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Assuming a standard sized, mid terrace house with four bedrooms, a kitchen with fridge, electrical cooker and washing machine, a bathroom with shower. What would be normal daily energy consumption over the year?

Could this feasibly be extracted by all the sunlight that falls on the building, that is on the roof, and building walls, assuming 100% efficiency?

(My future science-fictiony solution is a coat of paint on the building which has the property of photo-synthesising at 100%! (But of course much likely a lot less))

I just want to see just how feasible this would be without going into how one could manufacture such a paint.

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There are people who live "off the grid" using solar and/or wind plus a bank of batteries and an inverter. But the thing is that it costs a lot more than using grid power if it is available, and you have the environmental implication of that bank of batteries to think of. –  dmckee Dec 2 '12 at 4:16
I calculated once how much it would cost to get all the house's energy requirements from sunlight and the cost, where I live, came up to half the price of a house. –  anna v Dec 2 '12 at 5:50
There are indeed researchers at Caltech (and presumably elsewhere) who work on making just such a photosynthesizing "paint" for large-scale, cheap solar power. It's not entirely science fiction. –  Chris White Dec 2 '12 at 10:38
@White: Glad to know some-ones doing some useful work on my idea :-) –  Mozibur Ullah Dec 2 '12 at 14:54
@ann v: My lap-top would have once cost substantially more than my house :) –  Mozibur Ullah Dec 2 '12 at 15:03

5 Answers 5

up vote 6 down vote accepted

First, let's do some back-of-the-envelope calculations. The word for the average amount of Solar energy reaching the Earth's surface over the course of a year is "insolation." According to this page, insolation in populated areas ranges from $2.27\,\mathrm{kWh/day/m^2}$ in Norway to $5.26\,\mathrm{kWh/day/m^2}$ in Miami, Florida. In slightly different units this gives a range of $94.6\text{-}219\,\mathrm{Wm^{-2}}$. This is the total energy reaching the surface, and it's not thermodynamically possible to extract all of it, but since Solar radiation has an effective temperature of $6000\,\mathrm{K}$, you can get pretty close. So let's apply a factor of about 90% and say you could extract around $85$ to $200\,\mathrm{Wm^{-2}}$ with advanced enough technology.

Now, from here the US average domestic power consumption is around $2\,\mathrm{kW}$. (The US average is pretty high compared to most other countries.) This means that you would need around $2000/20 = 10\,\mathrm{m^2}$ of super-efficient panels to support you in Florida, whereas in Norway you'd need around $2000/85 \approx 23.5\,\mathrm{m^2}$. Both of these are doable as long as you live in a house rather than an apartment.

So basically, yes, taking 100% of our domestic power from Sunlight is entirely possible on the basis of how much energy is available. These figures don't include industrial uses, but there's more than enough power available for those as well, especially if you're willing to consider having extensive Solar power plants in the equatorial deserts instead of producing it all locally.

However, there are serious problems involved in storing that energy. It's not just that the sun only shines during the day, it's also that there's a lot more insolation in the summer than in the winter, especially in more temperate latitudes - and the energy is needed more in the winter. Cloud cover and day length both contribute to this seasonal variation. Batteries would be too large and inefficient to do the job for a single house, not to mention extremely expensive. So barring a major technological advance in energy storage, you'd probably still to do the storage in centralised plants even if everyone had their own local solar power generators. (E.g. by industrial production of hydrogen, or by pumping water into reservoirs, so you can recover the energy hydroelectrically when it's needed.)

This is another reason for envisaging large equatorial solar power plants. The sun is always shining somewhere on the equator, so with a global power grid you'd need a lot less energy storage. But of course this would be a huge mega-engineering project, and not without its environmental impacts, because of its scale, the amount of materials it would use, and the amount of land it would cover.

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Very sensible numbers, calculations, priorities, and conclusions. –  Luboš Motl Dec 2 '12 at 8:11
@Nathaniel Good calculation initially, so +1, but I'm not so optimistic as you regarding non-local power supply. The US power grid suffers enormous losses simply getting electricity into the cities from elsewhere in the same state. Either you need an entirely different distribution system or a conductor far better than copper. –  Chris White Dec 2 '12 at 10:34
Nice answer. I'm more optimistic about getting large-scale storage on say a small village/community size than getting fusion to work efficiently, and thats really without knowing any of the technological issues at hand :) –  Mozibur Ullah Dec 2 '12 at 15:00
Its an inversion of the current system, where power is generated centrally & consumed locally; whereas you're invoking local generation and central storage. –  Mozibur Ullah Dec 2 '12 at 15:07
@ChrisWhite yeah, transmission losses are an issue, but superconducting cables are not outside the reach of modern technology. Or maybe you could use the plants to produce hydrogen (or some other less bulky chemical energy storage medium) and ship it to where it's needed. Or a combination of the two. –  Nathaniel Dec 2 '12 at 15:19

Well, as has been mentioned, it is really an issue of your consumption rate. This physicist here has already made the transition to solar power and storage, complete with detailed description and numbers. He's a bit evangelical, but several of his posts are quite interesting. But yes, with an emphasis on efficient appliances and sparing use, one can have modern amenities on a solar power supply.

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One can add that the combination of geothermal ( popularmechanics.com/science/energy/hydropower-geothermal/… ) for heating and cooling with solar panels and batteries is the most efficient way. –  anna v Dec 2 '12 at 5:55
I have family in bangladesh living in rural areas. They don't really use fridges, as produce is available locally & seasonally; and they wash their clothes by hand as they have done for generations. Their power consumption is simply for light generation in the evening, I never did ask them whether they watched the telly with it. So its certainly feasible now for rural communities in developing countries. –  Mozibur Ullah Dec 2 '12 at 15:11

There exist photovoltaic membranes

photovoltaic membranes

They could obviously cover walls too. So the answer is that yes, it can be done.

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fantastic. Their websites a bit coy in describing just how much energy these membranes produce though. And I couldn't turn up anything after a bit of quick browsing. –  Mozibur Ullah Dec 2 '12 at 18:50
That is a cover website. here is a company icopal.co.uk/Products/Sustainable_Construction/Eco_Activ/… , and another one www2.dupont.com/Elvaloy/en_US/uses_apps/solar_roofing.html . Searched for "solar pv membranes" –  anna v Dec 2 '12 at 19:31
thanks for the info. –  Mozibur Ullah Dec 2 '12 at 19:49

a Dyson swarm will collect about $10^{24}$ or $10^{25}$ from the total $10^{26}$ watts emitted by the sun. So, definitely and without a doubt, solar energy is the energy of the future.

We just need to stop thinking in short sighted goals as coating the earth with solar panels; earth real estate is way more valuable that the energy density it can retrieve. Consider that at mercury orbit, the square meter of solar panel deployed in space might pay itself with the collected energy, even considering the inefficiencies of existing chemical energy conversion mechanisms for energy storage, such as water hidrolysis. Now that we know that mercury has ample water resources, this becomes a no-brainer

For energy production in earth surface, nuclear plants are way more green than the ecologist zealotry and propaganda would lead us to believe.

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a dyson swarm is a long, long time in the future. I'm thinking of technologies that my children might get to use, if thats not too short-term for you. –  Mozibur Ullah Dec 2 '12 at 18:52
in that case, our children will be fine with nuclear power –  lurscher Dec 2 '12 at 18:53
I don't have any problem with nuclear energy, but that doesn't mean we can't and shouldn't develop other alternatives. The nuclear & fossil-fuel lobby are very well established now. The renewable lobby is only just getting established. Theres plenty of zealotry around for everyone to share in... :) –  Mozibur Ullah Dec 2 '12 at 18:58
the renewable lobby is about subsidizing inefficient energy sources with money that would be better spent to develop more secure nuclear power plants. Nuclear plant designs will be inherently risky if they rely on the ocean as a thermal reservoir. You want efficient, green and safe energy sources more pressure and investment is required to develop alternatives to the problem of cooling –  lurscher Dec 2 '12 at 19:03
The renewable lobby is very much a new movement. We can only really guess at what efficencies can be made in the future, hence the content of this question. ENIAC weighed 30 tonnes, cost $6M, required 150kW, and ran less than 500 flops. Compare that to your laptop. To really do a cost-benefit analysis you must compare over time. Exactly how much did the manhatten project cost in todays term? In comparison the renewable lobby have cost far, far less, so far. –  Mozibur Ullah Dec 2 '12 at 19:15

Well, what is your electric bill?

At 100% efficiency, you could theoretically produce $1.36 \frac{kW}{m^2}$ from solar energy . Check and see if the size your house/roof would cover your average consumption. If so, then with enough batteries to last you throughout the night that you charge in the day, that would work.

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That power figure needs to be adjusted for the local latitude and time of year as well as for poor whether. –  dmckee Dec 2 '12 at 5:16
Well, yearly fluctuations and bad weather, I assume, would cancel out when averaged over an entire year. Unless the location of choice is close to either of the poles, adjusting for latitude isn't as crucial as coming up with a more reasonable figure for the actual collection efficiency. –  Benji Remez Dec 2 '12 at 5:24
That figure is insolation at the edge of the atmosphere. At sea level, it's more like 1 kWh/m2 at peak sun –  EnergyNumbers Dec 2 '12 at 8:07

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