Solar Energy for Homes

What is Solar Energy?

Wikipedia states “Solar Energy is the radiant light and heat from the Sun that has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation along with secondary solar resources such as wind and wave power, hydroelectricity and biomass account for most of the available renewable energy on Earth. Only a minuscule fraction of the available solar energy is used.”

In simple terms, Solar energy for homes, can be used to warm or cool, heat water or generate electricity.

Solar technologies can be characterized as either passive solar or active solar depending on the way they capture, convert and distribute sunlight.

Active solar methods involve the use of photovoltaic panels (Solar Panels),or arrays, which together with electrical or mechanical equipment, convert sunlight into useful outputs (such as electricity).

Passive solar methods involve techniques that rely upon the design or architecture of a building to ensure climate control by way of natural thermal conduction, convection and radiation (orienting a building to the position of the sun, selecting materials with favorable thermal mass or light dispersing properties, and designing spaces that naturally circulate air).

Solar Energy can easily be used to help transform an ordinary household, into a power saving and environmentally friendly one. This will prove to, not only save homeowners money in the long run, but also to improve the environment. There are many ways to take advantage of this free energy. The best option is to start by designing a house to include the latest solar energy utilization concepts. Most people however do not have the luxury of designing a house from scratch, but need to see what can be done to convert an existing home to utilize solar energy.

Solar Thermal

Hot Water

For hundreds of years, people have used the sun to heat water by warming dark containers left out in the sun. A lot of energy is used to heat water. The same amount of energy is used to heat water by one degree, (no matter what the starting temperature). So heating from 30 to 31 degrees, or 40 - 41 degrees, uses the same amount of energy! In most cases, up to 30-40% of a home’s energy consumption, is used, just to heat water for bathing, laundry and cleaning. By installing a thermal hot water system, households may save up to 500 kilowatt-hours per month on their electric bill, thereby saving money and reducing pollution at the same time. Installing a solar hot water system is normally the first and (most cost-effective) way to harness solar energy. Even if a photovoltaic system, is your primary interest, a solar (thermal) hot water system along with a PV system will provide the best overall solution. The main reason for this is that with a 30 - 40% lower electrical energy requirement, the cost of producing that electricity with a PV or hybrid (mixed) system will cost less.

The type of solar water heating system chosen will largely be determined by your climatic conditions, (as very cold temperatures may damage equipment). Technology for solar thermal has had great innovations in the last decade bringing better efficiency, cost-effectiveness and reliability.

Classes of Thermal Water Heaters

DrainBack Systems: State-of-the-art, fail-safe freeze protected with thermal limiting (active, indirect): Collector water is separate from potable water and the collector water drains into a special tank to prevent freezing and overheating concerns, once potable water reaches proper temperature or if no sunlight (heat) is available.

Drainback System

Glycol Systems: Indirect Heating, Differential or Photovoltaic (PV) Controlled Antifreeze Protection (active, indirect): Collector water is separate from potable water and contains non-toxic propylene glycol antifreeze. This is sometimes referred to as a “pressurized glycol” system and is freeze tolerant. The small electric circulation pump can be powered by a small PV collector.

Active Direct Systems: Direct Heating, Differential or PV Controlled (active, direct): Potable water is circulated from the storage tank to the collector when heat is available. No additional heat exchanger is required as the collector serves this purpose. The small electric circulation pump can be powered by a small PV collector. This system is for tropical, non-freezing climates.

Integrated Collector Storage “ICS” (passive, direct): Potable water is both pre-heated and stored in a roof-top unit before going into a conventional water heater. This basic system uses regular “street” or well water pressure to circulate water and does not require pumps or temperature controllers, but is subject to freeze damage.

Thermo-siphon (passive, direct): Potable water is naturally circulated from the collector to the storage tank positioned above the collector(s). Based on the principle that hot water rises, these self-contained systems heat water without use of pumps or controllers, but are subject to freeze damage. These are typically used in tropical and/or developing countries.

Each of the above systems has their own benefits, limitations and aesthetic considerations. There are many factors that go into selecting a system that meets your needs. Factors to consider include:
1) Cloudy days
2) High-demand times for hot water
3) Conventional Gas or Electric backup systems
4) Roof space
5) Climate
6) Looks
7) Cost and ROI

Systems may include back-up heating (using electric or gas) to ensure one is never without hot water. Having a dealer perform a professional site survey is your first step in having a properly sized and installed solar hot water system. Because there are different types of systems and each system requires proper sizing (based on total usage, peak demand and part of the country), it is a critical task to ensure its performance and durability.

Here is a great resource for more on the topic.

So what can I do to setup my own water heating system? Check out this really helpful link to get DIY Hot Water

Pool Heating

Heating swimming pools with the sun can greatly reduce energy costs, and is very effective in keeping a pool at the preferred temperature. Even if no gas or electric pool heater is installed, a solar pool heater will significantly extend your swimming season. If shade is keeping your pool too cool, solar heating is likely to be the best long-term option. Solar pool panels are made of a flexible and durable polymer material. Pool temperature is maintained using an electronic controller, temperature sensors and an automatic diverter valve. Most of the time, your existing pool pump is enough to operate the system. Solar pool panels come in a variety of sizes and can be attached to a roof or even ground-mounted on a frame. If an electric or gas pool heater is already installed, a solar pool heater will prove to significantly reduce operating costs by serving as the pre-heater. A professionally sized, selected and installed solar pool heating system will add value to your home and extend the swimming season of your home.

Solar Electric

Photovaltaics (Solar Panels)

A Photovaltaic (PV) panel

PhotoVoltaic Systems (PV) are a relatively new technology. The first photovoltaic effect was discovered by Edmund Becquerel, a 19-year old French experimental physicist in 1839. Albert Einstein received a Nobel Prize in 1923 for explaining the photovoltaic effect. But solar PV only reached a level where its power began to be useful for commercial purposes around 1954. The technology was mainly developed for space, (to power spacecraft).

solar energy for homes

PV uses semi-conductor material and sunlight to make electricity. The electricity made is a constant DC voltage, which can be converted by an “inverter” into alternating current (AC). This form of AC power is more useful since it is the type of power that is used to power the average home. DC power can also be used, if a home is designed to use it from the design phase, but it is not as efficient as AC power. PV solar panels, are relatively expensive and produce only small amounts of power output. A whole bank of solar PV panels are required to produce a relatively small amount of power. Typically 5 - 270W per panel. Recent technological developments have produced new forms of PV products for example, thin film and flexible thin film elements. Many of these new technologies and products are in the development stage and boast better efficiencies and new ways of harnessing more energy. For example there are new techniques and ways of harnessing UV (ultra -violet) radiation, which improves the efficiency and output of the PV array.

The main problems that PV arrays face is: 1) The high energy needed to produce them, 2) The low efficiencies in converting solar energy to electrical energy, 3) Low output power of a panel, 4) The high cost to produce. 5) PV panels and inverters are expensive.

PV systems that power buildings can be divided into four general categories:

Grid-Interconnected or “Grid-Tied”: These systems are the most popular and use special inverters to allow electricity to flow safely back into the electric grid. When solar power is generated, this power is typically first used by the building, and then surplus electricity can actually flow back into the grid, giving full retail credit per kilowatt-hour from your utility provider. Since there are no batteries, these systems cannot stored energy and are designed to shut down if the grid is down for safety reasons (mainly to protect utility line workers).

Grid-Interconnected with Battery Back-up: These systems offer customers continued power when the grid goes down, while still being connected to the grid for seamless power. Newer systems also accept other power sources, in addition to PV, such as wind or even traditional gas-powered generators to provide power and/or charge the battery at night and/or if the grid is not available.

“Off-Grid” PV: These systems are used when a completely independent or “stand alone” system is needed. Since no grid power is used, the system must be carefully designed based on power usage, peak demand and seasonal solar variations. Batteries are typically used to provide power at night, in low sun or high electric demand conditions. These systems are ideal for remote locations where no utilities exist.

Utility-Scale PV systems “solar farms”: These systems provide power for regional users by (or in cooperation) with electric utility providers.

Although the industry is rapidly developing with technological advancements the cost is still relatively high. Government initiatives and pressure from environmental groups is pushing solar power to the forefront thus increasing demand and pricing of PV panels. Once a PV panel has been produced it provides an ideal solution for a low energy, low carbon, low maintenance, sustainable design strategy. PV systems are rated by “standard test conditions” (STC) wattage during peak sun intensity. For most applications the sun reaches it's peak only once in the day so having a system specified to produce a certain number of watts does not mean that, that is what it produces all day. Most residential grid-tied PV array systems will typically range from 2 kilowatts to 8 kilowatts. The total energy per year it generates will vary depending on the location. A better solution is to look at a hybrid system, utilizing Solar and Wind energy in a single system. The climate and amount of useful wind and sun in the area concerned would be key to designing the system.