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Old 03-10-2012, 05:22 PM   #23 (permalink)
Ken Fry
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A few thoughts:

On batteries, you will consume about 500 Wh/mile, based on your 16 mpg. A 30kWh LiFePO4 pack would easily fit in your truck, giving you (using 80% of the pack) 48 miles range. LiFePO4 is one of the cheapest long term alternatives for batteries, at about $400/kWh*.

You'll get about 2000 80% cycles (vs 300 for lead acid). If you can find deep cycle lead acid for really cheap, they can be economical, but you'd have to replace them often.

The simplest possible hybrid would be charged at home, run to 20% SOC, then driven on diesel the rest of the way. Electricity is much cheaper than diesel fuel, so you'd be money ahead, if you can deal with amortizing the battery cost.

Based on your existing mpg, you are using about 30,000 watts (40 hp) continuously. Your generator could supply a good portion of that, and at pretty good efficiency, probably. To know whether this smaller but less sophisticated engine (than your Cummins) would provide 30,000 watts more efficiently than the Cummins would require some testing or digging around for BSFC charts for each. Ordinarily you'd expect that the smaller engine, being more heavily loaded would be more efficient. But a lot of small industrial diesels are not all that great, compared to a modern Cummins.

If you search the web, you can probably find a bsfc chart fort he generator engine (or at least a full load fuel consumption rating -- which for the generator is close enough, because you'd be running it at full load.

For the truck, if you can't find a bsfc chart (which will tell you what the consumption per hp-hour is at any load) you can ask around here, or you can scale the chart for a VW TDI and not be too far off. The specific consumption for the TDI at 12 hp is probably not too far from the specific consumption of the Cummins at 40 hp.

If I were going to guess, I'd say the Cummins (at this low load) would consume 330 grams/kWh, and the generator (at its high load) would consume 220.

Of course, you can avoid all the math just by throwing the generator on the back of the truck and trying it out.

* Not knowing the condition of your heart, I did not multiply that out for a 30kWh pack.
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