Help me make wise decisions - First timer

Re: Help me make wise decisions - First timer

esteban wrote: »

Well THAT is some info I can use!

Assuming I go the 24v direction, I'll use the Kid as you said, with one string of four GC2's and something like the 1000w 24v inverter as previously mentioned. I imagine that later adding 4 more panels, and jumping to 48v I'd need to replace all batteries right?? I read a LOT about how you don't want to mix old and new.

Mixing old and new is generally not a good idea because a battery's real capacity changes with time and use. The older it is, the more it is cycled, the more poorly it is maintained the lower it goes. SO then you can get a situation where the two 'identical' batteries in the same bank are really quite different and the charge/use characteristics of new ones don't match with the old ones. Inevitably this leads to the new ones 'aging' faster than they should and so dying sooner than they should. But if the batteries are, say, less than a year old and not abused you probably won't notice any difference in function or lifespan.

Going the 24v and 4 panel way, do I really need a combiner?? What type of fuses would I really need?? It seems (ignorantly) on the small side of things and relatively safe. I don't want to underestimate the potential of power either. I haven't done enough research on the combiner boxes yet, but on the surface of it they just appear to be a breaker more or less??

That depends on how you arrange the array. If the four panels are all in parallel, then you're definitely looking at using a combiner and fuses or breakers rated for the 'series fuse' number for the panel. Interestingly if you did put all four of these 36 Vmp panels in parallel and then went to a 48 Volt system later, you'd just add the other four panels to make series strings of two; same 4 space combiner and circuit protection rating. It's always best to wire for the expansion to begin with as it saves a lot of trouble later on. Nothing like just being able to pull some MC4 connectors and click another panel in-line!

Thanks again, your help is far more than appreciated.

I think in the short term I'll hook the system up to my beer keezer: http://www.homebrewtalk.com/f51/my-sears-kenmore-8-8cf-6-tap-how-thread-lots-pictures-447047/

I'll have to check what kind of power it truly uses in a day, but hopefully its a realistic load to keep my system cycling and "tending" my batteries. Certainly doesn't have to be hooked up to that, but it'd be kind of cool to have the sun keep my beer cold!

One thing you might want to get is a Kill-A-Watt meter. Frankly every one should get one, on or off grid with or without solar. Nothing like testing out everything you own and seeing where the energy hogs and phantom loads are!

Re: Help me make wise decisions - First timer

A combiner is not strictly necessary for only two parallel connections. The question is; will it stay at only two parallel connections? If you go up to 48 Volts and add the other four panels you would then have four parallel connections. You don't want to put them in series of four because of the Voltage difference/efficiency issue.

Now here is an important consideration: how far will it be from the array to the charge controller?
As the distance gets longer, the current higher, or the Voltage lower the Voltage drop in a given wire size increases. So if you were to use single panels in parallel on a 24 Volt system there is an increased risk of power loss from Voltage drop through the wiring.

So doubling up the panels for a 48 Volt (nominal) array would work on a 24 Volt system, and probably would work on a 48 Volt system as well. Just do the measuring and calculations first so that if you go up to 48 Volts doubling the array size (and thus current) will not cause problems with the wire run to the controller.

Combiner boxes are not necessary, but they do make the installation easier and neater. On the whole not a bad thing to spend money on. In this case it would be a four spot box like this one: http://www.solar-electric.com/misomnsoarco4.html

Re: Help me make wise decisions - First timer

esteban wrote: »

For the price would you say that is a good value in a battery? Locally the t105 golf cart version is $108, not sure if it's worth the difference?

Where I am $85 for a 220 Amp hour 6 Volt battery would be the deal of the century. Mine cost 2X that.
How's the warranty on them? How fresh are they (look for same and recent date stamp)?

What advantage does the T105 offer? Looks like the same battery to me: deep cycle golf cart 220 Amp hour 6 Volt. What am I missing?

Re: Help me make wise decisions - First timer

esteban wrote: »

Is there really a rule of thumb for panel wattage to battery amp hours or some type of conversion like that?

Only the rule-of-thumb guidelines of using a percentage of Amp hour capacity as a guide for peak charge current. And that has the variables of minimum to maximum current and efficiency factors for charge controller type.

For example if you want 10% of 220 Amp hours that's 22 Amps @ 12 Volts. You can multiply current times "standard" Vmp for the system Voltage (17.5 on a "12 Volt system") and get an array of 385 Watts.

Even then batteries and panels don't come in any size you want, so you have to make adjustments at the various stages of design to get numbers you can actually acquire in the real world.

Re: Help me make wise decisions - First timer

esteban wrote: »

Thank you!

With that info do you think 4 GC2's is a good pairing to the 4 175w panels? What if I went with 6 panels?

Is 8 GC2's a good match for 9 panels??

I would imagine that is on the low side of batteries to solar production. I'd think you'd probably want to have more like 8 L-16's or even 16 on the higher end. I think that just gives you more more backup

Nope.
It is a common mistake to think "I need more batteries". 90% of the time it's the other way 'round.
The peak charge current is a short cut to getting the batteries recharged fully in one sunny day. You don't want it to take several days to recharge the batteries. And that charge rate is net, not gross.

For example the 5% minimum peak charge current really only works for systems that have no loads while charging. Not many fall into that category.

The 10% rate balances well for most systems, allowing a reasonable recharge time even with moderate loads. If the loads are known to be heavier or the weather not-so-sunny then a higher peak rate would be used, up to 20% (after which flooded cells can have problems).

So 220 Amp hours @ 24 Volt battery bank. 22 Amps peak current on an MPPT charger under typical derating (77%) you get 685 Watts of array. But that is a minimum. If the sun is not so sunny or the loads are heavier than having more Watts helps. No one ever complained about having too much array, but there are a lot of complaints about the results of having not enough.

Just to look at it again from the array POV: four 175 Watt panels is 700 Watts. With the MPPT controller you get: 700 * 0.77 / 24 = 22.5 Amps. Hard to make a better match for 220 Amp hours.

Re: Help me make wise decisions - First timer

esteban wrote: »

Also now that I am this deep I've read plenty of other threads you've posted in, my question becomes if I should pony up the extra bucks and get a grid tied inverter.

First of all I'm confused by grid tied + battery backup vs ac coupled??? Sounds the same to me??

I think I'll be making more energy than I "need" and at some point it makes sense to sell the power back. That being said I don't want to be without power if the grid goes down, battery backup is a must.

What is the economical solution?

Completely different animals.

You're working up an off-grid system. There is not much choice in design.

A grid-tie system can be either standard, which has no batteries, or battery back-up which does. They supply power for critical load in the even of a grid outage.

AC coupling refers to connecting a standard grid-tie inverter to a battery-backed one via the AC lines to supply charging and supplemental power.

You shouldn't expect to build an off-grid system and then connect it to the grid; the designs have significant differences, not the least of which is the involvement of the utility and local inspector. "Building up" to a GT system is not a very practical tactic. For example the full eight panels you have come up to 1400 Watts, which is pretty small for GT. That kind of system is at its best the larger you can build it. There are numerous rules about how large a system you can attach to your service panel and in what manner.

Re: Help me make wise decisions - First timer

westbranch wrote: »

Wait, aren't you going for 4 panels in pairs (2 in series)? If that is the case then you have to have 8 or 10... ( 9 if you are having all parallel is OK...)

It's a matter of "now vs. later"; he plans to start with four, and then add the additional panels with an increase in system Voltage later (expand the two strings to three panels each and add a third string of three). At least that was the plan until the last post inquiring about GT systems.