Solar Generation: Part Two

 More about solar power, including some basics of electriciity. There is a brief introduction to solar thermal and hybrid PV/T. 

Also watch out for my predictions on solar power.

Solar Generation: Part One

How can you generate electricity? Here is a comparison of different methods including a comparison of energy return on energy invested. Guess which is the best way to generate electricity in you house?

How big a battery would I need?

Our house produces more electricity than we use, so in theory it would be very easy to unplug from the grid and become self sufficient. We don't do this for three reasons:

First, being connected to the grid means that we have electricity when the sun is not shining, its rays are blocked by heavy clouds, or by snow on the roof. We don't need to worry about batteries or generators because the grid is our back-up power supply.

Second, since we produce more energy than we use, we can supply energy to the grid and contribute electricity to the community. We wanted the house to produce more energy than it consumes, and we like to feel that the extra energy is being used and making a difference.

Third, they pay us for any electricity that we supply. They pay us very well: about twice what we pay for day-time electricity and five times the amount for night-time electricity. This is similar to the second reason, since we can see from the negative bills that our electricity is making a difference. We can safely assume that there is more demand and less supply in the day time, so we are filling some kind of need by selling our electricity. It's less safe to assume that our electricity is worth twice as much as their electricity, and easier to see the feed-in-tariff as a boost to the solar industry. Even then it is probably a good thing as the renewable energy industry and its exploitation of a resource that literally falls from the sky still seems to be getting less subsidy than exploiting fossil fuel reserves, and if we are to transition from fossil fuels we will need solar panels.

Regardless of the politics, the highly tangible and easily countable financial considerations mean that we try to sell as much of our day-time electricity as possible, and use their night-time electricity instead. Looking just at energy use this is a bad idea. Our main power consumption is for heating water, which we mostly use in the evening. Currently we are heating hot water at night and it is sat in the tank steadily losing heat for most of the day. Also, the tank is heated by an atmospheric heat pump, getting heat from night-time air, which is colder than the daytime temperature by something like 10 degrees at any time of the year. If we were using electricity in the day time from our own panels, then the heat pump would do a lot less work to get the heat from the outside temperature up to the temperature in the water tank, and the hot water tank would be losing a lot less heat before we use it. This could save us as much as 25% of our electricity, but we don't do it because using our electricity in the day time is over 300% more expensive.

Our contract for selling electricity runs out after ten years and we certainly will not be able to get the same price, but it's not clear yet what the financial calculation will be. If we were to start using daytime electricity, we would also think about trying to use the hot air under the solar panels, which would be even hotter and need even less work to provide us with hot water, but that's another blog post.

Back to the question in the title: If we were to disconnect from the grid and wanted to get a battery to keep us in power, how big would the battery need to be? I have seven years of generation and consumption data to give me an answer.

When I said that we produced more power than we consumed, this has been true for every year and every month. The lowest producing month was October 2017 (670 kWh), which was the least sunny October since 1917 with only 100.9 hours of sunlight. September 2018 had even fewer hours of sunlight (94.4), but we made 800 kWh. That's the same as our highest monthly consumption, 800 kWh, in February 2013.

The longest period when generation stayed above consumption every day was 153 days from 20th April to 20th September, 2016.

The longest period where consumption stayed above generation was for five days between 12th and 17th October, 2017.

If we need a battery to cover all our energy needs, then it may be for these five days. In the simplest calculation, we need a battery of 33.1 kWh (the shortfall between the 70.5 kWh consumption over those five days and the 37.4 kWh generated). That's one or two Nissan Leafs.

There were five times when the consumption stayed above the generation for four days: from 14th January, 18th June, and 23rd October, 2013, from 6th September, 2015 and from 19th October, 2017. Many of these grey-outs are in September or October, when consumption is at its lowest. The snowy days in the middle of January 2013 were at a time of much higher consumption, and for those we would have needed to store 53 kWh to make up the gap between 61 kWh generate and 114.2 kWh consumed. The Teslas have 60kWh batteries.

Although the meteorological data confirms September and October as the months most prone to sunlight shortages, when the roof is covered with 22 cm of snow, our heating needs may also peak.

So the short answer is, we would need a 53kWh battery. Anything smaller and we are still going to need to rely on the grid and pay the monthly connection charge, or we would need some other backup, so the value of a smaller battery is limited.

Since most of our energy is for heating, it may make sense for us to look at storing heat rather than electricity. Phase-change materials may be useful for this.

Also, a more thorough answer would look at charging efficiency, discharging efficiency and electricity leakage. The figures above assume 100% of the electricity goes into the battery, 0% of the charge is lost over time, and 100% of the charge comes out.

Future predictions

Here are some predictions based on current trends.

Computer chips will have one transistor per atom in 2025.

Every car will be electric by 2053.


There will be enough solar panels to cover all land on earth by 2056.

Two of these predictions are very likely to be wrong.

The first is based on Moore's law, which predicts that the number of transistors on a given size of chip will double every eighteen months.

The figure for electric cars is based on the recent increase in proportion of EVs, which in most countries is still less than one percent. The proportion may increase exponentially, and will of course stop increasing when it reaches 100%.


The figure for solar panels is based on a compound annual growth rate of 30%, which has been been happening for the past twenty years. I'm assuming that power output per area of solar panel will stay the same, which it probably won't. New panels will steadily produce more electricity for the same area, but the increase will not be large, let alone exponential.

Of these predictions, I think Moore's law is the most likely to come true. This law has held true for fifty years. I don't think atoms will necessarily stop it, since quantum computing is now a thing.

Moore's law has been enabled by the success of electronics leading to a steadily increasing budget for development of ever smaller chips. Developments have tended to compliment each other, rather than replace them. The budget is not increasing at a Moorean rate though.

These exponential growth rates are usually unsustainable since at some point they are limited by physical constraints of the real world. If things are getting smaller, of course, there is no limit. Right now there is a limit to our understanding of the very small, but if science shows us one thing it is that when we ask questions, sooner or later we find answers. The harder we look for the answers, the quicker we find them.

More interesting is Wirth's law, which states that "Software is getting slower more rapidly than hardware is getting faster." So all these improvements in the computer power are eaten up by extra complications and functionality that we don't necessarily need. I noticed this around 1992, and decided to stop spending so much time programming computers. I now wish I'd written a paper on it, like Dr. Wirth.



I'm pretty sure solar panel production will peak before we cover the whole planet, although I will not be surprised to see nature reserves clear cut for solar farms, massive floating arrays, or increased solar installation in space. They may even start making the panels up there. The economic effects of increased solar power will likely be that some electricity is effectively free, which will drive down the price of electricity, and reduce the value of the panels, making their manufacture less worthwhile. So I don't think this prediction will come true. I'm hoping to still be alive, and will be able to find out.

There will very likely be a point in the future when the only people not driving electric vehicles are stupid and rich, and I think this point will come sooner rather than later. By the time our computers are firing on subatomic logic, the majority of people will be buying new electric cars. I'm sure this will sound as ridiculous as someone predicting the wide use of steam trains in 1818, or motor cars in 1918. Also, we must not underestimate the size of the stupid and rich demographic, and its disproportionate political power. There will always be a bit of liquid fuel sloshing around, and we are unlikely to ever have 100% electric vehicles, but I think we'll be close to that long before 2053.

Here's an article from the Guardian about accelerating car sales. Here's another claiming that the electric vehicle revolution in Australia is stuck in first gear. The press is never shy to use motor-industry metaphors, but they don't realise EVs only need one gear. Also they may never have experienced the excellent acceleration of electric vehicles.

These solar panels... are they going to last?

Ugo Bardi writes about ​the energy return on photovoltaics. Citing an article from Bhandari et al. that looked at 231 studies on ​how much energy comes out of photovoltaics​, and how much energy went into producing them, he comes up with an average return of 11-12 for southern Europe. ​This sounds worthwhile.

(From Dale and Benson)

​This graph paints a slightly different picture. It plots the number of years it takes for panels to generate the energy it took to make them against the growth rate of solar production. The payback got at least three times better in ten years, and the growth also increased three times. This means that, so far, more energy has gone into making solar panels than has come out of them. Hopefully, the growth will stop at some point, and the line will swing into the green as panel production stops growing while the installed panels keep generating. That depends on economics. 

Older estimates were that panels would still generate 80% rated power after 20 years, but according to Engineering. com, panels produced after 2000 will still be producing over 90%, losing only half a percent per year. So technically the panels will still be generating.

Economics is about resources. Somewhere human time is factored into ​it. We consider this resource very precious. ​I remember large scale road building projects in the UK that would decimate forest, destroy habitat and create pollution ​just to take a couple of minutes off people's car journeys. There is an economic pressure to reduce the amount of human time needed for tasks.

Another view is that human time is infinite, and the natural resources are limited. The classical economic view looks at productivity and considers environment assets to be externalities and essentially deems them infinite.  

​Hopefully growth of solar panels will go down, and they will become net energy contributors, but there is a powerful economic mechanism supporting production. If growth increases and we start throwing away the old panels, then that line may stay permanently in the wrong part of the graph, and photovoltaics will have just helped in our longer mission of depleting the world's resources.

The only redeeming feature is that they work very well in space, so we can take them with us when leave the planet! 

​References:​

Bhandari, K. P.,  Collier, J. M., Ellingson, R. J. and Apul, D. S. (2015). Energy Payback Time (EPBT) and Energy Return on Energy Invested (EROI) of Solar Photovoltaic Systems: A Systematic Review and Meta-Analysis. Renewable and Sustainable Energy Reviews​,​ 47(July): 133–41. doi:10.1016/j.rser.2015.02.057.

Dale​, M. and Benson​, S. M., ​(2013​). ​Energy Balance of the Global Photovoltaic (PV) Industry - Is the PV Industry a Net Electricity Producer​? Environmental Science and Technology, 47(7), pp 3482–3489

​Green Rhino Energy looks more at the real cost of solar ​energy (warning: includes equations).

Just planning ahead to make a battery charger for electric cars

"Are we nearly there yet?" the kids ask from the back seat.

"Yes we'll be there soon," I say, and I'm sure we will be. Soon is always too late for some but takes others by surprise.  

So we are half way through the ten-year contract with the Chubu Electric Power Company, and when it ends there is almost no chance that we will be paid as much as the 48 yen per kWh we are now getting. The tarriffs have been steadily falling each year, as was originally planned. Solar panel prices have also been falling, so the calculation of return on investment remains a little short of the ten-year contract that electricity companies are tied into for domestic installations of less than 10 kilowatts. Installations over 10kW are considered commercial, and they are tied into a lower price for twenty years. The prices of solar panels, as with all commodities, is somewhat arbitrary, and it is not completely clear whether the government is deciding the feed-in-tarriff rate based on the price of the panels, or wether the price of the panels is being set so that the feed-in-tarriff will pay the cost back. 

   

I think this graph shows that costs of solar installations over ten years met the residential electricity rates in the middle of 2014. At that point​, in theory at least,​ incentives become moot since it's cheaper for people to buy their electricity in the form or solar panels than it is to buy electricity company​. Of course not everyone has the capital to be able to do that, but the feed-in-tarriff was still above the price people were paying for electricity. According to solar partners.jp, the amount you get for selling electricity is dropping by 2 or 3 yen per kWh per year. You could sell 1kWh for up to 33 yen in 2016, and it will be 30, 28 ​in 2018​ and 26 ​in 2019. So if I'm lucky and still able to get a new contract with my old panels, I may get over 25 yen per kWh when my contract runs out.

At 25 yen per kWh it's still worth my while to connect to the grid. My income from the panels will halve, but it will still be three times more than I pay for electricity. 

A worse scenario is that I get paid some market value for power generation, which could be around 11 yen. ​It may be a fixed rate or a floating rate. The worst scenario is that they don't pay me anything, but just expect that power to flow into their grid. I think that is very unlikely.

There has apparently been a deregulation of the electricity market, which in theory means I can shop around for the highest bidder for my electricity. Japan For Sustainability has an interesting story here about Renewable Energy Hopes and Hurdles Amid Full Liberalization of Japan's Electricity Market. "In April 2016, Japan woke up to a fully liberalized electricity market" the article begins, although even by ​June 2017 I can't help feeling that most people are still oblivious to this new reality. ​

Increased competition tends to bring down prices, which may be bad news for people trying to sell​ electricity​. You can find out here whether changing your electric company will give you cheaper bills: https://enechange.jp/try. It's easy to find companies that will sell you electricity, but it's harder to find those that will buy it off you, unless you have larger sources. I searched around the website for https://ne-greena.jp, who offer 100% renewable energy, but ​they are not interested in buying renewable energy​ from my roof!

At some value less than 20 yen per kWh, it stops making sense for me to pay the electricity company the monthly flat rate to connect to them, since we​ make more electricity than ​we​ use. The big question going forward for anyone investing in renewable energy is how much electricity will cost. Jay Carlis claimed in 2013 that electricity prices are not going down and he​re's a Guardian article from 2011 about electric cars taking over.

More information:

Support Japan for Sustainability

Statistics on solar generation and feed-in tarrifs in Japan

Do solar panels have a dark side?

While browsing through the battlefield of prejudices and preconceptions that is the internet, I came across the graphic below, proudly showing how much better coal and oil are than solar power. This was a retort to Bernie Sanders boasting about the great contribution solar power was making to job creation. They cite the broken window fallacy, which is the mistaken belief that breaking a window is good for the economy, because of all the work it for glaziers, carpenters and painters. I can't help feeling that the broken window that this metaphor really applies to is the global environment, which the economy has been breaking for the past couple of hundred years, and has yet to seriously think about repairing. ​Anyway, the author's conclusion was ​that it takes 79 solar workers to produce the same amount of electric power as one coal worker produces.

Of course, he is missing the fact that almost all coal workers' 2016 efforts have now been burnt, while most of the solar jobs were installing production capacity. If all of these workers stopped for 2017, then coal and natural gas would produce zero kWh. Solar, on the other hand, would produce more or less the same amount. In fact those panels installed in 2016 will still be producing power for at least the next quarter century. In addition, many of the jobs in the solar industry are leading directly or indirectly to increasingly efficient solar panels and better ways of using them, so when those panels eventually need replacing, their replacements will be more efficient, cheaper, lighter, less energy intensive and with a lower environmental impact in their production and disposal.

This guy has a similar story, and once again it seems to be coming from the right, and firmly putting renewable energy on the left wing, and the left field. "Our lives are improved by finding ways to reduce the amount of labor in them, not increase it​," they both claim​.

​Of course, a lot of labour-reducing measures have not lead to a reduction in labour but an increase. In the 1930s John Maynard Keynes predicted that ​his grandchildren would be working 15 hour weeks. He didn't actually have any grandchildren, so that part of his prediction was wrong to start with. But his sister's grandchildren, interviewed here and now retired, worked a lot more than fifteen hours a week. In fact one claims it was more like fifteen hours a day. Work has expanded to fill the available time. Computers have not yet liberated the masses from work, but have enslaved millions behind their keyboards. Cheap products have just allowed people to buy more. One of the​noble aims of the industrial ​revolution was to provide every man with his own shirt, but it has just led to many overflowing wardrobes. ​A kind of Jevons paradox exists here too, as we spend all our time using these labour saving devices. But I digress from the solar issue.

​The bottom line is, of course, that solar panels do require work, energy and resources in their production, and looking backwards it's difficult to argue that they are using less carbon. Looking forward there is a different picture, and solar power and other renewables make zero-carbon energy production possible. Burning fossil fuels does not. There is no reason to ever build another coal plant in the United States​, or anywhere else for that matter.

The western sun is strong

There is common wisdom in Japan that the western sun is strong. Of course it is not—the sun delivers just as much radiation in the West as it did in the morning in the East. And it delivers the most when it is highest and due South. In fact, less radiation may get through in the West as the air may be more hazy and dusty in the afternoon than it was in the morning.

Panels on a west-facing roof titled to the South

Some people are retrofitting solar panels onto pyramid roofs that slope four ways, and are encouraged by the wily sellers of panels to add them to the East and West sides as well as the South side. Panels facing due south will generate the most, and you could generate 20% less if the panels point East or West. The installers will charge the same wherever the panels go, and when grants are available they often do not depend on where the panels go. Orienting panels in different directions will give peak generation at different times of day which may be more useful than maximum total generation. Given a choice, people recommend the East side for panels, rather than the West side. If the western sun were stronger, they would be recommending panels on the West side.

One of my favourite local solar installations.
I wish they all had servos and tracked the sun! 

What is happening in both cases is that the temperature in the afternoon is higher, and in the normal state of affairs, the western sun is going to feel a lot hotter as the ambient temperature is already hot. In the morning it is relatively cool.

For the panels, efficiency drops as temperature rises, so the eastern panels will produce more electricity in the cool morning than the geometrically identical ones on the west that have to wait until the hotter afternoon to produce their electricity.

Trends in the generation

With five years of data from my solar panels, it should be possible to find the answers to some interesting questions. Like are these panels producing any less electricity as they get older?

I'd probably need to compare the generation each month with the actual weather data to get a proper answer, but as a first approximation, I tried to calculate a normalised generation figure for each month. I did this by first finding the average generation for that month, dividing that by the average of the generation for the same month each year, then multiplying by the average generation for every month. 

While I was about it, and since it's really easy to copy spreadsheet functions into different columns, I did the same thing for the consumption.  

And here is what it looks like:
 

Google sheets does its magic and produces a trend line, assuming that each of the points is dancing around a linear trend. And if we can trust this, there is a downward trend. Generation has gone down a little under 5% in five years. At the risk of digressing into a discussion of logarithms, let's say that's about 1% per year. 

Interestingly, there is also a downward trend in the amount of electricity we use. This has gone down almost 10% in the last five years. There are spikes and troughs for the months of March and August when we have been away, so I should probably work out a way of ignoring these. Another factor that will slightly affect both graphs is the slight difference in each month, since I'm using the month of the electricity bill rather than the calendar month. 

The 1% per year loss of generation is in no way surprising. On the other hand, it is a surprise If we are on a trend to use 2% less electricity per year, and it is a pleasant surprise. I've always imagined that low energy houses are at their lowest energy levels when they are new, and as they age, lose efficiency, and acquire extra gadgets they steadily use more energy. That does not seem to be happening here yet. 

The other question I'm sure the data can answer is how big a battery I would need if I went off grid. 

As a bonus, here is a chart of the daily generation and consumption that is not at all normalised.

Bloomberg predicting solar will be cheaper than coal

You can read the article and listen to the story here: 

bloomberg.com

Five years of solar power!

Our Suntech display panel congratulated us the other morning on five years of generating solar power. We've made over 60 Megawatt hours. That would keep a 60 watt light bulb going for over a hundred years. But we don't have any 60 watt light bulbs, they're all low-power leds.

In the same period we've used under 30 Megawatt hours. Around 45% of what we have generated. We sold around 90% of the electricity we generated, and bought around 75% of the electricity we used. I'm not sure how much sense this makes in environmental terms or for overall energy usage, but economically it makes sense since we only pay 11 yen for off-peak electricity, and they have been paying us 48 yen per KiloWatt hour for our solar power, totaling over 3 million yen. 

Our contract lasts for another five years, and we will see what is available at the end of that. In the meantime I can start working on my plan to use the hot air under the panels for our atmospheric heat pump, rather than the frigid night air. I think it will take that long to find a brave enough heat pump engineer to tackle the project, or to learn enough about heat pumps to try it myself. 

(Corrected 10th January: originally said "Gigawatts", changed to "Megawatts". We're not a nuclear power station!)

Cloud-tracking cameras to tackle dips in solar power output

This is a nice bit of technology. Compared to conventional power generators, solar panels present something of a challenge. It's fine on a clear sunny day, when you get a predictable output, peaking sometime around noon. If it's overcast you get a predictably low output. The problem is on partially cloudy days when the output will fluctuate each time the sun goes behind a cloud. 

So according to this article in The Guardian they have installed camera technology on a solar installation in Western Australia that will give a fifteen minute prediction of clouds to come, which can help switching on back up systems when needed, and can give a better idea of prices.

Or maybe we should not be worrying about storing solar energy

There's a conventional wisdom on solar power in particular, and renewables in general, that we need storage to make it work properly. According to brave new climate that will probably stop them from being effective. 

They look at the energy return on energy investment (EROEI) and cite the low score for solar. In other words, the amount of energy that will come out of solar panels is not really enough to make solar panels. This means they are not sustainable and rather than contributing energy, they are using up energy created elsewhere. He suggests we should not just talk about the actual energy used in the process of manufacturing the solar panels, but also things like food and education for the people who are making them. 

Anyway, an energy source with an EROEI of one would just produce enough energy to support itself, and would be of no use to the society. The threshold for useful energy sources is something like 7. 

I have sometimes watched fish jumping out of the river to catch a fly, and wondered whether they were using more energy to catch the fly than they got out of eating it. EROEI is a bit like that. 

He quotes an EROEI of 3.5 for solar panels in Germany. This is already marginal, and if we have to store energy from renewables, then we also need to add the battery infrastructure into considerations of the EROEI, which could make solar a net user of energy rather than supplier. 

There are two other considerations. First is that solar production costs are falling all the time, and this includes embodied energy. The other is that we may soon have batteries parked outside each house in the car. 

Lesson 10: generating power

First I asked how power could be generated, which elicited a long list, including the methods below that I had prepared earlier.

The first electric power was probably generated by water, just as water mills were probably the first regular power sources to be harnessed, long before the discovery of electricity or the scientific understanding of energy and power. In 1868 a hydroelectric power station was built at Cragside, a country house in Northumberland, UK. The first modern power station was built at Niagara Falls, 1895, producing alternating current that was sent over power lines to a town several miles away. Coal was first used to generate power in 1882, in Pearl Street, Manhattan. The first electricity was generated from wind in 1887 in Glasgow. The first commercial wind farm was commissioned in 1980 in Crotched Mountain, New Hampshire. Geothermal power began on a small scale in 1904 in Lardello, Italy, and was commercialised in 1911. Oil and gas are also used to generated electricity, using similar steam turbines to coal power stations.

More recently,  nuclear power was first generated in 1954 in Obninsk USSR. Silicon solar cells were first made in the same year, and the first large-scale solar power station was built in the Mojave desert, California, in 1984. Other forms of generation include biomass, tide and wave.

Which of these is zero carbon?

None of them!

Why not?

In each case, fossil fuels are used, and carbon is emitted at some stage in the construction process. Once solar cells have been installed or hydroelectric dams have been built, electricity can be produced without carbon cost, but we need to take account of the whole lifecycle when estimating carbon footprint. Radioactive decay does not produce any carbon, but the mining, transportation and purification of nuclear fuel do, and these must be taken into consideration. 

The more pertinent questions are: which is lowest carbon? which is cheapest? and which is best? I gave this question a little bit more depth by asking which is the best way to make energy if you're an electricity company; if you're a government; if you're a city; if you're a business or if you're a home owner.

There are at least three factors to take into consideration when we're looking at cost analysis. First is $ per kWh. Second is kilograms of carbon per kWh. Third is energy return on energy invested (EROI, or EROEI), kWh out per kWh in. You can see some comparisons in the table below from two different studies.

	Murphy and Hall (2010)	Scientific American (2015)
Hydroelectric	100	40+
Wind	18	20
Coal	80	18
Natural gas	10	7
Solar	7	6
Nuclear	10	5
Oil 1970	35
Oil 2007	12

If you are a homeowner, you would not want to live under a coal power station or a nuclear reactor, and most locations would not suit hydroelectric turbines or windmills, but living under solar panels seems like a good idea in most places.

The current economics of solar power  see costs falling, year on year, and the cost of the competition rising. Fossil fuels are finite, and the situation can be likened to hiding ten thousand yen in hundred yen coins around the room. The first few coins will be really easy to find, but as more are found, the time and effort taken to find each one will increase. You can see in Murphy and Hall's data above that oil in 2007 takes almost three times more energy to extract than it did in 1970.

Grid parity is the point at which solar power costs the same as other electricity available on the grid. Of course this will be different at the point of production to the point of use. If you are an electricity company considering building a new power station, the cost of solar electricity will need to be cheaper than other options such as nuclear, coal or hydroelectric. If you are a homeowner, then you are comparing the generation cost with the market value of the electricity, which includes the transmission costs as well as other overheads and profits of the electricity companies. In many places grid parity has been reached at the point of use. This depends greatly on the local cost of electricity, and local sunlight conditions, as well as local cost of solar panels and fees for installation. Conditions are skewed by grants and feed-in tariffs.

The advantages of solar power generation include no fuel, no pollution, no noise and a long lifetime. Solar power is modular so an array can be any size from a few watts to a few megawatts, to meet supply or demand, while other forms of electricity generation need to be on a large scale. The disadvantages and challenges include the high cost and relatively large area. Orientation must be carefully considered. Solar power is unreliable and varying: nothing will be generated at night time and clouds and weather make a difference. Sunny days produce a predictably high level. Overcast days produce a predictably low level. The worst days are partly cloudy, when generation will go up and down with each passing shadow.

This is a particular challenge for the electricity companies, who have long been working on the balance between electricity supply and demand. Unlike other areas of supply and demand, electricity must be immediately available when people turn the switch on. Usually the various users in the grid will average out, but George Monbiot, in his book Heat, writes about the FA cup final. When this is on, most TVs in England are tuned to the game. This is not such a big problem, but when half time comes, somebody sitting in front of each of those TVs gets up, goes into the kitchen and puts on the kettle. This creates a surge in demand bigger than the largest power station in the country. To cope with fluctuations in demand, there are hydroelectric facilities which pump water up the hill when there is too much electricity on the grid, and send it down again when more is needed.

I have an image of guy somewhere in Wales in front of a portable TV, glued to the first half of the game and ready to flick a switch as soon as the ref reaches for his whistle.

Storage may be needed to cover the unreliability of solar, but the extra cost of the storage, especially in terms of energy, may make an already marginal source of power unsustainable.

Will solar panels save us? Are they good for the environment? Until now more energy has gone in to making solar panels than has been generated from them, but that changed around this year, and as production becomes cheaper, the return on energy invested will improve. They may save us in the future.

I didn't properly have time to cover the installation of solar panels, the best orientation, angle to the horizontal and other conditions such as the avoidance of obstacles.

Also I didn't have time to talk about solar thermal collectors, which can make a difference to the energy use of a building. There are flat plate collectors and vacuum tubes, circuits and drain back systems. Challenges include overheating, freezing, hygiene, and once again we face unreliability and the need for backup

I also didn't have time to talk about PV-T hybrid systems that combine electricity generation and collection. In the process of collecting heat, the photovoltaic elements are cooled, which makes generation more efficient, and overall these kinds of panels can reach efficiencies of something like 80%.

References
Murphy, D.J. & Hall, C.A.S. (2010). "Year in review EROI or energy return on (energy) invested". Annals of the New York Academy of Sciences 1185: 102–118.

http://www.mpoweruk.com/solar_power.htm

http://www.theguardian.com/environment/2008/oct/17/wind-power-renewable-energy

http://www.edfenergy.com/energyfuture/the-energy-gap-climate-change

Guardian: Solar power in crisis

An elaborate article on solar in the Guardian from 20th October here:

Solar power in crisis: 'My panels generate enough power for two loads of washing'

A somewhat misleading title: how is panels generating enough power for two loads of washing a crisis?

The article is heavy on anecdotal details of consumers, suppliers and crystal-ball gazers. It even gives a few column inches to batteries, which are a clear challenge for an energy infrastructure based increasingly on variable supply. But it is somewhat lacking in deeper analysis of the actual topic in the title. It just seems to go on: Why, oh why, is the government trying to strangle this business?

Someone in the comments has done the relatively straightforward sums. Someone is paying four grand for your panels. There are a million houses out there with panels so far. That's costing people in Britain 4 billion pounds. Another 6 million houses and it's the same cost as the proposed new power station you call the most extensive object on earth.

The comments also mention that most of this subsidy is going towards Chinese businesses that are making the panels. Not that I have any objection to UK electricity buyers subsidising our comrades, although objections could reasonably be made.

This seems an interesting test case for the system of free market enterprise. What is happening is that the government is giving away bits of money, some in the form of grants, and some in drip-feed cash into the future.

There has been a mad rush for grants and an explosion of entrepreneurs setting out to install the panels. Some no doubt have done a fine job. Others sell panels for roofs that are not well suited to solar power, some delivering less than optimal installations.

I'm sure there are a lot of roofs that should have several more panels than were installed, and some that should not have any.

And if the government is going to pull the plug on subsidies, the solar installation industry will shrink. It's still going to make sense to some people to add panels without any subsidy, but for most people a financial incentive is needed to make the long-term investment for long-term savings.
It's a bit of a gold rush, so a lot of the people in the industry have only just arrived, and will head straight for the next gold-rush. The fly-by-night operations will vanish into the sunset, generating electricity in neither of those metaphors.

It would be good to see more rational subsidies, looking at where energy is used and where the best yields will come from. Couldn't they cap the amount of solar subsidies, and award them to the most worthy causes? For example prioritising arrays on south-facing terraces would provide energy where there are people. Installing panels in isolated areas may be a good way of reducing transmission power, but will really only be effective if local energy usage is synced with energy generation, and if there is some local storage. Otherwise there are going to be line losses both as energy is sent there in times of need and as it is sent back when generation is high.

If this is our energy infrastructure, then it needs some kind of long-term plan. The roads and railways were not built by letting people put down their own hard core or sleepers and rails and then giving them a few pennies each time somebody went past over the next ten years.

Golf loss is solar farm gain in Japan

An interesting story here from Electronics Weekly.

There's a triple victory here:

First, more generation of green power. (As well as tee power, fairway power, and a bit of bunker power if it's not too shaded.)

Second, less water wasted keeping the greens green.

And third, less people playing golf, which "has too much walking to be a good game, and just enough game to spoil a good walk." (Harry Leon Wilson, 1904)

A fully transparent solar cell that could make every window and screen a power source

This is really clever. Not sure how effective it will be though. I'm sure it could make every window and screen a power source, but it probably won't.

The clever part is that it diverts the invisible light coming in through the window towards the edges, where it is converted to electricity by solar cells. As well as the visible light we see, the sun has infrared radiation, at a shorter wavelength, and ultra violet, at a longer wavelength. Other approaches to solar glass have usually reduced the amount of light getting through, by applying a solar film over the windows, containing semiconductors. Since the semiconductors are not covering the glass, and the diverted light is outside the visible spectrum, this won't make any difference to how the windows look. 

I would show you a picture, but you wouldn't really be able to see anything!

Find out more at: extremetech.com

Do Google spreadsheets excel?

I started writing this post a couple of years ago, but after spending a few hours getting the charts working for http://minuszeroeco.blogspot.jp/2013/12/when-did-we-turn-heating-on-last-year.html, 

I ran out of time to write about it. 

It was about that time when I started banging against my head in an apparent ceiling on the amount of data a google sheet could hold. This was big data, but not that big. Or maybe it's just the greedy way I set up excel files. 

There is a new function in Google sheets now, called explore. A data bot goes in and looks at all your data, then plots graphs, scatter charts and histograms. It gives text descriptions of what is going on. I didn't need a computer to tell me that for every increase in generation of 10, "exported" increased by 10. But well done. This could have shown me a correlation that I didn't know about. 

This graphs is really good though:

It looks like it's been made with a thick paint brush, that has then started running in a few places. The line hints at the sine wave of the orbit around the sun. The cosmos has conspired with the climate to produce this one.

The histogram of solar generation is interesting too.

Eroi panels

In all attempts at reducing our environmental impact on the planet, there is a haunting question of whether it is worth it, or if the effort we've put in to do our bit is actually going to make things worse.

There's a scene in some World War Two movie where one Nazi turns to the other and asks, "are we the bad guys?" I often ask myself this question, and the answer is usually yes.

And so with solar panels, I wonder whether they really are making a difference to the planet, or if they are just another part of our plan to convert as much of the fossil fuels under the ground into carbon dioxide in the atmosphere as possible. If they are just leaves of garnish that have been grown with gallons of water and transported with gallons of oil to make our plates look a little greener.

Financially they seem to make sense. They're working for me everyday by just lying there in the sun on my roof, and I'm looking at a total payback of around 8 or 9 years.

There's also a sense of security that I have my own power source in case of emergencies. I know that they will only ever produce power in the day time, and if we were snowed under they wouldn't be very effective, but at least the sense of security is there. I'd be able to keep the fridge working on a sunny day.

But are they saving the planet, or are they just green bling? Are they like parsley on the side of the dieter's plate, next to the potatoes and the large piece of steak?

One metric that can shed light on this is EROI, the energy return on investment. We're familiar with financial returns on investment. For example, if I put 10,000 yen in the bank, with the 0.02% interest rate it will take three and half thousand years for the bank to pay me 10,000 yen in interest.

The energy return on investment tells us how many units of energy will come for every unit of energy we put in. For solar panels we need to consider how much energy was used in the manufacture and transportation of the panels, and their installation.

According to a review by the Energy Skeptic of a report on Spain's experience with solar power, the energy return for solar there is low at 2.45. Optimists put it higher, and with improving technology it is increasing all the time. However, the mines digging the materials out of the ground are not solar powered, the factories making the panels may have a couple on the roof, but most of their electricity is coming in from the grid, and the transportation is mostly powered by fossil fuels. Research at Stanford claimed that all historical energy used to make solar panels until now will be repaid between 2015 and 2020.

It's a different story to coal, which found an early use in steam pumps removing water from coal mines, and was instrumental in extraction of the energy source from the ground. Coal has a much higher EROI, around 18 according to meta-analyses by Mason Inman in Scientific American, retold here.

Nuclear, meanwhile, is rated as low as 1 by some, and designated a sink of fossil fuels. The nuclear industry give it a score between 40 and 60 and claim it is a global-warming saviour. Politics is very much alive in these figures:

Hydro-electric 40+

Wind 20

Coal 18

"Natural" Gas 7

Solar 6

Nuclear 5

(Data from Scientific American cited in carbonbrief.org - I couldn't thoil the price Scientific American charge to read the original article.)

So they may be helping save the planet or they may be helping to destroy it. On the other hand, it may be that the panels will help to drive up fossil fuel prices and get us off them quicker. An interesting statistic from wikipedia's article on EROI is that the energy return on investment for US oil and gas halved between 1970 and 2005. In other words, while solar power is becoming cheaper to produce, both in terms of money and energy, the more oil and gas we get out of the ground, the more energy we need to get what is left. 

As a metaphor for this, you can imagine that someone has hidden several pennies around your house, and you're trying to find them. You'll find the first ones fairly quickly, but as you go on, they will take longer and longer to find. You may go and buy a metal detector, at which point the metaphor reveals that improvements in technique may speed up your retrieval rate. This will not help when there is nothing left to retrieve. 

I remember at school hearing that fossil fuels were going to run out in thirty years. When I told my father this, he said that he had heard that when he was at school. My son is no doubt learning that same thing at his school. Fossil fuels are a finite resource, but they may not be exhausted. It's more likely that their cost will increase, while the cost of alternatives is decreasing. 

And when the energy economics switch over so that fossil fuels are unviable, at least a lot of us will have panels on our roofs to produce electrical power, and keep our fridges running on sunny days when the roof is not covered with snow.

They don't half write some nonsense about solar

This was going to be titled: "Solar has become the most efficient way to generate electricity"

Solar has now taken over as the most efficient way of generating power.

This happened now. Right now. At the precise second you read this sentence. Or this one. Or at the time I wrote it. Or at least sometime this week. Or this year. Or maybe next year.

Of course you can't really give a precise time, any more than you can decide the precise point where the economy changes from bust to boom, or exactly which sip of drink was too much the day before a hangover.

Also, there is no single way to determine whether solar is more efficient than other ways of generating power. If you look at the cost of a power plant per unit of energy coming out of it, then solar is certainly a lot more expensive than options such as coal or uranium. However, if you look at the cost of the energy at the point of use--for example your house--then solar is often cheaper, since the electricity is there where you need it, and you don't have to pay for the line costs. As well as the availability of sunlight, this depends on the cost of electricity, the cost of panels, and any subsidies, which are all local factors. And you probably should not include subsidies if you want to really know whether solar is cheaper, but then you should probably adjust for the subsidies that coal, oil, gas and uranium get.

And even though solar in many places is cheaper where you need it, it may not be there when you need it, since solar panels are less efficient if it's cloudy, and even less efficient if it's dark.
The Japan Renewable Energy Foundation seems to be quite positive about solar. Although they may be as biased as people on the other side whose heads are stuck in oil barrels.

Reuters has an article from June 25th with the ambiguous title "Japan to stop inefficient coal-fired power plants being built" which in fact is about Japan's plans to build efficient coal-fired power stations.

There seems to be a lot of confusion over solar in the press, especially in the Japan Times. I think the wind is changing right now, so the weathercocks are all spinning aimlessly and pointing in different directions.

According to Reneweconomy.com.au, Deutsche Bank claims there will be grid parity by 2017 in 80% of world markets. Wikipedia has a good page on grid parity, which mentions Matsumoto as an example, and shows that is is already here. This backs up the evidence I have on my electricity bills.

Meanwhile global coal production has been increasing at least since James Watt put the first steam engine at the top of a coal mine to pump water out, and since Fukushima Japan was helping this trend, so it's distinctly possible there are big contracts for importing coal, with big backhanders for Abe and his mates. Business as usual, or is it? Another factoid I heard recently was that coal uses more land than solar for generating electricity.