Combiner box questions

verdigo

I m looking to build or buy a combiner box for 4 panels rated at almost 8 amps each. Not sure if I'm using breakers or fuses yet, but am assuming 10 amps per panel. I have a buddy who has some old A/C breaker boxes to scavenge a couple of bus bars from. The combiner box will be located in a shed about 25 feet from the panels. Any advice would be appreciated on building this, or would I be better off just buying a manufactured unit. Thanks.

Dennis.

verdigo

Re: Combiner box questions

I guess I sort of put the cart before the horse in that I should introduce myself and give a description of what I am trying to accomplish. I have a couple of grape solar 280 watt panels. My plan is to build a grid tied/off grid system for a hobby as much as anything else. I spend a lot of time at my father'shouse taking care of him as he is totally disabled. I have so far built a structure to mount 4 of these panels. Afte doing a lot of reading on this forum and other sources I find I need to slow down and spend my money a bit more wisely.
Thanks.
Dennis

BB.

Re: Combiner box questions

There are prewired combiner boxes with fuses or breakers--Some are even available with MC 4 connectors.

And, there are "e-panels" that are prewired DC/AC power panels that are designed to connect up to an Outback or other brands of inverters/charge controllers, etc.

Like many projects, the first time you do them, it is sometimes very nice to purchase the pre-wired panels instead of buying all the piece parts, driving 4 hours to the cabin and find that you are missing a couple stupid little parts.

Another way is the build the power system at home on a plywood panel--Test it, then take the whole assembly to the cabin and bolt up.

Fuses will be cheaper, breakers are nice because they can be turned on and off (pulling fuses when under load can cause arcing and wear on the contacts).

Regarding the value for the solar panel fuses--There should be a fuse rating on the glossy for the solar panel... Normally somewhere around 1.56 to 2.0 time the Isc current. A 10 amp fuse on an 8 amp panel is a bit close and may false trip on you.

-Bill

Photowhit

Re: Combiner box questions

verdigo wrote: »

...My plan is to build a grid tied/off grid system ...

While there are hybrid systems (think expensive) in less expensive system you need to pick one or the other. If your refering to dangerous, not code compliant, cheapy plug in the wall 'grid tie' inverters off Ebay, I'd rather not help you.

A grid tied system will use a pretty high voltage string, or micro inverters at the panels and likely you won't need a combiner for a small system if indeed you can reach the voltage required.

For strickly off grid, charging a battery. Pick a battery voltage, then figure out how many panels you have, "a couple" or "4". For 2 panels you won't need a combiner box. For 4 feeding a 24 volt battery (provided they are 12 volt nominal panels) you likely can run 2 strings again with out a combiner box. For more than 2 panels, feeding in 3 lines or more, you would typically need a combiner box.

Since your some 25 feet from your pont of use? It's likely cheaper in the long run to combine at the panels and just run a single set of wires to the Charge Controller, Something like this fused box PV4 - MC4 might seem like a lot of money at $150, but if you mount your panels so they are oriented to feed / snap into the boxes MC4 connectors, you might be money ahead, when you consider all the odds and ends you'll need to put together to be 'code compliant' Box, breakers of fuses, mc4 cables.

niel

Re: Combiner box questions

verdigo,
welcome to the forum.

i think we should ask you what it is the loads aka purpose of your solar setup will be for? also, this should be elaborated on to know what you meant here by saying, "My plan is to build a grid tied/off grid system". technically, the way you said it it is contradictory. if a hybrid system that is actually a battery backed grid tied system is what you meant, then know that you can do this with some outback and sma inverters, but as was indicated already, they are higher cost inverters.

"After doing a lot of reading on this forum and other sources I find I need to slow down and spend my money a bit more wisely."

good idea.

verdigo

Re: Combiner box questions

Thanks for the replies. My intention is to first make this a grid tied system while building in the capacity to use as backup for power losses. So I guess for planning purposes it will be grid tied with battery backup. I have two of the grape 280 watt panels with plans to order two more. The battery backup will be 24 volts. The combiner box will be for a total of 4 panels rated at 280 watts, 36 volts at 7.7 amps.

Photowhit

Re: Combiner box questions

I admit to being ignorant of grid tied systems, which is what you appear to want to start with. I think you might want to do an SMA inverter for your grid tied system, I think they can later be tied to a sunny island system for off grid use. To be frank, I'm not even sure I got which is which right, but it might give you a place to start searching. I do think you likely will want to and may need to go with more panels to reach a grid tie voltage. Also I think you should likely have a target wattage as you won't want to buy and replace grid tie inverters as you expand your system.

I sure hope someone will come along with some more info, but searching SMA and sunny island may help you find threads that will aid you.

The very title of this thread wil not help you find the info you seek as for a grid tied system you will want to string panels to reach 240(?) or more volts for a grid tied system and won't need a combiner box until you add your third string of panels if you ever do...

vtmaps

Re: Combiner box questions

verdigo, another thing you need to do before you spend any money is talk to the local power company (poco). You cannot legally connect a grid tie system without following their rules and getting the appropriate permits. The cost and hassle of permits means that it is difficult to grow the system incrementally.

Many folks with non-permitted systems have discovered that when they feed power to the grid, their meter still runs forward so they end up paying the poco for the power they produce. Other folks with non-permitted systems have found themselves disconnected from the grid when the poco discovered their system.

Also, your insurance company may deny claims if your system uses any non UL listed components.

--vtMaps

verdigo

Re: Combiner box questions

I do plan on talking to the electric company as well as getting an electrician to replace the house breaker box. It's an old house. Did some reading about the SMAs. Nice. Expensive. I own and operate an automotive garage. I'm gonna have to flip a couple of cars to buy one of those. Iv been working on an old VW Bus for a camper of sorts, which is how I came about the buying the first Grape panel. Now its turned into something else. Did some reading on the Chinese grid tie inverters. I wouldn't mind playing with one of those, but I don't think I would walk away from one while in operation. One good size surge and it might burn down the house.

ggunn

Re: Combiner box questions

verdigo wrote: »

Thanks for the replies. My intention is to first make this a grid tied system while building in the capacity to use as backup for power losses. So I guess for planning purposes it will be grid tied with battery backup. I have two of the grape 280 watt panels with plans to order two more. The battery backup will be 24 volts. The combiner box will be for a total of 4 panels rated at 280 watts, 36 volts at 7.7 amps.

Do you realize that you cannot use the same inverter for a grid tied PV system as an off grid one?

Cariboocoot

Re: Combiner box questions

ggunn wrote: »

Do you realize that you cannot use the same inverter for a grid tied PV system as an off grid one?

Unless you buy a hybrid battery-based GT inverter. More money than either of the other two types but less than one of each.

Photowhit

Re: Combiner box questions

'Coot, Do you know anything about the GVFX Outback series? It looks like it is about the same cost as the Off grid inverters and the only problem I see with using them Off grid is they don't take generator input, at least not cheap gennys...

Curious, since my local power company has pressure from the state now to get a % of their energy for renewable sources, I'm considering one for off grid use with the idea that if they decide to welcome renewable sources (apply generated power toward $25 user fee) I might be willing to do a grid tied system. Works for me since I don't use other sources for energy.

Perhaps Robin or boB would know, I think they are a tiny bit less efficient.

Cariboocoot

Re: Combiner box questions

As far as I know there's not a lot of difference. Tighter specs on AC IN (but can be reprogrammed) as you said and different handling of the IN & OUT due to GT ability.

There's a debate going on elsewhere as to whether or not the gen support feature actually functions.

You can bet Robin and/or boB would know them inside-out.

ggunn

Re: Combiner box questions

Cariboocoot wrote: »

Unless you buy a hybrid battery-based GT inverter. More money than either of the other two types but less than one of each.

True enough, but when most folks speak of a GT inverter, that's not what they are talking about. I don't have a lot of experience with those (Outback?) inverters; can you run them in pure GT mode without batteries? I didn't think so, but as I say, I don't know them very well.

Cariboocoot

Re: Combiner box questions

ggunn wrote: »

True enough, but when most folks speak of a GT inverter, that's not what they are talking about. I don't have a lot of experience with those (Outback?) inverters; can you run them in pure GT mode without batteries? I didn't think so, but as I say, I don't know them very well.

No; hybrids of any brand are all battery-based. No batteries = no function. There's no "pure GT mode". But their existence is one of the reasons people get confused and think a standard GT inverter can be used as an off-grid inverter. There are a number of people running Xantrex XW's strictly off grid and more who use the for grid tie.

As my grandfather used to say: "You can't win for losing." :roll:

ggunn

Re: Combiner box questions

Cariboocoot wrote: »

No; hybrids of any brand are all battery-based. No batteries = no function. There's no "pure GT mode". But their existence is one of the reasons people get confused and think a standard GT inverter can be used as an off-grid inverter. There are a number of people running Xantrex XW's strictly off grid and more who use the for grid tie.

As my grandfather used to say: "You can't win for losing." :roll:

That's what I thought. You can't start with a GT system and take it off grid later unless you start off with a hybrid (which isn't really a GT system and you have to pony up for batteries as if it were off grid) or add a Sunny Island between the GT system and the grid, and even then the Sunny Island won't play nice with many GT systems.

stephendv

Re: Combiner box questions

ggunn wrote: »

That's what I thought. You can't start with a GT system and take it off grid later unless you start off with a hybrid

There's a fairly new product on the market over here that looks like it does allow this. Start off with pure GTI and then add a special battery module to provide either backup or off-grid use:
http://powerrouter.com/products/powerrouter-solar-inverter doesn't look like it's available in the US or Canada yet.

ggunn

Re: Combiner box questions

stephendv wrote: »

There's a fairly new product on the market over here that looks like it does allow this. Start off with pure GTI and then add a special battery module to provide either backup or off-grid use:
http://powerrouter.com/products/powerrouter-solar-inverter doesn't look like it's available in the US or Canada yet.

Interesting. Looking at the battery section, the largest battery it supports is a "5kW" (I assume they mean 5kW-h) 24V lead acid battery. That's only about 208A-h; that's not very big.

Photowhit

Re: Combiner box questions

ggunn wrote: »

You can't start with a GT system and take it off grid later unless you start off with a hybrid (which isn't really a GT system and you have to pony up for batteries as if it were off grid)....

I wonder what the minimal battery is? If you could just add some small AGM or even gel batteries and be Good -to-go, with an Outback GVFX3524. They would have mionimal capacity so you would basically have a Grid tied system until you wanted to have a 'real' back up battery bank.

Really a question for Robin or boB or second choice the Outback forum...lol.

Cariboocoot

Re: Combiner box questions

Photowhit wrote: »

I wonder what the minimal battery is? If you could just add some small AGM or even gel batteries and be Good -to-go, with an Outback GVFX3524. They would have mionimal capacity so you would basically have a Grid tied system until you wanted to have a 'real' back up battery bank.

Really a question for Robin or boB or second choice the Outback forum...lol.

That ol' ripple current issue comes up again.
I'd say 350 Amp hours minimum. And there you're at pretty decent capacity: up to about 4 kW hours available.

Photowhit

Re: Combiner box questions

That would aonly be if you intended to draw from the batteries, just figure to have the system go, "off line" basically defeating the backup, if the grid goes down, or perhaps I don't understand how these inverters work?

Cariboocoot

Re: Combiner box questions

At full output and full Voltage the power coming from the panels is pulsed DC (in order to maintain the Voltage set point), not steady DC. You need the battery capacity to filter the pulses into a steady DC input for the inverter.

Not the same as with a standard GT inverter that just takes whatever the panels feed it and turns it into whatever current it can on a continuous basis.

Photowhit

Re: Combiner box questions

Thanks! 9 12 15