For starters, the document emphasises a core distinction between domestic and commercial systems. Systems serving a single private residential dwelling are not intended to be eligible for the RHI; expect, then, plenty of attempts to capitalise on the grey areas in this definition. No doubt there are already householders devising cunning plans to start small businesses from their spare rooms to qualify early for the RHI.

Solar thermal on a commercial building

Under the proposals, the RHI will also only apply to heat used for certain ‘eligible’ purposes within a building. A building is defined as any long-lasting structure – fixed or moveable – which, except for doors and windows, is wholly enclosed on all sides with a roof, ceiling and walls. Now this is intended to exclude, say, external swimming pools. But indoor swimming pools seem to be included, even though they may in fact have large sliding patio windows or even a sliding roof to the outside.

The document continues to attempt to plug loopholes such as where heat is ‘rejected’ from a system. This would include, for example, a heat dissipation circuit of a solar thermal system – which would then be ineligible. All well and good; but what, apart from the speed of heat-loss, is the difference between heat export through a solar collector and that simply lost through an insulated structure?

In any case, however admirable the objective of excluding such systems, this is unlikely to be successfully accounted for without failsafe control equipment. There are clearly solar thermal designs on the market which advertise themselves as having a heat export function intended to operate when the internal insulated storage is becoming too hot – a situation which arises most commonly when storgae is inadequately sized for summer heat. Perhaps, then, the RHI will finally see an end to these.

Where it gets particularly convoluted is in the stated intention to avoid paying out for so called ‘parasitic loads’. Read what you will into this, but most renewable thermal systems of any note contain electrical readouts, safety controls or electrical circulation pumps. These will inevitably contribute to the heat within the system. In some cases the circulation is necessary to avoid safety discharge such as in biomass boilers. Ignitions and fans must energise for safe combustion. There is, mind you, mention of permitted “ancillary purposes” – so plenty more grey areas here.

Furthermore, it appears non-renewable content of biomass feedstock of up to 10% is also eligible. In the case of municipal waste streams, up to 50% is permitted. So it seems the ‘R’ in the RHI has been rather diluted in the attempt to keep solid fuel heating in with a chance.

Pellet stove

Anther peculiarity concerning biomass fuel types relates, ironically, to wood fuel too close to its natural form – namely the log! Many, I am sure, would like the idea of being paid to watch a roaring fire. But the RHI intends to make such applications ineligible on the basis that it could allow the burning of coal, or oil-impregnated briquettes.  For avid flame-watchers, relaxing in front of a pellet stove with a back-boiler may be the only option.

The consultation document, which is in two large volumes, also includes baffling attempts to include only distribution technologies that use liquid or steam. Air, for example, is excluded. Rather contrived when we consider that any space heating system will inherently use air to heat our bodies – where is the line on this rule meant to be drawn?

It appears to be fairly easy to take pot shots at the unenviable task of supporting renewable policies; cue a recent independent evaluation of the Low Carbon Buildings Programme (LCBP), the RHI/FIT precursor, a grant scheme which ran between 2006 and 2011. At over 100 pages, the evaluation does not make pretty reading, and picks over the pieces of a scheme that was in its time deeply unpopular. Some may remember, for instance, the closed tenders schemes, monthly quotas and crashing websites. Even the providers of the scheme evidently had little good to say of it. However, going back a little further, we come to the Clear Skies scheme, circa 2003. Here was a scheme that was enormously popular with both householders and installers – easy application forms, easy for installers and manufacturers, and easy money for the end-user.

So why, given this far more successful model, have we seemingly grasped defeat from the jaws of policy victory?

Despite the lack of formal evaluation, Clear Skies was a success for one very good reason. In a world of increasing complexity and over-funded self-analysis, it was a beacon of simplicity. Something much under-rated in government circles, it would appear.

This fairly sums up the frustration with the government’s PV feed-in tariffs debacle in the last few months. It also constitutes a stark reminder to us all that without subsidies, PV modules do indeed belong in far-away, sunny climes where they are best able to pay off their manufacturing pollution deficit. In the meantime, no-one could fail to notice the stampede of small PV arrays appearing on UK household roofs, not wholly unconnected to a plethora of full-page newspaper adverts offering ‘free solar’ without capital outlay to selected roof owners.

Against this backdrop of suspicion and ker-ching!, the eagerly-awaited Renewable Heat Incentive (RHI) announcement has now arrived. Intended to revive the faltering renewable heat market, it in fact contains – predictably – few concrete details and raises more questions than it answers. Suffice to say there is an offer of payment from central government funds for generating renewable heat. When this might take effect is a different matter.

The RHI is unfortunately going to be judged in the same light as the PV FIT, which revealed that the British populace is far more interested in its own bank account than saving the world. The problem here is that accurate fiscal analysis of capital investments is not the nation’s favourite pastime. In a nutshell, then, you are likely to get at least five times more tariff cash per kWh generated for PV for 25 years than solar thermal for 20 years, but it requires at least twice the capital outlay and four times the roof area. Crunch the figures in your own way, but solar thermal has been left on the proverbial starting line with not only a misfiring engine but its wheels missing too.

It gets worse for solar thermal given that some of the key innovative areas in mainland Europe – such as commercial solar air heating cladding and large-scale district heating – have been targeted for exclusion in the government’s proposals. These sectors alone are capable of spearheading the needed cost reductions in skills and production, but their fate appears doomed in the UK. This is a classic example of government policy interfering in a market that it has so far shown neither empathy nor logic.

Naturally enough, with the subsidies so skewed in PV’s favour, we are now seeing new electrical switchgear products that benefit PV. The bad news for solar water heating is that one of these quite sensibly encourages water heating immersion heaters to be automatically switched-on when the sun shines, rather than exporting the energy to the grid. Without skewed subsidies, this wouldn’t have previously made sense given that solar thermal is four times more efficient at converting the sun’s energy. Although PV initially appears to be a technology able to shun the chains of localised storage, a report by the American Physical Society’s Panel on Public Affairs (POPA) ‘Integrating Renewable Electricity on the Grid’ (pdf here) suggests that the variable nature of solar and wind resources mean that a national renewable electricity contribution would be difficult to reach without storage devices. This will all be painful news to combi-boiler owners aspiring to have PV on their roof as they will rarely have electrical immersion heater back-up. Perhaps one day house buyers will independently see greater value in heat storage rather than so much reliance on instantaneous devices.

Whatever their motives, the huge upsurge of households now engaging with solar energy is at least a small step towards creating a substantive low CO2 economy. At policy level, nevertheless, there are enough indicators with red flashing warning lights to demand caution. Take the study which found that the Elm Tree Mews development in York – designed to meet targets set for 2013 – had heat losses of more than 50 percent higher than intended in the design, and that renewable heating systems were not performing as they should. REAL Assurance, which underlies household renewable subsidies, has already had to attend to 100 serious complaints this year. On top of this, the BBC recently highlighted micro generation rogues on their website pretending to be MCS registered installers.

The statutory consumer body Consumer Focus, in its response to consultation on a micro generation strategy, highlighted high pressure sales techniques as the principle cause of consumer complaints in the solar PV market. Issues included sales representatives:

• offering 20 per cent discount on prices during their visit

• staying six hours in their home

• offering a large discount for monitoring

• demanding 35 per cent of the contract price as a deposit

Ironically, sales people were slated in the same report for offering solar thermal sales materials at the same time as selling solar PV systems! Unless this is a vendetta against solar water heating, this would suggest that even though there may be more situation-appropriate measures than PV on offer, such as cavity wall or loft insulation, these too might not be in the customer’s interests to mention.

With so much contradictory messaging and confusion, perhaps emigration makes the most sense for both solar thermal and PV after all!

Live webcast by Earthscan publishers on Solar Domestic Water Heating. Full version including David Thorpe’s talk on Sustainable Refurbishment available to download from this address.

The 1st Solar Industry Summit UK will bring together solar energy players from the UK and other parts of Europe, from across the industry sector: representatives from the political and financial worlds, manufacturers, installers and the press.

The full programme has now been released and can be viewed here.

While ongoing policy is a key feature, this leading industry conference offers presentations and discussion on a much wider range of issues facing the PV and solar thermal sectors today, such as technology developments, project planning, equipment and installer certification, quality issues, finance and marketing.

To register for this event, visit the SolarPraxis website.

Visit our stand to see the latest program releases and meet some of the team behind The Solar Design Company.

There is nothing that convinces us more that a government has lost the plot than when it uses its terminology incorrectly. It sets my teeth on edge when I see another posh suit stride up to the podium and expound the pros and cons of photovoltaic (PV) ‘large-scale, stand-alone & high-capacity systems’. This meaningless spiel makes as much sense as opening a outside window in an air-conditioned room.

The issue here is about sub 5 MWp (peak power) systems typically occupying sub 0.05 km² of land. Abroad, the largest solar PV ‘parks’ in the world are considerably above 50 MWp (footprint over 1 km²) and these are nowhere near ‘parking’ on the relatively dull, compact shores of the UK. So the government are getting worried about systems that are ten times smaller than what everyone else thinks is large. One wonders what the fuss is about.

Solar PV at the Centre for Alternative Technology

‘Stand-alone’ PV, which to the rest of the world  has for decades meant off-grid, now appears in UK government feed-in tariff tables to mean grid-connected. And as for the habit of substituting the meaning of peak power rating for ‘capacity’, when for example a battery capacity has long been measured in Amp-hours, I can only despair.

We’re heard a lot of this jargon recently. Forums worldwide are continuing to plump up column inches with a yes-no debate as to whether or not to fill the Cornish countryside with a few MW of PV ground-mounted ‘solar parks’. Particularly strange when, at the time of writing, none have so far been built. But house owners and builders can continue to rub their hands with glee, as the feed-in tariff is still fair game to their more modest roof areas. Nevertheless, technically speaking a large ‘solar park’ remains more cost-effective and efficient than a multitude of smaller systems. If all this feed-in furore is, seriously, purely for the benefit of anthropogenic atmospheric CO2 reduction, then we’ll need to eventually embrace the ‘king-sized’ PV arrays as much we have to with ‘monster-sized’ wind turbines. However, I think we can stop the pretence of these benevolent undertones when every other PV advert uses the latest irritating buzz word ‘bankability’.

Equally worrying are the reports that operational solar water heating systems are now being removed to give way to ‘small’ roof-mounted feed-in tariff PV systems. We can only shudder to think of the lifecycle energy merry-go-round that occurs when we short-shelve perfectly viable energy-capturing appliances. Still, I’m sure the more aspiring politician will spin this into a job-creation exercise: one job created taking solar down and another putting it up. But my response then is: ‘How many coalition MPs does it take to wreck a renewable energy policy?’

I really do think we should pay attention to the poor quality of equipment that is being put on our roofs.  Chinese products are increasingly exported throughout the world and yet a survey carried out by the Shanghai Commission of Consumers´ Rights in China showed that 65 % of solar water heaters were not working properly there. Here in the UK, the MCS scheme is meant to provide protection for consumers against this kind of problem. Certainly better than nothing; but this hasn’t stopped the Welsh Assembly Government (WAG) deeming an extra layer of hurdles the MCS called the ‘Welsh PV framework’. This will appoint a select group of contractors to finance, design and install photovoltaic panels on public sector buildings. The question this raises is what part of the MCS scheme is not good enough for the WAG and yet good enough for the Westminster government?

In Germany, the control of large PV systems comes from banks (hence the term ‘bankability’), and there is much rumour about a similar so-called approved contractor ‘white list’. There is no doubt of the success of the German PV market, which makes me think we are going to see more ‘white lists’ leaving many MCS installers wondering what they still have to do to access larger jobs.

If they find themselves out of PV work, I’m sure there will be no shortage of retraining opportunities to become heating engineers given the very sharp December temperatures we’ve just had. The Association of British Insurers indicates in December 2010 there were 190,000 claims for damage to homes and businesses, at a cost of some £900 million. This is a 35% rise in claims compared to the whole of winter 2009. Over 50% were for burst pipes. The Association also noted that this resulted in the highest total bill ever recorded for a period of freezing weather in the UK. Microgeneration or not, there are times when we just want our appliances to work no matter what terminology we use.

'The Energy Island' - image courtesy of VirginTech.org

Any hopes that these floating islands would be moored conveniently near to the UK should be quickly dispersed, as they would in fact be destined for the faraway seas of the Caribbean, South China Sea and Indian Ocean.

As you may expect, such islands would include wind energy, or ‘aero-generators’, to be mounted on height adjustable hydraulic masts allowing collection at different heights. On a 600 metre wide platform, the total peak output would be expected to be 18 MW peak. Wave energy also features with the same 600 metre platform providing an extra 9 MW. The more unusual sea current energy could be harvested, adding perhaps 10 MW.

The opportunity to gather solar energy would not be missed with different solar collector systems located over the 22 hectare platform. These would range from photovoltaic arrays through to concentrating high temperature thermal collectors, which reach 800°C and can be used to convert to electricity. Here a peak electrical output of 54 MW (e) and peak thermal 81 MW (th) can expected, which translates to continuous outputs of 13 MWe and 20 MW (thermal).

As if this wasn’t enough, the really clever bit comes next. Bearing in mind that all this energy has to be either used immediately or stored to be useful, the proposal is then to combine all electricity and heat to power a process known as Ocean Thermal Energy Conversion (OTEC). A simple way to consider this is to first think of the earth’s sea water as a giant solar collector. As the sun shines, natural thermal gradients build up where the ocean’s layers of water have different temperatures. As long as the temperature between the warm surface water and the cold deep water differs by about 20°C, an ‘OTEC’ system is claimed to produce a significant amount of further energy, with little impact on the surrounding environment. What happens is that warm seawater is flash-evaporated in a vacuum chamber. The resulting low-pressure steam is used to drive a turbine-generator. Cold seawater is used to condense the steam after it has passed through the turbine. So the initial renewable energy sources are multiplied by using the ocean temperature gradient to finally produce a useful 250 MWe. A hydrolysis plant then produces hydrogen from this electricity for temporary storage and then transportation back to the mainland by ships that have docked onto the island. We then burn this hydrogen to gain back the electricity and heat.

It just gets even better, once you realise that this complete process also has a byproduct of fresh de-salinated water with our given platform producing 240 million litres of desalinated water per day, an equivalent volume to that of a large tanker. Chilled water for cooling and nutrient rich cold sea water, taken from the deep ocean, are also usefully gained products.

The islands can also incorporate human habitation beyond that of the workforce, forming a novel pattern of living. A 22 hectare platform could house 1000 inhabitants, using, at 2 kW per person, less than 1/100^th of the energy produced by one module of the ‘Energy Island’.

So is this a technological dream which solves all our energy problems and even a chance to create new societies?

Such ideas were previously only imagined through science-fiction.  In fact I’m sure if he were alive, Stanley Kubrick would have loved a chance at a screenplay. I can see a panoramic, rose-tinted opening to all this. How about that these floating islands even become nation states unto themselves with radical new constitutions delivering fresh hopes from an increasingly war-torn mainland?

The chance to start afresh has always fascinated mankind. However, I wonder if these far-away refuges would be likely to receive some very unwanted attention. Believe it or not, pirates in fast speedboats still roam the Eastern seas and holding hydrogen containers to ransom would not be beyond reason. Should these islands in the sun become a little too desirable to habitat, the sight of refugee ships on the horizon may cause inhabitants some unease.

It is interesting to consider whether, as we tip to a global balance where corporations hold more wealth than governments, such floating island eventually would become heavily fortified, competitive factory ‘ships’ manoeuvring to gain the best oceanic hotspots before other corporate branded islands do the same?

The Virgin Earth Challenge website states there is an utmost urgency to save the earth and that its prize will go to a commercially viable design. But I wonder if the winner will address the ultimate challenge that corporate greed itself may well be part of the challenge?

This alone is not necessarily a problem, but when this is accompanied by reported forceful evictions associated with organised crime then the sun starts to bring its darker side to renewable energy. Parcels of land south-facing and unshaded with easy connection to the grid carry a premium. Large investors look for large Megawatt installations so this pressurises the small land owner to upsize. In the UK, although suffering from no known intimidation yet, we are starting to see predatory offers by land agents in Cornwall, notably one of the UK’s sunny locations. I’ve always wondered what motivated the so-called new breed of ‘green investors’ and their ambition to really save the world. Perhaps it’s really their pockets they are trying to save.

Speaking of which, it was interesting to note the UK Sunday Mail’s less than enthusiastic response to the ‘carpeting’ of the UK’s countryside with PV. They see foreign manufacturers as the main benefactors, whereas the losers are the non-land owning consumer paying for the feed-in tariff. Some would say that anything annoying a Mail newspaper editor is a good thing. Nevertheless, we can expect the pro-countryside lobby will be flexing its views at planning meetings around the country.

The real problem with PV is that such systems contain so many rare metals like gallium, indium, selenium and tellurium, not to mention copper for the connecting cables. Hence another unpleasant consequence to the solar boom will be more exploitative mining. This is already an issue for the rare Chinese neodymium in wind turbines and for the zinc, vanadium and lithium contained in electric vehicle batteries.

Large PV array in Bavaria, Germany

But to me the crux is the ominous rise of scrap metal thieving. Given we already have thefts of vehicle catalytic converters for just a few grams of platinum, there would appear little chance of survival for an unsupervised field full of copper cables. Perhaps in some perverse distant science fiction future, remotely located energy equipment will have to be made of non-recyclable materials simply on the basis that they are not worth nicking.

I suspect that the more intelligent thief will realise a PV module is worth more intact than as scrap. That is, until the point where we see universal indelible serial marking of modules visible under their laminate. Module and inverter theft is a rising insurance issue in the UK and will soon affect premiums. It is interesting to see how the most successful PV market in the world in Germany has been shaped by insurance and finance companies.

I was fascinated by how large PV systems over there are now routinely thermographed with an infra-red camera to catch tell-tale hot spots representing short-circuit and bad junctions. This expensive and skilled operation is taken not by the contractors but at the behest of the finance and insurance companies. It’s not unknown for poor-quality installations to burst into flames because of wiring faults, and insurance companies naturally want to minimise these risks.

Despite these obstacles, the PV market is roaring away with a surge of flash green cash. Evidence acquired by the Environmental Change Institute, who examined the consequences of the Low Carbon Building Programme (LCBP), indicates that the PV market is quickly maturing with prices lowering in relation to the array peak power. There is also little variance between installers and location. This is good news for those newcomers approaching the PV market. However, the report titled “Power from the People” reflects that the LCBP met few of its aims and was generally despised by the industry. In particular, the solar thermal (water heating) market provided Oxford University reviewers with little confidence when considered under the same criteria as PV.

In the context of the fervour that currently surrounds feed-in tariffs of all kinds, a sanguine summary of the above authors is worth repeating here: “There is a need for policies that support a holistic approach to both refurbishment of the existing housing stock and new build, treating micro-generation as part of a wider energy and emission savings agenda from the UK housing stock.”

PV feed-in tariffs are clearly not the holistic approach being called for here and there is little evidence that the forthcoming Renewable Heat Incentive (RHI) will be either.

Existing UK houses require energy efficiency measures to be undertaken

For decades the old-timers have consistently stated that renewables are only sensible once all energy efficiency measures are first applied. It appears that this message has been forgotten by the sharp-suited upstarts. Common sense has a nasty habit of coming back to haunt and it is nonsense to throw good energy after bad when we have too many heat-leaking buildings and domestic hot water (DHW) systems. Rewarding end users for feeding those heat leaks instead of plugging them is a mistake.

They may have taken a while to wake up, but quite a few treasured institutions are gathering a head of steam on this very issue. The Association of Conservation of Energy made it clear that “it is ludicrous that the (RHI) policy will allow efficient gas boilers (potentially subsidised recently by the taxpayer as part of the scrappage-scheme) to be replaced by heat pumps or biomass boilers. This replacement of heating technology reduces the energy performance of a property – lowering its Environmental Performance Certificate (EPC) rating saves a relatively small amount of carbon but increases fuel bills for the building in question, not to mention the costs borne by the taxpayer or energy consumers.”  The AECB (the sustainable building association) closely followed with: “The issue is the difference between renewable energy generation and consumption. Failing to make this distinction is a fundamental flaw in the entire (RHI) scheme.”

Even the venerable International Energy Agency gave in, in its latest Technology Perspectives, when it said that: “Increasing energy efficiency, much of which can be achieved through low-cost options, offers the greatest potential for reducing CO2 emissions over the period to 2050. It should be the highest priority in the short term.”

Solar thermal installation

Without the subsidies and in competition with the ease of the PV feed-in tariffs, it’s no surprise that in the last few months solar thermal had dropped off the proverbial cliff face in terms of sales. And yet a decent solar thermal system will annually convert the same area of solar radiation to useful heat over four times the rate of photovoltaic (PV) to electricity. How has such a perverse situation arisen?

The answer I believe is down to the thorny question of how to value renewable energy. A good example of this is the oft-heard claim that PV costs are approaching that of purchased electricity from the national grid mains – this is the so-called holy grail of ‘grid parity’. This phrase is frequently used now to boost confidence in PV but, in doing so, the protagonists are using extremely creative accounting. For transparency, the capital used to fund renewable technologies must first be factored in correctly to allow fair comparison. Hence, the analysis should consider the inflationary loss of capital if not otherwise gainfully employed as well as what rate of return could have been achieved in a stable investment like government bonds. More to the point, it is rare to see allowances made for the likely change of a grid-connected inverter within 25 years or the annual module degradation.

Of course there is plenty of emphasis on the expected price rise of on-peak electricity and so investing in PV is offered as an invitation to reduce future uncertainty. In effect this is achieved by buying one’s electricity in advance, assuming the sun will shine.

One might expect such shenanigans from the PV industry’s sales personnel but when it is also the public-funded Energy Saving Trust (EST) playing the PV enticement game then we have more to worry about. The use of its online ‘Cash back Calculator’ gives an over-optimistic financial analysis despite its small print caveats. On its website, clearly targeted at consumers, the graphical presentation of lifetime cashflow is shown as an ever-increasing straight line instead of what should be a diminishing curve.

My point here is that if you see energy production purely as an investment then, like with any investment, you need your wits about you; or else an independent financial advisor (IFA) who abides by the Financial Services Authority rules. Shouldn’t that be what the EST pins right next to its income savings promises?

If you are a commercial venture your difficulties have only just begun, since now you also have VAT, capital depreciation and tax offsets to consider. And yet this is where the opportunities lie, since the mass market will want simplicity and zero capital spend.  Hence I expect that the future of renewable generated electricitywill most likely be governed by the large financial institutions that have the security to fund the capital.  Soon we are likely to see installation companies simply requiring the hire of roof space. In return, the consumer who owns the roof benefits by a guaranteed future reduction in electricity bills. In this scenario, the independent small-scale renewable installers will soon become merely a historical anomaly.

Legionella pneumophila bacteria - image courtesy of bbc.co.uk

There’s an almightily clash of health policy coming our way very soon and it lies at the very heart of what defines a professional engineer who puts the public’s interest before self-interest. This concerns the eternal battle of all the higher creatures against that of the smallest – bacteria. The particular bacterium I want to focus on is Legionella pneumophila, which like many of its ilk ultimately seeks to devour us. Its name was coined from a large outbreak of pneumonia amongst the American Legion Convention in Philadelphia in 1976. The final toll was 221 cases with 34 deaths. Legionnaires’ disease now accounts for an estimated 18,000 hospital admissions in the USA. Over the years, more UK outbreaks have been recorded and clearly this is a matter of public health policy.

Species of Legionella bacteria are known to be natural inhabitants of water and can be detected in rivers, lakes and streams.  These eventually enter our piped water supplies, and poorly-maintained plumbing systems and air conditioning units are breeding grounds for Legionella. It grows in slimy bacterial colonies attached to surfaces such as the inside of pipes and water tanks. But bacteria can escape from these colonies into water flowing through them. Infection of humans is normally contracted by inhaling the bacteria in tiny droplets deep into the lungs.

Generally the mortality rate is between five per cent and 30 per cent among those who receive treatment and as high as 80 per cent in untreated patients, with the higher levels relevant to those who are immuno-supressed or have underlying disease. Research has shown that many people become infected with the bacteria without developing symptoms, so many cases of Legionnaires’ disease may go undiagnosed. There’s no evidence for person-to-person spread of the disease.

Solar thermal cylinders and expansion vessels

Most outbreaks and cases have been traced to contaminated water in commercial locations like hotel shower heads, air-conditioning systems and medical respiratory devices in places of work. However, there is increasing evidence that links both hot and cold household water storage with Legionella bacteria in the UK, and suspicion falls onto to our rather unique plumbing layouts which use either storage cisterns in the loft or expansion vessels on unvented and thermal stores.

The most common methods in workplaces to reduce the risks of bacterial build-up are thermal, biocidal and ultraviolet light. Newer methods include using air bubbles to cavitate and kill the bacteria. For households, the principal risk reduction is by use of temperature alone. Either the stored water is kept below 20 C. as ‘cold’ water or above 60 C. as ‘hot’. Anywhere between 20 C. and 45 C. favours bacterial growth and so water held for some days in this range is likely to require more intense temperature disinfection for an hour at 60 C. or perhaps even greater at 70 C. where the water passage is quicker. At first, this seems to be a simple task for heating engineers of setting thermostats and sizing storage accurately. However, there is a growing conflict with two other public protection measures.

Firstly, the fact that higher temperatures increase scalding risk; and secondly, the carbon emission increase from the extra energy for higher water storage temperatures. Once you now bring in the increased use of renewable energy such as solar, then we have a real conundrum since solar storage is often held for days at variable tepid temperatures. If the solar storage is otherwise fossil-fuel heated, there is a high risk that the solar contribution will fall well below par and storage losses increase. The nub of the issue is this: what’s the preferred scenario for a heating engineer – increase the risk of bacterial disease now or protect the future from the effects of global warming?

If you are a short-term thinker, you’ll side with raising all hot water and solar storage vessels used with showers up to 60 C. once a day. If you are a long-term thinker you’ll realise that the UK alone will ‘lose’ carbon dioxide mitigation from solar systems of the order of millions of tonnes over a decade, inevitably causing more human misery albeit at a later date.  A clear conundrum for the professional engineer.

For the eco-builder, there is a lobby position for our policymakers that may give hope. Firstly, let’s avoid using fossil fuel to heat solar storage unless absolutely necessary. A well-designed solar system does this anyway. Secondly, pass all solar-stored water through 60 C. for more than hour or as high as 70 C. where a non-storage boiler is used, such as a combi boiler. Use solar heating as a priority to achieve these temperatures by careful design, and thereafter fossil fuel back-up. Thirdly, provide thermostatic control of solar heating circuits and DHW to reduce scalding risks.

Finally, use low-energy techniques to reduce the risk of bugs growing in our water in the first place:

• Follow the guidance of water regulations and bylaws
• Reduce long pipes runs, especially to showers
• Use heat exchangers to separate out high-risk circuits
• Only put non-porous materials in contact with our water
• Provide ease of cleaning maintenance such as storage hatches
• Advise annual servicing of hot and solar water storage