Our Hydrogen Home - Is it Worth it?

An energy self contained home is the dream of many. Living in the islands of the Florida Keys, I know of several islands that have no connection to the main electrical power grid. Some of the home owners of the electrically remote island homes are very wealthy, others not so much. They deal with their power needs differently based on their financially situations. Hmmm, kinda like nations have to.

Alternate energy is a matter of cost and convenience. The less cash you have, the more inconvenience you can deal with. I like to look at the true cost for an energy self contained home (or Recreational Vehicle) every few years to see how things are shaping up. Wind and solar are the main energies chosen by the Island guys with Internal Combustion (ICE) Generators as backup. They all have to have backup generators because, they cannot store enough energy when the wind or sun is working to cover times they need energy. That adds significantly to the cost. Very significantly as fuel costs are over $3.75 a gallon. Fuel was less than a dollar a gallon when most of the island home energy systems were installed.

Because on building height limits, the massive, tall wind turbines are out of the question. This is an island tourist destination after all. Not creating an eyesore is important. Some of the older hydrogen home built in the past decade have nearly a dozen large propane style storage tanks, which are not only potential eyesores, they tend to float away in hurricane flooding. That is an expensive and potentially dangerous problem. The hurricane winds also tend to relocate wind generators.

As you can see, there are issues involved in designing an energy self sufficient tropical home. Even more if that home is to be a sustainable energy self sufficient home.

Learning from the screw ups of others is a lot cheaper than learning through your own screw ups. There is no way to avoid screwing up, but you can endeavor (I like that word)to minimize your screw ups and their magnitude.

Storage of energy is the big problem. Batteries are expensive, require maintenance and can be dangerous. While having some batteries is unavoidable, you want to get the right balance between cost, longevity, maintenance cost and safety. The telephone companies seem to have hit on the best battery storage ideas. They use massive 1.5 volt cells connected in series and parallel to provide the DC power they need. A compromise for residential consumers are large 4 and 6 volt lead acid batteries. Big banks of lithium ion sound great, but cost is prohibitive. Also, do it yourself installation and maintenance can be more dangerous. The 6 volts are cheapest initially, but specialty 4 volt batteries are a better choice. The four volt batteries have a warranted life of ten years and can last longer if properly maintained. Maintenance is pretty easy, just maintain water levels with deionized water and keep the connections clean. Any isolated island home should have three, required for the basic 12 volt systems that are less expensive. The high quality lead acid batteries would store nearly 15 kwh of energy at a cost of about $3000 USD. Medium quality 6 volts would require a bank of six batteries, $1300 USD worth, for about half the kwh and a quarter to about a half of the life expectancy, depending on use and maintenance. The lower capacity of the 6 volt batteries increases the chance of draw downs that limit the life. With batteries you basically get what you pay for, so I would not recommend a bigger bank of the six volts unless you get a killer warranty.

Hydrogen is by far a superior energy storage (battery if you will) medium. Hydrogen, because of cost, has not been used much in the Keys. That is starting to change. Home hydrogen electrolysers have not only started to drop in price, most offer something very nice, pressurized hydrogen. Compressing hydrogen in the past has been a big issue. The newer electrolysers produce decent amounts of hydrogen at a variety of pressures. Ultra high pressure, 5,000 to 10,000 psi, is ideal, but expensive. High pressure, up to 2,900 psi, is more affordable. Hydrogen is a small active atom that tends to want to be free. That puts some interesting, but not too complicated, problems on the table for storage. Soft materials absorb the energy of the hydrogen bouncing around where hard materials tend to get micro fractures fighting with the hydrogen. Luckily, steel or aluminum tanks can be internally coated with high density plastic to have both soft absorption and hard strength. The larger tanks or bottles are rated for 4500 psi which is fine for the 2900 psi electrolyser with some room for extra compression.

There are plenty of hydrogen electrolyser system manufacturers. Most are very proud of their products, meaning they are expensive. There are advantages to the higher cost systems. They are completely self contained with all the bells and whistles for those that just want a working system without the design headaches. HySTAT, has complete systems for off grid power using solar and/or wind if you have the cash. Their systems have a fairly good size foot print. Being self-contained, you have to be able to live with that. Mix and match systems offer more flexibility with of course more headaches, which I am now exploring. The price is pretty frightening too, which sends me into do it yourself mode.

The plumbing of the tanks, since it will take several to store enough hydrogen, will require either more expensive material or more frequent maintenance. Stainless steel, is a fairly soft metal, which is a good trade off between maintenance cost and initial cost. You can go into any dive shop and see air fill storage tanks with manifolds that look like what you would need for home hydrogen storage, the only difference is that it is a good idea to have the tanks lined with plastic.

Lining the tanks with plastic is pretty simple if you have the equipment. A process called rotational molding can coat the inside of the tanks by putting powered plastic inside the bottles then heating the bottles while slowly rotating the bottles in all directions to uniformly melt the plastic, forming a uniform layer inside the bottles. It is a little pricey, but more than doubles the life of the fairly expensive tanks. So this headache is not to hard to cure if you have space for low pressure storage.

You need to first be able to make the hydrogen and then use it. To make the hydrogen you need water, an electrolyser and power. The self-contained, higher price systems use any combination of electrolyser pressure and/or compressors. Every component added is an extra headache. Home hydrogen fueling systems, can reduce some of that headache. Designed to refuel hydrogen vehicles, more forklifts that on the road vehicles right now, they produce hydrogen at the pressure you need, approximately 5000 psi. To avoid warranty issues, the storage system would have to be manually filled.

Honda Motors has a pretty good idea. The Honda Home Energy Station, uses waste heat for home hot water heating and provide backup power. Unfortunately, it generates hydrogen from natural gas. Which is kinda stupid, since fuel cells can run off natural gas to begin with.

Low pressure hydrogen with compression is still an option. Looking back at the the first solar powered home, Mike has 10 1000 gallon propane tanks to store about forty gallons worth of gasoline equivalent hydrogen gas at 200 psi. Living in the country with not many neighbors, Mike can get away with this. Mike also has one hellava expensive system that is like a Rube Goldburg design based on what we need. The electrolyser he has is pretty much what we need though.

Building from scratch, like Dangerous Laboratories, is not for most folks. Cal State University built a hydrogen filling station that has a few good ideas worth looking into. this requires learning that 1 kilogram of hydrogen would occupy 11 cubic meters of space. All the hydrogen generators list production in Nm3/hr, which is Normal cubic meter per hour. Normal meaning Standard Temperature and Pressure (STP). One low pressure hydrogen electrolyser, the M2-EL2500-12.5, produces 0.83 Nm3/hr @ 60 PSI requiring 2500 Watts/hr. That would be 1 kg-H per 13 hours, just under 2 kg-H per day. Since we are planning a 12 volt system, that is a good choice. Production could be doubled by using two or doubling the voltage and using the M2-EL2500-25. At 60 PSI we would need to compress to around 4000 PSI. Hydrogen compressors are a little special. Hydrogen is an energetic molecule in more than one way. Being the tiniest of molecules, it is hard to contain. When it is not contained properly, it tends to cause explosions. We don't want that, so a compressor specifically rated for hydrogen is what we want. Hydropak makes low pressure compressors we need, unfortunately, their main website is in Turkish.

Converting the hydrogen into the power you want has three options; burning like propane, running a motor for a generator etc. or using a fuel cell for conversion to electricity. For the island home, the motor as in running a generator is the easy, cheap way to go. That is fine for a place that is not occupied all the time. The motor for the generator will need oil changes and maintenance just like any gas power motor. Other than aggravation, the generator simplifies things quite a bit. All the basic use for the generator would be for high load things like air conditioning and back up charging of the batteries if there is a high demand. A fairly inexpensive inverter can be used for 120 volt electric with the batteries providing power. Shopping wisely can reduce the demand of 120 volts appliances. This is very similar to most of the island off grid designs, the only difference is storing energy as hydrogen rather than buying more batteries.

Using a hydrogen fuel cell is another option. Ballard Power makes a home hydrogen fuel cell designed for 2Kw backup power system for $2600 USD. Two kw gives you 18 amps at 110 volts AC. Enough for most of the basic stuff. For air conditioning, a little known option is a natural gas drive condensing unit. The Trane Company used to make a condensing unit for air conditioning with a natural gas powered motor driving the compressor. It looks like that design has passed away, but the idea is good for the island home. Here you can just match a hydrogen gas driven generator when there is a need for cooling. Beefing up the fuel cell and inverters is always a possibility if you have the cash.

Ballard also makes a 20Kw fuel cell for $10,000. This is about the lowest cost per kw of any fuel cell on the market thanks to mass production for the materials handling industry. This would require a bit more controls than the other units and better consideration of the DC voltage range of the overall design.

This brings us to solar cells. Since the 12volt system is the standard for most solar residential applications, that is what we would most likely go with, unless we opted for the larger 20 kw fuel cell. In that case matching voltage ranges for the fuel cell and solar panel array makes more sense. This would also require another look at the hydrogen electrolyser input voltage. We only want to make hydrogen from "free" energy, that in this case is the solar panel array. Finally, the amount of hydrogen storage would depend on that decision as well.

Adequate hydrogen storage depends on demand and replenishment rate. Compressed hydrogen makes the space required more tolerable. At 2900 PSI, the space required is a lot less than the 200 PSI Mike used in his video. There are a variety of manufacturers of suitable storage tanks. They do not have the plastic liner, that you would have to arraign on your own at a rotational molding facility. Not lined will do, they just need to be inspected annually and may require replacement in five years or so. All the plumbing should be inspected annually. Being able to buy a ready made system would be great if you have the bucks, but they seem to be going out of business pretty regularly. If you have ever been to a dive shop to get a cylinder refilled, that is the basic system you want. A good compressor that doesn't contaminate breathing air will work and the tank manifold is rated for 4500 psi in most cases.

These 200 bar storage and compression systems are not cheap. You will be looking at $5000 USD easy. Home CNG, Compressed Natural Gas systems will work also. The price is about the same once you add the storage. There are a couple things you need to know now. First, I am not responsible if you blow your silly ass up. This is a do it yourself thing. Second, with reasonable precautions this system will work fine.

The first precaution is remembering that hydrogen is an energetic gas. At some time there will be leakage, you don't want that leakage to build up where it can go boom. A nice open detached shed should be the hydrogen system home. You can screen the shed in and cover it with tasteful looking lathe to make it look like a tiki bar, but don't box it in. Second, think valves, lots of high quality valves. Things break and you need to be able to isolate the broken things. Third, you need a low pressure tank for the electrolyser output which the compressor can then boost to pressure in the storage system.

A fairly good size propane tank can serve as the discharge tank for the low pressure electrolyser. The output pressure of a low pressure electrolyser is about 60 PSI. The volume of this tank just determines how often your expensive boost compressor runs. I would recommend a 100 pound propane tank as a minimum for a small compressor with a hundred gallon propane tank not a bad choice if you have the room. If you use a medium pressure electrolyser up to 200 psi, either of these tanks will be fine. More than that pressure, you can can the compressor and size the storage tanks for the pressure and volume you need. Right now, the low pressure electrolysers are cheap enough to justify the five grand for compressor and higher pressure storage. Remember, that the price is dropping on some of the home refueling systems, so this stage may soon not be needed, other than storage.

The low pressure electrolyser I selected above only makes about 1 kilogram a day on a good day. One kilogram is about 33 kilowatt hours of energy. So if you use the generator only design, you get about 1/3 of that as useful energy or 10 kilowatt hours because of engine efficiency. With a fuel cell you get nearly 2/3 or 20 kilowatt hours out of one kilogram of hydrogen. So unless you are a party hardy energy hog, you really don't need that much storage. Mike in the video had ten 1000 gallon propane tanks at 200 psi that only held 40 kilograms of hydrogen. One of the standard 5 foot tall air cylinders has a volume of about 2700 cubic inches or 1.6 cubic feet which is equal to about 12 gallons. At 3000 psi, the energy density of hydrogen is roughly 1900 watts per gallon, so each tank would hold roughly 20 KWh which is close to 2/3 kilogram of hydrogen. So 10 eight inch round by 55 inch tall cylinders at 2900 psi will hold 200 kwh of gross energy, about 6 kilograms of hydrogen.

1900 watts per gallon at 3000 psi is a good number to remember. That is not a lot of energy per unit volume. Also remember hydrogen likes to leak. The choice of high quality valves and plumbing is important. Lining the tanks with plastic helps reduce leakage, high density plastic or Teflon(r)seals all are important considerations. Ventilation as I said is a must. Hydrogen flashes in concentrations for 4% to 75% by volume. The number of connections with a ten tank storage system is about as much as I would even think about. Any more and larger high pressure tanks are definitely worth the extra money.

Using the 20kwh per tank we can start completing our design. With the generator only system we would get about 6.7 kw hours per tank. On a good sunny day, the cheap electrolyser would come close to refilling the tank. As long as you are not an energy hog, that is not bad. Remember, most cooling is required when you have the most sun. So the solar panels can take up a good deal of the air conditioning slack. With the hybrid system, the 2kwh fuel cell would deliver nearly 12 kwh per tank because of its higher efficiency. Depending on use, the air conditioning dedicated generator drop the kwh per tank towards the 6.7 number. With the more expensive larger fuel cell, you would stay near the 12 kw number. This makes a big difference in the number of tanks needed for storage. With the bigger fuel cell, three or four tanks should be plenty. Six for the hybrid system. These configurations would give you about two low to nearly no solar energy days of backup. Since the generator really doesn't care if it has hydrogen, propane or regular gasoline, the hybrid and stand alone generator system (both can charge the battery back while running) gives you a plenty of backup.

Cheating up to 4500 PSI is an option with the right tank system. That would increase the storage per tank to 31 kwh or very nearly one kilogram per tank. Remember each tank is 12 cubic feet of volume. The higher pressure would increase leakage and decrease the life of the unlined tanks. So the cheating up should only be for a short term occupied mode with the 2900 psi the normal unoccupied storage mode. I will have to double check, but the leakage at 4500 PSI is the squared ratio of the pressure change. So there would be 55% more leakage at the higher pressure. Nominal leakage at 2900 psi is only about 0.05% per day, livable. At the higher pressure, the pump should be the weak leakage link which may require solenoid operated isolation valves to protect the pump when not running. While 55% more of a small number doesn't sound like much, damaging the expensive pump would not be a nice thing.

While I am a big fan of hydrogen only, for the island off grid house, I would go with the hybrid system with either gas or propane as a backup energy source. That being the case, a 4 to 6 kw solar array is all that is required. That will provide enough energy for the electrolyser and battery charging with basic high solar conditions covering most of the needed daily electric, refrigerator and lighting. With expected higher air conditioning use, a larger 8 to 10 kw array should be considered. Nanosolar has the lowest cost per Watt at $1 USD, unfortunately, they are not for sale to the general public yet. Most panels currently available are close to $2 USD per Watt. That would tend to bring the budget mined down to 3 kw for the minimum array size. At 3 kw you can still generate hydrogen (2.5 kw per kilogram) and maintain battery charging if you are careful.

If you have been following my fantasy hydrogen designs, you may notice a few changes. One is the the 200 bar home electrolyser for $2300 USD. The only one using water as a source is kaput. Also the Honda Phill, which was a compressed natural gas system, which could compress and store hydrogen in a pinch, is also kaput. As mentioned earlier, the Honda home fill system is a natural gas reformer, not suited to the the off grid Island Design. This is making me take a new look at Dangerous Laboratories. Making hydrogen from water is a piece of cake. Separating the hydrogen from the oxygen produced is the trick. There are several low pressure PEM electrolyser designs, but you real don't need a PEM to make hydrogen. The second change is storage. Without the less expensive home electrolysers that can produce the higher 3000 to 5000 PSI, that increases storage space yet again. There are some tricks there I am researching. It seems that only Ballard Power is sticking to their game plan and staying solvent financially with their materials handling angle.

For the hydrogen compressor, I am pretty sure a metallic diaphragm two stage compressor will fill the bill. The solid metallic diaphragm is a natural protection for the pump in case of high pressure leakage. Being oil free, the diaphragm design is also likely to have a longer life. I just have to locate one that is small enough for a home application that doesn't have the medical gas compressor cost. That will bring everything back to being viable again. I'll be back to this when I find out.