Copanas

May 30th, 2006, 8:45 PDT

Hi,

I was wondering if anyone could help me out?* I am helping a friend design and install a two small systems for two off-grid yurts she has on her property in Vacaville, CA.

The first yurt will use PV direct to run a solar chill evaporative cooler which uses 35-50 Watts.

We have been thinking of using a Sharp 80 Watt panel Vmax=17.1V and Imax=4.67A with a Linear Current Booster rated

at 7A and 12V.

It looks like we might have to place the panel a minimum of 100ft from the yurt.* At a distance of 200ft in wire length.* It seems like this would cause a large voltage drop and require that we use #2 gauge wire.

Cost wise, as well as performance, would we be better off using a higher voltage panel (for example a 165WAtt, Vmax 34.6, Imax 4.77A) with a 24V evaporative cooler and 24V rated Linear Current Booster to cut down on our voltage drop?

Also, any suggestions on brands of Linear Current Boosters?

System #2

This is a larger yurt that would have a battery back-up for a small refrigerator, laptop, cell phone charger, one compact flourescent and if possible an evaporative cooler.*

It seems like too large of a load to have the evaporative cooler and refrigerator on the same battery system, so we were thinking of running the evaporative cooler direct separate from the batteries.

Summer (Vacaville is very hot)

The Load:

DC

Sundanzer chest refrigerator* 12V 168WH/day

AC

1 compact fluorescent* 15W *4 = 60 WH/day

Cell phone (5W *12 hours * 4 days)/7days = 34.29WH/day

Laptop (50*3hours * 4days)/7 days = 85.714 WH/day

Cd/player/Radio 15W * 3 hours = 45 WH/day*

Total AC = 225WH/day x 1.15 to correct for inverter loss = 259WH/day

To Calculate number of panels:

AC + DC = 427WH/day

427 / 12 = 36 Amp Hous/day

Multiply by 1.2 to compensate for loss from battery charge/discharge = 43AH/day

43AH/day* divided by average sun hours per day 5.1 = 8.37A (the total amp hours required)

8.37A divided by panel peak amps (sharp 80W Vmax 17.1, Imax 4.67A) = 1.79 panels = 2 panels in parallel

Battery Bank Calculations:

43AH/day x 3days = 129Amp hours

129Amp hours / .5 discharge = 250Amp hours

A Golf cart 6V with 220 Amp hours

250/220 = 1.13 batteries

Can I use one battery if it will only give me a 3.8% charge?

PLus will the refrigerator load, since it is summer and over 90 degrees bring that 3.8% down even lower? Any way to bring this up* to the 5-10%?

This system will have some of the same wire distance issues as the direct system for the smaller yurt mentioned above, as we are working to see if we can get it closer, but it may be 100 feet away as well.

Should we switch to a 24V refrigerator and change the panel voltages to match?* Also, given the hot climate and a small system, should we use a charge controller with MPPT? Any suggestions for battery chargers?

This is a lot of questions I know!* But, any help would be greatly appreciated!*

Thank you!

I really appreciate this discussion forum, it is very helpful!

Beth

I was wondering if anyone could help me out?* I am helping a friend design and install a two small systems for two off-grid yurts she has on her property in Vacaville, CA.

The first yurt will use PV direct to run a solar chill evaporative cooler which uses 35-50 Watts.

We have been thinking of using a Sharp 80 Watt panel Vmax=17.1V and Imax=4.67A with a Linear Current Booster rated

at 7A and 12V.

It looks like we might have to place the panel a minimum of 100ft from the yurt.* At a distance of 200ft in wire length.* It seems like this would cause a large voltage drop and require that we use #2 gauge wire.

Cost wise, as well as performance, would we be better off using a higher voltage panel (for example a 165WAtt, Vmax 34.6, Imax 4.77A) with a 24V evaporative cooler and 24V rated Linear Current Booster to cut down on our voltage drop?

Also, any suggestions on brands of Linear Current Boosters?

System #2

This is a larger yurt that would have a battery back-up for a small refrigerator, laptop, cell phone charger, one compact flourescent and if possible an evaporative cooler.*

It seems like too large of a load to have the evaporative cooler and refrigerator on the same battery system, so we were thinking of running the evaporative cooler direct separate from the batteries.

Summer (Vacaville is very hot)

The Load:

DC

Sundanzer chest refrigerator* 12V 168WH/day

AC

1 compact fluorescent* 15W *4 = 60 WH/day

Cell phone (5W *12 hours * 4 days)/7days = 34.29WH/day

Laptop (50*3hours * 4days)/7 days = 85.714 WH/day

Cd/player/Radio 15W * 3 hours = 45 WH/day*

Total AC = 225WH/day x 1.15 to correct for inverter loss = 259WH/day

To Calculate number of panels:

AC + DC = 427WH/day

427 / 12 = 36 Amp Hous/day

Multiply by 1.2 to compensate for loss from battery charge/discharge = 43AH/day

43AH/day* divided by average sun hours per day 5.1 = 8.37A (the total amp hours required)

8.37A divided by panel peak amps (sharp 80W Vmax 17.1, Imax 4.67A) = 1.79 panels = 2 panels in parallel

Battery Bank Calculations:

43AH/day x 3days = 129Amp hours

129Amp hours / .5 discharge = 250Amp hours

A Golf cart 6V with 220 Amp hours

250/220 = 1.13 batteries

Can I use one battery if it will only give me a 3.8% charge?

PLus will the refrigerator load, since it is summer and over 90 degrees bring that 3.8% down even lower? Any way to bring this up* to the 5-10%?

This system will have some of the same wire distance issues as the direct system for the smaller yurt mentioned above, as we are working to see if we can get it closer, but it may be 100 feet away as well.

Should we switch to a 24V refrigerator and change the panel voltages to match?* Also, given the hot climate and a small system, should we use a charge controller with MPPT? Any suggestions for battery chargers?

This is a lot of questions I know!* But, any help would be greatly appreciated!*

Thank you!

I really appreciate this discussion forum, it is very helpful!

Beth