wire for close to battery voltage for highest efficiency while the sun is up, but not in maine.

If you think you need 8 panels, go with 10 or 12. Or buy lots of generator gas.

vtmaps · January 2016

oil pan 4 said:
Low sun, over cast, I would try wiring the panels for the highest voltage the MPPT charge controller could handle. Normally, anywhere else I would wire for close to battery voltage for highest efficiency while the sun is up, but not in maine.

Why do you think that a higher string voltage would work better in low sun or overcast conditions?

--vtMaps

oil pan 4 · January 2016

In the hopes of at least getting some power to the batteries when the panels are covered with ice with over cast skys.

vtmaps · January 2016

vtmaps said:
Why do you think that a higher string voltage would work better in low sun or overcast conditions?

oil pan 4 said:

In the hopes of at least getting some power to the batteries when the panels are covered with ice with over cast skies.

Higher string voltage will not help. If there is enough sun to get any power at all, the panel voltage will be the same at all illumination levels.

--vtMaps

Speedunlimited · January 2016

vtmaps... why do you say Midnite Classic 150, not the Classic 250... and maybe more panels would certainly help...

BB. · January 2016

In general, the higher working voltage, the lower output current.

80 to 90 amps typical for 150 vdc max

60 amps to battery typical for 250 vdc panel max voltage.

High array voltage if you have very long cable run to the array, or higher Vmp panel voltages.

-Bill

softdown · January 2016

This is almost too easy: 4 more panels = 3000watts. We all agree that is pretty good power.

Each panel has ~50VoC
Three panels per series = 150 VoC
Four series for ~3000 watts

MidNite 150 is perfect for the cold weather of Maine due to VoC tolerance.

Well....looks like it could be done this way. Folks may recommend two panels in a series. Would need to spend more for the combiner box.

vtmaps · January 2016

Speedunlimited said:

vtmaps... why do you say Midnite Classic 150, not the Classic 250... and maybe more panels would certainly help...

The Classic controllers are more efficient with lower input voltages... quite a bit. With a 48 volt battery, the Classic 150 can handle 5022 watts with an input voltage of 70 volts, but only 4438 watts with a 110 volt input. With 200 volts into a Classic 250 you are down to 3095 watts. The Classic 250 is great for a 72 volt battery... it's the ratio of input to output voltage that is important. The last thing you ever want to do is run 200 volts into a Classic 250 that is on a 12 volt system... 835 watts maximum.

Let's put some meaning to this. Low efficiency means heat production. The maximum power that a Classic can handle is limited by the heat it produces. When you operate a Classic at its limits, it is on the verge of melting... it will limit its output to prevent damaging itself. Robin Gudgel (cofounder of Midnite and Outback) has written on the Midnite forum that he would not design a system to run at its limits for hours on end... it will shorten the life of the controller. The further you are from the limits, the better. That's good conservative design practice.

In the OP you mentioned that you were considering a Flexmax 80 or a Classic 250. If the Flexmax can handle your input voltage, then so can the Midnite. In fact, the Flexmax will be damaged by voltage over 150, whereas the Classic 150 will stop producing power above 150, but will not be damaged by voltages up to 198 (on a 48 volt system).

--vtMaps

peakbagger · January 2016

If you want a frustrating hobby to drain money out of your bank account go off grid, otherwise write the check to the utility. Most folks buy a cabin to enjoy other hobbies. The only rational for off grid is a SHTF scenario.

softdown · January 2016

When I was designing my system I received several warnings about creating a "black hole in the universe" if I did serial connections with three panels with a VoC of 45. Was told that Hyper VoC could easily be hit on a very cold morning before the sun was strong enough to turn the FM80 on...which would draw down the voltage. Was told, on the Outback forum, that Hyper VoC would be highest before the sun even rose. That would be the time that my FM80 would go interstellar.

1) My FM80 is fast asleep when it is dark.
2) I have never seen a voltage reading over 84 using two panels. That would be 126 volts using three panels. Nowhere close to the 150 volts to create a hole in the universe.

However.....though the warnings would appear to have been misplaced, the result has been satisfactory. I believe that charging a 48 volt bank at 80-84 volts is pretty close to optimal. Significantly more efficient than charging at 120-126 volts?

vtmaps said:

Speedunlimited said:

vtmaps... why do you say Midnite Classic 150, not the Classic 250... and maybe more panels would certainly help...

The Classic controllers are more efficient with lower input voltages... quite a bit. With a 48 volt battery, the Classic 150 can handle 5022 watts with an input voltage of 70 volts, but only 4438 watts with a 110 volt input. With 200 volts into a Classic 250 you are down to 3095 watts. The Classic 250 is great for a 72 volt battery... it's the ratio of input to output voltage that is important. The last thing you ever want to do is run 200 volts into a Classic 250 that is on a 12 volt system... 835 watts maximum.

Let's put some meaning to this. Low efficiency means heat production. The maximum power that a Classic can handle is limited by the heat it produces. When you operate a Classic at its limits, it is on the verge of melting... it will limit its output to prevent damaging itself. Robin Gudgel (cofounder of Midnite and Outback) has written on the Midnite forum that he would not design a system to run at its limits for hours on end... it will shorten the life of the controller. The further you are from the limits, the better. That's good conservative design practice.

In the OP you mentioned that you were considering a Flexmax 80 or a Classic 250. If the Flexmax can handle your input voltage, then so can the Midnite. In fact, the Flexmax will be damaged by voltage over 150, whereas the Classic 150 will stop producing power above 150, but will not be damaged by voltages up to 198 (on a 48 volt system).

--vtMaps

softdown · January 2016

Different strokes for different folks. Off grid solar is a challenge and it is exciting. Was 56 when I got my present system operational. Now I am 57. Frustrating at times.....yes. What worthwhile endeavor is not occasionally frustrating? I love my dogs and often tell them that I have the "best dogs in the valley". I also say "you can't have nice things when you have energetic dogs,"

Everything is a trade-off. Off-grid costs more. It takes a lot of time to do it right by yourself. It takes a lot more money to have somebody else do it right. Panels are cheap now. If we can get the battery problem solved, then off-grid solar will smell like roses.

If the grid goes down, we will probably still have power. That is worth a significant amount. Solar flares may strike ~3 times/century and effect the electrical grid. A Carrington Event (circa ~1860) could knock us back to the Dark Ages for a long time. We are 100% dependent on a grid that has possibly increased in delicacy due to technological evolution. i.e. - I can wipe out most of my high tech items by looking at them cross eyed.

We are also in the midst of increasing global tensions. Russia and North Korea have the technology, and possibly, the motivation to knock out our grid. I don't think Russia would do it. Since we keep poking and prodding N Korea, while talking about taking it out, the possibility of a strike, or counter strike, does exist.

Having said that......$7,000 for a grid tie is dirt cheap. Think it would have cost me over $50,000.

peakbagger said:

If you want a frustrating hobby to drain money out of your bank account go off grid, otherwise write the check to the utility. Most folks buy a cabin to enjoy other hobbies. The only rational for off grid is a SHTF scenario.

vtmaps · January 2016

softdown said:
When I was designing my system I received several warnings about creating a "black hole in the universe" if I did serial connections with three panels with a VoC of 45. Was told that Hyper VoC could easily be hit on a very cold morning before the sun was strong enough to turn the FM80 on...which would draw down the voltage. Was told, on the Outback forum, that Hyper VoC would be highest before the sun even rose. That would be the time that my FM80 would go interstellar.

1) My FM80 is fast asleep when it is dark.
2) I have never seen a voltage reading over 84 using two panels. That would be 126 volts using three panels. Nowhere close to the 150 volts to create a hole in the universe.

However.....though the warnings would appear to have been misplaced, the result has been satisfactory. I believe that charging a 48 volt bank at 80-84 volts is pretty close to optimal. Significantly more efficient than charging at 120-126 volts?

The term "HyperVoc" was introduced by Midnite to describe a feature of their controllers... the ability to exceed (within limits) their maximum working voltage. Outback controllers do not have "hyperVoc".

If your Voc at standard temperature is 45 and you put three panels in series on an Outback controller, you are very likely to damage the controller in cold weather. And yes, as you were told on the Outback forum, the damage will be done early in the morning while the controller is asleep.

--vtMaps

Mountain Don · January 2016

With three serially connected panels having a rated Voc of 36.1 our system has recorded a peak voltage of 141. So uber high voltages do occur in the real world.

mike95490 · January 2016

My generator is down for a bad mounting bolt ! Days of rain in the forecast ! Got a temp fix in place till the real hardware store opens up Monday. Hard to see,but the nut started to strip the threads, letting the engine wobble more, messing up more threads
Then there is the battery maintenance, replacement, fussing over the gear, all the stuff you would pay the electric company for, YOU get to do. When my inverter fails, it may take me 3 days to get a new one, do I buy a $4000 spare to have sitting here ?
http://tinyurl.com/LMR-Lister

Image: https://us.v-cdn.net/6024911/uploads/editor/bt/3yhomnt8oehl.jpg

softdown · January 2016

Spare genset? I've carried a number back and forth to the repair shop. Having a "$400" spare is likely wise.

Speedunlimited · January 2016

Well after reading the above comments I have upped the panels to 12... and I'm not sure if the previous comments were under the understanding that it would cost approximately 7k just to connect to the grid... that's not including the monthly electric costs... I think I should be able to recoop my solar costs within 5-6 years... after that it's money saved... my last electric bill shows that I only used 650kwh and after doing some research I see that I can get a dryer, water heater and well pump that runs on 110v... so I guess I may not need the 220v inverter and just keep it 110v. My biggest electrical consumption will be in the evening watching tv.

Speedunlimited · January 2016

Cost of items so far figured

12 x SolarWorld Sunmodule 260Watt Poly - $3500

Midnite Solar Classic 150 MPPT - $600

10 Mighty Max 12v 200ah Solar Power Battery - Deep Cycle - $3500

Inverter - $2000 (Could Be less with only 110v vice 220v)

Combiner Box - $400

Misc - $500

Ground Rack System - $500

vtmaps · January 2016

Speedunlimited said:
10 Mighty Max 12v 200ah Solar Power Battery - Deep Cycle - $3500

I don't see any way to use ten 12 volt batteries in a 48 volt system? For your first system, I would recommend flooded lead acid batteries. Your system looks unbalanced to me and I predict a short life for those AGM batteries.

Speedunlimited said:

I'm not sure if the previous comments were under the understanding that it would cost approximately 7k just to connect to the grid... that's not including the monthly electric costs...

7k is cheap to get on the grid. You will spend much more than that on your system. And you will have ongoing costs. Don't forget the cost of generator fuel and maintenance. And don't forget another ongoing cost.....

Speedunlimited said:

I think I should be able to recoop my solar costs within 5-6 years... after that it's money saved...

No, after that it's money spent on new batteries. And after that, money spent on new electronics and new batteries again. Also, your investment in the system is at risk of lightning damage. Hope is not a good strategy for mitigating lightning strikes. Make sure to include the cost of lightning mitigation in your budget.

--vtMaps

zoneblue · January 2016

On the flipside is that its a seasonal cabin. I dont know about maine but here they tend to hit those hard with high daily charges (to recoup their infrastructure costs). If thats so, it migh sway the balance, but in general id agree with vt, off grid is a marginal cost effective proposition.

Just look at the batterys alone: If you consider that a 10kWh battery with 2500 cycles to 25% DOD will deliver 6250kWh over its lifetime, and costs 2500 dollars, then that works out to = 2500 / (2500 x 10kWh x 0.25) = $0.40/kWh. Ignoring all the other system costs, thats already more than what youll pay for grid power.

Vic · January 2016

softdown said:

When I was designing my system I received several warnings about creating a "black hole in the universe" if I did serial connections with three panels with a VoC of 45. Was told that Hyper VoC could easily be hit on a very cold morning before the sun was strong enough to turn the FM80 on...which would draw down the voltage. Was told, on the Outback forum, that Hyper VoC would be highest before the sun even rose. That would be the time that my FM80 would go interstellar.

1) My FM80 is fast asleep when it is dark.
2) I have never seen a voltage reading over 84 using two panels. That would be 126 volts using three panels. Nowhere close to the 150 volts to create a hole in the universe.

However.....though the warnings would appear to have been misplaced, the result has been satisfactory. I believe that charging a 48 volt bank at 80-84 volts is pretty close to optimal. Significantly more efficient than charging at 120-126 volts?

Completely agree with vtmaps ...

soft..,

You mentioned that you " ,,, have never seen a voltage reading over 84 volts ...", and go on to imply that this voltage reading is an operational voltage, like Vmp.

You could check the 'Stats" pages on your FM CC, and look for the Max Voc. What does your FM note as that Maximum Voc? You might be surprised what it shows.

The FM CC will can easily be damaged while it is "Sleeping", because the Input voltage detector, that helps the CC know when to Wake-Up, is still connected to the PV voltage into the CC during Sleep -- it is this circuitry that can be damaged, and after that damage, the behavior of the CC can become an unknown.

I, too, have tried in the past to note the origin and application of the term, "Hyper Voc", but to no avail.

Just to try to add to the discussion, Vic

arby · January 2016

I have a 48 volt system, and wired my panels to 72 volts nominal. (125" away from controller) I have seen at least 125 volts from the panels. The reason I went with the 72 volt nominal is what I read in the MX60 manual.---

<<

When sizing an array, it is recommended that the nominal array voltage be higher than the

nominal battery voltage. Below is a list of recommended nominal array sizing:

Nominal Battery Voltage Nominal Array Voltage (recommended)

12 V 24 V (or higher)*

24 V 36 V (or higher)*

36 V 48 V (or higher)*

48 V 60 V (or higher)*

60 V 60 V (low temp is less than 5° F) or

72v (low temp is greater than 5° F)>>

WaterWheel · January 2016

Speedunlimited said:
Combiner Box - $400
Misc - $500
Ground Rack System - $500

I suspect your ground rack for twelve 260 watt panels will cost closer to $1300.

softdown · January 2016

Specialized aluminum solar racking is pretty expensive. One may be able to find a local welder who can use 1/8" angle iron to deliver exactly what you want. These racks have to properly primed and painted of course. Rust-o-leum has a good reputation for stopping rust.

The local Amish seem to favor 4x4s for ground mounted systems. I think they may coat the below ground section of the 4x4s with roofing tar for preservation.

It is not uncommon for the Amish to accumulate a plantation of sorts. Beautiful, spacious, and simple homes. Steering away from technological indulgences that become worthless after a few years.

foolami said:

Speedunlimited said:
Combiner Box - $400
Misc - $500
Ground Rack System - $500

I suspect your ground rack for twelve 260 watt panels will cost closer to $1300.

Dave Angelini · January 2016

mike95490 said:

My generator is down for a bad mounting bolt ! Days of rain in the forecast ! Got a temp fix in place till the real hardware store opens up Monday. Hard to see,but the nut started to strip the threads, letting the engine wobble more, messing up more threads
Then there is the battery maintenance, replacement, fussing over the gear, all the stuff you would pay the electric company for, YOU get to do. When my inverter fails, it may take me 3 days to get a new one, do I buy a $4000 spare to have sitting here ?
http://tinyurl.com/LMR-Lister

I would always have a spare and I would try and figure how to live on less energy when you have to. I believe one can live on less than 4 KWH per day, but having a system that can produce 30+ makes it very easy to go for weeks of bad weather. You may be coastal and have solar challenges that most in the south west areas do not have. It is always easier to avoid a generator when some of your solar is tracked.

I use to be a diesel Marine/electrical guy and vibration on less than 4 cylinders is always the enemy. We would say " the good news is that engine will run forever, the bad news is everything connected to it will break "

mike95490 · January 2016

Well, I do have a spare genset, and have new bolts on hand, just need time to change them out ! So many chores even in winter !

Solar in an Off Grid Cabin in Maine

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