First Project

jayjay

Hi. I do not yet have any solar experience other than building a solar cooker years ago in the boy scouts but want learn as much as I can about solar and wind so I can eventually add them to my home. To begin with, I would like to build a small solar generator that I can use in a detached garage at my place with no electricity in it. All I would have to run in this garage is a couple of flourescent lights. I would then like to take this solar generator and use it when I go camping to run a few small lights, perhaps a small refrigerator, thus the reason for making it portable and only using 1 battery.

First, I live in central Wisconsin. From the charts I have seen, we get around 3-4 hours of chargable sunlight per day (around 2 in the winter). I am thinking of putting an 80 watt solar panel on a portable cart that I can aim at the sun manually. I know I need to run this into a charge controller, into a battery, and then into an inverter. What I do not understand is how to size each item ... and how voltage plays a difference. Obviously, I need to end up with 115VAC out of the inverter, but I've ready about 6V, 12V, 24V etc systems and don't quite understand why the difference or the advantage/disadvantage of each.

I'm assuming the panel is a 12V system and a single deep cycle battery would be a 12V battery. Can someone steer me toward the basics so I can understand this a bit better?

Thank you very much.

Cariboocoot

Re: First Project

The "easy out" would be to tell you to read this forum 'til your eyes start to cross.

But really, start with the FAQ section.

Basically it all comes down to anticipated loads. It's very important to determine both the maximum Watts you need at any one time as well as the total Watt hours per day (or between recharging). That information sets the basis for everything else. Starting with "X Watts" of panel and seeing what you can do with it generally leads to disappointment.

Here's some basic math with your 80W panel and your (best case) 4 hours of good equivalent sun:
80 Watts @ 80% efficiency = 64 Watts * 4 hours = 256 Watt hours per day.

Factor in losses in wiring, charge controller, and inverter you'll probably find you've got about 160 Watt hours of AC power available. That isn't much. About ten hours of a 13 Watt CFL.

The reason behind the different DC system Voltages is that as Watt requirements go up for any given Voltage, Amperage increases (W = V*A). As such, the higher Wattage needed the better it is to increase the Voltage and keep the Amperage down, as it gets difficult to handle (bigger fuses, high losses to heat, greater line loss).

Welcome to the forum! I hope we can help you avoid the Ready, Fire, Aim! syndrome.

dmiller

Re: First Project

Cariboocoot wrote: »

I hope we can help you avoid the Ready, Fire, Aim! syndrome.

What? and miss all the fun?

You'll want an AGM battery if your moving it around. You'll also avoid the freeze problem. And can do much faster absorption charging, plus the rate of self discharge is much less when the panels not in the sun for awhile......Just assume everything is better with AGM except price per watt and watt per pound.

Cariboocoot

Re: First Project

dmiller wrote: »

What? and miss all the fun?

You'll want an AGM battery if your moving it around. You'll also avoid the freeze problem. And can do much faster absorption charging, plus the rate of self discharge is much less when the panels not in the sun for awhile......Just assume everything is better with AGM except price per watt and watt per pound.

Yup. I totally agree. Except for "the freeze problem": a charged FLA will not freeze. Not even on Baffin Island. Well, probably not even on Baffin Island.

BB.

Re: First Project

Here is a nice thread with lots of solar information for the beginner.

Working Thread for Solar Beginner Post/FAQ

Not arranged into a nice book yet--but gives lots of pointers to other projects and websites for further information.

Also, this might be a nice thread. A person starting from ground zero designed and built his own portable solar PV system--so lots of questions and answers:

Emergency Power

And, please feel free to ask more questions on this thread (not trying to drive you to FAQs ).

But, basically:

1. Conservation--Choose loads and devices that use as little power as practical for your off-grid needs. It is almost always cheaper to conserve a kWattHour than to generate a kWatt*Hour.
2. Measure your loads--Know the peak power (Watts or Amps at what voltage) and energy used in a day (Watt*Hours or Amp*Hours)
3. Design the system--Do the paper design first. It is alot cheaper than buying hardware because it is on sale or on Craigs list (usually :roll:).
4. Don't forget safety--Lead Acid batteries are relatively dangerous devices... Filled with sulfuric acid and hydrogen gas. And even "car sized" batteries can output around 1,000 amps into a dead short. In some ways, a large battery bank is more dangerous than your 120 VAC wall outlet.
5. Now buy/locate the parts you need and build out the system.

-Bill

dhsola

Re: First Project

Here are a few links to some ready-made portable setups that might get your imagination going..

http://www.powerportstore.com/PowerSafes%20AR.htm

http://www.amazon.com/Portable-Solar-Power-Supply-Watt/dp/B001NJRRJY

http://www.amazon.com/Mono-crystalline-Portable-Briefcase-Solar-Charger/dp/B000GDC2MA/ref=sr_1_1?ie=UTF8&s=hi&qid=1265092619&sr=1-1

http://www.powerenz.com/store/index.php?_a=viewProd&productId=153


I bought this true sine wave 300W inverter, (two) 20Ah VRLA battery and backpack. Works well; no complaints.
http://www.alienbees.com/battery.html
I run two 50W panels through an inexpensive ($30) 10A PWM controller.
The foldable Brunton Solaris thin-film panel would have been more "portable", but.. I wasn't willing to part with $800!

BB.

Re: First Project

You can take a look through the links dhsola supplied... They are more towards portable power and not really aimed at a long term/fixed/all weather installation... And if you need portability, you pay a lot $$$ for portability.

Once you have sized your system and selected the components--then you can look at some turnkey product and see if they meet your needs any better or not.

Solar is not cheap power (at least if it is done right). It is just cheaper than the alternative of bringing power long distances and/or riding through storms/local disasters using a generator and lots of fuel.

-Bill

jayjay

Re: First Project

Thank you very much for pointing me in directions to better understand... while I have a long way to go, some questions popped up while trying to understand how best to size this project with as reasonable cost as possible, yet to get the job done. I'm not close to buying yet as I don't have a proper grasp on how to size parts, but hopefully with my continued reading here and some help I can get to that point in the future...

So, to see if I have this part down:

For a single PV Panel, I want to get the biggest bang for the buck, thus a Kyocera KD185GX-LPU Solar Panel @ $498.00 seems to be the lowest cost per watt panel, as compared to the Kyocera KD135 at $425.00.

Charge Controller: a 10amp SunSaver at $66 compared to a 20amp Sunsaver at $86 - - - not sure how to determine what would best suit this type of project. In my garage, for example, if I run 4 CFLs at 13 watts each, that is 52 watts at 115V is only .45 amp ... am I figuring that correctly?

Battery: the Sun XTender PVX-340T AGM 12V Battery at 115.00 has 34 amp-hours of storage space... if my above calculation is correct at .45 amp, then I should be able to run those 4 CLFs for 75+ hours (not counting system loss, of course).
If that is the case, the 185 watt panel (at 80% efficiency) with 4 hours of sun should give me 592watt-hours per day of charge. Do I divide the watt-hours by the voltage to arrive at amp-hours? If that's the case, that is around 5 amp-hours per day of charge, so it would take 7 days just to charge 1 battery with one panel? Is that correct?

Inverter: What is being called a Sine Wave Inverter ... is that the same as a modified sine wave inverter (better quality), or is that dead-bare minimum for lights and such? The Samlex 150watt 12V Sine Wave Inverter is much better priced than the Exeltech XP125 125watt 12V Sine Wave Inverter, but perhaps I would be getting exactly what I am paying for? (or perhaps on this sort of system to run lights, and a possible small refrigerator during camping trips) it would be fine?

Then the cabling, too, --- I would plan on putting the battery, inverter and charge controller in a carrying case so it's easy to haul around -- so could I just use standard battery cables to hook the charge controller to the battery and the batter to the inverter? How about cabling from the PV Panel to the inverter -- I'd like a 50' cable for this (or maybe even 100')... how do you size these cables? And on a system of this small size, is it wise to put a fuse in line somewhere or could I use a standard 115AC breaker?


I realize I've asked specific questions about brands of hardware and I am not trying to get someone to endorse one product over another - - -just trying to get an understanding of comparing product A over product B.


Thank you.

Cariboocoot

Re: First Project

Okay, something you really should read to get familiar with the nomenclature:
http://forum.solar-electric.com/showthread.php?t=6136

Modified Sine Wave is a bit of a misnomer (as has been discussed many times around here) because it implies "sine wave" when that is exactly what is absent! "Modified Square Wave" or "Multiple Stepped Wave" would be closer to reality.

I understand your wanting to get the most bang per buck. Those Kyoceras are a good deal. Just remember: 135 Watts is more like 100 Watts. This is likely to produce about 7 Amps on a "12 Volt" system, so there's certainly no need to buy a 20 Amp charge controller. That also means you could handle 70 to 140 Amp/hrs of battery - so figure around 100 Amp/hrs like one of these:
http://store.solar-electric.com/de8a92ampho1.html

Maximum DOD of 50% gives you 50 Amp/hrs to work with. @ 12 Volts, that's about 600 Watt hours (not including losses). 25% DOD would be better, and give a longer over-all battery life.

It's the losses that will get you. Line losses, efficiency losses, conversion losses. For instance your "50 feet" of cable from a single "12 Volt" panel is going to be a problem; not very high Voltage to begin with (around 17 VMP) put through that much wire will require significant AWG to keep losses to a minimum.

Not really a good idea to use AC breakers on DC current; they're not designed to properly interrupt the power. You should have fusing between the charger controller and the battery, and again between the battery and the inverter. Wire sizing has to be able to accommodate the current draw too. That would be "10 Amps" between the CC and the battery, easily handled by even 14 gauge on a short run. But the lines to the inverter may require much larger cable, depending on which inverter you choose. Something like the Morningstar 300 Watt (pure sine wave) http://store.solar-electric.com/mosu300wasiw.html would use 300/10 VDC (shutdown Voltage) = 30 Amps. That's at least 8 gauge or more depending on length so 4 gauge battery cables would be a good idea.

Again; this is just generalized and not specific. Just to give you some idea of what is involved with calculating and making choices.

BB.

Re: First Project

jayjay wrote: »

For a single PV Panel, I want to get the biggest bang for the buck, thus a Kyocera KD185GX-LPU Solar Panel @ $498.00 seems to be the lowest cost per watt panel, as compared to the Kyocera KD135 at $425.00.

Some of this is your call... Look at the physical size of the panel(s) and what you want to do with them. 135 watt panel is sort of transportable (protect it--still 1/8" thick tempered glass). 175 watt panel is about as large as one person would want to move/install by themselves.

In general, the larger panels tend to be less expensive per watt. However, check out shipping charges (or if it fits in your car if you drive it home).

Charge Controller: a 10amp SunSaver at $66 compared to a 20amp Sunsaver at $86 - - - not sure how to determine what would best suit this type of project. In my garage, for example, if I run 4 CFLs at 13 watts each, that is 52 watts at 115V is only .45 amp ... am I figuring that correctly?

Charge controller needs to manage the current from the solar panels--It does not matter what the loads are specifically (unless you are using the LOAD terminals that is present on some controllers that can turn off lights at night or if the battery is going dead).

The AC vs DC power... You need to know what voltage at power is at and wire based on the current (times 1.25 safety factor). Also, Many AC items draw power at other than P=I*V would predict. For things like motors and CFL bulbs--there is a Power Factor of 0.5-0.6 that means more current flow.

For example, 4x 13 watt CFL bulbs:

• P=I*V*PowerFactor
• I=P/(V*PF) = 4 x 13 watts * 1/(115 volts * 0.55 PF) = 0.82 amps

Now, you will need an inverter to run these devices... And they are Power Converters--so we need to know the PF and Amperage to size the Inverter, but otherwise we need to know the battery voltage (assume 10.5 volt cut-out for 12 volt bank) and inverter efficiency (assume 0.85). Note that Power = Volt*Amps only if PF=1.0:

• VA=V*I= 115 volts * 0.82 amps = =94 VA minimum inverter rating
• I= 4*13 watts * 1/10.5v cut-out * 1/0.85 invt eff * 1.25 safety factor = 7.3 amps 12 VDC fuse/wire rating
• Average Power at 12 volts = 4*13 watts * 1/0.85 invrtr eff = 61.2 watts
• Average Current at 12 volts = 61.2 watts / 12 volt battery = 5.1 amps typical load for inverter

Battery: the Sun XTender PVX-340T AGM 12V Battery at 115.00 has 34 amp-hours of storage space... if my above calculation is correct at .45 amp, then I should be able to run those 4 CLFs for 75+ hours (not counting system loss, of course).

Note your major mistake is that you are looking at the 115 VAC current... Not the 12 VDC current (which is ~10x as much because the voltage is 1/10th as high)... Remember, P=I*V so is V is 1/10th then V must be 10x as much for the same Power:

• 34 AH / 5.1 amps typical *50% recommended discharge = 3.3 hours

You could discharge to 80% maximum discharge--But that would really only be recommended for an emergency or rarely (like weekend RV trip, cabin, etc.).

If that is the case, the 185 watt panel (at 80% efficiency) with 4 hours of sun should give me 592watt-hours per day of charge. Do I divide the watt-hours by the voltage to arrive at amp-hours? If that's the case, that is around 5 amp-hours per day of charge, so it would take 7 days just to charge 1 battery with one panel? Is that correct?

I like to use 0.77 derating (instead of 0.8)--But that is a small issue. So, assuming summer time use (again, I believe your are mixing 120 VAC and 12 VDC):

• 185 watts * 4 hours of sun * 0.77 derating = 570 Watt*Hours per day

To recharge your battery bank... Roughly a AGM is 0.90 efficient whereas a flooded cell is roughly 0.80 efficient. To recharge a 34 amp*hour 12 volt AGM battery:

• 34 Amp*Hours * 14.3 volts charging * 1/570 WH per day * 1/0.90 battery charging eff = 0.95 of a 4 hour rated solar day

Note--it usually takes a few hours of taper charging to fully charge a battery to 100% state of charge--so it is going to take a bit more than 1 day to completely recharge (instead of 0.95 days).

Inverter: What is being called a Sine Wave Inverter ... is that the same as a modified sine wave inverter (better quality), or is that dead-bare minimum for lights and such? The Samlex 150watt 12V Sine Wave Inverter is much better priced than the Exeltech XP125 125watt 12V Sine Wave Inverter, but perhaps I would be getting exactly what I am paying for? (or perhaps on this sort of system to run lights, and a possible small refrigerator during camping trips) it would be fine?

Sine vs Square Wave inverters has been addressed... For 80% of devices the square wave will work OK... For 10% a square wave inverter may cause early life failure (from overheating) or possibly immediate death of a device (wall wart transformers and power supplies frequently do not do well on MSW inverters).

A couple inverter FAQ's to read:

All About Inverters
Choosing an inverter for water pumping

Then the cabling, too, --- I would plan on putting the battery, inverter and charge controller in a carrying case so it's easy to haul around -- so could I just use standard battery cables to hook the charge controller to the battery and the batter to the inverter? How about cabling from the PV Panel to the inverter -- I'd like a 50' cable for this (or maybe even 100')... how do you size these cables? And on a system of this small size, is it wise to put a fuse in line somewhere or could I use a standard 115AC breaker?

Solar PV systems do not usually do too well at "portable"... The panels are large, heavy, and made of single weight window glass--Yes the glass is tempered--but one whack with something hard and you have a piece of modern art instead of something that generates electricity.

There are various portable panels out there--but we need to talk about those if you want a "Hiking PV System" and probably use some version of Lithium Battery (light weight and high energy content). Lugging around Lead Acid batteries on a hike is not going to be very fun.

A Honda eu1000i genset and a couple gallons of gasoline is going to give you a lot more power for any short term hike/excursion.

Thoughts on this Portable Solar Setup
Lithium Iron Phosphate Batteries; LFP; LiFePO4 discussions

If you want to place the panels 100' from the charge controller/battery bank--Then you probably want to look at a MPPT type charge controller.

MPPT can take high voltage / low current solar panels and efficiently down convert to low voltage / high current needed to charge the battery bank (think the DC equivalent of an AC Transformer).

Depending on the model/size of charge controller--you can run an MPPT charge controller on a Vmp=100VDC array pretty easily (send the 100 VDC the 100', then down convert with the MPPT charge controller for the 12 VDC battery bank).

However, if you are going to power 120 VAC devices... You can have the solar panels + charge controller + batteries + inverter at one location and just send the 120 VAC to your loads

Sizing of the cables depends on voltage, current, and allowed voltage drop (you can withstand 3+ volt drop on 120 VAC, however voltage drops over 1.0 volts will kill many 12 VDC appliances).

Before we get into the details of designing the wiring/fuses for your system--should really decide on the loads, battery capacity, inverter, and charge controller needs first.

Hope this helps.

-Bill

jayjay

Re: First Project

Charge controller needs to manage the current from the solar panels--It does not matter what the loads are specifically (unless you are using the LOAD terminals that is present on some controllers that can turn off lights at night or if the battery is going dead).

I am going to take this piecemeal so it's not confusing . . . I need to understand each piece:

In figuring a charge controller, disregard the load you plan on running your system with and look at the current from the solar panel to the battery... if that is the case, for the 135watt Kyocera panel, the current at max power is listed as 7.63 amps.
I would take 1.25 X 7.63 and arrive at 9.5375 amps. Thus, a 10amp Charge Controller should work fine for this project?

If that is the case, then the Xantrex 12 amp PWM charge controller should work fine. The SunSaver 10amp would be about half the price of the Xantrex ... for this simple circuit, that appears to be the best bet (assuming spending $200 plus for an MPPT controller at this level would not be worthwhile).


NOTE: I know I'm asking a lot of questions -- I want to understand this fully so when I do my home I don't make serious mistakes... I have a large home so the cost of doing it will be substantial.

Cariboocoot

Re: First Project

jayjay wrote: »

NOTE: I know I'm asking a lot of questions -- I want to understand this fully so when I do my home I don't make serious mistakes... I have a large home so the cost of doing it will be substantial.

This is the absolute best strategy to take!

I will try to give you some basics on how you size the main components of an off-grid system.

Inverter: must be large enough to handle the maximum Wattage used at any one time. If you've got even one item that draw 1000 Watts, you need at least a 1000 Watt inverter plus capacity for whatever else will be running at the same time. It doesn't matter if the big load is a microwave run for two minutes; if you haven't got the 1000 Watt inverter capacity, it doesn't run at all.

Batteries: you need enough capacity to supply the over-all power need between recharge cycles. In other words, if you use 1200 Watt hours per day (no matter how it's divided up) you need that much in battery capacity, times at least two because you never want to draw batteries below 50% State Of Charge. On a "12 Volt" system that's roughly 200 Amp/hrs minimum @ the "20 hour rate" (industry standard). As in: 200 Amp hours/2 = 100 Amp hours * 12 Volts = 1200 Watt hours. Roughly.

Solar panels: you need enough capacity to recharge those batteries in the time the sun shines. This is usually estimated as "4 hours of equivalent good sun" per day. The goal is not just to replace the Amp/hrs "used" but also to replace them at the rate recommended by the battery manufacturer. This is expressed either as "C/#" (C/8, C/10) or as a % of the Amp/hr capacity (5%-10%-13%).

Charge controller: has to be able to handle the current output by the panels as explained above.

Wires & Fusing: sized to carry not only the maximum expected current (plus NEC margin) but also sufficient to keep Voltage drop at a minimum over the length of the wire.

How are we doing so far?

BB.

Re: First Project

jayjay wrote: »

In figuring a charge controller, disregard the load you plan on running your system with and look at the current from the solar panel to the battery... if that is the case, for the 135watt Kyocera panel, the current at max power is listed as 7.63 amps.
I would take 1.25 X 7.63 and arrive at 9.5375 amps. Thus, a 10amp Charge Controller should work fine for this project?

If that is the case, then the Xantrex 12 amp PWM charge controller should work fine. The SunSaver 10amp would be about half the price of the Xantrex ... for this simple circuit, that appears to be the best bet (assuming spending $200 plus for an MPPT controller at this level would not be worthwhile).

Yes, for a PWM controller--you are correct (the 1.25x the current is really for wiring and fuses. NEC requires derating for all solar charge controllers... But I think they are going overboard a bit (piling safety factor on top of safety factor).

In the end, use the above rules of thumb to get "in the ball park"--then read the manual for the controllers you are interested in (manuals are usually very clear on solar panels supported and wiring/breaker/fuse requirements).

Some very nice options to have (and does account for increasing prices):

1. Remote Battery Temperature Sensor--Very nice to have, almost a requirement for fast charging/good battery life (especially if controller is not mounted in same temperature area as battery bank is).
2. 3 stage with Float mode--Very nice if your battery bank is going to sit for weeks/months between uses under solar charge (cabin/RV in storage, etc.).
3. Digital Display--Nice for debugging when something eventually goes wrong.
4. Remote Battery Voltage Sense--I like, but only available on the much more expensive Morning Star MPPT 45/65 Amp Controllers and their PWM 45/60 amp sisters.
5. Networking/computer interfaces--If you like to autolog the the data--may be worth it to you. Some networking options give you access to more software settings in the controllers.

-Bill

jayjay

Re: First Project

Thank you ... I think I am grabbing the basics of at least choosing Panels and Charge Controllers. . . the batteries have me a bit stumped, so I'll skip that for now and focus on the inverter.

It appears that to size an inverter correctly, I need to know the output power (wattage) that will be running from it as well as the input DC voltage from the battery(ies), whether I want a modified sine wave or Pure sine wave inverter. (not talking about grid-tie non-battery systems yet at this point).

Is that the basics of choosing an inverter?

BB.

Re: First Project

Pretty much... Although, there are "details":

1. Average load in Watts (or VA--Volts*Amps; important for motors--something called the Power Factor that takes into account that motors use more current--Amps--than would be indicated by the "Watts" Measurement)
2. Peak Starting Load (motors can take 4-5x the starting current as running current. So--for example, an Energy Star (modern efficient ~17 cuft refrigerator/freezer) and a couple CFL bulbs is recommended to use a 1,500 Watt Inverter even though the average compressor load is ~120 watts plus ~500 watts for defrost/icemaker heaters).
3. True (or Pure) Sine Wave Inverter vs Modified Square/Sine Wave Inverter... TSW inverters are quite a bit more expensive than MSW inverters. Your utility power is a "Sine Wave" and TSW output utility "shaped" voltage and current wave forms. MSW inverters output a form of Square Wave that works OK for ~80% of the devices out there and can cause problems with ~10% of the devices (can cause overheating/early life failures, typically small wall transformers, inexpensive electronics, and some induction motors)
4. You also need to know the capacity of your battery bank (too heavy of inverter load will quickly discharge your battery bank and can damage the battery). And how you are going to recharge the battery (do you have enough solar panels / AC battery charger / Genset to properly recharge the battery bank).

Regarding TSW vs MSW inverters--here are a couple Inverter FAQ's:

All About Inverters
Choosing an inverter for water pumping (good MSW/TSW article)

-Bill