My Head Exploded

[parnold]

Alright, I'm going to be one of those annoying people who asks a question without looking for the answer. I'm at work, and I don't have time to sift through endless threads to get what I need. It's rather simple, and I should know it, but..

Given an 80 watt solar panel, tied into an inverter to convert to 120v. Let's pretend there is no power loss from the inverter. I'm thinking 80 watts at 12v should produce 800 watts at 120v, but like I said my head exploded.

I'm assuming that power loss through an inverter is going to be in the area of 25%???

I know there are guru's out there who can tell me if I'm off the wall. I'm trying to figure out if it is worth spending the money on a grid tying inverter to utilize my solar panel for the 350 days a year I'm not camping. I know what a kilowatt of power costs.

[myoung]

Solar panels have more inefficiencies than generally believed IMHO.

By way of example, here are the stats for our home's solar array. We have 34 panels at 235 watts each nominal for a gross potential of 7.99 kilowatts. From that we get daily output that varies from about 39 kilowatts in December to 57 kilowatts in April. Despite the long, sunny days in the summer, we only get about 50 kilowatts a day in July/August owing to daily temps of 100 degrees plus. Performance falls off dramatically with temps above 80 degrees and at angles of incidence that are suboptimal.

For a full year, we generate 15 megawatts, which works out to 41 kilowatts a day or 1.2 kilowatts a day per 235 watt panel. So, for comparison, this works out to about 5 times the nominal wattage per day.

I'm sure that your output would be less because of your higher latitude (we are a 33 degrees north) and fewer cloudless days (we have over 320 days of full sunshine a day).

As a good working number, my best guess is that you might generate 4x the panel's wattage or 4 x 80 = 320 watts a day in New Jersey.

[parnold]

Mike:

Thanks for the very detailed answer, that is exactly what I was looking for. At 15 cents a kilowatt hour here in Jersey, my best hope would be to save maybe $20.00 a year. I'd probably save more buying power strips to turn off all the phantom power users.

[myoung]

Mike:

Thanks for the very detailed answer, that is exactly what I was looking for. At 15 cents a kilowatt hour here in Jersey, my best hope would be to save maybe $20.00 a year. I'd probably save more buying power strips to turn off all the phantom power users.

I agree. Phantom power can be quite a bit. I would guess our usage at over a kilowatt a day with all our electronic gadgets. Something like burning a 50 or 60 watt lightbulb all day long.

[Oldragbaggers]

You lost me at "Alright,....."

[48Rob]

As a good working number, my best guess is that you might generate 4x the panel's wattage or 4 x 80 = 320 watts a day in New Jersey.

Mike,

Thanks!
I ponder over this now and then, your real world experience is very valuable.

Rob

[bdosborn]

Given an 80 watt solar panel, tied into an inverter to convert to 120v. Let's pretend there is no power loss from the inverter. I'm thinking 80 watts at 12v should produce 800 watts at 120v, but like I said my head exploded.

80 watts is 80 watts, the voltage doesn't factor into the energy costs for your exploding head.

Ignoring inverter efficiency, 80 watts * 5 hours a day of full sun is 400 watt-hrs.

0.4 kw-hrs * $0.15/kw-hr =6 cents a day. Add in losses and its probably down to 4.5 cents a day.

Mike,
I believe you're confusing kilowatts and kilowatt-hrs. I think you meant to say your array output is 50 kw-hrs in July, etc.
Bruce

[myoung]

Correction accepted, Bruce. The basic arithmetic still applies.

[terryjones1]

Given an 80 watt solar panel, tied into an inverter to convert to 120v. Let's pretend there is no power loss from the inverter. I'm thinking 80 watts at 12v should produce 800 watts at 120v

With an 80 Watt Solar Panel, you will be able to produce up to 80 watts DC.

Current = wattage/voltage

DC current = 80/12
DC current = 6.66 amps DC

AC current = 80/120
AC current = .66 amps

wattage = current x voltage

DC wattage = 6.66 x 12
DC wattage = 80

AC wattage = .66 x 120
AC wattage = 80

The wattage doesn't change (assums no losses).
There will be lots of losses and inefficiencies.
You can not have a power gain through an inverter.

[Ocelli]

Ahh yes...ohms law

[parnold]

Ahh yes...ohms law

I always felt Ohm's law was discriminating.

[Engineer Guy]

I built aspects of our self-designed Solar Retirement House from info gleaned at 'Home Power Magazine'. It all used to be free, but they - like many - now charge for content.

Their Articles are these incredible, self-contained Tutorials that you can build off of. For Solar Systems, they show the System Schematic; list all Components and Manufacturer Websites; show hard data on how the System actually performs; and discuss Real World aspects of the entire Installation.

Personally, I would subscribe and have access to all their Articles if I were seriously looking for info I don't already know. These Guys are hard core, off-Grid Folks 'walking the walk' in Northern California. The System 'drawbacks' and actual Energy generated are discussed at length. To my way of thinking, you also review plenty of installations in their Stories; not just this-or-that singular example from an Utility, etc...

Home Power Magazine - Solar Systems

[parnold]

My curiosity has certainly been satisfied by everyone's answer, and I appreciate the education!

In the grand scheme of things, I think I have much better options to invest monies in if I was so inclined, like new windows in my 90 year old house, or perhaps that stuff they call insulation. I think my ROI would be quicker if I spent money in one of those areas as opposed to solar. Maybe when I retire I'll look into the solar stuff a little more seriously. The cost of using the one panel I have now, is not worth investing in the equipment to tie it into my home grid. Even if I purchased a cheap grid tie converter, the payback would at best be 6 to 9 years.

Engineer guy, thanks for the link, looks like some interesting reading that I have saved for a better time. (like when I'm not at work)

[Richard A.]

Given an 80 watt solar panel, tied into an inverter to convert to 120v. Let's pretend there is no power loss from the inverter. I'm thinking 80 watts at 12v should produce 800 watts at 120v, but like I said my head exploded.

I'm assuming that power loss through an inverter is going to be in the area of 25%???

An 80 watt solar panel will give you a bit LESS than 5 amps DC.

An inverter running at 800 watts AC will draw 80 AMPS of 12VDC current.

5 amps of 12VDC will give about 50 watts out of an inverter.

[Forrest747]

I find that if you give a 2 year old a 9 volt battery at some point they are going to learn ohms law and how it taste.[youtube] http://m.youtube.com/#/watch?v=2MRze9CV ... VhXc&gl=US [/youtube]