This paper evaluates the application of solar thermal systems for hot water heating in typical British commercial buildings. It examines key variables including solar irradiance, collector tilt angle, and ambient temperature to estimate energy performance, then applies the Solar Energy Factor and Solar Savings calculations to compare solar and conventional heating systems. A financial analysis incorporates UK Renewable Heat Incentive (RHI) tariffs, Feed-in Tariff rates, and retail energy price projections to assess economic feasibility and payback periods. The paper also quantifies achievable CO2 emission reductions, finding that solar thermal systems can deliver meaningful carbon savings and become financially attractive — particularly when supported by government incentive schemes — while noting that realized benefits depend heavily on building type, system design, and site location.
One central issue facing policymakers and electric utilities around the world is the need to identify how to satisfy the rapidly increasing global demand for electricity without increasing greenhouse gas emissions in the process (Holton, 2005). The need is clearly great, but time is also of the essence. Projections of a tripling of electricity demand by mid-century are common, and electricity generation is already responsible for an estimated one-third of all greenhouse gas emissions (Holton, 2005). In this setting, identifying viable alternative energy resources represents a timely and valuable enterprise.
One promising alternative for electricity production is solar power, but following the end of World War I, the world made the switch from coal to petroleum rather than to solar. In the historical analysis, petroleum was found to be more efficient and dependable, especially for the war effort, with Britain making the change from coal to oil for its warships. Winston Churchill was instrumental early on in encouraging this transition:
"Oil is a much more flexible fuel than coal and holds within it a denser concentration of energy. Because it can flow, it is more easily transported. It is cleaner when burned. Much of the time, it was cheaper than coal. Three barrels of oil have the heating capacity of 1 ton of coal and at the prevailing prices early in the century, the oil usually cost only half as much as coal. Because of oil, the number of men tending the furnaces on a steamship could be reduced from 100 to four. Loading a ship with coal had taken 100 men toiling for a week; now one man in one day could load a ship with enough bunker fuel to cross an ocean." (p. 251)
By sharp contrast, solar energy has since taken root throughout the United Kingdom, but the technology has not been widely adopted to date (Miller, 2004, p. 19). Given recent incentive programs by the UK Government and the impetus provided by the European Union's target of producing 22% of its electricity, and 12% of all energy, through renewable sources by 2010, the time is right for many businesses to consider deploying solar thermal systems of their own. Although EU leadership acknowledges that its target goals will not likely be met, if more countries follow the lead established by the UK they may have a chance of succeeding. Absent additional support, the European Union's leadership believes that renewable energy will account for only 10% of total energy production (Miller, 2004).
Renewable energy currently accounts for 6% of energy supply, compared to 40% for oil, 23% for natural gas, 16% for nuclear power, and 15% for solid fuels (Lander, 2005). Although wind energy applications are being deployed in Germany and Denmark, these technologies have been less well received in France because the electric utility does not want to share its power grid with other energy companies (Lander, 2005). Likewise, Lander advises that, "In Britain, until recently, builders of windmills could not obtain permits from local authorities to erect turbines" (2005, p. 117).
Despite these constraints to progress, few companies can afford to ignore the environment any longer, with the UK Government setting ambitious targets for reducing carbon dioxide emissions by 20% by 2010 and 60% by 2050. To help companies achieve these objectives, in 2001 the government established the Carbon Trust, an independent organization that helps UK businesses and public sector organizations find ways to reduce their carbon footprint. It does so through a number of means — for one, by providing small and medium-sized enterprises (SMEs) with interest-free loans of up to £100,000 (£200,000 in Northern Ireland) to help them invest in energy-efficient equipment (Hawser, 2006). According to Bradford and Bean (2011), in 2010, the United Kingdom's solar water heating market for both small and large-scale installations grew by 18.1%, to 73,640 kWth of installed capacity. These authors assert that, "This is perhaps surprising given a 13.1 per cent decrease across the rest of Europe. An uncertain economic outlook, high fuel prices, and the proposed introduction of a Renewable Heat Incentive seem likely reasons for continued growth in the UK" (Bradford & Bean, 2011, p. 1).
Many Europeans are also growing concerned about the imminence of peak oil, which many experts project to be around mid-century, as well as recent signs that energy costs are threatening national security (Lander, 2005). According to Lander, "In 2000, a rise in the price of fuel was compounded by higher taxes, which ignited protests and blockades by truckers from Britain to Germany. At this point in time, the expectations among many observers and policymakers are that high prices will rekindle an appreciation for windmills, solar panels and other alternative energy sources in the United Kingdom" (2005, p. 2). Moreover, the UK lags behind other EU member states, with only 1.3% of its energy currently being generated from renewables compared with 8.5% across Europe (Bradford & Bean, 2011). In order to meet the EU-wide target of 20% by 2020, it is clear that renewable resources must be exploited to their maximum advantage. According to a recent report, solar water heating has the potential to deliver up to 6.3% of this EU-wide target, making it a potentially important technology for the future energy needs of the continent. The introduction of the Renewable Heat Premium Payment Scheme, Renewable Heat Incentive, the Feed-in Tariff, and the Scottish loan scheme are important steps in helping to bridge the gap (Bradford & Bean, 2011).
There remains a paucity of real-world performance data for solar thermal systems. To this end, this project evaluated the application of solar thermal systems in hot water heating in commercial buildings in the UK. At present, commercial enterprises account for about half of the UK's carbon emissions (Emery, 2008). Different solar thermal systems were investigated and compared with conventional hot water systems in terms of application, energy consumption, environmental impact, cost, and efficiency.
The aims of the project were as follows:
1. Compare solar thermal systems with conventional systems in terms of energy usage, financial analysis, environmental impact, and efficiency.
2. Determine the energy production and energy savings that can be achieved.
3. Determine the energy cost with renewables and the payback period of the system in order to evaluate the feasibility of the proposed system.
4. Consider the carbon dioxide emissions and environmental impact of the solar thermal system.
5. Determine the carbon dioxide emission reductions that can be achieved.
The project evaluates the application of solar thermal systems in hot water heating in commercial buildings in the UK. Different solar thermal systems were investigated and compared with conventional commercial hot water systems in terms of application, energy consumption, environmental impact, cost, and efficiency. The study is divided into six chapters. Chapter one describes the background of the project and discusses the aims and their importance. Chapter two provides a review of the relevant peer-reviewed literature, and chapter three presents the study's methodology, including the study approach, the data-gathering method, and the databases consulted. Chapter four comprises an analysis of the data developed during the research process, and chapter five presents a discussion of the findings. Finally, a summary of the research and its important findings are presented in the concluding chapter.
The methodology used for this study involved calculation of the annual performance of the solar thermal system and the study of solar heating economics. The long-term performance of the solar domestic hot water (SDHW) system was estimated using collector physical characteristics and relevant weather data as inputs. Cost and CO2 reduction analyses were performed using local data available from both commercial and professional bodies.
A majority of current thermal rating programs require equipment to be tested in accordance with a standard test under specified conditions. This approach provides reliable data because it is possible to replicate such tests within an accepted uncertainty band. There are, however, some rating programs that combine a standard test with a calculation procedure to produce a performance rating — such as the energy guide label for electric and gas hot water heaters. A similar method has been developed to provide a practical rating system with the goal of presenting an easily understood comparison between SDHW systems and conventional hot water systems. Note that the performance any individual commercial enterprise experiences may differ due to location and hot water usage.
The thermal performance rating is based on the system design and performance projections derived from testing of the collector components used in the system, or from testing and evaluation of the system as a whole. The type of auxiliary system (e.g., gas or electric) utilized will have a large impact on the overall performance of the system. These differences arise because different types of auxiliary systems have varying standby losses and fuel conversion efficiencies. Although the auxiliary system may affect the solar system's performance, in many cases the solar output is mostly independent of the auxiliary system used. Because gas backup systems have lower efficiencies and higher standby losses than electric systems, it should be expected that the entire system's performance (including backup) will be lower, even if the solar output from both system types is equal.
The Solar Energy Factor (SEF) was used in this study to calculate the performance rating for solar water heating systems. The SEF is calculated as the amount of energy delivered by the system divided by the electrical or gas energy put into the system. The resulting Solar Energy Factor is expressed as a number comparable to the Energy Factor (EF) assigned to conventional water heaters by the Gas Appliance Manufacturers Association (GAMA), with the exceptions noted in the Rating Parameters section taken into account.
The key variables in the calculation are as follows:
QDEL — Energy delivered to the hot water load. Using the specified rating conditions, this value is 43,302 kJ/day (41,045 Btu/day).
QAUX — Daily amount of energy used by the auxiliary water heater or backup element with a solar system operating (kJ/day). To convert to kWh, divide this value by 3,600 (3,412). To convert to therms, divide this value by 105,000 (100,000).
QPAR — Parasitic energy: daily amount of AC electrical energy used to power pumps, controllers, shutters, trackers, or any other item needed to operate the SDHW system (kJ/day). To convert to kWh, divide this value by 3,600 (3,412).
Source: OG-300 Certification of Solar Water Heating Systems (solar-rating.org)
The Solar Energy Factor can then be converted to an equivalent Solar Fraction (SF). For the standard electric auxiliary tank, the Energy Factor is 0.9; for gas tanks, the EF is 0.6. The Solar Fraction is the percentage of the total conventional hot water heating load (delivered energy and tank standby losses) provided by solar energy.
Note 1: An alternate definition of Solar Fraction is frequently used, in which solar fraction is the portion of the total water heating load (losses are not included) provided by solar energy. This alternate method will yield higher solar fractions. Researchers should use caution when comparing solar fractions for specific systems, inputs into energy codes, or outputs from f-chart applications, to ensure the same calculation procedure has been followed.
The Solar Energy Factor can also be converted to an equivalent Solar Savings (QSOLAR), where:
QCONV — Daily amount of energy used by the auxiliary water heater or backup element without a solar system. The standard electric auxiliary tank has an energy usage of 47,865 kJ/day (45,369 Btu/day). The standard gas auxiliary tank has an energy usage of 72,203 kJ/day (68,439 Btu/day).
EF — The Energy Factor is the ratio of delivered energy to input energy for the reference electric auxiliary tank without a solar contribution. The balance of the energy is lost to the surroundings due to standby losses and conversion efficiency.
QSOLAR — The Solar Savings is the amount of the total conventional water heating load (delivered energy and tank standby losses) provided by solar energy minus any parasitic energy use. To convert to kWh, divide this value by 3,600 (3,412).
Based on the foregoing, the Solar Savings calculation provides the amount of the total conventional hot water heating load (delivered energy and tank standby losses) provided by solar energy, less any associated parasitic energy use.
The following parameters are used for calculating daily energy savings and the Solar Energy Factor. These conditions are identical to those used in the US Department of Energy test for water heaters (Federal Register, vol. 55, no. 201, pp. 42161–42177, October 17, 1990) with the following exceptions:
Since the DOE test does not cover solar water heaters, it specifies no solar radiation. Therefore, a 4,733 Wh/m²/day (1,500 Btu/ft²/day) solar radiation profile has been added as specified in SRCC document RM-1, "Methodology for Determining the Thermal Performance Rating for Solar Collectors."
The draw profile has been set to begin at 9:30 AM solar time. An outdoor ambient temperature profile has been added as specified in SRCC document OG-300, with an average air temperature of 14.4°C (58°F). The amount of energy to be drawn from the system was obtained from the April 1994 GAMA Consumers' Directory of Certified Efficiency Ratings for Heating and Water Heating Equipment (p. 134), since the DOE test results are eventually normalized to an energy-type draw. The performance of the systems is determined from a computer simulation rather than by the actual test specified by the DOE procedure.
Table 1: Rating Parameters
Environmental Temperature: 19.7°C (67.5°F) | Auxiliary Set Temperature: 57.2°C (135°F) | Water Mains Temperature: 14.4°C (58°F) | Total Energy Draw (QDEL): 43,302 kJ (41,045 Btu) | Approximate Volume Draw: 243 l (64.3 gal) | Draw Rate: 0.189 l/s (3.0 gpm) | Draw Type: Energy | Number of Draws: 6 — one at the beginning of each hour starting at 9:30 AM.
Source: OG-300 Certification of Solar Water Heating Systems (solar-rating.org)
Notes on the rating parameters:
1. A comparison of different water heating systems can be achieved using the Energy Factor (EF) and the Solar Energy Factor (SEF); these calculations can also be used to estimate average annual operating costs for the specified rating conditions.
2. The SEF includes all of the specified conditions for the DOE EF test, plus several solar-specific conditions.
3. The EF and SEF can be used to compare solar and electric system energy use on a one-to-one basis.
4. A higher SEF or EF indicates less conventional energy use, and consequently lower operating cost.
Table 2: Comparison of Electric and Solar and Gas and Solar Thermal Systems
Electric systems: Yearly Cost = 365 days × 12.03 kWh/EF × cost per kWh.
Example (assuming electricity costs $0.12/kWh):
Typical electric water heater (EF = 0.86): Yearly cost = 365 × 12.03 / 0.86 × 0.12 = $612.69
Typical solar system (SEF = 2.0): Yearly cost = 365 × 12.03 / 2.0 × 0.12 = $263.46
The solar system saves $349.23 ($612.69 − $263.46) yearly. This figure can be used as the energy cost savings basis for an economic analysis of a solar hot water system under the standard DOE (EF) and SRCC-OG 300 rating conditions (SEF). Other factors such as initial cost, maintenance, inflation, interest rate, and replacement costs also need to be considered in any full economic analysis.
Gas auxiliary systems: Yearly Cost = 365 days × 0.4105 / EF × cost per therm.
Example (assuming gas costs $1.60/therm):
Typical gas water heater (EF = 0.6): Yearly cost = 365 × 0.4105 / 0.6 × 1.60 = $399.55
Typical solar system (SEF = 1.1): Yearly cost = 365 × 0.4105 / 1.1 × 1.60 = $217.94
The solar system saves $181.61 ($399.55 − $217.94) per year. As with electric systems, other factors such as initial cost, maintenance, inflation, interest rate, and replacement costs also need to be considered when making an economic analysis.
"Efficiency limits, energy costs, RHI tariffs, and payback periods"
"CO2 reduction potential and environmental trade-offs of solar thermal"
"Research synthesis and investment case for UK solar thermal"
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