Wiring and Charge Controller question

flighthouse · August 2009

I have 6 x 55 watt (3 amp / 17 volt) solar panels. Now that I have solar panels, I need to get a charge controller.

I see that charge controllers are rated by amps. For instance there are 10 amp charge controller and 25 amp charge controllers. My question is, how do I know what size to get? I guess that I don't know exactly if I'm going to wire up these solar panels in parallel or series. Should I measure 3 amp x 6 panels = 18 amps and make sure I get a charge controller more than that? What is the math and wiring configuration?

Or maybe since the voltage on a charge controller appears to be the point at which the charge actually starts happening (like 12v charge controller won't charge if the load is under 12 volts), then does that mean a 10Amp charge controller won't start charging until it reaches a 10amp load?

Thanks in advance.

niel · August 2009

Re: Wiring and Charge Controller question

what is it you plan to do with them? it's hard to advise you when we don't know what you have in mind.
controllers are regulators and are rated for the maximum amps they can pass and do not wait for a load to present itself of that magnitude to start working. they will pass smaller currents at the times of other charge stages if working properly.

flighthouse · August 2009

Re: Wiring and Charge Controller question

I plan on getting a deep cycle battery or two and a 1000w inverter and plugging a power strip into it then using all the free solar electricity I can in my house. Hoping to run several routers (for computers), a computer, and possibly a refrigerator.

Ok, so do not exceed the amps on the charge controller got it. But I can exceed the volts right? My solar panels put out 17 volts but the charge controller says 12 that I'm looking at.

I still don't know if I'm supposed to hook up the panels in series or parallel. What are the calculations of it when I do? If I hook them up in parallel is it PV1_amps + PV2_amps + PV3_amps = total amps, or do I need to take the reciprocal? And for bonus points, what the equation for volts?

Cariboocoot · August 2009

Re: Wiring and Charge Controller question

flighthouse wrote: »

I plan on getting a deep cycle battery or two and a 1000w inverter and plugging a power strip into it then using all the free solar electricity I can in my house. Hoping to run several routers (for computers), a computer, and possibly a refrigerator.

Free solar electricity? Nothing is free. Solar electric costs run anywhere from $0.50 per kW/hr for a grid-tie system to $2.00 per kW/hr for off-grid, depending on your location, prices, and any incentives available.

So let's go back to analyzing what you want to do before you spend the money.

Maybe you want a grid-tie system to reduce your monthly electric bill? It probably won't be worth the investment unless you've got a good solar location and there's some incentive program to help off-set the capital investment.

When you design a stand-alone (off grid) system, the first thing you look at is the loads you want to run. Although you can build a system by other constraints (this is what I have, this is what I can afford) you then have to deal with the limitations of available power ('frige goes off at 1 AM 'cause you stayed up too late watching TV).

The third possibility is you want to experiment with solar to see what its capable of. In this instance the only $ consideration is how much you can afford to spend. What you get for it is variable.

One of the best things about this forum is that the participants aren't gung-ho "solar is the one and only answer at any cost" fanatics. We always try to consider the expense so that you get the best return out of your energy $.

So what's your end goal here?

You can give us lots of info like location, budget, on/off grid, intended use ... And we can give you lots of potential solutions.

The first thing that will be recommended is that you get a Kill-A-Watt meter (or similar) and check your existing loads and see where the energy is going.

BB. · August 2009

Re: Wiring and Charge Controller question

Regarding "free solar" for the home office... Many people start there with a small system for educational use. Such a small system ends up not being very cost/time/labor effective for various reasons.

Very rough numbers, you are paying $0.10-$0.20 per kWhr. An off grid system is going to cost you $1.00-$2.00+ per kWhr (small systems are more costly than larger systems on a $/kWhr basis)...

So, if you are trying to save money, this is not the way to go if you have utility power.

If you trying to learn about solar for future use--You can build a "medium" sized system (like you are asking for). Or, you can start with a much smaller system for experimentation (and use on a camper for for emergency use to power a couple lights, radio, small TV).

Back to your question... Solar panels are, in some ways, like any ordinary battery. They output Voltage and Current and you just need to match them to your needs/loads.

So--working backwards. If you have a 12 volt battery, it requires around 14.5 to 15.5 volts to properly charge. The Charge Controller needs about 1-2 volts drop across it to operate (the typical solar charge controller only "drops" voltage, it cannot increase voltage). And you may have another 1 volt wiring drop.

So, for a 12 volt system, the "ideal" solar panel with charge controller would be rated:

15 volts + 2 volts = 17 Volts Vmp (Volts maximum power).

There are two major classes of charge controllers... The "simple" (tyically older/less expensive) PWM (pulse width modulation) where the solar panel Vmp is most efficient when Vmp~17 volts; and MPPT (Maximum Power Point Tracking) where Vmp (for a typical higher end controller) needs to be 17<Vmp<140 volts of solar panel--a MPPT solar charge controller can efficiently converter high voltage/low current from the solar panels into low voltage/high current for the battery bank.

The charge controller (both types) basically controls the averge charging current into the battery to obtain ~14.5 volts (bulk/absorbe) while charging, and once charged, reduces the voltage to ~13.8 volts (float) for long term battery storage (i.e, trickle charge).

The basic eletrical terms--Voltage adds when panels (or batteries) are connected in series. Current adds when panels (or batteries) are connected in parallel.

With energy--it is neither created or destroyed (wasted energy is typically disapated as heat). So, you need a little electrical math. Here is a basic one that may help:

Electricity for Boaters - BoatSafe.com

In reality, the basic steps for any cost effective solar RE system are:

Conservation: Always get the most efficient, least amount of energy used devices, you can. And turn them off when not needed. As good as any other rule of thumb--for every $1 you spend on conservation, that is $10 you will save on building your solar RE system.
Defining your needs: How much peak power (peak watts), how much average power (watts*hours of use per day), how much usage by season (in winter, solar PV generally produces less energy). Is this for emergency use, off grid use, or to be used with utility power...
Define the System to meet your needs.

Also, we are working on a detailed post/thread for new people... If you wish please check out this thread and see if it is of any help to you:

Working Thread for Solar Beginner Post/FAQ

-Bill

BB. · August 2009

Re: Wiring and Charge Controller question

I forgot to add:

Do not buy anything until you have done a paper design that will meet your needs.

There is a lot of product out there--and it is expensive and frustrating to buy stuff that looks good, and find out that it will not meet your requirements/expectation.

Many of the heavily promoted "solar kits" out there are really just expensive (high markup) junk that will not do 1/100th of what they claim (of course, there are kits out there that are fine for new users--but they are much more expensive and cannot make claims of running your fridge on solar like the hyped kits do).

-Bill

flighthouse · August 2009

Re: Wiring and Charge Controller question

Thank you all for being so helpful. I have read the beginners FAQ but still had a few remaining questions and I appreciate the help. You've put me in the right direction for sure.

I suppose I will elaborate more on my situation. My goal has changed so many times already and I haven't even finished. At first I thought solar was 'the way to go!' and started researching it. I quickly learned there are alternatives to saving money and the earth like using a kill-a-watt and stuff. I still was interested in solar power so I turned the goal into “make me the very best solar panel system possible for under $1000”. After about 4 months of looking and researching I found 6 x 55 watt seimens panels for $2/watt. So my remaining budget is $340 to make the panels work for me. I first thought about using one of those grid-tie into a GFI outlet type inverter but that looked illegal to say the least and doesn’t really educate me much. This means I’m now trying to get an off grid setup with a battery bank, but I am not trying to go off the grid by any means. The goal is to not only to learn and understand how this works but I will gain some electricity out of it and also (my favorite part) use this in a disaster setting to run fans, lights, heaters, chargers or whatever to survive if the grid goes down. The other thing is that I live in always sunny Tempe Arizona and it just makes sense to start using the sun’s power.

So my future parts list here to get things finished up is:

$100 deep cycle 12 volt battery (not sure where or which one yet, seems pretty expensive to ship these, and have shopped around locally yet)
$100 inverter (the xantrex xpower 1000w is what I have my eye on, some of them are as low as $50 in places)
$100 charge controller (I am looking into going a little higher and get the blue sky MPPT one but that’s only if I can score really good deals on the other stuff)
This leaves $40 left for wires, and maybe some mounting stuff. This will be mounted on the roof but I have a lot of materials that I think I can do this with already.

I think it’s a very close budget but it’s a challenge that I like doing. I don’t mind buying used or waiting for craigslist to post a sweet deal.

After this project is complete I will evaluate the efficiency of this system and reality of it and may consider upgrading to a larger system. I am pretty sure I will be getting some extra batteries first though.

BB. · August 2009

Re: Wiring and Charge Controller question

About my only suggestion--I would suggest a small True Sine Wave inverter (read inverter FAQ's here if you are interested) to run your electronics and other critical type products (wall warts, etc.).

The MorningStar 300 Watt 12 volt TSW Inverter is really nice (low power, efficient, built well).

Larger inverters and MSW inverters tend to waste power on small systems. MSW inverters also can damage about 10-20% of the items plugged into them. The other 80-90% work fine (although, they may run a little hot).

Handy meters:

Kill-A-Watt (get one no matter what)
RC Battery Meters (good for smaller DC power/battery logging)
Battery Monitor (really need one on system to understand battery state--too expensive for small systems unless you will move up later)
Hydrometer+Thermometer (for flooded cell battery--to accurately measure charge)

All the other is a matter of choice. Of course, our host stands by their equipment--so that would be a good list to start from (even if not purchasing from NAWS).

1 Big panel vs 4 smaller panels--easier to mount and wire, harder to store and transport (camping, etc.). Big panels tend to have better $/watt pricing--but if you get a good deal on small panels--your choice.

In general, as you "grow" your system, most of the components will have to be changed out (larger currents, different battery bank voltages, etc.). Starting small and cheap is not the worst place to begin. Avoiding "junk" is worth it--saves on frustration down the road.

-Bill

Cariboocoot · August 2009

Re: Wiring and Charge Controller question

So you've already got 330 Watts of panels and want to know how much of a system you can build from it?

Pretty good start, having that much panel. It's about 50% of what I run the whole cabin off from.

Ideally you'd want to connect them up to say 30-45 Amp charge controller. It could charge a set of Trojan T105's at 225 Amp/hrs and power a 1000 Watt inverter.

Your CC budget is a bit thin, especially for MPPT. You could get a SunSaver 20 for the money: http://store.solar-electric.com/ss-20l.html
The thing is, the charge controller is the 'brain' of the system and it's worth spending the $ on to get a good one to start with. I spent big bucks on an MX60 to begin with, and it's been there through panel, voltage, and inverter upgrades.

The batteries are going to be more like $100+ each (http://store.solar-electric.com/cr225am6vode.html) unless you go with El Cheapo Not Really Deep Cycle and don't care how long they last. To that end, you'll probably want to be able to re-charge them without the panels.

Bill's recommended Morningstar inverter is a good choice, but if budget is a bigger concern there's also the Samlex line: http://store.solar-electric.com/sasiwain1.html

Just a few suggestions/ideas - nothing written in stone. You have to look at what's out there and decide what is the best choice on your budget. Before you buy something, ask: there's a lot of really bad equipment out there (BZ charge controllers, for example).

I think you're looking at potentially 800 - 1000 Watt/hrs per day harvest.

Wiring and Charge Controller question

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