Wednesday, February 11, 2015

Solar PV: opinions, merits, challenges

I read a lot about solar photovoltaics (PV). Some people believe they will save the world and that, in the future, we'll have electric cars with a solar panel on the roof (let's call them techno-utopians). Others believe that solar is useless. Interestingly, that latter group fall into two main groups (in my experience):
  1. fossil-fuel-loving climate-change-deniers, who think that solar will never replace coal/oil/gas
  2. devoted environmentalists, who believe that the cost of manufacturing solar PV outweighs its benefits (presumably, they believe that some sort of return to a non-industrial society is therefore required)
I have sympathy for the environmentalists, and can see where they're coming from, but I think they're wrong. I also think the deniers are wrong. I believe that solar PV can replace many uses of fossil fuels, and is starting to do so right now.

Making solar PV

Solar PV panels are reasonably energy-intensive to manufacture. They are a semiconductor and, although they don't require the same level of precision as (say) computer chip fabrication, PV factories still require clean-room manufacture. They also require a large number of obscure material inputs. This is energy-expensive. However,
  1. Even with current technology, a solar PV system is thought to be energy positive after as little as a few years (ie. it has produced all the energy in its manufacture). [1] (remember that the system will generally last well over 25 years)
  2. There is much research into lower energy cost solar panels. This may reduce the energy and material inputs still further

Solar PV performance

The amount of sunlight falling on the ground represents an absolute maximum to what energy a PV panel can produce. However, given most panels operate at well below 20% conversion efficiency, there's a lot of headroom! In other words, I'm not sure that lack of winter production is quite as bad as it is often made out to be.

PV panels "thermally derate", which means their production decreases when they're hot. On cold days, they work much more efficiently. Thus, if panels are oriented for winter production, cooler temperatures mean that they'll work more efficiently. This increase in efficiency tends to partially offset a lack of winter sun intensity. Of course, a cloudy day is a cloudy day, and production will be lower. Such is the nature of renewables.

What is solar capable of at a domestic level? Evidence

I have a 2 kW system at home, facing due north at about 22deg inclination. I have taken regular meter readings for the last 12 months, and throughout last winter I exported on average 3 kWh/day to the grid (in other words, the panels' average production was greater than this, because some of their power was consumed on site and not exported). I live at latitude 35 deg, in a climate that is often overcast and rainy in winter.

The data I've collected are shown in this article. Note that the winter data look artificially bad because at the time we had an electric storage hot water system that was consuming about 6 kWh/day (now replaced), some of which was produced by our solar PV and hence not exported to the grid.

My feeling is that my family of four could go off-grid with the system we have now. It would not be hard for us to live within our solar PV energy budget as it currently stands. It is possible that we are doing this right now, however winter 2015 will show whether our solar PV production exceeds consumption. Right now, I'm betting it will.

But, solar PV can't power industrial society!

The simple fact is that we do not know if we can run an industrial society on solar PV and wind power -- we've never done it before. I think that, given that an industrial society can be run on 1% (or less) of current power consumption, that it is possible to do this -- though there would be challenges. The question is: do we have the political will to vastly reduce our energy consumption to enable a complete transition to renewable energy?

I think we need to conceptually separate technical and political limitations. I especially think we should not limit political considerations based on incorrect technical opinions (eg. someone saying "we should not invest in solar or a transition to renewables because it is technically infeasible to replace fossil fuels and maintain our society": the latter part of that statement is unproven)

Solar is not a silver-bullet -- there are no silver bullets -- but solar can do a lot. Some people think that anything that is not perfect is useless. That logic is fallacious, in my opinion.

Off-grid versus grid-tied solar PV systems

While I'm at it, I also tire of criticisms of grid-tied solar, as if only off-grid systems have merit. In broad strokes, having a network will almost always represent better resource use than having batteries, because it means that resources can be shared (compare the installation and maintenance energy-costs of batteries versus a grid connection). If a network is available, it is best to use it (even if it is a "network" of two dwellings). By all means add some batteries if you want, as this can help the network function more effectively, but setting up batteries as an off-grid system means one requires a massive excess of storage for the rare occasion that it's needed.


Our current way of life is unsustainable. This means it won't continue. We cannot keep burning fossil fuels. Solar PV offers an alternative energy source that is available right now, that can probably allow us to maintain many/most important aspects of our society. 

It is not certain that we will successfully transition from fossil fuels to renewable energy. Failure to do this means our civilisation will collapse. We need to be installing as much solar capacity as possible, as quickly as possible, and not waiting for some pie-in-the-sky, perfect technology to appear. 

To the greenies who don't believe in solar PV or renewables, I say: fine, don't use them. But don't keep using coal/oil/gas powered electricity -- you know that road is a dead-end.


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