Sunday 16 October 2011

Technology or Training?

Solar Trial Highlights how to get the most from Solar Water Heating Systems

The Energy Saving Trust (EST) has recently published the results of the most comprehensive study ever of the performance of solar water heating.  Eighty eight homes, 12 months of monitoring and millions of data points later the results are out and the report brilliantly highlights both the strengths and weaknesses of this technology.

Customers were clearly delighted with their solar heating systems, with 84% of households being “satisfied” and 50% “very satisfied”.

Those systems that were categorised as “well installed and properly used” achieved excellent results with the report showing a typical energy saving of 1,500 kWh/year, corresponding to the solar system providing around 60% of the household’s hot water energy.

The report also found many systems where users had timed their back-up heating in a way that was detrimental to the energy saving.

Most solar systems in the study used a twin coil cylinder, where the solar system heats the whole volume of the cylinder from the base, with the back-up heater (most often a boiler) heating only a portion at the top of the cylinder.  Read a fuller explanation of how a twin coil cylinder works here.

If the household controls their back-up heater well, it is timed to be on for a short time and switch off before the main period of hot water use starts.  As hot water is taken from the top of the cylinder, cold water enters at the bottom.  The cylinder has plenty of cold water in it for the solar system to work on the next day.

An example showing good use of back-up heating is shown in the image above. The main water use is in the evening and the following morning. The best time to time the back-up heater is to come on around 18:00, after solar energy input is over, but before hot water use starts. If the cylinder is large enough, and well insulated, then water use the following morning will be covered and there will be no need for a morning timing of back-up heater.
By contrast, if the back-up heater runs during or after hot water use, then the cold water let into the cylinder is quickly heated up.  By the time the solar system starts to work, the only cold water available is at the very bottom part of the cylinder where the back-up heater couldn’t reach.  Once this zone reaches its maximum temperature, there is nowhere left for the solar panel to put its heat; it switches off and solar energy that could have been collected goes to waste.

An example showing poor use of back-up heating is shown in the image above. The main water use is in the evening and the following morning (as before). The back-up heater is timed to coincide with morning water use, and runs after water use is finished, ensuring that most of the cylinder is already hot as the day begins and severely limiting the amount of solar energy that can be collected.

One approach is to try and educate the householder about how to get the most from their solar heating system.  Better information from their solar installers might have lifted more of the households in the study into the higher performing category.  After the systems in the study were installed, a new installer standard, the Microgeneration Certification Scheme (MCS), came into force.  It requires installers to leave printed materials and durable stickers about the place to explain how to get the best performance out of the solar system.

The problem with this approach is that as we move from solar heating being a fringe hobby to a mainstream technology, more and more diverse people will end up in houses with solar heating.  Unlike the sample in the EST trial, these people may not have bought it for themselves – it may have come with a new house, been fitted by a social landlord or a previous owner.  They may not be bothered about optimising their solar saving, or able to program the boiler timer.

Fortunately there is a technical fix that reduces the sensitivity of solar water heating systems to the user settings of heating systems.

If the solar heating system provides a larger volume of water that the back-up heater cannot heat, then there is more likely to be cold water available for the solar system to heat when there is sunlight available. This can be achieved by selecting a twin coil cylinder with an adequate solar dedicated volume, or having a separate solar cylinder that pre-heats water before it reaches the main cylinder. 
According to the Domestic Heating Compliance Guide, the solar system should provide at least 25 litres of solar dedicated volume per square metre of solar panel aperture area, but few do.

Specifiers of solar heating systems who are installing solar heating for others (for example social landlords or property developers) should consider carefully before choosing solar heating systems that rely upon achieving user-behaviours to achieve results.   Particular care should be taken with systems which retro-fit onto existing cylinders without providing any solar dedicated volume.  Although these seem attractive because there is no need to replace the existing cylinder, they are extremely sensitive to the timing of back-up heating. 

Instead, consider systems that are much less sensitive to user behaviour – specify hot water storage with an adequate solar dedicated volume.

Wednesday 5 October 2011

FITs and Starts

It doesn't have to look rubbish
According to a former US President, the nine most terrifying words in the English language are "I'm from the government and I'm here to help ".  The UK solar PV industry is preparing to demonstrate the truth of this in spades.

Many in the solar industry describe the development of  the UK solar PV market as a massive success for the government's Feed in Tariff (FIT).  Nothing could be further from the truth.

The FIT has inflated a bubble in solar PV, which may well burst in 2012 with spectacular results.  At home, we regularly recieve a couple of calls a day from telesales centres trying to get an appointment for a high pressure sales visit.  So called "PV for free" companies are installing panels onto houses with offers that seem too good to be true.  In my own village, a meeting promoting a bulk-buy PV scheme was standing room only. 

So just how has PV replaced double glazing as the short-hand industry for pushy sales tactics?

The Department of Energy and Climate Change (DECC) set the tariff levels based on PV prices in 2009, and created a clumsy review process which has tied their hands for making changes.  Subsequently, a perfect storm has hit global PV manufacturers causing a crash in prices.  The result - returns on investment that would make a loan shark blush.

Realizing that their own FIT schemes were becoming unaffordable, Germany, Spain and Italy have massively scaled back the levels of support for PV.  Rates of PV installations have fallen as a result.

At the same time, the Chinese government has identified PV as a strategic market, and offers cheap loans and incentives to Chinese companies to invest in PV manufacturing.  Business plans based on projections of continued growth supported investment in capacity.  We have seen factories in China that are fully equipped, with staff practicing assembling modules as they await orders.

Overcapacity has resulted, and inevitably a race to the bottom on prices.  It is reckoned that the cost of PV modules has fallen by about 33% in the last 12 months.

To be absolutely clear, this price reduction is all about in a global market where the UK demand is still an irrelevance.  It is not to do with technological breakthroughs, or economies of scale.  It's simple supply and demand.

Where does this leave the UK PV industry, as DECC ponders how to change the "unaffordable" scheme it has in place?

Any business person will tell you that rapid growth is difficult to manage well.  It is normal for businesses to accept losses during a scale-up phase as they invest in capacity - training and equiping new staff, investing in developing new processes and systems.  They do this in the expectation of future profits.  As the early growth rates slow, and more stable conditions emerge the early investments are recouped.

What is absolutely unhelpful is stop-start government support that creates massive demand up to an artificial deadline, followed by a collapse.  How can you expect sustainable long-term businesses to develop under such conditions?  Expect announcements of redundancies and business closures if the FIT is reduced.  Consumers will be left high and dry if they have subsequent problems, but the installation company is no longer around.

The madcap race to install systems before April 2012, when the next review of tariff levels comes into force is likely to lead to installation issues that could harm the image of the industry for years to come.  Systems are being crammed onto roofs to maximise financial yield, and with no consideration for other issues, such as the resulting aesthetic of the roof and its visual impact in our villages and towns.

So, where to go from here?  DECC needs to try to find a way to deflate this bubble gently, perhaps with a steady programmed reduction in the value of the tariff, rather than a single large drop.  The solar industry needs to lobby for a realistic tariff scheme that would support sustainable business growth rather than the simplistic strategy of fighting for the highest level it can get.