The Domestic RHI and Solar Thermal Stores

The Law of Unintended Consequences Strikes Again

The domestic RHI was structured with the intent that the complementary combination of solar thermal with other heating technologies would be actively encouraged by receiving double subsidy for the domestic hot water energy.  Unfortunately, the wording of the legislation has prevented installers using the simplest way to implement a combined system (the thermal store) because it rules out solar systems that can make even a theoretical contribution to space heating.

Thermal Stores in Hot Water

Solar thermal systems can make a contribution to space heating as well as domestic hot water (DHW) preparation, especially in spring and autumn where the days are still bright and there is a demand for space heating.  These systems are not yet as common in the UK as those for domestic hot water, but in more developed European markets such as Germany and Austria, so-called "solar combi systems" are popular.

In a thermal store the domestic hot water is heated in a heat exchanger
and the contents of the store pumped around the space heating circuit

A good way to combine solar thermal with space heating is to use a thermal store, essentially a large (typically 500 litre minimum to 1,000 litre) hot water cylinder with heat inputs from both solar and the backup heating system and with outputs to domestic hot water and space heating.  Typically the body of water in the thermal store is heating system fluid (primary water) and domestic hot water is heated on-demand in a heat exchanger as it flows to the hot tap.

Both heat pumps and biomass heaters operate well when running continuously rather than cycling on and off, so charging a thermal store is a good technical solution that improves the overall efficiency of the heat pump or biomass boiler.

Where the designer is seeking for the solar to make a reasonable contribution to the space heating, the solar panel array installed is large (around 12-18 m² for a domestic property).   The coverage of domestic hot water of such systems can be very high, 70% and above.

Where the designer is aiming for solar to mainly cover domestic hot water the panel array is smaller (typically in the range of 3  - 6 m²).  In this case there is still a theoretical possibility that the solar energy will contribute to the space heating, though in practice the system is sized with the aim of supplying 60-70% of water heating.

The current domestic RHI legislation completely excludes systems that can contribute towards space heating.  

The text in the RHI regulations defines an eligible solar system as follows:

a)     is designed and installed to provide heating solely to a single eligible property and solely for an eligible purpose using liquid as a medium for delivering that heat;

(b) meets the requirements set out in whichever of the standards for solar thermal plants specified in paragraph 1(5)(a) and (b)“eligible purpose” means, in relation to heat generated by— […](b) a solar thermal plant, the purpose of domestic hot water heating for an eligible property;

An implementation of solar where there is even a theoretical possibility of the solar contributing towards space heating is completely excluded from the scheme.

The reasoning behind ruling out solar space heating was that the domestic RHI is “deemed” – the solar energy is not measured, instead it is estimated using an approved calculation and the calculation only works for domestic hot water.

However, by ruling out any solar installation that does not solely heat domestic hot water, the domestic RHI has made the combination of complementary renewable heating technologies such as solar and heat pumps less likely. Solar thermal has lower associated carbon emissions than any form of back up heater, so every unit of solar thermal heat that can be used, whether for space heating or domestic hot water reduces carbon emissions.

Configurations where the solar is offsetting a proportion of fossil fuel space heating are also disincentivised by their complete exclusion from the domestic RHI.

When installing biomass or heat pumps with a thermal store, the additional cost to add a solar coil into the store is very low, making the marginal cost of adding solar thermal more attractive.  The domestic RHI would provide greater value for money if it encouraged, rather than discouraged such systems.

So how could the domestic RHI be changed to include solar space heating?

Two Suggestions

Two options occur, though I’d be pleased to hear of any other suggestions (please use the comments section).

First, it would clearly be possible to use a heat meter to measure the solar input into the thermal store.  Solar space heating systems cost more than solar systems aimed only at domestic hot water.  A requirement to fit a heat meter would be a relatively smaller proportion of the total installed cost and energy benefits, and houses that can fit large thermal stores are relatively thin on the ground, so it wouldn’t be too much of a cost for the scheme administrators to deal with the meter readings.

A second approach would be to allow space heating systems onto the scheme but to give RHI payments only for the domestic hot water energy provided, and calculate this with the current deeming method.  I’ve looked at this with the help of two years'  of data from a solar space heating system provided by Geoff Miller of GreenLincs Energy.  Simulations have also confirmed that the solar energy generated by a system providing solar space heating and domestic hot water is always higher than the same sized system targeted at only domestic hot water.  The RHI wouldn't be over-paying for solar heat.

The best outcome would be for it to be the choice of the homeowner whether or not to go to the expense and hassle of having a heat meter.  If they wanted the extra payments for space heating, then they would need to install a heat meter, otherwise they could claim for only the solar heat in their domestic hot water.

This has formed the basis of a proposal submitted to the Department of Energy and Climate Change (DECC) yesterday outlining how the scheme could be improved by allowing solar space heating.

Solar Joins the Big Guns

Notable by its absence from the Department of Energy and Climate Change’s (DECC’s)  2011 Renewable Energy Roadmap, has solar energy fared any better in the 2012 update?  The solarblogger investigates.

On December 27^th DECC released an update on the UK’s progress towards meeting binding targets from the EU to generate 15% of all energy from renewable resources by 2020.  They also shared current thinking on how this target might be met.

Plenty left to do

Progress to Date

In 2011, renewable energy rose to 3.8% of all energy consumption from 3.2% in the previous year.  The lion’s share of this increase came from renewable electricity.  Its share of all generation rose 27% to 38 TWh, and now represents 10.4% of all UK electricity generation.

HELPFUL NOTE

TWh = Terawatt-hours, equivalent to one thousand GWh (gigawatt-hours) or one billion kilowatt-hours – see “Slippery when Watt”

The average house uses around 4,200 kilowatt-hours per year – see “How much electricitydoes the average house use?”

Wind turbines contribute 17 TWh, nearly half of the renewable electricity generation, with a further 14 TWh generated from burning biomass, and the remainder from hydro-electricity.  PV solar generation currently produces a just-visible slice in the bar chart.

Renewable heat on the other hand trails behind, at 14 TWh of energy, an increase of only 5%.  Although heat accounts for 46% of the UK final energy use, it is only recently that government support mechanisms that reflect its importance have been brought forward.

The Renewable Heat Incentive (RHI) for commercial buildings has been in place for just over a year with mixed results, and will be followed by an RHI for domestic buildings in the late summer of 2013.

Outlook

Electricity

DECC reckons to have reasonable visibility of the future deployment pipelines for wind and biomass electricity generation. 

There’s just under 5GW of biomass generation plant under construction or in planning, to make a total of 8GW of generation capacity.  Assuming a similar load factor to the current capacity, this would deliver around 33TWh/year.

If all the wind capacity identified in DECCs pipeline is developed, that would total 26GW, and produce annual generation of about 68TWh assuming a 30% capacity factor.

Just these two technologies, plus the existing hydroelectric capacity could then contribute 108TWh/year, or around 30% of current electricity demand.

This may sound a like a real achievement – and it is, but when you consider that electricity for lighting and appliances accounts for only 8% of final energy use of the UK you can appreciate the scale of the challenge we face.  The goals for the other two major energy uses – heating (46% of final energy) and transport (41% of final energy) need to be similarly ambitious, and this is where the roadmap starts to feel rather thin.

While 28 pages are devoted to renewable electricity, only 7 are spent on heat and 4 on transport.

Renewable Heat

The Renewable Heat Incentive (RHI) is the main mechanism for pushing forward the adoption of low carbon heating technologies. 

A quick look at the Ofgem RHI website shows that in its first 13 months of operation, the scheme has so far paid out on 0.066 TWh of renewable heat generation, a rather pitiful contribution compared to the electrical technologies, but hopefully one that can grow rapidly as awareness of the scheme increases and consistent support is sustained over a significant period of time.

98% of heat under the RHI is currently from biomass boilers.  The scheme has so far been spectacularly unsuccessful at stimulating take up of either solar heating or heat pumps.  See my blog article on the success of the RHI to date here.

The solar industry has greater expectations for a domestic renewable heat incentive, which after many delays, is expected to launch in Summer 2013, see my blog article on the consultation here.

Transport

The transport section of the report is the thinnest, with little in the way of concrete action to discuss.  This reflects the global nature of the challenges to develop new automotive technologies, and the need for technological breakthroughs, particularly in energy storage which are acknowledged in the report.

So What for Solar?

The document was, on the whole, pretty good news for solar energy in the UK.

The potential of Solar PV to make a significant contribution to the UK energy mix is recognized for the first time, with an estimated 2020 deployment of between 7 and 20GW, contributing between 6 and 8 TWh per year.  DECC believes that grid-balancing challenges and the evolution of PV costs over the next few years will determine the level.

DECC also revealed their intention to develop a PV Strategy document during 2013.

For solar thermal technology, the best news was that DECC re-iterated their determination to launch a domestic RHI in summer 2013, listing it as a key priority.

Just What's Wrong with the Commercial RHI?

Just over one year in, how’s the commercial Renewable Heat Incentive doing?

In November 2011, the Department of Energy and Climate Change (DECC) scored a world’s first, launching a kind of Feed in Tariff for heat.  Called the Renewable Heat Incentive (RHI), the scheme pays out for each kilowatt hour (kWh) of useful heat generated by a range of low carbon heating technologies including solar thermal, heat pumps and biomass boilers.

In its first phase, the scheme is open only to non-domestic installations, with a scheme for householders to follow in summer 2013.

(For more on the domestic RHI, read my earlier article: “The Domestic Renewable Heat Incentive for Solar”)

How’s it doing?

So, are civil servants from other countries going to be beating a path to the UK to learn how its done?  On the basis of the performance to date, we don't need to worry about putting more border agency staff on at Heathrow.

OFGEM are administering the scheme, and you can get hold of performance data here.

And the winner is...

The chart shows the number of installations of the three most popular technologies, although it can be seen that the scheme is having mixed success.

The scheme has supported 679 installations of biomass boilers, but only 36 ground source heat pumps and 33 solar thermal systems since it began over 12 months ago.

In terms of eligible heat generated, the skew towards biomass is even more marked with 65.5 GWh of biomass heat generated, compared to a total of 0.9GWh from all other technologies.

To put this in context, the Feed in Tariff stimulated 30,000 installations in its first year.  According to DECC's heat strategy, electricity for lighting and appliances is only 8% of final energy use whereas heating is 46%.  

So the problem isn’t so much runaway take up of biomass as the unpopularity of the scheme as a whole.

How to Fix It

Beyond the obvious first response of making the tariffs higher, is there anything else that OFGEM and DECC could do to improve the success of the scheme?

Here are some suggestions.

• Increase Awareness  - develop case studies with businesses that have benefitted from the scheme and work with the trade associations to disseminate the case studies to other potential customers.
•  Streamline the application process – one of the most common problems with applications has apparently been the quality of the schematic drawings showing the location of heat meters.  OFGEM could develop standard schematic layouts, which applicants could select from, rather than commissioning their own drawings. 

Do you have any comments on the scheme or how it could be improved for solar thermal and heat pumps?  Perhaps you have direct experience of making an application?  Please make a comment below.