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Off-grid battery/solar systems. Who is running one?

Started by Dave Shepard, June 13, 2015, 08:35:34 PM

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John Mc

1270d - Here's the web site we used when I was working for a PV installer here in VT. No need to put in the number of sunny days. The site draws from a database to calculate the average "sunnyness" for your area.

http://pvwatts.nrel.gov/

If you were doing a roof mount, an 8/12 or a 9/12 pitch roof would theoretically give you the best total energy output per year, given the seasonal solar conditions in your area. Highest total output is usually the target for a grid-tied system.

I'd consider going with a steeper roof for an off-grid system in your area for a couple of reasons: (1) It sheds snow better (PV panels are pretty good at shedding snow anyway, but it never hurts to help it along) and (2) For an off-grid system, you generally want to favor winter production to help counter the lower amount of sun at a time of year when most people use more electricity - steepening the angle gives it a bit better output in the winter. (and you only lose about 0.5 - 1% off your total output by using a 10/12 or a 12/12 pitch instead of a 9/12 which is close to peak total output in your area).

I'm not a fan of trackers. They do increase the output of the PV panels, but they add complexity and cost to a system, and the moving mechanical parts are far more prone to breakdown than the PV panels and associated electronics. If you have the space, it's almost always a better deal financially to just add more panels to get more output, rather than mounting them on a tracker. (10 or 20 years ago, it made sense to put them on a tracker: PV panels were very expensive, so you wanted to get everything you could out of them. They are so cheap now, it's generally better to just go with a fixed mount.)

You should talk to your system designer about possible future expansion. THere can be things you do now to make that easier. For example your "home run" wiring (wires that run from your PV system to your circuit breaker panel could be oversized to allow for future expansion without having to pull new wires (at the very least, make sure any conduit is sized to accommodate future expansion - you don't want to have to tear than out just because you added a few panels).
If the only tool you have is a hammer, you tend to see every problem as a nail.   - Abraham Maslow

grweldon

I started small with 750W of panels and a 456AH battery bank and a 1500W inverter. I recently added 900W more of panels and will install a 4000W 120/240V Magnum split-phase inverter. With the 1500W inverter I run a small 150W fridge continuously, 8 LED twin-tube 4' lights 4-5 hours on weekends, run a computer and 450 watt-per-channel (output) amplifier. I run small power tools (circular saw, drill, etc) and if I'm careful and don't put too much load on it I can run my chop saw and crosscut 2x8 lumber. I plan on adding 230 more AH of batteries and 1KW more panels eventually. I'm very happy with the way that things work and I'm anxious to get the 4K Magnum hooked up.  I have no other source of power at the farm but plan to run a 24VDC booster pump to charge a bladder tank for water pressure with collected rainwater as the source.  Haven't tackled water heat yet but I think propane will be added in the future for water and ambient heat. As I said, I like it.
My three favorite documents: The Holy Bible, The Declaration of Independence and The Constitution of the United States.

1270d

Thanks for that calculator.   It looks like a 10 kw system would be close to my current needs and maybe with a small wind generator would do the trick.   

Any ideas or info about batteries and bank sizing?

John Mc

Quote from: 1270d on November 21, 2017, 05:37:01 AM
Thanks for that calculator.   It looks like a 10 kw system would be close to my current needs and maybe with a small wind generator would do the trick.   

Any ideas or info about batteries and bank sizing?

Batteries and bank sizing is outside my area of experience (my former business partner would have something to say on this, but he is swamped these days - lots of folks trying to get their system in before the end of the year.)

I know that 10 KW is large for a typical grid-tied system for a residential home in our area (I'm in VT, but conditions are similar to Michigan), but the goals are different for a grid-tied system (you are just trying to handle the average load for the year, rather than with off-grid where you have to deal with a seasonal low in production in the winter - right at the time most people in our type of climate have a seasonal high usage).

The one thing I can say is you should look hard a conservation FIRST, then size your system for the remaining load - of course if you have no kids now, but they are in your future, the added load may well dwarf any conservation efforts.
If the only tool you have is a hammer, you tend to see every problem as a nail.   - Abraham Maslow

1270d

I have four kids now and expect more. Conservation is going to be difficult, but of course some is possible.

Any thoughts on the types of batteries?   Lithium ion seems to be the thing now but I'm pretty much priced out of those products.   My house plan will be somewhat geared towards efficient electrical usage since this is an entirely new construction project.

gww

I am using a fork truck battery.  I think there are plusses and minusses on them, faster self discharge for one.  It was the cheapest to get the most with suposed good longivity.  Very heavy.
Still not cheap.  Mine is 48 volt 800 amp hour.  That is 24 2volt batteries in a steel case.  Weighs one ton.
Cheers
gww

1270d


Stuart Caruk

Before I got sick and figured I was going to die, I set up a 20 @ 300 watt panels on a lot in Roatan. Turns out it was waaaaay cheaper to produce power, and way more reliable than RECO provides. Power down there is all made from diesel generators, when they run...

Biggest problem was leaving the island. Batteries, solar panels, wire, inverters... anything not welded down just disappears.

When I go back down, I want to set up small buildings with a porch holding up a flat sloped roof set at 22.8 degrees to maximize the solar gain. Each building should be able to get me a 12 - 15 Kw array. Hopefully if I get the panels up on the roof, and running at a high enough voltage, they will be much harder to steal. Since I sold my old lot and mill, this time I'm looking at trying the south side of the island. On a much larger lot with access to some very deep water close to shore.

I plan to work on proving the feasibilty of compressed air energy storage, for storing solar generated power for use a night time. Think of it as an air battery, or a 55 cubic meter energy storage bag sitting in 1800' of water.
Stuart Caruk
Wood-Mizer LX450 Diesel w/ debarker and home brewed extension, live log deck and outfeed rolls. Woodmizer twin blade edger, Barko 450 log loader, Clark 666 Grapple Skidder w/ 200' of mainline. Bobcats and forklifts.

bdsmith

Battery technology is advancing now that photovoltaics are well established.  Saltwater batteries are the newest storage technology but the company has had some financial problems earlier this year.  They bear watching.

maple flats

If I were superstitious (we got married on Friday the 13th, over 50 yrs ago) I wouldn't say this, but my battery bank that was rated to last 7 years has now passed the ninth year since being connected. So far, so good. But as mentioned earlier, the only use of that battery bank is as back up power to heat a very small room in my sugarhouse where my reverse Osmosis unit is stored, it can not freeze. The only other use would be for lighting the sugarhouse in case of a power failure during a boil. Fortunately that has never happened (yet).
logging small time for years but just learning how,  2012 36 HP Mahindra tractor, 3point log arch, 8000# class excavator, lifts 2500# and sets logs on mill precisely where needed, Woodland Mills HM130Max , maple syrup a hobby that consumes my time. looking to learn blacksmithing.

maple flats

Here, on the 43rd parallel, snow on the panels is a major issue. If you get much snow, be sure you have the ability to remove it from the panels. Just 6" of snow on panels can cut the watts to near zero. My most recent solar install has snow issues, it is on a south facing second floor wall over a garage roof. I have a 24' handle on a snow rake but rarely can get all of the snow off. It seem to need another handle, but then I wouldn't be able to lift the head without kinking the handle. As it is, I seem to miss the upper 18". If the sun is good and the temp is about 24F+ it soon slides off, but if colder it doesn't slide. If it warms to about 28F it slides off if it is not totally overcast.
My ground mount array at my sugarhouse is no issue clearing snow off.
logging small time for years but just learning how,  2012 36 HP Mahindra tractor, 3point log arch, 8000# class excavator, lifts 2500# and sets logs on mill precisely where needed, Woodland Mills HM130Max , maple syrup a hobby that consumes my time. looking to learn blacksmithing.

tule peak timber

Quote from: Stuart Caruk on November 22, 2017, 01:52:47 AM
Before I got sick and figured I was going to die, I set up a 20 @ 300 watt panels on a lot in Roatan. Turns out it was waaaaay cheaper to produce power, and way more reliable than RECO provides. Power down there is all made from diesel generators, when they run...

Biggest problem was leaving the island. Batteries, solar panels, wire, inverters... anything not welded down just disappears.

When I go back down, I want to set up small buildings with a porch holding up a flat sloped roof set at 22.8 degrees to maximize the solar gain. Each building should be able to get me a 12 - 15 Kw array. Hopefully if I get the panels up on the roof, and running at a high enough voltage, they will be much harder to steal. Since I sold my old lot and mill, this time I'm looking at trying the south side of the island. On a much larger lot with access to some very deep water close to shore.

I plan to work on proving the feasibilty of compressed air energy storage, for storing solar generated power for use a night time. Think of it as an air battery, or a 55 cubic meter energy storage bag sitting in 1800' of water.
Very interesting....I'm racking my brain for alternative energy storage my self.
persistence personified - never let up , never let down

moodnacreek

 lRan my sawmill for several years  with an old diesel on used motor oil. In warm weather I run my cummins gen set on 70% used veg. oil.   The diesel has to be I.d.i. [pre combustion chamber] style. The injectors have to be easy to get out and provide access to the pre cups so you can clean the deposits. The fuel needs to be as clean as you can get it. An old 318 cat. with pony start is what I had.  They had these in gen sets also. These old engines can be fitted with new generators yet to day.

bdsmith

1270d,
Since you are building new, you might consider a low voltage DC  wiring system for your lighting.  LEDs are low voltage, high current devices.  Most use between 3 and 5 volts DC.  The 120VAC to 5 VDC converters use between 10% and 15% of the energy of the LED fixture.
If you had a few solar panels that fed the lights directly or charged a 6V battery bank, you could reduce the amount of generation you need.  You also wouldn't need 14 gauge ROMEX for wiring and could install it without the need of a licensed electrician.  I have seen systems with Cat5 wiring.
You would need to source converter-less LED bulbs like automotive bulbs.  There are various styles of industrial bulbs available.

Ljohnsaw

Quote from: bdsmith on January 23, 2018, 11:12:24 AM
1270d,
Since you are building new, you might consider a low voltage DC  wiring system for your lighting.  LEDs are low voltage, high current devices.  Most use between 3 and 5 volts DC.  The 120VAC to 5 VDC converters use between 10% and 15% of the energy of the LED fixture.
If you had a few solar panels that fed the lights directly or charged a 6V battery bank, you could reduce the amount of generation you need.  You also wouldn't need 14 gauge ROMEX for wiring and could install it without the need of a licensed electrician.  I have seen systems with Cat5 wiring.
You would need to source converter-less LED bulbs like automotive bulbs.  There are various styles of industrial bulbs available.
I think you mean low current.  Some of the automotive bulbs I was planning to use draw around 0.03 amp at 12v.  However, I wouldn't go light gauge wiring.  With DC, voltage drop is a big deal (when you start looking a long runs or cumulative loads).  Standard 12 or 14 gauge wire is not all that expensive and then I would be pre-wired should something come along in the future that would make me want to convert to 120vac.

The county was trying to say I wasn't following code for my DC install.  I asked him to show me the code - he couldn't find it either. ;)
John Sawicky

Just North-East of Sacramento...

SkyTrak 9038, Ford 545D FEL, Davis Little Monster backhoe, Case 16+4 Trencher, Home Built 42" capacity/36" cut Bandmill up to 54' long - using it all to build a timber frame cabin.

maple flats

My newest array, totally off grid was installed by a solar contractor. I asked that they be tilted for maximum energy in the winter, they mounted then slightly flatter than summer best energy. Now I have issues with snow, if tilted steeper for winter sun they would self empty better and if I need to use the snow rake it would be easier.
I could call them, but I think I'll just change it myself. I'll do that this coming early-mid fall. I will need to find a way to support the bottom edge of the array (6 panels mounted landscape 3 over 3). Then brace it, cut each diagonal brace, drill for bolting with the appropriate overlap and then lowering the lower edge and bolting the braces overlapped, of I may buy 4 aluminum angles  in a larger dimension, drill for both summer and winter settings, then remove enough of the existing ones to bolt that on for winter, and then each spring, adjust for summer. Before I go that route I'll study the production charts to decide if the summer gain would be worth the effort. If not enough difference, I'll just leave them at winter angle all of the time.
logging small time for years but just learning how,  2012 36 HP Mahindra tractor, 3point log arch, 8000# class excavator, lifts 2500# and sets logs on mill precisely where needed, Woodland Mills HM130Max , maple syrup a hobby that consumes my time. looking to learn blacksmithing.

OntarioAl

Maple Flats
I am puzzled by the angle that your panels were installed my research says to stand them up more for the winter and lay them down for the summer.
best winter angle is latitude of the installation plus 15 degrees
best summer angle is latitude minus 15 degrees
Hope this helps
Al
Al Raman

John Mc

Quote from: OntarioAl on March 15, 2018, 12:14:04 AMI am puzzled by the angle that your panels were installed my research says to stand them up more for the winter and lay them down for the summer.

That is correct. You want them aimed squarely at the sun at mid-day. Since the sun is lower in the winter, the panels should be standing up a bit more than what is used for summer time or for a "general-purpose" year-round setting.
If the only tool you have is a hammer, you tend to see every problem as a nail.   - Abraham Maslow

Lumbergent

I started solar for my large tree house at the edge of my forest. Not knowing the difference between AC and DC the startup was painstaking.
What I did learn fast was these simple rules of thumb.
1- Make sure you have twice as many panels than your storage can handle. Living up north we have lots of rain and clouds. During the day when the batteries are fully charged and it is sunny our power comes directly from the panels and leaves the batteries bank for the evenings.
2- Amazingly Solar panels are more efficient when its cold than when its hot. A really hot day is not an efficient electric day. 
3- Solar panels are getting cheaper and more powerfull every year. So buy into panels only for your immediate needs.
4-It is not efficient to use an inverter (from DC to AC) We were hardly using power at all and our new batteries were discharging. Apparently the inverter was using enough power to discharge our power bank during rainy spells. We ended up cutting out the inverter and started running everything on DC. DC Refrigerators are more expensive but they use WAY less power. I also found out that something as insignificant as those little inverters we use for our cell phones use power if left plugged in an AC outlet even with nothing charging.
5- To run everything on DC you need to rewire everything with multistrand wires. LED lights and Cell phones run on DC. . With a propane and wood stove and a DC refrigerator we are completely off grid.

BTW up here in Quebec power comes from a gouvernment owned monopoly. They do not buy back excess power, but feeding into the grid apparently turns the electric meter backwards so it becomes sort of like a credit on your futur bills. I'm not sure how it works but I am far from that reality.
Electricity up here is extremely cheap compared to most parts of the world so going solar power is not economical. Just practical in remote places.
Futur Hobbit

John Mc

Solar Panels were getting cheaper in the US until the Trump administration put a 30% import duty on them (most are made in China).
If the only tool you have is a hammer, you tend to see every problem as a nail.   - Abraham Maslow

Lumbergent

Futur Hobbit

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