I understand the volts and amps, but can't get past the max PV watts

[TruckerKevin]

Ok, very noobish here.

I have 6 panels from Newpowa that are 100 watts each. I only have 4 hooked up, because I am still using the cheap PWM controller that came with the kit. My plan is to upgrade to an MPPT controller then connect all 6 panels in a parallel/series configuration that will put me at 60 volts and 10 amps. This cheap PWM controller that it came with the kit had no documentation whatsoever, neither in the box or online, all I can find on it is it is a model SLC-GP2430F and the box says 30 amps. Since google shows me nothing, I have no clue what the maximum anything else is on it (Newpowa didnt seem to know either, he just kept repeating 30 amps as the specs)

So I know I need to move on/up to an MPPT controller anyway. And I am currently trying to find one that will work for now. I have studied for the last few days and I understand how wiring in parallel, series and series/parallel affects the voltage/amps etc. But what I can't seem to wrap my head around is the total watts. I will soon have a 600 watt system, and as far as I understand it, that is not going to change no matter how I wire the panels. Regardless how I manage to raise the volts or amps, I am still going to have a 600 watt system. Is this right?

So, as I shop for a controller (am trying to keep a certain budget for now) I need to look at the column that says "max pv watts" and keep it over 600 watts for a 12 volt system? Or is my understanding still not there quite yet . Because it seems to be forcing me to a more expensive mppt controller as everything I have looked at seems to favor less than 400 watts pv for a 12 volt system.

I know its probably a dumb question, I just don't want to throw anymore money at anything until I am sure

 

[gnubie]

Yes, no matter how you wire the panels they will produce a paper 600W, unless you chop the ends off the leads and reverse wire them. When sizing a MPPT controller you have to take the battery voltage and amp hours into consideration too.

If you have a 30A MPPT controller, that 30A applies to both the solar input and the battery output. This gives you a maximum power out to the battery of around 360W (will be higher as battery voltage rises) even if you have notionally 600W of solar available on the controller's input.

You also need to consider how many amps your battery can accept without damage. 30A into a 45AH lead acid battery is not going to end well.

Another gotcha is you need your array voltage to always be higher than the battery voltage, by a reasonable margin too. If you have 12V class panels you really want to have at least two in series but their combined open circuit voltage must never exceed the controller's maximum input voltage.

When it comes to PWM controllers the battery voltage and amps from the panels sets the wattage. The PWM controller connects the solar array to the battery and the battery loads the panels sufficiently to pull them down to its voltage (unless you have far too much solar panels). This is why its important to match battery and panel voltages and why the '12V' terminology for a panel exists. If you hook up a panel that produces 36V and 5A to a PWM controller and 12V battery maximum watts is 60 - 12 x 5. If you hook up a panel that produces 17V and 5A to a PWM controller and 12V battery maximum watts is still 60 - 12 x 5. So to see how many watts your PWM controller can provide, check the total Imp of your 100W panels (they should be in parallel) then multiply that by nominal 12V and there you go.

 

[MurphyGuy]

600 watts is 600 watts no matter how you arrange the volts and amps. Watts is VOLTS times AMPS.

Don't go buying garbage. A 600 watt system, while small, is still enough to do some real work. Get yourself a Morning Star controller or a Victron.

Just remember, when a charge controller says something like 100/30, that's 100 volts maximum input and 30 amps max to the battery.. It is NOT 100 volts in and 30 amps in.

What you really want to do is give us the VOC (Open Circuit Voltage) and Imax or Short Circuit Current.

 

[TruckerKevin]

It seems like Newpowa discontinued those 100 watt panels within the last 2 days, but here is what I know about the specs that I wrote down on scratch paper while I was researching this

17.2 volts at pmax
5.82 amps

Does that tell enough? If not, I will call the company

 

[Forbisher]

600w ÷ 12V is 50A
So look for a 50A SCC
Your Newpowa 100w panels are 20Voc
3S 2P would be 60Voc
You could use a 100V max input SCC
6S would be 120Voc so 150V max input.

What battery chemistry and Ah?

 

[TruckerKevin]

• Maximum power (Pmax): 100W Voltage at Pmax (Vmp):17.0V Current at Pmax (Imp): 5.89A is what I just dug up

 

[TruckerKevin]

Bingo, MBR I understand. I wished I would have just humbled myself and posted this a week ago, it would have saved me quite a bit of legwork.

Thanks to all contributors in this thread, I learned from each response

 

[TruckerKevin]

What battery chemistry and Ah?

Okay I was hoping to evade that one lol. I am right now using 2 Everstart 29 series marine batteries, yep, the Wal Mart ones. I know thats bad, they belong in my boat so I already owned them and did not have to spend anything to get going. I am saving to get the Battleborns in a few months.

 

[Forbisher]

What battery chemistry and Ah?

Okay I was hoping to evade that one lol. I am right now using 2 Everstart 29 series marine batteries, yep, the Wal Mart ones. I know thats bad, they belong in my boat so I already owned them and did not have to spend anything to get going. I am saving to get the Battleborns in a few months.

Dumping 50A in those batteries will not be good for them.
How many Battle Borns are you planning on?
The info you give about your system and use will get you better advice.

 

[JoeHam]

• Maximum power (Pmax): 100W Voltage at Pmax (Vmp):17.0V Current at Pmax (Imp): 5.89A is what I just dug up

You should use Voc when calculating for a Solar Charge Controller but it sounds like you are planning enough headroom to cover that.

 

[TruckerKevin]

Sorry I am late to my own party, I fell asleep last night

I will try to explain my position a bit better, and what I hope to do in the future.

We bought an old house across the street, it is off grid and will be for a long time because it is in terrible shape. We are in the process of gutting it, and it will probably be at least 2 years or longer before we get it in good enough shape to wire it up for grid (If I choose to).The existing wire is already cut up and gone

I use a generator to power heavy stuff like the window AC on days when its hot whenever we go over there to work on it. I bought the 2 panel Newpowa solar kit because I was intrigued in solar, and figured it would be a good test for that house. I had the attitude that if it did not work well, I would just throw them on my carport and use them for small stuff. I was really pleasantly surprised at what the panels do run, and it convinced my wife too, she is always skeptical. We run 2 lamps with LED lights, a TV, a sawzall, and a big industrial fan, amongst many other little things. It does it all so far, we use solar over there exclusively unless its raining/cloudy and very hot for an extensive period. I added 2 more panels to the kit to make it 4 in all. The reason I bought 2 more (making 6) is because I ran across a coupon deal and got them cheap. Even if I do not use them on that system, I could find a place elsewhere.

My ultimate dream would be to build a system like Will did in his 48 volt video with the MPP solar inverter. I would love to have that all in one solar inverter, perhaps tie something to the grid so we can use solar whenever possible but use grid power when we must, etc. Now I am finding that the biggest issue with that is, to build up an existing system so I can eventually end up with something like that. There is lots of math (that I am slowly beginning to understand now thanks to this thread).

Batteries are also a thorn. As I admitted, I am using 2 Wal Mart marine batteries in parallel, and I don't even think they are true deep cycle. BUT< I already had them unused just sitting in my boat (did not do much fishing this year). At least they got me going. I plan to upgrade them asap when the finances allow. So far, what I read, the battleborns are the better option. So of course if I ever wanted to build the 48 volt option, we are looking at what, 4 of them in series? That is a good chunk of change.

I hope this clears up my goals a bit better. I know that was a lengthy read, at least nothing is in the dark now

 

[Hedges]

If you assemble a system that runs off PV, using power when it is generated and never drains the battery, then lead-acid will last a long time.

Starting batteries are designed to deliver 3500W for 10 seconds and be recharged immediately afterwards. They should last 3 to 5 years being used that way, but draining them several times will wear them out quickly.
"Deep cycle" trolling motor batteries can handle some number of deep discharges.
Good AGM batteries for PV applications might last 500 discharges to 85% DoD or 5000 discharges to 10% DoD.

http://sunxtender.com/pdfs/Sun_Xtender_Battery_Technical_Manual.pdf

Lithium batteries might give you 3500 deep discharges - 10 years of cycling every night. But you pay considerably more upfront. Lower cost per kWh of cycle, but larger investment.

PV panels and inverters can cost less than $0.05/kWh, amortized over a decade. Lithium or lead-acid batteries will cost $0.15 to $1.00/kWh amortized over their life. So storing PV generated power in a battery for later use isn't a great deal. You're better off putting in 3x as much PV (same cost as lowest cost of ownership battery) to handle variations in power usage during the day, and live in darkness at night (or limit night time consumption to 1/10th or less of battery capacity.) The panels should last 25+ years and the inverters 10+ years, bringing cost well below $0.05/kWh

See the links from Real Goods I provide here, with battery cost per kWh:

connect battery to the MPPT input of a grid-tie inverter

Can this work? Or totally stupid?

diysolarforum.com

The trick is how to provide the AC power needed but avoid charging the batteries at too fast a rate. If you use separate MPPT chargers for the batteries and a battery inverter to power your loads, the charger won't know if it is putting 100A into a 30 Ah bank of old automotive starting batteries, or if the 100A is going to an inverter to power your table saw. Maybe some systems have communication to address that.

What can make it work is AC coupling with grid-tied inverters. A hybrid inverter with built-in charger ought to be able to do it to. I use the SMA Sunny Island battery inverter (my picture) which I have programmed for 85A charge current. That is 0.21C for my 405 Ah 48V battery. (I think a 100 Ah battery which I used at first would also work, except that my several refrigerators and freezers continue operating at night, drawing about 1 kW). I have more than 10 kW of PV on grid-tie inverters (Sunny Boy) which respond to frequency shift by reducing their output. So while the sun shines, I can run air conditioner and other large loads. The battery inverters deliver any current surge needed to start motors, but that only lasts 1/4 of a second.

If you put only a couple things like LED lights and telephone on a critical loads panel, and use a relay (or thermostat wire) to shed all other loads at 10% DoD or when the sun goes down, you can run everything directly off PV and avoid cycling batteries. Then you don't need to spend more on batteries than everything else combined. You can also program it to connect grid or generator at some DoD.

 

[TruckerKevin]

Hedges, that was a really good read. Thank you for taking the time to post all of that.

It is great to learn so much information here, verses jumping all over the internet and piecing it together with misconceptions

 

[MurphyGuy]

You would be surprised at how much power solar arrays can provide. Our entire home is powered by solar, and not some backwoods redneck cabin, but a full brick home with 2 refrigerators, 3 freezers, welder, plasma cutter, air compressor, three computers, well water pump, sump pump, etc. You name it, we have it.
This year, we're even going to heat the home (partially) with electric heat because we have so much surplus energy.

We used to have a $130/month electric bill, now its $7 for the meter charge.. and the solar system will be paid back, in full, in 6 years.

My advice is go big.. For $10,000, you'd never have an electric bill.

 

[Hedges]

"an old house across the street, it is off grid"
Unfortunate that is across the street, not next door. How urban, or rural, is this?
Any chance you can hang a wire between trees across the street, or drill underground (if no underground utilities; mark with chalk and "call before you dig" to make sure), or snake a wire through a storm drain?
Buy a utility meter and ask a neighbor to let you plug in and pay him for power? I did that with a mountain property; only problem was ants moved into the meter and jammed it with grains of sand.

 

[TruckerKevin]

It is off grid because it is in poor shape. Here in Southern Illinois, abandoned houses are plentiful, I think most of them were built back in the coal mining boom days. Many people lived, and died here, and their kids moved on elsewhere in the meantime and never came back for the homes that were left for the inheritance. It is crazy the amount of houses that have been empty for 20 years or better. Grass and weeds growing up and engulfing them. We basically bought it on a note, a tax sale. I threw an incredibly low ball offer for it and was shocked to find I was the highest bidder.

We are in the process of gutting it, we will remodel it with a new floor plan and rewire it slowly. I can get it on grid at that time. Right now, the circuit breaker box is stripped and all the old wiring is cut. Needs to be upgraded anyhow. In the meantime, we use 4 solar panels to give us "something". Actually it impresses us on what we can do just on those panels and 2 trolling motor batteries. We also have a generator for when the days we decide to work over there and it is cloudy, or raining and we need to power heavier items like the window AC. We only need the power when we decide to go over there and work on it.

Its more or less a hobby house, gives us something to do and dream about. I just so happen to like the solar thing. It is no bigger than 900 square feet, if we choose not to add on. Should be easy to heat and cool. And now is the time for me to choose what I want to do with it, before we start rebuilding. I have always wanted to build my own home. This is the next best thing, because it is nice on the outside but we can strip it to the shell inside without having to go overboard with permits.

I can go a few different directions if I like. Right now, I am leaning more toward making it on grid with perhaps a grid tie inverter. Like someone else had mentioned, I could probably go 100 percent solar.

I kind of like the idea of installing a gas stove, water heater and dryer. We are on the edge of town, a very small town of 500 people. They could care less what we do out here, we could run extension cords through the walls lol. In fact, I think that is what is in there now!