help with power choice

A pretty big one. 3kWh minimum for the round trip, assuming it's flat. 5kWh or more if it's not.

If you can charge completely at work, then this would cut the battery pack size down considerably.

Another thing to consider, is that speed is an extremely important factor. Speed takes much more energy for the same distance, meaning EVs make much more sense running slower. Try running some numbers to figure out exactly what speed you really need (unless of course you have to keep up with traffic).

Distance = rate * time

time = Distance/rate

1.25 hrs = 50/40
1.43 hrs = 50/35, or ~16 minutes longer than 40 mph
1.67 hrs = 50/30, or ~25 minutes longer than 40 mph

Talk to the guys at Thunderstruck motors. They have hands on experience with projects like yours. They have good quality Hi-power brand LIFEPO4 batteries in 30AH and 50AH that they use in motorcycles that give range like you are looking for.

Here is a link to a web page that has a calculator designed for figuring out how much energy (calories) a rider (or motor) will need to under various conditions.

http://www.kreuzotter.de/english/espeed.htm

Here are some example results I punched in;

My bike, 230 lb rider, 100 lb bike, touring tires, 600 watt motor = 24 mph, 20 mile distance, results in a use of about 1900 calories. My bike has 60 volts and 20 amp hour batteries.

Your proposed trike, 230 lb rider, 500 lb bike, touring tires, 5000 watt motor = 50 mph, 50 miles distance, results in the use of about 19,000 calories. That would need about 72 volts and 180 amp hour batteries.

So, to sum up. Your project is possible, even if you don't recharge at work, but if you can charge at work it will cut the battery size in half. Being a trike, it could carry large batteries, so I say go for it!

One final note, thes numbers are calculated using the hands on the handlebars profile, and picking a profile that is much more streamlined, reduces the power and battery requirements drastically. So you might consider some sort of fairing to reduce drag.

Tom

P.S. I am using a linear "guess" for the relationship between calories and volts times amp hours, which I think will work.

Another thing to look at is cost.

Lead is the cheapest way to get portable energy, at least up front. Lithium is the most expensive up front but lasts 2/3 times longer than lead, you also don't need to recharge it after every ride to keep the batteries healthy. Nickle Metal Hydride is a nice compromise, you can get hybrid car used packs for a nice price.