Solar energy is synonymous with renewable and sustainable energy. It is clean as well as green. Solar power embodies everything that we aspire for from an energy source now as we realize the harmful effects of fossil fuels.
Solar devices aim to harness the energy in the sun’s rays and convert it into usable energy form, be it as electricity or thermal energy to heat water. Solar power is equally effective in heating and cooling interiors of both residential and commercial buildings.
The solar technology used to capture the power of the sun can be either active or passive in design. To a layperson, this may not mean much other than choosing from an array of options. But your choice can make a huge difference in efficiency as well as savings.
How does active solar energy work? How can you implement passive solar in the building design? It is not an easy choice to make or compare passive and active solar energy.
However, you should understand the difference between active and passive solar energy before going solar shopping. This article will make this easier for you with active and passive solar heating examples. Here you will also find the advantages and disadvantages of both, along with a comparative analysis.
What is active solar energy?
As the name indicates, an active solar energy system actively collects, stores, and converts solar energy to a usable form. In this, an external device using air or liquid is used to harness the sun’s energy. A solar panel is an example of an active solar device.
Active solar devices can be used to generate electricity or heat interiors. It is a good choice to heat water. Often liquid is used to capture solar radiation as liquids are better conductors compared to air. However, the air has the distinct advantage of not freezing up in winter.
Liquid collectors are usually referred to as hydronic collectors while those using air are just air collectors. Active solar collectors can be big or small, depending on the requirement. While smaller systems are enough to provide energy to homes and buildings, larger utility-scale systems are used to power entire towns and communities.
The energy collected by an active solar collector can be stored for later use.
Active solar energy examples
Active solar energy systems come in a wide range of choices to suit the occasion. While photovoltaic cell panels are the ideal choice for capturing solar energy, converting it into electricity, and storing it for future use, solar collectors are the better options for heating needs.
Active solar collectors are used for space heating, water heating, and pool heating needs. When used for space heating, both liquid-based and air-based devices are effective. Liquid-based systems typically have enormous water tanks to capture, store, and distribute heat using radiant slabs, pumps, hot water baseboards, and central forced air. Air-based systems use rock bins to store the heat and blowers and ducts for heat distribution.
Active solar water heating devices may heat water directly or indirectly. In direct heating, the water is pumped to desired locations using pipes. In indirect heating, antifreeze is used to capture solar energy and a heat exchanger is used to transfer the heat to the water. In both cases, a storage tank can be introduced if necessary to store the energy for later use.
Active solar pool heating systems differ from water heating systems in that they don’t use a storage tank. The pool water is allowed to flow through the solar collector, where it gathers heat. Then, it is brought back to the pool, thus heating the pool water. This circulation of pool water is maintained to maintain the temperature of the pool. In this instance, there is no need for a storage device.
Advantages & Disadvantages of active solar energy
Pros of active solar energy
- It helps in harnessing solar energy irrespective of the design or orientation of the building.
- It helps to gather solar energy from a large area.
- It can capture solar energy, convert it to any desired form, and store it for later use.
- It can be used to meet our diverse needs like electricity demand, space, and water heating.
- Active solar heating systems can eliminate or reduce the need for conventional heating systems using fossil fuels.
- It can help in reducing greenhouse gas emissions and pollution levels.
- It can help you generate more energy than you need and export it to the grid in lieu of credits or payment.
- It can help you avail of the numerous incentives including the federal tax credit offered for its installation.
- It comes with a long lifetime and generous warranty offers.
Cons of active solar energy
- It is expensive.
- It uses elaborate equipment and infrastructure to capture, convert, store, and distribute solar energy.
- It requires regular maintenance. This means extra expenditure.
- Fluids used to capture and store heat may not be eco-friendly. They may release toxins when heated up.
What is passive solar energy?
Unlike active solar systems, passive solar systems don’t rely on external devices to capture solar energy. It is entirely dependent on the orientation, design, and construction of the building. Passive collectors are used to harness solar energy to heat and cool the interiors of buildings. It can also be used for daylighting.
The law of thermodynamics is used in passive collectors. That is heat is transferred from a warmer to a cooler surface. Passive solar energy is used for heating, cooling, and daylighting building interiors. A typical passive solar collector allows sunlight to enter a building through open windows and provides heat and light to the interiors.
The effectiveness and success of passive solar systems depend on the amount of sunlight received and the thermal mass of the walls of the building. It is a good choice for homes and small buildings.
A building designed for passive solar energy uses all three modes of heat transfer – conduction, convection, and radiation to help with the heat collection and distribution. Unfortunately, passive solar systems cannot store the collected energy.
Passive solar energy examples
As no external mechanical devices are involved in the collection of passive solar energy, its success entirely depends on the orientation of the building as well as its design. The windows, walls, and furnishings inside the building play a huge role in passive solar energy collection.
Homes and commercial buildings can benefit from designing them to allow for passive solar energy collection. Having longer walls, more windows, and more window surfaces on the south side of the building is ideal for this. The southern side of a building receives more sunlight than any of the other sides.
Allowing sunlight to stream in through open windows helps with heating the interiors. Or having a glass structure on the southern face of the building helps in absorbing more of the sun’s energy. With proper design, this heat collected can be distributed throughout the building using natural convection.
Advantages & Disadvantages of passive solar energy
Pros of passive solar energy
- It doesn’t require external devices for capturing solar energy.
- It is simple, easy, and cheap.
- Once incorporated into the building design, there is nothing more needed.
- It can reduce your energy bills.
- It is a healthy choice as everything about it is natural.
Cons of passive solar energy
- It is heavily dependent on the climate of the location, lie of the land, orientation, and design of the building.
- The number, position, surface area, and design of windows have too much importance.
- The materials used in a building’s interiors and furnishings need to be chosen with care to absorb and retain heat.
Active vs Passive solar energy
As listed above, both active and passive solar systems have their benefits and drawbacks. The choice needs to be made based on each situation.
If you are planning to construct the building, it would be a good idea to include passive solar energy in the design. In an existing building, there is not much you can do about letting the sunlight in. Not all is lost for present buildings altogether. Adding more insulation to the roofs, floors, and even walls helps in retaining the heat inside. Increasing the thermal mass is another approach for existing buildings to avoid loss of heat.
On the other hand, new building owners can do a lot to integrate passive solar energy into their design. Sun tempering can help you save 15-20% of your energy bills. This includes having longer southside walls, increasing the number of windows and window surface on the southside, and constructing the building on an east-west axis. This will ensure that the building receives maximum exposure to sunlight.
In addition to implementing passive energy systems in the building’s design and interiors, you can also adopt active solar systems like PV panels and solar collectors to provide heat and electricity to the building. This can help in reducing your reliance on fossil fuels, do your bit for the environment, and at the same time save on your energy bills.
If you are opting for a solar battery or net metering, you can gain complete or almost complete energy independence.
If you have to choose between the two solar energy systems, active and passive, passive is always cheaper than active systems and easier and less expensive to maintain. The downside of a passive system is that it is completely reliant on the weather. In summer, the building may overheat and on cloudy days, it may not help at all. There is no provision to regulate the temperature of a passive system, whereas an active system can be better controlled.
Passive solar systems use only a small portion of the sunlight received by the building but an active system can capture most of it with the right capacity and positioning. Solar energy harnessed by an active system can be used in a multitude of ways while passive solar energy can come in handy for moderate heating and lighting needs during the daytime.
If you have already built your home or choose to live in an apartment, you no longer have the luxury or opportunity to incorporate passive solar energy into the design of the building. In case, your home is perfectly placed to exploit the sun’s energy, well and good. Otherwise, you will have to depend on active solar energy options like PV panels and solar collectors.
Unlike in many other situations, here, there is no need for you to choose between the two. You need not waste your time on active solar heating vs passive debate. You can use both active and passive solar energy together to tap the full potential of solar energy.