The SolTech Solar eTrike

A Solar-Human hybrid powered touring trike

The SolTech Solar eTrike (SeT) design is open source technology, meaning the design is non-proprietary, open to modification/development provided no proprietary claims are made and all improvements worth mentioning are open to being tested and copied by others. Those who are DIY all the way can/should just have at it and have fun. Those who are not as DIY will need help from the DIY enabled who may or may not be semi-professionals "in business" to help others. Those who just want to make a buck should fade into the woodwork. Some exchange of money may be involved for services rendered, but ideas and knowledge are to be freely shared.

The starting point for the SeT project are the realizations and evidence detailed in The Limits to Human Power, the summary being "for average humans power assist is needed for practical transportation purposes." E-bikes and e-trikes are hybrid human/electric powered vehicles that provide the needed (by most) assist. What, then, are they? See: What is an E-Bike?. Currently there are those that seek to enable the human-power challenged to ride pedal enabled cycles that function as bicycles, as e-assisted human-powered hybrid cycles. And then there are the e-bike pretenders that are actually e-motorcycle wannabes trying to use bicycle technology to avoid licensing, registration, insurance, and other issues while hoping to use the bicycle transportation infrastructure when they feel like it until they are banned. Low-power vehicles should not be confused with mid-power ones (see: A Guide to Low-Power Cycle Tech and Cycling Power and Speed). Aside from going green by questioning the need for speed, there are health and safety issues to consider (see: Cycling Health and Safety).

If e-bikes and e-trikes are to be car alternatives (see: Car2), then the idea, the promise, the potential of this technology-of-enough needs to be reduced to practice. The SeT is one offering to consider. All options are to be considered and SolTech is willing to link to other offerings. As a starting point, consider SolTech's SeT.

The SolTech SeT Offering

In so far as possible, the SolTech design avoids starting from scratch. Existing components have been sourced and combined to create the desired functionality. Having come to a realization that a recumbent trike would best serve as a platform to build a solar light-weight electric assisted hybrid vehicle (or SeT), the next step was to look at current offerings for one that would serve. The SolTech pick is a Greenspeed Magnum. Other offerings should be considered and may be chosen, but the Magnum, all things considered, was chosen and will be the assumed starting point. Those who judge no offerings to be suitable will have to start by designing and building a trike/bike from the ground up.

Given that for the sub-athletic, e-motor assist is needed at times (and for some, all the time), then are there any complete e-motor systems that would serve? Or is it necessary to procure bits and pieces and fashion a system from available parts? Turns out that of the many offerings, the Falco e-Motor system is state of the bleeding edge art at a reasonable get-what-you-pay-for price, so no need to start from scratch. Many might consider the relentlessly touted and overpriced Bionx system, but it turns out, on close scrutiny, it is not even a close second to the open technology of Falco's premium e-motor system.

For charging without depending on the AC grid, 200 watts of solar panel are enough. If all riding is from a home base, out about and back, then any e-bike could go solar by using a fixed 200 watt solar generator to plug into. If light-weight panels are used (three pounds per 100W), however, they can be mounted on the trike (a bike would be far less stable) and charge the battery when parked and/or power the cycle while under way. For more power while under way, which would allow for long distance off-grid touring, just add more panels as needed and join a Sun Tour America outing.

The DIY Option

For those having a shop, the time, and inclination: (1) Buy a suitable bicycle technology based vehicle. (2) Add e-motor system. (3) Add solar panels and make it all work. All the how-to info needed is detailed below. If all goes well you may spend more time riding the solar e-cycle than working on it.

For those with more money than DIY time and ability, find someone with the time/ability, buy all the components, and have them help you to build a complete system. Or just write a check as ask when delivery can be expected.

SolTech exists to develop technology, but if asked for help will do what can be done. If help is needed and money extremely limited, then one option is to pitch a tent near the SolTech shop (in Tucson, AZ), use the needed tools (theirs), and get such hands-on help as needed when available. In addition to all the money needed to buy all the components, plan to offer a bit to cover utilities and wear/tear on the tools used. And after the first week, donating some money "to the cause" will help pay bills and keep the enthusiastic help coming.

The Cost in US Dollars

Those going with the DIY option can design their own SeT using such of the following components as they wish. Otherwise, to duplicate the SolTech design: procure most of the following as a starting point. Some items optional. To avoid sticker shock on seeing total, retail prices are listed. Shopping around may find better deals. Shipping and tax not included and will likely be approximately equal to amount that could be saved by shopping around.

Another cost is weight. Dragging weight uphill is very energy costly, so less is better. Up to a point it pays to spend more money to get less weight, but with e-motor assist there is no need to be fanatical like some human-power only performance types get over saving a gram. Still: simplify and add more lightness.

Component Overview (detailed with links below)

Greenspeed Magnum trike without extras (new), 42 lbs, 19090 g, $3290

Headrest, $139
Fenders, $99
Accessory post x2, $58
Accessory mount x2, $50
Grab bars, $30
Rear rack, $125

Bike stuff:
Trunk bag, $20
Spoke adjuster, $5
Multi-function tool, $35
Tire repair kit, $15
Air pump, $10
Lubricant, $10
Lock tight, $5
Spare parts, $50

Pannier for camping/touring gear, $70

Tent, $75
Sleeping bag, $100
Biomass woodgas stove, $100
Kelly Kettle Camp Stove, $105
Quality air mat, $100
Helmet, $35
Visor (cap), $5
Pepper spray, $10
Lights, $45
Mirrors, $30
Safety flag on pole, $15
Tow harness, $25
Lights, fixed mount, $40
Wheel lights, $15
Horn, $40
Lock chains, $50
Motion detector alarm, $6
Reflective Yield Symbol, $10
Bottom Bracket Tool, $20
Bicycle tool kit, $50

Cargo trailer (detachable trunk), 27.2 lbs, 12360 g, $190

Fairing, Windwrap WGX, 4 lbs, 1600 g, $574

Sun cover, $75
Body sock, $375

Falco e-Motor, vertical drop out (pick one):
250W, 9.9 lbs, 4500 g, $595
350W, 9.9 lbs, 4500 g, $695
500W (recommended), 9.9 lbs, 4500 g, $795
750W, 13 lbs, 6000 g, $995
1000W, 16.5 lbs, 7500 g, $1195
1500W, 16.5 lbs, 7500 g, $1395
Falco e-Motor add-ons:
Freewheel adapter (included with motor?), $20
Freewheel, 9 sp, $49
20 inch rim, spoked to motor, $98
Crank sensor, $20
Half-twist throttle, $20
Wireless control console with +/- button, charger, cable, $49 with motor or $148 as replacement.
Console mount, Topeak Bar Extender, $15
Ant+ USB stick programmer, $49
Axle nut x2 (included?), $14
Torque arm x1, $20
Torque bar x2, $14
Waterproof battery connectors, $40
4-Pin Round Connector Cable Set, $19
Heart rate Ant+ wireless monitor, $49
Falco lithium ion battery, (pick one or, as Falco is open technology, other batteries will work):

48V Rear rack mount 11.6Ah 556Wh, $995
36V Bottle mount 9Ah 324Wh, $545
36V Bottle mount 11.6Ah 417Wh, $695
36V Rear rack mount 11.6Ah 417Wh, $695
48V AC battery charger, $99
36V AC battery charger, $50


AllCell Naked batteries (needs Falco's Delphi connector added and replaced power out wires with 10 AWG):

48V Naked 13Ah with charger, bag, 650Wh, 8.1 lbs, 3680 g, $846
48V Naked 20Ah with charger, bag, 1000Wh, 12.5 lbs, 5680 g, $1216
Holder strap, $20

Solar 200W 24V module, 42.9 inches x 42.6 inches:

100 watt light-weight monocrystalline bendable solar panel, 3 lbs, 1370 g, x2, $440
Frame, $150
support rods, $50
Genasun custom Li MPPT solar charge controller, $320
Each additional 200W 24V module, $970
48V DC to 12V DC converter, $25
12V socket, $8
USB socket, $18
Connector wiring, $20

Trike stand, $50

DIY tools, $0 if you have them, more if you don't

Drill press, $80
Band saw, $375
Dremel, $160
Soldering set, $50
Bike repair and maintenance book, $30
Hand tools, $365

One to three months full-time DIY labor, $0 (or maybe add $5,000 if you just want it delivered)

Total component/stuff cost: $10,000
Total tools, $0 to $1000
Total labor, $0 to $5000

The SeT Competition

All SeT designs, being open technology, co-evolve and so there is not a zero-sum game with one winner as is the hoped for outcome with competing proprietary products. Open technology designs will fertilize one another and variations may thrive to fill different niches according to their merit. But SeT does have competition in the form of alternative design concepts. Cars are alternative to e-cycles. So the average e-cycle could be compared to the average car. SeT is not an average e-cycle offering and should not be compared to average e-bikes much less to low-end Walley World $450 specials. A SeT will be new as there are no used ones. So a SeT will cost more than a used car. A SeT is a low-volume high-end design that pushes the outer edge of what might be called the "Technology of Enough" as distinct from the "Technology of More" as applied to transportation needs (as distinct from wants).

A SeT, then, should be compared to a high-end automotive offering. The SolTech SeT's competition, then, would be something like the Hennessey Venom GT. Both are pushing the high-end of functionality, but functionality as alternatively defined. One technology is the end of a line of inquiry asking "what technology is enough to meet human transportation needs, including long distance travel?" The other asks "what are the technological limits in terms of more power and speed that humans can be conditioned to want and pay for?"

Ask a different question, get a different answer:


Power and Speed vs Getting There Fast Enough
  Hennessey Venom GT SolTech SeT
US dollar cost: $1,250,000 $12,500
Curb weight: 2,743 lb (1,244 kg) 88 lb (40 kg)
Power: 1244 hp (927,650 watts) 0.67 hp (500 watts)
Energy source: fossil solar/human
Speed: 270 mph (435 km/h) 20 mph (32 km/h)
Efficiency: 15.9 MPG 1,670 MPGe
Wh/mile: 2,200 Wh/mi 20 Wh/mi
Seating for: 2 1

So the venomous Hennessey GT costs 100x more, weighs 30x more, uses 1800x more power, yet is only 13x faster (actually closer to 10x faster as 20 mph is top speed by choice only as top illegal speed could be well over 27 mph), is 110x less efficient, but it has room for a hot date. The technology is comparable, but the design concepts are not compatible. They are different. The difference boils down to a choice between a 'Culture of MORE!!!!!' fuelled by exponential competitive growth lubricated by advertising, and a 'Culture of Enough' that is sustainable. Choose wisely.

Since a SeT, unlike a high-end sport car, includes everything needed for long-term touring, perhaps it would best be compared to a high-end RV. A top of the line Winnebago ($365K), with all the stuff you might fill it up with and tow behind it could easily exceed $500,000, meaning some actually spend that much to go slumming with the RV crowd. Compared to a Hennessey, a Winnebago seems cheap at twice the price—just not as fast.

Solar bicycles exist and the first 50 buyers can have the Maxun One for $127,000. Not suitable for touring, but if you get what you pay for you can own a future museum piece (in the Museum of Questionable Design).

How to Make a SeT

Start with a trike. I got my Magnum used for $2600. The first time out rain turned into hail. The possibility of weather exclosure arose and a Windwrap fairing that could be covered to also fend off the summer sun was added. Some accessories are needed but are not included with the trike or motor to allow for choices, which is as it should be. Just expect to spend more than the base price.

I don't use the headrest, but my wife thinks it is essential. Fenders are not needed, at least most of the time, so are optional. The king pin posts the fenders mount to are needed if mirrors are to be mounted on the trike instead of using a helmet mirror. So choices and more choices, some obvious and others not, and plenty of minutia. But let's focus on the how-to stuff that has to be done and how to do it. Some details are better shown than spoken of, so scrutinize the photos as needed (yet to be added).

The Magnum was already made and I made only a few tweaks. I ride off pavement and slopes can be steep, so low gear was not low enough. I human-powered the Magnum for over six months before adding e-motor assist. I replaced the 30 tooth chain ring with a 24 and when the Falco motor was added, I used a 11-34 freewheel to replace the 9-32 cassette. The motor doesn't need or use that low a gearing, but I want to be able to human-power my way anywhere if need be. Otherwise, it was all good if you like red or blue. Otherwise Utah Trikes will paint it your color, or you can strip it down to the frame and DIY.

Adding the motor involved adding a tire and tube to the rim and spoked motor from Falco. I kept the original wheel in case I ever want to restore it, and put a slightly wider Schwalbe Big Apple 2.15 on the motor wheel to see how it worked. It worked, but stock is 2.00 and would have been fine to use. A little filing of one drop out was needed. I installed two of the torque bars, which may be enough, but I also put a torque arm on the drive side, leaving room on the other side for a trailer hitch, and had to get a longer screw to fasten the torque arm to the fender mount. In low gear the chain was slightly closer to the rear fender and touched it while riding in low gear which made a noise. I ground away a bit of the fender to create more clearance.

The Falco has a console but doesn't need one. Default settings allow the torque sensor built into the motor to sense peddling and assist will be added. A throttle is not even required. Because of the bar-end shifters, adding a throttle was a challenge. No place for a thumb throttle. I added a half twist throttle by removing the rear shifter and foam grip. The half throttle went on but the shifter cable had to be rerouted. I drilled a hole above the throttle and another where the steering bar curves to put the cable through the throttle. The foam grip was cut and put back over the cable and the shifter reassembled.

I also installed a crank sensor. This was not a straightforward install. A special tool is needed to remove the bottom bracket nut. The sensor bracket goes between it and the frame. The metal bracket the sensor is attached to makes it stick out way too far. I hammered on it to bend it at the frame, removed it, and hammered it on an anvil to remove the right angle bend. The part the sensor attaches to has to be bent to be vertical. This part had to be put on and off many times to get it right, but it can be bent to work. The other piece, the magnetic ring that sticks on the small chainring, had to be drilled out to a 2 inch hole using a drill press and Dremeled to clean it up so that it clears the bottom bracket and the sensor bracket. Although the disk sticks magnetically to the chainring, I centered it and added a few spots of Goop to keep it centered. To connect the crank sensor and throttle to the motor requires an extra 4-pin cable set and a Y cable that came with the crank sensor but the product description does not mention it. So there is a 4-pin connector of right length coming out of the motor. The Y connector plugs into it, and the throttle and crank sensor plugs into the Y connector.

A 6-pin connector comes out of the motor, is longer than it should be, and plugs into the wireless module for the console which has a short cable. To make removing the rear wheel easier, the 6-pin cable should be shortened and the module cable lengthened. I used a hose clamp covered with heat shrink tubing to hold the wire bundle from the motor. A zip tie could be used, but would have to be cut and replaced any time a flat was fixed or wheel removed. Otherwise zip ties were used. The wireless module box was fastened on the frame just behind the joint where the frame folds.

I went with 48V batteries not because of a need for speed, but for higher torque should the need arise. Throttles have their use and need not be twisted until they don't turn any more. The Delphi power plug cable for the motor was on the short side as was the cable from the battery. To install the battery I had to lengthen to battery cable. This was done by adding a custom Y power cable connector that allows two batteries to be used in parallel. I have two 13 Ah batteries and can use both should a big mountain get in my way.

Mounting the console and assist/regen plus/minus button required using a third-party accessory mount that forms a tee. It was clamped to the front derailer shifter. A metal rod was covered to allow the button to be mounted on. This involved using a section of 3/4 inch dowel, drilling a hole down the middle the size of the rod, then cutting it in half. The tee part was used to mount the console. It is intended to be zip tied to fasten the mount, but the curve does not match the accessory mount so I Goop glued it on to form a custom gasket, then added the zip ties for extra holding power. The brake handle was lowered as only three fingers fit. My index goes on top of the accessory mount and touches the plus/minus buttons. It is also used for shifting. The housing for the accessory mount was squarish so I ground it round for the comfort of my index finger. The other hand does the throttle if needed and the set up is all good.

Mounting the battery or batteries can be done by putting them in a bag with carry strap and using the strap to suspend them from the back of the seat. I ended up making custom battery holders, however, from 2 inch straps and side opening buckles to attach them to the seat. Easy off and on, room for two, no direct sun, not obvious, and good air cooling. There is room for two 20 Ah naked AllCells should the need exist. The Falco system install was not an easy DIY process, more of a prepared dealer install. Programming the Flaco is also an involved process. The good news being that it is an open system and can be done, tweaked to perfection, without hacking it (unlike Bionx).

The last big add-on was the solar modules. If travel is from home, out and about, then back, a fixed solar power generator works, but for off the grid touring, mounting light-weight panels on the trike is necessary. Mounting them using a rigid aluminium truss is an option, but I like to keep things flexible as they are less likely to break. So I mounted using fiberglass rods and tubes, such as used for tent poles. They are light, absorb vibrations, and give rather than break. I combine two 100W panels using an aluminium frame to make a 24V 200W module, and carry one or two modules supported by fiberglass poles as needed. If towing a trailer, another one or two can be added to provide up to 800 watts of nominal power. To minimize windage, modules are carried horizontally, so output is always less than the nominal wattage. At a stop, if the horizontal modules provide more power than needed for recharging (180W), then no real need to angle to point directly at the sun.

Significant assist can be provided by the modules alone, and travel without a battery is doable. The battery, however, provides assist at night, at dusk, and when riding in the shade. Solar charging, which occurs while going downhill, when under human only power, or when output is greater than assist provided allows long distance travel without requiring a huge battery that has to be plugged in to AC overnight to recharge. Adding solar costs more but money is saved by using smaller batteries. If a battery lasts five years, solar panels can last 20 or 30 years and end up costing less than replacing big batteries that would otherwise be needed. The real pay off from going solar is freedom from the plug, a huge plus while touring.

Each module requires a Genasun custom solar lithium battery charge controller. For Falco or AllCell batteries, order controllers having 54.4V charging voltage for 48V batteries and 41.8V for 36V batteries. These controllers are expensive, but they are for "mission critical" applications and solar touring who-knows-where is mission critical. Unlike other MPPT controllers, these want a lower voltage than output, so 24V in, 54.4V or 41.8V out. If amperage is more than needed to charge the battery, it will power the motor. If motor draw exceeds module output, the battery supplies the difference. It is possible to travel most of the day and end up with a full or nearly full battery. Aside from the cost of the system, what's not to like?


Greenspeed Magnum trike and accessories, USA.

Bike stuff:
Trunk bag
Spoke adjuster
Multi-function tool
Tire repair kit
Air pump
Lock tight
Spare parts
Pannier for camping/touring gear
Sleeping bag
Biomass woodgas stove
Kelly Kettle Camp Stove
Quality air mat
Visor (cap)
Pepper spray
Safety flag on pole
Tow harness
Lights, fixed mount
Wheel lights
Lock chains
Motion detector alarm
Reflective Yield Symbol
Bottom Bracket Tool
Bicycle tool kit

Cargo trailer Aluminum 2 Child Bicycle Trailer (detachable trunk)
The quick, easy, and cheap way to go is get a child carrier trailer with 20 inch wheels made of aluminium. Another is to make a trailer starting with two front suspension forks and bolting them together.

Winnetriko Option:
Note: This option approaches the ultimate in flexible exploration options (okay, it doesn't fly, go underwater, or teleport, so not all that close to ultimate). Add wheels to a 50 pound or less stand-up kayak paddleboard and use it as a trailer to support up to 600 watts of solar modules. To explore inland waterways, paddle it and/or use a small electric motor intended to power kayaks. A paddle board could even support a SeT and could be used for crossing waterways. For touring, the ability to explore most any waterway would greatly add to versatility. Along coastlines, you could even go surfing (but leave the SeT on shore). For the Winnetriko option, definitely add one or two geared hub motors to the trailer. Set up camp near a body of water: take the paddleboard out to explore the watery world, and take the SeT out to explore surrounding lands. When you run out of road, including jeep trails, hike. After a week or so, move on to follow the good weather (thy eternal summer shall not fade). In the USA there are over 188 million acres of Nation Forest to explore, not counting 2 million acres of National Monuments and 245 million acres BLM lands. Why own a speck of vacation property, other than to build a house and fill it with stuff you don't need at great expense, when you already have use of millions of acres for the cost of the technology that enables you to have what you need while exploring it? And beyond the borders of every country, there is the planet.

Fairing, Windwrap WGX
Sun cover
Body sock

Falco e-Motor Info
Note: In many countries 250W motors are the largest allowed. In Canada 500W is legal. Only in the USA are larger motors allowed on public roads. 750W is legal everywhere in USA, while some states allow larger motors. 750W should be considered by obese riders with low human-power output planning to cycle in areas having steep slopes. The 250W to 500W motors are the same motor, just limited as needed to meet local legal requirements. To pull hills, more than 250 watts may be required, so 500 watts is recommended for most USA and Canadian residents. For extra hill climbing power that may be needed pulling a trailer, consider adding one or even two 500W geared hub motors to the trailer and only use while climbing. The direct drive motor, then, can be used for regenerative braking going downhill. This would allow up to 1500 watts total power for climbing while, unlike a mid-drive system, retaining regenerative braking ability.

Falco e-Motor Store
Note: When ordering motor, add rim and spokes, and they will come laced onto motor for you. Add freewheel, crank sensor, wireless control console, and Ant+ USB stick to allow programming. Although two torque bars (washers) may be enough, I also added a torque arm. Waterproof battery connectors x2 if you wire for two batteries or use a non-Falco battery. 4-Pin Round Connector Cable Set is required to add crank sensor. Heart rate Ant+ wireless monitor allows you to monitor the main power source, your human power output. If heart rate low, you're slacking and may consider stepping it up.
Console mount, The Topeak Bar Extender, for mounting console.
Falco lithium ion battery:
Note: Falco batteries come with connectors to fit motor and charger. They are plug and play. You can use other batteries but will have to rewire. I got a Naked 13Ah AllCell battery made for a different e-bike and had to open it up and solder new power out wires to the BMS to replace the sub-standard wiring and buy Delphi plugs. Falco batteries will need the wire lengthened, but that is a relatively easy matter of splicing in a length of 10 AWG wire.
For touring favor 48V over 36V. Although 48V systems are usually promoted for extra speed, they also provide extra torque for hill climbing, and for touring, that is a plus.

AllCell Naked batteries (needs Falco's Delphi connector added and I replaced power out wires with 10 AWG):
48V Naked 13Ah with charger, bag
48V Naked 20Ah with charger, bag
Holder strap for battery

Solar 200W 24V module requires:
100 watt light-weight monocrystalline bendable solar panels from Renogy
Frame/support rods
Genasun custom Li MPPT solar charge controller
48V DC to 12V DC converter 10A 120W
12 Volt Dash Socket
USB and 12V DC Socket
Connector wiring

Trike stand

DIY tools:
Drill press
Band saw
Soldering set
Hand tools


The Low-Cost SeT

Some would have to pinch a lot of pennies to afford the above high-end touring SeT. For the disabled living on SSD or SSI, touring may not be an option. We all age and with enough aging we all become disabled to varying degrees and will need e-motor assist and a trike to remain upright. At some point even Lance Armstrong would need an e-trike to keep on biking.

Trikes intended to enable the elderly to keep on biking are many, have been around a long time, and can be found cheap on Craig's List or at thrift shops/estate sales. Add a geared or direct drive hub motor to replace the front wheel, or add a geared hub motor to a bicycle trailer used for hauling children, which are also available used and cheap. Put two 35Ah AGM scooter batteries, about 50 lbs, in the trailer and still have plenty of room for groceries. Wire batteries in series for 24V, and use to power the 250W to 500W hub motor. Again, not so good for cross continent touring, but it would get you around. Add 100 watts of solar panels to the trailer with cheap solar controller, and if not used all the live long day, it will get you out and about as needed.

There are complete e-trikes for about $1200 and up, just add a reasonably good trailer (under $200) and solar for about $200 more. Or get the trike you want, new or used, the trailer you want, new or used, and put an e-motor kit (about $800) on it, then add solar. .

If in a hurry or can't buy used, consider:

Trike: A delta (one stearing wheel in front) upright as recumbents are not common nor cheap. For short trips, sitting on a well padded post works fine. An alternative, if you have a bike but need more stability, is to add 16 inch side wheels to the back wheel (Stabilizer Wheel Kit for about $190) of the bike you have, know, and used to love. A new trike will cost about $250 and up. Buying a complete e-trike includes a trike of someone elses choice which means you better like what you get. By adding batteries and a motor kit, you pick the trike, but you have to figure out how to motorize it. A reasonably good e-motor front-wheel hub motor kit is not something you'll likely find used, and will be about $800 without the battery.

Batteries: In thinking cheap, think lead acid battery (aka brick), but think reasonably good AGM battery. A purpose made 24-Volt Bicycle Battery Pack costs about $120 for 10 amp-hours (Ah). Just as when buying solar panels you want to think in terms of cost per watt, when buying batteries think cost per Ah, so, for the $120 pack, $12/Ah. For a heavy rider with a heavy trike powered by heavy batteries, 10 Ah is minimal. Since heavy is cheap, perhaps heavier is cheaper. Two 12V 35 Ah sealed maintenance-free batteries cost about $130, or $3.72 per Ah. Hook them in series for 24V and have over three times the capacity. Since cheap and heavy tend to go together, don't go for ultra-light. 35 Ah at 24V will take you places. For about $120 you can get three 12 Ah batteries at 36V hooked together used for mobility scooters which comes to $10/Ah. The 35 Ah batteries are best buys. Three for $195 at 36V and 35 Ah would really take you places for $5.70/Ah.

Motor: For cheap, a 24V motor kit with a 26 inch front wheel can be had for about $270. If you need a 24 inch wheel, a 24V motor kit costs about $320. You can spend a lot more for an e-motor kit. If three 12V batteries are used, then a 36V system allows more choices as 36V is the most common voltage e-bikes are run on, but will cost a bit more. For reasonably good, think 36V and $600 for a kit.

Solar: By putting 45 to 70 lbs of batteries on a trailer, the trike by itself could be used unpowered for short trips or carry a small battery for medium trips, and the trailer could be hooked up to go get groceries or to go for a long ride and do the heavy lifting. To charge the batteries you could just get a $30 24V charger and plug in to AC, or put some solar panels to the top of the trailer. No need for a separate fixed base solar generator to plug into if you have a trailer. Two 50W Watt 12V Solar Panels in series costs about $180. Add a 24V solar charge controller for $10, bungee cord the panels to the top of the trailer, and you have a cheap SeT.

So total cost for a 24V e-trike comes to $250 for a new trike, $200 for batteries and cheap inefficient charge controller, then $270 for a motor kit, or $720 minimally, plus DIY time trying to put it all together and make it work. Add a $200 trailer and $200 for solar charging, add a bit for wire and whatnot, and $1200 is minimal. Easier is to get a $1200 e-trike, a much better system, add batteries, a trailer, and solar panels for $600 and you have a $1800 SeT. If at all DIY challenged, pinch more pennies and think $1800 and up. Even if you can put together a bunch of bits and pieces and make them work, maybe you have other things to do.

For most, get a ready made e-trike ($1200), three 12V 35 Ah sealed maintenance-free batteries for a 36V 35 Ah pack($195) and then a reasonably good trailer ($190) to load down with the batteries and allow a place to mount panels. The nominal battery capacity is 35 Ah, far more than most e-bike batteries, but to make the batteries last, they don't like being discharged more than 50%, so they provide about 18 Ah which is still more than most, but not more than will likely be used, so 70 lbs of battery on a trailer may seem excessive, and is close to it, but it's the price you pay for cheap but functional.

Adding panels to a trike can be challenging, but for a decent 36V 500W e-trike, the easy option is to get a 36V 90 watt system with MPPT solar controller designed for a golf cart ($420) and put it on top of the trailer using bungee cords. The total comes to a bit over $2000, which is more than minimal, but it will be more likely to work, and for a little more, you'll get a lot more. Not good enough for touring the planet, but good enough for getting around town without being disabled by the ongoing expense of a car. A $2000 SeT would require new batteries every few years, but otherwise it would be cheap.


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