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Comparison of Domestic Solar Photovoltaic Energy and Ground Source Heat Pump (Geothermal) Energy


This discussion compares domestic solar photovoltaic and ground source heat pumps (geothermal) energy generations in terms of mechanism, costs, energy savings and advantages or disadvantages of these two systems.

An Overview of the Technology

Photovoltaic energy converts sunlight into solar energy using solar cells and semiconductors. These semiconductors are made of silicon and when these are exposed to light, they produce photovoltaic energy that is clean and safe. The term photovoltaic refers to photo or light and volta, or electric energy conversion and the photovoltaic effect is the production of a volt or electricity using semiconductors and solar energy. Individual solar cells, also photovoltaic cells are connected to form solar panels and these are connected to create photovoltaic arrays that can power large buildings. The amount of available light and and amount of power needed could determine how much energy is produced.

Geothermal heating is the direct use of geothermal energy for heating applications and geothermal heating capacity is installed around the world satisfying 0.7% of global primary energy consumption. Geothermal heating directly uses geothermal energy and no energy conversion is needed, so thermal efficiency is high.

A Description of How It Works

Photovoltaic systems (PV system) use solar panels to convert sunlight into electricity. The system is made up of one or more photovoltaic (PV) panels, and these panels convert sunlight directly into electricity. PV systems also have AC/DC power converters which are inverters and these have racks that hold the solar panels, as well electrical interconnections and mounting for components. Photovoltaic system has power point tracker, battery systems, charger, solar tracker, solar concentrators, and energy management software and these components help in the energy conversion process. PV systems provide energy to a consumer, to lamps and weather instrument and PV systems with large grid provides energy as needed by many customers.

The electricity generated is stored and used directly or fed into large electricity grids and these are powered by central generation plants. These are combined with domestic electric generators that feeds into a small grid and PV systems are designed this way as they provide the highest energy yield. Solar Energy has practical applications and PV systems are important in our daily lives. PV systems can power small consumer items including calculators and wristwatches. Solar power also helps provide power for communications satellite, water pumps, lights, appliances and machines at homes and workplaces. Road and traffic signs are also powered by converted solar energy and photovoltaic solar energy is one of the cheapest and cleanest source of energy. Space vehicles have also successfully used photovoltaic energy.


Solar PV Energy
PV Energy System

On the other hand, geothermal energy originates from the heat that is retained within the Earth and from radioactive decay of materials, solar energy is absorbed at the surface. Most high temperature geothermal heat is obtained in regions with tectonic plate boundaries where volcanic activity is close to the earth. In these regions, ground and groundwater are found at higher temperatures. Even cold ground contains heat in moderate climates and the heat can be extracted with a heat pump.

Heat pumps transfer heat from a cool space to a warm space and enhance the natural flow of heat from a warm to a cool area. The heat pump has a loop of refrigerant pumped through vapor compression refrigeration cycle and moves heat. Airsource heat pump heats pure electric heaters and can extract heat even from cold air and are more efficient although efficiency may decrease below 5 degree Celsius. A ground source heat pump can extract ground heat in the winter (for heating) and transfers heat back into the ground in the summer (for cooling). Although some geothermal systems can do only heating or cooling and can't do both.

Some Facts and Figures (Costs, Energy Savings, Number of Installations)

Photovoltaic energy is a cheaper form of energy and the costs of production has been reduced through widespread use of production and technological advances. The average retail price of solar cells is at $2.43/watt. For large scale installations, prices are below $1.00/watt and crystal silicon solar cells are now used and have been developed at lower costs of production. Energy costs for using photovoltaic systems have been declining and the costs are at USD 2200/kWp. Installation charges for solar panels has 10% capital costs, 1% operating and maintenance costs. Panels are usually mounted at an angle and adjusted seasonally according to solar declinations.

Solar tracking utilizes access to sunlight and raises the total energy output.

The thermal efficiency of a heat pump is greater than 300% when compared with electric heat being 100% efficient. A heat pump gives 3 to 5 times more heat energy than electric energy it consumes, output is higher than the input. Total installation costs for geothermal energy generation is $8,000 and despite the high costs of installation, there is substantial improvement in reliability and efficiency. Initial costs are 2 to 5 times conventional heating system in most residential applications and the cost of installation is affected by size of the living area, geology, location and insulation features. Geothermal energy could have highly variable energy prices

Ground source heat pumps are the most efficient heating and cooling systems on the market. Commercial systems heat pumps maintenance costs in the US are historically been between $0.11 to $0.22 per m2 per year, much less than the average $0.54 per m2 per year for conventional HVAC systems. Energy savings from heat pumps are significantly high at 40%-60% compared with other sources of energy.

A Summary of Advantages and Disadvantages of Both Technologies

Pros of Geothermal Energy

Pros of Photovoltaic Energy

Cons of Geothermal Energy Generation

Cons of Photovoltaic Energy Systems

Case Study Example

PV Solar

For a PV solar case study, the team at AVC Energy installed a 16 panel Solar PV system on a house in Wakefield, West York shire, UK. Solar energy generation is supported by a Government backed scheme, and this technology generates an estimated $2,100 in payments and saves 1,206kg in C02 emissions.

Geothermal

In a case study described on ground source heat pump, it cost $20,000 to purchase and install the pump, which involved laying 600 meters of plastic tubes almost five feet under a family garden and linking this up to a state-of-the-art boiler and water tank.

The pump allowed the family to do both heating and cooling and their energy bills have dropped to $80 a month or $980 a year.

Conclusions

The studies and examples here show that both the energy systems can be energy efficient and cost savings are ultimately more for geothermal systems despite the high costs of installation. Ground source heat pumps allow both heating and cooling and solar energy panels in PV systems only allow heating and the system is affected in snowfalls and extreme weather conditions. Thus despite being a clean energy system, solar energy may be ideal as a secondary rather than primary source of energy in a household or large building.

References

Al-Mohamad, Ali. "Efficiency improvements of photo-voltaic panels using a Sun-tracking system." Applied Energy 79, no. 3: 345-354.

Andrews, Rob W, Andrew Pollard, Joshua M. Peace, “The Effects of Snowfall on Solar Photovoltaic Performance ", Solar Energy 92, 8497.

AVC group - Alternative Energy, Wakefield Case Study.

Bloomquist, R. Gordon. "Geothermal Heat Pumps, Four Plus Decades of Experience". Geo-Heat Centre Quarterly Bulletin 20 (4) (Klmath Falls, Oregon: Oregon Institute of Technology)

Energy Saving Trust. Case Study on Ground source heat pump , Stirlingshire.

Graham, Michael. Low-cost PV solar kit preferred by diy-communities. Treehugger.com.

Hughes, P. Geothermal (Ground-Source) Heat Pumps: Market Status, Barriers to Adoption, and Actions to Overcome Barriers. Oak Ridge National Laboratory.

Office of Energy Efficiency Ground Source Heat Pumps (Earth Energy Systems)". Heating and Cooling with a Heat Pump. Natural Resources Canada, Office of Energy Efficiency.

Pearce J. M. "Expanding Photovoltaic Penetration with Residential Distributed Generation from Hybrid Solar Photovoltaic. Combined Heat and Power Systems". Energy 34: 1947–1954.

Virginia Tech GHP Technology - Department of Mines, Minerals and Technology

PV - RESEARCH TECHNOLOGY

Solar Energy

Solar energy is the purest form of energy resource and therefore "does not compromise or add to the global warming." It is considered as an alternative source of energy that is distinct from that derived from fossil fuels such as oil. In a single second, the sun radiates more energy than humankind has consumed since time eternal. Notably, solar power has remarkable great potential even though current global consumption is quite low. Specifically, as of 2005, world consumption of solar energy constitute only 0.05% of the global energy supply. The reason for this is because albeit it has great potential solar energy remains very costly to develop especially in terms of technology and infrastructure. However, the "European Solar Thermal Industry Federation (ESTIF)" explains that solar energy may be the best alternative for remote places on earth, for a decentralized energy supply. As of 2009, there was a global cumulative installed solar energy capacity of 22,928.9 MW, an increase of 46.9% from 2009.

There are two general types of solar energy, namely, solar thermal and solar PV. As will be shown below, the main differences between these two technologies pertain to conversion and storage of captured sunlight. With solar PV, semi-conductor technology is used so that sunlight may be directly converted into electricity.Therefore, PV only operates when the sun is shining, must have a power generation mechanism to ascertain that there is constant supply of electricity. In contrast, solar power operates through the use of mirrors so that sunlight may be concentrated. The concentrated sunlight is subsequently used as direct source of heat. Due to the ability of solar thermal to produce heat, its energy storage mechanisms come in various forms.

Solar Thermal

The Sun is the source of an "enormous amount of radiation energy to its surroundings: 174 PW (1 PW = 10 15 W) at the upper atmosphere of the Earth." As energy from the sun touches Earth, it has been doubly attenuated by (i) the atmosphere, 6% through reflection and 16% through absorption; and (ii) the clouds, 20% through reflection and 3% through absorption. An additional "51% (89 PW) of total incoming solar radiation reaches the land and the oceans." Solar thermal power has the potential to capture energy from the sun.

In relation to these, solar collectors and thermal energy storage components comprise two kernel subsystems used in solar thermal applications. Solar collectors necessitate excellent optical performance so that it can absorb heat as much as possible, while thermal storage subsystems need (i) high thermal storage density, at a small volume and low construction cost; (ii) excellent heat transfer rate, so that heat is absorbed and released at the necessary speed; and (iii) long-term durability. The solar collector serves as an energy converter that converts solar irradiation energy "either to the thermal energy of the working fluid in solar thermal applications, or to the electric energy directly in PV (Photovoltaic) applications." With solar thermal applications, sunlight is absorbed through a solar collector as heat so that it is converted and transferred to a working fluid, either in the form of air, water or oil. The working fluid then carries heat that may be used for heating in households, or for the charging of a thermal energy storage tank so that the heat may be drawn from it at a later time, including during night or cloudy days.

There are two general categories of solar collectors, based on concentration ratios. The first is a non-concentrating collector and the second is the concentrating collector. A non-concentrating collector "has the same intercepting area as its absorbing area." In contrast, a sun-tracking concentrating solar collector typically has concave reflecting surfaces for the purpose of intercepting and focusing the solar irradiation to a much smaller receiving area. This results in a heightened heat flux such that the thermodynamic cycle can attain higher Carnot efficiency when operating in higher temperatures.

PV Solar Power

PV conversion is a process wherein sunlight is directly transformed into electricity minus the use a heat engine. PV devices are desgined simply, are not costly to maintain and may be constructed as stand-alone systems to generate outputs ranging from microwatts to megawatts. Because of these characteristics, PV devices are used as sources of power, for pumping water, for "remote buildings." Because of the various applications of PV, there has been an increasing demand for it.

A (PV) power generation system is comprised of "multiple components like cells, mechanical and electrical connections and mountings and means of regulating and/or modifying the electrical output." These systems’ outputs are measured according to peak kilowatts (kWp), which refers to an amount of electrical power expected to be delivered by such system when the sun is directly overhead on a sunny day. Connections are made between a grid and a larger independent grid, in many instances a public electricity grid, so that power may be fed into that grid. These grids come in different sizes. Some generate only a few kWp used for residences, while some generate as much as tens of GWp especially when used for solar power stations. There are times when PV may be combined with other forms of power generation, like for instance, a regular generator that runs on diesel or other renewable energies such as wind. The result of such combination is called "hybrid power generation system." Hybrid systems such as these are beneficial because they reduce consumption of non-renewable fuel.

PV Technology Materials

Solar cells typically need some sort of material to absorb the sunlight captured in the cell structure for the purpose of absorbing photons as well as generating free electrons through the PV effect. As mentioned earlier, the PV effect is the means through which sunlight is convered to electricity through PV. Considering that sunlight is a pure form of energy, when it strikes a PV cell, enough energy is radiated to negatively charged atomic particles so that, in turn, their energy level increased thereby freeing them. There are built-in barriers within the cell that interacts with these electrons so that voltage may be generated. It is this voltage that drives "a current through a circuit."

The most widely-used technology used for supplying power into PV applications is silicon technology. Currently, more and more HV power systems use multi-crystalline silicon as well as monocrystalline silicon that are ideal for "high-efficiency solar cells." There are also "thinner wafers and ribbon silicon technology" popular. Nevertheless, in recent years, certain dynamic and exciting thin polymers that can generate sustainable yields of electricity have been developed and used. These include (i) "cadmium telluride (CdTe) and cadmium sulphide (CdS)" typically by means of "close spaced sublimation (CSS)" processes that are ideal for large area applications; (ii) organic and polymer cells that are believed to enhance stability because of improved active materials, capability to encapsulate, and more efficient use of UV filters.

Uses of PV Technology

Typically, batteries are used for storing energy generated by solar or wind in order to ascertain that there is 24/7 supply of power. However, these batteries may be easily damaged by "weather conditions" such as "temperature, relative humidity, barometric pressure, wind speed," among others, thereby requiring assessment for both efficiency and working life degradation within harsh environments. To note, temperature and humidity are critical weather parameters that impact battery efficiency and working life and these must be carefully taken into account in the selection of battery for energy storage purposes.