Re: Charging an EV using Wind and Solar Energy

[ted.lowe]

i've excerpted this post from a discussion on our listserve to continue the discussion here in the forums.

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Thanks for tossing out some numbers David!

>very practical (and in case anyone is wondering no it would not be up while moving, only when parked.) Here are some

in my experiences talking with the public on both RE and EV's in the past 5 years, about 95% of them think that a wind turbine (or such) on a moving vehicle would generate 'perpetual power'. Egads... shows much more education we need to do! i normally launch into a discussion on Newton's laws of the conservation of energy, energy conversions, and efficiencies, etc. and when their eyes glaze over, i say, just joking! i reassure them that they are in the large majority of people that think that we can generate power 'perpetually'. i think people are a combination of 'dumbed down', 'naive' and 'idealistic'. Just because i want something to be true doesn't make it true!

>numbers to work with. Most of us in Illinois have access to class 2 wind or better. In class 2 a Bergey 1kW turbine (2.5 meter dia) is capable of averaging 6 kWh a day on a 60ft tower. If you drop the tower down to 30 ft you get 4.4 kWh. One could have a turbine at home that you pull up next to daily or if on the road I suppose you could set it up when you stop.

Absolutely, we need RE powered charging stations everywhere! Imagine parking lots with solar carports with EVs inside charging during the day instead of frying in the wasted sun. This vision was shown on the NREL (national renewal energy lab) website in the mid-1980s! i'll send a link if i can find it. The technology is here now, cost and political will are the obstacles. Another reminder that our mission is right on!

>So now the question becomes how many miles can you get out of a kWh of electricity. On this I will defer to the list. Anyone got an answer?

General rule of thumb: about 2 miles per battery. Each of our batteries hold about 1 kwh. So my s-10 with 20 batteries, has about a 40 mile range (actually more because of how i drive) and holds about 20kwh with a full charge. ($2.10 in '06). Keep in mind that YMMV based on size/shape/weight of vehicle, driving habits (jack-rabbit vs timing lights), driving pattern (local vs. highway), low rolling resistance tires, etc. etc. Also, it takes more than 20kwh to put 20kwh into a battery pack..charger efficiency, inverter efficiency (if electricity is from wind or PV), wire losses, power factor, battery type effects, temperature, etc.

With David's numbers, assume a bergey 1kw on a 60 foot tower, average (year round), that would generate 12 miles of range for me each day.

If you want to know how much a PV system of different sizes/tiltes/azmuiths will generate in a day, use the excellent application called PV Watts on the NREL site: http://rredc.nrel.gov/solar/codes_algs/PVWATTS/

My home PV system is a 2kw DC system rated at 1800 W AC which is the MAX it will do. I have 12 * 167W Sanyo PV modules (total 2004 W DC). My inverter is a Sunny Boy 1800U model. My array is mounted flat on my roof at 17 degrees tilt and that roof face is 37 degrees west of south. Average sun hours per day is 3.5 in IL.
Plugging my system into PV Watts (version 1) gives: 2.23 mwh/year or 6.1 kwh/day. See these images for the input and output of the PV watts application for my system. Play around with it... it's fun and informative to get real!

http://www.fveaa.org/members/tedlowe/ftp/solar/tedlowe-2kw-pvwatts-input.jpg

http://www.fveaa.org/members/tedlowe/ftp/solar/tedlowe-2kw-pvwatts-output.jpg

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At 1/31/2007 09:13 AM, David Serafini wrote:

>Chad,
>
>I have joked about mounting a wind turbine in the back of my truck in the past. As I said before it would be a statement and not very practical (and in case anyone is wondering no it would not be up while moving, only when parked.) Here are some numbers to work with. Most of us in Illinois have access to class 2 wind or better. In class 2 a Bergey 1kW turbine (2.5 meter dia) is capable of averaging 6 kWh a day on a 60ft tower. If you drop the tower down to 30 ft you get 4.4 kWh. One could have a turbine at home that you pull up next to daily or if on the road I suppose you could set it up when you stop.
>
>So now the question becomes how many miles can you get out of a kWh of electricity. On this I will defer to the list. Anyone got an answer?
>
>-------------- Original message --------------
>From: <mailto:chadmccq%40comcast.net>chadmccq@comcast.net
>Thank you for your response. I think I included wind just because of a small article I just watched on a show on the discovery channel called "How Its Made". Really i was thinking something closer to the solar voltaic cells that could snap together or maybe in just roll our if there flexible and light weight enough.
>
>And to answer the question why an S-10? My cart is not completely tied to that horse. My intend is kind of a motor home for just me and maybe another. So as to live of the grid and be completely mobile, you know kind of follow the sun and write a book about my life kind of thing. Is it possible?
>
>You obviously have a grteater background in science. I know only enough to get my self in trouble and before I waste my available resources I figured I should talk to some people smarter than I am.
>
>And 400 watts worth of power to produce or reclaim from nature via wind is enough to re-charge my battery back? Do you own a EV? I have two but there very small scooter and I got a bug to get off off big daddy oils dependency.
>
>chad
>six years with GM as a line worker
>two years as an electrician
>eight years in the active duty military (still in the guard 1st Lt Signal Corp)

[rick.mouche]

Ted,

My son Peter is interested in charging our EV car with Solar power.  He is a Jr in High School and his favorite subjects are Math (calc BC) and Physics (AP).  He also takes courses in electronics and computer repair.  He is in the planning stage and working on a spread sheet with some calculations.  He is looking for someone to give him some help and guidance.  How large of a system would one need? Could one make a car cover with photo cells and have it charge in the parking lot or in the drive way?  How far could one go on an 8 hour charge?  Where to get the materials to build the system?  How to design the system to charge the 96 volt battery pack?  All of these and I am sure many more questions.  If someone wants to help a potential future engineer, please let us know. 

[scott.taylor]

Rick,

In short, the answer is YES, it can be done.  I can say that because I have done it myself on a smaller scale.  Rather than a car, I have an electric powered scooter and I have shown that I can completely recharge my batteries using the power collected from the sun in one day.

I have five 85 watt solar panels that are used in parallel to charge four 105 amp-hour 12v batteries.  I consume about 80-90 amp-hours on my 10 mile round trip commuting to work (which I hope will go down some as the temperatures go up).  And if I almost completely discharge my scooter, it takes about 2200 watt-hours to recharge it (or about 180 amp-hours).

Let me pass along some of what I have learned so far.

1. Plan for 50-100% more source power (solar or wind) than the numbers show you need. The power output numbers for solar panels and wind generators will be for ideal condition and new products.  For example, so far, my 85 watt solar panels have been producing about 60 watts per panel of power in full sun (although I think I can squeeze a bit more out by addressing my wiring losses).  You will rarely have the ideal conditions the manufacturers use to rate their products, we do not have 365 days of full sun in Illinois, and there are other losses.

2. The amount of power needed for a car (or bike) cannot be delivered by solar panels mounted on it.  There is simply not enough sun hitting the area of a car to produce the needed power.  There have been exceptions, like the SunRacer (http://www.fossweb.com/resources/pictures/631497843.html), but these are feather weight high technology vehicles not practical for street use (yet).

3. Since you probably can't carry the power system with you and you will more often be driving when the sun is shining, you will need to store the power you collect for later conversion into your car.  Of course, wind generators could collect power at night, but winds are generally lighter after the sun goes down.  If you store the collected power, there will be losses both in the storage and conversion back into your vehicle.  But putting the power into the electric grid is also a means of storage for later use.

4. Something I didn't realize when I started this, is the faster you pull the power out of a battery, the less power it will deliver.  This is the reason I have 420 amp-hours of battery to replenish 90 amp-hours of power used.  You don't want to use all of your batteries capacity or its life will be greatly shortened, so figure on using half the battery capacity.  Then depending on how quickly you draw the capacity out, you will need more storage to compensate for how quickly you pull the power.

5. There are two kinds of solar/wind power systems, grid-tied and off-grid or stand-alone.  Ted uses a grid tied system that puts the power generated back into the electric power grid, but he then plugs into the grid to recharge his truck.  This is probably the most efficient use of solar power because you use everything you collect, but you generally cannot use your solar or wind power if the electric grid goes down.  I have opted for an off-grid system because I like being able to use the power for backup.  If the power goes out for several days, which is becoming more likely, you will appreciate being able to generate your own.

6. As voltage goes down, wiring losses go up.  You will need much bigger wires to supply the same amount of power at 12 volts or 24 volts as you would at 120 volts.

7. Although it is possible to cost justify such a system, the payback times can be many years.  But it is also hard to put a price on having your own source of power if gas shortages arise or power becomes spotty.

Hope you find some value in this and I'm sure I or others can help with answers to your questions.  Tell your son to keep working those numbers and then sincerely consider the investment!  I am certain that being able to independently generate our own power is in our future.

Here are some useful formulas...

Watts = Volts * Amps (I assume 12.0 to 12.3 volts for batteries)

1 Watt-hours = 1 watt for 1 hour.  In other words, if you are consuming 1 watt for an hour, you have consumed 1 watt-hour.

Same is true for amp-hours, 1 amp-hour = 1 instantaneous amp continuously for one hour.

Kilo mean 1000, so 1 kilowatt = 1000 watts.

Scott...

[rick.mouche]

Scott,

Hey this is Peter. Thank you very much for the information. One can only learn so much in high school electronics and physics so any inputs (especially self observed) are nuggets of gold for me. What was really surprising was having to count on a lower real life rating for a solar panel. I guess even industries that are trying to help the environment have to try their hardest to sell equipment. Also I will take your advise on not charging the batteries fully to heart since I know that right now we charge our car all the way to full. This info was especially useful since batteries are expensive.
Thanks again

[scott.taylor]

Hi Peter,

Glad you found some of this useful and I'll be glad to answer any questions I can.  And promise I won't answer any I can't. :-)

Just to be clear.  I am sure the solar panels are capable of delivering as rated, but it will be a very rare day when all of the sun's energy is hitting the earth.  Even on most "clear" days, you will notice the haze caused by the jet exhausts that reduce the energy hitting the ground and being in Chicago, the sun is at an angle that reduces the power.  So given the same conditions, we will always get less power in Chicago than say, Miami.

Also, I was not suggesting you don't fully charge your car batteries, you definitely should.  But for the longest battery life, you don't want to regularly discharge them much more than 50%.

I store my solar power in batteries and then transfer that power to the bike at night.  So my solar storage batteries store more than twice the capacity I need to fully restore my bike batteries.

Hope that helps if I wasn't completely clear.

Scott...

[ted.lowe]

Let's try to quantify the expected results of solar charging an EV and create a Fact Sheet to handout to people.

To get us started, i'll toss out a link to this excellent tool that let's you see how much a PV system will generate given various parameters.  PV Watts is on the National Renewal Energy Lab's (NREL) website:

http://www.nrel.gov/rredc/pvwatts/version1.html

This link and a year's worth of clean energy web surfing links are here:

www.illinoissolar.org/links

Use PV Watts 1 with Chicago data (close enough for most of us).   My 2kw PV system parameters are:

Azimuth: 217 (degrees from north)
Tilt: 17 (degrees from ground)
DC rating: 2 (kW)
DC to AC derating factor: 0.77 (typical)

And the "ding-ding-ding" results are:

$245/year of electricity
http://www.fveaa.org/members/tedlowe/ftp/solar/tedlowe-2kw-pvwatts-output.jpg

You can run a variety of 'what if' scenarios to see the effects of different system sizes, azimuths, tilts, single and double axis tracking, etc.  Ideally, i'd have my 2kw system on a two-axis tracker without any shading from dawn to dusk (but i don't live in an ideal place nor am i living an ideal life:-) :p

This will help us get a quantitative idea of what the sun can do for us on the supply side.    On the demand side, we need to get good quantitative details of how much power our EVs use per mile.  Ultimately, it's all about watt-hours/mile folks!!!   This is the part (data collection, analysis and display) of the 'Knowledge is Power' project i'm focusing on (as i mentioned in my talk at our last meeting).  Stay tuned...

[ted.lowe]

Last night Rick Mouche and Co. asked about solar charging an EV.   Here are some details of a concept what i call PV2EV (Photovoltaic (PV) directly charging an EV's battery bank).  First some background on solar charging.

Efficiency is the ratio of output power to input power.  EG, a 50% efficient battery charger would put 50% of the input power into the battery and waste 50% in the form of heat.

Each conversion of energy from one form to another is at most 100% efficient but in reality always less than perfect.  EG, A wind turbine converts wind energy into mechanical energy into electrical energy.  Each conversion step loses some energy.

We normally charge our EVs with AC power from the grid with a battery charger (AC to DC conversion).  Typical AC to DC conversion efficiencies are in the range 50% (VERY POOR) to 91.5% (VERY GOOD).  The battery charger's DC output voltage must be matched to the EV's battery pack voltage to properly charge.

Consider my current situation for (partial) solar charging my S-10 EV.  My house has a (DC rated) 2kW gridtie PV system.  The most AC power it will generate is 1800W.  My Zivan NG3 battery charger draws about 3500W, so my charge could be up to 50% solar.

It looks like this:

2kW PV Array (DC output) -> Sunny Boy Inverter (DC to AC) -> Zivan NG3 Charger (AC to DC) -> S-10 EV (120V DC) Battery Pack

The efficiency of the PV array is about 16% (incident sunlight photons to output power aka electrons).

The efficiency of the Sunny Boy Inverter is about 93% (very good).

The efficiency of the Zivan NG3 is 85% (good).

PV2EV eliminates the Inverter and Charger conversions, but requires a DC to DC conversion (to match the output voltage of the PV array to the battery pack voltage).  It looks like this:

Solar-Array (DC) -> DC-to-DC Converter -> Battery Pack (DC)

The DC-to-DC Converter also performs a charge-regulation function to prevent the battery pack from over charging when its full.

For off-the-shelf nominal voltages, like 12v, 24v or 48v, DC to DC Converters are readily available in the commercial marketplace (because they are used in off-grid solar energy systems).

But for PV2EV we need the DC to DC Converter output to match our Battery Pack voltage.

EG, my S-10 EV has 20 * 6 V DC batteries for a nominal value of 120V DC.  My 2kW PV array outputs a DC voltage of between 200 and 264.  The maximum power output of the PV array occurs when the output voltage is 216V.

There are no such commercial products yet that convert 216V DC input to 120V DC output.  (DING DING DING: EVX-PRIZE idea:-)

If i hooked up the solar array directly to the battery pack, the batteries would charge, but not efficiently!  The PV array output voltage would be clamped to the battery voltage (far less then the maximum power voltage of 216V).  So the DC to DC Converter is needed and should use a method called MPPT (Maximum Power Point Tracking).  This method essentially decouples the input voltage from the output voltage and lets the PV array maximize it's output while converting the input power to the needed output power (voltage and current levels).  Read more about the CRUCIAL CONCEPT of MPPT here (and google MPPT): http://en.wikipedia.org/wiki/Maximum_power_point_tracker.  Here is an awesome site that shows how to implement your own MPPT (hint, one of my EVX-Prize entries will borrow from their info:-): http://www.drgw.net/workshop/MPPT/mppt.html

More later...

[alan.woodman]

It's interesting to read the comments about using the sun to provide electricity for recharging electric cars.  My experience with solar energy has been using the sun to heat hot water to provide very effective cost and energy savings.  Over the past 3 years my passive solar hot water (PSHW) system has provided virtually all our home hot water needs with the added plus of boosting my furnace's heat output with water-to-air heat exchangers on their blower inputs.  When the water is hot enough the furnace blowers turn on and the hot water, without any gas, can raise the home air temp another 2 to 3 degrees.  I've had winter heating bills nearly 50% less since the system was installed.  I have four 32 sq. ft. panels since we live north enough to not receive as much overall sun as southern states.  It's too bad I can't get electricity so efficiently but there is no maintainence, inverters or batteries to service.  I think Ted also has PSHW but my panels occupy all the south facing roof area and I can't find a suitable place for any PV panels.  Wish there was a hot water powered car :-)

[ted.lowe]

This just in...  the solar charging MPPT (max-power-point-tracking) technique in silicon at last!

http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1037,C1078,C1089,P89360

This first IC handles only 2a and a limited number of cells in series, but EVentually, more chips will be designed for a plug-and-play solar EV charger!

i recently bought a DeWalt 36V tool battery pack which has 10 of the A123 Systems LiFePO4 batteries in it.  The above IC (LT3652) supports LIFEPO4, so i'm going to try it out.  Could make a very cheap and easy solar powered UPS for a computer system (or other small system).  Stay tuned :-)

[bruce.jones]

Well, regarding the wind turbine on a car idea, there are actually vehicles that work using this approach, as unlikely as it seems.  First of all, they are mechanical as opposed to electrical. The February 2009 issue of Popular Science  http://www.popsci.com/node/32069  article "Running Against the Wind," describes a vehicle called the "Ventomobile" powered by headwinds entering a turbine with blades shaped to strike a balance between harvesting power and minimizing drag.  It's actually feasible and a fascinating article, but believe it or not, the idea is an old one.
In the corresponding comments to the article, someone mentioned a 2004 book, "The First American Farm Tractors" where Mr. H.M. Fletcher of Plainview, Texas in 1913 completed development of a traction plow that was run by wind. Gas Review magazine for April 1913 carried a feature article about Mr. Fletcher and his wind powered plow that he could guide in any direction.  I have not read these books or verified the plow, but am going to try and find em.   

[ted.lowe]

Yes, Bruce it can be done, but not as simply as 99% of people think (like just putting a conventional wind turbine in the truck bed:-).  With the appropriate amount of average wind speed, we could all be driving sail-vehicles.  i've been fascinated while researching this issue by some of the contraptions people have come up with.  Here's one eg, http://khabarbike.vox.com/library/post/a-sail-bike-from-the-netherlands.html.  Bikes (velobikes) seem especially implemented because they are much lighter...