I apologize if this topic has already been covered, but I could not find any existing posts that covered my question or provided any more information than I've found elsewhere.
I want to know if any member of this site has made a solar panel add-on to charge the NiMH IMA battery in a Honda Insight. I have found a few instances where Insight owners have included adding a solar panel to a multitude of other modifications including MIMA (Manual IMA), add-on batteries, and fifth wheels for pure electric drive, but I haven't been able to find any details on just the solar panel charging piece and this is the only piece I'm interested in.
To be perfectly clear about my intention here, I just want to provide maintenance type charging for the factory NiMH battery by connecting a few solar panels mounted within the cabin of the car. I do not expect to get huge gas mileage increases or make any modifications to how the factory IMA functions. I just want a system I can leave in place at all times that can restore the charge to the NiMH battery over a period of a time without any risk of overcharging or damaging the battery.
I've read enough to know this is certainly possible. So, naysayers need not respond to this post.
My goal is to be able to drive a little heavy on the battery, park the car for around eight hours on a sunny day, and come back to find the battery's charge restored. Any help or guidance that can be offered would be MUCH appreciated and would entail absolutely no liability on the part of the adviser. I'll research any solutions I learn of and take full responsibility for anything I eventually install.
The charging of the NiMH has been covered several times... The source of electricity is usually AC.... Do searches and you will find topics for grid charging and such... The DC sources for NiMH charging can be seen on mikes V-Boost system of additional batteries...
All the information you will need are under those topics...
You will be using the DC from a solar panel instead of a rectified to DC from AC Grid power... and you will be doing trickle charging instead of the high amps of the V-Boost system.
If the Key is turned off the additional energy you pump into the NiMH will not be accounted for by the BCM which will cause a recal so the BCM can figure out the current SoC....
This kind of project can void your warranties , kill your car , and kill you.... so know what you are doing... or get someone else who does to do it... or learn more about it yourself .... or don't do it.
This topic is also better located under the modifications section than the general section.
56 cells yields 180 VDC @ 85ma, three of these in parallel will yield 180VDC @ 250ma.(168 cells 42 Watts)
The pack can take 250-300MA constant charge without damage, but will generate some heat and if charged to full each day, will likely shorten the cycle life of the pack. On the other hand, this topping off will keep the subpacks balanced, and could actually help the pack longevity in that regard.
As Ian correctly indicated, you are playing with some serious voltage and power when fooling with the pack, so both legs of the solar panel should be isolated with 1000V diodes, and an in line 500ma fuse would also be wise.
You may want to check out Peter Perkins thread about a grid re balancer here: viewtopic.php?f=4&t=7055
Have fun
I was thinking of doing this as well, here's my math:
three 56 cell series strings using the shell 1/4 watt panels = 42 watts.
About $205 shipped = $4.88/watt (not bad, but you need to assemble them too)
2.4" x 2.4" = 5.76 square inches/cell
144 square inches/square foot =6.25 watts/square foot
42 watts / 6.25 watts/square foot = 6.8 square feet of cells, maybe it'll fit below the glass? You would have to strategically park the car.
Assuming five hours of full-time equivelent sun in a day (reference- "got sun, go solar"), thats 42 watts x 5 hrs = 210 watt-hrs per average sunny day
With a usable 4 amp-hour capacity of the battery modules, thats 144 volts x 4 amp-hours = 576 watt-hours = 3 days to go from 20% SOC to 80%.
One day = about a 20% increase in the SOC. More in summer, less in winter
Here's where it gets a little fuzzy because now it depends on if you can use this energy effectively. You can look at it as the IC engine does not have to produce that 210 watt-hrs/day so that directly saves some amount of fuel. (anyone have any figures for gas to IC to elctricity efficiencies in wh/gal?)
Of course if your car is just charging all day, you would need to have a place for this charge to go- a partially depleted battery- so you would need to have some manual control over IMA so you can shut down with a depleted battery to avoid going past an 80% SOC on a regular basis.
Another way of looking at it is the efficiency of the motor assist. 210 watt-hours produced at the solar panel should get about 90% of that, 189 watts into the battery. An efficient EV (probably few better than an Insight) uses maybe 170 watts/mile from the battery. 189watts/170 watts/mi = 1.1 miles.
Thats a mile/day from the sun. If your daily commute is only 11 miles, you see a 10% reduction in fuel use (11-1 divided by 10). If you commute is 101 miles, you get a 1% reduction in fuel used.
Then there is the cost. $205 for the cells, a few bucks for diodes, a fuse, wire, misc materials, solder, electricity to solder = say $250 to save a mile a day.
Say 60 mpg, gas is about $3.50 today in California = 5.83 cents/mile (3.5/60). You would save this every day if yoiu use your car regularly.
$250 / $0.0583/mi = 4,288 sunny days for the payback, or 11.75 years. That is actually a good payback for solar panels. Without subsidies, a home system typically has a 30 year or so payback. Actuall payback time would be less, assuming the cost of gas keeps going up- likely.
Of course this is hard to justify financially, but the green factor is ultra high, as would be the feeling of getting that mile from the sun! I think I'll do it.
Of course this is all theory, I have not done this-yet. I'm not an electrical enginneer but I am a marine engineer. If there is anything I missed in the math, I invite a correction.
Mark
I just put a deposit on a '05 5-speed, seal the deal next week!
Of course this brings up an exellent case for plug-in charging as well.
If you returned home (or anywhere there's a suitable plug) with a 20% SOC and charged up to 80% with relatively clean + cheap grid power, you could avoid using gasoline to produce that 576 watt-hrs of power (4 ah x 144 volt).
My power from Pacific Power in nor cal is $0.09 / kwh.
Assuming a 90% charger efficiency and 90% battery charging efficiency, that 576 watt-hrs of battery storage uses 711 watt-hrs from the grid (576/.9/.9).
.711 kwh / 1kwh x $0.09/kwh = $0.06 or 6 cents for a full charge
Say 60 mpg again and $3.50/gal = 5.8 cents/mi
5.8c x 3 miles = 17.4 cents
17.4 - 6 = 11.4 cents saved per 60% charge of the stock battery pack from the grid.
With a booster pack, the gasoline avoidance could add up to alot more. It's this avoidance that I'm after, not really the $'s.
I believe you could achieve the same results more safely and easily with these panels by using them to charge an additional 12 volt battery. Use this 12 volt source to reduce the load cased by the 12 volt system. Because the energy to charge the 12 volt system is derived from the IMA motor that first generates 144 volts and then is converted by a switching power supply there is a considerable loss of efficiency. For this reason the reduction of load on the engine will be greater than the motive energy derived from the IMA battery directly, especially as there is a loss of efficiency due to the switching motor control. The math would be somewhat complex, but I believe this would be twice as efficient at extending the range or efficiency of the Insight. You would also not be dealing with lethal voltage levels. Connecting this system in to the regular battery would likely be done with a high current diode, a fuse, and a switch or relay. If you use a relay it could detect a low voltage condition on the system and switch in the regular 12 volt system.
A interesting test to verify the effectiveness of this system would be to monitor the charge current to the 12 volt battery prior to making any modification.
__________________
Kip Munro
The laws of physics don't need changing, but rather our attitude and values. 72.8 LMPG
IMHO it is not so clear.
Not so sure on the benefits of charging the 12V battery vs the HV battery.
The 12V battery load during the day, is pretty light, I am guessing no more than 1-2 amps?
The dc/dc will stop charging the 12V when the float voltage is reached.
The dc/dc drops 144 to 13V or ~ a 10:1 reduction in voltage, and a 10:1 increase in current.
Lets say we need 10A @12V (lights, and other loads) this would only draw 1 amp from the HV battery. Since we cannot charge the 12V to a higher voltage than the float voltage, any solar charging would just boil the fluid out of the 12V battery, and not provide additional capacity.
Charging the HV battery which is allowed to swing from 120VDC to nearly 180VDC will allow topping off of that battery.
Guess we would need to do some testing to see which way provides the best efficiency?
Also the guy will deal on the price of the solar cells if you get several cases of 170 cells, bringing the delivered cost down to less than $4 a watt.
Each one Gallon of regular Gasoline has ~36634.658658 Wh of chemical energy.
But the ICE is not 100% efficient ... and many factors effect it.
At 15% Efficient you get about ~5,495.2 Wh of mechanical energy out of every 1 gallon of gasoline in.
At 40% Efficient you get about ~14,653.8 Wh of mechanical energy out of every 1 gallon of gasoline in.
That would only be the direct offset.
Indirectly... additional Electrical power would mean you might be able to stay in a high % Efficiency like lean burn more... which would thus improve the ICE average % efficiency... so you would indirectly offset more gasoline due to this.
I am estimating between 0.04367449 and 0.016377934 gallons of gas will be offset for each 1 Ah from the 144V NiMH battery that did not come from gasoline use.
Depending on allot of other factors that reduction in gallons of gasoline used could result in a MPG increase of various amounts ... I am expecting between ~10% minimum and ~64% Maximum increase... but for how long will be controlled by how much you can store.... ~5 minutes out of a 1 hour drive is not much total effect.
The Stock IMA NiMH batteries could not hold more than ~4Ah of non-gasoline energy at best ...
Two other factors need to be considered. First, the weight (and drag if they're mounted externally) of the solar panels. Depending on how often you find opportunity to park in full sun, I could see them actually being a net loss.
Second, the lost opportunity. Take those solar panels, mount them in a sunny location, and use them to cover part of your home electric load.
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Solar Panel Add-On for Insight?
