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.

Conclusion

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.

References

[1] http://www.nrel.gov/docs/fy04osti/35489.pdf

Progress report on water systems

Here is a brief update on how the water systems I've installed are faring.

Hot water

I have written articles about my hot water systems here and here.

The system was finalised at the beginning of September 2014, and has worked flawlessly since. We have not boosted it through Spring/Summer -- in fact, I have shaded the collectors to stop it boiling. Some things I really like about it:

• I now have shorter "runs" of pipe between the hot water system and where I use the water, which means less waste
• Because water is effectively heated instantaneously within the hot water system tank (discussed in previous articles), it has no taste, and so can be used to make tea and cook with. There is also no concern with Legionnaires' disease.

Rain water

I have written about our rainwater systems here and here.

We have been exclusively using rainwater since the beginning of September. This includes watering the garden, washing clothes and people, toilet flushing. At the beginning of September, we had ~35 kL of stored water of which I estimate about 30 kL is usable (due to the position of the tanks relative to input/output feeds, etc) -- this was not something I previously considered. Because the system was not completed until December, we did not capture the Spring rain maximally, and Spring rains were very sparse this year. It has been a relatively cool and dry Spring.

We have been very frugal with water, and have captured our washing machine grey water, and grey water from the kitchen for use on the garden (we don't keep washing machine grey water if washing nappies). Until last weekend, I estimate that we had used about 23 kL or a bit under 200 L/day.

I (very roughly)  estimate that this water is used as follows:

• 6 - 8 toilet flush/day: 50 - 70 L daily
• 1 load of washing / day: 70 L daily
• kitchen sink: 30 L daily
• garden direct watering: 50 L daily
• bath/showering: 30 L daily

Clearly, the big users are the toilet and the washing machine. 

Toilet

The toilet is a total loss, because that water goes straight to waste. I want to replace one of our flushing toilets with a composting toilet. This will save a lot of water, and also give us more compost.

Washing machine

Most of the washing machine water we use in the garden, though in a sub-optimal way. This probably seems like a lot of washing, but we have two young children, one of whom is in the process of toilet training (ie. we still wash nappies, as well as soiled clothing)

Bath/shower

I generally wash in the shower every 2 - 3 days, and sometimes use the bath after the kids. They have a bath every 2 - 3 days. My wife often showers at work.

Lessons learned

• Some water is easy to save, and grey water represents an easy saving if it displaces fresh water on the garden.
• Timer taps make it easy to waste water on the garden. Also, it is hard to measure how much water is being used. I set up a timer tap out the back on the vegetables and fruit trees (separate circuits). Given the amount of grey water we have, it is almost possible to water all our trees and vegetables with grey water only (note that there are hygiene implications of watering vegetables with grey water -- make sure you do your research if you plan on doing this). In future, I will consider watering more by hand and less by the drippers
• I accidentally let about 5000 L out of the tank via the vegetable drippers. I wanted to give the vegetables a bit of water before a very hot dry day, but forgot to turn them off until the next day. In future, I will never leave a tap running without an auto-off or an alarm to remind me.

Likely outcome for the Summer of 2014/2015

We will probably run out of water this Summer. I think we have about 5000 L (accessible) remaining in the tanks, which will last only about 25 days. I doubt we will get significant rain in that period. (We have had about 15 mm of rain in the last 4 days, which is very unseasonal, and is factored into this estimate). We are in the fortunate position to be able to switch over to town water easily.

Plans and thoughts for Summer 2015/2016

• I would like to have one toilet replaced with a composting toilet by next Summer
• I might add some extra sheeting to the pergola which will increase the rain collection area (very important for catching every drop of Spring rain)
• We now have all the tanks installed and connected, so will maximally collect the Spring rains in 2015
• I will try to do more to keep "dirty" clothes separately in the laundry, and wash them irregularly, keeping them for dirty tasks. This can hopefully ease the washing load

Conclusions

Water is one of those things that requires a whole system to perform well. Any compromises in subsystems will compromise the whole system. We are getting closer to the ideal that I modelled here, at which point I think we will operate (almost) solely on rainwater. I am hopeful that next Summer, even if we don't have a composting toilet, we will go a lot closer. Even this year we might well have made it through summer, had I not accidentally released that water. 

I think this system shows that it is possible to be self-sufficient for water with a relatively small amount of storage, however it does not leave any margin for error. In a fully off-grid scenario, I would want double the storage, even if it was rarely/never used. Of course, in such a scenario space would be less of a premium than it is in an urban environment!

----------------------

This article was written by Angus Wallace, and first appeared at guesstimatedapproximations.blogspot.com.au

 

When does it make sense to go off-grid

Consider a household that already has enough PV to cover their personal use, just not always at the times they want to use it. They might consider going off-grid by buying batteries, etc.

This is the situation I'm in. We use about 3 kWh/day, and are exporting, on average, about 7-8 kWh/day -- so we certainly have plenty of power. If we went off-grid, we'd probably want at least 5 days' power, so 15 kWh storage. I haven't priced this exactly, but I think such a system would be at least AU $8000.

What would this save us? Well, currently our exported power is sufficiently above our consumption that I estimate our bills will be $0 henceforth (ie. I think we are exporting enough power to pay for our consumption and the grid connection). Therefore, there's no benefit to us doing that!

In fact, at current electricity prices, I can't think of a situation where doing this would be justifiable. Perhaps if we were paid significantly less (ie. as the difference between what we pay to use power versus what we are paid for supplying power becomes greater, such a system would become more attractive. What sort of difference would be needed to make this worthwhile?

I'm assuming a fixed cost of $8000 to take ourselves off-grid. I recognise that for most people (because of their greater consumption) it would be more expensive. However, in that case their savings would be greater. It's not proportional though: because we use so little power, the connection fee makes up a sizeable proportion of our bill.

Exploratory model

I have done some basic modelling of how variations in our electricity billing would affect the payback of a basic off-grid system.  There are two main components to our bill -- a quarterly service fee (connection fee), and a charge per unit of energy (kWh) used. I've modelled a range of fess and tariffs, which are shown in the table below. Different connection fees are shown across the top, and different tariff structures (the difference between our consumption tariff and the Feed in Tariff (FiT)) are shown down the side. The values in the middle is the estimated ROI for the appropriate fee-tariff combination. My belief is that the "difference in tariffs" will go up, while the basic consumption tariff stays about the same and that the quarterly connection fee will also go up. There is talk of increasing the cost of connection, so that "solar users pay their fair share" (factually incorrect: it's not that houses-without-solar subsidise houses-with-solar, but that houses-without-airconditioning subsidise those with airconditioning. Utilities don't want to discourage consumption. These articles discuss in detail.). Also, the cost of off-grid battery storage is likely to decrease markedly in the next few years, but for simplicity I've only considered an $8000 system.

I've colour-coded the data, and believe that the red ROI levels are uncompelling. The orange is marginal but might be considered by someone who was passionate about being off-grid. The green results are starting to look economic.

I modelled the payback on the basis of varying the difference in consumption tariff and the FiT. At the moment, we pay AU$0.35 / kWh for electricity we use and get AU$0.24 / kWh for electricity we export to the grid. The difference is AU$0.11 -- but I expect this to increase in the future (especially when the FiT decreases in 2016). I've also modelled changes in the quarterly connection fee. Now, it is $70/quarter, but I think it's likely to increase.

Results

With our current tariff structure, I estimate the ROI for an off-grid system to be 6% -- this is not compelling. If the tariffs remain the same, but the quarterly cost increases to $130, I estimate the ROI to be 9% -- still marginal. Similarly, if the quarterly cost remains $70 but the difference between import and export pricing rises from AU$0.11 to AU$0.22 (quite possible in 2016), then I estimate the ROI to be 9%. If the difference between import and export pricing rises to AU$0.30 AND the quarterly cost increases to $100 (I consider this reasonably likely in the next 3 years), then the ROI is 12% -- this is starting to look like it could worth doing. Couple that with a 25% decrease in the price of off-grid systems in that time (given that some people are predicting a 50% decrease in price by 2020, this seems plausible) and the ROI is 15% -- I would consider doing this, and I bet a lot of other people would too.

Caveats

One caveat is that because we use so little power, changes in the quarterly connection fee have a big affect on the ROI. For households that use a lot more power, this will be less important and only the "difference in tariffs" will have much effect.
A second caveat is that this model does not consider any on-going expenses associated with maintenance of an off-grid system.


This post was written by Angus Wallace and first appeared at guesstimatedapproximations.blogspot.com.au