What Is Primary Energy?

Primary Energy

Primary energy is a form of energy that is found in nature which has not been subjected to any artificial (human) conversion process. It is the energy contained in materials such as oil, natural gas, and coal which can be released by burning them.

The process of converting primary energy into other, more useful, forms of energy, involves energy overheads and efficiency losses and these mean that more primary energy is needed than is delivered as useful energy (heating for a building or electricity).  By way of example, let's follow the path of natural gas extracted from a giant gas field in Qatar and destined for the UK to make electricity in a power station (illustrated above):

Once extracted from the underground reserves, the gas is pumped through a pipeline to a processing facility.  Here it is cooled to -162C, the temperature at which it becomes liquid and loaded aboard a specialised Liquefied Natural Gas (LNG) tanker which transports it to the UK.  The gas needs to be kept cold during transport and this is done by insulating the containers it is carried in and allowing some of the gas to vaporise off.  Some (but not all) ships capture the gas and use it in turbines that drive the ship along.

At the UK port,  the liquefied gas is transferred into storage and kept at a cold temperature to remain liquid.  When it is needed it is re-gasified and pumped into to the UK gas network.  Finally, it arrives at an electrical power station where the gas might be burnt in a modern Combined Cycle Gas Turbine (CCGT).  This is the most efficient type of power -  because in addition to the heat from the combustion being used to raise steam and drive a turbine, the exhaust gases drive a second turbine.   The turbines drive rotating shafts which produce electricity in a generator set.

There are losses at every stage in this journey from gas deposit to electrical energy.  From an energy point of view, losses include the primary energy content of electricity or other fuels used as well as any burning or losses of the natural gas itself along the way.

A proportion of the gas is lost to the atmosphere and some may be flared (burnt off) at the rig or as part of the process filling the LNG tanker pressure vessels and during transportation.  The pumps to move the gas through the distribution system use electricity.

Up to 10% of the natural gas is bunt to drive turbo-compressors that refrigerate the gas to liquefy it for sea transport.

As it crosses the ocean, the LNG carrier will lose 0.1 - 0.25% of its gas each day.  This is allowed to boil off to maintain the low temperatures  - that means up to 5% of the shipment is lost between Qatar and the UK in a typical 18 day transit.  In addition the carrier uses either oil or the transported gas itself to drive its engines.  Some carriers can recycle the boil-off with re-liquefaction plant on board, but this also comes at an energy cost.

Gas sourced from the North Sea will consume less energy in its transportation than gas from Qatar or the USA, but taking a weighted average of all UK gas supplies (based on figures in SAP10.1) - energy or losses equivalent to around 12% of the heat energy in the gas is used up simply getting it to a house or power station in the UK.

The best CCGT power stations have a conversion efficiency of  54% (HHV) meaning that to generate one unit of electrical energy, gas with an energy content of 1.85 units must be burnt.

Putting all of these losses together - extraction, processing, transportation and then conversion to electricity - mean that to put 1 unit of electrical energy into the grid, you need to start off with gas in the ground that contains something like 2.1 units of heat energy - so the electricity generated this way is said to have a primary energy factor of 2.1

Primary Energy Factor for Grid Electricity

Other forms of electricity generation will have differing primary energy factors, so the average primary energy factor for grid electricity is a weighted average.  This will include energy from solar panels, wind turbines, burning biomass and bio gas, nuclear power as well as gas and oil, each with their own primary energy factors.
 
Although solar panels convert electromagnetic (light) energy to electricity and wind turbines do the same with the kinetic energy of wind, because these resources are considered inexhaustible, the convention is that renewable energy of this type has a primary energy factor of 1.0

According to SAP 10.1, the weighted average primary energy factor for UK electricity in the period 2020-2025 is expected to be 1.51.

The primary energy factor for electricity also varies depending on the generation mix that is contributing to UK electricity supply at any given moment in time.  SAP 10.1 uses monthly values to take into account that renewable energy contributes different amounts of energy as the seasons change.

The Carbon Intensity of UK Grid Electricity

What it Means for Low Carbon Buildings

Take a look at this chart. It's nothing short of astonishing. Up to 2012 the amount of carbon dioxide emissions associated with the delivery of one unit (kilowatt hour, or kWh) of electricity in the UK was hovering around 500gCO2/kWh. Since then, the amount of carbon dioxide that is emitted for each unit of electricity has plummeted. In 2016 the average was 269gCO2/kWh, a fall of nearly half in only four years. This change has far-reaching implications for regulators, not least those involved in ensuring the low carbon transition of the UK building stock, both newly constructed buildings and the improvement of the existing stock.

So what's behind the fall?

The first factor is the retreat of coal-fired power stations. In 2012, the government's Digest of UK Energy Statistics (DUKES) has coal fired power stations producing 44% of our electricity nuclear plants were suffering from outages and gas prices had risen, so coal use was at a high. By 2016 the corresponding figure for coal was only 9%. In the same period, gas fired power stations rose from 24% to 42% of UK power generation. This matters for two reasons. First of all, because coal is made up of long-chain hydrocarbons, with a higher ratio of carbon atoms to hydrogen atoms it produces about 60% more carbon dioxide than natural gas for each unit of heat energy produced in burning. Second, gas is more often burnt in a Combined Cycle Gas Turbine (CCGT) power plants with conversion efficiencies of up to 60%, compared to 40% for conventional steam turbines.

The second factor is the increasing contribution from renewables in the electricity supply. Enormous amounts of wind energy, biofuel fired generation and solar energy have come online. In 2012 renewables and 'other' represented 11% of UK electricity supply. In 2016, this had risen to 27.8%.

As a result the average carbon intensity of electricity in 2016 at 269 gCO2/kWh was only just higher than that for gas (216 gCO2/kWh). When you add in an efficiency for a gas boiler at (say) 80%, the gap disappears.

This is huge.

For years electricity has been the bad boy in low carbon building design. People fretted as a series of reports from the Energy Savings Trust showed that heat pump installations in the UK were operating nowhere near their advertised efficiencies and were consequently underperforming gas boilers for carbon emissions. Simple resistive electrical heating by panel heaters or immersion heaters for hot water were to be avoided at all costs.

Four short years later and all this is is turned on its head.

And we're only just getting started with renewables. In September, Dong Energy announced that it would move forward with the world's largest offshore wind farm, Hornsea 2 off the Yorkshire coast, with development costs that had fallen by half compared to previous offshore farms. A couple of week later, and not to be outdone, the UK's first subsidy-free solar farm was announced. It's still a bit of an outlier combining solar with battery energy storage and using pre-existing grid connections from with an earlier development, but it's a clear sign of the direction of travel. The carbon intensity of grid electricity is heading only in one direction.

But there's another wrinkle to consider. The carbon intensity of the grid is not a static value. It varies constantly as the mix of generators fluctuate to meet different levels of electricity demand and in response to changes in wind and sunlight. On 11th June this year, it was windy and sunny at the same time. Records tumbled. The carbon intensity of grid electricity in the middle of the day on was below 80gCO2/kWh.

So now the moment when you choose to take power from the grid is a strong determinant of the actual instantaneous carbon emissions your electricity use is creating.

Some uses of electricity - for example for preparing domestic hot water, or to some extent space heating buildings could be relatively time independent.  If I'd known ahead of time that carbon emissions would be so low on 11th July, I'd have been able to set a timer for my immersion heater to heat water for me at midday and got my tank of hot water at fully one third of the carbon emissions of using gas heating.

And the technology to do this is just around the corner.  This awesome new grid carbon intensity forcasting service has been recently launched by the National Grid the Met Office and WWF, with an API that software developers could use to do just this kind of thing.

 

So where does this leave low carbon building?

The current building regulations in England and Wales were last reviewed in 2012 and set minimum carbon emissions rates that developers must design to. The carbon intensity of electricity in the approved calculation (the Standard Assessment Procedure or SAP) is currently 519gCO2/kWh, which was accurate at the time. Now it is woefully behind the curve.

Buildings are normally intended to be long-lasting. If we allow ourselves to imagine a future where digital technologies, the smart distribution of electricity, demand response, energy storage and renewables combine in a so-called 'Smart Grid' then a number of significant observations about low carbon building emerge:

• Even based on the current carbon intensity, never mind the future direction of travel over the life of a building, it is utterly beyond me that any new build or significant refurbishment should include gas heating.

• The current enthusiasm among UK policy makers and local authorities for district heating (for example this recent consultation by Scottish government) could also be a troubling dead end. District heating itself is neither intrinsically clean nor green - it all depends what heat source you put at the other end of the pipes you're going to dig up all the streets to install. Gas fired combined heat and power may be seen as low carbon at the moment, but how long will it look so appealing if electricity continues on its current path?

• Building codes are currently focused on regulating carbon emissions. In a world of low carbon electricity you can meet a carbon target with a draughty garden shed full of electric fan heaters. It's time to move to energy targets (kWh/m2) to create buildings that sip energy and liberate power for the demands created by the electrification of transportation.

If I was building my own Grand Design right now, my future-proof forever home based on these observations here's what I'd go for:

• High levels of insulation and air tightness to drive down space heating demand to a practical minimum

• Eliminate the wet heating system - I'd go underfloor electric coupled to a high thermal mass floor to allow price and carbon responsive electricity purchase to heat the slab at times of excess renewable generation

• Direct electric hot water cylinder - again allowing price-responsive purchase of electricity as well as diversion of excess generation from...

• the inevitable....beautiful solar panels on the roof - as many as possible!

Could this be the future direction energy efficient buildings? What do you think?

What does Energy Cost?

Where can you find authoritative data on energy prices?

The energy savings from solar heating is the main economic argument for choosing to install a system, and this will continue to be the case even with the imminent arrival of the domestic Renewable Heat Incentive in the spring of next year.  For solar PV systems the fall in cost of equipment and installation and the accompanying reduction in the Feed in Tariff means that own-use savings on electricity bills have become a much more significant component of the economic justification.

Energy prices have been changing rapidly, so it’s important for renewable energy businesses to have access to up-to-date, accurate and trustworthy price information to show to customers when modelling the financial benefits from their investment.

A quick survey of colleagues at a recent Solar Trade Association meeting produced the following list of resources.  Do you have any to add?  Please use the comments section below.

UK Government Statistics

There’s a wealth of energy statistics on the gov.uk website, and the challenge can be finding the information you want.

https://www.gov.uk/government/collections/domestic-energy-prices

By their nature, the statistics are backward-looking so often more than 12 months out of date.

Energy prices are often presented either as ‘average energy bills’ or stated as a percentage of 2005 costs.  The best source I could find was in the Quarterly Energy Prices publication, in which the following two tables show the unit price of energy:

Table 2.2.3 Average annual domestic electricity bills in 2012 for selected towns and cities in the UK with average unit costs

Table 2.3.3 Average annual domestic gas bills in 2012 for selected towns and cities in the UK with average unit costs

Sutherland

The Sutherland tables are a fixture of the energy industry, compiled quarterly since 1976 they show domestic energy costs heating and hot water costs across a range of standard house types across the UK.  The data is apparently used by government in preparing its own statistics, but there is a cost to accessing the data.

http://www.sutherlandtables.co.uk/

Boilerjuice

Boilerjuice.com is an online quotation website for heating oil.  It publishes average prices of UK heating oil:

http://www.boilerjuice.com/heatingOilPrices.php

Nottingham Energy Partnership

NEP publishes current average prices for electricity, gas, and heating oil together with many other fuels.  Also available are reports analysing trends over time.  This was the most relevant reference I could find for current energy prices.

http://www.nottenergy.com/energy_cost_comparison/

 

Do you know of any resources you can share?  If so, please let us know in the comments section below.

 

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?

 

 

 

Information is Beautiful

Why the solar thermal industry should embrace data logging

by guest blogger Ben Whittle

Who is this person that the Solarblogger has invited to wax lyrical on the rather un-sexy subject of data that you have never heard of before, I hear you ask?

Some might say my claim of authority to write on this subject is sketchy at best: I’ve only lived with and monitored a solar thermal system for less than 6 months, and I have only seen data from a few installations ever. But maybe that is exactly why it is a subject that needs discussing in the solar thermal industry… because I have been installing and designing solar thermal systems for around 10 years and I can count the number of installations I’ve seen that have monitoring on them on one hand, (and one of those installations is my own). And when I say we need more data-logging, I don’t mean turning on the heat quantity measurement function, I mean proper data-logging: measuring temperatures at the top, middle and bottom of the store, pump on and off times, boiler trigger times, heat measurement, the lot.

Over all the years I have worked in this industry I have seen a lot of mistakes made in designing and installing systems (and some of them were my own mistakes). How do I know they were bad designs and mistakes? Because I had to go and fix them. How can we possibly move on as an industry if we can’t try and make some sense of what mistakes were made in the past, and learn from them? Of course we have made leaps and bounds in some areas: the quality of the panels, plumbing, tools and fittings we are using (thank the lord for press fit pneumatic tools and filling pumps!), the MCS standards, the list goes on. OK, great, we can install stuff quickly and efficiently and it doesn’t leak… what’s the next step? Actually measuring how the systems are performing. Because I can tell you in the UK we have a long way to go in terms of getting our solar thermal systems to perform as well as can be achieved as seen across mainland Europe and America , and keeping track of performance is the only tool that can help us do it.

Now of course there are all sorts of reasons as to why we don’t normally achieve performance levels of a high quality Austrian installation… predominantly that is because the average UK house doesn’t have space for a 500-1000litre hot water store in the 700mm wide airing cupboard. But let’s put aside the things we can’t tackle and talk about the things we can.

To my knowledge there are only 2 or 3 solar thermal trials of any significance that have been published in the UK on solar thermal, and probably the best of these was conducted by the Energy Savings Trust three years ago. For those that are interested it’s called “Here Comes the Sun – A field trial of solar hot water systems”. It’s a great document, short (24 pages) and to the point. It tells you what you need to know – the biggest impact on solar thermal performance has nothing to do with evacuated tubes or concave reflector plates or low emissivity glass. But how did they reach those conclusions? By measuring things and writing it down – and, you know, analysing it and stuff.

And that is where we need to be going as an industry – looking at data, working out how to improve things, and changing our behaviour to suit. Not only will measuring performance allow us to understand the mistakes we make, it can inform our design decisions and help us to improve everything we do… and of course there are other benefits to consider as well.

1: Data logging is another chance to “add value” to your installation work. It’s a slightly more expensive controller, or an additional bit of kit to be sold, and a chance for your geekier clients to play with a spreadsheet or two. Now if you haven’t had a great experience installing solar thermal and the thought crossing your mind right now is “yeah right, and the customer is going to use this data to beat me with like a stick when it all goes wrong,” then I really am talking specifically to you. Because there are thousands of systems out there in the world that do perform absolutely perfectly, and as an installer you need to understand how they work.

2: It’s a chance to fault find, and take the correct action if things do go wrong, instead of guessing.

3: It will help you understand how people interact with their solar systems.

4: It can help get you out of trouble if the cause wasn’t your fault. One of the few logged systems I have seen was a school pool system that was constantly stagnating and losing pressure after being installed. When the data card was posted back to the company I worked for, it didn’t take long to diagnose the fault. The college maintenance man had been turning the system off at the main switch on a regular basis (even though it had a sign on it saying “Solar – do not switch off”). We were even able to re-program some of the settings using the data card and send it back to them in the post to plug back in. That’s quite an unusual feature specific only to the controllers made by Watts industries as far as I know, but a pretty handy one for commercial systems.

Just imagine what could be possible if we all took this a bit more seriously – imagine coming in to your office on a hot summer day in a few years from now after installing a 1000 systems across your local area, to find a couple of automatically generated emails where your data server had logged some de-pressurisation warnings at a couple of properties. You could then log on to watch some live system data to check them, and dispatch a maintenance team to fix them before your client was even fully aware there was a problem. All part of the regular maintenance contract you sold them at the time of installation…. There is no reason why this fantasy couldn’t come true, and it’s up to us to make it happen. It is already happening in the world of heat pumps.

As an aside, maintenance contracts are another area I think we need to explore further as an industry. I recently saw a report suggesting a very significant proportion of people who buy solar thermal systems would be happy to pay more than £100 for regular servicing, another possible revenue stream for any installation business.

Red=panel, Yellow = top tank, Blue = mid tank, Grey = low tank

R1 = solar pump on, Rs = boiler on

My own system does not have anywhere near enough data yet. I’m currently measuring temperature at 3 heights in the store, the solar controller also controls my boiler so I can also measure how frequently the boiler is getting activated, and I’m also getting estimated energy yield using the heat quantity function on the controller and estimated flow rates. In an ideal world I hope to add a water meter to measure my hot water usage, and a proper electronic flow meter for the solar controller to measure the glycol flow rates, and an electrical meter to measure electrical consumption. But I must be doing something right because I am currently hitting 2100kWHours of energy from my installation, after being installed for less than 6 months. And thanks to the EST solar study I know that the average UK installation is usually generating 1500kWH in a whole year… and I would never have found that out if I hadn’t bothered to log the data. Of course that generation figure could be inaccurate, and I mean to find out if that is the case by getting more and more accurate data over time.

I should probably qualify that performance figure by pointing out that I do not have an “average” UK system, so I’m comparing apples with pears… but I hope to explore that issue in a further blog post, looking into hot water storage, and how we might start improving solar thermal performance in the UK.

 

Consumption Assumption – The Proportion of Solar Electricity Used in a Home

The answer is 50%, now what was the question?

Three very different distributions,
each with the same average - 50%

If you have a solar PV system fitted to your home, then the amount of electricity you generate is changing all the time as the sun travels across the sky and clouds come and go.  Your electricity use also changes as you switch electrical appliances on and off.  

If solar electricity production exceeds your electricity use at any moment, power flows out of your home to supply the electricity grid (called export).  If, on the other hand, your electricity use exceeds the electricity produced by the solar panels then all of the solar electricity is used in your home and supplemented by power drawn from the grid.

Over the course of the day your electricity meter will record the flows of electricity into your home (for which you will be billed). If you can meet your electricity needs with a unit of electricity from your solar panels, then you save yourself buying that unit from your supplier.  

This saving on electricity bought represents an increasingly large part of the financial benefits of owning a solar PV installation.

So what percentage of the electricity that is generated by a solar PV system is actually used in a building?

It seems that the UK solar industry has found a rather simple way to answer this question:

Q: Retired couple at home during the day, 1kWp system

A: 50%

Q: Working couple no-one at home during the day, 1kWp system

A: 50%

Q: Working couple no-one at home during the day, 4kWp system,

A: you guessed it, 50%

For smaller residential solar systems claiming the Feed in Tariff (FIT) , the government decided that it wouldn't measure exported solar electricity, only generated electricity.  However, the design of the scheme was to reward people with money for everything they generate, plus a little more for the energy that is exported.  So it came up with a way of calculating the exported energy. A figure of 50% is multiplied by the generated energy to calculate a value for the exported electricity. 

The industry has embraced that figure as if it represents some kind of truth written on tablets of stone. Every presentation of financial benefits from the FIT I have seen assumes that the household will use 50% of the energy it generates. 

When the UK FIT was paying people £0.43 for each unit (kWh) of solar electricity generated and electricity cost £0.14/kWh all that really mattered to the financial calculation was how much you generated, not how much of it you used yourself (called self-consumption). 

PV prices have fallen dramatically and to keep the financial benefits consistent the FIT now pays new installations much less, about £0.15/kWh generated.  In the meantime electricity costs have risen to around £0.15/kWh.  Self-consumption is becoming the greater part of the financial benefit. 

To illustrate this, let’s consider a house with a 2kWp system installed. To keep the maths easy, we'll assume its in a very good location and generates 2,000 kWh per year.  What happens to the financial return as the proportion of energy used in the home changes?

How the make-up of Feed in Tariff Benefits has Changed Since Launch
Savings on electricity bills forms a much larger proportion of the financial calculation

When the FIT launched, any inaccuracy in the self-consumption figure was much less significant than today.  The value of the savings on the electricity bill represented only 14% of the total benefits (assuming this figure of 50%).

Now the proportion of the benefit that comes through electricity savings is 30%.  Inaccuracies in the self-generation assumption have a much bigger impact on the financial returns calculated.  If solar prices continue to fall then the FIT will fall too, and this trend will continue.

As an aside, the table above is absolutely not an advert for so-called PV switches that divert solar electricity to an immersion heater in your hot water cylinder .  Once you ‘degrade’ high value electricity to heat, you reduce its value to that of the cost of the fuel would have used to heat the water.  In 80% of homes this is gas, so it’s not 15p/kWh you’re saving, but more like 5p/kWh. 

(See the outspoken guest blog from Tom Seppings of solaplug for more on this point).

Far better to use it to power electrical appliances if possible, or store it in a battery, an emerging technology already causing great excitement in the industry.

Your Guess is a Good as Mine

How good a guess is 50%?  What evidence was the government’s choice based on?  If anyone has information on this, I’d love to hear it. Please post a comment at the bottom of the article.

Let's pause to consider averages for a moment. The graphs above show three 'distributions', each of which has an average of 50%. Only the top one (1) would strongly justify using the average value for all customers. 

My hunch is that the reality is most like the bottom distribution (3), with two distinct groupings - households with people at home during the day, and households where people are out at work and school during the day. 

I also suspect that the 50% figure was arrived at when the average PV system size was much smaller than it is today. Falling prices have brought larger installations within the reach of more people (capped by the 4kWp tariff band limit). In 2011, the EST had the average system size as 2.75kWp.  Today it is 3.75kWp. The larger the system, the larger the midday energy peak, and the less likely it is that there's sufficient instantaneous electricity use in the home to mop up the solar electricity. 

Yet the industry persists with presenting financial benefits based on this 50% figure.  

Does anyone know of any work that has been done on the profile of electricity demand during the day in homes with differing types of occupancy?  How could the solar industry offer its customers a better prediction of how much solar energy they will consume themselves?

Do you think solar PV systems will become smaller to increase the proportion of self-consumption as levels of FIT support falls and electricity prices rise?

Let's hear what you think - post a comment below.