Solar Guppy:

I live in Guatemala, and I have decided that it is time to learn about RE and begin seriously pursuing the issue. I expect to spend about three months learning and planning, while at the same time exploring my house for ways to reduce energy use.

Once my house is about as efficient as I can make it, I expect to need to generate about 450 Kwh per month (current use is 725 Kwh, but below 300 Kwh the price drops from US$0.22 to US$0.10 so buying some from the grid is fine).

Given ambient conditions (lat. 15N, long. 90W, 5000ft above sea level, reasonably sunny), it seems to me at first blush that one of your 24-cell PV arrays with a Sunny Boy 2500U would do the trick.

Of course, then the newcomer starts thinking:

- What about the Kyocera 158G's? Pros/cons? Other PV cells to consider? How to choose?

- How do I mount the cells? What do racks cost to either make or buy? How does one make racks?

- ...and about a billion other questions.

It strikes me that a HOWTO of your system (how it was built, with a little instruction, and the pricing and costs for building it) would be an invaluable resource to those of us just starting out.

Maybe you could even do a little "how I would do my PV array if I were redoing it today" thing.

These are just some ideas on information you could share which would likely be extremely valuable to a bunch of people. Food for thought.

Well done! And thanks for providing a good example. :-)

Let me think about your questions for a few days. Meanwhile here are some for you:

Would your array be ground mounted or on a roof?

At 5,000 ft, does the weather ever get hot?

Are all the popular PV models available in Guatamala?

What is the grid voltage and frequency to the subscriber?

What is your precise latitude?

Regards

Pete

Thanks, Pete!

I'll take the questions one by one:

Roof or ground: The array would be mounted on my roof. Said roof is two-slope ( /^\ ), made of flat unsurfaced concrete, with the top ridge running roughly north-south and the downslope of each side at approximately 15 degrees from horizontal. Each side of the roof probably has 600 sq.ft. of space available. All treetops can be eliminated and there should be no shade at all.

Heat and altitude: At 5,000 ft, it does indeed get hot (since we're not that far from the equator), but generally climate and altitude balance out well. We average 72oF year-round, no one I know has air conditioning or heating or any insulation... they call Guatemala the "Land of Eternal Spring" and it generally lives up to the claim.

We call hot 85 or 90oF, where you go outside and you sweat and get uncomfortable. But it never hits Miami levels, or El Salvador levels. One of the things I want to do in the next few months is actually measure this kind of thing.

PV availability: You're kidding. 90% of the country uses less than 300 Kwh per month, and they pay $0.08/Kwh. The other 10% has trouble swallowing $15,000 to $20,000 budgets for a PV system, even if it will pay for itself over time.

At this point I am not yet aware of _anyone_ really out there selling PV or RE in any real way to the consumer. (Might be a good opportunity when prices come down a bit and I learn more.) Whatever I buy, I have to bring in from the USA (luckily, within my means to do so).

Grid V and Hz: It's either 110V or 120V, and I think it's 60 Hz. I believe it to be similar or identical to US systems.

Precise latitude: How precise? My best guess is 14.5N, but it could also be around 14.6N. Good enough? If not, I'll get more detail.

Thanks for all the help and information!

Rodolfo

Kyocera makes great solar panels. KC120 vs. KC158? KC120 is 12v and the KC158 is 24v. I sell both for about $3.90/watt (lower on large orders) so price is the same per watt. Choose the panel based on size/fit, shipping ease...

Joaquin,

A couple of questions (and thanks in advance for your patience):

1. Given that both the KC-120 and KC-158 panels from Kyocera have approximately the same cost, is there a reason (any reason) you would prefer one over the other? Perhaps the 158 for fewer connections? Is the wattage per square meter equivalent, i.e. same technology?

2. It seems to me that the BP Solar SX-150 panels would generate a slightly lower cost per watt. Is their quality better/equal/lesser? How about their physical size (power per area)?

3. Basic question alert: if the grid in Guatemala is 120V, how can I use a Sunny Boy 2500U which is 240V? If I have to convert it somehow, is there an energy loss in the process?

4. ***ume you had a maximum ambient temperature of about 30-32 degrees C (86-90 F), what is the most cost-effective way to max out an SB-2500? 24 x KC-120? 20 x KC-158? 20 x SX-150?

I am trying to figure out how to do these calculations myself but have not gotten very far. The objective is to realize max power from the inverter (thus most efficient system overall), then get lowest possible cost per watt.

Thanks!!!

Rodolfo

Hi,

FWIW, I wanted to address one aspect of your post; I am pretty sure it will effect your other questions...

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>Rodolfo J. Paiz said:
Basic question alert: if the grid in Guatemala is 120V, how can I use a Sunny Boy 2500U which is 240V? If I have to convert it somehow, is there an energy loss in the process?
<HR></BLOCKQUOTE>

I believe you should rethink using the 2500U if your grid connection is only 120v.

Even if you could find a suitable conversion method to connect a 240v unit to 120v, the 1800U would most likely be more efficient (asuming the conversion method would have at least a 1% efficiency loss).

Also, asuming that you really need at least 2500w capacity, 2 1800Us may still be more cost effective (depending on the immediate and long term costs of the potential conversion method).

Finally, 2 1800Us would also give you some additional flexibility with 2 separate arrays, such as array orientation differences and future expansion (which may or may not be a consideration for you).

I urge you to try out the string sizing application at the SMA web site (go to www.sma-america.com and then click on String Sizing) You can get a pretty good idea of how well to match up panels to an inverter.

-Roger

Rudolfo,

Before installing a batteryless grid-tie inverter, there are several things you should check out.

Grid-tie inverters are very picky about line voltage. While most installations are no problem, occasionally the power is too high or too low voltage. If the grid voltage is out of spec, the inverter will simply refuse to operate. You should get a digital voltmeter and monitor the voltage for several days to see what actually happens with your power. The inverter specifications say what voltages are acceptable. The SunnyBoy is probably more picky than other inverters because of their use of grid impedance for grid quality testing.

You may need to get the power company to adjust the voltage to your house. This will require power company knowledge and agreement with your installation. Since you will probably have the first grid-tie installation that your power company has ever encountered, they will at least be confused, and probably hostile. Grid-tie in the USA has generally required government laws that have been rammed down the throats of the power companies. Even after they publicly accept the benefits of solar, they continue to throw all sorts of barriers in the way of actually installing the equipment. There are a few government run power utilities (notably the Sacramento Municipal Utility District (SMUD)) that are active installers of grid-tie, and are in better financial condition as a result. The reality is that grid-tie PV is a good deal for the power company, but most of them start out quite hostile.

The power system in the USA is generally thought of as 120 volt, but in fact is actually 3-wire 240 volt. The three wire connection provides two 120 volt legs, with the option of using either 120 volt or 240 volt circuits. Heavy loads such as an electric stove or clothes dryer are typically connected to the 240 volt circuit. The rest of the house is wired for 120 volt access. An inverter can be connected as either a 120 volt or a 240 volt appliance, depending upon choice of which circuits are used. Note that 120 is not an exact figure - it may actually be anywhere between 110 and 135 volts, depending on how long the wire is from your transformer and how much your neighbors are using. On one day, my "240 volt" service varied from 245 to 257 volts. I've seen the "120 volt" connection at 133 volts (the power company did some major work soon after I saw that and it's back down around 127 volts).

Most of the power meters used for billing are capable of running both forward and backwards. Even though mine worked both ways, the power company insisted on installing a new meter that had been calibrated for bi-directional use. There are power meters that either cannot run backwards, or even worse, count backwards the same as forwards (you pay the power company at standard rates for the power you send to them!!!). You want to get this one right!

Given your pioneer status and the potential problems with a batteryless grid-tie system, I suggest that you seriously consider a battery system. Something like a Trace SW4048 with 4 AGM batteries. An OutBack or RV Products MPPT charge controller should provide close to the SunnyBoy performance. If you can wait for it, the OutBack inverter should be available for grid-tie usage soon. The OutBack inverter is designed by the same people who designed the SW series, and they know how to improve on the SW design.

/Rob

The first thing to consider is that the KC120 is 12v (nominal) panel while the KC158 is a 24v panel. So when figuring the # of panels for either inverter make sure you the right volatges. Second if you have 120v 60hz then I would also recommend the 1800. Why add a transformer to the 2500?
http://www.kyocerasolar.com/PDF/KC120-1.pdf http://www.kyocerasolar.com/PDF/KC158G.pdf