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Author Topic: Photvoltaics (PV)  (Read 8311 times)

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AGelbert

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Re: Photvoltaics (PV)
« Reply #15 on: January 13, 2014, 02:58:44 pm »

When I set out to build the Bug-Out PV Kit, I did so for a number of reasons. There were a number of questions I had in my own mind...

What is a reasonably sized portable PV Set-up? Is it even practical to design a mobile PV kit? How much would such a kit cost at current prices?

How many and exactly what kind of batteries would be required for such a system?

How much power could such a set-up yield, and what could you do with it?

How often would you need to resort to a grid-based battery charger or a portable generator to keep the batteries charged?

How easy would it be to monitor the system and keep the batteries properly topped off. Would I need to check them daily? Weekly? Hourly?

Some questions I forgot to ask, but would eventually answer:

How much storage space would it take to accommodate all the parts of this system?

How much would the system weigh?

All the handy calculators on the internet designed to help you estimate PV system size work the same way. They begin by getting you to estimate your daily power needs, and then help you figure out how many amp-hours of battery storage it might take to provide that amount of power. After that, you calculate how many panels you need to keep those batteries charged, based on how many sunny hours per day you expect to experience, and how many days of no sun you might need to plan for, based on your geographic location.

For a kit like the one I envisioned, I needed to work from the other direction. How many panels were practical to carry around? What kind of panels were available that met the criteria of being easily portable? Were they 12 Volt? 24 Volt?

I decided to buy 12 Volt 120 W folding panels, with light weight integral folding legs, made sort of like a card table. I first bought two of those, and then eventually decided I could add a third one, after I bought my charge controller, which I figured out would work well for up to about 400W in panels. (The folding panels I got from Solar Blvd were equipped with primitive charge controllers, but I chose to bypass those leaving them in place for back-up)

The cost for the panels was $190 each, or $570 for the 360W total.





I also learned, by reading about other people's adventures, that it takes about 400W in panels to keep a 12 Volt 225 Amp hr battery bank (made of two heavy duty 6V Golf Cart batteries from Sam's Club) charged, in an average sun environment. I bought the batteries from my local Sam's and paid $220. It would have been slightly less had I shlepped a couple of dead 12V batteries to the store to offset the "core charge", but I didn't.




Why 6V g-cart batteries? Simply, they are the best bang for the buck. 12V deep cycle batteries are generally rated at about 50-60 amp hrs, cost about the same as the g-cart batteries. It would take four of them to give the same storage as 2 of the ones I got, and they would need to be wired in parallel, which is something to be avoided with batteries if you can. (Although many people do it anyway.) Gel batteries are nice, but cost much more than wet cell lead acid batteries. The only advantages are that they don't have the potential for leakage, and they don't have to be ventilated. For me, I didn't need to pay double to get those features.

I also learned that such a 400W system is not an uncommon size for RV's, and that I could buy the basic wiring harness, with various junction boxes, switches, circuit breakers, and the correct wiring, along with the Blue Sky charge controller I liked, and a matching battery monitor, from a  small Mom and Pop RV solar outfit called AM Solar.

I had already sourced the controller from Solar Blvd, but I bought the rest of the kit from AM. If I'd bought the complete the kit from AM Solar (They call these kits "system cores ". The appropriate one for my system was their Sunrunner(tm) Signature Series 25/6 PRO Core.) it would have cost $815, including the combiner box.

That price includes a lot of gear. An MPPT charge controller and matching battery monitor (expandable to grow the system if desired), a custom metal box for the charge controller designed to overcome some problems with wiring heavy wire to the CC., Two 30 ft lengths of #6AWG, a bridge shunt for wiring the battery monitor, a temp cable for the batteries and wiring for the battery monitor, and a combiner box with bus bars for paralleling the three panels into one circuit. Also included are all the tiny bits you'd have had to buy yourself after you figured out you needed them. AM kits are well thought out.











That kit basically got me wired from panels to charge controller to batteries. To get AC current, I needed additional battery cables, another fuse, and an inverter. I chose the Morningstar 300W Sure-sine for its durability, simplicity, low cost and small size. I paid about $200. The #2 AWG battery cables I needed (six short ones with lugs and heat shrink installed) cost me $108 from Don Rowe, a company that sells inverters and cables.




I had a big plastic mil-surp box in the garage that once held dental equipment of the Gulf War era. The batteries and the electronics, fuses, switches and other paraphernalia will mount inside the box, once I make some plywood bread boards to fit the lid and bottom of the box.



Total cost for the completed kit, which I hope to finish this week, will be less than $2000.

The biggest surprise? Weight. The panels weigh 30 pounds each, the batteries 64 pounds each. Inverter weighs 11 pounds. the entire kit should tip the scales at roughly 250 pounds! Yeah, a lot more than I would have thought.

From the beginning, the one major requirement I had for the system was that it should power refrigeration. I researched a variety of refrigerators, both 12V units and 120V AC. Nice 12V chest style units could be had that would be compatible, but they were about $750 minimum. EcoCool makes a nice midsize 12V fridge for about $1100 that is efficient enough to run off my little system....but I kept looking.

Just before Christmas I watched one of Lamar Alexander's videos in which he evaluated the 3.1 cubic ft. Edgestar. These are little 120V AC units the size of a large dorm fridge, with separate freezer and fridge. They can be had for under $250 bucks, and their Energy Star rating is 338kWh/yr. They draw maybe 75W for a few seconds when the compressor kicks on, and then only use about 30W continuous while the compressor runs, which is about 50% of the time, based on ambient temperature and how often you open the fridge.

I ordered an "open box special" for $129.95 from an online seller, CompactAppliance.com, and waited...and waited. Finally I checked back and saw my order had been cancelled. My guess is that they sold the unit before I clicked on it, or some such...maybe they never had it. They get some bad reviews for customer service. So before I ordered another one for the regular price of $232, I checked around some more.

I found two other brands of 3.1 size refrigerators that are even more efficient than the Edgestar. Avanti makes one. And Sears sells one under their Kenmore brand. Energy Star rating of 270kWh per year. That's the energy used by the interior light of most refrigerators...unbelievable. And I bought one at my local Sears on sale for $159.95. Score!




I have some 12V LED lights I picked up at Home Depot. I'm continuing to research lights.

When the kit is functional, sometime this week, I intend to experiment with running fridge, lights, laptop, phone charger, AA battery charger, etc., just to see how it all works out. I've answered a lot of the questions that came to me in the beginning, but I expect that I'll be learning a lot more very soon, and answering the rest of the questions on my list, and maybe some more I forgot to ask.

Oh yeah. How big is it? The whole shooting match will fit easily in the trunk of my car (not including the fridge), with room to spare.


 And this system would be perfect to integrate into a bug-out van or small camping trailer.
Hope deferred maketh the heart sick: but when the desire cometh, it is a tree of life. Pr. 13:12

 

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