06-02-2009, 06:27 PM
Let me attempt to design my system based on the theory you (TY) presented for Chris.
Chris needs 7820 watts per day, I need 15000watts per day.
System 1 - Simple ratio:
7820 watts (7819.5 actual) is to 9.240kw as 15000watts is to X - X=17723.78 or 17.724 kw.
System #2 - Calculated using your format. I'll do mine in red:
Ok, let's take the 7819.5 watt hours and round it up to 7820. Let's say you go with a 48 volt nominal system rather than 24.
7820 / 48 = 162.9 amp hours per day
Ok, let's take the 15000 watt hours.
15000 / 48 = 312.5 amp hours per day
I'm going to multiply that by 1.2 to account for batter losses, wiring losses, and add a safety factor. These numbers can be calculated much more intricately, but I'm not going to do that and 1.2 is a safe number.
162.9 x 1.2 = 195.5 amp hours
312.5 x 1.2 = 375 amp hours
Here is Hilo, Hawaii the worst insolation (daily sun hours) if you're using the wrong inclination, etc according to nrel.gov (http://rredc.nrel.gov/solar/old_data/nsr...state.html) is 2.9 hours per day. We'll use that number to build in additional safety.
We divide 195.5 by 2.9 which equals 67.4 which is your total PV array current in amps.
We divide 375 by 2.9 which equals 129.31 which is your total PV array current in amps.
Now we'd have to choose a solar panel. As an example, I'll use a Sharp NE-165U1 which is 165 watts and is rated at 4.77 amps.
That means we take our 67.4 amp PV array from above and divide it by 4.77 which equals 14.1 or 14 such solar panels in parallel. We aren't done. We take our system voltage of 48 and divide it by the module voltage which is 12. That means we need 4 modules in series. Multiply that by our 14 panels and we find out that we need 56 total panels. Not cheap.
That means we take our 129.31 amp PV array from above and divide it by 4.77 which equals 27.11 or 27 such solar panels in parallel. We aren't done. We take our system voltage of 48 and divide it by the module voltage which is 12. That means we need 4 modules in series. Multiply that by our 27 panels and we find out that we need 108 total panels.
If we multiply our 108 panels by the 165 watt output we get 17820 watts or essentially the same number we derived via ratio above.
I'm not sure the above array calculation is correct. Not familiar with these panels, but I wonder if they are perhaps 24 volt panels, not 12, meaning an array is 2 not 4, therefore cutting panel requirement in half to 54 versus 108.
Let's look at battery sizing. We determined our daily amp hours was 195.5. Standard reserve time (how many days of juice your battery bank has) is 3. You can go higher or lower but we'll use 3. So 195.5 x 3 = 586. However, we NEVER want to go below 50% capacity on our batteries or we'll kill them. So we divide the 586 by .5 and get 1173 amp hours. We then choose a battery type. I'll choose a golf cart battery with 225 amp hours of capacity. 1173 divided by 225 = 5.2 which we round up to 6 batteries needed in parallel. Since our nominal voltage is 48 and the battery we chose is 6, then we put 8 batteries in series. We multiply that by our 6 batteries in series and come to the shocking realization that we need 48 golf cart batteries. That means we'd likely go up to L16's which are more expensive but live longer IF you take good care of them.
Daily amp hours was 312.5. Standard reserve time is 3. So 312.5 x 3 = 937.5. However, we NEVER want to go below 50% capacity on our batteries or we'll kill them. So we divide the 937.5 by .5 and get 1875 amp hours. We then choose a battery type. I'll choose a golf cart battery with 225 amp hours of capacity. 1875 divided by 225 = 8.33 which we round up to 9 batteries needed in parallel. Since our nominal voltage is 48 and the battery we chose is 6, then we put 9 batteries in series. We multiply that by our 6 batteries in series and come to the shocking realization that we need 54 golf cart batteries. That means we'd be checking 54 times 3 or 162 cells every month.
THIS is why if you're going to be off grid, cutting down on your energy consumption is first and foremost. You need to ditch the guzzlers and get that 7820 watt hour number WAY DOWN.
How much is this going to cost you? I did a QUICK search and a 12kw (you're almost 8kw) system on ebay WITHOUT BATTERIES and a ton of other needed equipment is selling for $41,000: http://cgi.ebay.com/solar-panel-off-grid...RCH:US:101 and that includes 72 solar panels.
Based on the $/kw costs of my system, this theoretical system would cost only $182K. A show stopper for me.
As I questioned earlier "Why would someone build a 9.2 kw system to generate 7820 watts (7.82 kw) on a daily basis?" Now I ask, why would I build a 17.82kw system for my 15kw requirement?
Quote from TY: "As for battery banks, my post stated golf cart batteries. There's no way you'd want 48 of them. You'd definitely jump up to L16's (as stated in my post) which is what I'm guessing you have."
I have to ask - why even use them for an example? If you could get them at $75 each, that's $3600. And no, I do not have L16's
David
Ninole Resident
Chris needs 7820 watts per day, I need 15000watts per day.
System 1 - Simple ratio:
7820 watts (7819.5 actual) is to 9.240kw as 15000watts is to X - X=17723.78 or 17.724 kw.
System #2 - Calculated using your format. I'll do mine in red:
Ok, let's take the 7819.5 watt hours and round it up to 7820. Let's say you go with a 48 volt nominal system rather than 24.
7820 / 48 = 162.9 amp hours per day
Ok, let's take the 15000 watt hours.
15000 / 48 = 312.5 amp hours per day
I'm going to multiply that by 1.2 to account for batter losses, wiring losses, and add a safety factor. These numbers can be calculated much more intricately, but I'm not going to do that and 1.2 is a safe number.
162.9 x 1.2 = 195.5 amp hours
312.5 x 1.2 = 375 amp hours
Here is Hilo, Hawaii the worst insolation (daily sun hours) if you're using the wrong inclination, etc according to nrel.gov (http://rredc.nrel.gov/solar/old_data/nsr...state.html) is 2.9 hours per day. We'll use that number to build in additional safety.
We divide 195.5 by 2.9 which equals 67.4 which is your total PV array current in amps.
We divide 375 by 2.9 which equals 129.31 which is your total PV array current in amps.
Now we'd have to choose a solar panel. As an example, I'll use a Sharp NE-165U1 which is 165 watts and is rated at 4.77 amps.
That means we take our 67.4 amp PV array from above and divide it by 4.77 which equals 14.1 or 14 such solar panels in parallel. We aren't done. We take our system voltage of 48 and divide it by the module voltage which is 12. That means we need 4 modules in series. Multiply that by our 14 panels and we find out that we need 56 total panels. Not cheap.
That means we take our 129.31 amp PV array from above and divide it by 4.77 which equals 27.11 or 27 such solar panels in parallel. We aren't done. We take our system voltage of 48 and divide it by the module voltage which is 12. That means we need 4 modules in series. Multiply that by our 27 panels and we find out that we need 108 total panels.
If we multiply our 108 panels by the 165 watt output we get 17820 watts or essentially the same number we derived via ratio above.
I'm not sure the above array calculation is correct. Not familiar with these panels, but I wonder if they are perhaps 24 volt panels, not 12, meaning an array is 2 not 4, therefore cutting panel requirement in half to 54 versus 108.
Let's look at battery sizing. We determined our daily amp hours was 195.5. Standard reserve time (how many days of juice your battery bank has) is 3. You can go higher or lower but we'll use 3. So 195.5 x 3 = 586. However, we NEVER want to go below 50% capacity on our batteries or we'll kill them. So we divide the 586 by .5 and get 1173 amp hours. We then choose a battery type. I'll choose a golf cart battery with 225 amp hours of capacity. 1173 divided by 225 = 5.2 which we round up to 6 batteries needed in parallel. Since our nominal voltage is 48 and the battery we chose is 6, then we put 8 batteries in series. We multiply that by our 6 batteries in series and come to the shocking realization that we need 48 golf cart batteries. That means we'd likely go up to L16's which are more expensive but live longer IF you take good care of them.
Daily amp hours was 312.5. Standard reserve time is 3. So 312.5 x 3 = 937.5. However, we NEVER want to go below 50% capacity on our batteries or we'll kill them. So we divide the 937.5 by .5 and get 1875 amp hours. We then choose a battery type. I'll choose a golf cart battery with 225 amp hours of capacity. 1875 divided by 225 = 8.33 which we round up to 9 batteries needed in parallel. Since our nominal voltage is 48 and the battery we chose is 6, then we put 9 batteries in series. We multiply that by our 6 batteries in series and come to the shocking realization that we need 54 golf cart batteries. That means we'd be checking 54 times 3 or 162 cells every month.
THIS is why if you're going to be off grid, cutting down on your energy consumption is first and foremost. You need to ditch the guzzlers and get that 7820 watt hour number WAY DOWN.
How much is this going to cost you? I did a QUICK search and a 12kw (you're almost 8kw) system on ebay WITHOUT BATTERIES and a ton of other needed equipment is selling for $41,000: http://cgi.ebay.com/solar-panel-off-grid...RCH:US:101 and that includes 72 solar panels.
Based on the $/kw costs of my system, this theoretical system would cost only $182K. A show stopper for me.
As I questioned earlier "Why would someone build a 9.2 kw system to generate 7820 watts (7.82 kw) on a daily basis?" Now I ask, why would I build a 17.82kw system for my 15kw requirement?
Quote from TY: "As for battery banks, my post stated golf cart batteries. There's no way you'd want 48 of them. You'd definitely jump up to L16's (as stated in my post) which is what I'm guessing you have."
I have to ask - why even use them for an example? If you could get them at $75 each, that's $3600. And no, I do not have L16's
David
Ninole Resident
Ninole Resident