Renewable Energy

[friartuck]

I am currently working for a client who wishes to use renewable energy.

Whilst I would like to think that I am a 'green' engineer, I am finding it difficult to find a suitable renewable energy source.

I am sure that there are plenty of systems out there, but in the UK climate, I am finding it difficult to justify there use.(please note that I am not anti-renewable energy, I just need a system that I can justify)

My findings so far are as follows:

a. PV Cells

Ridiculously expensive. (£4500-00 per kWp kilo Watt peak)With meaningless pay back periods. (The solar array would need to be replaced before the system has had time to pay back)

Typically PV cells are only 12-14% efficient and outputs are based on 1000W/m2 (i.e. the panel is located in the sunny tropics--not cloudy old Britain-where the solar intensity is generally less than half of this)

b. Water Solar (To heat hot water for domestic use)

Comments similar to the above. Payback is a little better. Orientation is very important and in my instance, the building roof is poorly oriented.

c. Ground Source Heat Pump (Boreholes)

Clients don't want to pay out a few thousand pounds to see if the land has a suitable heat source.

Also, many are anti ''underfloor heating'' (Required in order to use the low grade heat source)

d. GSHP-Slinky Coils

We don't seem to have enough land to put the thousands of metres of coils.

Plus when you add all the ancillary items like ground works, borehole digging, maintenance etc, the costs get really high.

e. Wind Power

Nobody likes to look at these. We get protests from planning and again, the payback depends on the location of the turbine.
I have found that in our windy climate, these can be cost effective (which surprised me)

f. BioMass (Wood pellet Burning)

This worked out quite cost effective. The wood pellets are very cheap to buy and running costs were low. Pay back was around 8-10 years but maintenance costs made the overall scenario more expensive.

We also needed high chimneys (clean air act), full stainless steel chimneys, a large fuel bunker and a bigger plant room. The fuel is classed as carbon neutral and I made this option the best of all the bunch.

Concerns

It seems that trying to justify renewable energy is difficult when you know that the plant will never pay back.

I am also unsure (even on ecological grounds) if putting something like solar PV cells is actually worth it.
Are we causing MORE damage to the planet by using something like this. I could understand it if costs were low and payback quick (i.e. paybacks of less than say 10-15 years)

But if a system has to be replaced even before it has paid for itself, then are we causing more damage--(and doing the 'green thing' for the wrong reasons.

Carbon Burden

Another thing that I find hard to understand is that we utilise renewable energy so that we can reduce the amount of carbon used.
Are we sometimes in danger of actually using more carbon by using some of these less efficient methods of renewable energy. I would guess if we took into account the extra carbon needed to replace/maintain plant, then the whole exercise was probably a waste of time and caused more damage to mother earth.

I am sure I have opened a can of worms here, but I would be interested to hear other peoples views.

I look forward to receiving the benefit of your experience

Tucky


Friar Tuck of Sherwood

 

[IRstuff]

Did you consider biodiesel to be non-viable?

In general, I agree with your comments. The problem is that renewable and bio energy are rife with ideological overtones, which is why there are big controversies relative to true cost. All parties concerned have vest interests is getting answers favorable to their "cause."

This makes it very difficult to get rational analyses. I agree that solar cells are non-benign to the environment, although they've gotten better now that before, due to more vigilance in keeping the environment cleaner. Nonetheless, solar cells use chemicals that have no normal uses and are quite toxic.

And yes, it's unclear about the end-to-end breakeven point for the planet, since the bookkeeping is rather contorted. But clearly, just the immediate energy required to make the solar cell itself will take years to make back.

TTFN

 

[AbbyNormal]

I doubt the bore holes would be a gamble to see if there was enough energy, the boreholes work in climates found in Canada.

It is just an expensive first cost.

Passive solar is a good strategy for heating.

 

[ChrisConley]

Active solar water heating has an acceptable payback, if you can arranged for suitable orientation, and storage. The downside is that you don’t really get to reduce the size of your boilers.

Ground source heat pumps have a hard payback, but depending on the fuel source compared against we've been able to find payback. Our issue tends to be that electricty has three-times the cost per watt as natural gas. And with GSHP systems only 3.5 times more efficient....

I tend to focus on energy efficiency - waste heat recovery, demand control ventilation, efficient delivery of heat/cooling, efficient production of heating/cooling, passive solar strategies..

I've found over the years that a well designed building using standard energy sources will outperform a building using exotic energy sources.

If I was going to push an owner, I'd get them to spend more money on the building: walls, windows, use of daylighting, passive solar, and then use a high efficiency system: condensing boilers, air side heat recovery.

 

[IRstuff]

Right..

What you don't use to start with, you don't need to figure out how to recover.

TTFN

 

[GMcD]

What Chris said- take $$ out of the mechanical systems budget and put it into better envelope materials and especially windows, with exterior shading. Being in England- can't the Carbon Trust folks help out? They seem to have sources and good advice for assisting with low energy/alternate energy systems and procurement. Passive building design is the biggest bang for the buck- design the building to require as little outside energy first, then apply the systems design to it.

Low consumption plumbing fixtures, minimized heat losses and gains, natural ventilation with powered DOAS with heat recovery, etc.

The justification has to start with a realistic baseline. Too often, the status quo as the baseline isn't really the right comparison. There has to be some accounting for life cycle costs, embodied energy (as you've recognized), and the accounting for the environmental damage costs.

 

[trashcanman]

All the above is quite right. Probably what Conley said makes the most sense. Invest in good insulation & weatherstripping, and fluorescent lights.

Solar energy is fine, until the sun goes down, or is hidden behind long cloudy days you have in England, in winter, when you need the solar heat most of all.

I am amused at all the frantic effort at "green engineering". Suddenly it seems, the earth is depending on man for it's survival. I assure you, that the earth will be here long after man is gone (or the Lord comes back, which ever is 1st).

The payback struggle is interesting too. If the so-called "alternative" energy sources are so great, why are they being used so little? It is because the market will not support them. They are just not economical. It is the same reason you don't see steam engines pulling trains anymore. Diesel beats steam in terms of cost/ton-mile, maintenance, and reliability. The market killed the steam locomotive. It might in the future kill the diesel-electric locomotive too.

Ask the client what he is most interested in - a bldg. economical to build and maintain, or a "green showplace" (hang the cost).

 

[macmet]

I am curious to the hear more about this statement

"Pay back was around 8-10 years but maintenance costs made the overall scenario more expensive."

That seems much longer than I expected. How big of system are you looking? What are some of the high maintenance costs you refer too?

 

[friartuck]

Macmet

The wood pellet scenario is fine until you look at the 'real' costs. Sometimes its convenient to look at installation costs only, but when you add on the hidden extras, they can make a difference.

For instance, PV cells should be a 'fit and forget' installation, but a wood burning boiler is different to a gas fired plant. Gas boiler tend to get looked at annually, but a wood burning boiler has a wood delivery system (which can get blocked and certainly wears out)..Also the ash pan needs to be emptied regularly-just like a coal burning plant.

If you have a system fitted to a school, the caretaker empties the ash pan out and you don't have to pay out any extra for regular maintenance.(since he is there and it just becomes one of his daily duties) But if you have an office installation, the office staff won't take too kindly to going into the plant room and cleaning up.

The extra cost of a visit per week by a specialist maintenance company to clean out the ash pan adds up to a few thousand pounds a year. and if the difference between running a gas boiler and a wood boiler is not much different, then you may find that it actually costs more to run the wood system.

The pay back problem would be less on a large boiler plant, but we have only a very small system.(the building is about 10000 sq ft. and is very well insulated. The boiler plant is only around 80-100kW.

Hope this clarifies things


Friar Tuck of Sherwood

 

[macmet]

That is certainly a small boiler plant.

 

[friartuck]

Yeah but most new build is well insulated and has small boiler plant

Gone are the 'good old days' when all boilers had to be floor mounted and connected to a large free standing chimney.

U values (Thermal transmittance factors) have dropped drammatically over the last couple of decades. When I first started in this trade, the average heat loss was as high as 60W/m3-70W/m3 and now is lower than 15W/m3.(some large warehouse projects we have done are as low as 5-6W/m3)
Boiler plant can now be wall mounted instead of floor mounted.

We did a school last year. It was designed for around 300 kids and the boilers were rated at 100kW.

One of the problems we have now is getting good control. Since the rooms are so well insulated, the emitters are really small.The biggest loss is the infiltration.
So when the doors are opened, the air change goes up very quickly, as does the heat loss and the radiators can't react fast enough.

Older buildings had a good thermal mass and stored a lot of the heat. New builds tend to be very lightweight (thermally)





Friar Tuck of Sherwood

 

[hmm97]

Here in US it is same situation except; that there are incentives or tax deductions being paid by government(s) that make a project closer to be economical.
Ther are also cases of private organizations, chemical factories, utility generators that need to advertise for their project being green, etc.
Those are the cases where we use any of the above mentioned "Sustainable Design".
Of course this is not a bad thing. By paying incentives, governments encourage try-and-error cases, R&D, and developement of new designs such as :
grey water use, natural ventilation schemes, etc.

 

[lilliput1]

Economics is not there for renewable enery source. We design for "green" only when the client wants to be certified per LEED as a showcase. The project must meet prerequisites before being eligible. Best way we have found to realy save $ is using variable speed drives. Geothermal heat pumps is not considered as renewable energy source in LEED, however you can show energy saving in heating and get LEED credit there.

 

[KiwiMace]

In the US, you can in some areas pay a premium on your electricity bill to buy sustainable source energy. This premium is a few percent and is intended to support the building of larger scale, and more worthwhile plants onto the grid. eg. Biofuel cogen plants on dump sites etc.

What I think most owners are really asking for is an improvement over the base efficiency required by code, and in some cases willing to pay a small premium to achieve that.

Look at the LEED guidelines for ideas, and case studies for what engineers have found the most cost effective. Sustainability is more than just a source of energy issue. You can, for eg., get a LEED credit for putting in bike racks and showers, thus providing a sustainable transportation mode to the place of work.

 

[danw2]

I know I'm a cynic, but I suspect most clients aren't as interested in paying the full costs of renewable energy as they are in appearing to honor the idols of renewable energy.

So make sure you provide for the 'appearance' of renewable energy. Give them what Chris Conley suggests, "a well designed building using standard energy sources will outperform a building using exotic energy sources", and throw on several very obvious, highly visible, renewable energy tokens - some pre-heat hot water solar panels on the roof that can be seen from the driveway.

Who's gonna see the wood pellets?

The tokens advertise a 'commitment to renewable energy' but limits their costs and they'll love the lower energy bills with high efficiencies elsewhere.

Dan

 

[mizzoueng]

You mentioned wind power. Which style of turbine are you speaking of? There are two primary styles of Turbines, horizontal (wind mill) and vertical (conical). The vertical style is primarily used in the residential sector, but I bet you could find some that would work in the industrial areas. Maybe use them to power systems that do not require constant power, ie. emergency lighting, handicapped powered doors, powered overhead doors, fire suppresion system, bathroom exhaust fans, fire dampers, etc.

 

[lilliput1]

Energy simulation shows that sometimes it is better to go with less insulation on the roof. Some building interior require cooling year round. The added roof insulation resulted in bring in more outdoor air under economizer cycle in winter resulting in more fan energy and more humidification load.

We also found that skylights with higher shading coefficent (higher heat gain) at times can be better because it reduces the heating requirement of the building.

 

[stanlsimon]

If you want to get some efficiency first of all beat the architect into submission, reduce excessive glazing, orientate shading to increase winter solar influx and reduce summer influx.

Then think about combined heat and power coupled with heatpumps. See Dr. Threlkeld's analysis of such systems in "THERMAL ENVIRONMENTAL ENGINEERING" 2nd edition page 422. You should get a COP of around 5 by using engine jacket and exhaust pipe heat exchanger to warm make up air and aid the heat pumps to heat the building.

Many buildings already need a generator for back up power, for longer run time hours you will need a better generator (which can operate on biodeisel) giving you extremely low energy use without bizarre or untested machinery.