30x40 Earth Berm Passive Solar in Maine

[Bishopknight]

MountainDon,

I talked to my electrician, he says 12v is the way to go because a 120 watt panel at 17 volts open circuit produces much more than a 120 watt panel at 31 volts open circuit. He does agree that its more efficient to convert from a higher DC voltage to AC.

But were going with a 4 guage aluminum wire from the combiner box anyways.

I just want the most efficient system without using inverters if I can. I'd like to run DC lighting and some DC appliances like the pump. If I add more panels in the future and wan t to run an inverter, so be it but for now, I'd like to just get the most bang for my buck out of my panels.

Curious what you think or anyone else thinks who is interested/experienced in solar panel efficiencies. 


Electrical Notes:
On a side note, here are a couple of things I've learned about running service to meter to panel cable.

"4 ought triplex" is the service entrance cable. That runs from the closest telephone pole to your meter outside your house. The number of bends must be less than 360 degrees and definitely less than 270 degrees . A straight line is preferable for pulling the wire through the conduit. The wire should come up 8 ft from the ground at the meter and 35 ft from the ground at the telephone pole.

From the Meter to the panel, the wire is called "200 amp SER" ( if you're using a 200 amp panel). Iits run should be as short as possible. If its too long, you may need an expensive disconnect switch. Either way, you should use 4 guage aluminum SEU cable if you're going with a standard 200 amp connection ( like mine ). 2" grey conduit should surround the wire in and out of the meter as well. The U in SEU stands for the shape of the cable. SEU cable is normally in a grey jacket, where as SER is normally a 3 strand un-jacketed set of wires twisted together.

[MountainDon]

MountainDon,

#1....  I talked to my electrician, he says 12v is the way to go because a 120 watt panel at 17 volts open circuit produces much more than a 120 watt panel at 31 volts open circuit.

#2....  But were going with a 4 gauge aluminum wire from the combiner box anyways.

#3....  I just want the most efficient system without using inverters if I can. I'd like to run DC lighting and some DC appliances like the pump. If I add more panels in the future and wan t to run an inverter, so be it but for now, I'd like to just get the most bang for my buck out of my panels.

Curious what you think or anyone else thinks who is interested/experienced in solar panel efficiencies. 

First, I guess I had forgotten that you were building a DC only system, and using a 12 VDC battery system voltage.

Re: #1....  A 120 watt panel produces 120 watts, plus or minus factory allowed variance. Let's say it's 100% efficient. So at 17 Voc the amps would be 120/17 = 7.0588. At 31 Voc the amps would be 120/31 = 3.870. So yes, the amps are higher at 17 Voc, but it's still 120 watts either way; watts are watts.

A charge controller designed to accept a nominal 24 VDC input (approx 34 Voc) and charge a 12 VDC battery bank should work as well as a charge controller designed to accept a nominal 12 VDC input 917Voc) and output to a 12 VDC battery bank. The real difference comes in when one uses a MPPT controller compared to PWM or any of the cheaper controllers.

Re: #2....  Aluminum wire has more resistance than copper. If we were to run a 12 VDC panel set pushing 45 amps (your max), 15 feet through #4 AWG wires, we have a voltage drop of 5.72% using aluminum and 3.46% using copper. Or another way to look at it, #4 aluminum wire is equivalent to #6 copper wire, as far as current carrying ability.

Re: #3....  If the distances from the batteries to the various points of use are short the power losses in those wires can remain low enough to not be a large source of power loss. Originally I considered doing a predominantly 12 VDC system in our cabin. However when I ran the wire lengths and loads and calculated the losses it didn't appeal to me. But that's me.

If you are running 12 VDC lights and things then using a 24 VDC battery system would make no sense at all. You would have to center tap the 24 V battery pack to get a usable 12 V and that is bad for batteries. Or you'd have to buy a 24 to 12 VDC converter and that would have some inefficiencies just like an inverter.

The other factor that I applied to our cabin situation was that we also desired some AC; microwave, the ability to tun a vacuum cleaner, a TV and DVD player, a toaster... So we would have AC wiring as well. Mixing DC and AC, even with fool proof DC dedicated outlets, would be easy for me to keep straight, but if I wouldn't be there maybe others would have issues. AC and DC mixed, also used up about twice as much wire, required a second breaker panel, and so on. In the end, for me/us I decided it was a poor choice.

You probably know that DC requires DC rated switches and breakers. Also if there is any AC in the building, not the room, but anywhere in the entire building, the NEC requires the outlets to be keyed differently. That's so an AC thing can't be plugged into a DC, and vice versa. If there is no 240 VAC wiring in the building 240 VAC outlets can be used for DC power.

[MountainDon]

It just hit me that a Voc of 17 volts seems a little low for a panel that is rated at 12 volts nominal. That 17 volts sounds more like the Vmp, Maximum Power Volts. That's actually the more useful figure for calculating outputs.

Voc is important when calculating the series string size in order to stay well below the maximum voltage rating of the charge controller. Voc on a 12 volt panel wouls more likely be in the 21 to 22 volt range.

[Bishopknight]

Thanks MountainDon,

I'm definitely going to get a MPPT like the one outback sells asap. I'll be using 4/0 ought aluminum SEU for the combiner box to controller wire, so the losses will be tolerable whether 12 or 24v. And I agree with you regarding the distances and losses.

I plan on having a sub panel next to my main panel. Above the panels, I'll be able to move a circuit from the AC main to the DC sub.

I wired my rooms in mind for solar application, so i split the lights from the outlets. I should be able to run all my lighting circuits from the DC sub-panel as well as a future water pump as well. The lone DC outlet, I planned to use a 240vac outlet there. I didnt know that about the breakers having to be DC current, thanks for the tip! 

I did find a company on the internet in china that sells 12vdc florescent bulbs that can also run on 24v dc ( link below ). I'm going to contact them about buying some and see if its possible.

Question: Do you know if all 12v florescent bulbs can run on 24v as well?

http://www.solsco.com/12VDC_lamps_dclights_3Watt.html

[MountainDon]

I didn't know that about the breakers having to be DC current, thanks for the tip! 

Square D makes the only commonly available NEC approved breaker that I know of. It's their QO series. They can also be used for AC. Take the standard QO breaker, approved for 120 VAC; it is also NEC approved for DC systems up to a maximum of 48 Volts. In practice that limits it to 36 volt systems maximum as breakers must have a safety factor calculated in. A 48 volt system would surpass the approved rating. The amperage stamped on the QO breaker is the same for AC or DC. As far as I know they only fit their QO panels.

[MountainDon]

Also regarding fluorescent lights...

It is the ballast component of a fluorescent fixture that determines the actual input voltage. Lamps with built in ballasts like the common household CFL's are built to work on a single voltage; 120 VAC. As you found, CFL's are also available in DC voltages of 12, 24 or 48 from a few places online. I've seen them at solarseller.com; I've bought from solarseller and been very happy. But I've never bought the CFL lamps.

They have one piece ones...
http://solarseller.com/dc_fluorescent_lights__12___24_volt__ballasts__screw_in_ballasts__low_voltage7e.htm

and two piece ones...
http://solarseller.com/dc_fluorescent_lights__12___24_volt__ballasts__screw_in_ballasts__low_voltage7d.htm
are interesting as the ballast is one piece and the tube another. It would make changing to a different voltage or a change to a different color temperature tube possible.

Those lamps are made in the USA!!

You can also change an ordinary household fluorescent fixture from 120 VAC to 12 VDC operation by replacing the ballast, or any DC range up to 56 VDC. The same tube is used. Iota Engineeering sells a variety of ballasts for DC voltages. They must be matched to the tube type and number of them.
http://iotaengineering.com/dc.htm  They have an online selector; input tube type and it comes up with what ballasts will work.

Iota products are made in the USA as well (AZ). I have several different products of theirs and have never had a problem. They are also user friendly with email inquiries.

Knowing the above, I suspect that the catalog listing "12V or 24V", means that you can order a 12 VDC or a 24 VDC lamp. I could be wrong; it is conceivable they could build in a voltage selector switch.    However when I was looking at this I never ran across such a lamp.


I don't want to sound like I'm trying to talk you out of a 12 VDC system. However for others who are wondering about the same and reading this, here's another of my own personal reasons for deciding against 12 VDC for my main lighting. 1. These DC voltage things cost about $15 each; the 120 VAC ones $3 or less in bulk. 2. I can buy the 120 VAC almost everywhere, though I'll pay more like $5 if I can't get to a discount/warehouse store. 3. I've had CFL's fail in less time than what I'm supposed to get; I'd hate to have that happen with a $15 lamp.

Once again that's simply my way of looking at my needs or wants. I'm making it known to maybe help others.

FYI, Frequent cycling of any CFL shortens the lamp life. Rapid on, then off sequences can shorten the life of a CFL to less than that of an incandescent lamp. That's only one reason why I hope the government does not outlaw incandescent lamps. Incandescents are ideal for closets and other spaces that are lit for short periods.

FYI, each CFL or separate DC ballast has a small inverter (DC to AC) in it.

[Bishopknight]

Thanks MountainDon,

I still feel like 24v is the way to go.

Thanks for the info about the Square D breakers also. 

[pagan]

Bishopknight,

I was considering a 12 vdc system and then thought about 24 vdc. After looking at what was available for lighting and electronics in dc I decided to go with an inverter. When the inverter's humming away using 20 watts per hour to power a 13 watt CF light I think I might have made a mistake, but overall I think it was a good choice. My system provides all the electricity I need and I have pure sine wave ac power. When I get everything wired in I think I might throw in a couple of dc lights though, that way I can run some lights without the inverter.

[Bishopknight]

Ya, mine might be similar to that down the road too, in use that is.

There are pros and cons to each type it seems.

MountainDon,

I'm curious what kind of light you use for your closets. I'm thinking maybe a 24vdc LED light using the E26 socket? A flourescent would be a bad choice for obvious reasons.

Here are the 24v ceiling fans I found. Unfortunately, they don't have wiring for lights in them it seems.
http://store.altestore.com/Lighting-Fans/Ceiling-Fans-DC/RCH-Fanworks-1224V-Vari-Fan-42-Ceiling-Fan/p6682/

[MountainDon]

There is no single right way. We're all different so we make different choices. 

Our cabin will have a couple Thinlite compact FL fixtures under the kitchen cabinets, above the counters. They will be operating off 24 VDC. One reason for them is I wanted some DC lights in case the inverter developed a problem. But all other electrical is 120 VAC off the Outback Inverter. I bought those from solarseller... very good prices compared to most RV dealers... they are used in many RV's.

Here are the 24v ceiling fans I found. Unfortunately, they don't have wiring for lights in them it seems.
http://store.altestore.com/Lighting-Fans/Ceiling-Fans-DC/RCH-Fanworks-1224V-Vari-Fan-42-Ceiling-Fan/p6682/

Check The Solar.Biz as well. I bought the RCH Vari-Cyclone from them. The Cyclone model has wind tunnel developed blades and moves more air for the power consumed than the typical flat paddle blades in the standard model. Combine that with the Solar Converters electronic variable speed control and you have a real cool package. Mine is 24 VDC as well.

http://thesolar.biz/RCH%20Fan%20Works%20DC%20Fans.htm

The way it's built it's impossible to fit lights to it. There are a few 120 VAC ceiling fans that use the Cyclone blades. FYI, these blades were designed by the same guy who designed the propeller for the Gossamer Albatross (Across the English Channel, man powered flight.)




Closet Lights:
The cabin does not have closets; hooks on the wall by the door, two large chest of drawers for clothes, towels and stuff. Plus there will be box storage under the bed. Remember it is a part time residence.

At home virtually all the lights are fluorescent. We've had F30 and F40 style tubes in many places for 25 years. All the other commonly used lamps were converted to CFL's something like 10 years ago; maybe more. I just switched them out over time. 

Most closets are wide and only one shirt deep with wide sliding doors, so there's no real need to a light in them. One larger closet has a light. It also has a skylight so much of the time the light is not turned on. The light in there is a 60 watt incandescent. It is actuated by a photocell / motion sensor switch with a manual on-ready-off override. If it daytime it's bright enough so the light does not come on. When it's darker the motion sensor turns the light on when you enter.

I also have the same switches in a couple other spots like the front entrance & garage. Those are also controlling incandescent lamps, not CFL. My reasoning is they are seldom on and then only for short times. Incandescent is better suited for that purpose in my opinion. CFL's don't always put out their full lumen rating until they warm up; another reason to avoid them for rapid on-off locations. I believe there is more to be lost with the premature death of a CFL than is lost with limited time use of an incandescent lamp.

I also feel that at their current development level LED's don't deliver enough light for the purchase dollar expended.

[Bishopknight]

Thanks MountainDon,

This entire house is a "process". Anyone thats read my blog knows I've changed my mind numerous times on numerous things.

I am glad though I'm at the more interesting parts of building my house, namely energy efficiency. For instance, I'm considering building my own "passive solar batch water heater"

I found a great article over on DIYSolar using PEX that details the steps.
http://www.builditsolar.com/Experimental/PEXCollector/PEXCollector.htm
Naturally, I'm a huge fan of pex due to its ease of use plus, I already have all the materials on hand that I don't need ( extra 1/2" pex leftover, aluminum sheeting, caulk, plywood, 1" polystyrene insulation )

Plus, this is something I can build at home too.

Btw, as far as progress goes, 5 doors are in with doorknobs. Drywall has been hung in the master bedroom, closets, guest bedroom , hallway and part of the living room and office. More pics coming next week

[speedfunk]

More pics!!!!  Yeah, the energy stuff is def. the fun stuff.   Evacuated tubes maybe?  That build it solar site is a really great resource!

[glenn kangiser]

You're doing great BK.  Thanks for the update.

[Pritch]

Thanks for the link, BK!  Sounds like a great project.  One thing I noted from Gary's plan is that he emphasized that polystyrene would not stand up to the high heat and that there is another "poly-something-or-other" (technical term)  that was better suited. 

-- Pritch

[Bishopknight]

I assume you mean the the pex-alum-pex Pritch. Yes you're right, I cant use my regular pex in the actual heater.

Anyways, I have pics from this past weekend that are going to go up tonight. I haven't been updating this blog with pics lately because I'm either up in Maine 3 or 4 days a week or working like crazy to just keep up with the cost of building this house. When I am home, I usually spend my free time with my lady. We saw Star Trek last night. It was excellent.

This past weekend:

• Bought a used Vermont Castings Resolute Acclaim Wood Stove off craigslist for $400
  http://www.vermontcastings.com/content/products/productdetails.cfm?id=141
• 
  Murray Oil came out to install the propane lines for close to $400 in labor and materials. By drilling lines and moving insulation, I saved myself 2 hrs of his labor
• hung about 8 sheets of 1/2" 12' drywall
• Installed the shower/tub valvebody, icemaker and washer dryer valve hookups with pex. I had to order the icemaker and washer dryer box online because lowes doesn't sell them
• Tested the Goulds 1/2 HP pump I bought off craigslist for $50. It ran but had no suction, even after I filled the intake with water. It may be broken. This bummed me out slightly. Getting water to pump in is a big goal for me right now.
• Created a new 8x4 work bench
• Cut a hole in the roof and installed the 3" DWV vent stack and roof jack, then carefully insulated around where the pipe went through the top plate.
• contact cement clued 40 mil shower pan membrane to the sides of the tub, then laid 1/2" DUROCK over it with galvanized 1 1/4" screws
• Returned a $494, 200 amp meter disconnect and found the same thing on ebay for $50 with $53 shipping. I needed one because my meter is 30 feet from my main panel and code requires a disconnect if the distance is more than a few feet.
• Started framing the gable end trim
  

Next weeks task list

• Buy a shallow well pump from Home Depot $177 and install it with the pressure tank
• Pressure test the pex lines and check for leaks
• Have more drywall delivered and finish drywalling ceiling and some remaining living room areas
• Run the remaining electrical conduit and finish up preparations for power hookup

I also bought a "Flip" video recorder for $60 on Amazon. It takes up to 30 minutes of video and converts it to .mpg so I can upload it to youtube or my website. I tried it out last night and it works great. I hope to test it out this weekend in the house, giving a 3 minute tour of the entire place
http://www.amazon.com/Flip-Video-Ultra-Camcorder-30-Minutes/dp/B000V1PXL4/ref=sr_1_4?ie=UTF8&s=electronics&qid=1242125249&sr=8-4

[HomeschoolMom]

Can't wait for pics!!!!

[EcoHeliGuy]

Hey BK

I have been having problems with your website, most of your photo's arn't loading, but If I open them in a new tab they do.

I am using safari, If your on windows you can download a windows version of safari for troubleshooting.

Keep the photo's and Video coming   

[Bishopknight]

You're the 2nd person to mention that. Sorry about that McBane, its probably because I'm trying to link pictures from google picasa incase my bandwidth explodes or something.

I'm probably just going to put all pictures up there though. I haven't experienced any bandwidth problems yet so if something happened, I'd just deal with it then.

[Bishopknight]

Heres the 1 and 2" conduit, tri-plex and 4 ought SEU wire for the meter to panel connection. I also got a 100' of 1" water line.


Most of the kitchen drywalled but pex elbow sections not hung until I can pressure test them. The utility room is not drywalled at all where pex or DWV is located. 


Main hallway hung with drywall with an above head storage compartment which will hold quite a bit of things.


Shot of the shower. Next time I will photograph the actual pex installation I've done.


Another view of the living room. The 4 ought quad-plex SEU is not installed yet because I had to order a 200 amp disconnect combo box.


Shot of the entryway.


My master bedroom with queen bed and tv/dvd combo unit ( great for relaxing and watching Battlestar Galactica on )


My $400 craigslist Vermont Castings Wood Stove. This sucker is heavy.

[Alasdair]

BK,
It's looking good, You're fairly rattlin along there! Great buy on the stove - we just got an "aspen" by vermont castings on kijiji for $500 cnd and considered that a good deal! I checked out your vid on youtube. I thought you came across very well. Good of you to put your hard won knowledge out there for others. Nice one.
Al

[MountainDon]

My $400 craigslist Vermont Castings Wood Stove. This sucker is heavy.

Oooh! A porcelain one.     

Heavy... nothing but the best recycled American V8 iron... well maybe not just V8's   

[bobtheengineer]

Just one question for you.  Based on an observation, I haven't ever seen before.  What was the reason for putting lumber perpendicular to the roof trusses?  I've always seen it done, with the drywall attached directly to the btm chords of the trusses.  There must be a reason for what you did, just curious.

[MountainDon]

I'm not sure why BK did it; sometimes that is done as it provides a method, a chance, to even out any irregularities the the trusses or ceiling joists. There was some other reason I read about and have forgotten. 

[sjdehner]

Hey Bishop,

You're certainly making some nice progress out there in the hinterlands...your place looks great! All that dry-walling...ugh. But it's wonderful to have it done.

Today marked the "end" of our building process here on the coast. Continued success and joy with your project!

Nice stove too. We have a VC's Encore on the main floor (also porcelain) and a little Aspen for the insulated basement. The top-loading is nice but we noticed that we have to add fresh rope gasket each season.

Thanks for sharing more pictures,

Shawn & Jamie

[Bishopknight]

Thanks Alasdair, I just tossed that video up there. I look tired in it.  I'm having fun with it all though.

LOL MountainDon 

Hey Bob, those are 1x3 strapping. I did it to make laying the drywall easier and also to be able to put up the insulation back in January without stapling it to the trusses. Also, when a piece of drywall doesnt land right on the next strapping, I can just put up a scrap piece ( if theres room ) and not have to cut the drywall. Works out really nice for us lazy drywallers MountainDons right also, I heard it helps with smoothing out irregularities. I was a little worried just going end to end on truss with drywall and the strapping was really cheap so it worked out good for me.

Congrats Shawn and Jamie! I've shown your site to my girlfriend. Your house is beautiful. You've accomplished something many people can only dream of.