Back to the Future - Hydrogen Power Motor Coach

Note: This is just a scratch pad I am using to clean up the RV of the Future post. If it cleans up good I am planning to publish it.

I live in a motor home. Once you discover that 75.3% of the stuff stored in your garage is never going to be used, more than half the clothes in your closet don't fit and that the few useful things you have stored only mean work you are not really serious about under taking, it is easy to down size to a motor home. Everyone's idea of the perfect motor home is not the same.

Determining the perfect motor home boils down to a cost versus inconvenience ratio. The cheaper you are the more inconvenience you can accept. I am a middle of the road personality with a cheaper than normal reality. So I am going to describe the logic I use determining my concept of the RV of the Future.

A little background first. Motor homes are generally big. A 30 to 36 foot long RV is not uncommon, like a fairly large bus. Unlike a bus, RV generally do not get driven very often or very far over their life. So the power plant for motoring along the road, a large diesel or gas engine is pretty much a waste. Since the drive motor is very large, a smaller generator motor is used since it is more efficient for producing electrical power than the monstrous main engine. Hot water can be furnished by either the main motor or the generator motor, but generally a separate propane hot water heater is used because keeping the fuel powered motors running is expensive both in fuel and in maintenance costs. Combining all these functions would seem to be efficient, but how? Fuel cells are how!

A motor home needs a motor. For this hydrogen version we are going with the Azure Dynamics AC90 Electric traction drive and controller. I toyed with in-wheel electric motors, but they were limited on torque. The AC90 has enough torque with proper gearing to handle the estimated 12,000 pounds (approximately 6,000 Kg) that the complete vehicle will weigh. Thanks to Azure Dynamics design for hybrid trucks and buses, this saves me a lot of time calculating all the performance variables. This big beast is not cheap, suggested retail for the motor and required controller is right at $11,000 USD.

While they are not a perfect match, a pair of Ballard Power FC Velocity 9SSL fuel cells which can provided 40kW of power for a total cost of $20,000 USD, are our power plant both for the motor and normal electrical needs in the motor home.

I don't want to get into too much detail so I am just going to mention that power inverters for house electric, cooling systems for the fuels cells, basic energy management system and assorted electrical stuff will be needed, adding another $9,000 USD to the combined power plant cost using reasonable quality components. Remember, that is just an estimate, you can throw as much money at all these things that you want. That will give us roughly $1000 USD per kW initial cost. In the normal world that is about $20,000 USD more than the standard gas power plant of typical motor home. Diesel pusher motor homes are about mid-range between the gas and hydrogen options.

The fuel cell option does a lot of neat things though. It not only replaces the main engine, it also replaces the generator, hot water heater and has enough electrical power to use less expensive and more reliable appliances.

Unlike most hydrogen or electric vehicles, the motor home fuel cell option reduces the overall weight of the vehicle by about 500 pounds. That is mainly because it replaces the generator and the main motor.

All motor homes have a battery bank for house use and starting. With the fuel cell version we are just going to upgrade the batteries. While lithium ion batteries are great option, specialized lead acid batteries have a long life, 10 years, which is nice for this application. These will take back all of that weight savings since they have a lower power density than the Lithium Ion batteries. The longer warranty, lower cost and ease of maintenance make the good old lead acid batteries my choice. At over $3000 for a set of three, that sounds like a lot, but $300 a year replacing used batteries is not uncommon for RV users.

If you just want to be green and impress your friends, this basic FCRV (Fuel Cell Recreational Vehicle) would do the job. Personally, I am cheap. So a home hydrogen refilling station using solar panels to make my own fuel is a must.

The home hydrogen refilling station and solar panels to provide juice needed to give me the best bang for the buck. There are a variety of manufacturers providing 3 to 5 Kg per day home hydrogen refilling systems for about $2300 US. A solar Photovoltaic array on the roof of the RV costs about $1 a watt using Nanosolar's panels. A 25 foot by 8 foot (approximately 18 meters squared)array would produce approximately 2 kw per hour during daylight hours (10kw per day average). With current fuel prices, these systems pay for themselves in a year or two depending our your RV use habits. The battery bank will hold about 16kW worth of electric, so the solar panels will top off the batteries during the day plus offset daytime electric use. At night the batteries take over to provide uninterrupted power. If there is really heavy electrical demand, the fuel cells will kick in as needed.

It makes no sense to use hydrogen to make hydrogen, that is a losing situation. So the inverter running the home refilling station will have to be smart enough not to drain the batteries or run when the fuel cells are charging the batteries. That is a pretty simple job for the energy management system. Storage of hydrogen is not much of a problem for motor homes. The center line of the chassis offers plenty of space to install 3000 psi tank systems. While higher pressure systems are available, just matching the pressure range of the home hydrogen refilling system is all that is needed. High Density PolyEthylene (HDPE) lined steel or aluminum tanks are a less expensive option to the carbon fiber tanks being developed. Hydrogen is an energetic little atom, so the HDPE lining is recommended to contain those little rascals and prevent long term damage to the tanks.

About 30 kilograms of hydrogen storage would give the FCRV a similar range as a standard 30 gallon fuel tank. The hydrogen tanks require over 4 times the volume for the same energy, but that is no big deal for a 30 to 36 foot RV. The density of hydrogen at 3000 psi is close to 1 pound per cubic foot. Converting to metric that is about 16 Kg per cubic meter. 2 cubic meters which is about 70 cubic feet, may be a lot of space for a car or truck, but in the FCRV that is only 6 ft by 12 of center line chassis space. Not that hard for a RV being built chassis up. There is still plenty of room for fresh, black and gray water tanks plus reasonable basement storage.

To maximize the hydrogen production, electrical use needs to be decreased with higher efficiency. RV's are not very well insulated. Adding insulating window coverings, reducing window area and adding a little insulation to the shell of the RV will do wonders. The typical RV has two main air conditioning systems normally rated for 13,000 BTU. Only one at a time is used most often. The attention to insulation will reduce the required A/C capacity. So two smaller 8,000 BTU units capable of running at the same time if needed, will reduce the overall energy required for space conditioning. AT 8,000 BTU, approximately 900 watts with a duty cycle of 50%, air conditioning would require 4.5 KW per day in cooling season. A refrigerator/freezer with ice maker is approximately 1KW per day with lighting and electronics averaging less than 1 KW per day. Properly designed, during the worst energy usage season, an extra 3.5 Kw per day would available for hydrogen electrolysis and battery trickle charging. Luckily, peak cooling demand time is also peak solar time. So if that second A/C is needed, it won't over tax the energy system.

Getting back to the drive system, the power provided by the FCV 9SSL cells is not enough for acceleration and climbing grades. The batteries will have to kick in to provide performance when needed. The capacity of the batteries can provide about 20 minutes of boost power. That is enough for most situations. It will require a little more attention to driving economy, limited to actually doing the speed limit most of the time. The estimated top speed of the loaded FCRV is about 80 miles per hour. Normal acceleration would be a little over 5 meters per second giving you a 0 - 60 mph time in the high teens to low twenties of seconds. That is respectable for a big motor home.

The life span of the fuel cells is a big question for most people. The Ballard Power product has a life listed at 8,000 to 12,000 hours. That is based on the efficiency of the heart of the fuel cell, the Proton Exchange Membrane (PEM). This is a maintenance issue. Changing the PEM every 10,000 hrs should cost in the $1,500 to $2,000 range every five years. That of course depends on how much driving time the FCRV gets on the average. Most RV's never get driven more than 20,000 miles. So the PEM maintenance may only be needed every ten years. Do note that the FCV 9SSL is made for use in fork lifts. Before Ballard Power signs off on this design, they would have to re-evaluate what warranty they may offer if they approve the alternate use. They do make a bus module with a cost range of $300,000 to $600,000 USD. That is way beyond the price range of all but the wealthiest RV enthusiasts. They are working on automotive fuel cells that would be more compatible price wise.

Based on my own RV, monthly electric and propane cost are around $150 USD. So over five years, that is $9,000 USD. If you factor in the lower lot rental between a full hookup and dry campsite, about $200 a month average, that is another $12,000 over five years. So if you live year round in your motor home, the fuel cell system comes close to paying for itself in five years. Back country campers can really use the self contained benefits of the FCRV. Also, responders to natural disasters could really use the FCRV for their jobs where power and lodging are not readily available.

It may be a little early to jump into a FCRV, but the overall cost is getting more inline if you consider all the advantages. Ballard Power may also consider diversifying the use of their FCV9SSL line. Not only can it be a valid option for automotive, it would be a great option for replacing the expensive battery packs in the new electric vehicles.

This PDF provided by the department of energy details the validation of hydrogen fuel cell vehicles. While future cost versus performance of the fuel cells will decrease, Ballard's material handling fuel cells used by Plug Power may have a jump on the competition. Time will tell.