30x40 Earth Berm Passive Solar in Maine

[glenn kangiser]

[Bishopknight]

Thanks everyone for your help. I'm definitely taking all opinions seriously.

I subscribed to Homepower earlier this morning and got serious about expanding my PV knowledge. I took screenshots of 2 possible layouts ( from articles ) that I may use to achieve a grid-tied ESP ( emergency service power ) setup.

I have a question: In a grid-tied battery backup system, is 48vdc my primary option? And why?

I really like the combiner box in the bottom left of this diagram. I read that the junction boxes of solar panels are only rated for 7amps each. If you daisy chain 3+ panels in a row, the wire is not rated to hold that current and may potentially fry the panel or drop amps.
These are not what I'm using, just screenshots of other peoples setups


This is similar version from a different homepower article.

[glenn kangiser]

That is why I question the "professionals" that appear as authorities on some of this stuff.

As voltage goes up, current goes down and smaller wires are required.

3 -12 volt 100 watt panels produce 300 watts at 12 volts parallel or 25 amps, but 3-100 watt panels daisy chained produce 300 watts at 36 volts or 8.3 amps.  Our 125 watt x 12 v panels are about 10.4 amps

One of our 135 watt solar panels at 17 volts produces 7.94 amps.  They are daisy chained - (series) in two panels and paralleled in two.  Amp - hence larger wire sizes are required for parallel - not series.

They will always have a safety factor in their wire.  I think that what they are saying may be BS.  Maybe they want to sell combiner boxes.  The new outback inverters will take several daisy chained panels and the Grundfos pump we daisychained many panels together.

[glenn kangiser]

The bottom picture - while maybe a generalization, would lead you to believe that the batteries don't require a regulator - I wonder if that is really the case - doesn't seem it could be as possibly if it is sent to the grid things may be OK, but when the grid is down the batteries would get all of the power and be destroyed without regulation.

I think the reader has to already understand what these "pros" are saying to safely use their information.

[MountainDon]

Re: the first drawing. Connecting the panels in parallel like that is not wise, IMO. Connect them in series. HOWEVER to do that you need the right charge controller. The less expensive controllers may not be able to handle the voltage resulting from the series connection.

Also, that setup as drawn might have another problem DEPENDING on the panel being used. If the panels were of the nominal 12 VDC output variety, connected in parallel, using a typical low budget charge controller, on a cloudy day they may not be capable of putting out enough volts to actually get a charge into the batteries. (Seems like the batteries are wired for 12 VDC)

PV panel output voltages range all over the place, 12 to 50 VDC and even higher.

[MountainDon]

Are you planning to be grid tied? If so check with the power company to see what they allow. As well they may have a list of equipment that they authorize; it may not include everything out there in the marketplace.

Here in NM until a few years ago the power company did not allow grid tied PV systems to have a battery backup system. Now they do allow that but there must be an exterior manual transfer switch so the power company crew can disconnect or isolate the battery / inverter section from the system. This ensures the crew won't get zapped by the backup if the crew is working on the power grid side. Outside and not locked; they must be able to visually verify the circuit is broken.

I don't think either of those drawings are totally accurate. They don't show an AC disconnect or transfer switch. No DC fuses or breakers between the inverter and batteries. And as noted no charge controller in the second simplified system. (no neutral or grounds)

[glenn kangiser]

I question the value of drawings and information that are simplified enough to be dangerous.  That was a problem I had with Backwoods Home magazine also.

[MountainDon]

Here's the best drawing I've found showing a hybrid PV grid tie system with battery backup and a generator. It's from an Outback publication. Even it leaves out things like the disconnects, fuses and/or  breakers for the batteries and inverter..... It is a divided system; that is a sub-panel is used to power the essential electrical equipment; refrigerator/freezer, computer and internet, iron lung... 



What's pictured shows a single inverter giving up to 3500 watts 120 VAC only; gets more complicated if you need backup 240 VAC or more watts total. The Outback inverter will automatically feed power to the sub-panel when the grid kicks off. It well also not use power from the grid to charge the batteries at night when there is no PV power. There are also examples of simpler systems.

Outbacks website has loads of info resources, revolving around their products, of course. Goto
Resources | Documents | Brochures and download the Backup Power Solutions PDF document. Another good one is the Grid-Interactive Solutions brochure. Lots of other stuff there to read.

[glenn kangiser]

I think Outback is much better than the generic unknown name grid only one I saw.  What use is grid only?  None for me.

[MountainDon]

FYI, Outback was founded by three engineers who used to work for Trace. After Trace became Xantrex they became disenchanted and set out to build the better equipment they wanted to build ans Xantrex did not. Or so the story goes.

Their equipment is US designed and US assembled. Some parts are imported to have competitive pricing. Still very good stuff, IMO.

Outback should pay me.    Sorry if I exhibit a bias.

[ListerD]

Great info! Thanks 

But I have to ask, looking at their graphic in the pdf, what dork powers their toaster and coffee pot on a limited source like a battery backup? Kind of a heavy load no?   I'd liken that to having a water storage tank where the whole bottom is the valve, one use and it's all gone. 

[glenn kangiser]

Dork -- that's me.

We do the toaster, Microwave, coffee pot, welder, rock crusher, 1 1/2 horse water pump, washer, gas drier w/standard electric motor, etc.

Many of these loads are intermittent  - ie: not long periods of time so the overall draw doesn't kill the system if it is big enough.  Ours is larger than many but even a small system could take quite a bit. 

Our standard semi-efficient refrigerator is one of our heavy loads but we also have a smaller efficient 1934 GE Monitor Top refrigerator and 2 freezers.

An electric heater is another story.  Just the straight draw for a long period of time will kill the batteries.

[ListerD]

Dork -- that's me.

Heh, oops    I just learned with our hunting cabin years ago that toasters and the like (anything with a heating element) was bad news. So I learned to do it over a fire. 

We do the toaster, Microwave, coffee pot, welder, rock crusher, 1 1/2 horse water pump, washer, gas drier w/standard electric motor, etc.

How big is your system?

[glenn kangiser]

We have around 2600 watts of panels and a 1kw wind generator.  Since I put it on the tracker we  have around 15 kwh or more to play with per day.  More if we get some wind to play with.  More once I get more panels on the tracker.

The heaters are bad but if used intermittently they are not as bad. A propane cookstove, water heater - drier  can save a lot of electrical panels.  You are right about that.

Say 1000 watts for 6 minutes is only 1/10 kwh so doesn't kill the batteries too bad.  Still depends on the system.

[Bishopknight]

Ok,

So going 24v is making alot more sense now, especially with alot of cloudy days in Maine where with 12v, the current may not reach the charge controller.

I also agree, I've heard great things about Outback. My next goal is to find an inverter/charge controller by outback that will allow me to start with 6 panels but expand as well and be grid-tied. The search is on.

[update] - I might be able to use my existing Tri-star TS-45 along with a 24v inverter that has subpanel power hookups. I'm glad I have all this time to think about this. Its a complex subject of balancing cost and functionality. 

[MountainDon]

Outback makes 2 charge controllers. They differ only in the amps they can handle, 60 or 80. Max volts is the same.

Calculate your power needs first. Then the storage capacity needed. Depending on what you need for storage is sometimes easier to go to even 48 VDC as the system basis. No difference on the Outback equipment pricing.

The nice thing about going to a 48 VDC system is that you might be able to reduce or eliminate parallel strings. A single string of batteries or cells than can supply the required storage amount is ideal. Doing this may require the use of more expensive batteries in some cases. It's worth exploring before you buy equipment.

I'll have to add some of this to the off gid topic, or cross link.

[glenn kangiser]

Only bad thing about one string of batteries is that one bad battery or even cell and the whole system is down.  With parallel battery strings - you can keep the power going and weed out the bad ones.

Maybe Don knows a reason that isn't the best but it's what I do.

[MountainDon]

Answer is over HERE:

[Bishopknight]

That makes sense.

I did some analysis of my current setup if I were to dedicate it to powering the new house office:

Batteries: 88 AH * 4 (qty) * 12v = 4224 WH

Office power demands: 240 watt = computer, monitor, printer, desk light, speakers ( used my kil-a-watt to get data )

My solar panels output: 130 ( watt ) * 3 ( qty ) * 4 ( hrs ) * .85 = 1326 WH

My panels will supply 5 hrs of usage per day. My batteries will store 3.5 days worth of charge.

Adding a 4th solar panel would allow 7 hrs of usage per day ( 1768 / 240 = 7.3 )

[Mike 870]

Don't forget to correct for inverter inneficiency (if you're running one), and battery inneficiency.  Also I couldn't tell from your numbers what depth of discharge you are assuming for your batteries.

Another thing to consider is that batteries are sometimes rated for different speeds of discharge (discharged over X hours).   The amp hour rating can change accordingly.

[Bishopknight]

Good point mike,

My batteries were old to begin with ( used data backup batteries from the Gamestop Headquarters in Grapevine, TX ) so if I only get 2-2.5 days backup, they will do, until I buy some Rolls or Trojans.

My inverters name brand does not inspire confidence in me either, "Go Power!" LOL

[EcoHeliGuy]

First post,

Ok I have been studying building an earth bermed home, have rob boys book.

I see too things about you house I'm not sure about. Hoping you can shed some light.

First I understand what your saying about not worrying about frost in the foundation due to being bermed, but your not berming the front, so shouldn't you have lowered the footer here? I know you can insulat the ground area around, but I would have still gone lower in the front.

Second I do not see anything done about possible radon gas?

oh ya can you also keep posting the cost, I love this part. It helps alot.

Oh yes the stove air supply, I lived two hours east of Calais Maine, we tend to say "eh" alot, but anyway I know the moister problems we have and, I would have suggested poking hole in the bottom of that pipe in each rib, this would allow the moister to drip out.

and last I was wondering why you decided to berm so little on the side of the house?

[Bishopknight]

Hey McBane,

All good questions, I'll give you my personal viewpoint on them.

First I understand what your saying about not worrying about frost in the foundation due to being bermed, but your not berming the front, so shouldn't you have lowered the footer here? I know you can insulat the ground area around, but I would have still gone lower in the front.

My front is built up on 2-3 ft of sand pad, which resists frost heave. Also, this spring I plan to bury a skirt of XPS around the un-bermed areas of my foundation for peace of mind. The ground froze too fast after I poured my foundation that I could not do it last fall.

Second I do not see anything done about possible radon gas?

I'll have a drainage skirt around my foundation that should vent the radon off.

Oh yes the stove air supply, I lived two hours east of Calais Maine, we tend to say "eh" alot, but anyway I know the moister problems we have and, I would have suggested poking hole in the bottom of that pipe in each rib, this would allow the moister to drip out.

I am considering pouring a resin into the vent to mold into the bottom ribs, therefore creating a gradual dripway for the moisture to escape to. Personally I dont think it will be much of a problem though, we'll see.

and last I was wondering why you decided to berm so little on the side of the house?

I wanted windows partially on the sides. I didnt want to feel like I was looking out of a tunnel.

Thanks for the questions, feel free to ask anything.

- BK

[Dog]

Hey Bishop...it seems like your timing is working out really good. Since we're well into winter the building part has slowed. Good to be figuring out the power.

The days are already getting longer! 

[Bishopknight]

I'm not giving up yet Dog!

I went up there Saturday to try melting the ice. I had 70k and 115k BTU reddy heaters going for 5 hrs but was unsuccessful. The inside got up to about 80 degrees quickly but the thermal mass in the slab and walls was why the floor wouldn't melt.

I have a new plan though. ( I wish I thought of this up there! ). I may try again this weekend but in a different way. If I angle the heaters down at the slab and heat it up, I may be able to warm the cement slab floor up enough to create separation from/release the ice above it.  Atleast just enough so I can use this tool to get under the ice, pry it up, break it and toss it outside.

Sort of like peeling wallpaper, attack one area at a time.



I also bought another anderson 400 series, triple casement window for $200 this weekend. 6ft long by 3 ft tall.  Brand new, still in box, retail is $750 the guy said. He bought the wrong one for his house and couldn't return it.