Solar Panels and PHEVs

[skruse]

Contact the National Renewable Energy Center in Colorado. They have "boiler plate" work books for estimating energy demand (based on latitude, elevation and heating-and cooling-degree days). Coupled with your life style, this will give a good estimate. As photovoltaic panels become more efficient, you may need plus or minus one more panel. A tracking PV system (follows the sun throughout the day) will increase output with fewer panels.

A better built house with super windows, SIP roof and lots of thermal mass will require less electricity. Use of Sunpipes and clerestory will increase natural lighting and decrease electricity demand. Efficiency is the key to making good decisions.

[boulder_bum]

<div class='quotetop'>QUOTE(EricGo @ Aug 31 2007, 04:49 PM) [snapback]505174[/snapback]</div>

Apologies boulder if this stuff is obvious, but your response makes me think a primer may be useful:

1 kilowatt (kW) = 1000 watts. This is a power measure
1 kWh (kilowatt*hr) is an energy measure

power * time = energy.

You buy PV by the watt, but decide how to size your system by matching energy production to consumption.
[/b]

Thanks Eric, I did assume 1 kW was 100 watts, but one of the things that confuse me (I know this is pretty basic stuff, but I'm just starting to learn), is how the advertised power of a system translates into electricity for the day.

For example, you can buy a set of, say, 100W solar panels, but what does "100W" mean? Is that the energy collected per hour or second or day? Is this the max capability or an average (accomodating for clouds passing overhead)?

Does anyone know?

tripp, thanks for the info on the 4 mi/kilowatt estimate. If I can figure out some of the basics (with all your guys' help) and maybe get a copy of the prospective house's energy bill I can start crunching some numbers.

[daniel]

<div class='quotetop'>QUOTE(efusco @ Aug 31 2007, 01:02 PM) [snapback]505109[/snapback]</div>

... Someone mentioned that it would take 5 200Wh panels charging 8 hours a day to fully charge the Volt PHEV40 battery.
[/b]

You mean the battery that GM says doesn't exist yet, but they're "working real hard" to develop? I think anybody reading this and waiting for a Volt is going to be too old to drive before the Volt exists. Never underestimate the capacity of American business to deceive.

[EricGo]

I had earlier posted that a Prius requires about 200 - 250 Wh per mile. Multiply by 4, and convert 1000 watts to 1 kW, and you get Tripp's 4 miles per kWh.

Note: NOT kilowatts. It is kilowatt*hr.

What you are calling 'electricity' is energy, measured in the US as kWh. You will get to know and love that unit of measure, as you size your system. Pull out a utility bill; it will show you how many kWh of electricity you used this past month. My utility lets me see a year of my use on it's web site.

A solar panel is spec'd to it's maximum power rating. Course, it's not always working at maximum efficiency. so the energy generated is a sum of how it did through all the seconds of the month. Not so good at night or on cloudy days, for e.g. Don't try to figure this out with math; just ask your installer how much energy a month each kW of PV on your house is going to generate. S(he) will also tell you how much each kW of PV costs installed, and how much roof area is required.

Check out nmsea.org for oodles of information. I'm sure CO has something similar -- I just do not know a web address.
A nice primer: http://nmsea.org/Education/Homeowners/Buyi...lar_Systems.pdf

[boulder_bum]

Pardon my ignorance, but I'm still unclear about how the solar panels work.

Okay, so panels are rated to their maximum power rating, but, again, what is the unit of time in which it can potentially generate that sort of energy. Does it generate that sort of energy every second? Hour? Day?

Also, if you'll humor me, if an electric car would use .25 kWh/mi, how does that relate to the solar system in the context of the above question? In other words, to travel 40 miles a day, how long would it take 1 kW worth of panels to generate the necessary energy (10 kWh) when running at full capacity?

[Bobwho]

<div class='quotetop'>QUOTE(Boulder Bum @ Sep 1 2007, 08:03 PM) [snapback]505596[/snapback]</div>

Pardon my ignorance, but I'm still unclear about how the solar panels work.

Okay, so panels are rated to their maximum power rating, but, again, what is the unit of time in which it can potentially generate that sort of energy. Does it generate that sort of energy every second? Hour? Day?

Also, if you'll humor me, if an electric car would use .25 kWh/mi, how does that relate to the solar system in the context of the above question? In other works, to travel 40 miles a day, how long would it take 1 kW worth of panels to generate the necessary energy (10 kWh) when running at full capacity?
[/b]

Hours times kilowatts equals kilowatt hours. Therefore with a one kilowatt panel it will take ten hours of full sun to charge the car. Now the efficiency of the panel comes into question. The panel must have a solar tracker in order to charge at anything near 100% of the rating. Any clouds or other obstructions will decrease the amount of power generated.

I hope this helps.

[viking31]

<div class='quotetop'>QUOTE(Boulder Bum @ Aug 31 2007, 07:11 PM) [snapback]505182[/snapback]</div>

Thanks Eric, I did assume 1 kW was 100 watts, but one of the things that confuse me (I know this is pretty basic stuff, but I'm just starting to learn), is how the advertised power of a system translates into electricity for the day.

For example, you can buy a set of, say, 100W solar panels, but what does "100W" mean? Is that the energy collected per hour or second or day? Is this the max capability or an average (accomodating for clouds passing overhead)?

Does anyone know?

tripp, thanks for the info on the 4 mi/kilowatt estimate. If I can figure out some of the basics (with all your guys' help) and maybe get a copy of the prospective house's energy bill I can start crunching some numbers.
[/b]

OK, here goes. Three terms are useful to know and understand when dealing with electricity. Watts, amperes, and volts. A good analogy is to think of electricity as water traveling through a hose or pipe.

Watts is how much water passes through the hose (this is how the power company measures your usage).

Amperes is how big (as is diameter) the hose is (this is how much electricity at any given moment is passing through the wire with respect to voltage).

And volts is the pressure of the water in the hose (the more volts the smaller the wire gauge needed to carry any given load. For example, motors can be made smaller (cheaper) with the same power as a larger lower voltage motor. House wiring (as in Europe's 230 volts for residential use vs. our 110-120 volts) can be a smaller gauge. BUT, the greater the voltage the more dangerous the circuit with respect to accidental electrocutions. You can use equations to figure out other values such a kilowatt hours, wire sizes needed to carry a certain load safely and such but I will leave that for you to research ;-)!

So what you are primarily interested is how many kilowatt-hours a cell can generate during the day. If a cell can generate 100 watts in ten hours it will generate one kilowatt hour, or about 9 cents of electricity in my neck of the woods. That's the same as a 100 watt light bulb burning for 10 hours, or five 100 watt light bulbs burning for 2 hours, and so on.

That's IF the sun is at the angle needed during all that time to generate 100 watts. Keep in mind the angle of the sun will change with the seasons and of course during the course of the day. It may be cloudy (think Chicago or many northern areas during the long winter months) where power output will be low. While here in FL they may be effective more often than most areas we have to worry about hurricanes and tropical storms ripping the panels off their anchors. It has also been stated that some panels degrade significantly over time.

I admire people who put significantly amounts of PV panels on their houses and pay little or no electrical costs to the utilities. But the upfront costs are high and currently with today’s electrical costs it seems unlikely you will recover your investment from an ROI point of view.

Let's hope soon PV cells will be priced in the future to effectively compete with the utilities in the future.

Rick
#4 2006

[boulder_bum]

Thanks guys! Everyone's information has finally helped me understand some basic information and some of what I'll need to consider.

I deeply appreciate your help!

[tripp]

<div class='quotetop'>QUOTE(Mad Hatter @ Aug 31 2007, 04:43 PM) [snapback]505173[/snapback]</div>

True, but I found the swamp cooler to pretty darn ineffective if we got above 92-93 F. I'm currently planning a heat-pump geothermal system for next year. We get triple digits too often, and if I wanted to be that hot and humid, I'd live in Texas.
[/b]

You must have higher humidity than us. We're comfortable above 100 F. The heat pump is a good idea though. How much would that cut down on your energy usage?

Wp (Watts peak) is usually measured at 25C (77 F). At higher temps the efficiency drops some. Most panels are rated to produce 80% of original after 25 years. This is a very common spec.

Rick, in CO we get pretty generous rebates from the State and the Utility. That, coupled with the fact that you can often deduct the interest from financing (plus the fact that rates creep up inexorably) and the ROI is pretty good.

To quote Ferris Bueller... "If you have the means, I highly recommend picking one up."

No one is using trackers anymore (except for CSP and utility scale PV installations) because they're not cost effective. They can require expensive maintenance. It's cheaper to just add more panels to get the output you want.

[Sufferin' Prius Envy]

<div class='quotetop'>QUOTE(Mad Hatter @ Aug 31 2007, 03:43 PM) [snapback]505173[/snapback]</div>

True, but I found the swamp cooler to pretty darn ineffective if we got above 92-93 F. I'm currently planning a heat-pump geothermal system for next year. We get triple digits too often, and if I wanted to be that hot and humid, I'd live in Texas.
[/b]

Just like here in Sacramento, you too have the ideal climate there in Kelseyville (low humidity and a large differential between high and low temperatures) . . .
http://www.wrh.noaa.gov/forecast/MapClick....2&map.y=124

. . . for a Whole House Fan.

http://www.eere.energy.gov/buildings/info/...an.html#Cooling

WHY MAKE COLD AIR WHEN YOU HAVE IT PROVIDED FOR YOU, FREE OF CHARGE, AT NIGHT!
JUST SUCK IT INTO YOUR HOUSE!!!!!

We rarely have a need to turn on our air conditioner, because, on most nights, we can chill down the house with the whole house fan. In the morning we close-up the house and it stays comfortable until the next evening- at which time we can turn the whole house fan back on. The other benefit of the whole house fan design is the attic gets the heat blown out for no extra cost. We do not have, or need a separate, and less efficient, attic-only fan.

Our house was built in the 1920's and is not all that well insulated (I am working on it) and the house also still has the original, double hung, single pane, inefficient and drafty windows.

You can run a whole house fan all night for less than what it costs to run a central air conditioner for only one hour.

The best way to use a whole house fan is to chill down the interior with the coolest night air. And I do mean chill!
The walls, furnishings, cabinets - everything - is cool to the touch in the morning. The house is then closed-up during the day and has no problem staying comfortable.

The same concept works in the spring and fall to warm-up the interior during the warmth of the day.

The cost of our whole house fan has been paid back many fold since I installed it seven years ago. My summer electric bills are basically the same as my winter electric bills . . . and I have gas heat!

PG&E will also give you a $100 rebate!
http://pge.com/res/rebates/whole_house_fans/index.html