Saturday 30 November 2013

How to Lower Energy Bills

The way the energy companies structure their tariffs encourages high consumption. 

Try to imagine a fee structure for gas and electricity that would encourage people to conserve energy. Forget for a moment how energy is delivered and what the costs look like for energy companies. We're not designing it to suit them. 

I suspect that you've come up with a scheme where the price of the energy you buy rises for each extra unit you consume, perhaps something like this.

A rising 'marginal cost' of energy would encourage investment in energy saving technologies

Energy companies have the technology to include information on your bills about how your consumption compares to similar properties around you, perhaps the price per unit could stay low until you exceed the average consumption in a comparison group. 

In this utopian vision, pricing signals would be incentivising people to invest in energy saving measures for their properties to reduce their energy use.  This would then lower the average energy use.  The level at which prices jump would fall over time, driving people to further reduce energy use. 

Burn baby, burn

Instead energy companies have structured prices to suit themselves. There's often a fixed "standing charge" which you pay even if you use no energy, helping ensure they recoup their fixed costs. Then there's a band at a higher price per unit for the first so many units, falling to a lower price per unit for all energy used above this level. 

If I had asked you to design a fee structure that encouraged high levels of energy consumption, you'd probably have come up with something like this. 

Which shouldn't be a surprise, really. 

We've left the fox in charge of the hen house.

The more you use, the lower is your average price per unit. The less well off, struggling to afford their bills and conserving the amount they use are paying the highest price per unit of any of us. 

Unsurprisingly perhaps,  energy companies structure our bills to reward higher consumption

Energy companies are being allowed to structure our energy bills to encourage us all to burn the planet and to discourage investment in energy efficiency.  

The current bluster about freezing prices temporarily or rolling back the 'green crap' is tinkering at the margins. (See my earlier blog - The State of the Debate).  A bold reformer would mandate an inversion of pricing structures to lower costs for the less well off and encourage us all to invest to use less energy. 

This would be market economics red in tooth and claw. Forget the Green Deal, forget Feed in Tariffs and Renewable Heat Incentives.  Forget all of the bewildering array of centrally planned, market distorting energy efficiency schemes.  Price energy use accordingly and watch it all happen based on millions of people doing what's right for them and their home. 

Wednesday 27 November 2013

Optical Properties of Solar Panels


All you ever wanted to know about Incidence Angle Modifiers…

When light strikes a transparent material, some of the light is reflected, some is absorbed on the way through and the rest is transmitted.  For low iron glass of the type used in solar panels with the light arriving ‘straight on’ (perpendicular to the surface) the figures are typically 8% reflected, 1.5% absorbed and 90.5% transmitted.

Light incident on a the clear cover for a solar panel is mostly transmitted, but some is absorbed or reflected
 Most of the light incident on a solar panel does not arrive perpendicular to the surface, but at some other angle as the sun moves across the sky over the course of the day and year.  The incidence angle is defined as the number of degrees between a ray of light and the line perpendicular to the surface.  As the angle of incidence increases so does the proportion of light reflected at a glass surface.  Since the light is not travelling straight through but at an angle with a longer path through the glass the proportion of light absorbed by the glass also increases.

As the light arrives at shallower angles, the proportion reflected increases

 The effect  light angle has on solar panel performance is quantified by a property called the Incidence Angle Modifier (IAM).  The IAM is measured and reported as part of the standard test procedure for solar panels and is defined as the efficiency of the solar panel at a given incidence angle divided by the efficiency when the light arrives perpendicular.  It takes into account not only the changes in transmission at the glass, but also any changes in reflection at the absorber.
For a flat plate solar collector, the IAM starts at a value of 1.0 when incidence angle is 0 and decreases as shown in the diagram as the incidence angle increases.

The incidence angle modifier captures the loss of efficiency as the angle of light changes from straight on

Evacuated tube type solar collectors have a different geometrical relationship with the light from the sun.  Only the light arriving on the centreline of the tube will arrive at the glass with an incidence angle of zero, as you move away from the centreline, the incidence angle increases and the so the proportion of light reflected and absorbed also increases.  This is partly explains why evacuated tube collectors often have a ‘zero loss efficiency’ (or optical efficiency) lower than that for flat plate solar collectors (the other factor being the gaps between the glass outer and the light absorbing surface inside).
Since a tube has circular symmetry, the proportion of light transmitted is unaffected by the direction the light is coming from.  The light passing through the outer glass wall for a single tube would be unaffected by the angle the light arrives from in the transverse direction (around the tube).

The geometry of a tubular solar collector gives higher reflection losses for light arriving straight on
but has circular symmetry, so the reflection doesn't change as the light angle changes
An evacuated tube solar collector is made up from a number of tubes installed side by side.  A gap is left between the tubes so they don’t touch one another and there is a gap between the outer glass and the inner light absorbing surface.  Consequently, a proportion of the light is not collected and passes between the tubes.

Tube collectors have gaps between each tube which cannot collect light

Some evacuated tube collectors have a tubular shaped absorber (so called Sydney Tubes or tube-in-tube collectors).  A feature of the geometry of these is that as the angle of incidence increases in the transverse direction (around the tubes), the absorber area increases compared to the effective area of a planar absorber – less light passes through the gaps. 

Tube collectors with tubular shaped light absorbing surfaces 'close the gap' as the light arrives at shallower angle

The transverse IAM for these products rises higher than 1.0 before falling to zero as the angle approaches 90 degrees. 

The IAM for a Sydney tube collector rises above 1.0 as the light arrives at shallower angles

All this is just another reason why you can't compare solar thermal panels by their simple gross efficiency.


Wednesday 20 November 2013

The State of the Debate

On the subject of energy bills our political masters prefer to treat us like children 

1. What a Grown Up Conversation about Energy Bills Looks Like


Electorate: "blimey, these energy bills smart a bit. I'm not very happy about that."
Government: "Yes, we can see why, prices for gas have doubled since 2005. There's a growing middle class in the developing world who want the same standard of living as us and fossil fuels are getting more expensive to extract.  I'm very sorry but we can't control the global price of energy."

Electorate: "are you saying that it's just going to keep on getting worse?"

Government: "no, we're saying that energy is going to get more and more expensive, but your bills are calculated by multiplying the cost of energy by the amount you use."

Electorate: "so you're telling us to share our bath water and wear two jumpers in winter?"

Government: "the UK has among the least energy efficient housing in Europe! perhaps it's time to start thinking about investing in your home. Why not install insulation or solar water heating to reduce your heating bills or make your own electricity with solar PV panels?  We have support schemes to help with the costs of these measures."


2.  What we get Instead

Electorate: "blimey, these energy bills smart a bit. I'm not very happy about that."

This Lot: " the energy companies tell me that it's all down to the green tariffs (which, by the way, the other lot brought in). We'll make the horrible bills go away for you, leave it to us."

The Other Lot: "No, no, no!  It's all down to those nasty profiteering energy companies.  Leave it to us, we'll make a law to stop price increases so those fat cats can't charge you so much money.”
It's time our politicians squared with us.  Go on, tell it how it is, we're all grown ups here, aren't we?

Sunday 10 November 2013

Heat and Power

Early signs of a rebalancing of the renewables market

The Microgeneration Certification Scheme (MCS) November newsletter was recently released, and a graph caught the eye of the solarblogger.  It is reproduced below.

The total number of MCS registered installers has been falling for some time.  Companies registered to install photovoltaic (PV) solar technologies dominate the numbers, and since the painful tariff adjustments of 2011, the number of registered companies has been steadily falling.  In the last 12 months the number of solar PV installers has fallen from around 4,300 to around 3,000.

Two features of the scheme may mean that even these figures are an over-statement of the number of active PV installation businesses.

First, since businesses renew annually with the scheme, a company decision to exit a market can take some time to feed through into the figures.  Falling registration figures will trail by an average of six months.

Second, renewal is significantly less expensive than a new registration with the scheme.  This asymmetry causes business to retain their MCS registration even when they are not actively working in the market “just in case things pick up.” 

Industry colleagues estimate that around 10-25% of MCS registered PV installers are not actively selling solar PV.

But none of this is news.

The thing that really jumped off the page for the solarblogger was that while the registered PV installer numbers have continued to fall, the total has actually risen since August 2013. 

There has been an increase in the number of businesses registering to install heating technologies such as biomass, heat pumps and solar thermal. 

Details of the domestic Renewable Heat Incentive (RHI) were announced in July 2013.  This scheme pays households that install heat-generating renewable technology and will go some way towards rebalancing the UK government’s lopsided support for renewables.  A successful domestic RHI alongside a stable Feed in Tariff could deliver long term growth for both renewable heat and electricity.

It seems like industry might just be starting to believe in the RHI.