Wednesday, 21 September 2011

Solar scam?

Another question is how far the electricity from these panels will get, and the answer is probably not very far. 

So, are these solar panels actually going to make any difference in the grand scheme of things?

The answer is, after considering all the considerations and taking into account all the actualities, most definitely, absolutely and categorically: maybe. 

Speaking selfishly, my immediate financial worry is how much electricity will be lost between the panels and the electricity metre, which keeps track of how much we are selling. Unlike this person in the US who found the metre running backwards, when you get solar panels in Japan, they put on two metres. One for elecricity you buy and one for electricity you sell. 

For a start, the power conditioners, which convert the DC to AC, will maybe lose 5 percent. Then there are wire losses. 

My first calculation, based on 9.12 kWatts of power going into 100 volts, i.e. 90 amps of current, passing through regular house wiring, was that it would lose about 90 Watts per metre, or one percent. If the panels produce 50,000 yens worth of electricity per month, that's 500 yen. Once it left the house, this electricity would only reach the immediate neighbourhood. Actually this estimate is wrong because I was looking at low voltage and thinner wire.

The hot water pipes, if un-insulated, would have been losing 100 watts per metre, which is comparable. In the case of hot water pipes, insulation will reduce the heat loss. In the case of electric wires, it's the opposite problem. The power is lost because they are not conducting perfectly, and so electrical insulation is our enemy. Obviously we want electrical insulation around the wires, otherwise we'll get a shock.

The answer was wrong, but I think the science was right in my calculation. Based on Ohm's law, V = IR, we can see that the voltage drop over a metre of wire is going to depend on the current running through it. This is why electricity is sent over long distances at very high voltages. The power lost is determined by Joule's law, P = VI, and as V = IR, we get P = I2 R. For the same transmission power, doubling the voltage will halve the current. Halving the current will mean a quartering of power losses. 

In my first estimate, losing 1% every metre of cable, the electricity from my house would not get past the neighbourhood. 

Actually, the voltage is going out at 200 volts in thicker wire--22 square millimetres, which has a resistance of 0.008 ohms--and the power loss is about 1.6 watts per metre. So the electricity from the house would reach about 4 km, i.e. the other side of Matsumoto city centre and a living, working and shopping population of at least 100,000. 

Even if the electricity from these panels does not get very far, the panels will mean that less electricity comes into the neighbourhood. That electricity would be coming from dams, thermal, or nuclear power stations hundreds of kilometers away. Nagano prefecture has several dams, but almost all of them belong to Tokyo Electric, and consumers in Nagano don't even see the electricity coming from them, or going to them. Two of Chubu Denryoku's dams are on Tenryu river 100 km away. One is 50 and the other 100 Mega watts; in total 0.3% of Chu-den's capacity. The thermal power stations are all further away.

But, long distance transmission is typically hundreds of thousands of Volts. This has traditionally been done in AC, going back to the current wars of the 1880s and Edison's fried elephants. You can see a picture, the caption of which is "Edison am Phonographen. (Nach einer Phonographie)". My German's not very good, but this probably means: "Edison pissed off. (At losing current wars to arch-rival Tesla)"

AC voltage switchers have been around for a long time, but DC voltage switchers are relatively new. Long distance DC transmission is possible, and would make sense for large-scale solar farms. 

But if the electricity were being transmitted at 200 kv, that's a thousand times more voltage, a thousand times less current and a million times less power loss for each metre of cable. So the electric companies lose the same in a km of their cables as I do in a millimetre of mine. For each metre of cable in my house, they could send electricity to Tokyo and back.

Of course they have to get the voltage up and down, which has its own losses, and when long-distance AC power cables reach a town or village, the voltage is stepped down to one or two hundred volts, which can be used in houses, offices or factories, so it will lose at the same rate on the local grid as electricity from domestic solar panels.

This kind of small scale production is still rather new, and goes against Tesla's model of big production and distant transmission. This model has allowed dirty power stations, first coal then nuclear, to be built far away from centres of population. A big problem with AC is that it cannot be stored, and must be there when the power is switched on. Rather than energy that can be saved, it is power that must be used. DC can be stored in batteries; technology that is developing rapidly now that most people have one in the phone in their pocket. The only kind of AC storage available is when hydroelectric dams are used to pump water up a hill when there is excess supply, and let it down when there is excess demand. 

Another issue, for another blog, is the variability of output from the panels, especially on partly cloudy days, when it could rapidly change as the sun goes behind and emerges from clouds, and what can be done about that.