Tag Archives: renewable energy

Solar water heating

solar_water_heaterIf there is one renewable energy solution that can be safely recommended at present, it is solar water heating. There is one condition though: keep it simple. Lots of complex system exist to pump water around, to place the water tank below the roof or to retrofit your existing geyser, but these solutions only bring additional costs and reliability issuesIn the end, a simple passive collector with vacuum tubes connected directly to the water tank is all that is needed. 

Provided that you select an elegantly simple solution as described above, solar water heating is a great deal for three primary reasons:

First of all, at the risk of sounding like a bit engineer-like, everyone should know that solar hot water respects the second law of thermodynamics. Basically, this law causes useful energy to be lost to heat every time that it is concentrated or converted from one form to another.

For example, traditional water heaters use electricity which was converted from coal or gas at a 40-60% efficiency in large powerplants operating at very high temperatures. Solar water heaters, on the other hand, only concentrate the heat from the sun a little bit in order to heat up water to the temperatures that you require.

This fundamental respect for the laws of nature together with the simplicity of a passive solar water heater leads directly to the second point: solar water heating is attractively cheap. When compared to solar PV, a simple passive solar water heating system would typically cost you about 4 times less per unit of electricity saved.

Finally, solar water heating mostly avoids the primary problem hampering solar PV: intermittent output. Because the geyser storing the hot water is well insulated, it can effectively store in the heat that was collected from the sun over a long period. In comparison to solar PV therefore, solar hot water not only serves its purpose when the sun is shining, but also after the sun has set.

Naturally, solar hot water will work a lot better in hot and sunny places than in cold and cloudy places. After a hot sunny day, solar water heater will typically still offer a burning hot water for your early morning shower. For a cold cloudy day, however, the electric heating element built into the solar water heater will be required if you want to shower in the morning.

Solar water heating is also an excellent poverty alleviation mechanism. It is cheap and simple, does not need any connection to the electrical grid, and most poor people live in hot climates which are well suited for solar water heating. Hot water might sound rather simplistic, but a simple hot shower can add great hygienic benefits and the boiling temperatures reached in the geyser can even be used for sterilizing drinking water.

Yes, solar water heating cannot solve our energy problems, but it can certainly make a contribution. Water heating typically consumes about 40% of the average household’s electricity usage and millions of households cutting most of this sizable component can certainly make a significant contribution to the big picture.

solar water heating capacity

So, if you live in a reasonably sunny location, please consider spending a few minutes on the Internet, finding a certified hot water heater installer, and getting one of these elegantly simple pieces of engineering on your roof. It is a great way to simultaneously save money and save the environment.

Filed under: Consumption patterns – The green economy

Energy storage

As we have briefly discussed in the previous two posts on rooftop solar and micro wind turbines, one of the major obstacles faced by these technologies is their intermittency – the fact that they only generate power when the wind is blowing and the sun is shining. For interested readers, this and other challenges are discussed in much more detail in other pages.

The most convenient tool through which the intermittency can be addressed is energy storage. And the storage technology attracting the most attention is battery storage.

It certainly is true that cheap battery storage can help a lot with integrating intermittent renewables into modern electricity grids. If much of the large solar output around mid-day could be stored for consumption in the evening when demand usually peaks, solar power would be of much greater value to society.

Palmer - Solar alignment with peak

Actually, if energy storage technology was cost-effective, it would be great for our electricity systems regardless of intermittent renewables. We generally use significantly less electricity at night than during the day and peak-demand often lasts for only an hour or two. This variable load causes an inefficient use of power infrastructure. If cost-effective storage could shift some electricity generation from the night to the peak periods, we would need fewer power plants and would be able to operate these plants at a greater efficiency (shown below).

effect of electricity storage

Unfortunately, however, battery storage is still far from being cost-effective. Yes, like most clean energy technologies, battery costs have been declining significantly in recent years, but we will require much greater declines before it can be economically deployed. For example, I recently had an online discussion with a staunch solar advocate (and installer) who quoted me a solar power system with battery backup which can generate electricity at about $0.90/kWh – about five times the standard retail electricity rate.

From a more fundamental perspective, the problem with battery storage is that it consumes a large amount of energy in the manufacturing process. The vast majority of this energy will inevitably come from fossil fuels, implying that a solar power system with battery backup or actually have a rather large carbon footprint. As an example, a recent paper examining the potential of rooftop solar in Australia (one of the best places for solar deployment on Earth) found that such a system would only generate two times the amount of energy that was used in the manufacturing process over its entire lifetime  – an Energy Return on Investment (EROI) of 2:1.

This is a sizeable problem not only because of the large carbon footprint implied, but primarily because it is impossible to run a complex civilization like ours on such a low quality energy source. The chart below illustrates this by showing the energy return on investment required by several different levels of societal complexity.

Hierarchy of energy needs

One battery-oriented idea which deserves mentioning is the use of battery capacity in electric vehicles as a grid storage mechanism – so-called vehicle-to-grid (V2G) storage. This approach needs a massive fleet of electric vehicles, requires a similarly massive network of smart-chargers which can withdraw/store electricity in this massive fleet of electric vehicles, and also proposes the use of EV batteries (which are designed primarily for a a high power-density) for grid electricity storage (which requires a design specifically aimed at low costs and long lifetimes). For these reasons, this approach will also not be viable for many decades.

Despite these challenges, however, it is possible that battery storage can play a non-negligible role over coming decades as prices further decline. Cost-effective energy storage will open up a wide range of opportunities that have never been available to grid operators before. Until such a time, however, battery storage is not recommended as an option to reduce your personal carbon footprint. The batteries themselves still have a very large carbon footprint and currently available battery backup systems are inherently unable to support our civilization. There are many other much simpler and more efficient mechanisms for cutting your footprint.

Filed under: Consumption patterns – The green economy

Rooftop solar – Part 1: Reality check

Almost all environmentally conscious people love solar power and would gladly host a few shiny panels on their roofs. Indeed, from an ideological viewpoint, it is hard to find anything more attractive than the promise of abundant clean energy offered by solar power. However, even though rooftop solar can be a good way in which to reduce your personal carbon footprint, it is important to remain objective about the potential of this technology.

Given the enormous amount of positive press that has surrounded solar power over the past decade or so, one would think that it is taking over. The reality is, however, that solar power contributed only 0.17% of global energy in 2012 (BP Statistical Review). Despite rapid growth, solar remains a tiny energy source (about a tenth of the thin orange slither in the figure below).

Global primary energy by source

Yes, it is certainly true that the cost of solar panels has been coming down very impressively for many years now. In fact, the panels themselves are now mostly less expensive than all the other equipment and labour required to establish a working solar power installation. However, the graphic below from the International Renewable Energy Agency clearly shows that solar power remains substantially more expensive than all other sources.

Renewable energy prices IRENA

Residential rooftop solar panels are the most expensive kind of solar power available. These installations cannot benefit from economies of scale, are often installed at non-ideal angles to the sun and also present practical challenges stemming from the simple facts that a slanted roof presents a difficult working environment and that every roof is different.

Solar advocates would claim that rooftop solar in some locations is now cheaper than grid electricity (e.g. the picture below). Unfortunately, it is incorrect to value solar power at retail prices which include the cost of fuel, powerplant infrastructure, powerplant operation and maintenance, and electricity transmission and distribution. In very hot regions where solar power coincides well with maximum electricity demand from air conditioning, solar power can potentially defer investment in future power infrastructure, but in most locations, the only major cost avoided by rooftop solar power is the fuel that is burned in power plants. This cost is typically around $0.04/kWh, implying that the cost of rooftop solar in most locations remains 5-10 times greater than the cost it avoids.


Of course, if you use solar power to go completely off-grid, you can fairly claim that solar power has displaced the entire retail cost of electricity. Unfortunately, off-grid systems are much more expensive than grid-tied systems because they include batteries. Living completely off-grid also requires lifestyle changes than very few people in our modern society will be able to make.

It is therefore clear that large-scale deployment of rooftop solar will be a very expensive business. If all of these costs are carried by the environmentally conscious person installing the panels, this would not be a problem, but the reality is that the wide range of incentives for solar PV is socializing these costs in a highly unsustainable manner. For example, Germany is currently in a position where generous solar PV subsidies is creating a rather perverse wealth transfer from poor people who spend a substantial portion of their disposable income on energy to rich people who can afford the initial solar PV capital investment.

One should therefore carefully consider any decision to install rooftop solar. The next post will go into a little more detail on when rooftop solar can be a good idea.

Filed under: Consumption patterns – The green economy

PS: Those with a more technical interest in intermittent renewables such as solar PV and wind can check out the articles on this page. Most of these articles are also published on the popular energy discussion forum, The Energy Collective, where they have been discussed by a wide range of energy enthusiasts. More specifically, a good scientific overview of the potential of rooftop solar in one of the most ideal countries, Australia, can be viewed here