DIY Manual

5 | P a g e 10-543-1 REV A
DIY Manual
• For a 2-string 24V bank, use eight 6V batteries rated at 190Ah:
o (6V x 4) + (6V x 4) x 190Ah = 9120Wh
• For a 3-string 12V bank, buy six 6V, 250Ah batteries:
o (6V x 2) + (6V x 2) + (6V x 2) x 250Ah = 9000Wh
NOTE: For best battery bank health, avoid more than 3 parallel strings when using flooded or
sealed batteries. Too many strings can lead to imbalanced cells due to increased resistance.
Most Lithium batteries allow multiple parallel strings. Check with the Li batt manufacturer.
NOTE: The above example called for 6.67 batteries at 6V and 225Ah. And combos were given
showing how different Ah rated batteries could be used to make the bank. Let’s pretend you
select the 6V, 225Ah batteries and you only buy 6. Your solar system will be slightly undersized
in batteries, and you will not be able to power all loads for the desired length of time. Conversely,
if you round the 6.67 required batteries to 8, then you will have excess energy.
Step 3 PV SIZING
From the load analysis, we plan to consume 4500Wh every day, so that energy needs to be
replaced with solar power.
How many solar hours of sunlight are available in your area?
• Solar irradiance charts (easily found online) show the
amount of average sunlight across the US. You can use the
annual average.
• If you live off-grid, you may want to pick the winter
average, which will be fewer hours than the annual
average. This in turn will mean a larger system in terms of
panels and batteries.
• Let’s say your annual average sunlight hours is 4.7 hours.
Now we decide the quantity of the solar panels for your system. Let’s
use a typical 250W panel. The number of panels required is …
1. 4500Wh / 4.7 hours (of sunlight) = 957W
2. 957W / 250W (panel) = 3.8 panels.
Confirm the math: 3.8 panels x 250W x 4.7hrs = 4465Wh. In other words, 3.8 250W panels in
the sun for 4.7 hours will generate 4500Wh (4465Wh) of energy to fill the battery bank from 50%
to 100% DOD.
Again, partial components (3.8) won’t work, so now we decide to either round down to 3 panels
or up to 4. Hmmm? Let’s put this conundrum on hold for a while; we need to first select the
Consider increasing the
total PV array by 40%:
20% to account for
battery inefficiencies
AND 20% for solar
energy losses due to
panel orientation,
resistance,
atmospherics, dust, and
dirt.