Category Archives: energy storage

Solar Power

A large solar array in Westboro, who knew?

A large solar array in Westboro, who knew?

I am now an expert on solar power. A few nights ago I listened to a few talks about it, so there. Here are a few things I now think I know.

Solar panels cost has declined, sure. But what about other costs? Not so much. There are lots of other costs: framing, the installation, permitting, financing, site selection, the transaction costs to move power back into the grid, getting your tax rebate, political uncertainties, maintenance, the control electronics, the power-inverters, etc. etc.

For example there was a period a few years back when the price of panels rose, people who built arrays during that interval are a bit cranky about that. For example in my state the tax credit pool is draining out so the current boom is coming to an end.  I was quite amused by one person’s complaint about how hard these projects are to get past a New England town meeting.  That’s was principally about risk and financing.

So, coordination and other harder problems have come to dominate the industry. The cost decline of these systems is leveling off.  This is why you see these efforts to build arrays using robots.

All that makes large projects much more effective v.s. small ones. We have done a lot of projects here in Massachusetts over the last few years, and it’s employed a lot people. But reading between the lines I get the impression that many of those jobs were on little projects where the costs were disproportionately in the coordination costs.

Hot water? It was interesting to see the experts react to a question about solar water heating. They sort of did a collective sigh. Apparently a system that has moving parts and fluids is a pain. I guess that goes to explain why they are so rare. Most of my neighbors have little solar garden lights, none of them have solar heating of any form.

And yet, I look forward to steam-powered garden gnomes.

Reverse Archimedes Screw Turbine

My home is a short walk from Mill St, where the first falling water powered mill was built by the colonists.   That stream had a number of mills along.  But, after the 2nd world war when housing covered the surrounding hills.  Removing the trees, adding the roads and storm drains sucked the water out of the ground quickly after storms.  The water in the stream become less dependable the mills closed.

All of New England was once home to mill towns.  Each was situated along a river where falling water could be tapped to power the mill.  Power rather than labor, markets, or supplies defined these businesses. This model imploded when coal became a preferable source of energy.  When you drive thru these old mill towns you can see lovely homes and mills that are now quite pitiful.

This is an American pattern.  If the business models shift we just abandon the cities that fit that model   We leave them to the poor.  The coal based cities need flat water to get the coal and they had better labor and access to supplies and markets.  These were flat water cities.  Later when coal was replaced by electricity, and cars replaced to walking, and phones and procedures replaced hands on management abandoned flat water cities.

Anyhow, there are lots and lots of little mill ponds and dams all over New England.  Sooner or later these dams will fail, but in the meantime I’ve often wondered why we can’t convert them to micro-hydro generation.  Is power too cheap to make it worth the bother?  Are the coordination costs or the regulatory barriers to difficult.  Maybe the engineering doesn’t work.

This chart shows what kind of tech ou should use for various hydro scenarios.



Most of New England’s old mills had water wheels; and the water didn’t fall very far.  How far the water falls is called “head”, and that’s the Y axis on that chart.  So from this chart we learn that we want to look into something called “Archimedes.”  That turns out to mean “Archimedes screw,” or actually something called a “reverse archimedes screw turbine” … though calling it a turbine is pretty silly.screw

Apparently these are extremely rare, though their are some in the UK, and there is somebody working on it in Canada.  This is a nice video of one running, and here is a nice animated version.  I have no idea if these are a good or a bad idea.

This chart, reportedly, shows feasiblity.  They still need a lot of water.  Which tends to suggest why this paper is so pessimistic.  The entire cost/benefit of the 19th century New England mills lived it would appear in a very different world.

I wonder if these would be practical for energy storage as well.  All the good hydro-storage sites are taken, but if they don’t need as much head then, presumably, other venues would become viable.

Using Freight Trains to Store Energy

Grid scale energy storage systems are all such cool hacks.  Here’s a new one which will be popular with all you model train geeks.  In this scheme they build a specialized railroad, based on those used in mining, and haul freight cars full of somehting heavy (gravel?) back and forth between two rail yards.  The video (which is only tollerable if you turn the sound off, also skip the 1st 2 minutes) illustrated the idea.

668MW Facility from Advanced-RES on Vimeo.

Sadly one of my favorite schemes, Iowa Stored Energy Park, didn’t work out (lessons learned (pdf)).

Cost of Energy

I’d love to see an energy budget for heating with pollard wood.

I was taken aback some years while playing with various ideas for heating my house ago to realize that natural gas was significantly cheaper than wood.  Here is a table that illustrates that.

  • Coal – Powder River Basin – $0.56
  • Coal – Northern Appalachia – $2.08
  • Natural gas – $5.69
  • Ethanol tax credit – $5.92
  • Propane – $13.28
  • Petroleum – $13.43
  • #2 Heating oil – $14.74
  • Jet fuel – $15.48
  • Diesel – $15.59
  • Wood pellets – $17.33
  • Gasoline – $17.81
  • Corn ethanol – $23.46
  • Electricity – $26.31
  • Cellulosic ethanol from corn cobs – $30.92

I also spent a bit of time looking at coal as an alternative.  As a child I lived for a period in Pittsburgh and the house had an unused coal bin in the basement. The house was heated with natural gas. It turns out mankind has burnt all the good coal, and what is left is harder to burn.  It stinks, so you need to have a lot of scale to handle it well.

That natural gas is so dominate says something about housing density.  Quarter acre plots are probably the upper limit of when it’s worth running the pipes.  Of course that distribution infrastructure is a tempting target for monopolists.

Those numbers are US based.  Natural gas is less reliable and more expensive in Europe.  I mentioned monopolists didn’t I?  Ben recently did an wrote something similar, looking at biomass, for rural Britain and he too make the point the author of that table makes, that “there just isn’t enough biomass to meet present energy demands.”    While that point is right on, I don’t think we are going to find the one solution; or at least not for quite a while.

Daily Energy Storage

The drawing at right is the schematic of an air conditioner based on phase change.  In this case wax that melts at 22C (72F).  The wax is encapsulated in tiny spheres and then mixed with water to create a fluid.  That slurry is pumped thru the radiator (labeled: cool-phase condensing rods).

At night cool outside air is used to solidify the wax, and during the day inside air is cooled by melting the wax.  This is analogous to how I cool my house; cooling it at night and sealing it up during the day.  I let the building provide the thermal mass.

They claim you can use it to store heat over night, but I assume that’s only going to work if you warm the house over 72F during the day.  But maybe the slurry is a mixture of wax for different temps.

They can store about 4kWh of energy the slurry.  That’s not a lot as air conditioning loads go (a medium sized room?); but they claim the capital cost per cubic meter and much lower operating costs.

The manufacture is currently testing units around London.  The box looks like a clunky old steam radiator.

So, interesting that a daily cycle, room sized, phase change scheme might show up in the market soon.  There are daily cycle, office building, phase change schemes where in a block of ice is frozen each night.  I’ve thought it would be a hoot to build something similar that was yearly cycle, and house sized.  More here.

Energy per passenger-mile

From Chapter 2 of the “Transportation Energy Databook” from the US department of Energy (with slight format changes).  The Commercial air numbers maybe high do to freeloading cargo.

Thousand BTU/Passenger Mile
4.2 Public Transit Buses
3.9 Personal trucks
3.4 Cars
3.3 Commercial Air
3.0 Rail - commuter
2.8 Rail - transit
2.6 Rail - intercity
2.2 Motorcylces
1.3 Vanpool

My motorcycle/scooter riding friends may continue to gloat. And no this is not an excuse to to drive rather than take the bus, since adding you to a bus costs about zero btu/mile; and of course motorcyclists who ride in packs should get a car.


Maybe somebody can explain what’s actually going on here.  MIT has a press release out, it crows about the discovery of a catalyst for splitting water (the pod cast there is good) into it’s constituent hydrogen and oxygen.  Now I thought that was pretty simple stuff.  What’s the hard part?

My model of using hydrogen as an energy storage system was that it became inconvenient in other parts of the system.  Hydrogen is a pain to store; transport, etc.  The conversion of hydrogen back to energy required over engineered devices; like fuel cells.  I’d presumed that making hydrogen wasn’t a problem.

In any case they formed a thin film of cobalt and phosphate on a conductive glass.  When they slip the water, using electricity, they get oxygen.  I gather that what’s good is that they get the oxygen directly and not thru some inconvient intermediary?  Apparently their is a second step that helps to assure they get the hydrogen more directly as well, and I’m not following that either.  This second step while straight forward typically is done using platinum as a catalyst; so there is some separate story about how to work around that cost – but that’s not part of this invention.

Apparently it’s very nice that this all happens at room temperature and neutral PH.  I guess that’s good, presuming that the existing efficient processes are far from that.

There is apparently a subplot about how the water isn’t pure; but has a dose of phospate in it so the thinfilm is self repairing.

I guess these are my questions.  First how much does this simplify existing practice.  Second is this actually significanlty more efficent than existing practice.  And finally, and I think this is outside the scope of the press release, what is the round trip efficency and complexity of an energy storage scheme based on this?

Update: This posting over at The Oil Drum is quite snarky and dismissive of this “breakthru.”  It is a refresing counter point to the ripple of republished MIT PR.  Presuming it is correct then what’s different is that existing high efficency electrolisis schemes are more complex than this.  How much that effects the capital costs isn’t clear to me, but not much looks likely.

Update: This video is pretty nice and reasonably clear.

Cost of Heating

Any  amateur  economist knows that if two goods can substitute for each other they will, overtime, adjust their prices to about the same level.  So obviously the choice between oil or gas for heating your home shouldn’t be a matter of price.  So, being a gadfly, I found myself taking the contrarian point of view in an  argument  last fall.  At the time it was much cheaper to heat your house with gas, and it has only gotten worse.  This is, of course,  bizarre.  But as this chart shows it’s been true for years and years.

Those are US Department of Energy forecast numbers.  They are published annually, for example here are the recently released 2008 numbers.  That link is a good place to get a sense of what the numbers mean.  I drew the numbers for the other years from this page.  Even amateur economists are right some of the time.  I can’t believe that’s stable.  Maybe I should be trying to lock in my natural gas fuel price for next winter.

Negative Energy

I have sighted a new urban myth: Electric heating is cheaper than oil heat! Here in Boston people heat with both gas and oil, and the cost per unit of heat between the two has diverged rapidly over the last few years. Those who heat with oil are looking for ways out of their plight. Apparently the rumor making the rounds that it is cheaper to use electric. That’s not true.

In related news Martin  brings my attention to a company EnerNoc that sells negative energy, i.e. load shedding, to the utilities. They use telecom and widgets to shift power consumption from high demand time periods into low demand time periods. Martian’s example is the fridge. You chill when power is plentiful and let it coast when others are paying higher prices.

I assume that EnerNoc’s role in all this is to aggregate small power users into a large enough pool to be worthy of selling to the utilities. It’s a interesting example of a coordination problem. There are of course other ways to approach the problem; ones that are less dependent on a thicket of contracts and ongoing coordination signals controlled by a middleman and enabled, as Martian, points out by the telecom infrastructure.

The obvious alternative is to just broadcast signal; and let the demand side react to the signal by selling some simple technology that responds to the signal in reasonably simple ways. That alone would enable substantial contributions from the demand side. But you can improve the incentive structure either thru regulation or by using statistical sampling to tell which customers have gotten with program; and then reduce their tariffs.

The amount of signal that needs to flow from the grid operators to the consumers is small, in the sense that you can broadcast it. A signal only needs to flow back the other way sufficient to assure that the incentives play out right. It is stupid to presume that the only incentives that are available are monetary or that they need to be executed with fastidious accounting. Most social systems have very fuzzy accounting and they work just fine, thank you!

The puzzle to be solved here is how to draw more of the peripheral demand into a load balancing system. Reading about EnerNoc’s approach isn’t the first time I’ve seen discussion of this. For example Bruce Schneier mentioned a regulatory attempt at something similar. I liked that one a lot, it provided a way to signal household thermostats. He was concerned that the resulting system would attract hackers. I presume he’d be just as sanguine about the security of the EnerNoc system; probably more so since it’s a closed system.

Such concerns are appropriate, but for heaven sakes I wish smart people like Bruce would stop pretending that these cases are somehow unique. It is the very rare large scale system that doesn’t have vunerable choke points. Hubs who’s failure can bring the entire system to it’s knees. Telling designers not to build large systems because of those risks is lame. Helping them know how to build them so they are safe and robust is hard, yes. But these systems get built because they generate mind boggling amounts of value. So it’s better to do the hard job and forgo the short term pleasure of a bit of hysteria.

Speaking of load shedding: turning your car’s engine off when you stop is more efficient than you thought.

Solar Islands

These are cool! They are huge, they float, and they include steam, balloons, and your choice of ocean going or deserts with optional canals. They would be better if they included a giant watch spring to rewind them every day. Real life steam punk! I might have called them solar turn tables.

Solar collectors need to point at the sun. So there is a lot of mechanism to rotate them through out the day. These clever guys decided to mount a huge number of mirrors on a turntable and rotate the whole thing. This can work by arranging the mirrors in strips, each strip runs in a line toward the sun. This is easy to understand by watching this little video.

They are building one in the desert; it’s not too big. The unit costs goes down the larger you make them; particularly the power plant. You can get a sense of it’s scale because, I assume, those are your typical big trunks scattered around the site.

They have two additional tricks. The rim of the turntable floats in a channel. Then a membrane is stretched over it and air pressure under it supports the mirrors and the pipes.

Now if they would just hook these up to a fireless steam engine, and or a solar lime kiln I’d be even happier.