Need a little help getting started

Re: Need a little help getting started

Welcome to the forum.

A couple of things you should reconsider right off the bat. First would be a 12 Volt system. Second would be any system at all. The reasons being that 12 Volt systems aren't very practical for most applications and battery-based back-up in general is fairly expensive compared to an efficient generator when it comes to supply power for occasional, short outages.

Now some terminology. What you're looking at supplying is Watt hours, not simply Watts. If you got this number from a "worksheet" chances are very good that it is extremely inaccurate. One good thing to invest in right away: a Kill-A-Watt meter. You can use that to measure the real power consumption of everything you plug in under actual usage conditions. That will give you a far more accurate Watt hour number than any mere calculation can. These things are worth their modest cost (about $30) for anyone looking into saving energy or building a system or supplying back-up.

Here's a third thing to forget: bargain equipment like those 78 Amp hour batteries. Used batteries are scrap metal almost all the time. Avoid like the plague.

As far as using the system "even during the good times" remember that solar energy comes at a very high cost and unless your utility is charging ridiculous amounts per kW hour and/or is dreadfully unreliable it is not worth the investment.

Now let's talk about supply those Watt hours (if you haven't given up and run away yet). For a back-up system the first thing you determine is the needs for the critical loads. Do not try to supply 68 kW hours a day from solar. That would require an investment around $250,000. No, I'm not kidding. You'd be looking at around 5,700 Amp hours of 48 Volt battery and 35.5 kW of array with about seven charge controllers.

Scared yet?

Re: Need a little help getting started

elesaver wrote: »

Thanks for the first set of advice. No, I'm not scared yet.;) I do want a solar system. I have watched youtubes with examples of what has been done and if they can do it, I can do it. (I'm not trying to be haughty, but you get my drift.) I get the message about the used batteries, so I'll scrap that.

Please do not rely on Youtube as a source of information. There are many videos on there that are fabricated and/or outright lies.

I'm looking at the worksheet and think that my miscalculations are on the refrig and freezer. The worksheet suggests 1200 watt hours per day and a small chest freezer may be 1000 watt hours per day. I've corrected those errors and now I have a more reasonable idea...I'd like to generate 3-4000 watts per day. Now, that's more like it, I would say. that includes this calculation for the following:

refrigerator 1200 W hrs/day
freezer 1000 W hrs/day
TV 540 W hrs/day
LED lights 20 W hrs/day
microwave 400 W hrs/day

Good, but let's look at this. The numbers for the 'frige/freezer are not unrealistic. Your TV may draw 100 Watts or 200 Watts or just about anything, depending on the size, type, and how it is set up (yes that makes a difference). My 42" LCD would use 540 Watt hours in about 4.5 hours if I let it. 3 hours if I didn't have the backlight turned down. LED lights are nice and use very little power, but it's amazing how easy it is to leave them on. The microwave is going to hit the system for 1000 Watts or more when running, but generally only gets used for a few minutes a day. This is important to remember as the system must supply that 'hit' of high Watts even though the Watt hours is small.

In order to generate 2-3 Kw, I should be able to configure a system. 12V seems the easiest to me but in reading, 24 volts is more efficient. I will have to do more study about panels that can generate what is needed to accomplish the goal. More suggestions are welcomed. And, be advised, I'm not offended with criticism. That's how we learn...or at least, I do. Thanks again.

24 Volts is more efficient and easier to deal with from a wiring standpoint. Here's a little piece about system Voltages: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power

2-3 kW hours is not difficult to achieve, but it's not small or cheap. In the short form 2kW hours would require around 1.5kW of array in most places. In the long form it looks like this:

2,000 Watt hours AC / 0.90 conversion efficiency = 2,222 Watt hours DC + inverter consumption 480 Watt hours (full-size inverter on all day) = 2,702 Watt hours DC / 24 Volts nominal = 113 Amp hours used * 4 (for 25% average DOD) = 452 Amp hour 24 Volt battery bank.

That's not unreasonable and can be supplied by two parallel strings of four 225 Amp hour 6 Volt 'golf cart' type batteries which are about the best bargain in batteries these days.

To recharge that you'd have a 10% peak current target, or 45 Amps @ 24 Volts / 0.77 (efficiency of panels & MPPT controller) = 1402 Watt array.

Some things can improve this, such as making use of power the panels can generate after the batteries are charged which would otherwise go unharvested. I have nearly the same capacity system but with a small amount of battery and panels because most of the power is utilized this way (during the day) and the batteries need only carry the small overnight load. I also have 3,200 feet of elevation improving my array efficiency (it runs about 82% efficient instead of the typical 77%).

You can also supply the power by sacrificing some battery life by allowing deeper DOD and thus use less battery and panel.

We haven't talked budget, but that is an important factor. The 24 Volt system outlined above is going to cost some serious money. You are looking at thousands of dollars for that. Again, not a wise expense for occasional outages. If you want to spend less but still experiment you can scale the project way back and still have enough money for a decent generator. You can even skip the panels and controller and recharge with a generator during the day and run off the quiet batteries at night. Also remember that if the power is out due to inclement weather chances are the panels will be too; they only work in sunshine.

Re: Need a little help getting started

elesaver wrote: »

OK. Now we're getting someplace. I know this is going to cost. With just some investigation without "shopping," I know that 12V 100 W panels are about $275 ea. so if I get 4, that's $1100. The batteries are out of sight but to have 8 ea 225 ah 6V would be $2400 or more. I have a 2000W, 4000W peak inverter but want to upgrade to a true sine. I have a small charge controller (10 amp) but would need to upgrade that. Electricity costs are going to go up, never mind the times that the power goes out. I live in the SE so the sun is available and there are no trees around the area of installation. It just seems "logical" to use the "free" energy of the sun if possible.

Okay here's one way to save money: don't buy the "12 Volt" panels. If you're looking at a system over with 400 Watt array you can buy "GT" type panels for a lot less per Watt and have enough money to buy an MPPT type controller to connect them up with. Take a look at the per Watt pricing here: http://www.solar-electric.com/hiposopa.html You'll see "12 Volt 140 Watt" panels at around $2 per Watt while the larger "GT" type are near half that. The difference in price per Watt * 400 or more Watts makes up for the cost of the needed MPPT controller.

I don't understand why a 24V system would be more expensive than a 12V system unless it's my terminology. If I wire 12V batteries in series, I have a 24V output. If 12V panels are wired in series, they have a 24V output. It would seem that you would need fewer panels and fewer batteries to produce the same amount of power. Have I missed the boat here?

It depends on a lot of things, but chiefly whether or not the systems are the same size in terms of Watt hour ability. If you compare two very basic inverters of the same power from the same company there's little difference in price between 12 and 24 Volt versions. But usually when you go up in Voltage it's because you need greater capacity. The batteries will be a big difference here, as you need enough to supply 24 Volts instead of 12. Sometimes that's the difference between four GC2's and two GC2's. You might also need a different charge controller even though the power is the same because sometimes the ones that will handle 12 Volts will not handle 24. Here's an example of that: http://www.solar-electric.com/ss-10l.html 12 Volt version is $54, 24 Volt version is $5.20 more. For $43 you can get same current capacity but 12 Volt only: http://www.solar-electric.com/ss-10.html So more than system Voltage goes in to determining cost as it varies the equipment choices.

My earlier comment about saving on a 12 Volt system was based on down-sizing the requirements so that you could use a single set of GC2's (about 1.2 kW hours @ 50% DOD), minimal panel (5% rate to maintain/finish charge, Bulk charging done by generator), and inexpensive inverter around 1.5kW (about $500).

As far as a generator goes, I don't like the noise or the upkeep...gasoline, oil change, etc. If the power is out, gas stations can't pump the gas or the gas supply is gone, so there you are. Plus, gasoline prices are bound to increase.

Thank you all for your suggestions and help. I will keep working on this.

Well the good inverter-type generators are not noisy nor do they use large amounts of fuel. Upkeep is pretty easy too. I've manage 6,000+ hours on a Honda EU1000i with only oil changes. I find gasoline advantageous because the same fuel goes in everything; I don't store it, I keep it on hand.

There's always more than one way to achieve the same end.

Re: Need a little help getting started

elesaver wrote: »

Your comments are certainly valid, icharus...if we look at today's electricity. What if electric rates triple or quadruple? What if there is no grid? These are also things that need to be considered. Just sayin'.

That depends on what your electric rates are now, of course. Around here they'd have to go up 10 fold or more before off-grid made sense. That's unlikely to happen. Even in places where grid power is expensive off-grid power is still more so; 2X at least.

As for the grid going down ... always remember how many people make huge profits from it. That is a major incentive to keep it operational, and one unlikely to change in the near future.