I could be wrong. I was quite surprised too. When I first got that result, I thought “that can’t be right”. Check the numbers yourself. I was assuming 2 suns/day average insolation (ie., 2kWh/day/m2), of which ~40% is recoverable as heat, bearing in mind that the tubes are tilted, so you can’t actually cover a solid area with them. I should stress that I was talking about distributed heat collection, not centralized solar thermal electricity generation, which is only marginally more efficient than PV. I’m aware of the shortcomings of concentrating solar and I consider it a niche technology, at best.
HH is correct that solar energy flux in the UK is all wrong - it doesn’t match what we want. Insolation during the winter is <10kWh/m2 per week, and variable. If your heating load is 150kWh/week then you need >15m2 of panel area, and a big tank. But so what? Including the special insulated tank and all the pipes and control systems, that’s about £6000 worth of kit; if you install it in a new-build house, that’s the bottom-line price. If the equivalent cost of electric heating is £0.2/kWh, and assuming 150kWh/week in winter and 50kWh/week in summer (you still need hot water, remember) that’s 4770kWh/year, or £950. The solar system pays for itself in <7 years, even in sunny old Britain. That’s assuming a completely standard house design, not an ultra-efficient one. Again, you can easily check my figures if you think they’re wrong.
And you could improve on that. Where are the absorption-cycle aircon systems that can soak up that massive amount of extra heat available in summer, and use it to pump heat out of your living room? Why are there no absorption-cycle refrigerators on the market? The technology is there. The market demand is not, because no houses are being built with solar hot-water systems to connect them to. The only appliances in your house that actually NEED electricity are the lights and the electronics, and they use a very small amount.
I don’t really understand the issue with freezing. Most solar-heating systems don’t take the water outside - in fact, if you did that, I’d say the biggest danger would be from water boiling and causing a steam explosion. They normally use a more suitable heat-transfer fluid to bring the heat back to the tank and the water circuit. The main complexity is in the heat exchanger, which must be designed so that the (toxic) heat transfer fluid can never get into the water.
Sure. In Taiwan, we have the opposite problem: too much heat (don’t forget that water has a high specific heat capacity - I bet water heating is still your main energy expenditure). But the solution is as I described above: absorption-cycle aircon, which takes in high-quality heat (from the solar collectors) and very low-quality heat (from your room) and expels medium-quality heat (into the outside air). You can do the same thing with a reverse sterling cycle too. Far better, of course, would be to design buildings properly so that the don’t heat up so much in the first place. I like cooking myself, and my first choice for fuel (if no gas is available!) would be biomass. Yes, I know, you can gasify biomass, but why bother?
A little aside, on the topic of air-conditioning. People think of wasted energy as just, well, wasted. It’s “disappeared”. Often, that isn’t the case - it’s gone elsewhere, like agricultural runoff. Example: imagine a typical community in Taiwan in the middle of summer, with a couple of hundred aircon units blasting out (roughly) one megawatt of heat into the surrounding air. That’s 80% solar heat, which was not only collected completely unintentionally, but has actually been “upgraded” to high-quality (lower entropy) heat by the aircon units. Yes, it’s an enormous waste, but it also warms up the surrounding area; and when you’ve got everyone doing the same thing, the whole city ends up feeling hotter. Which means people crank up the aircon.
2kWh/day, tops. In a more-efficient future, I expect domestic lights and electronic appliances should consume no more than 0.5kWh/day.
No, I don’t, and I wouldn’t try (I’m in a standard high-rise in Danshui). We will always need power companies. I don’t believe in the “self-sufficiency” thing, although there’s no harm in people putting panels on the roof if, like you, they have the ideal orientation for it. I just think that future “power stations” are going to be ad-hoc affairs, a couple of hundred meters across, installed where they’re required on empty spaces that nobody wants or that can do double-duty.
Not hard at all - especially if, as I suggested before, we start “at the bottom”. The picture looks hopeless if you focus exclusively on the industrialized countries, but if you look elsewhere, you see nothing but opportunities.
Now I’m glad you mentioned that, because that’s exactly the sort of thing we’ll see more of in the future. More haste, less speed. I envisage a future where things trundle along at a more leisurely pace, but yield faster end-to-end journey times because of operational improvements.
Example: my farmland is down in Miaoli, and it takes me three hours to get there. 40 minutes on the MRT, 15 minutes buggering about at the station, 30 minutes on the HSR, another 10 minutes waiting, 20 minutes on the train, and 45 minutes on a scooter. Now, that’s 80km as the crow flies. I’ve achieved an effective average speed of 30kph, despite the fact that I spent some of that time at 300kph.
Assuming some hypothetical future transport network that might cover a meandering 160km getting me there, I’d still only need to hit 60kph to achieve the exact same result. That transport system would have to offer me a clear end-to-end run. In that scenario, I’d have a much less bothersome journey, and I’d use so little energy (I’d guess about 5kWh, max.) that it could be easily solar-powered. I don’t know where people get this idea that we have to live like the Amish to be energy-efficient.
But that’s my point. It’s ho-hum. It’s the kind of airhead stuff you’d read in Apple Daily. Why is that a problem? Because it’s the most common form of journalism on all environmental issues, and it shapes public thought. We can’t afford ho-hum. This stuff is