WA8LMF Mirror of WB4APR Website - 21 July 2008 APRS Solar PHEV


Bob Bruninga, WB4APR

My Solar Plug-In-Hybrid-Electric Vehicle. . . . Power to go.

See video at the Wash DC IEEE PHEV Convention

See the Solar Prius PHEV power point presentation.

SOLAR-PHEV: . The solar panels can provide as much as 215 peak Watts of power good for about 1.7 KWh of free electricity when parked for 8 hours in the Arizona sun. . Unfortunately, only 0.8 KWh or less is available from the average Maryland Sun. . Where you live makes a difference as can be seen in this plot of annual solar flux:

But with 200 watts of solar panels, this equates to about 1 mile of free all-electric range for each hour of full direct sun (about 200 W-Hrs).

PURPOSE - Power-to-GO: . The purpose of this conversion is to put solar panels where they can be more useful than stuck on the roof of my house. As an augmentation to vehicle fuel economy, they may only gain 10 to 20% in MPG. But they do help and they do provide a minimilistic ability to run on no gas and no plug-in electricity for very short trips in the case of extreme shortages. . Like many other solar energy projects or PHEV conversions for hybrids, this investment has an indeterminate cost-effective break-even point, because it solely depends on how much you need power when you are not plugged into the grid. Solar Power portability gives peace-of-mind where there is no gas or plug-in electricity available. . See more about Prius Field-Day Power.

More photos of the final installation after 6 months: Roof Rear, Front, Driver corner, Side and Hood,

Payback: . If you can take solar power where you need it, then its value can be far greater than 10 cents per KWH. . And if you need power in the field, and don't have any, then solar power is cheap at any price. . Just consuming it in the Prius is an equivalent payback of 25 cents per KWH which is better than the 10 cents at home. The incentive for this conversion comes from the simple economics of solar power:

COST: . The cost of this conversion is about $2500 for the solar panels and $500 for the optional added battery capacity. The intent of this S-PHEV is not to try to run the Prius on all electric to improve MPG to over 100 as most PHEV conversions promise, because the economic pay-off approaches the point of diminishing returns. The cost savings of simply improving fuel economy from 50 MPG to 100 MPG is only going to save the driver of a 15,000 mile per year car, about $450 per year for $3 gas. . For expensive conversions, it is hard to justify a break-even point.

PHEV BATTERY: . The primary purpose of the PHEV battery in this conversion is not so much to guarantee longer range on electric alone, but to have a place to stuff the solar power without any risk of overcharging or over cycling the original Toyota HV battery. . The photo at right shows my added 9 Amp-Hour cells in the wheel well prior to being wired together in series. My PHEV algorithm and controller is very simple. It provides current to the Prius when it is running in EV or Stealth mode, but does not waste energy by parallel circulating currents with the OEM battery when not needed.

The discharge controller feeds power into the Prius to extend gas mileage but at a low enough rate (half hour) to not excite the Prius computers. Also, the controller will not waste energy from the OEM battery back into the PHEV battery. The only time the PHEV battery is charged is during regenetive braking, from solar power, or from over night plug in.

Bottom line: . If you are going to invest in solar power anyway, you may as well put it on your car where you can use it to offset the cost of gas and where you can take it with you wherever you go or might need it. Field events, emergencies, or just watching the kids soccer match (with the Prius electric A/C)... This array has been designed to just fit the size and shape of the Prius while having a good voltage capacity for easy charging.

ANALOG INSTRUMENTATION: . The retro analog instrument panel shown to the right keeps me well informed of not only the power going into and out of the HV battery and solar panels, but also the economy of the gas engine via a tach and vacuum gauge. . The left meter is 150 to 300 volts and the right one is -50 to 0 to +100 amps. . (click for full size image). . This simple instrument panel is much easier to use than having to use a laptop for such displays. . The APRS ham radio below the dash is not related to this conversion but with an attached GPS provides tactical situational awareness of the positions, status and messages of similarly equipped mobiles in the surrounding area. The APRS network is linked to the internet and so you can always see where I am. Or using APRS, you can see where all the other Ham radio operators are with their bybrids. (this idea to use a special ICON for hybrids only began on 3 June, so it will take a while to catch on.).. Bob

IEEE Conference on PHEV Technology, Washington DC, 19 Sep 2007: [IEEE conference link]

My Do-it-yourself Solar PHEV was invited to this meeting in contrast to the commercial Plug-In Hybrid Conversions that were prominantly on display. We were offered a free $25 parking space. (Mine is the second from left). Only problem was, that no one told the parking lot zombie, and it took us an hour of wrangling to get out of the valet parking lot after it was over!

The other three Prius had 5 KWH or so(?) of added Lithium PHEV batteries costing several thousand dollars? . In contrast, my 2 KWH Lead-Acid batteries only cost about $500, and mine was charging the whole time parked in the sun, while they spent the first hour trying to find a place to plug in. Well, actually, the other Prius just plugged into 115 convenience outlets, but the E-BOX to my right was all electric and they had to find a 240 volt 50 amp outlet to plug in. They drove 100+ miles from Deleware on all-electric and the box was thirsty.

As I was driving away, a photographer came over and did a quick interview. . (Frame at right). Although he completely missunderstood the 80% State of Charge, he did capture some of the gyst of what I was saying See his video.

VEHICLE-TO-GRID: . Look carefully over the shoulder of the T-shirt guy and you will see the portable electric meter they take with them. Because, you see, the Ebox can both SOURCE and SINK energy. This demonstrates the Vehicle-To-Grid technology which has some real interesting promises for meeting peak power demand.... That is, if 75% of the Vehicles in the USA were PHEV's, then the installed instantaneous POWER capacity in those 150 million cars sitting in their parking lots all over the USA, represent FIVE TIMES the entire Electric Generating Capacity of all USA Generating plants combined!

Yet charging those 150 million cars overnight only takes 7% off the power grid at night when there is excess capacity. They estimate if we can figure out how to signal demand and pricing info to those 150 million cars, then the utilities would be willing to pay as much as $2k to $4k per car over the life of the car, to take back a few % during peak demand the next day... (I hope I got the facts right?)

ALTERNATIVE ENERGY: We can do it. Just reducing our oil demand by 25% will prevent $200 MILLION per day from going to the destabilization of the Middle East. That keeps a lot of money out of the hands of the terrorists. Shown to right is my daughter's high school environmental project using a solar panel and a car battery to run her room off-grid. In the tree you could also see my ladder going up to where I hope to install my 400W wind turbine for backup emergency power and a small contribution to energy self sufficiency.

PRIUS #2: . That was so much fun, I am now starting to consider Prius #2. . It needs some rear-end work. . But to my surprise, the Code of Maryland does allow a wood 2x6 to be used as a bumper as long as it is made from hard wood with a 3/16th inch steel re-inforcement.


With a little hammering and some wood, I hope to build a pick-up rear end. The big gain will be replacing the rear hatch with a solid plexiglas contour. This new hatch will give 20% better visibility, eliminate the rear-view blockage caused by the spolier, eliminate the sun-blocking tint, and allow for another 100 watts of solar panels in the bed of the trunk. These solar panels are out of sight for driving, but tilt-up when parked. The up-tilt not only eliminates shading, but can give good sun angle to the south in the winter.

Of course aerodynamics will suffer. But this car is intended as the local drive-around town commute car usually never getting above 50 MPH, not for high speed traveling. And besides starting as a salvage vehicle it only cost 1/3rd the going rate.

TOWING: Towing the Prius on anything other than front wheels off the ground is not recommended. However, for moving my projects around the neighborhood and back, I made a small tow bar that configures to the front bumper hook and allows me to tow the Prius as shown below:

The parallel angle irons extend beyond the pivot point to maintain solid contact with the full width of the tow hook coming out of the bumper. This assures that there is little left to right movement so that the towed car will track the towing car. See the side view and a closer view. You can see that the bolt is tightly compressed to an internal spacer and 4 washers to keep the tight spacing for proper tracking.

PARKING PAWL: and then you have to put the towed Prius into Neutral. Which of course is impossible to do unless you can get it to READY state (and if you can do that, why do you need to tow it?). Anyway, get into neutral, set the parking brake and then remove the fuse under the hood that powers the parking pawl. Its a 30 amp fuse that I think it is labeled PCON MOTOR. You will get the red-triangle of death and check-engine lights, but they will go away (eventually) when you replace the fuse.


Bob Bruninga, WB4APR Naval Academy Satellite Lab

WA8LMF Mirror of WB4APR Website - 21 July 2008