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.




  1. If you're not going to use battery storage, you WILL use coal/oil/gas powered electricity. More than half the time. PV makes no electricity at night and very little during very cloudy weather. Your last sentence can't be followed unless a drastic change is made. Really drastic. One that isn't very compatible with our existing methods of this industrial society. All power usage ceases at night without storage.

    Yes, we need to manufacture as much PV and other renewable energy technologies as we can NOW but don't fool ourselves that we will have a society that in any way resembles what we have now powered by it. A lot of the processes to manufacture PV are not at all compatible with just a few hours a day of electricity that PV by itself can provide. If you want to manufacture PV, you WILL be using fossil fuel electricity to do it.

  2. Hi August,

    This is a rabbit-hole that is a post onto itself. Some thoughts:

    I haven't done an exhaustive study of night-time energy use at my house, but from the times I have taken an evening and morning reading, I think it's generally 1 - 1.5 kWh. The vast majority of this is refrigeration. Refrigeration is something that can be shifted to daytime-only by use of a phase change system (eg. which stores energy as frozen refrigerant that is "released" slowly over time to keep a fridge/freezer cold.

    You are right that any energy drawn from the grid is potentially sourced from fossil fuels. Where I live our grid electricity is about 30-40% wind power, but the nuances of carbon trading mean that the "renewable" parts of that power are actually sold to other customers (offsetting coal-powered energy). Also, there will still be times where wind and solar aren't producing and so any consumption is coming from coal/gas -- in which case even the purchase of GreenPower doesn't stop consumption from increasing the electricity spot price (thus supporting fossil electricity).

    However, that's a separate thing, and is not an argument against the grid per se, but rather a call to reform utility level power generation! ;-)

    Yes, that last sentence is a gauntlet being thrown. The whole "if it's not perfect it's useless" thinking really bugs me. Frankly, I can't believe that greenies would criticise solar PV while continuing to use coal power. I suspect it's just a defence for inaction.

    Regarding changing society to accommodate renewables, I'm not convinced society _needs_ to vastly change -- however, if we mismanage this transition, it _will_ vastly change (for the worse). I think we could reduce society's energy consumption by 99% and still preserve its essential fabric. But we won't know unless we try ;-)

    Cheers, Angus

  3. Hi Angus,
    Man, how hot was it outside today? I worked outside all day and am now feeling not so good... Forgive me in advance if anything that I've written here doesn't make sense! ;-)!
    As a general observation, your writing style has changed with this entry - and I approve - as you are critiquing as well as providing real world observations.
    Your winter average solar PV production matches my expectations of the 4.2kW PV system here. With a lot of mucking around you may be able to increase your winter output significantly.
    I noted that your panels are tilted at 22 degrees which is reasonably flat-ish and increases summer energy production over that of winter. A good rule of thumb is to angle the panels to that of your latitude. Having said that mine are at about 34 degrees - which is close enough. Adjustable panels aren't that much of a drama as tilt legs are readily available.
    Of course we could run an Industrial society from renewable energy sources, it just won't look like our current expectations of energy usage. I can freely arc weld for 10 months of the year for example.
    Off grid has resilience value because being at the end of the line for the grid network, the power goes out all of the time and during a bushfire it is deliberately cut off and electric pumps are a wonderful thing in those circumstances.
    Well done you, keep up the good work. It will be interesting to see how you progress as winter closes in. Not to stress, it took me 3 years of mucking around and adaptions to kick the generator habit completely. And, over the next few months I'll chuck another panel on the roof which will bring it to 4.4kW of PV.
    Cheers. Chris

  4. G'day Chris,

    Yeah, it was roasting. We got the cool change at 3:30pm -- dropped 15 degrees in about an hour. Of course, we got no rain! But we did open every window in the house ;-) Went out and bought some extra insulation for the roof too...
    I agree about increasing the inclination of my panels to favour winter production -- it is something I've considered doing. I ran the numbers for our solar HWS, and found that about 45 deg is a very good compromise between annual and winter production: At 15 degrees from perpendicular to the sun's rays (which are at 60 deg from zenith at the winter solstice here), you lose about 4% of production (in winter) but still keep good production in summer.

    Your point about grid reliability at the end of the line is a good one, and makes an off-grid or battery-augmented grid connection extra appealing.

    Heh -- maybe the heat was making me grumpy ;)

    Cheers, Angus


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