Very New - Suggested Reading and Battery Question

draines

Hello-

I am very new to the solar world and trying to wrap my head around what I am getting in to. Can anyone suggest a good, legitimate, starting book to read? I have some electronic background but would call it novice at best, especially as it relates to solar and battery storage principles.

I have a very basic starter system to see how things work and test out my long-term interest before making any major investments. Currently I have:
•1x Renogy 50 Watt Solar Panel
•10 Amp PWM Charge Controller
•2 20' extension solar PV cables AWG 12
•Whistler Pro-2000W 2,000 Watt Power Inverter
•Powersonic PS-12350NB - 12 Volt/35 Amp Hour Sealed Lead Acid Battery

I will be setting this up to run some small appliances and maybe as a camping accessory while I learn.

Now the battery questions...while running my AC 'device' through my inverter while my panel is charging my battery, how does the power transfer happen?
Mainly, lets assume I am running a 40W/hr device while receiving 50W/hr of power from my panel, and 10W/hr loss through inverter. What is going on with my battery? Do I consider this usage from the battery? Or is this simply a wash in my daily calculations? I think it is a simple rookie quetion, but maybe I'm oversimplifying?

Told you I was new....Thanks in advance for any input and advice on where to start!

BB.

Re: Very New - Suggested Reading and Battery Question

Welcome to the forum Draines.

draines wrote: »

I am very new to the solar world and trying to wrap my head around what I am getting in to. Can anyone suggest a good, legitimate, starting book to read? I have some electronic background but would call it novice at best, especially as it relates to solar and battery storage principles.

We have a solar FAQ thread that has lots of links/information to solar/conservation/etc. projects... Take a look through there:

http://forum.solar-electric.com/showthread.php?5556-Working-Thread-for-Solar-Beginner-Post-FAQ

We do have a post on books in that thread:

http://forum.solar-electric.com/showthread.php?5556-Working-Thread-for-Solar-Beginner-Post-FAQ&p=54329#post54329

I have a very basic starter system to see how things work and test out my long-term interest before making any major investments. Currently I have:
•1x Renogy 50 Watt Solar Panel
•10 Amp PWM Charge Controller
•2 20' extension solar PV cables AWG 12
•Whistler Pro-2000W 2,000 Watt Power Inverter
•Powersonic PS-12350NB - 12 Volt/35 Amp Hour Sealed Lead Acid Battery

I will be setting this up to run some small appliances and maybe as a camping accessory while I learn.

From a quick look at your system--You have the mistake that almost everyone makes on their first system... Lack of "balance". People usually overestimate how much power a system can generate and underestimate how much power they use/need.

For example, a 50 watt solar panels getting 5 hours of "noon time sun" per sunny summer day:

50 watts * 5 hours * 0.52 off grid system efficiency = 130 Watt*Hours of "AC Power" per day

Take your 2kWatt inverter and run it at 1,000 watts:

130 WH per day / 1,000 Watts = 0.13 hours = 7.8 minutes of "run time" per day

Your 35 AH @ 12 volt lead acid battery, if you run it to 50% state of charge would last on a 1,000 watt load:

12 volt * 35 AH * 0.85 AC inverter eff * 0.50 max battery discharge * 1/1,000 Watt load = 0.18 Hours

In reality--A 1,000 Watt load would probably instantly "flatten" your 35 AH battery:

1,000 watt load * 1/0.85 AC inverter eff * 1/10.5 minimum inverter voltage = 112 Amps of 12 volt DC current

So--We usually suggest people start with their loads (measure/estimate power needs; Watts) and how many minutes/hours per day they run the loads (Watts*Hours=WH per day).

You can also start with some part of your system (inverter, battery bank, solar array)--And size components that would work well with them.

Either way--We can help you get on the right track.

Now the battery questions...while running my AC 'device' through my inverter while my panel is charging my battery, how does the power transfer happen?
Mainly, lets assume I am running a 40W/hr device while receiving 50W/hr of power from my panel, and 10W/hr loss through inverter. What is going on with my battery? Do I consider this usage from the battery? Or is this simply a wash in my daily calculations? I think it is a simple rookie quetion, but maybe I'm oversimplifying?

Don't over think--This is just like your car's electrical system. The battery is the "Heart" of the system... You have an alternator to charge (plus regulator), and loads. When the engine is off, the battery supplies 100% of the power to the loads. When the engine is running, the Battery acts as a "buffer" to keep the bus voltage around 12-14.5 volts, and the alternator+regulator keeps the average battery voltage at ~13.8 to 14.2 volts (engine running).

As long as the generator/alternator/solar array keeps the battery voltage around 13.8 to 14.2 volts or so, the battery is charging. When the battery falls below ~12.7 volts, the battery is discharging. To keep the battery happy, you need to recharge the battery to keep it >~50% state of charge and "on charge" long enough to get it back >~90% state of charge a couple of times per week. Discharged lead acid batteries do not store well and will "sulfate" over days/weeks/month or so, and be permanently "Dead".

Told you I was new....Thanks in advance for any input and advice on where to start!

Good place to start... Measure your loads will a kill-a-Watt meter, or DC WH/AH meter, and/or an AC/DC Current Clamp DMM. Any/all of these tools are very handy through the rest of your life.

How would you like to proceed?

-Bill

draines

Re: Very New - Suggested Reading and Battery Question

Thanks BB! Great information and thanks for the links!

I have a kill-a-watt meter and have been collecting the data to see where I currenlty consume. I am realizing that like most households the numbers are pretty eye-opening. Someone on here, maybe even you, stated that its "cheaper to conserve electricity than to generate it"...I am seeing the value of those words quickly.

My gut reaction is to buy more panels and more batteries...but my reaction is just that...a reaction. I see I need to get an acutual number of watt and amp hour used and design then figure out what components I need.

So to try and understand your calcs - If I wanted to make a cup of coffee in a small coffee make with is 650W and 5.5A:
I could use my 35AH battery to power it through the inverter. That would be a 5 minute brew time at 650W/60min = ~11W/min, so, ~55W per brew.
This would allow me to get 2 brews (110W total) a day without going below my 50% DOD.
Did I oversimplify that one??

I'll do more reading befoer I waste your time! Thanks again for your help....I'll keep at it!
Dan

BB.

Re: Very New - Suggested Reading and Battery Question

draines wrote: »

Thanks BB! I have a kill-a-watt meter and have been collecting the data to see where I currently consume. I am realizing that like most households the numbers are pretty eye-opening. Someone on here, maybe even you, stated that its "cheaper to conserve electricity than to generate it"...I am seeing the value of those words quickly.

Yep--Building a system to handle our daily "grid loads" that we all use--Pretty scary when you cost out what it would cost you to do the same thing off grid with a solar power system (you are becoming your own utility--And pretty much, pre-paying your next 10 year utility bills up front with the installation).

My gut reaction is to buy more panels and more batteries...but my reaction is just that...a reaction. I see I need to get an actual number of watt and amp hour used and design then figure out what components I need.

Gut reaction--Avoid that. You will be, many times, just wasting your money. Load calculations/measurements are the key to a happy owner (and owner's spouse).

So to try and understand your calcs - If I wanted to make a cup of coffee in a small coffee make with is 650W and 5.5A:
I could use my 35AH battery to power it through the inverter. That would be a 5 minute brew time at 650W/60min = ~11W/min, so, ~55W per brew.
This would allow me to get 2 brews (110W total) a day without going below my 50% DOD.
Did I oversimplify that one??

My first suggestion--Get a campstove/propane powered Mr. Coffee and a good thermos:

http://www.amazon.com/Coleman-5008C700-Camping-Coffee-Maker/dp/B001K7IDVU

Next--Watts is a "rate" (like miles per hour). Watt*Hours is an amount (like miles driven).

And watch your units... Watts is a "all in one" unit--Voltage and Current... Amps and Amp*Hours is missing the voltage:

If I wanted to make a cup of coffee in a small coffee make with is 650W and 5.5A

650 Watts / 120 VAC = 5.42 amps @ 120 VAC
650 Watts / 12 VDC = 54.2 amps @ 12 VDC

Getting 54 amps from a 35 AH lead acid battery is a bit of a stretch.. Typically, C/5 discharge rate would be the maximum sustained load for a lead acid battery:

35 AH/ 5 hour load = 7 amps recommended draw

So, just from a battery sizing point of view, you would need a 12 volt battery:

650 Watts * 1/0.85 AC inverter eff * 5 hour/C max load * 1/12 volt battery voltage = 319 AH @ 12 volt battery bank minimum (in my humble opinion)

That would be a 5 minute brew time at 650W/60min = ~11W/min, so, ~55W per brew.

I would stay in hours--Watts is actually a "Joules per Second" number--But we use Hours because all the numbers would be 3,600x larger due to the seconds to hours conversions.

650 Watts * 11 minutes * 1/ 60 minutes per hours * 1/0.85 AC inverter losses = 140 Watt*Hours of energy used
140 WH / 12 volt battery voltage = 11.7 Amp*Hours @ 12 volts

So--1.5 cups of coffee from the 35 AH @ 12 volt battery bank--If it would work--Which, as the question is stated, it would not.

-Bill

draines

Re: Very New - Suggested Reading and Battery Question

Yeah....your equations:

650 Watts / 120 VAC = 5.42 amps @ 120 VAC
650 Watts / 12 VDC = 54.2 amps @ 12 VDC

It's fundamental....but I have been missing the big picture between 120 VAC and 12 VDC.

I'll start with some small AC appliances before I brew a $300 cup of coffee!

Thanks again for your help, and most importantly, thanks for not ridiculing those of us who are trying to learn. I see you post a lot to help the beginners.

Have a great day!
Dan

BB.

Re: Very New - Suggested Reading and Battery Question

draines wrote: »

It's fundamental....but I have been missing the big picture between 120 VAC and 12 VDC.

It is a common error--And even when we talk with others on the forum--The volts frequently get lost in the discussion with all the Amps and Amp*Hour discussions.

I'll start with some small AC appliances before I brew a $300 cup of coffee!

I know that everyone wants to experiment... And we encourage folks to do that. However, the rules of thumbs do work and give most people a vary reliable system that meets their needs.

AC is great--But much below a 300 watt AC inverter (call it 100 watt loads), DC is frequently the better solution for small system--Assuming you have native DC loads.

Thanks again for your help, and most importantly, thanks for not ridiculing those of us who are trying to learn. I see you post a lot to help the beginners.

This would be a very quiet forum if we just told everybody to Google their questions.

We all started at ground zero in life--And it was the help of others that moved us forward. Just returning the favor to the next group.

In general--A good way to learn is to "study/understand/document" your loads. We then help you walk through the load analysis, a paper design of the system, and then help with selection of products that may work well for you.

It is difficult to understand a wide ranging discussion (0.5 to 1 kWH per day camping solution vs a 100 kWH per month system for an off grid home)--It is hard to grasp the details when there are so many "what ifs".

Design for a system for your needs--Understand that--Then build on that knowledge tends to be the least frustrating.

Have a great day!
Dan

You are are very welcome. Feel free do stick around and document your system--That will help others too.

BB. wrote: »

Add this link to our Solar Beginner Post:

Emergency Power

Basically a very long thread that starts from the beginning with a few vague requirements through design and assembly for a "portable" solar RE off-grid power box.

And here is another example by Mike90045 called the Solar Monolith:





Update pictures/information here.

And her is another poster that documented his growing off grid/backup power system for his home:

http://2manytoyz.com/ (scroll down for solar projects)

-Bill

PNjunction

Re: Very New - Suggested Reading and Battery Question

Interestingly enough, the user's manual for this controller has about the most pertinent information in the application manual (pdf link on page) I've ever seen from a manufacturer for the layman like myself. Even though you already have a controller, you might want to take a look at this manual:

http://www.samlexamerica.com/products/ProductDetail.aspx?pid=60

Covers FAR more than just the controller and goes into details about solar setups in general. Best I've ever seen, and devoid of hype. Highly recommended, even though I don't currently have that controller either.

westbranch

Re: Very New - Suggested Reading and Battery Question

PNjunction wrote: »

. you might want to take a look at this manual:

http://www.samlexamerica.com/products/ProductDetail.aspx?pid=60

Covers FAR more than just the controller and goes into details about solar setups in general. Best I've ever seen, and devoid of hype. Highly recommended, ......

I agree, it would make for required reading for NewBees.