OFF GRID POWER; various thoughts on...

[Squirl]

 

I was just curious.  I know it has been something I have been dealing with at my site and I'm just a little south of you.  In the winter the angle is at 27 degrees.

[AdironDoc]

I was just curious.  I know it has been something I have been dealing with at my site and I'm just a little south of you.  In the winter the angle is at 27 degrees.

Squirl, it sounds like you mean the sun is 27 degrees from the horizon? For panel rack angle, I'm using the winter formula of latitude (mine is 43) x 0.89 + 24.  For me, winter setting is 62 from horizontal. Adding your solar angle from horizon to my panel angle, we have just about 90 degrees as both our angles are complementary. Makes sense.

I've actually set mine to autumn/spring as a happy medium as I don't plan on using the camp much during the winter months. Latitude x .98 -2.3 gives my current 40 degree orientation. Come summer, I'll just set the legs a bit lower and slightly loosen the turnbuckles. Magnetic declination was 13 degrees west of magnetic south, though my cellphone compass makes me wonder about it's accuracy. It's my understanding that even if we're off by a fairly wide margin, panel outputs don't suffer much?

http://www.macslab.com/optsolar.html

[Squirl]

It isn't the panel angle I have to worry about, it is the trees.  At the angle for the winter the tree's shadow is double its height.  In addition the back part of my property is pine which don't give up their brush in the winter so no sun would get through if I put the panels to close to the trees.  Each foot taller I place the panels equals 2 ft closer to the tree line I can put them.

[AdironDoc]

It isn't the panel angle I have to worry about, it is the trees.  At the angle for the winter the tree's shadow is double its height.  In addition the back part of my property is pine which don't give up their brush in the winter so no sun would get through if I put the panels to close to the trees.  Each foot taller I place the panels equals 2 ft closer to the tree line I can put them.

That's a problem that I can't imagine a solution for. It doesn't help that pine reach well over 100ft either. Can you clear a few so at least you get a few hours of peak sun? I have a wind turbine and cobbled together a 60ft mast out of galvanized pipes jointed with couplings and guyed to the ground. My turbine isn't light but with a gin pole it's not too bad to hoist. I'm just thinking, if you get a couple panels on a galvanized pole mount, say, two 10ft lengths, add a gin pole and hoisted her up and added some guy wires, would you be in full sun?

[Squirl]

I think I found the solution so far, I just have to make sure I implement it correctly.  My house is currently around 125 ft from the tree line.  I also have around another 50 ft closer to the road that I can play with.  If I put them up 10 ft with a large base the trees can grow to 100 ft without effecting it.  Within a few years I will try and remove the trees.  Pine, especially the ones I have, are generally worthless and I would rather have fruit trees anyway.  Wind will be more of the primary source in the winter but because of cost and inspection issues I will probably only have solar and generator power for the first year.  I just thought I would share some of my issues because it looks like you have a similar setup.  How far is it to the tree line for you?

[AdironDoc]

I think I found the solution so far, I just have to make sure I implement it correctly.  My house is currently around 125 ft from the tree line.  I also have around another 50 ft closer to the road that I can play with.  If I put them up 10 ft with a large base the trees can grow to 100 ft without effecting it.  Within a few years I will try and remove the trees.  Pine, especially the ones I have, are generally worthless and I would rather have fruit trees anyway.  Wind will be more of the primary source in the winter but because of cost and inspection issues I will probably only have solar and generator power for the first year.  I just thought I would share some of my issues because it looks like you have a similar setup.  How far is it to the tree line for you?

Getting your panels up 10ft shouldn't be too hard, especially with the pole mounted setups. If you were to use 10ft galvanized pipe with threaded ends, it would give you some flexibility. I'm assuming you'd cement a section into the ground at the base. If your base is a short threaded stub, add a coupling, then a 10ft length above it. In this way, you have the option of hoisting it up in the future and adding whatever length you needed. My treeline is around 130ft to the south, but as close as 60ft to the west, what you see along the creek in the photo. I'm getting full sun from 10am to 3pm. I don't know much about panel outputs vs. time of day other than solar insolation charts put me at an average of a little less than 4 hrs. That means I most want to capture 10am to 2pm.

[MountainDon]

Before digging a hole and planting a section of pipe it might be a good idea to read some of Unirac's sizing and installation information. It might also be a good idea to use a larger diameter pole than you might need for the planned current installation. A larger pipe could then be used for a future expansion. Dave Sparks who comes and contributes here uses nothing less than 6 inch pipe for that reason, IIRC. Look for used drill pipe, it can be found in many places at a fraction of the cost for new pipe. That's what I have in 4 inch, 1/4" wall, 4 1/2"OD. You don't want the wind blowing it over.

Not sure I would depend on a threaded connection. Pipe can be had in up to 20 foot lengths.

Unirac's info can be found here.

[Squirl]

There is a great sizing chart for pipes and bases and complete walkthrough guide in a free article from homepower.

http://homepower.com/view/?file=HP108_pg28_Schwartz&pdf=1

[AdironDoc]

Before digging a hole and planting a section of pipe it might be a good idea to read some of Unirac's sizing and installation information. It might also be a good idea to use a larger diameter pole than you might need for the planned current installation. A larger pipe could then be used for a future expansion. Dave Sparks who comes and contributes here uses nothing less than 6 inch pipe for that reason, IIRC. Look for used drill pipe, it can be found in many places at a fraction of the cost for new pipe. That's what I have in 4 inch, 1/4" wall, 4 1/2"OD. You don't want the wind blowing it over.

Not sure I would depend on a threaded connection. Pipe can be had in up to 20 foot lengths.

Unirac's info can be found here.

Good point about oversizing, Don. Still, after seeing the pricing on official mounts for my solar panels, my jaw dropped. I looked at the actual hardware which, seemed to me, to be hugely overpriced for its simplicity. Clips and racks ended up costing more than my panels. Same was true of the wind turbine setups.

I decided a DIY approach was in order. The threaded galvanized pipes I'm using are holding nearly 100lbs at up to 50ft height. That follows the recommendations of the turbine manufacturer. The caveat is they absolutely MUST be guyed at a number of levels. Further, they must be of high schedule/wall thickness. I figure at 20ft, solar panels posts should be similarly supported at 4 cardinal points due to materials fatigue from being buffeted by winds. Turnbuckles and anchors checked frequently.

[MountainDon]

   PV modules are presenting a much larger surface area to the wind. That was one reason I decided to go with the Unirac system. According to them is used with their recommended pole, depth, height, amount of concrete our set of panels should live through winds to at least 90 mph (because my pole os over sized for the current module array). I've recorded gusts as high as 58 mph.

[AdironDoc]

  PV modules are presenting a much larger surface area to the wind. That was one reason I decided to go with the Unirac system.

Certainly heard good things about Unirac systems. Easy to assemble and fit like a glove. Was the setup costly?

[MountainDon]

Darn. I thought I answered this. 

IIRC the rack I used was about $500 and the used drill pipe about $20 plus some gas that was cheaper back then. 30-40 mile drive X2.

[Squirl]

Temperature correction.

There is a lot of literature on adjusting Voc for cold weather with charge controllers and wiring, but not on the output side.  I have not seen a single sizing guide with adjustments or anything in the literature about adjustments for charge controller output watts because of temperature.  I have seen the normal 1.25 safety factor adjustment for the NEC.  You can seen this in the panel ratings and the NEC rating for many charge controllers.  Am I right that there is no temperature adjustment needed?

[MountainDon]

Here's my take on this...
Once the charge controller has processed the incoming power and is putting it into the battery, that power is, what it is. So many volts and so many watts. Nothing more, nothing less. It doesn't matter what the temperature is to the power coming out of the charge controller. At least is what I think.

The temperature matters to the batteries mainly as a function of reducing the amount of power (watt-hours or amp-hours) that can be withdrawn from the batteries. As for charging the batteries, colder weather may be an advantage when high rates of charge may be encountered as the batteries won't get hot as fast. That is just a guess, I have nothing to back that up.

Battery capacity is reduced as the following chart indicates...



We need more rated capacity in the battery bank as the battery temperature decreases.
At about 25 degrees F the battery bank should be 25% larger to compensate for temperature losses. Or keep the batteries warm.

[Squirl]

I was more concerned with an increase wattage from the increased voltage from the cold.  Most of what I had read was that the increased voltage tends to be when there is low solar radiance and almost no amperage.

[MountainDon]

Yes.  I'd think all that should be covered by using the numbers for the cold induced high voltage. Mostly that is a spike but long enough to harm the voltage sensitive parts. The highest voltages recorded remain in memory accessible to the factory service techs.

[cabingal3]

maybe someone can answer this question for me....when we went to our cabin this weekend,all my oil lamps had frozen fuel in them.If i lit one-will the glass that holds the lamp oil break?? or should i wait for the oil to unthaw???

[MountainDon]

I've not had lamp oil gel or solidify but I have lit the lamp when it was in the 20's and had no issues. The olive oil in the kitchen cupboard solidify in the cold but thats never been a problem.

[rick91351]

As far as the globe cracking it really would not do much good to light it if the fuel is jelled.  What do you use for fuel?   What type of lamps?  Like a tables lamp with a simple wick or an Aldan?  Or like a Dietz type lantern.  The Dietz will take hot gases back in to the tank which causes a draw and heat up the oil some what.  But if it is that cold I think I would next year look at some anti-jell like the truckers use in their diesel.  However kerosene is not supposed to jell.  Just doing a little quick research here and basic fuel grade kerosene does not jell till after -22 degrees.  I think I would do a little research on your fuel as far as what you are using. 

As far as what to do, set them some where they can gently warm and your fuel will return to normal.

     

     

[PorkChopsMmm]

Don, how are your batteries holding up to the cold? Mine are in a similar type enclosure and uninsulated. I think the cold is hitting them hard because they seem to have lower power output then in the Fall. I am thinking of putting some rigid foam around them to help hold in the heat they generate from charging.

[OlJarhead]

Don, how are your batteries holding up to the cold? Mine are in a similar type enclosure and uninsulated. I think the cold is hitting them hard because they seem to have lower power output then in the Fall. I am thinking of putting some rigid foam around them to help hold in the heat they generate from charging.

I seem to be having this problem quite a bit myself.  I can get them above freezing in the day and keep them 10-12 degrees warmer then outside temps because of the porch they are in but clearly I'm losing capacity due to the cold.

I plan to insulate mine also but alas, time is something I never seem to have enough of.

[OlJarhead]

maybe someone can answer this question for me....when we went to our cabin this weekend,all my oil lamps had frozen fuel in them.If i lit one-will the glass that holds the lamp oil break?? or should i wait for the oil to unthaw???

I took a very cold lantern this weekend, poured fuel in it and lit it.

The flame is not very hot and it warms the glass up slowly.  I think you would be fine with yours because you need to let the fuel thaw anyway so light the wood stove, thaw the fuel and then light the lamps

[MountainDon]

As the little chart above indicates there is capacity loss dur to cold temperatures. For the most part I don't notice any difference that affects our winter use. But that's why I used 12 of those batteries instead of 8. After a few years of use I'm quite certain that 8 would be sufficient for three season use; spring, summer,fall. That's pretty much what I calculated. I added 4 "extras" as I knew there would be winter loss of capacity.

I can see a lower voltage reading at the end of a typical winters day than at other times of the year. Also we don't have a full three days of autonomy in the winter, without dipping below 50%. Fortunately our winter times at the cabin seldom go more than 2 1/2 days; 2 overnites.

I tossed around the idea of insulating the batteries a lot before getting to the point of installing the PV system. Because our winter use is limited by the fact of the road being impassable once the snow gets serious I decided it would not do a lot of good. Here's my train of thought on that. When the cabin sits idle there is zero use of electricity; the inverter is shut down, there are no direct DC uses. So all that happens on a sunny day is the charge controller kicks in when the sun hits the panels hard enough. The system goes through a short bulk charge then switches to absorb for a couple hours. Then it floats until the sun goes low in the sky. The bulk period is so short there is very little heat generated. The absorb is low powered enough that again there's little heat generated. Float does nothing for heating. Time between visits is two weeks minimum. I figure that even if we left the batteries warm, by the time they went through two weeks of the above mentioned cycles there temperature would still be down to the cold ambient air temperature. Insulation only slows the transfer of heat; if there is no noticeable amount of heat to slow, the benefits of insulation are minimal to none, IMO.

Our cabin is pretty well insulated, R25 floor, R19 walls, R45 ceiling, good low-e windows. When we leave the interior and contents is likely to be 70 - 75 degrees F; sometimes we leave some fire in the firebox. Typically by the time we return the interior of the cabin is usually colder than the outside air temperature when we snow shoe up in winter. Last trip it was 40 outside and 28 inside. We have many more hours of cold than we have hours of weather warmed by the weak winter sun.

It seems to me that if my batteries were in an insulated box there would be no real operating advantage in winter. Now, if our use pattern was different, longer weekends or a week or more at a time, that would change things. Anyone living in similar conditions in a full time residence would certainly benefit from an insulated battery enclosure. In a full time occupancy it might even be a benefit to have a solar air collector heater to keep them warm.   But for our type of winter use and winter temperatures I'm not convinced that insulation would bring great benefits.

Anyhow that is my reasoning for our situation. Others may differ.

[PorkChopsMmm]

Don, thank you! As always a very thorough response. Looks like I need to verify my loads, insulate my batteries, and possibly double my bank (my only option at 48v). I don't think we will be back until March... That will give me the summer to get everything set up before next winter.

[OlJarhead]

Don, this is why I put mine in the porch   I can see a rise well above freezing inside the porch when the sun is out and gain about 12 degrees at the coldest part of the night/morning.  I figure with good insulation I can improve the gain by reducing the loss thereby improving battery life and useability.