Bathing in Sunshine - Solar Heating for Swimming Pools

If there’s a better application for solar heating, it’s hard to think of it

Among the running costs for swimming pools, energy ranks pretty high.  For an indoor municipal swimming pool, water heating makes up around 25% of the energy use, for an outdoor pool without space heating or lighting requirements, water heating rises to 65% of the total (see reference here).  So it will come as no surprise that more and more pool owners and facility managers are considering investing in solar water heating as a way of reducing their environmental impact and cutting energy bills at the same time.

How do you Heat a Swimming Pool with Solar Panels?

The integration of a solar heating system with a swimming pool is relatively straightforward.

 
The simplest and lowest-cost form of solar heating for a swimming pool is to divert the pool water filtration circuit through a series of black plastic or rubber pipes which are placed in direct sunlight.  Unglazed solar panels like these will raise the temperature of a swimming pool, but only in good weather.

A more sophisticated solar heating system would use glazed solar panels such as flat plate or evacuated tube solar panels and will add heat to the swimming pool on more cloudy days or on days that are sunny but cold. For an outdoor pool, this can mean a much extended swimming season. For an indoor pool, this means making a contribution to lowering running costs all year round.



How a solar swimming pool heating system works
Click for larger version
Copyright Viridian Solar

A more sophisticated solar heating system would use glazed solar panels such as flat plate or evacuated tube solar panels and will add heat to the swimming pool on more cloudy days or on days that are sunny but cold.  For an outdoor pool, this can mean a much extended swimming season.  For an indoor pool, this means making a contribution to lowering running costs all year round. 

Since these types of panel are used all year round, they often have a solution of antifreeze running in them rather than the pool water.  In sub-zero temperatures this prevents freezing water from damaging pipes and solar panels.  A heat exchanger is added to the pool filtration/heating circuit, so that as the pool water circulates through the filtration circuit it picks up heat from the solar circuit.  (See the diagram above).

As an added bonus, glazed solar panel systems can be configured to produce water at temperatures suitable for domestic hot water.  In a municipal pool the solar system can then provide heat for pre-swim and post-swim showers.  In a domestic swimming pool, the solar system can also provide hot water for use in the house.  In this case, the solar circuit has a motorised valve which can divert the solar heat to a heat exchanger coil in a hot water cylinder.  (See the shaded part of the diagram).

The solar controller decides whether the temperature rise in the solar panels is high enough to produce the hotter temperatures required for showers and will divert the heat to the cylinder as a priority.  Once the cylinder is completely hot, or if the light levels are so low that only lower temperature output from the solar panels is possible, the controller switches the motorised valve to circulate the solar fluid to the pool heat exchanger.

So Why is a Swimming Pool Such a Good Application for Solar Heating?

The efficiency with which a solar panel works is strongly influenced by the temperature that it is being asked to work at.  If the temperature is above that of its surroundings , then some of the energy collected from the light is lost from the panel by conduction, convection and radiation.  The greater the temperature difference, the greater the losses, the less heat that ends up being transferred into the pool or hot water store and the lower the efficiency with which the solar panel works.

A solar heating system heating a cylinder for domestic hot water might start the day at 10°C, and operating at an efficiency of more than 80%, but finish the day operating at 70°C and an efficiency of less than 30%.

By contrast, swimming pool water is usually in the range of 25-27°C for fitness swimming up to 29-31°C for children’s swimming.  These much lower temperatures mean that the solar panel is operating at towards the highest efficiency levels all day long, so the annual energy yield of each solar panel is much greater for a swimming pool application than for domestic water heating.

Solar energy is also a variable source of energy, where the available energy on one day could be ten times more than the next.  When using solar energy to heat domestic hot water, the volume of water available to be heated in the hot water cylinder will often limit the amount of energy that can be collected.  Once the cylinder is all hot, the solar system has to switch off – there’s nowhere to put the sunlight for the rest of the day.

By contrast, a swimming pool is a very large body of water.  It takes large quantities of energy to change the temperature by only a fraction of a degree.  This large volume can absorb heat from the very sunny days and hold it over for days with lower solar energy.  The Pool Water Treatment Advisory Group advises that swimming pools can operate very satisfactorily at temperatures 1-2 degrees lower than their advised maximum.  It is therefore possible to allow the pool temperature to fluctuate within a small range to make the most of the sunny days when they come.

Chart showing solar energy addition to an indoor
swimming pool with year-round usage

Finally, solar energy availability is seasonal.  Indoor pools that are used all year have a fairly constant demand for heating energy, so the solar system can be economically sized to meet heating demand in summer, requiring back-up heating in other seasons.

Chart showing solar energy addition to an outdoor
swimming pool with May to October useage

An outdoor pool is likely to have a use profile that almost perfectly matches the availability of solar energy – with the most hours spent without a cover being during the best weather.  The solar can even contribute towards reducing the heat-up spike at the start of the season if the pool can be heated for a few weeks before opening.

Practical Considerations for Solar-Heated  Swimming Pools

When considering whether your pool is suitable for solar water heating the following issues should be considered:

 

 

·         Available Area.  The area of solar panels required can be chosen to emphasise energy saving or most rapid payback of the cost, and will depend on factors such as insulation levels of the pool, hours spent uncovered and will differ for indoor or outdoor pools.  Your solar specialist should be able to predict energy savings with specialised software.  As a rule of thumb to check whether you have enought room for solar panels, the solar panel area being equal to between a quarter and a half of the surface area of the pool is a good starting point.

·         Over-shading.  Avoid locations where the solar panels would be shaded by other buildings or trees for large parts of the day during the seasons where the pool is in use, as this can seriously diminish the performance.  Bear in mind that trees and hedges can grow.

·         Orientation.  Solar panels do not have to face directly south to work well, anywhere between east and west on the south side is good.

·         Plant room space.  For heating the pool, very little additional space is required.  For a system that is also heating water for showers, a solar hot water cylinder will be required.

Eight Point Nine More Good Reasons to Go Solar

Since September 2011, a government scheme, the Renewable Heat Incentive is rewarding owners of solar heating installations with cash back for every unit of energy the solar system generates (currently 8.9 pence per kWh for 20 years).  The scheme is currently suitable for indoor pools only and non-domestic situations (that is, not for those attached to single houses).

From summer 2013, the scheme will be extended to domestic houses, and systems installed before then can still qualify for the payments once the scheme starts.

More information on this incentive scheme can be found here.

Solar Heating and Solar PV – Which is the Best?

There’s only one way to find out.....ask the solarblogger!

Solar Heating Panels (left) and Solar PV Panels (right), but which do I like more...?

(Images, Viridian Solar)

Two Technologies Separated by a Common Language

In solar heating systems, solar panels (sometimes called solar collectors) absorb light and use its energy to heat up a fluid flowing through the panel.  The fluid circulates around a loop of pipe-work and drops off the heat by warming a hot water store (cylinder) for later use.  (A more detailed description can be found here).

By contrast, solar electric (often called photovoltaic, or PV) systems convert light directly into an electric current.  Power electronics equipment (called an inverter) conditions the electricity so that it matches that used in the building.  If the building is not using sufficient electricity at that moment in time, electricity flows out into the power grid and is used somewhere else.  (For more details click here).

Both technologies work well, even under the sometimes cloudy skies of the UK.

OK, so which Solar Technology is better for me?

Roof Area Required

For a typical family home, an area of three or four square metres of panel area is needed for a solar water heating system.  By contrast, the average solar PV installation for a domestic property is 2.8kWp (source STA), requiring around 20 square metres of panel area.

Carbon Emissions Avoided

Solar heating systems are most commonly generating energy to replace the use of a gas heating system, whereas solar PV systems offset the use of grid electricity.  Taking the gas boiler efficiency into account, generating clean electricity saves twice the amount of carbon dioxide emissions per unit generated than does heating water to prevent a gas boiler firing.

As the carbon intensity of grid electricity is brought down by wind turbines, PV farms and nuclear power stations, the difference between the two technologies will reduce.

Of course, in an electrically heated home a unit of solar heat has the same carbon value as a unit of solar electricity.

Orientation

Both technologies will give good results when facing generally towards the South and anywhere between East and West.  Domestic scale solar heating systems are normally less sensitive to orientation than PV.

Shading

Obviously, since both systems require light to generate energy, over-shading is a Bad Thing.  However, solar PV systems are more sensitive to shade than solar heating systems.

A patch of shade over a small part of one PV panel can have a multiplier effect - significantly reducing the output of the whole panel, and other panels in the wiring group.  Designing the layout, positioning and wiring scheme for a PV system to avoid shading effects can be a very important part of ensuring a good annual energy output.

Solar heating systems do not suffer from this multiplier effect, so are much less sensitive to shading.

Integration with Building Services

A solar PV system is pretty much stand-alone.  The only integration with the systems in the building is to be connected to the wiring at the main consumer unit (fuse board).

A solar heating system requires a hot water cylinder to store the heat during the day for later use, so space needs to be found for this if there is not already a cylinder cupboard.  Connections need to be made to the existing heating system.  Solar heating raises more integration considerations than solar PV.

Servicing and Maintenance

Both types of solar system require minimal maintenance.  Unless installed in an unusual location, solar panels are adequately cleaned by the action of rain.

The inverter in a solar PV system generally has a lifetime less than that of the solar panels, and may need to be changed every 10-12 years, at a cost of £500 - £1800 for the inverter, depending on the size of the system.

Solar heating systems need only routine inspection to check for problems.  However most use a heat transfer fluid with a limited lifetime.  This may need to be replaced every 5 years or so at a cost of around £50 for the fluid.  The circulating pump will also have a lifetime of around 10 years.

Energy Savings

Studies have shown that a solar heating system for a family home will produce between 900 and 1,500 kWh of heat energy each year.  Taking into account the boiler efficiency, this might give fuel savings of between 1,300 and 2,100kWh per year.  The savings are limited by the hot water use in the building.

With gas at 5p/kWh, savings from household energy bills would be in the range of £65 - £105 per year,  or £90 - £150/year (electrical heating, assuming a mix of daytime and overnight electricity tariffs).

A well-located and un-shaded solar PV system will produce around 850kWh per year per kWp under UK weather conditions, so our average domestic system of 2.8kWp will produce 2,380kWh per year.

However, unlike solar heating which stores the energy for later use, most grid-connected PV systems export any excess generation to the power grid.  This means that the generation is not limited by the demand of the building, but the energy saved in the building depends greatly on the electricity usage patterns.  If the occupants are at home and using electricity during the daytime (and especially during summer), then a large proportion of the energy generated will displace electricity bought at 15p/kWh.  If not, then the energy saving accruing to the householder might be a small proportion of that generated.

Households with PV systems can make changes to make the most of solar electricity generation, for example using timers to cause washing machines or dishwashers to come on during the middle of the day.

Yes, Yes, but which type of Solar Panel is the best?

Inevitably, it depends:

If your household uses lots of hot water, but does not use much electricity during daylight hours, then solar heating may make the greater savings on energy bills. If, however, you have high electricity use during the daytime and low hot water use then solar PV would definitely be the better choice.

If your goal is to reduce carbon emissions, you don’t care where the energy is saved, and you’re on the gas grid, then PV is likely to be the better choice.  The energy generated by PV has higher carbon intensity and solar heating output is limited by the household demand for hot water.

If you have a large, clear roof area available then this is suitable for PV.  If the roof has a smaller area available or you want a more discreet-looking installation then solar heating may be the better choice due to the smaller panel area.

Of course, if you still can’t make up your mind, there are systems available that include both solar technologies together with matched solar panels.

A Word about Government Incentives

In an effort to cut through to the fundamentals, this discussion has deliberately steered clear of government incentive schemes for renewable energy such as the Feed in Tariff and forthcoming Renewable Heat Incentive. 

Such schemes obviously greatly influence the relative attractiveness of renewable technologies and are likely to be just as influential in decision making as the factors discussed above.  Up-to date information on these two incentive schemes can be found here.

Who Pays for Greener Homes?

Why does the cost of building a new home matter to house builders?

This may seem like a stupid question, but I’m not talking about the cost of a pallet of bricks, ton of cement or roll of glass wool.  I’m talking about additional costs from meeting tighter environmental regulations. 

Specifically, why do developers of new homes care about the higher building costs from building to ever higher standards of energy efficiency?  Still seem like a stupid question?  Let me explain further.

Let us first accept the argument that “people won’t pay for this stuff”, that a more energy efficient home will command the same price as a less energy efficient home (an accepted wisdom that some in the construction industry are now starting to question). 

Let’s also assume that house builders are price-takers.  The price of a house is largely set by the “second-hand” market because buyers always have the choice to buy an existing rather than a new home.  So if building costs go up and prices stay the same the house builder’s profits are squeezed, right?

Well, not necessarily.  If changes to regulations are published well in advance of coming into force, and if regulations are applied consistently to all developers, then the price that any developer is prepared to pay for land should fall to preserve their profit margin.  Since all buyers of land build to the same regulations, they are all affected equally.  All the “pain” of the new regulations will fall onto the landowner selling to the developer. 

The value of an acre of agricultural land is around £5,000 per acre.  The same land with planning permission to build houses would sell for millions of pounds per acre.  The windfall that accrues to landowners when planning permission is granted is so massive that a squeeze on their margins is of little consequence to their decision to sell and certainly would not win them any sympathy from anyone else.

So can anyone answer the question – why do house builders care about costs?

Please use the comments section below.


You may also be interested in the following posts:

A Million Missing Low Energy Homes
Zero Carbon Homes – Carefully Check the Small Print

Less is (worth) More – Why House Builders should be Selling Sustainability

“Housebuilders could make more money if only they properly sold the lower running costs of new homes to their customers.”

So says a recent report from the influential NHBC Trust, Today’s attitudes to low and zero carbon homes, which shows how house-builders are losing out because they lag behind their customers in their views on energy efficiency and renewable energy.

It’s an impressively thorough piece of research, based on a large number of interviews with the general public and group sessions with occupants of new and low-energy homes.  The report is full of information on current attitudes and views towards energy efficiency, renewables and buying homes.  Knowing that all readers of the solarblogger are important and busy people, who might struggle to find the time to digest the whole 130 pages, here are some key points from the report.

Energy Matters

People are becoming more and more aware of energy costs and their impact on the environment.  Fully 96% of people surveyed said that their energy costs were important to them, 65% saying they were very important.

Surveying people who had moved into new homes, an overall majority said that the energy efficiency features made the home more attractive.  Those living in homes that had been built to a higher level of energy efficiency placed even greater emphasis on this.

People will pay

The house-building industry has been so concerned about the additional costs of building to higher levels of energy performance, it is missing out on an opportunity.  The survey indicates very strongly that energy efficiency does influence people's buying decisions.  Rather than seeing energy efficiency measures as a costly inconvenience, house builders could turn this on its head and promote the benefits to prospective customers.

Energy efficiency was the equal sixth most important factor in choosing a home to buy or rent.  Although location, number of bedrooms and other traditional factors achieved higher scores, energy efficiency still achieved a score of 3.7,  with 1 being not at all important and 5 being very important.

One of the most surprising outcomes from the study is illustrated in the chart below.  When asked the question "If the price of an energy-efficient home were £10,000 more than another similar home that was not so energy-efficient, but it offered to save you £750 a year on your energy bills compared to the other home, would you consider paying this?", 69% of people said yes.

The chart also shows the breakdown by age group, with younger (first time) buyers being more likely to be attracted to an energy efficient home.  However, in all age groups the majority would consider paying more for a home that saved them on energy bills.

It is possible that the forthcoming Green Deal will make the value of energy efficiency even more evident to people.  The cost of insulating a solid wall property to achieve performance approaching that of a new home is around £12,000.

People Place More Value on Familiar Technologies

Solar panels (both solar heating and solar electric) and low-energy lighting are the energy saving features with the highest awareness among buyers - 84%.  Awareness falls quickly for other energy generating technologies such as heat pumps - 31% and mechanical ventilation with heat recovery (MVHR) - 17%.

High awareness feeds through into desirability (with the exception of wind turbines).  The chart below shows which eco-features are the most likely to make a new home attractive to a potential purchaser.

Tips for Marketeers

1. Avoid confusing terminology 

People overwhelmingly preferred the term Energy-efficient home to Eco-home, Zero-Carbon home or Green home. Green or Eco was thought to convey the impression of alternative, ultra-modern home with non-traditional materials. Zero carbon causes doubts whether anything can be truly zero-carbon.

Confusing or Negative Associations	More Positively Received
Eco-home Zero-carbon home Green home	Energy efficient home
Air-tight	Draught-free and warm
Grey water recycling	Waste water re-use for toilet flushing
Biomass boiler	Wood chip/pellet burning boiler
Mechanical Ventilation and Heat Recovery	System for introducing fresh air from outside while retaining the heat from expelled air
Solar Thermal	Solar heating
Photovoltaics	Solar electric

2. Emphasise the energy savings

The survey found that people were motivated towards energy efficiency mainly for the positive impact it has on their household finance.  Protecting scarce resouces came second and helping combat climate change came a distant third.

Marketing should emphasise the financial benefits of living in a new home relative to other choices, with simple comparisons that make the savings clear.

The survey showed that people are confused about the sources of CO2 emissions, with many not rating energy use in homes in the top three sources.  Industry, cars, planes and even livestock were often selected ahead of homes. If people were aware that housing accounts for 30% of energy use and more energy is used in housing than in industry, road transport or aviation, this might influence their buying decisions.


3. Choose visible technologies 

A home with visible technolgies such as solar panels gives the sales team a hook on which to hang the many other features (such as higher levels of insulation and draught-proofing) which are not so evident to a buyer viewing a property. 

4. Choose technologies to meet targets that buyers find attractive

Some technologies clearly are more attractive to buyers more than others.  The cheapest option for achieving compliance with building regulations may not be the most attractive to prospective buyers.  Homes with more attractive packages of energy efficiency technology may sell more quickly or achieve higher prices than those that are simply cost-optmised to meet regulations.

5. Consider offering enhanced efficiency as a cost option

When selling off plan it is common to offer better kitchens, or bathrooms or other features at an extra cost.  Why not give the customer the option to increase the energy efficiency of their home beyond regulations to lower their bills further?  For example, meeting regulations with a solar heating system, but offering the option to add a solar electric system alongside.

 

"People won't pay for all this stuff"

House builders often claim that their experience is that people won't pay more for homes with "eco-features".  They might say they will (perhaps to market researchers compiling reports), but when it comes time to sign the cheque they won't spend the money.

But have they really tried to sell efficiency?  Are the sales people knowlegeable about the features and benefits?  Does the marketing material explain the features in simple terms and the benefits in a meaningful way?  Has the package of energy efficiency technology been chosen to appeal to buyers?

Please add your thoughts and comments below.

They Work for you, Don't They?

What's going on in there?

Sometimes it it feels like the UK solar industry believes that the reason for the existence of the Department of Energy and Climate Change (DECC) is to help solar businesses thrive.  This attitude seems to lead to an industry view that it's only incompetence that drives DECC to  fiddle around with the Feed in Tariff and leaves it unable to get on with implementing a domestic Renewable Heat Incentive.

The bad news for the solar industry is this: DECC doesn't work for you.

Solar industry commentators seeking to  offer their advice to our public servants might do well to take a walk in the shoes of the people on the other side of the table.  What are their goals and motivations?  Perhaps if we take a moment to understand, we would be able to present our aspirations in a way that is more persuasive.

Euro-Vision

The top-level drivers for renewable energy in the UK come from legally binding directives from the European Union (EU).  In response to the Kyoto Protocol, the EU set the so-called 20-20-20 targets.

By 2020 the EU as a whole will:

·         Reduce greenhouse gas emissions by 20% compared to 1990 levels  (UK 16%)

·         Provide at least 20% of energy consumption from renewable energy sources (UK 15%)

·         Reduce primary energy use by 20% through energy efficiency measures

Each national government has been set its own targets such that the EU as a whole meets its overall target.  The UK target where it exists is given in brackets.

Clearly these targets overlap.  For example reducing total energy use will increase the proportion of renewable energy even if this stays at the same absolute level. 

The energy efficiency target has produced a number of directives from the EU on the energy efficiency of products, cogeneration, and the energy performance of buildings.  This last directive requires that all new buildings in the EU should be “Nearly Zero Energy” by the end of 2020.

UK Policy

UK policy must take into account the legally binding obligations that arise from these EU directives. 

In 2008 the UK government introduced the Climate Change Act, the world’s first legally binding targets to reduce carbon emissions (reducing by 80% from 1990 levels by 2050 and 34% by 2020).  The 2020 target is more challenging than the EU requirement, but is only a recommendation from the Committee on Climate Change.  The 2050 level is legally binding, although it’s not really clear who gets punished if the target is missed.

In its first report to the European Commission on progress towards the 2020 Renewable Energy Target, DECC lists 45 measures that have been implemented with the goal of achieving the UK target of 15% of energy from renewables.  Among these are:

·         Renewables obligation – payments to large scale renewable electricity generators (e.g. wind farms)

·         Feed in Tariffs – financial incentives for smaller-scale renewable electricity

·         Renewable Heat Incentive – financial incentives for renewable heat generators

·         Building Regulations –new homes to be zero carbon from 2016, non domestic from 2019

·         Electricity Market Reform – Contracts for Difference to pay investors in low-carbon electricity

·         Planning Policy – to encourage renewable energy projects to go ahead

·         Renewable Transport Fuel Obligation – requirement to include biofuel in petrol and diesel

Know Your Place

Clearly solar energy is only a part of the solution to the massive challenge of meeting these targets, but how big a part?

DECC has given a clue to its thinking with its Renewable Energy Roadmap, published in July 2011.  It estimates that 234 TWh per year of renewable energy will be required to hit the 15% target, and proposes the following breakdown as one scenario to meet this:

	Technology	Mid-range estimate
1	Onshore wind	28 TWh
2	Offshore wind	46 TWh
3	Marine energy	1 TWh
4	Biomass electricity	41 TWh
5	Biomass heat	43 TWh
6	Heat pumps (non domestic)	19 TWh
7	Transport	48 TWh
8	Other (domestic, solar)	14 TWh
	Total	240 TWh
	Target	234 TWh

Disappointingly, but perhaps not unexpectedly it can be seen that the government is taking a big-industry, top-down approach to the problem.  Only 6% of the total is expected to come from domestic installations of heat pumps, solar heating and solar pv. 

However, to put this in context, 14 TWh per year from the domestic stream would be met by either:

·         9 million domestic installations of solar water heating

·         6million domestic solar pv installations of 2.8kWp (17 GWp total)

 Even at this level, the challenge is significant and is likely to require attractive and sustained government incentives to support deployment.   DECC’s focus on unpopular technologies that could get bogged down in local planning appeals means that solar pv and solar thermal may have an even bigger role to play in meeting the challenge and underlines the case for urgent progress with the domestic Renewable Heat Incentive.

Reading List

EU 

406/2009/EC:Effort Sharing Decision (20% CO2 reduction by 2020)

2009/28/EC : Directive on the promotion of the use of energy from renewable sources (20% by 2020)

Proposed: Energy End Use Efficiency Directive (20% reductionby 2020)

2010/31/EU Directive on the energy performance of buildings

UK

Climate Change Act 2008

FirstProgress Report to the European Commission on increasing use of renewable energy UK

UK Renewable Energy Roadmap