Got my solar power off-grid system up and running (finally)

[kahle]

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I've been working on this for a long time and I finally got my solar power system all set up and functioning. I ended up designing it myself mostly because I couldn't find anyone that was willing to do much more than just sell me a package. I made the mistake of buying my Solar Panels back in 2007 when I first started thinking about this. That turned out to be a HUGE mistake because the price of PVs has dropped considerably since then. If I had waited until this year to buy them I would have paid 1/4 of what I did back then.

The good news is I found a 2000 Watt Pure-Sign Wave inverter on Amazon for only $340 bucks.

Anyway, I've never seen any kind of guide that would tell you the proper ratio between you PV watt size and your battery KWh size. I ended up with only 250 watts of PV and 5.4 kWh for a battery bank. In my case, I often only use the cabin on weekends so there is a long time for recovery. That's why I figured I could get away with this particular ratio. But some of the cabin kits I saw had even worse ratios than that.

I went with a 24v system because (1) I don't really have any need for any 12V DC takeoffs, and (2) doubling the voltage allowed me to use smaller wiring.

I got a 2000 Watt inverter even though my lighting load is pretty small. Maybe 300 watts total. But my occasional loads, a circular saw, a hair dryer, a vacuum cleaner or a waffle iron should run without an issue there. The inverter eats up about 50 watts of power just being on and maybe a smaller one would consume less. I'm not all that familiar with inverters. Maybe that's a big energy debt to pay for the small amount of power I actually need?

My charge controller can handle another 500 watts of PV if I want to add them later. But I'm just going to see how well this works first before I start to tinker.

Anyway, anybody want to critique my design, feel free.

Paul

[rreidnauer]

I've been working on this for a long time and I finally got my solar power system all set up and functioning. I ended up designing it myself mostly because I couldn't find anyone that was willing to do much more than just sell me a package. I made the mistake of buying my Solar Panels back in 2007 when I first started thinking about this. That turned out to be a HUGE mistake because the price of PVs has dropped considerably since then. If I had waited until this year to buy them I would have paid 1/4 of what I did back then.

Yea. I made the very same mistake. Thought there was going to be a supply/demand issue when energy prices went nuts back then, and I thought I done real good at $4/watt. (LOL)

The good news is I found a 2000 Watt Pure-Sign Wave inverter on Amazon for only $340 bucks.

Anyway, I've never seen any kind of guide that would tell you the proper ratio between you PV watt size and your battery KWh size. I ended up with only 250 watts of PV and 5.4 kWh for a battery bank. In my case, I often only use the cabin on weekends so there is a long time for recovery. That's why I figured I could get away with this particular ratio. But some of the cabin kits I saw had even worse ratios than that.

Really? Actually there is a standard, and I know I've even posted it on these forums several times. Anyhow, the best ratio is 20:1 (battery watt-hours to panel watts) It's basically figured by taking the top 25% of your battery bank's capacity, and figuring five hours to recharge that. However, the ratio gets smaller if you are using more power and/or figuring multiple 'non-charging' days. A lower ratio isn't harmful, just inefficient.

I went with a 24v system because (1) I don't really have any need for any 12V DC takeoffs, and (2) doubling the voltage allowed me to use smaller wiring.

I got a 2000 Watt inverter even though my lighting load is pretty small. Maybe 300 watts total. But my occasional loads, a circular saw, a hair dryer, a vacuum cleaner or a waffle iron should run without an issue there. The inverter eats up about 50 watts of power just being on and maybe a smaller one would consume less. I'm not all that familiar with inverters. Maybe that's a big energy debt to pay for the small amount of power I actually need?

Using a modified wave inverter is way more efficient on standby power usage. It's what I use in my RV right now, since I don't have any AC motors that need to be driven. (the only real need for pure sine wave) You may want to consider getting a second inverter to run the lighting and resistive loads, and save the pure sine for your AC motor needs.

My charge controller can handle another 500 watts of PV if I want to add them later. But I'm just going to see how well this works first before I start to tinker.

Usually charge controllers are rated in amps. What do you got? I STRONGLY recommend MPPT charge controllers. (that's a type, not a brand)

Anyway, anybody want to critique my design, feel free.

Paul

[rreidnauer]

Oh, and is that AC switch being used on DC?

[loghousenut]

Oh, and is that AC switch being used on DC?

I think that switch is on the AC side. I'm wondering if you couldn't bump up the wire size from battery to inverter. Not a long run but that is the side where less resistance really matters.

I can't chime in on the sine wave inverter thing. When we bought our inverter, we thought we were getting a bargain at $1 per watt for our 2,000 watt Trace square wave. I guess it has been a few years. By the way, that inverter and the expensive solar panels are still going strong in the bus after all those years.

[kahle]

Oh, and is that AC switch being used on DC?

I must confess that that standard light switch is the one I use to isolate the PV array from the rest. I figured it wouldn't matter much since it's only a 10 amp load. Did I figure wrong?

[rreidnauer]

I thought so. Yes, it could come back to haunt you. DC can carry an arc quite easily when opening contacts. And in an AC only rated switch, the open contact gap is small, and opens relatively slow, which allows a DC arc to burn the contacts. The main time you'd do damage, is turning the switch off when the panels are in full sunlight. Eventually, the switch won't turn back on, or worse, could catch on fire with a sustained arc. (you'll hear the hiss of an arc in the switch)

[kahle]

The charge controller I got is http://www.theinverterstore.com/30-a...-24-volt.html# this one which does not specifically say it is MPPT but from the description, I figured that it was the same thing. This is rated at 30 amps.

The reason I used the AC switch is that I didn't see any DC switches listed anywhere. Can you point me to a supplier? Or better yet, an actual switch?
I'm not sure it makes much difference, I only use the switch when I'm working on the control panel and I'm hoping that part is done with for now.

Ron mentioned the size of the wires I have used between the battery and the inverter. I thought they looked small too. But those are the wires that came with the inverter so I figured they had to be sized correctly. No? Should I upgrade?

[loghousenut]

They are not the largest battery cables in the world. In the dark ages the folks over at Home Power Magazine always preached upsizing those inverter cables. Said it was cheap efficiency that lasted longer than the installer. We used 0000 size on our 2000w system but twice the length you have.

As for the AC switch, I thought Rod was talking about the master switch. When I built the 12 system in the bus some 30 years ago I put in mostly used 110v switches and they are still going strong. They don't work anymore but they look good.

Probably ought to either change it or eliminate it altogether. I'd feel safe with no switch there at all.

[rreidnauer]

That charge controller you have is PWM. (pulse width modulation) You won't get all the power available out of your panels, like you would with an MPPT. (maximum power point tracking) It's all in how they function, and I won't go into all that, but PWM will create panel performance losses of around 30%. (you will only get about 70% of the rated power of the panel) MPPT will have practically no losses. (in fact, I've seen slightly over 400 watts being extracted from my 350 watt array at one point!) But the real advantage isn't the performance loss advantage. It's the flexibility the controller provides. I can use the same controller to run a 12, 24, 36, 48, or 60 volt battery bank, and I can send any PV voltage from bank voltage up to 150 volts to the controller. The advantages being, it makes expanding the system easy, and your wire sizes can be much smaller and have lower loses at those high PV voltages. Granted, you will pay for that benefit.

The switch: I'd trade it out for a DC breaker instead.

As for wire size to the inverter, like LHN said, bigger is always better. I found the cheapest places to get heavy cables made up are at those battery warehouse store locations. But you don't have to abandon you existing cables either. You can always parallel on another of equal gauge.

I put in mostly used 110v switches and they are still going strong. They don't work anymore but they look good.

I'm still trying to figure out what politician LHN is trying to mimic with that line.

[StressMan79]

Don't remember but I think ac switches are OK up to 50 volts dc.

[loghousenut]

Don't remember but I think ac switches are OK up to 50 volts dc.

Not that one.

[Longhare]

Congrats, Paul!

Just curious, what batteries did you go with?

[kahle]

OK, so now I feel stupid, yeah I remember being told to make sure I got an MPPT charge controller way back when. So, I'm shopping for one now for this little system and I find that there's a number of really cheap ones and some really expensive ones and they all say they do exactly the same thing. But now I'm suspicious. I only need to handle about 40 V max input and about 10 amps max output. Got any recommendations?

[kahle]

Ah Longhare. I went with 4 Full River DC224-6 AGM batteries. These are 6 volt 224 Ahr batteries but they aren't the flooded type. The AGM (Glass Matt) batteries won't freeze on me over the winter. My PV setup is out in an unheated garage up in the mountains and it gets durn cold up there at night. Years ago I actually froze a flooded lead-acid battery but that was probably more because I had let it discharge than an actual problem with the ambient temperature. Anyway, I wanted to avoid that issue tis time round. The batteries are connected in series to make one 24v battery.

[rreidnauer]

OK, so now I feel stupid, yeah I remember being told to make sure I got an MPPT charge controller way back when. So, I'm shopping for one now for this little system and I find that there's a number of really cheap ones and some really expensive ones and they all say they do exactly the same thing. But now I'm suspicious. I only need to handle about 40 V max input and about 10 amps max output. Got any recommendations?

Yugo and Mercades say they do exactly the same thing too.

Recommendations? Think ahead. 40v in, 10a out . . . . . . . . . for now. What about in a year or two when you want to add panels and get more power?

I wouldn't rush out to buy an MPPT controller at this point, just so you have the best. See how your system performs for you for now.

BTW, AGM batteries can freeze too when left discharged, but other damage is done to the battery any time of the year by sulphation when left below 75% SOC for extended periods.

[hotshotrucking]

very interesting info, most I don't understand but aside from many who believe the grid will go down across the country which is a strong possibility just the shear cost of electricity at today's rate and what it will be lets just say 5 years down the road. I went online to read up on the cost of a system and pulled out my current bill and at the top in message it said they were requesting a rate increase. As many of you stated the cost of the panels has dropped, and there seem to be some tax breaks on purchases state & federal. If I retire or when I retire (approx 10 yrs) I just cant imagine spending 25% or more of my income to light my home so yes I'm going to research a solar system in hopes of enjoying my freedom.
I noticed the system that is rated for my current usage but what kind of life expectancy do you expect to get? the one I looked at has a 25-year reliability and warranty, and would be 32 260 watt solar panel system. I'm sure I could go with less but this system says it would more than cover me with 5 hours of average sun light each day. I'm going to continue to research the panels but you guy's that are on them up and running I'm sure have learned a lot the sites don't tell you.

[rreidnauer]

Stay away from thin film panels and short of a big hailstorm, the panels will probably outlast you. My solar panels are 25 years old and I have seen them produce 15% over rated power recently. A well cared for battery bank can last 20 to 25 years. (Edison batteries last indefinitely) Buying reputable brand name products would probably be the wise move.

[StressMan79]

Edison batteries have 2 major down sides.

1. Getting them is not easy.
1.5 most equipment is made to run on lead acid
2. This is bc ldac charges AND discharges @ around 2 v/cell. Charging nife cells occurs@1.7 v. Discharge happens @ 1.2.
A. You have to make a 12v inverter operate fron 10-22v, not 11-15.
B. You lose that delta v in efficiency. 1.2/1.7=70.6% right off the bat.

Sent from my Galaxy S4 using Forum Runner

[rreidnauer]

Yup, if you get hung up on efficiency, then you won't like the Nickle-Iron Edison batteries. They also experience more idle energy losses than Lead-acid, but as long as they provide the power needed, who cares? My panels are also lower efficiency compared to today's panels, but I really doesn't matter. All the efficiency factor means is they produce more wattage per area. All I care about is they produce the wattage they say they will, and that I have enough power for my needs.

The 12 volt argument is pretty mute, as any whole-house system would never be operated at that voltage. More likely 48 volts or higher, and with that, makes matching Edison cells to an inverter/charge controller that much easier.

[StressMan79]

Indeed. Except you pay for each watt you get, say $1000 assuming 100%, you'll need $1300 to run nife batteries.

And 12 volts was only an example. I have a 24v system. Cheap inverters and leds are available... any higher and you naad green energy products... read expensive

Sent from my Galaxy S4 using Forum Runner

[Timberwolf]

Edison batteries have 2 major down sides.

1. Getting them is not easy.
1.5 most equipment is made to run on lead acid
2. This is bc ldac charges AND discharges @ around 2 v/cell. Charging nife cells occurs@1.7 v. Discharge happens @ 1.2.
A. You have to make a 12v inverter operate fron 10-22v, not 11-15.
B. You lose that delta v in efficiency. 1.2/1.7=70.6% right off the bat.

This would be great... in ENGRISH!

[loghousenut]

Peter only speaks Gibberish... You get used to it and just kinda nod your head like you understand.










hahhhaw

[donjuedo]

This would be great... in ENGRISH!

I, Peter (donjuedo) can't speak for Peter (stressman79), but I can provide a little overview about that battery type (you may already know).

Thomas Edison invented a special type of battery using nickel and iron, and instead of acid, he put in potassium hydroxide, if I'm not mistaken (going from memory here). The symbol for nickel is Ni and the symbol for iron is Fe, so a nickel iron battery is often called a NiFe battery, as well as an Edison battery.

Stressman abbreviated because as "bc" and lead acid as "ldac", so that might have thrown you off a little.

NiFe batteries are available from ironedison.com, a US company sourced from China, IIRC. I also found a Chinese source, and the batteries look identical, except for the logo. They gave me a price quote, but I don't recall how it compared to Iron Edison pricing, mainly because I'm not ready to buy, yet.

My first choice for a charge controller is the same Outback model Rod has, but when I scoured the manual, it looked like the low voltage setting to shutdown (to protect batteries) is not low enough to make good use of NiFe batteries, despite a distributor claim to the contrary.

NiFe batteries can drain quite a bit lower than conventional lead acid, so in that way, store and deliver more energy than lead acid that seems the same size. Also, you can ruin a lead acid battery much more easily than a NiFe, and I'm sure I'm going to make mistakes.
:-/


Peter

[Little Eagle]

So i have a question that has been wondering through my head as i really know nothing of solar power, would i need to wire the home with with different wire for solar or can you use the same wire inside as if you were hooking to city power?

[donjuedo]

I have visited a home with 12 volt lighting built in, but that is very non-standard, and I would not recommend that.

It's best to wire the home normally, the solar power is delivered through what's called an inverter. Quite simply, it's an electronic box that takes in 12 volts DC, like car batteries charged by solar panels, and puts out 120 volts AC, like a normal home uses. It would connect to your home's wiring near the breaker panel.

It might look like this:

/------ 120 volts AC <-- inverter <-- 12 volts DC <-- battery bank <-- MPPT charger <-- solar panels
|
switch --> home wiring
|
\____120 volts AC <-- power grid

There are many options to consider, like wiring for 24 battery packs instead of 12. Both can work. Some folks use 48 volts, and that's fine, too.

You could plan to feed the grid with your solar power during the day, and use the grid at night. That's what my brother does, so there are no batteries.
You could go "off grid", and use batteries for power after the sun goes down. Batteries can be the most expensive part of a system.
You could combine options, and use batteries and connect to the grid.
You could throw in a generator to complicate things. OK, for back up, for various reasons.

[Little Eagle]

I have visited a home with 12 volt lighting built in, but that is very non-standard, and I would not recommend that.

It's best to wire the home normally, the solar power is delivered through what's called an inverter. Quite simply, it's an electronic box that takes in 12 volts DC, like car batteries charged by solar panels, and puts out 120 volts AC, like a normal home uses. It would connect to your home's wiring near the breaker panel.

It might look like this:

/------ 120 volts AC <-- inverter <-- 12 volts DC <-- battery bank <-- MPPT charger <-- solar panels
|
switch --> home wiring
|
\____120 volts AC <-- power grid

There are many options to consider, like wiring for 24 battery packs instead of 12. Both can work. Some folks use 48 volts, and that's fine, too.

You could plan to feed the grid with your solar power during the day, and use the grid at night. That's what my brother does, so there are no batteries.
You could go "off grid", and use batteries for power after the sun goes down. Batteries can be the most expensive part of a system.
You could combine options, and use batteries and connect to the grid.
You could throw in a generator to complicate things. OK, for back up, for various reasons.

Ah ok, being a trucker i have a inverter in my truck to run my crockpot and such so i know what you mean now. Good to know i can still run the wiring normally i was unsure about that part. Thank you for the advise.

[BoFuller]

I wired my house like a normal house and now I'm ready to install the solar. Currently I'm planning on 12 panels on the roof (235V) and either 16 or 24 Trojan L16RE-B (6V) batteries, then either one or two Outback 3648 Inverters. I did a worksheet and figured one inverter and 16 batteries would be enough until I factored in my water pump, then it looks like I need a second inverter and 8 more batteries..

[BoFuller]

Actually I'm sticking with the 16 batteries and single inverter. I exchanged my one hp water pump for a 1/2 hp unit.