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Kris De Decker


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Great posting!

I've often had to put up with people who asked, "How many solar panels do I need to run my electric baseboards, hot water heater, and hot tub."

Sometimes, I just don't know how to respond to such comments.

Heat is a low grade of energy; electricity is a high grade of energy. They each have their need and appropriate sources, which you've summarized very well here.



Another excellent article - it should prompt more thinking about energy quality along with energy quantity. I think that our current energy systems provide such an extravagant supply in the developed Western world that we have somewhat lost a nuanced sense of energy application. This article is especially good when combined with your essays on pedal powered technology for mechanical (versus electrical) outputs.

Kris De Decker


The Solar Fire P32 costs 7500 dollars not Euros



Kris, thanks for the enlightening post - I work in the solar industry and try to follow diligently the options available, but still have missed number of these. I suspect you may already be aware of it, but if not, you might be interested in a company called Cogenra. As the name suggests, it's a cogen system (solar), and while it's proprietary and definitely still high tech, I believe it's compelling. YMMV, keep up the great work



What about using a heat pump coupled with solar photovoltaic or wind? This works pretty well for heating living spaces, since the temperature differential required is not that great. However it's obvious that we can capture more thermal energy from a given area of sunlight than we can electrical energy with current technology.

There are solar panel factories that run on the power of their own solar panels, and there is no technical reason why more intensive processes (like aluminium smelting) couldn't be run off the sun (either thermally or via photovoltaic) - it's only an issue of cost and raw material availability.

Joe V.


Mention should be made of another approach to low-tech solar concentration, which is the so-called infinitely large solar furnace using a grid of small, flat mirrors, each aligned so as to form, in affect, a fresnel mirror panel. Here's one such example, which can easily be adapted on a small scale for use as a solar stove (concentrating sunlight onto the bottom of a cast-iron skillet), or other similar application:


Made larger, these panels can be used to generate extremely high temperatures, useful for the types of industrial applications mentioned in the article.

I made a small version of this concentrator, starting with a box of 12" mirrored tiles purchased at a local hardware store, cut into 2" squares using a simple glass cutter, the mirrors mounted to a simple perforated masonite panel using the method described in the above link, such that each can be adjusted to focus its light onto the common focal point of the panel.

~Joe V.



A generally good article on solar power and factories, but some basic errors of fact (or at least emphasis) which could easily have been checked using a search engine.

For example it says:

"Though today in some locations it may be as cheap to produce electricity with wind or solar energy as with gas or coal, it still remains significantly cheaper to produce heat with oil, gas or coal than with a wind turbine or a solar panel. This is because it takes 2 to 3 kWh of fossil fuel thermal energy to create 1 kWh of electricity, so it is at least 2 to 3 times cheaper to make heat by simply burning the fossil fuels directly than to use an electric renewable technology at grid parity."

I note – this true ONLY if pollution and environmental damage is allowed to remain uncosted into the price!

The current price regimes for fossil fuels of all types include no value for damage already done to the environment at a local let alone a global level and does not include a value for damage being done right now. So there is a 300-year debt to be recovered and that debt is still being incurred until we price fossil fuels to account for the externalities inherent in their extraction and use. The price regimes also take no account of long term scarcity – our economic system assumes that resources are infinite (by assuming that as one resource diminishes, and so the price therefore increases, more of the same resource will be found (as the higher price makes it ‘more cost effective’ to use lower grade or less easily accessible resources). That economic thinking also says that if one resource is exhausted entirely then another will always be found to take its place.

This is how humans have lived for eons – we stay in one place until what is available to sustain our lives is used up, or the waste we produce makes it unliveable (or often both) – then we simply move to a new place and start again. Of course we live on a finite Earth and are now finding that we can no longer do that – so we have no choice but to create an economic system to account for that, or modifying the economic system we have to not allow uncosted and uncharged for externalities – because in that finite closed system we live on we all pay in the end anyway!

A further example the article says:

"Solar panels and wind turbines do not need fossil fuels to operate, but they do need fossil fuels for their production. You won't find any factory manufacturing PV solar panels or wind turbines using energy from their own PV solar panels or wind turbines."

Again I note that this is simply not so – there are many, many PV panel factories using solely renewable energy including from roof top panels on the factories. These factories are also using various forms of renewable energy for process heat (<400 degrees C). They are in Europe, USA, China, Brazil, India – you name it. Sure they are not the majority and there must be more, but your article says there are none.

There are a number of other errors of fact or emphasis or claims of ‘all’ or ‘none’ where it should be ‘some’, but I see no point in doing a point by point correction.

As I said, the mag is a good one, but this is poor research and journalism from what purports to be an ‘in-tune’ online source. If readers like me find errors that are as egregious as I think these are, then your credibility will take a hit. That’s the reason I raise my concerns – in the hope that it can help the mag improve.

Kris De Decker


@ Bloss:

"this is true ONLY if pollution and environmental damage is allowed to remain uncosted into the price!"

Of course, but unfortunately that's how it is. Whether you and I like it or not. Nevertheless, even if pollution and environmental damage would be included in the price of fossil fuels, it would still remain cheaper to use solar energy directly instead of producing electricity using wind turbines or solar panels and then converting that electricity into heat.

"there are many, many PV panel factories using solely renewable energy including from roof top panels on the factories."

Could you give at least one example? To my knowledge they don't exist.

Paul Nash


Thanks Kris, for yet another great article. With all renewables, when we start looking of an end use that matches the nature of the energy being produced, we will find more and more reasons to do renewables.

I have been particularly impressed with the approach of Solar Fire and Glasspoint. Solar Fire's effort to eliminate a lot of unneccesary complexity, and produce something that can be built by almost anyone, anywhere is commendable - it allows communities, anywhere, to start to produce their own energy, and industry, instead of relying on imports.

The Glasspoint approach has focused on industrial customers, and they too have succeeded in eliminating a lot of high tech complexity, at the cost of a large greenhouse area. The performance specs are impressive - about 56% on the incoming solar energy is delivered as high temperature, high pressure steam. The application for steam assisted oil recovery, while maybe not the most eco-friendly application, is, from a functional point of view, an ideal use, as it does not need 24/7 steam, it just needs X GJ or BTU per day/week.

It has just been announced (8 Aug) that Glasspoint has won a contract with the government of Oman to build a four hectare, 7MW system, for steam assisted oil recovery.

This system can also be used for crop drying, seawater desalination, ethanol distillation, food processing, hospital heat and many other applications that use process steam.

Best hopes for appropriate solar solutions!



I've worked some in solar, and I think it's true that many PV plants (including an older one of Evergreen's in MA, now closed) have installed arrays, (sometimes mainly for testing), but I've never heard of a plant that generated even close to its net energy requirements onsite, let alone operated off grid. Other hand, wouldn't surprise me at all if some manufacturer bought enough green credits from wind etc., to offset the carbon karma of their plant; IIRC there's at least one brewery that does that, as part of a corporate image.

From a technical standpoint, that works fine up to double-digit penetration of unschedule-able renewable sources. Beyond that, we'll have to figure out storage, whether physical or behavioral in nature - but as an engineer in the field, that's a problem we'd love to have already.

This article prodded me to discuss a couple of engineering nits and a general gripe on the subject: http://fiveislandsorchard.wordpress.com/

Kris De Decker


More comments at The Oil Drum:



Very nice article. BUT Please edit your statement: You won't find any factory manufacturing PV solar panels using energy from their own PV solar panels, because it is very inefficient (and thus utterly expensive) to convert electricity into heat
Converting electrical energy to heat is very efficient. Electrical heaters are comparable cheap and require low maintenance. Its just the electric energy which is costly and to valuable to waste it as heat. The efficiency loss is the part to generate electricity but not to convert electricity to heat.

Kris De Decker


@ Matthias: corrected.

José A. de Souza Jr.


A much more efficient use of concentrated solar energy would be in using it to gasify biomass in order to make syngas. Up to now gasification has been considered uneconomical (et pour cause!) basically due to the fact that a lot of feedstock must be burned to get some fuel. Not to mention the ensuing pollution. But central power towers and computer-controlled fields of sunshine-following mirrors can change that picture. Not only can clean electricity be obtained through renewable syngas in modern combined-cycle power plants but erzatz fuels like green diesel, gasoline and aviation fuel and nearly everything else currently derived from fossil oil and gas(http://www.sundropfuels.com/). Yes, there's plenty of sunshine and biomass (including what we deem as "garbage") to power modern industrial and more sustainable societies about anywhere on Earth.

Randy Childers


I'm greatly encouraged to see this article -- personal DIY solar heating and power generation for the home is something I've been thinking about and working on as well. This definitely validates the effort.


Baksa Péter


"Geothermal energy produces heat, but its potential is limited to regions that have volcanoes".
Not necessarily, for example Hungary has a high geothermal gradient but no volcanoes.

It is accessible everywhere using heat pumps. Drawback is you need unefficient electricity to run a heat pump, but if you run it on solar power... There is less solar power during winter.
However I'm a bit skeptical about this, I don't know what would happen if whole Europe would be heated by heat pumps, that would surely affect soil temperatures. Could you do an article on that?

Brian R. Earley


Run in vacuum to reduce heat....
Brian Robert Earley



And wait till you drink the coffee !


Mike Hunt


A local business in Lunenburg, Nova Scotia has developed and is using a solar furnace as part of its business: http://www.prosolartec.com/



Good article!!

Concentrated solar heat would be pretty cost effective to implement for a factory that requires heat for processing. While biomass won't meet all manufacturing heat needs, it may make for a good backup to solar concentrators. Burning bio briquettes made from agricultural waste or trash, rather than wood, could work in order to preserve our trees and reduce material in landfills.

Thermal oil could be heated, then pumped to the point of use, if steam and the high pressure that comes with it are not desired, at least, for some of the low to medium heat needs.

As well, the heat could also be used to provide refrigeration in cooling systems based on absorption, rather than compressors. I'm thinking of the food industry, here.

Heat storage can be achieved with molten salts or thermal oil in insulated holding tanks, which would allow for production at night and during cloudy days.

Lastly, thermoelectric generators might be employed to convert the waste heat to electric.

Concentrated sunlight is not the sole purview of industry. It can also be employed at the home user level, I believe. Heating oil, then pumping it to the point of use---water heating, refrigeration, home heating, thermoelectric generators---doesn't seem out of the realm of possibility for the do-it-yourself crowd. Adding a rocket stove, fed with bio briquettes, to a solar hot oil system as a backup source of heat should also be possible.

We do have alternatives to fossil fuel, despite what energy companies say, and this is one of them.



Thanks for the interesting articles.
I have a few of questions. Firstly, how much land would be required for solar collectors to provide the heat requirements of various types of factories.For example what type of factories could convert their existing roof space to meet their heat requirements? What type of factories would need to relocate to convert to solar concentrator technology and how much additional space would they need and how would that influence the overall sustainability of solar manufacturing?

On a more personal scale, I am wondering to what extent solar concentrators could be used for cooking heating a house in winter? At what point would the winters be too cold to use solar heat? My interest in this is more than theoretical as I have an interest in potentially building a future home outside of the limits of the existing electricity grid. It would not be difficult to implement a photovoltic solar and battery system to cover my modest electrical needs but cooking and house heating are rather more difficult. I do not wish to burn fossil fuels to achieve my heat needs and I would prefer not to burn biomass either as I do not wish to move somewhere more remote partly to enjoy cleaner air and then go and pollute it myself.

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