Author Topic: Understanding Electricity and Solar Energy  (Read 962 times)

civil4life

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Understanding Electricity and Solar Energy
« on: January 24, 2019, 11:09:36 AM »
I am not sure if this is best posted here or the DIY section.  I put it here and figured someone could tell me if it is better question for the DIY section.

First I am a licensed Civil Engineer that works in transportation.  I say this to let you know that I am not someone without any technical background at all.  However Electrical Concepts have always completely baffled me.  I have no idea why I cannot grasp the various concepts.  I even took an electrical engineering course in college, but I pretty much relied on a friend to pull me through it. 

This is where I need some help.

I am looking into buying my dad a solar kit that he could use for running a pool pump and/or use as a secondary energy source for his camper.

I would like to understand the various specifications in order to purchase a system that will provide the energy necessary.

Could you please explain in laymanís terms Voltage, Amps, Current, Watts etc.  How they are all related and their relevance in how they meet the various product specifications.

And/Or

Point out videos, tutorials, or other resources that will explain these things.

Thank you in advance.

CowboyAndIndian

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Re: Understanding Electricity and Solar Energy
« Reply #1 on: January 24, 2019, 11:25:27 AM »
@Syonyk should be able to help. He has a sweet setup where he runs his home office off a solar/battery setup.

Here is his blog https://syonyk.blogspot.com/


nereo

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Re: Understanding Electricity and Solar Energy
« Reply #2 on: January 24, 2019, 11:42:31 AM »
Quote
Could you please explain in laymanís terms Voltage, Amps, Current, Watts etc.  How they are all related and their relevance in how they meet the various product specifications.

Photovoltaic cells run on Direct Current (DC).  Under most circumstances you will need inverters to change from DC current to AC current unless all the devices you are plugging in run on DC.

Voltage is the 'pressure' of the electromagnative force.  For most PV arrays it will be somewhere between 18-24 volts.  In the US household current running on AC is 110-120v.  Think of it like water pressure in a pipe.  The pipe can be big or small and have the same voltage.

Current is the total amount of electricity running through a circuit.  It's typically discussed as the number of Amps (amperage = current). 
Amperage = Watts / Volts.  Think of it like the diameter of a water pipe.  A really big pipe can carry a lot of water even if the pressure (voltage) is low. 

Wattage is the amount of power.  One watt = 1 joule per second. You can calculate how many watts a circuit has by Voltage x Amps.  Example:  110 volts x 15 amps = 1,650 watts.  This would be typical for a household plug on AC.  Note that you can increase total wattage either by increasing the voltage or the amperage.  In our pipe analogy it's both the diameter and the pressure inside the pipe (in other words: how much total water flows through the pipe every second).  A pipe with a large diameter and under high pressure is going to carry a lot of water (er... watts).

« Last Edit: January 24, 2019, 12:04:42 PM by nereo »

Cadman

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Re: Understanding Electricity and Solar Energy
« Reply #3 on: January 24, 2019, 12:42:48 PM »
Having designed a PV system for my home, an off-grid building and our camper, I'll weigh in that for this application, you need to start from the back and work forward. I'll also add that most solar kits are far more expensive than the sum of their components, and that you're usually better off buying your own charge controller, panels and lead acid batteries.

What you need to figure out is how many amp-hours you need in your system. Hopefully your loads are DC or you'll need an inverter (expense and loss of efficiency). Only once you've sized your battery bank will you know how to proceed with panels.


Syonyk

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Re: Understanding Electricity and Solar Energy
« Reply #4 on: January 24, 2019, 03:39:32 PM »
I see I was hailed...

I am looking into buying my dad a solar kit that he could use for running a pool pump and/or use as a secondary energy source for his camper.

Don't.  You'll buy him something that won't work, and will sit in the corner, having paid too much money for it.

A pool pump is a fairly power hungry, grid-AC-powered device.  To offset some of the power use, you'll need a grid tied system that uses the power grid (requires permits, inspections, has to meet code, etc), or an illegal backfeed inverter with a power cord (illegal, also dangerous, probably voids house insurance policies if in use).  Alternately, you'd need an off-grid capable system to allow him to isolate the pool pump, which is big bucks and not something you buy for someone as a gift.

That's also almost (but not quite entirely) incompatible with a solar setup for a camper - assuming 12V.  Typical house panels are 60 cell panels, typical 12V panels are 36 cell, and you pick the proper one for your use.  Little suitcase panels with a bag and stand can be useful for people with campers to charge 12V systems - my inlaws use a pair of those when they camp in their motorhome so they can keep the batteries topped off.  But, again, not something to randomly buy for someone without knowing what their setup is.

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I would like to understand the various specifications in order to purchase a system that will provide the energy necessary.

Well, for a pool pump system, you're at a couple grand for grid tied, probably $15k-$30k for an off grid capable system that can run a pool pump, depending somewhat on how powerful the pump is and how much you care about winter, but it's not going to be a hands-off system.

Again, you need to find out what he actually wants/needs for this stuff.  You don't just buy people a solar gizmo and it magically works for both grid power and camper use.

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Could you please explain in laymanís terms Voltage, Amps, Current, Watts etc.  How they are all related and their relevance in how they meet the various product specifications.

No, you can search yourself for basic EE courses.

Seriously.  This is a bad idea and you're unlikely to buy him something he can actually use.  Rethink your plan.

Curmudgeon

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Re: Understanding Electricity and Solar Energy
« Reply #5 on: January 24, 2019, 04:30:49 PM »

Voltage is the 'pressure' of the electromagnative force.  For most PV arrays it will be somewhere between 18-24 volts.  In the US household current running on AC is 110-120v.  Think of it like water pressure in a pipe.  The pipe can be big or small and have the same voltage.

OK so far.

Quote
Current is the total amount of electricity running through a circuit.  It's typically discussed as the number of Amps (amperage = current). 
Amperage = Watts / Volts.  Think of it like the diameter of a water pipe.  A really big pipe can carry a lot of water even if the pressure (voltage) is low. 
Well, almost.  Current is the total amount of water flowing.  You can get a high current/flow through a small pipe, if you have enough voltage/pressure, or through a big pipe, using less pressure/voltage.

Quote
Wattage is the amount of power.  One watt = 1 joule per second. You can calculate how many watts a circuit has by Voltage x Amps.  Example:  110 volts x 15 amps = 1,650 watts.  This would be typical for a household plug on AC.  Note that you can increase total wattage either by increasing the voltage or the amperage.  In our pipe analogy it's both the diameter and the pressure inside the pipe (in other words: how much total water flows through the pipe every second).  A pipe with a large diameter and under high pressure is going to carry a lot of water (er... watts).

True, wattage is power, but to extend the water analogy to cover this we would need to think of using water flow from a pipe to power something - say, a turbine or waterwheel.  The power you can get from such a device would be related to two things:  First, the flow rate; and second, the pressure behind the flow.  You can get a similar amount of power by using a low flow rate, but with a lot of pressure behind it; or with a very fast flow rate, but not much pressure behind it.  But again, not really related to the diameter of the pipe.

The diameter of the pipe is analogous to the diameter of a wire.  In a thick wire, you can get a lot of current to flow, without using much voltage to drive it.  In a wide pipe, you can get a lot of water to flow, without using much pressure.  So, diameter relates to resistance, measured in ohms.

civil4life

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Re: Understanding Electricity and Solar Energy
« Reply #6 on: January 24, 2019, 06:10:38 PM »
I have heard the water analogy before, but has been a while.

So am I understanding this right?

From the water analogy using the continuity equation Q = VxA, 

Q = Flow = Current
V = Velocity = Voltage
A = Area = Wattage


Could you go into a little bit of an explanation on the build up and discharge of a solar panel?

@Syonyk I knew the pool was most likely not a possible option.

The camper would be like the example you provided.  My parents have a 12 volt battery they use when they are camping somewhere without electrical hook up.

Syonyk

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Re: Understanding Electricity and Solar Energy
« Reply #7 on: January 24, 2019, 10:17:51 PM »
Could you go into a little bit of an explanation on the build up and discharge of a solar panel?

They're screwball power sources.  They're a constant current source up towards a knee voltage, then once you get past the maximum power point, the voltage (and power) collapse very rapidly.  They behave somewhat close to an old unregulated charger, but their maximum power point varies rather significantly based on illumination, temperature, age of the panel, and it wouldn't surprise me if in 15 years, someone worked out that phase of the moon mattered as well.

I've done some writing here that tries to explain some of the behaviors of panels further, though if you're working out volts/amps/etc, I'm not sure if it will make much sense.  https://syonyk.blogspot.com/2018/05/why-typical-home-solar-setup-does-not-work-off-grid.html

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I knew the pool was most likely not a possible option.

I mean, it's possible, just not cheap, and not a random one-off gift, unless you've paid off all the relevant authorities having jurisdiction...

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The camper would be like the example you provided.  My parents have a 12 volt battery they use when they are camping somewhere without electrical hook up.

Is charging it a limiting factor for them?

Again, this is the sort of stuff you should talk to them about, not just randomly buy as a gift.

However, if you insist on that, a 100W folding solar panel with bag is probably useful.

You might be interested in my writeup on building a small solar setup for our camper. No pictures yet, but the fundamentals are there. I ended up building my own 'solar suitcase' out of a pair of 100w panels, but even this was insufficient to keep my batts charged after a couple cloudy days and a narrow window of insolation due to northern MN folliage.  http://www.linearlook.com/shasta/solar.html

Off grid power consists of "Designing for the winter, then having a generator for when winter sucks."

My office is handwavingly designed for winter, though I'm adding 50% more panel this year (not sure what I'll do with the excess during the summer - probably export to the house system, eventually).  I still need a generator, though this winter has been far better, so far, than previous winters.  Partly, it's learning my power system - the first winter I was still learning (and it was a bad winter), last winter was better but just a lot of dark weeks and I didn't trust the pack to run down, and this winter has been both sunnier and I've been willing to run the pack harder.

Ecky

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Re: Understanding Electricity and Solar Energy
« Reply #8 on: January 25, 2019, 05:47:48 AM »
I have heard the water analogy before, but has been a while.

So am I understanding this right?

From the water analogy using the continuity equation Q = VxA, 

Q = Flow = Current
V = Velocity = Voltage
A = Area = Wattage


Could you go into a little bit of an explanation on the build up and discharge of a solar panel?

@Syonyk I knew the pool was most likely not a possible option.

The camper would be like the example you provided.  My parents have a 12 volt battery they use when they are camping somewhere without electrical hook up.

My understanding of the analogy is that it's:

Q = Flow = Wattage
V = Velocity = Voltage
A = Area = Current (amps)

Because velocity x area = total flow, and volts x amps = total watts.

A lot of amps through a small wire will "break" the wire (burn it up) - you're trying to stuff too much "area" through a pipe that isn't big enough and it bursts. But, you could get the same amount of energy through that same wire safely if you cut the area in half (amps in half) and double the voltage. This is how power companies send power through the grid to millions of homes through relatively small wires - they run at relatively low current with extremely high voltages. When it gets to your house you slow it down for your own uses.


Car Jack

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Re: Understanding Electricity and Solar Energy
« Reply #9 on: January 25, 2019, 08:47:18 AM »
I'm going to try to explain a few disjointed ideas.  I'm a power supply design engineer and have some experience with solar chargers (not a ton).  I will not get into technical jargon (at least I'll try).

First, from the solar panel, you want to charge a battery.  The battery would then go through an inverter which converts the battery voltage into something your pool pump can use.  But there are a few things to understand.  The battery may be a low voltage, like a car battery at 12V.  In order to run a pump at 110 Vac, you need to both step up that voltage and convert into AC.  I'll stick with just the step up.  Ok, very little jargon.  Power is Volts times Amps.  Let's ignore the ac part and pretend the pump takes 120Vdc (to make the math easy) at 10A to start up.  So we're talking startup power of 1200W.  Ideally, that means a 12V battery needs to supply 1200W/12V or 100A.  That's a good slug of current.  If nothing else, I hope this explains why you need a battery in the system and can't just come off the solar panels.

Ok, for the solar panels.  You are indeed running from DC.  But along with this, you want to run at the most efficient load possible to pull the most power possible off the panels at all times.  Indeed, you could just blindly set a current and pump that into the battery.  But a microprocessor controlled system can test the efficiency of the panels real time and adjust to pull the ideal current from the panels and then use that to charge the battery. 


radram

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Re: Understanding Electricity and Solar Energy
« Reply #10 on: January 25, 2019, 08:59:30 AM »
Another reason to pass on this project.

So many of you are combining water flow and electricity. Don't you know how dangerous this is? I am surprised this thread did not explode :)

Syonyk

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Re: Understanding Electricity and Solar Energy
« Reply #11 on: January 25, 2019, 10:17:41 AM »
Ideally, that means a 12V battery needs to supply 1200W/12V or 100A.  That's a good slug of current.

Yeah, then you find those "6000W" 12V inverters and wonder how they don't fuse the battery terminals...  My office is on a 48V pack, the house will be on a 48V pack... there's still an awful lot of current flowing around (I'm using a pair of 4/0 welding cable for the battery interconnects, mostly for voltage drop reasons), but trying to pull serious power out of 12V is just crazy.