Newbie - Need some help from you experts

rchlaveka

Fairly new to the solar game. I have 2 - 145Watt 12volt panels
Vm (V) 18.7V
A 7.75A
Voc (V) 22.3V
Isc (A) 8.37A

I would like to run them as a 24 volt, have purchased 4 - 6 volt Golf Cart Batteries ...215AH each which I assume I need to run in series to get to the 24 volts

A couple questions:
1. What size breaker between the panels and the control charger, the control charger and the batteries and the batteries and the inverter?
2. Do I need to get a 24 volt control charger and 24 volt inverter
3. For this 290watt system, do I need a MPPT controller?
4. Is a 30 amp control charger and a 1000 watt inverter the right size?
5. What gauge cable do I need from battery to battery in series and from to and from the batteries and inverter and control panel

Lastly, Any suggestions on what brand and type on the inverter and control charger

I apologize for my lack of knowledge

Thanks

Cariboocoot

Re: Newbie - Need some help from you experts

Welcome to the forum.

You can wire the two panels in series for 24 Volt (Vmp 37.4, Imp stays the same at 7.75).
You would need a charge controller that can handle 24 Volts. Most of them will do 12 or 24, some you have to order a different model for. As this is very low current, you could use a 10 Amp controller (providing you're not planning to expand) like this: http://www.solar-electric.com/ss-10l.html There really is no point in using an MPPT type controller here.

However, that amount of panel will have a very hard time recharging 215 Amp hours @ 24 Volts. The maximum charge rate would be 3.6%, which is way below the minimum recommended 5%. This would be barely a maintenance charge.

If you have a 24 Volt system and want to use an inverter it must be a 24 Volt inverter.

It's probably a good idea if you let us know what you want to use this for, as loads are the all-important basis for design of any off-grid system.

rchlaveka

Re: Newbie - Need some help from you experts

This is going to be my SHTF setup. I just want it for when the Hurricane hits Houston etc. i want to set the batteries up, keep them charged with either the panels or battery minder and have enough for the bare necessities of living when the power goes down.

What do your recommend to overcome the minimal charge of 3.6%?

Any advice on a 24watt inverter for this setup?

Cariboocoot

Re: Newbie - Need some help from you experts

To overcome the solar charging shortfall there's only two solutions: more panel or less battery.

How you should do this is decide what you need to keep running if/when the power goes out and for how long. Then measure the consumption with a Kill-A-Watt meter to get real power usage figures under typical conditions.

For example, you probably want to keep the refrigerator going. So you plug it into the K-A-W and let it run for a few days. This will give you a daily average consumption you can count on. Let's say 1200 Watt hours per day. On a 24 Volt system that would be about 56 Amp hours @ 24 Volts (not including inverter consumption).

What inverter you choose will also depend on what you want to keep running. It must be able to meet the continuous and surge demands of the load. Again the refrigerator example: it may run at 130 Watts, but on start-up could draw 1,000 +/- and with built-in defrost will probably grab 500 Watts from time to time (most auto-defrost units these days can not be run without that function).

To look at what you could get from 215 Amp hours @ 24 Volts: maximum 50% depth of discharge is roughly 100 Amp hours or 2.4 kW hours available. That would just about run the refrigerator for two days, especially if you have some panels to at least partially replenish them. If you want full solar recharging you would need around 670 Watts of panel, and there you are into expensive MPPT charge controller territory.

What you can expect from your two 145 Watt panels: about 800 to 900 Watt hours per day. Keep in mind there can be a really wide variation in this, especially under bad weather conditions as panels output drops drastically if they don't have direct, bright sunshine.

Is this making sense?

westbranch

Re: Newbie - Need some help from you experts

rchlaveka wrote: »

This is going to be my SHTF setup.
Any advice on a 24watt inverter for this setup?

OK so can you list just those ESSENTIAL items you NEED to power and their watts consumed and for how long?

rchlaveka

Re: Newbie - Need some help from you experts

It makes sense to me...when you say less battery, I don't know what that means...I have to tie 4 together in series to get to the 24 volt...right?
If I added 2 more panels, that would give me 580 watts...still going with a 24 volt set up, would the battery bank be ok then? Also would I need to go with a 30 amp controller? could i still get by without a MPPT or should I go that route at 580?

Cariboocoot

Re: Newbie - Need some help from you experts

rchlaveka wrote: »

It makes sense to me...when you say less battery, I don't know what that means...I have to tie 4 together in series to get to the 24 volt...right?

You have to put four 6 Volts in series to get 24 Volts, yes. But batteries come in different Amp hour capacities as well as Voltages. So if you haven't got the batteries already you could look for lower Amp hour 12 Volts, or go for a 12 Volt system. Either is possible.

A bit about system Voltages here: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power

If I added 2 more panels, that would give me 580 watts...still going with a 24 volt set up, would the battery bank be ok then? Also would I need to go with a 30 amp controller? could i still get by without a MPPT or should I go that route at 580?

At 580 Watts you could get some benefit from MPPT. With a PWM controller the total current is just the Imp of the string(s). In this case 7.75 * 2 = 15.5 Amps.
With an MPPT controller it's more like Watts * efficiency / nominal Voltage or 580 * 0.77 (typical) / 24 = 18.6 Amps.
Peak charge rate for 215 Amp hours then becomes 7.2% and 8.6% respectively.

rchlaveka

Re: Newbie - Need some help from you experts

I am not looking for a lot...maybe the refrigerator or freezer, a fan and power tool in the garage or a coffee pot in the morning. A small TV would also be good or a radio. Basically, after Hurricane IKE, we had a 5000 watt gas generator that kept the refrigerator and freezer up and a window unit in the bedroom, but gas was hard to come by. In Houston, you can't make it without at least a fan in the room, so I would be using this mainly as a "get by" until the power comes back on.

One other question...would a Battery Minder or Battery Tender help

Cariboocoot

Re: Newbie - Need some help from you experts

Well the coffee pot can be a killer as they are usually 1000 Watts or more, if only for a few minutes. A freezer will usually stay cold for many hours, and a 'frige can be 'minimized' with as-needed cycles.

You can use your generator to charge batteries, extending your gen run-time capacity by making better use of its capacity. In other words one of the loads won the generator would be charging the batteries which would then supply the power via inverter while the generator is shut off.

A battery maintenance charger is a good idea, as left untended the batteries could die just sitting there (unless they get charge from solar). As for completely recharging them from an AC source (gen or utility power) you need a better charger like one of the Iotas http://www.solar-electric.com/bach2.html

It probably does not make sense to sink a lot of money into this for occasional and/or short outages. But if you suffer recurring long outages then the batteries/gen/solar in some combination becomes more practical.

vtmaps

Re: Newbie - Need some help from you experts

rchlaveka wrote: »

I would like to run them as a 24 volt, have purchased 4 - 6 volt Golf Cart Batteries ...215AH each which I assume I need to run in series to get to the 24 volts

Uh oh... this sounds like Ready, Fire, Aim. Batteries should be the LAST thing you buy. They are sulfating while you build your system. Find some way to get them charged ASAP.

Batteries are the most difficult decision in building a hybrid or offgrid system. Your batteries will spend most of their life in float. Some types of batteries are designed for that type of life, yours are not. (although golf cart batteries are a very good choice for 'learner' batteries).

--vtMaps

rchlaveka

Re: Newbie - Need some help from you experts

A couple other questions:

1. If I add a second set of 145Watt panels, how should I wire them? I planned on wiring the first 2 in series to get 24 watts, how do i wire them now that I would have 4?
2. I have a refrigerator in the garage, and was thinking I could have the array power the refrigerator and that would help with the Floating issue...I plan on getting a Kilo-Watt-Meter to check out wattage use, but maybe you guys already know if this is a good plan
3. What size controller should I get, and can I run all 4 panels into that one controller?

Cariboocoot

Re: Newbie - Need some help from you experts

rchlaveka wrote: »

A couple other questions:

1. If I add a second set of 145Watt panels, how should I wire them? I planned on wiring the first 2 in series to get 24 Volts, how do i wire them now that I would have 4?

Two parallel strings of two in series. Vmp will be double that of one panel and Imp will be double that of one panel.

2. I have a refrigerator in the garage, and was thinking I could have the array power the refrigerator and that would help with the Floating issue...I plan on getting a Kilo-Watt-Meter to check out wattage use, but maybe you guys already know if this is a good plan

If the garage is cool the refrigerator will be more efficient and run less often. That will save over-all kW hours.

3. What size controller should I get, and can I run all 4 panels into that one controller?

If it's the right size controller. They are rated in maximum output Amps. Since these panels have an Imp <8 two strings would be <20 Amps, thus a 20 Amp (or larger) controller would be fine.

rchlaveka

Re: Newbie - Need some help from you experts

So, I just wanted to check

With 4 145watt panels, if I wire to in parallel and then then tie the two sets together in series, I will get 24 volts
Then, I have 4 - 6volt 215AH batteries in series to get 24volts
If a ,refrigerator is operating at 600watts, would this system work without discharging over 50% of batteries? If not can I add a trickle charger or battery minder to help?

Cariboocoot

Re: Newbie - Need some help from you experts

rchlaveka wrote: »

So, I just wanted to check

With 4 145watt panels, if I wire to in parallel and then then tie the two sets together in series, I will get 24 volts

Other way 'round: you want to wire two in series to make a string that is 24 Volts. Then you make another of the same, and parallel the two 24 Volt strings.

Then, I have 4 - 6volt 215AH batteries in series to get 24volts

Yes: that will give you 215 Amp hours @ 24 Volts.

If a ,refrigerator is operating at 600watts, would this system work without discharging over 50% of batteries? If not can I add a trickle charger or battery minder to help?

First, a refrigerator's running Watts is usually less than 200. Second, it does not run constantly. Third, the total amount it uses in a day would be measured in Watt hours, which is what needs to be compared against the battery bank capacity. So if a refrigerator draws 120 Watts and runs 1/3 of a day total it consumes (120 W * 8 hours) 960 Watt hours. 50% of 215 Amp hours is 107.5 * 24 Volts (nominal) = 2,580 Watt hours. That is more than the refrigerator example uses, so it should be covered.

The problem is you have to include the inverter's consumption and the system losses and the fact that the 'frige will draw a bit more when it starts, runs variable times, and probably will kick in to defrost mode from time to time. On the up side if the panels can fully charge the batteries they will probably also have a bit of 'extra' power on most days to run the 'frige "for free".

My 16 cubic foot 'frige uses an average 1200 Watt hours per day inclusive. My battery bank is 232 Amp hours @ 24 Volts. It works fine, even with all the other stuff running. But because of that other stuff I have to do a bit of load management.