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Discussion Starter · #1 ·
> One day we all want PV to offset our household usage, excellent.
> But, the average household array, to achieve this, occupies between 50-80%
> of
> roof space, that's in the order of 500-1200sqft if you'd like me to pull a
> figure from the darkness ;)

It's not quite that bad. I have a 3.4kw array that provides all the power
we need and then some. It's only about 250 sq ft.
Mine is on trackers so it performs a bit better than a fixed roof mount
array, but a roof mounted one would only need to be 20-30% larger to
produce the same output.
FWIW my array is averaging about 20kwh a day last month and about 30 kwh a
day back in June.

> I did some math a while back for a truck, figuring I could fit roughly
> 800-1000watts
> covering the bed, it would net me between 3-4 miles of range.
> Not exactly on the good side of the cost benefit analysis.

Yeah there are only a couple ways that a vehicle mounted array would work.
Either you build a light weight, high efficiency EV that is covered in
cells like a solar racer; or you have a vehicle that spends most of the
week sitting in the sun and you only drive it on weekends.

It occurs to me that something like the first idea isn't that far fetched.
A small three wheeled enclosed vehicle (like a Corbin sparrow, but
smaller) that has perhaps a 1 meter^2 array and a pedal generator.

If you could get the energy requirements down to about 30-40 wh per mile
(at 30-35 mph) this could have a range of perhaps 15-20 miles on solar
power with pedal power extending that another couple miles.
Might be enough for someone with a short commute.


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Discussion Starter · #2 ·
"I.e. in Portland Oregon during December the Sun at noon will be approx 67
degrees down from straight up. The cosine of 67 is about 0.39, multiply
that by the rated output of your panel and that's about how much it will
produce at noon, it will fall off from there before and after noon."
At least it will on the occasional clear day in Portland in December. :^))
--
View this message in context: http://electric-vehicle-discussion-list.413529.n4.nabble.com/Dirt-to-Wheels-analysis-tp3076445p3160688.html
Sent from the Electric Vehicle Discussion List mailing list archive at Nabble.com.

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Discussion Starter · #3 ·
How about using an array that has a DC output that matches the DC
charge voltage voltage of your EV. Then you don't have any DC-AC-DC
conversion losses. Mount the array on top of a carport. Then have a
grid tie inverter that can be switched in when the EV is charged, so
that the surplus energy is not wasted.

Anybody attempt this?


[email protected] wrote:

> I basically agree that solar panels on an EV are generally not very
> useful, however the efficiency of using stationary panels to charge
> an EV
> isn't necessarily that bad.
>
> As an example, my array uses Enphase micro inverters, one inverter
> per panel.
>
> They are rated at 99.6% efficient for MPPT and 95% efficient (CEC
> weighted) for converting DC to AC. So far my experience agrees with
> these
> figures.
>
> So basically 95% of the energy produced by the panels get's sent to
> the
> grid. Couple this with a decent charger and you'll see and overall
> panel
> to battery efficiency in the 90s (discounting charge efficiency of
> course)
>
>> the argument for/against solar on the EV is one the longer debates
>> on the
>> EVDL. the main argument against a SEV [solar EV ;)] is that panels
>> on a
>> house can be oriented more efficiently than on a vehicle. however,
>> one
>> issue that is not considered is the inefficiencies of charge
>> controller
>> from the panels to the solar batteries and then again the DC/DC
>> converter
>> from the solar batteries to the EV batteries or worse the inverter
>> from
>> the DC solar batteries to AC and then a charger back to DC for the EV
>> batteries
>>
>> charge controllers are from 70-90% efficient and DC/DC are from
>> 80's-90's%
>> [inverter/chargers combos are worse], yes i know these are very
>> very rough
>> numbers, but the end result is total efficiencies from the high
>> 50's to
>> the low 90's. placing panels in non-optimal orientation will have
>> similar
>> efficiency losses, provided that the panels can be hooked directly
>> to the
>> main EV pack which can be done if the panels voltage match the pack
>> charge
>> voltage.
>>
>> furthermore some panel types do well in non-optimal orientation [e.g.
>> laminates], so if done correctly, the house vs EV solar panels
>> issue is
>> nil.
>>
>> also if you compute the power received from the panel vs weight
>> you'll
>> find power densities similar to the better batteries out there and
>> similar
>> cost.
>>
>> if you place them on the vehicle correctly the aero drag is also nil
>>
>> i think the solar on the EV should be the next big challenge to
>> hobbyists
>> like the 100 miles on one charge was.
>>
>>
>> harry
>>
>> Albuquerque, NM
>> current bike: http://www.austinev.org/evalbum/1179
>> current non-bike: http://evalbum.com/1000
>>
>>
>> --- On Tue, 12/21/10, [email protected] <[email protected]> wrote:
>>
>>> From: [email protected] <[email protected]>
>>> Subject: [EVDL] Solar PV was: Dirt to Wheels analysis?
>>> To: [email protected], "Electric Vehicle Discussion List"
>>> <[email protected]>
>>> Date: Tuesday, December 21, 2010, 1:28 AM
>>>> One day we all want PV to offset
>>> our household usage, excellent.
>>>> But, the average household array, to achieve this,
>>> occupies between 50-80%
>>>> of
>>>> roof space, that's in the order of 500-1200sqft if
>>> you'd like me to pull a
>>>> figure from the darkness ;)
>>>
>>> It's not quite that bad. I have a 3.4kw array that
>>> provides all the power
>>> we need and then some. It's only about 250 sq ft.
>>> Mine is on trackers so it performs a bit better than a
>>> fixed roof mount
>>> array, but a roof mounted one would only need to be 20-30%
>>> larger to
>>> produce the same output.
>>> FWIW my array is averaging about 20kwh a day last month and
>>> about 30 kwh a
>>> day back in June.
>>>
>>>> I did some math a while back for a truck, figuring I
>>> could fit roughly
>>>> 800-1000watts
>>>> covering the bed, it would net me between 3-4 miles of
>>> range.
>>>> Not exactly on the good side of the cost benefit
>>> analysis.
>>>
>>> Yeah there are only a couple ways that a vehicle mounted
>>> array would work.
>>> Either you build a light weight, high efficiency EV that
>>> is covered in
>>> cells like a solar racer; or you have a vehicle that spends
>>> most of the
>>> week sitting in the sun and you only drive it on weekends.
>>>
>>> It occurs to me that something like the first idea isn't
>>> that far fetched.
>>> A small three wheeled enclosed vehicle (like a Corbin
>>> sparrow, but
>>> smaller) that has perhaps a 1 meter^2 array and a pedal
>>> generator.
>>>
>>> If you could get the energy requirements down to about
>>> 30-40 wh per mile
>>> (at 30-35 mph) this could have a range of perhaps 15-20
>>> miles on solar
>>> power with pedal power extending that another couple
>>> miles.
>>> Might be enough for someone with a short commute.
>>>
>>>
>>> _______________________________________________
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>>
>>
>>
>>
>>
>> _______________________________________________
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>>
>
> _______________________________________________
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Roger Heuckeroth
Advanced Carbon Systems
304 Blue Mountain Road
Saugerties, NY 12477
www.advancedcarbonsystems.com
Phone: 845-247-9089
Toll Free: 866-834-5674
Fax: 845-247-0441
[email protected]



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Discussion Starter · #4 ·
>>
>> Don't forget to take the panel angle to the sun into
>> account. Typically a
>> panel mounted on a vehicle will be pointing straight
>> up. The off angle
>> losses during winter will be at least 40%-60%.
>>
>
> also a roof system will only be 100% two days a year [in fact an
> infinitely small time twice a year, then an infinitely small time twice a
> day for 178 days a year]. in other words, a roof mounted system also
> suffers seasonal losses.

Yes but not nearly as much. A properly angled roof mounted array will be
between 92% and 100% (at noon). This is MUCH better than a vehicle
mounted array that is running 39% to 92% in the northern states or 59% to
98% in the southern states.

Remember that that this is related to the cosine of the difference so if
you're off by 10 degrees then you only lose about 1.5%. A roof mounted
array will be within 10 degrees around 90 days a year.

> even a tracking system is not 100% unless its a
> 3 dimensional system that requires an input of energy [i.e. < 100%].

True, however a tracker like mine (passive tracker, uses the heat from the
sun for movement) with seasonal adjustments is within 10 degrees pretty
much all year long. That means I'm running 98.5% to 100%.

> plus, parking a solar EV in front of some windows or a light colored wall
> will help out quite a bit for improving those angle inefficiencies [this
> is an added bonus not a requirement].

Negligible, maybe a couple percent and only if you can park close to a
wall that is north of your vehicle (assuming northern hemisphere)

>
> the main point: the roof system has a better efficiency due to orientation
> but the EV system has better efficiency due to skipping the converting
> process. these two independent factors allow for the possibility that an
> solar EV might be ok.

The conversion efficiency advantage is nowhere near enough to make up for
the off angle losses. A 5% conversion advantage isn't going to make up
for a 60% off angle loss, not even for an 8% loss.

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Discussion Starter · #5 ·
> How about using an array that has a DC output that matches the DC
> charge voltage voltage of your EV. Then you don't have any DC-AC-DC
> conversion losses. Mount the array on top of a carport. Then have a
> grid tie inverter that can be switched in when the EV is charged, so
> that the surplus energy is not wasted.

You can not exactly match the array to the battery.

Battery charge voltage changes during charge by about 8% for PbA (say from
135v to 146V)
PV output will vary depending on time of day, clouds, dirt/dust on the
front suface, etc.

You can hook the panel directly to the batteries but you typically lose
about 20% of you energy that way. Using a MPPT tracking charge controller
or an inverter (like mine) with MPPT and a quality chargers will only lose
around 10%

So it's less complicated and generally more efficient to just use a grid
tied array and your EV's normal charger.

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Discussion Starter · #6 ·
Lee wrote:
>If you keep the current the same, then voltage rises as
>light level rises.

It is not a typical load which keeps current constant.
In fact, solar cells mostly behave as current sources
with a voltage cut-off that is virtually only temperature
dependent. The current is linear to the irradiation.

>The voltage only falls at higher light levels when you
>have a MPPT, because it is increasing the current at
>high light levels.

No, this is not how MPPT works. It searches for the
operational point that provides max power.
The earlier post of "cowtown" has a reference to a
very instructive thesis work from Hannes Knopf.
I read it many years ago and now re-read some of it.
In there are clear I-U characteristics of solar cells
when varying different parameters, such as temp and
irradiation. This will clearly illustrate what I
fail to convey in words.
It also exactly matches the behavior I noticed from
the MPPT in my (commercial) PV inverter.

Regards,

Cor van de Water
Director HW & Systems Architecture Group
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] Private: http://www.cvandewater.com
Skype: cor_van_de_water IM: [email protected]
Tel: +1 408 383 7626 VoIP: +31 20 3987567 FWD# 25925
Tel: +91 (040)23117400 x203 XoIP: +31877841130

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