I have seven 240w panels, two 205AH 6V golf cart batteries, 3000W 12v inverter

tom-from-texas

I am looking for general recommendations on how to build out my system.

I have seven 240w panels, two 205AH 6V golf cart batteries, 3000W 12v inverter, 800W 12v inverter, 20A charge controller.

I have been taking the well-traveled path of beginners: "Buy first, plan later".
I hope to build a system to replace about 25% of my current electric usage. I use 800 KWH per month except in the summer when it doubles. I live near Dallas. My grid power is underground and 99.9% uptime, so I don't need much battery backup.

My thoughts so far:

1. Build a single panel system with one 240w panel (35v open) , the 20 A charge controller, two golf cart batteries in series, and the 3000W inverter. This would be my power failure system. Having the big inverter would let me run a heaver load for 10-20 min when needed. I know I don't have enough battery to feed it all day.

2. Buy a grid tie inverter. Looking for suggestions on size and brand. Think lower priced options, has anyone had good experiences with any of the lower priced units?

3. Roof mount the 7 panels. Looking for suggestions on mounting cheap on my asphalt shingled roof. The panels will be directly over my electric service entry, so wiring can remain pretty short. I have a hundred feet of 6 AWG cooper from another unrelated project that I can salvage.

-- OR --

I could expand out my 12v system.

4. Tie 7 panels together in series 245v feed a good MPPT charge controller into a 12v battery bank. I am thinking I would want about 8 more golf cart batteries.
Then I would have 10 205ah 6v batteries connected to give 1025AH @ 12v.

5. Then I would connect my 3000w 12v inverter to this and power several rooms in the house from the inverter.

6. I think I would have about 7 kWh coming from the panels daily and have about 6 kWh of usable battery.

7. By the time I buy the MPPT charge controller and 8 more batteries, would I be better off just going grid tie if I don't really need the battery backup?

Cariboocoot

Re: I have seven 240w panels, two 205AH 6V golf cart batteries, 3000W 12v inverter

I believe you have no choice but to buy an MPPT type controller, because the specs on those 240 Watt panels are bound to be like Vmp 30 and Imp 8. As such the Voltage they produce is too low to properly charge a 24 Volt system and yet too high to transfer all their power potential to a 12 Volt system.

A single 240 Watt panel is not going to do much for charging, say, 220 Amp hours @ 12 Volts either as you will only get about 15 Amps out of it. Might just be enough (6-7% peak rate) so long as it is not expected to provide loads as well and the losses are minimal.

Grid tie inverter do not come in a "low price option". The ones that do are unsafe and illegal. For GT you have to go the whole permit & permission route with the utility and inspection. As such it is really only practical for the system to be large, since the process is the same for any configuration. Do not ever buy one of those "plug-n-play" inverters sold all over the Internet.

I think what you really need to do is define what you're trying to get from solar: back-up power, off-grid power where no utility is available, reduced electric bill (false economy most of the time), or experiment for learning.

NorthGuy

Re: I have seven 240w panels, two 205AH 6V golf cart batteries, 3000W 12v inverter

If you do not need a battery backup, the best way is to just buy a GT inverter and connect your panels to the grid.

Since you already have batteries, I would buy a charger that could charge them from the grid and maintain them charged. In case of outage, they would provide some emergency power.

If there's a real bad emergency, you can always dig out your 20A charger and connect one of the panels to the batteries.

westbranch

Re: I have seven 240w panels, two 205AH 6V golf cart batteries, 3000W 12v inverter

the first step in reducing your 800KWh bill would be to buy a Kill a Watt meter and start looking at the loads of individual items in the house and switch out incandescent lights for CFL`s or LED`s. replace older appliances with newer Energy star ones etc... there are some postings here about swimming pool pumps and their loads etc. Enjoy the hunt for those elusive KWh`s.

hth

bmet

Re: I have seven 240w panels, two 205AH 6V golf cart batteries, 3000W 12v inverter

NorthGuy wrote: »

If you do not need a battery backup, the best way is to just buy a GT inverter and connect your panels to the grid.

Did the OP mention the specs of these panels? Are they UL Listed? Personally, I wouldn't recommend a GT without knowing if his solar panels met the minimum requirements for a utility connection.