Solar Setups Different than SMB Solar?

[billwilson]

wilson sports two 180 watt kyoceras and a blue sky controler w/ remote panel
will try to dig up exact specs

i actually may have one of the largest arrays

i wanted to be able to run
fridge
24/7
lights
6 hours
laptop
4 hours
cell charger
4 hours
tv/dvd player
4 hours

so far i am good to go

[coyotearms]

Originally Posted by Okie

With additional computer equipment, I conservatively estimate meeting my total 2.7 kW-hour per day requirement with about 3-5 panels (depending on the panel's power output).
Returning to my original question, I would appreciate advice from people who have created custom solar setups. What have you built?

If the 2700 W-hr/day is the dc load from 12 V, relying completely on solar would require it to provide 225 amp-hr/day. To do this day in and day out taking the well-accepted 50% limit of discharge from the batteries, would mean having up to 450 amp-hr batteries. But no matter how many batteries you had, you would still have to provide 225 amp-hr in some combination to charge batteries and run equipment each and every day. This would be pretty challenging, and most likely require a generator to take the load at peak times while charging the batteries.

It is possible that the system I have put together could shed some light on what is possible with solar. Along with, let's say a 1100 W-hr/day load for the "regular stuff," I decided to have hot water based on a 110 VAC, 1500 W, 2.5 gal hot water heater SMB installs (also have an inverter). A 700 W microwave is the other high power device, that we can assume, along with the water heater are above and beyond the 1100 W-hr/day load. The water heater and microwave are quite low duty cycle appliances. However, if the microwave is used at full power, say, 1 hr a day for 700 W-hr/day, and the water heater also runs for a total of 1 hr for 1500 W-hr/day, that is 2200 W-hr/day, for a grand total of 1100+2200 = 3300 W-hr/day, exceeding your total of 2700 W-hr/day---it didn't take that much, did it?

The solar system I have consists of four Kyrocera KD135SX-UPU panels and three 100 amp-hr AGM batteries. I chose these panels primarily because it was the brand SMB used and the dimensions of this model filled the roof space except for a roof fan. The photo shown is before adding the last two panels, which still has not been done. So what follows here is based on calculations and zippo time actually using the system of four panels.


The panels are connected in parallel for a total rated output of 4x135 = 540 W, which is larger than any of the posts in this thread so far. They are connected together in a combiner box I built and sent to SMB (seen it next to the fan in the photo above) and used with the Blue Sky 3024iL controller and IPN-ProRemote wall mount monitor, which provides control for up to 32 amps of charging current. This controller has about twice the capability of the Blue Sky controller SMB was using at the time (summer of 2010) and just large enough for the four panels I chose. Instead of using SMB's guidelines that assume 8 hrs. of great sun allowing the panels to work at max output, it is more sobering to consider more realistic conditions. The 135 in the model number refers to a peak power of 135 W @ 17.7 V & 7.63 amps, which corresponds to an incident radiance of 1000 w/m^2 and 25 C. These are not typical conditions---less radiance and higher temperatures yield lower the output current. For example in the summer at peak times the radiance in Seattle (where I live) is only 700 W/m^2, and panel temperatures can be 75 C. According to sizing methods in the Kyocera catalog, Seattle has about 3.5 full sun hours (FSH) in summer, which means the equivalent of 3.5 hours of 1000 W/m^2 of sun. Using data for this particular panel and the method Kyocera gives based on FSH, at 13 V, each panel generates about 8 amps for a total for four panels of 8*4*3.5 = 112 amp-hr/day, but the 3300 W-hr/day requires 275 amp-hr/day! Without the microwave and hot water heater, the 1100 W-hr/day or 92 amp-hr/day is easily accommodated. [Edit (2/12/2011): [s:3fzt926t]But that ignores the angle effect of panels lying flat on the roof! In addition, the above estimates are for summer. From other data on the web for the collection of cities including Seattle, Sacramento, L.A., Phoenix and S.F, average winter radiance is a third of summer values (sun lower in the sky and more clouds)![/s:3fzt926t] Actually the Kyocera catalog contradicts itself on pgs. 6 and 12. Based on calculations described in my 1/12/2011 post in the thread, the FSH apparently is the average for the year. It is also more accurate to say the Kyocera method ignores tilt angle.]

Based on the the nitty gritty numbers above, it should be clear that one must conserve, conserve, conserve, and even in the summer, four 135 W panels are not one too many, even when traveling further south of Seattle, and I cannot expect to use the microwave or hot water heater at all when camped in one spot for days relying on solar alone. For my backup plan, I have a propane system, 2-burner stove top and an external connection for another propane stove or BBQ used outside. Having a propane furnace also justifies the propane system. Clearly during the winter when coming back from skiing it is the propane stove that will be used for hot water and cooking! One nice feature of the 110 V water heater is that for trips when driving each day, the water heater can be turned on while driving (I have an optional 140 amp alternator), so when pulling in for the night we have "free" hot water. Keeping the water heater on for the few hours until bed time, could result in small enough duty cycle that the solar and driving the next day could be enough that it will supply hot water from breakfast through dinner each day depending on how much hot water is used. If this level of backup does not work, running the engine just while the hot water heater and microwave are being use should help a lot (again that's 140 amps to feed those guys). Lastly, I have left space just behind the rear axle for a fixed propane generator, or could spring for that cute Honda 2000 W portable generator. The vehicle is diesel, so the latter choice is a bit problematic as it uses gasoline (life is always a compromise).

It may be interesting to note that the fixed 2500W Onan propane generator SMB installs weighs 115 lbs, virtually identical to the weight of the four solar panels! That one fact alone is food for thought when wondering if one should just scrap the idea of solar all together if one has the "extra" 1600 W-hr/day load but only expects to use it for a limited times, during which the generator could be fired up. That suggests just living with a couple of house batteries that get charged while driving and when the generator is running the heavy duty equipment! If it weren't for my interest in learning about solar, trying to be as green as possible, and not wanting to hear a generator, I probably should have just gone with the generator. . .

Edit (2/8/2011): It is also may be interesting to note that the cost of the entire solar system described above, propane system, propane stove, AC water heater, microwave and propane furnace was the cost of just the diesel furnace and diesel hot water heater (approx. $6400 vs $6100 for both systems having the same number of batteries). More food for thought?

Edit (2/9/2011): The comparison of prices above was done to show alternatives even, as in my case, if you have diesel. A few more things to note. The current way to do diesel hot water and furnace is with SMB's Espar D5, which with the flat plate heat exchanger, is $6370, which makes the comparison dead equal. Also note that I supplied the solar panels, electronics and combiner box and paid for the installation for a total cost for all the solar of $2900, which was probably somewhat less due to installing stuff sent to them. SMB's price for a gasoline or propane generator is about $3800, which could bring one again back to the idea of skipping the solar and just going with a generator IF the HEAVY electrical load is for a limited time each day.

[Advanturetrek]

Bill and CoyoteArms,

Thanks so much for the detailed and helpful posts.

We're editing our solar plan and should be able to post more information soon.

[coyotearms]

Originally Posted by billwilson

wilson sports two 180 watt kyoceras and a blue sky controler w/ remote panel
will try to dig up exact specs

i actually may have one of the largest arrays
so far i am good to go

As my post indicates, only 2 panels are installed as of now too. What I have found with two and just doing weekend trips, solar brings the batteries back up over the days between trips. A recent trip ended with a night time 300 mi non-stop drive back home. At the start of that drive my batteries were down to 72% (used the 110 VAC water heater and microwave). When I arrived home they were down to 70% with just the refer being the load! That was when I realized the Sure Power battery isolator was dead (and since replaced). Guess what? Parked where the rig was in the shade most of the day, and certainly not fully sunny, in a few days the batteries were at 100%! And no, shore power was not used! The real test of how well solar works is when it has to do its job day after day while camped off the grid in one spot.

[billwilson]

Pulled out my invoice from Affordable solar



two 180 Kyocera watt panels
BLue sky DB3024iL controler
Blue sky remote sisplay
wire and hardware and shipping
$2,181

they estimated:
with 5 hours of sun - 1782 kWHr/day

[coyotearms]

Affordable Solar's estimate appears accurate. Using the Full Sun Hour (FSH) method to estimate solar output (see my post below) you get a similar estimate. I believe you are in SOCAL, and according to the Kyocera catalog (pg. 6) your summer FSH rating is 5.5 to 5.9, compared to 3.5 to 3.9 in the PNW. So one would expect your system would produce about 5.7x360 = 2.1 kW-hr/day on a sunny summer day in SOCAL. That compares fairly well with Affordable Solar's estimate of 1.782 kW-hr/day (after moving the decimal over three spaces). The FSH calculation is probably somewhat high because the wattage is normally not the peak rating but at the charging voltage (around 13 V) and current (for which a detailed spec sheet is needed), but there is not a model number given. In any case, the estimates only correspond to summer in SOCAL.

[billwilson]

Originally Posted by coyotearms

Affordable Solar's estimate appears accurate. Using the Full Sun Hour (FSH) method to estimate solar output (see my post below) you get a similar estimate. I believe you are in SOCAL, and according to the Kyocera catalog (pg. 6) your summer FSH rating is 5.5 to 5.9, compared to 3.5 to 3.9 in the PNW. So one would expect your system would produce about 5.7x360 = 2.1 kW-hr/day on a sunny summer day in SOCAL. That compares fairly well with Affordable Solar's estimate of 1.782 kW-hr/day (after moving the decimal over three spaces). The FSH calculation is probably somewhat high because the wattage is normally not the peak rating but at the charging voltage (around 13 V) and current (for which a detailed spec sheet is needed), but there is not a model number given. In any case, the estimates only correspond to summer in SOCAL.

Translation:
The Big Ass Flat Things on the roof of my van will:
-allow me to see at night
-charge my phone
-play w/ my laptop
-keep the beer cold
-and can watch dvds
... providing the Sun Gods are happy

[coyotearms]

I wish we even had Sun Gods in the PNW, so we would have a chance to make them happy.
Translation:
Up here divide all currents, voltages and up-times by 10. . .

[Advanturetrek]

For anybody interested, here's the source for data on "full sun hours" broken down by location and time of year. The data in the Kyocera catalog is probably based on this.

The "Solar Radiation Data Manual for Flat-Plate and Concentrating Collectors" (aka "Red Book"):
http://rredc.nrel.gov/solar/pubs/redbook/

PVWatts (same data but with a handy interactive map):
http://www.nrel.gov/rredc/pvwatts/
http://mapserve3.nrel.gov/PVWatts_Viewer/index.html

The "solar radiation" number found in these sources is numerically equal to "full sun hours."

Solar is a lot more complicated than I thought it would be ... but that's what keeps this project interesting!

-Peter


Footnote: Solar radiation is measured in kW-hr/m^2/day and "full sun" is 1 kW/m^2. Divide the first by the second to get full sun hours per day.

[coyotearms]

Originally Posted by Okie

The "Solar Radiation Data Manual for Flat-Plate and Concentrating Collectors" (aka "Red Book"):
http://rredc.nrel.gov/solar/pubs/redbook/
PVWatts (same data but with a handy interactive map):
http://www.nrel.gov/rredc/pvwatts/
http://mapserve3.nrel.gov/PVWatts_Viewer/index.html
The "solar radiation" number found in these sources is numerically equal to "full sun hours."
Footnote: Solar radiation is measured in kW-hr/m^2/day and "full sun" is 1 kW/m^2. Divide the first by the second to get full sun hours per day.

Great links. I actually based my estimates on the first link above using "Data Files in ASCII Text Format, Averages of solar radiation for each of 360 Months, 1961-1990 for 239 U.S. sites...." but decided to present similar findings in my previous post based on FSD's from the Kyocera Catalog for easier public digestion. I just gave the friendlier PVWatt a spin, and for Seattle it gave 3.34 FSD compared to 3.5 in my previous post using the Kyocera catalog. The manual for the ASCII data indicates the data is based, in part, on measured data, so it does take account of weather. So everything needed is there once you pick the panels you want.

One big take-away I realized after re-visiting the sizing issue with PVWatts is about the difference between just mounting the panels flat on top of a rig (easy) or having a tiltable system (challenging). It really doesn't matter that much! At least that is what I observed using Seattle data considering a tilt of 45 degrees, which is close to the ideal for that latitude. Over the entire year, the solar radiation only increased by tilting from 3.34 to 3.78 kW-hr/m^2/day (13%). It is actually a tad less with tilting for May-July! Also note, the comparison assumes when tilted the rig is also parked so the panels point directly South (any other direction, and the radiation is diminished). With zero tilt it doesn't matter which way you park (on flat ground). Just pull in any which way and have a beer! In winter it is a different story, but zero times zero is just about zero anyway.