Solar system disconnetable from panel?

Bmanc21

I am helping a friend design a "simple" PV system for his "on" grid cabin. He's looking for a back up for when the utilities go down (often from what I understand). He does not want to have a permanent set up for his panels, and so I thought about some type of cart with the panels mounted on it. He'd be able to roll it out when needed to charge the batteries, and safely store it while he is not there. He may not be around for a month or more at a time. The cart would contain controller and batteries also.

Here is where I am getting confused. Given the type of set up I described, how could we tie his battery bank (12v) back into his existing breaker panel so that specific circuits can be powered? It needs to be able to connect and disconnect from (potentially) an energized breaker panel. I thought about a disconnect and maybe an Anderson type connector. Does there need to be a disconnect added in case the power comes back on?

What do those with more experience think? Thanks in advance.

BB.

Re: Solar system disconnetable from panel?

The traditional method is to use an automatic or manual transfer switch. Or, just use an extension cord.

Some people, for small loads, have even built their own automatic transfer switches with a double pole double throw relay.

Larger off-grid inverters will even include their own internal transfer switches (and even internal AC to DC battery charger). These basically become a larger UPS system (with a much larger battery bank) that you can run part of your home from (many places with afternoon power outages and such that last less than a day--Battery backed AC power is very common for homes). And add solar panels later as needed/budget permits.

The big problem with small solar pv is that the systems really do not produce a lot of power. More than enough for a few lights, radio, laptop computer--But not usually enough to provide the ~1.5kWH per day required to run a refrigerator.

So--before buying/building anything, I like to suggest that they write down what they would like/expect to power--And perhaps purchase a Kill-a-Watt meter or equivalent to measure their estimated daily loads.

Solar panels + batteries are not cheap, so understanding the needs is important before starting such a project.

-Bill

niel

Re: Solar system disconnetable from panel?

in addition to what bb said the solar could be minimal being the system is a backups for utility tied circuits. the minimal will depend on the loads and battery bank capacity selected, but the pv could keep a full battery bank floated and the power mains can be shut down for the time away providing you have no loads connected. if you will need loads to run while away then in an outage you would want enough pv to put at least a day's worth of capacity back into the batteries.

what is usually done is a branch circuit of proper capacity is taken from the existing breaker panel and wired to the transfer switch and then your inverter or to a inverter with built in transfer switch as was said already and some also have built in chargers to automatically start a charge to the batteries when the power comes back on. the concept is simple, but implementing can be complex and confusing for some that aren't familiar with it. the inverter i have (magnum mms1012) is one with transfer switch and charger built into it and it's pretty slick in operation. it is a good idea to use a sub panel for loads after the inverter that are to be backed up unless it is just one circuit and then you can fuse it or put in a breaker for the one circuit. i also use a midnite epanel to mount my inverter to and it allows for easy connections for pvs, batteries, ac in, and ac out.

Bmanc21

Re: Solar system disconnetable from panel?

Thank you for your replies. That makes good sense. One additional question about making up the connection. Since this will be connected and disconnected on (potentially) a periodic basis, how would you do that? Could I just run an extension cord from an inverter to the outside connection from the manual transfer switch? Would it be ok to use the described set up while grid power is still on?

niel

Re: Solar system disconnetable from panel?

i'm not sure i am following what your concern is. what specifically are you referring to to be switched periodically? in the case of my inverter it allows utility ac to pass until the utility ac goes down and it switches the inverter on automatically. in the case of a manual switch it means when the utility ac goes down that you won't have power until you manually switch the inverter on and this should isolate that inverter and branch circuits being backed up from the utility power should it reappear. you would need a way to know the utility power came back on and go switch off from the inverter and back over to the utility.

in reference to your last question i have to make this clear. at no time shall ac from both the inverter and the utility be active on the same circuit at the same time or sparks will fly due to them being out of phase with each other to one degree or another and thus creating a massive short. if you are in doubt of how this gets wired then go for somebody to install this for you that knows what they are doing as things can go radically wrong. maybe studying over some of the connections involved in an epanel can give you a better prospective of what's involved and how it's done, but keep in mind they are using inverters that are automatically switched over too. you will soon see it is simple, but complex too and you won't need the controller or its associated circuits if no solar is involved. the wiring and mounting of a manual or automatic transfer relay would also need to be incorporated for your particular inverter. an epanel may not need to be bought either, but it would involve many other smaller boxes and could confuse or make things more complicated without it.

http://www.midnitesolar.com/pdfs/E-Pnl_Instructions.pdf