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.

 

A Million Missing Low Energy Homes

The "Housing Standards Review" is set to eliminate a crucially important driver for renewable energy uptake in the UK and the way the government has gone about it is an absolute disgrace.

Solar panels on new homes - soon to be a thing of the past?

In a recently launched consultation, the Department for Communities and Local Government (DCLG) has revealed its intention to halt a practice where local authorities can require property developers to build to an energy efficiency standard higher than the current building regulations or insist on renewable energy (the so-called Merton Rule).

The background to the Housing Standards Review is that there has been a proliferation of overlapping (and sometimes conflicting) technical standards created in recent years, and local authorities are imposing a variety of these on developers, creating an unnecessary regulatory burden.  

DCLG convened a series of working groups covering eight thematic areas, one of which was energy.  The Energy Working Group concluded that the government should scrap rules that allow local decisions on the energy efficiency of new construction and rely solely on the national Building Regulations to drive future improvements in new build housing.

The justification for this change is that the Building Regulations are ‘moving towards Zero Carbon Homes’ by 2016 so there’s no need to have these alternative requirements – you can’t get better than zero carbon, right? 

While this argument is superficially persuasive, as soon as you scratch the surface you quickly find otherwise – let's take a look at what’s been happening at DCLG since the ‘Greenest Government Ever’ came into power:

• New Social housing was intended to be at zero carbon by 2013, paving the way for the commercial developers to follow.  This was scrapped and social housing is now built to the same energy performance as commercial housing.
• The definition of a ‘Zero Carbon Home’ has been diluted so that electricity use from plug-in appliances is misleadingly not included, making it more like ‘30% Carbon Home’
• The 2013 building regulations are late and will not be implemented until well into 2014, allowing at least 100,000 homes to be built to a lower energy efficiency.
• These new regulations represent only a tiny (6%) improvement on the previous ones for energy efficiency, when a 50% improvement was required to have any realistic chance of delivering 30% Carbon Homes by 2016.
• The ‘Allowable Solutions’ consultation may allow developers to pay a tax instead of building genuinely low energy properties.

(See my earlier blog on progress towards Zero Carbon Homes here)

If you had a suspicious mind, you might suspect that DCLG held back on the spectacularly unambitious 2013 building regulations to allow the Housing Standards Review to reach its conclusions based on a belief in government intentions to actually deliver Zero Carbon Homes in 2016, a belief that would have been difficult to continue to hold once the 2013 regulations were revealed.

If you were also of a cynical disposition, you might predict that DCLG is going to announce that it will put back Zero Carbon Homes to 2019 (just keeping within the 2020 deadline in the EU Energy Performance of Buildings Directive), but only after leaving the 2016 target in place long enough to use it to justify killing off local rules for higher energy performance and renewable energy.

Houses are not built to new regulations immediately; it takes many years until granted planning permissions turn into completed homes.  If Zero Carbon Homes is delayed until 2019, it will be 2022 before large numbers of homes are built to this level of performance.  DCLG will have created a ‘Lost Decade’ and a million homes built with unnecessarily low energy efficiency.

Economics not your Strongest Suit?

The ‘Impact Assessment’ for the changes proposed in the consultation claims a net benefit to the economy of more than £0.5bn.  It is claimed that £93m would be saved over the next 10 years by abolishing the Code for Sustainable Homes and £195m from abolishing local targets for renewable energy.

So that’s around £30m a year.

To put this saving in context, have a look a the turnover and profit of just the top three commercial housebuilders in the UK:

 

Source: Barratt Homes plc, Taylor Wimpey plc, Persimmon Homes plc

The Impact Assessment claims that this £30m/year is the ‘net benefit to business’, but what it actually presents is the net benefit to property developers, who no longer have to pay for environmental technologies or renewable energy. 

An Impact Assessment should assess the benefit to the economy, not one favoured sector. 

The businesses that would have supplied environmental technologies to help these new homes outperform the Building Regulations will be adversely affected, but the Impact Assessment takes no account of this.  Nor does it attempt to estimate the cost of improving these low efficiency homes later on. 

The Impact Assessment in support of the proposal is flawed and should be repeated taking into account the net effect of the changes on the whole economy.

Not Helping Anyone…. Except Rich Landowners

If building regulations are clearly signalled in advance and consistently applied, then developers can decide how much to pay for land with certainty about their build costs.  So the only thing building to a higher environmental standard will do is slightly reduce the massive windfall that landowners get when they convince a local authority to allow them to sell to property developers.

Conversely, if building costs are reduced then developers, in a competitive market for building plots, will bid up the value of land to a point where their profit margins are maintained. 

I’ve already written about this, often overlooked issue here: 'Who Pays for Greener Homes?'

Surely this isn’t the government’s intention?  To hamper the development of a clean energy industry and land the country with extra costs for upgrading homes that could have been built to a higher standard of energy efficiency – all so that a few rich landowners get a bit richer.  Not this government, surely?

Whatever Joined up Government Looks Like, it Ain't This

At the same time that DCLG is busy paving the way for a million low-efficiency homes, another government department has to shell out taxpayers’ hard-earned money to financially support people in improving the energy efficiency of existing homes.

The Department of Energy and Climate Change (DECC) is spending your money trying to convince people to upgrade the energy performance of their homes.

And boy is it hard work.

It is simply much easier and cheaper to install energy efficiency into a new home as it’s built rather than doing it later once someone is living in it.  It’s ‘common sense’ isn’t it?  It’s so much simpler to do it properly the first time than have to come back and do it all again later.

Compare the cost of putting thicker insulation into the wall as its built with the cost of fixing more insulation to the outside of a building, rendering it, and re-setting all the windows.

Or the hassle of getting a rig into your garden to drill a bore hole for a ground source heat pump – knocking down walls, tearing up your beautiful lawn – compared to doing it when it’s already a building site.

Or the cost of replacing all your radiators, - suitable for a gas boiler, but not big enough for an air source heat pump - compared to installing suitable ones in the first place.

Consider the cost savings from installing solar panels in the roof at the same time as the scaffolding is there for the roofers to tile the roof.

You get the idea.

DECCs incentives such as the Feed in Tariff, Renewable Heat Incentive, and Green Deal need to be set at an even higher level than simply supporting the extra costs to overcome people’s aversion to turning their house upside down to do the improvements.  (So called barrier costs).

The lack of progress in driving up standards in new homes is going to cost the country more in the long run.

How to Fix This

A situation where each and every local authority makes up its own environmental targets is an unnecessary burden on developers.  In my own business, we’ve helped many house builders discharge local authority renewable energy requirements in all parts of the country, and while they are all similar they are also all ever-so slightly different.  There is definitely a case for simplification.

However, the Building Regulations are not providing a pace of improvement that is sufficient.  Nor is the Zero Carbon Homes ‘end point’ adequate – the definition is too weak and proposals to allow property developers to ‘buy’ their way to Zero Carbon will result in homes that are little improved over today's.

The Building Regulations are not some 'gold standard' for energy efficiency that it is impossible to improve upon, they are nothing more than a minimum standard, a lowest common denominator.  Local authorities should be encouraged to exceed this minimum standard  where is is viable, and the assessment of viability should be a local decision in keeping with the DCLG's own Localism Act.

The route to simplification is not for central government to impose a one-size fits all, lowest common denominator standard, but instead to provide a limited menu from which local people can choose.  Fortunately the hard work has already been done because this is a description of the system in Scotland.  Here the building regulations have a special section with a limited number of alternatives to the minimum standard (Bronze) so providing local choice and simplification of regulatory burden for developers at the same time.

See my earlier blog on what we can learn from sustainable construction in Scotland here.

Why not adopt or adapt this sensible Scottish idea for the rest of the UK?

UPDATE
How to make your views known to DCLG, with template email can be found here

Zero Carbon Homes – Carefully Check the Small Print

Let’s call it what it now is – the Zero Changes to Homes policy

As the government revealed its most recent changes to the building regulations on energy efficiency that were breath-taking for their lack of ambition, industry professionals are left wondering what’s happened to the inspirational goal of zero carbon construction.

The solarblogger caught up with an architect friend, Marcus Nelson of MEPK, over coffee at a construction trade show earlier in the year.  He was reflecting on the spirit of innovation that the government’s policy to achieve Zero Carbon Homes (ZCH) within ten years had sparked in the years immediately after its announcement in December 2006.

“There was a sense that we were all striving to achieve something worthwhile, that it was an ambitious challenge but one that we could achieve by coming together as an industry.”

Where had that feeling gone, we wondered.

Not Quite Zero

The first sign that this challenging aspiration might be watered down was the decision over what should be included in the definition of zero carbon.

The initial announcement of the policy ‘Building a Greener Future’ in 2006 proposed a common sense definition:

“For a new home to be genuinely zero carbon it will need to deliver zero carbon (net over the year) for all energy use in the home – cooking, washing and electronic entertainment appliances as well as space heating, cooling, ventilation, lighting and hot water.”

However, government announced in 2011 that to qualify as a ZCH, only so-called ‘regulated emissions’ would need to be reduced to zero.  Regulated emissions are those that come from heating the home, providing hot water for bathing, and electricity for lighting, pumps and fans. 

So-called ‘unregulated emissions’ would not be included in the definition of ZCH.  These include for example emissions from electricity used to run appliances such as fridge, freezer, vacuum cleaner and washing machine, as well as electronic devices such as television, playstation and charging your phone.

Housebuilders had argued that they shouldn’t be held responsible for the electrical equipment that people use in the homes they build, and the government had accepted that argument.

Why stop there?  Why not argue that housebuilders cannot be held responsible for how often people choose to take a shower, or the fact that they want to heat their homes to a temperature higher than outdoors.  The precedent of taking an average for domestic hot water use and internal temperature is well established, and there is no reason why we couldn’t take an average electricity use for appliances and gadgets too. 

A common sense, “man in the street” definition of a ZCH would include the carbon emissions from running such essentials of modern day life as fridge and freezer.  Instead, fully one third of the emissions from a 2006 home have been ignored and will not be addressed by the ZCH policy.

As the chart shows, for a three bedroom end of terrace home of 85 square metres floor area with the average 2.55 occupants, this means that zero now means 15 kgCO2/m2.

One is left with the suspicion that the definition was chosen simply because it made the goal easier to achieve, and in the hope that no one would notice that zero doesn’t really mean zero any more.

Do as I say

As well as announcing the goal of all new homes being zero carbon by 2016, government also set out to use public procurement to drive the required innovation in construction products and techniques.  From April 1 2008, all new social housing built with public funding had to achieve Code for Sustainable homes level 3, a level of CO2 emissions 25% lower than the building regulations at the time.

The concept was that as the building regulations tightened up towards zero carbon by 2016, social housing would pave the way.  Always one step ahead of commercial building, helping to develop skills and knowledge in the industry, providing a scale market to drive down costs of new technologies and providing a set of ready-made solutions for the commercial developers.

In 2011, as social housebuilders were getting ready for the move to meet Code for Sustainable homes level four (a 44% reduction in carbon emissions from 2006 regulations), the government quietly dropped this requirement.  From then on, developers of social housing need only build to the same environmental standards as commercial builders.

Some social landlords have held the line and moved to Code 4 anyway, but with tightening allocations of central funding, most have not.  As the chart shows, the environmental sustainability of social housing will have remained almost static for the eight years.  By 2016 social housing should have already been building to true zero carbon for three years, demonstrating techniques and technologies ready for commercial construction to follow.

The Building Regulations that Never Came

In August 2013, around one year later than expected the government finally announced changes to the building regulations that would come into force from April 2014.  Instead of requiring a further tightening of the energy efficiency of new homes to a point half way to zero carbon, an improvement of only 6% was made.

As the chart shows, the ZCH programme is now well off target even for the watered down definition.

You can almost write the script for what comes next:

Government issues a consultation on the 2016 building regulations

Housebuilders lobby that the drop to ‘zero’ is too fast
2016 building regulations impose only a small carbon reduction
2019 promised for ‘zero’

Zero Carbon Homes was visionary and challenging, a kind of 'Apollo' programme for the construction industry.  Unfortunately instead of JFK, we got Eric Pickles...

“But why, some say, the moon? Why choose this as our goal? . . . Why climb the highest mountain? Why, 35 years ago, fly the Atlantic? . . . We choose to go to the moon in this decade and do the other things, not because they are easy, but because they are hard; because that goal will serve to organize and measure the best of our energies and skills . . .”

JF Kennedy

"For years badly-placed wheelie bins and the proliferation of multiple bins have created a blot on the landscape.  By ensuring that developers create appropriate waste storage areas when designing new homes, we can tackle the ghastly gauntlet of bin blighted streets and driveways."

Eric Pickles 2013

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See also: 'A Million Missing Low Energy Homes', comment on the Building Standards Review Consultation, also from DCLG.

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Let's Get Down to Brass Tacks

How to Sell Solar With the RHI

 

The shape of things to come?  Solar heating and solar PV in a combined installation.
Image courtesy : Viridian Solar

Perhaps inevitably, the first reaction of the solar industry to the new domestic Renewable Heat Incentive (RHI) has been to compare the financial returns for solar heating to the Feed in Tariff (FIT) available for solar photovoltaic panels.

A quick, back-of-envelope comparison is not normally favorable to the RHI, but a more considered evaluation raises some interesting points.

So, before you screw up your envelope and toss it in the bin, read on…

Wide Applicability

Solar water heating requires a much smaller area of roof than PV.  An area of 3 or 4 square metres (2-3 kWth) is ample for most households.  The average PV installation according to the Energy Saving Trust has reached 3.75 kWp or around 22 square metres.  Solar heating therefore is more useful for partially shaded roofs, where only a small part of the roof area can be used.

Because it takes only a small portion of the roof, it can also be more palatable for customers who are interested in the impact of the solar installation on the looks or re-sale value of the home.

The RHI will require only loft insulation and cavity walls to be filled, and only where it is practical to do so.  This means that any building can qualify at modest cost.  The FIT is limited to homes that can achieve EPC D, and many cannot except at exceptional cost. (I’m expecting the FIT to migrate towards similar qualification criteria to RHI – watch this space).

Solar heating is also less affected by orientation or the location of the installation, with a lower drop-off in energy yield for east or west facing roofs or installations in the north of the country.

These factors all contribute to a large potential customer base for solar heating.

Sweet Spots

As the Feed in Tariff (FIT) rates have fallen, energy savings start to feature more and more highly in the financial returns calculations.  Solar companies are starting to get used to the idea that the financial returns for PV now depend much more on the customer’s patterns of energy use and therefore the sizing of the system.  (See my blog on self-consumption of solar electricity here.)

The Renewable Heat Incentive for solar is set at a level where the return on investment also relies upon the amount of energy saving the customer achieves.  This creates “sweet-spots” with above average financial returns:

Larger families

On average, the more people in the house, the more hot water the household uses for showers and baths.  The same solar installation will produce a greater annual energy output when there’s more cold water to be heated up, and the MCS deeming method captures this.

Oil or electric heating

The more expensive the heating fuel being saved, the better the returns that are achieved.  Off gas grid installations will have a higher return on investment.

Cost Sharing

Installing solar heating at the same time as other necessary work can transform the return on investment.  The installation of a solar cylinder can be as much as one third of the cost of the installation.  If a customer was planning to replace an old hot water cylinder anyway, then going solar at the same time would make a great deal of sense.  The same argument goes for roofing repairs, where roof access costs can then be shared.

Rather than relying on chance to provide opportunities for cost sharing, the solar industry now has a gold-plated opportunity to create its own.

From “Either-or” to “Both-and”

A solar installer can create cost sharing to boost the return on investment for customers very simply.

Create your own sweet-spot by offering to install both solar PV and solar heating together. 

The shared costs of travel, roof access and roofing works provide obvious cost reductions, but it goes much further than that.  Because the average sales price per install is boosted the costs of customer acquisition (sales and marketing, survey) are also shared across more revenue.

Counting All the Pennies

When preparing a financial calculation for solar water heating there are a couple of important points that are easy to miss out.

First, the saving on the energy bill is not the same calculation as the solar energy added to the hot water cylinder.  The fuel burnt to create the same level of heat is higher because the back-up heater will operate with efficiency below 100%.  In fact, it gets better because the “summer efficiency” of boilers is lower than the “winter efficiency” because they have to heat up just to prepare the domestic hot water.

The new version of MIS 3001 proposes a range of “solar efficiencies” for different back up heaters, but a few of the more common ones are shown below:

The energy saving is the solar energy input to the hot water cylinder divided by the boiler efficiency.  Depending on the efficiency of the back-up heater in the home, the fuel saved can be as high as double the solar energy.

Second, the customer is getting a brand new hot water cylinder as part of their solar installation.  If it’s replacing an old cylinder with lower performing insulation and if it’s carefully installed with insulation on all the connecting pipes (not just the solar ones), then there is a significant energy saving for the customer.  When replacing an old cylinder with a properly installed new one, the energy saving averages 750kWh/year, adding around 50% to the energy saving.

These savings are real and they are significant, they should be taken into account in any presentation of the financial benefits of solar heating. 

Getting Emotional

The solar PV market has spent the last few years selling a financial product.  Cold, rational arguments about return on investment, fuel price inflation and comparative returns from ISAs have crowded out the emotional reasons people still have for buying into renewable energy: energy independence, climate protection, conveying their values to others.

Solar heating and solar PV top the charts as the renewable technologies most people know about and understand.  This is especially true for solar heating.

When you step under a hot shower provided by a solar heating system, you are provided with an intuitive, physical link to the energy you are producing.   A customers’ relationship with solar water heating is intimate and emotional.

After all, which other renewable energy technology do you get naked with?

People are not cold, profit-maximising robots - they are individuals with a wonderful capacity to  surprise. The solar industry needs to re-connect with all the emotional reasons for installing solar – oh, and by the way it makes great financial sense too.

The Domestic RHI for Solar

In-roof solar heating panels - image courtesy Viridian Solar

On 12th July, the Department of Energy and Climate Change announced the details of the Renewable Heat Incentive (RHI), an incentive scheme to promote the uptake of renewable heating such as solar panels, heat pumps and wood pellet boilers in the domestic residential sector.

This new scheme, starting in spring 2014, has the potential to be a complete game-changer for solar heating in the UK.  

Here is a summary of the most relevant aspects for solar heating.

Payments

Owners of qualifying solar heating installations will be paid at least 19.2p per kWh of renewable heat generated for seven years.

This figure of 19.2p may be adjusted upwards (up to a likely maximum of 21.7p/kWh) subject to a review of the tariffs on the non-domestic RHI scheme that is expected to conclude in the autumn.

The payments will be made quarterly in arrears and index linked to the Retail Price Index (RPI) with annual adjustments to tariff levels.  People who have already received a Renewable Heat Premium Payment (RHPP) or other government subsidy will find their payments trimmed back each quarter so that the total subsidy is decreased by the amount of grant they have already received.

Deeming

The heat energy against which the domestic RHI will make payments is calculated rather than measured with a heat meter.  For solar heating, the energy figure will be taken from the Microgeneration Certification Scheme (MCS) certificate.  The calculation will be performed by the solar installer according to the method given in the MCS installer standard, MIS 3001, a calculation based on a modified version of SAP.

The MCS solar thermal working group has been working on an imminent new version of MIS 3001, which has some significant changes to the energy calculation compared to the current standard. 

The 2012 consultation on the standard indicated some of the changes being considered:

• Hot water demand is based on the actual number of people in the house, not a notional occupancy calculated from the floor area.

• The fuel bill energy saving is calculated by dividing the renewable heat input to the solar hot water cylinder by the efficiency with which the back-up heater works, this efficiency taking into account the summer-bias of solar energy production.

At the same time, a new version of SAP has been released (SAP 2012), which introduces different solar irradiation for locations throughout the UK, and increases the hot water demand for homes without electric showers.

Full details of the new calculation have not yet been revealed. However, the Solar Trade Association has published the following estimates based on SAP 2012 and its understanding of the likely shape of the energy estimate in MIS3001:

Number of people in the house	Deemed Renewable Heat (kWh)	7 Year Tariff Payments (£)	Assumed System
1	867	1,166	2 m2 panel area, 150 l cylinder
2	1,006	1,352	2 m2 panel area, 150 l cylinder
3	1,383	1,859	3 m2 panel area, 210 l cylinder
4	1,746	2,347	4 m2 panel area, 250 l cylinder
5	2,242	3,014	6 m2 panel area, 300 l cylinder
6	2,428	3,263	6 m2 panel area, 300 l cylinder
Other assumptions: UK average irradiation, south facing, 30 degrees roof pitch, shading – none or very little, no electric showers in home, twin coil solar cylinder Source: STA

Target Market

The domestic RHI provides financial support to eligible renewable heating systems that provide heat to a single domestic property.

The domestic RHI is available to owner-occupiers, private landlords, registered social landlords, self-builders and third party owners of renewable heating systems.

Apart from self-builders, new build housing is not eligible for the scheme.

It applies in Great Britain.  The devolved administration in Northern Ireland may launch a similar scheme as it has done with the non-domestic RHI.

While you may often hear DECC saying that the scheme is ‘targeted’ at off-gas-grid properties, the scheme is open to all.  This just means that the value of the energy savings for off-grid properties will be higher due to the more expensive oil or electric heating that is no longer being burnt.

Second Homes

The deeming method will mean that second homes have a lower occupancy, and therefore the deemed water use and renewable energy will be much lower.

Second homes that are Holiday Lets (and therefore considered to be businesses) would be eligible for payments under the non-domestic RHI.

Qualification Criteria

For a solar system to qualify for domestic RHI payments, the following criteria must be met:

1. The installation must be registered on the MCS database – this means it must have been installed by an MCS accredited installer using solar collectors that are MCS or Solar Keymark certified
2. The property will have a Green Deal Assessment (see note below)
3. Loft insulation of at least 250mm and cavity wall insulation where these are possible.
4. The installation is ‘meter-ready’

Self-build properties are exempt from the second and third requirements as they will be built to current building regulations.  In this case an Energy Performance Certificate (EPC) is sufficient.

The ‘meter-ready’ requirement means providing isolation valves for accessible pipework sufficient for a heat meter to be retrofitted into the system without draining it down. 

The optional additional payments for taking part in the Metering and Monitoring Service Package are not available to solar thermal installations.

Link with the Green Deal

In order to join the RHI, a customer needs to have had a Green Deal Assessment (GDA) of their property, but they do not have to act upon the recommendations of the assessment.  

The exception to this, (as for the RHPP), is that to enter onto the scheme you must have loft insulation to a depth of at least 250mm and cavity walls must be filled (where possible). If these measures have already been done (or are not feasible), the GDA will not list them as recommendations.  If they were done subsequent to the GDA, the householder will have to get a subsequent EPC as evidence.

If the householder does want to take up any of the Green Deal recommendations they do not have to enter into a Green Deal finance arrangement, they could pay for it themselves or borrow the money elsewhere.  

From the above, it seems that the most cost-effective route is for the householder to get loft insulation and cavity wall insulation done before applying for the GDA, thereby avoiding the costs of a subsequent EPC.

Solar Thermal in Conjunction with Other Renewable Heating

Neither heat pumps nor biomass work at their highest efficiency when preparing domestic hot water and this is especially true outside of the space heating season, where the heater has to fire up just to make hot water.   For this reason DECC wanted to provide additional support to installations that use renewable heating in conjunction with solar water heating.

Where a solar thermal system is installed alongside a heat pump or biomass boiler, both technologies will receive payment for the full deemed heat.  This means that householders installing both technologies will in effect be paid twice for the water heated by the solar system, once at the solar tariff, and once at the tariff for the space heating technology.

Legacy Systems

People who already installed a solar thermal system on or after July 15^th 2009 are also eligible to join the scheme (called legacy systems).  

The installation must have met the MCS standards prevailing at the time of installation, and the deemed heat for a legacy solar system will be the energy saving estimate entered onto the original MCS certificate. The test of the install date will be the date on the MCS certificate.

In order to manage the numbers applying to join the scheme, OFGEM will phase the opening of the scheme to legacy applicants – details to be announced.