View Single Post
Old 02-18-19, 09:24 AM   #25
Robaroni
Journeyman EcoRenovator
 
Robaroni's Avatar
 
Join Date: Jun 2013
Location: Delhi, NY
Posts: 332
Thanks: 20
Thanked 53 Times in 40 Posts
Default

Quote:
Originally Posted by BillG View Post
Good. We agree on one thing. The 30 Ah battery, utilizing 25% of its charge, is 90 Wh, not 225 as previously stated. 90 Wh is only enough for one single night, and will fail if there is a cloudy day.

I'm not as optimistic on the panel output. From PVWatts (a free online calculator from NREL), a December day will average 141 Wh, and a July day will average 346 Wh. Yes, it is enough to charge the battery on a perfect day for one single night of use, but just barely, and will fail to provide a single night of charge to the battery in December if there is a less-than-perfect day, or if the panel gets dirty. This assumes an MPPT charge controller, because a PWM controller would provide quite a bit less capacity.

I'm not intending for this to be a pissing match, but I'd hate for the original poster to purchase the system based on incorrect assumptions or wrong math, and then have to buy it again. It is always less expensive and more satisfying to do it right the first time.
141/60=2.35 hours of sun. He lives in Ca. I took the cap. Sacramento because it is further north. Even if there data is wrong at 9 plus hours it will never be 2.35 hours. What is the US location of your data? Where is the link? I supplied a link.

Here's another link to Ca.


"Using a yearly average, there are 5.38 daily peak sun hours across the state of California. This number is calculated for a fixed solar panel."

"California hosts a very favorable environment for solar panels, with high average peak sun hours and a lot of sunny days.'

https://www.turbinegenerator.org/solar/california/

Sacramento:
188 sunny days
partial sunny days 77
total number of days with sun 265

https://www.currentresults.com/Weath...f-sunshine.php

In the winter under worst case conditions, living in northern Ca. he still has plenty of sun.

Your advice is to use two 75 aH batteries:

12*75*2 = 1.8KwH total. At 25% = 450wH. A 7 watt ( I originally used a 5w LED because I eliminated the losses from converting from 120 to DC by using an LED that runs on 12V) will mean that he has 450/7 = 64/14.82 =4.31 days with absolutely zero sun to charge the batteries during the day. Which clearly will never be the case as 265/365= 72.6% of the time there is sun in Sacramento.

So let's look at the cost of your lighting an LED for 4.31 days of zero sunny days.

two 75aH group 24 batteries = $214 *2 = $428

https://www.ebay.com/itm/VMAX-XTR34-...frcectupt=true

To charge 1.8kw*.25 = 450w; 450/5.38 = 83.6w so we need a module that will do that:

A 100w module with a charge controller: $115

https://www.ebay.com/itm/PV-SOLAR-KI...frcectupt=true

115 + 428= $543

As opposed to

12v 30aH battery $89


100w module with charger $115

total = $204

I used same module and battery manufacturer in both assessments.

https://www.ebay.com/itm/VMAX800-Gol...frcectupt=true

Difference is $339 more It's not realistic, he's only lighting a small LED. Will there be the rare time when the system might go two days or about 50% discharge? Maybe.

And what's your solution for the LED? I included an inexpensive circuit to run a 12VDC LED. Are you using an inverter with 120v mains? If you are then you have to add the cost of an inverter and the losses from the double conversion the the $543 it already costs.

Even if I doubled the batteries it only adds another $89 to the total cost and he could do that at a later date so he doesn't have to spend for what he might not need. My design can grow, if yours is overkill what's your recourse? You already spent more than you had to and again we're only lighting a small LED.
Robaroni is offline   Reply With Quote