Charge Controller

cokebbeh

Hello All,
I got 4, SUN- 130 Watt Solar Panels (VOC 24.10V, VMP 18.80V, ISC 7.11amp, IMP 6.55amp). I want to buy a charge controller, inverter and some batteries. In an earlier post, someone suggested that I buy 4 - 172ah batteries (12v); MPPT 30a charge controller; True Sine Wave (TSW) inverter.

A few more questions:

>>> I observe that 6V batteries are cheaper. Is there anything wrong with a 6v instead of 12v battery. These batteries will be used in a tropical environment with temperatures around 80 to 90 F year round.

>>> Should I buy a 1000 watt or 2000 watt Inverter? I see that true sine inverters can be quite expensive, but I saw one on e-bay with the following specification (XANTREX Prowatt SW2000 2000 Watt TRUE SINEWAVE INVERTER) for $388.95. Is this a good inverter; it is cheaper than the others I have seen.

>>> Any recommendation on the MPPT charge controller. Will a 30a or 40a be better...

Any other suggestions will be highly appreciated

mike95490

Re: Charge Controller

Battery life will be shorter in a warm environment. Can't do much about that, but try to keep them in a sheltered spot.

What are your loads you are trying to run?

Do you have any back-up generation, in case of stormy weather?

The SUN panels you have - any notices on them about Positive Ground systems ? That can be an important factor with them, limiting your choice of charge controller.

http://www.smartgauge.co.uk/batt_con.html Has sketches of battery hookups, and why. I'll assume you are creating a 12V system. I'd personally go with 4, 6V deep cycle batteries. Odd that you say the 6V are less expensive than the 12V. Most of the cost is the contents of lead, and there is not an appreciable difference in same size case of batteries. Be sure you get deep cycle, not a marine or starting battery.

icarus

Re: Charge Controller

Don't buy anything until you can get a ACCURATE estimate of your loads. Battery bank sizing (and potential longevity) is very dependent on being proper sized. The general rule of thumb is a battery bank should not be routinely drawn down more than ~50%, and ideally more than ~20-30%. Then it should be FULLY recharge within a few days, or it's life will be shortened significantly (and quickly!) The issue is exacerbated by hot battery location. Make sure that any controller/charger comes with a good temperature compensating system.

As for the inverter size, to be most efficient, once again you need to define the loads. An inverter is most efficient when it is more fully loaded. Running a 200 watt load on a 2kw inverter doesn't make much sense.

I think that before you go one step further forward, you take a few steps back. You are at risk of the most expensive aspect of RE, and that is the Ready, Fire, Aim! syndrome. Buying the wrong hardware now, will cost you dearly going forward. I would design your system from the ground up using the expected loads as you guide.

I suggest as a start you read and understand some of the following:http://www.batteryfaq.org/
http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries

There are tremendous resources on this site, and some very sharp folks, many on whom have "forgotten" more about this subject that many of us will ever know. This allows folks like you to take advantage of their knowledge without having to reinvent the wheel for each new system.

Good luck, and welcome to the forum,

Tony

Cariboocoot

Re: Charge Controller

"The 6V batteries are usually cheaper". The main reason for that is because companies build and sell a lot more of the "golf cart size" 6V's than they do of 12V's. Nothing wrong with 6V vs. 12V. In fact, as the bank capacity goes up, you're more likely to use multiple 6V than multiple 12V; you end up with simpler wiring configurations and less chance of uneven battery current flow.

I agree with Mike; check carefully which SUN panels you have. There's two different makes with "sun" in their names and some of them are (+) ground which causes some connection difficulties (needs a controller which can take positive ground panels). I can never remember which is which.

As for inverter size, you really need to know your loads. There's no sense buying too large of an inverter, spending extra money and using up additional 'idle current'. By the same token, nothing is more frustrating than finding out you can't run something because the inverter won't handle it (particularly 'surge' or 'start-up' loads). Don't count on an inverter's surge rating for anything; they are happiest running below 75% of their maximum 'run' rating. Take a look at the choices offered by NAWS to begin with: http://store.solar-electric.com/inverters.html

I also agree with Mike about the need for a back-up power source. Everyone needs back-up power.

We seem to be assuming this is an off-grid application.
Some rough calculations based on your 480 Watts @ 24V panels:
Max array current would probably be under 20 Amps. If your going with a 12V system you'll need an MPPT controller to "down convert" the higher array Voltage. So you'd probably need either the Outback or the Xantrex to handle up to 40 Amps current (could be less due to efficiency losses).
Based on the available maximum charge current, you should be able to handle up to 400 Amp/hrs of battery even with efficiency losses. That's about 200 'usable' Amp/hrs, which means up to 2.4 kW available per day/charge window. Based on that, up to a 2000 Watt inverter should be doable.

Again I stress: rough calculations. No 'fine tuning' involved (i.e. use of specific panel Voltages, calculations of line loss, et cetera).