Guide: Installing a solar panel on the HCH-II (step-by-step)

Discussion in 'Articles' started by msantos, May 7, 2008.

  1. msantos

    msantos Eco Accelerometrist

    Thinking of a solar panel for your Honda Civic Hybrid ? Here's the why and the how.

    [xfloat=left][/xfloat]Manuel Santos - CleanMPG - May 8, 2008


    As many of you have noticed, the arrival of summer seems to spark renewed interest in all sorts of “Sun” related activities and gadgets. One of these is solar panels for automotive applications … and for good reason not only because we always wonder about what else is all that radiated solar goodness good for but also because there's something fascinating about having a solar panel installed in a car – call it the “wouldn’t it be cool to have that” factor.

    Still it is mostly due to the overwhelming number of requests that I’ve had that I decided to produce this somewhat more detailed step-by-step guide of how to install a small solar panel on your second generation Honda Civic Hybrid. Of course, many of the steps illustrated in this guide may be applicable to many other vehicles particularly the first generation Civic Hybrid but despite any potential similarities, I offer no explicit guarantees that these alternate installations will parallel the exhibits in this guide.

    Also, many of you are eager to know what an install like this actually does for your fuel economy and in truth I say that it totally depends on the circumstances. For some folks this mod may offer little or no benefit, and for others (such as myself) this is likely to be a pretty effective “must have“ option.

    What this modification does

    Like in the first article, the objective of this mod is to install a solar panel to charge and supplement the 12V power losses on the HCH-II. As in the previous article, it makes sense to repeat that this solar panel installation does not charge your hybrid's battery pack.

    Then, what are the benefits, and why?

    True to Honda's design philosophy of "man maximum, machine minimum", the HCH-II has a power management system that is best described as a design of optimal minimums. The consequence of such a design is that very little "electric headroom" is available for accessories with larger power signatures without these having a measurable impact on the average fuel economy. To put it mildly, the small 12V battery is hardly able to sustain the power demands of anything else beyond the OEM equipment already in the vehicle.

    Now, add one or more after-market systems (i.e: Audio, alarms, corrosion inhibitors, air pressure pump, etc) and this headroom is not only gone but we are now operating in a slight power deficit. To make matters worse for some folks, add 4-6 months worth of below freezing temperatures and you will no doubt see a good chance for trouble.

    At its worst, the 12V accessories battery life will be shortened due to it running at a less than ideal charge level for extended periods of time. At best, you may have an IMA crash or a chronic dip in your fuel economy.

    The idea behind this project is that any “solar charge” you get into the 12V battery (especially when the car is parked in a bright day) will not be diverted from the IMA system when the car is running. In traditional vehicles this is not as severe a concern since the 12V battery charge is obtained directly from the alternator with minimal downstream losses due to energy conversions. On many hybrids such as the HCH, the 12V battery charge is obtained from the DC-DC converter, which it in turn often gets the "energy" from the traction battery. While it may appear that this process is not much different from that of a traditional vehicle, the fact is that on the HCH, the energy that arrives to the 12V has already been subjected to many more energy conversion losses and therefore arrives to the 12V battery with a higher cost premium.

    The following diagrams provide a very rough idea of what is truly happening and why the 12V charge is more costly for the Civic Hybrid strictly on the basis of watt-hours.



    As implied by the above diagrams, the energy conversion losses are measurably higher in the Civic Hybrid particularly when it comes to charging the 12V accessories battery. This is because the 12V subsystem is much further downstream than the energy path of a traditional car. Also by implication, this means that more kinetic energy (hence fuel) is required in order to generate similar amounts of electrical energy to power the vehicle’s accessories. How much more? It certainly depends on the actual 12V loads... but also on ambient temperature, the amount of time a vehicle is driven per day, driving conditions and other smaller factors.

    Sure, the solar panel does not produce that much current to help the vehicle while it is in motion, but over the course of several hours of exposure while stationary in a sunny parking lot, it begins to make a small and measurable difference. Over the long haul these small differences *can* become significant in more ways than one.

    Just for giggles: "What is the gasoline equivalent of the energy provided by this solar panel?"

    This is where things can get a little complicated. Using a regular gas only Civic as an example, we can arrive to an estimate of this energy with the following approach:

    Solar Panel energy calculations:
    The nominal energy provided by this solar panel over an 11 hour day:
    Power: 130 x 17.5 = 2.275
    Energy: 2.275 x 11 x 3600 = 90.090 KJ

    A liter of gas has approximately 32 Mega-Joules of effective energy (less if blended) and that means that running the solar panel will net you the equivalent energy contained in 2.8ml of gas. Then also assuming that the regular Civic engine has an efficiency of 25% we find that it takes 11.2 ml of gas to generate the equivalent energy provided by the solar panel. That is roughly equivalent to 2.4 tea spoons of gasoline saved in every liter of gasoline used...

    Is this a lot? No, definitely not in the case of the regular Civic.

    Things don't look significantly better for the Civic Hybrid either. This is assuming that it can travel further than the regular Civic on the same amount of fuel... and perhaps in the hands of an attentive hybrid owner we're probably talking twice the distance? Despite the added gas engine efficiency of the HCH over the non-hybrids (up to 6-10%), the HCH is further burdened by downstream energy losses mainly due to the 12V subsystem which are estimated to be at best 40-50%. So we would save at most 5 tea spoons of gas. Hummm...

    Definitely not a big case from the fuel efficiency angle either. However, things are not as simple as they may appear either.

    For example, what is the benefit to FE if with this mod I can avoid or reduce the chance of an IMA forced regeneration by making it easier to maintain and manage the SoC? What is that worth to me? What about the 12V battery life? What if it can prolong its life by a year or two (perhaps more?) by having it always topped off?

    In any case, if you like the extra edge on your side and you don't mind the "novelty" aspect of it then this mod may be for you too ;)

    A common question:"Why not do the same to charge the traction battery (the NiMH battery pack)?"

    Although a good idea, it is still betrayed by three simple constraints:
    Cost, safety, warranty

    Yes, it will likely be done someday once somebody designs an affordable cooperative charging system that is both effective and safe but one thing is certain regarding the OEM warranty: such a modification/enhancement will definitely void it for sure.

    Some words of CAUTION before we begin

    As usual, I cannot take responsibility for anything that may go wrong if you attempt this mod on your own. If you feel like this may be over your head then you’ll do well giving the job to a car audio shop or a skilled friend. And always keep in mind that even if you succeed in getting the setup to work, it should look professional enough to withstand the scrutiny of Honda technicians should you ever need to take the car in for any kind of warranty work! Also, remember that the system must be easy to disconnect upon request from a technician or service department. In other words consider the examples and steps illustrated in this guide as the minimal specification of your install and if you EVER deviate from this example then do so to make it better and more robust.

    Step by Step

    First and foremost, let’s introduce the solar panel that we will be using in this install. By the way, I purchased quite a few of these panels which over the next few weeks will find their way into 4 different HCH-2’s and one 2007 Prius, so I expect this installation process to remain relatively unchanged. I will update this article if I encounter any additional optimizations worth mentioning.


    What it looks like when mounted

    This particular panel produces a maximum power output of 2.4 watts and its nominal operating specifications identify the voltage at 17.5 volts and the current at 130mA. Yes, the voltage is significantly higher than the 12V level the HCH-2 battery is rated for, but the load of the battery and the other “always on” devices on the system bring it all back down to the nominal 12V level. So, there’s really nothing to worry about here.

    Why not use a larger panel? Well, the truth is that a 5W or larger panel will likely overcharge the tiny 12 volt battery and may require a charge controller to keep things safe. Since a charge controller costs in the vicinity of $40 many may find a 5 watt or larger panel too expensive and overkill for this application.

    In this exercise we will be installing this panel on the rear dash as illustrated in the following picture. To do this we will need to drill a little “pass-through” hole (the smallest possible) on the trim into the trunk area. To accomplish this I used a 5mm drill bit and I gently drilled the hole upwards from the trunk. One thing I noticed is that there’s a “wool like” white lining underneath the trim that may need to be parted before spinning the drill bit through. Otherwise, you could risk bunching it all and reducing the benefits of the inner lining.

    [​IMG] [​IMG]

    Use a 5mm drill or smaller to create a pass through hole for the solar panel wire

    Now, before we do any more work we need to prep the solar panel for installation. If you notice, the panel’s wire exits through one of the sides horizontally. Personally I find this protrusion aesthetically unpleasant so my objective is to do away with this by opening the solar panel and finding another way to route the wire out of the solar panel’s enclosure.

    Remove the plastic caps and then the screws fastening the back side of the panel

    Determine the best location for the new hole where the wire will exit through


    [​IMG] [​IMG]
    Thread the wire through the new hole after using some hot glue inside the panel

    In this particular situation I simply made a small hole on the enclosure and passed the wire through it. You’ll also notice that I’ve cut the wire leaving only 2 feet worth. I’ve also chosen to discard the connectors included with the panel since I prefer to use my own for the reasons that will become evident at a later point in this article.

    With the new hole made on the back of the unit and the wire re-routed and passing through it, the protrusion is no longer there (just a tiny imperceptible hole remains). At this point I can choose to plug it with bit of black silicone putty if I am focused on this minor detail. After this step is complete we will secure the wiring inside the solar panel with some hot glue and then screw the unit back on to its original state.

    The left over hole can be covered with tape or black silicone putty

    The next step will involve setting the anchor points for the solar panel. As many of you will notice we’re using a combination of adhesive foam and Velcro. While we could use the four stainless steel screws and have the unit securely fastened to the rear dash, I dislike the idea of making so many holes on the dash and also not being able to remove at will (cleaning or other reasons). So, my experience has shown that the method I illustrate here suits me just fine, it is quiet, reasonably solid and easy to live with.

    To begin, I cut a couple of small strips of adhesive foam (roughly 2 to 2.5 inches long). This foam is pretty wide (roughly 1 inch wide) and it provides plenty of support to the panel.

    The closed cell foam tape and the industrial Velcro used to secure the solar panel

    TOP: loop velcro , MIDDLE: hook velcro, BOTTOM: Foam pads

    This foam can be found at home depot in the weather proofing section and its adhesive properties seem to be good enough to withstand the coldest days (-45F) and also the hottest (110F) without coming loose. Although not absolutely necessary, you may also sand the foam pad on the outboard edge to make it easier for the solar panel to land on it as flatly as possible.

    I also cut three strips of industrial Velcro. This Velcro can also be found at Home depot or other hardware stores and does a pretty good job of securing and silencing the setup.

    Foam and Velcro pads ready to be placed on the rear dash

    Two of the smaller strips (hook side) were "glued" against the foam pads while the larger segment will hold the panel at the lower end. You may choose to use a different number or length of Velcro strips but I have found these to offer the securing effectiveness it needs without being a pain to pry the panel off at a later time. The remaining strips (loop side) that match the 3 (Hooks) segments will be glued against the back side of the solar panel as shown below.

    Solar panel with the loop side Velcro pads on

    To make sure that the Velcro and the adhesive foam adhere properly, I simply wet a couple of cotton swabs with some alcohol or vehicle wax remover and wiped the surface of the dash trim where the Velcro and foam will attach. Doing this will ensure that any oils, dust or surface treatments (like Armorall) don’t get in the way of a solid adhesion. :)

    Once the foam pads and Velcro are attached, we can then feed the wire from the solar panel downwards through the small hole we made earlier from the trunk. Doing so may require getting a stiffer wire (fish tape) trough the orifice first just to make sure the conductor arrives on the other side without too much fuss. Once the wire is on the other side we simply “press” the solar panel onto its final support points and just let it be for a good day or so. You may choose to place a small book on top of the panel to make sure some pressure is applied while the adhesive does its job. Prying it off too soon may reduce the effectiveness of the adhesives... so we should be careful in positioning the Velcro and the pads as you should only give yourself one chance to get this right.

    What the mounted panel looks like from the inside of the vehicle

    Anyway, at this stage we’re ready to start working on the wiring. The first thing we’ll need is to make sure that this installation is protected by an inline fuse. You’ll also need to do some crimping because quite frankly we want the install to be easily disconnected should Honda ever raise it as a troubleshooting issue.

    A good collection of male/female connectors and your average crimper


    The other tools...

    There are many different types of inline fuse assemblies and I don’t really have a preference for any in particular. As long as they are effective and easy to work with then I am pretty much OK with them. These fuse kits can be found in most auto parts stores (NAPA and Auto-zone) or the automotive departments of larger retail stores (Walmart, Sears).

    For protection I would suggest using any fuse rated for 500mA or higher, but no higher than 5A. In this install I chose to use a 3A fuse as it is very common and easy to find replacements for.

    The original retail inline mini fuse kit with a bullet type connector. Fuse is absent.

    The inline mini fuse kit altered to fit a different "flat" type connector. Fuse is mounted.

    ... and an alternate inline fuse kit configuration

    Running the wire(s)

    We only really need to run one wire all the way from the trunk to the fuse panel underneath the driver’s side dash. The wire that we are talking about will carry the positive (+17v) voltage from the panel and will be connecting to the inline fuse which in turn will connect to an available fuse socket on the fuse panel (the actual connection to the fuse panel will be done later). This wire can be easily routed through the trunk into the passenger cabin from behind the seat on the driver’s side) and underneath the side trim. If done patiently and properly it should not only remain easily concealed but also very safe. The alternative to this is to remove the plastic trim and secure the wire against the vehicle’s metal structure. It is up to you.

    TIP: Use some heat shrink tubing or wire loom while running the wires through any the vehicle's pre-drilled holes.

    Examine the path for your wiring before laying it out

    Running the wires and crimping the connectors inside the trunk


    Lastly we can connect the remaining wire (ground) to a suitable ground point on the vehicle. In the trunk you’ll find a few grounding points around the tail light areas (under the trunk lining) and you’ll also find several on the IPU chassis. I often chose to establish the ground connection on the IPU chassis which can be easily accessed by pushing the seat cushion just a little. If this approach is still awkward for you, then you may choose to remove the seat back entirely or adopt another ground point in the trunk area. However, first we should prepare our ground end connector:

    Using the panel's remaining ground wire or another equally suitable wire we attach a proper connecting end to it

    An example of a possible ground point connection in the vehicle's trunk area is provided below. Usually these ground points are found close to the tail lights underneath the trunk vertical lining.
    Connecting the newly crimped U connector to the ground point.

    Once all the wiring is in place we should use a voltmeter to see if the +17 volt wire arriving from the panel provides the expected voltage readout (it kind helps to be outdoors for this to work :) ).

    There are several empty fuse locations where to plug the solar panel we chose socket 6

    If we read 17 Volts on the red wire, then we simply plug the (red) wire onto an available fuse kit connector (as shown in the following picture). If you can not read 17 volts, then make sure all the connections are properly secured before attempting to connect.

    Plug the solar panel into the fuse kit only after testing for a 17Volt reading.

    Optional improvements

    You may choose to also install a small LCD current meter to measure the amount of current your panel is providing to your 12V system. This will help you assess how effective the panel is and whether it is working for you at all.

    (Actual "installed" images will be provided soon)


    From a rather personal perspective this solar panel is an absolute necessity because my car has several “always on” systems, two of these (Alarm and surveillance, along with the Electronic rust protection) consume too much for the little OEM 12V battery to take. A panel like this will not only help supplement those losses but will also ensure that even in the coldest of days your 12V battery will remain healthy.

    Of course, this mod also helps the fuel economy aspect since less IMA charge is diverted to keep the 12V subsystem topped off and that means I don't have to work as hard to manage my SoC. ;)

    If you have any questions or feedback regarding this modification please submit them on this thread.


    Last edited: May 16, 2008
  2. Geedoug!

    Geedoug! New Member


    Before I saw your post on installing a solar panel, I had this idea for my 2001 Prius (which I bought today): Installing a small solar panel that would charge a small supplemental battery (like the 12 volt / 7 amp hour lead acid portable power system battery (that I just bought for another purpose). This battery would be used to run a block heater which would come on when the car was first turned on (or, better yet, when the remote was used to unlock the doors to sped up the process.) Excess power from the solar panel could, perhaps, be used to charge the existing 12 volt battery.

    I don't know nothin' 'bout no electricicals, so what do you think? Any merit to this idea?

    Thanks. Your newbie friend,
  3. ericbecky

    ericbecky Member

    Thanks for a detailed write up.
    I'm sure others will have more feedback.
    I look forward to seeing more.
  4. msantos

    msantos Eco Accelerometrist

    Hi Gary;

    The idea has a lot of merit and has already been discussed a few times here at CleanMPG.

    In order to achieve something like that, your solar power generation would have to be massive and in addition to that, you would need a good array of SLA batteries simply because a standard block heater eats roughly 400 watts and you cannot really afford to completely deplete your batteries - otherwise their life is very short. To add insult to injury, the engine block takes a good couple of hours to warm up effectively. I believe you can see our problem as it clearly starts getting very impractical: Massive solar panel(s), beefy battery bank, power control circuitry, etc....

    With that said, the biggest culprit or impediment is energy storage efficiency and the implicit conversion losses. The less conversions there are the more efficient the solar recovery system is; and despite the current state of technology and progress, I am afraid we're not there yet. :(


  5. seftonm

    seftonm Veteran Staff Member

    Great writeup and find on the panel, Manuel!

    I finally managed to find the panel pictured in the installation. I did some testing on its output and found that connecting the panel to my car's electrical system brings the panel's voltage down to about 12.6 volts. On an overcast day, the panel put out about 30mA, which increased to 90mA on a sunny day. The panel angle affects the output more than I thought it would. Laying it horizontally reduced current flow to about 70mA on the same sunny day. Best results for me were with the panel at a ~40 degree angle from horizontal. My windows also really kill the output. Simply putting the panel on my car's roof at the same angle increased the current from 90mA to 140mA. I don't have any significant tint on my windows, but the glass may be designed to absorb some solar energy.

    I will have to create some sort of device to keep my panel up at an angle for optimal output. I'd also like to capture the energy that is being lost through my windows, but I don't know if that is possible.
  6. msantos

    msantos Eco Accelerometrist

    Glad you managed to find one as they kind of cleared out in a big hurry. ;)

    I certainly agree with you that the windows account for a measurable loss in the panel's output as I see that as well. However, there may be other attributes of an install that can have a small bearing too. Here are some observations I also made in my case:
    - The panel's output is significantly lower if the panel is installed on the front dash as opposed to the read dash. Why? Here are some of the possible reasons:
    • In my case, the rear glass has a lower tint gradient
    • Depending on the sun's angle, the glass refraction factor is less aggressive so the light travels "more" perpendicularly through the glass (in my case).
    • The rear dash is in a bright color and with the reflective index of the rear window that helps bounce some light back down into the panel. The front dash is very dark in color and that helps kill the output by a tiny bit. This effect appears more noticeable in a cloudy day.
    A sun-tracker module? I suppose making one from an assortment of RC or toy components could be effective. The way I see it , the tiny challenge is when powering the semi-smart tracker circuit (even if built entirely on CMOS tech) as it begins to eat into the battery in a not so bright day especially since the panel is not assured of the clear view of the sun like a normal fixed application would. :eek:

    Making a manually operated one would be very cool indeed. ;)

    Capturing energy lost through the windows? That is a great idea.
    On an almost related note, my dream is to one day find a practical solar voltaic/LCD film that can be applied under the windows (glass embedded is even better) to capture the light while the car is parked and also provide an adjustable tint factor when driving it. :)


  7. psyshack

    psyshack He who posts articles

    I wish I had thought about this when I had my 06 Civic EX. Its battery and charging system was junk. It had no headroom at all. They cut it so close I put it in the poor engineering category.

    Im sorry to hear the HCH-II suffers from the same issue. :(
  8. cephraim

    cephraim Noob

    Any updates on this mod?
  9. cephraim

    cephraim Noob

    FYI, I decided to try something similar in my Nissan Altima Hybrid. No FE info yet, but I posted some pics over here.

  10. Tofuman

    Tofuman Member

    would this benefit a non-hybrid car in terms of FE?
  11. seftonm

    seftonm Veteran Staff Member

    It can't hurt, Tofuman. I use mine mainly to keep my battery up during the dead of winter. Sometimes my car won't move for 2-3 weeks, and I noticed the battery felt kind of "flat" for that first start after sitting that long, especially if it was during one of our -20F cold snaps.

    I was cleaning out my car today and noticed that the wire had broken right where it meets that springy part on the side of the panel. My panel was mounted in the back of my car on a shelf that tilted up with the hatch when it was opened. Maybe that repetitive movement was too much for that joint to handle? I'm not sure how to fix it yet, but will investigate soon.
  12. drimportracing

    drimportracing Pizza driver: 61,000+ deliveries

    I velcroed one to my dash a few weeks ago, it gets plugged into the cigarette lighter and it produces enough power during the day to fully charge the battery after an insane amount of night time driving 5X a week and also will power my radio, which used to never play when the ignition switch was off and the power switch to the radio was on. Also during the day when I FAS I don't lose any radio time when I turn the ignition back on at a green intersection. That's way cool.

    The first day I got up and went towards my car I thought my neighbors were listening to NPR. :) They weren't. I now power off my radio when I come home at night so it doesn't play in the carport while I sleep during the day from the solar panel. Mine is a 1.5watt output amorphous solar panel from regularly $15.99, on sale occasionally for $12.99 - Dale
    Last edited: Jan 10, 2009
  13. jkp1187

    jkp1187 Well-Known Member

  14. fuzzy

    fuzzy Mild hypermiler

    Speaking not as a car hound, but as an electrical engineer with a hobby-size solar panel on my house roof for the past 15 years:

    Is 1.5 Watts a lot? No, it is tiny.

    How long will it take to recharge a battery with this? It will never recharge. Even under ideal conditions -- mounted outside the car (no glass in the way), no clouds, no shading -- it would need an automatic sun tracker pointing it directly at the sun all day, just to collect enough energy to make up for the self discharge of the battery.

    If you had it at the South Pole during summer, with 24-hour sunlight and an automatic sun tracker, it might charge the battery in a few weeks, depending on the battery size. And not counting the power to operate the tracking motor.
  15. fuzzy

    fuzzy Mild hypermiler

    From your description, I must seriously question whether it is charging the battery at all.

    Is your cigarette lighter turned off when the ignition is off? If so, plugging a solar charger into the lighter cannot charge the battery while you are away.

    The fact that the radio will not normally play with the ignition off, but will play with the solar charger plugger in, very strongly hints that this is the case.
  16. greenrider

    greenrider Well-Known Member

    Would a larger, 5 watt solar cell such as this be too much of a good thing?


    Just thinking about doing this DIY this summer.

  17. msantos

    msantos Eco Accelerometrist

    Hi Mike;

    For the HCH-II a 5 Watt solar panel is not too much.

    In fact, I've added yet another 2.4 W solar panel to my daily commuter precisely because I had to revise my original requirements. Going much above 5 Watts would likely call for a charge controller.


  18. psyshack

    psyshack He who posts articles

    This is looking like a much needed mod for the HCHII. The windows are tinted in the wifes car. Would I need to go for a bit larger panel to make up for the tint?
  19. msantos

    msantos Eco Accelerometrist

    Hi Jeff;

    Its funny you mention that. I now have a total of 5+ Watts of solar generation available which is not only more than enough to keep my 12V demands in check, but also to provide a tiny bit of surplus power.

    After seeing the 2010 Prius with a solar roof powering the cars ventilation system, I revisited the idea and I am thinking of powering a small DC fan with roughly 160-180mA @ ~12V on tap.

    Is this what you were thinking of doing as well, or just keeping the 12V topped off?

    Anyway, just to stimulate additional thinking among the community I'll introduce the following:
    [​IMG] [​IMG]

    There are many areas where a fan like this be placed. My preference is to install it in the trunk area between the lining and the outer body shell and then drive a duct all the way to the rear dash. Open a neat hole in the rear dash right around the IPU vent and cover the hole with a nice grille. Then, make sure we have a temp activated switch that will kick the fan ON and also place a blocking diode to make sure the power comes from the solar panel and not the 12V battery.

    By my rough estimations this fan (55CFM rating, 1800RPM, 5-blade design, 32dBa, low noise) can move a bit of stale and hot air out of the car when under the scorching sun. More would be better, but in my books this is definitely better than the alternative.


    Last edited: May 26, 2009
  20. psyshack

    psyshack He who posts articles

    One step at a time. :) My main concern is how much the tint would hurt the panel's ability to keep the 12v topped off?

    I'm sure folks here will get PIII's with the panel option. I'm also sure the ins. for such a config'ed car would be higher seeing the hail we get here.

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