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Solar Water Heater and Photovoltaic Technology

This section includes information on:

• How the Technologies Work
• What Is Solar Water Heating
• What Is Photovoltaic
• Payback Periods or Return on Investment (ROI)
• Benefits of Solar Energy
• How to Go Solar
• What Would it Take For You to Go Solar?

Residential solar energy systems can be divided into two broad design categories:
1. Solar water heaters (also called solar thermal systems) are used to heat water.
2. Photovoltaic systems are used to generate electricity.

As a typical home will still be connected to municipal utility services for water and electricity (grid-tied), solar energy systems should be considered as an offset or supplement to traditional energy requirements. For cottages or lodges not connected to utilities (off-grid), solar can be a primary – but seasonal – energy source.

What Is Solar Water Heating
By absorbing the sun's radiant energy and converting it into heat energy, a solar water heater pre-heats cold municipal water before it goes into a home’s hot water tank. Energy conservation and cost savings are realized by using less conventional energy sources to heat the water in a traditional water heating system. In Ontario, depending on a resident’s hot water consumption, solar water heaters provide approximately 50% of annual water heating needs. Most solar water heaters rely on the existing natural gas or electric heater as an auxiliary back-up heater. This ensures that hot water needs are met when it is very cloudy or there are reduced sun hours.

Solar Collectors
Solar Collectors are the solar water heating ‘panels’ that are usually mounted on a roof or other area of abundant solar radiant energy. They are only one – but essential – component of the complete solar water heater. Below is a description of the more common designs:

Unglazed Solar Collectors
Unglazed solar collectors are mainly used in applications of pool heating or seasonal water heating. Usually flat black in colour, these collectors absorb radiant energy to heat circulating water. However, the collectors are usually uninsulated and suitable for three-season use only or regions of moderate temperatures. During winter months they must be protected from freezing or drained.

Glazed Flat-Plate Solar Collectors
Flat plate solar collectors consist of a series of pipes set into a flat copper or other metallic plate under a glass-covered insulated box. The glass cover traps the heat produced when solar radiation falls on the plate. The accumulated heat is transferred to a fluid in the pipes; usually water or an anti-freeze fluid such as glycol. The heated fluid is then released through the use of a heat exchanger into a hot water storage tank. Other important components are a control system, a pump to circulate the liquid and a second conventional hot water tank.

Evacuated Tube Solar Collectors
These solar collectors consist of a series of small copper pipes encased in separate highly insulated glass vacuum tubes. The vacuum prevents heat loss and maximizes heat to be transferred to the circulating fluid in the pipes. For even higher temperatures, reflectors are used to focus the solar radiation onto the tubes. Some evacuated tube systems require a second storage tank, while other designs incorporate the collector and hot water storage tank all in one unit on the roof.

Types of Systems
There are three common types of solar water heating systems: Glycol, Drainback, and Thermosiphon.

Glycol
A Glycol solar water heater is, in the Canadian climate, the most prevalent type of solar domestic water heater. Glycol, a non-toxic liquid that will not freeze, is used as the heat-transfer fluid. By using glycol instead of water, more options are available for the plumbing of the system because a slope for a drainback model is not required. As a result, the glycol system is often easier and simpler to install than a drainback system. The main drawback of a glycol system is that it requires a maintenance schedule for every 5 to 10 years. Maintenance is for replacing the glycol and for inspecting or replacing the expansion tank on the system.

Drainback
A drainback solar water heater uses water as the heat-transfer fluid. The benefit of using water over Glycol is that Glycol needs to be replaced every 5-10 years, but the water can remain for the life of the system. As a result, a drainback system is the more maintenance-free option.

Water is pumped from a storage tank through piping and into the solar collectors (panels). It is called a drainback system because the water must have a way to drain out of the collectors in freezing conditions. A drainback tank is installed to collect the water and store it until the collector temperature warms up again. Design of a drainback system is dependent on the water in the pipes having a clear downward slope from the panels to the storage tank. If the panels need to be installed on the opposite side of the house than the hot water tank, a drainback system may not be possible.

Thermosiphon
Less common in Canada than drainback or glycol systems, the thermosiphon solar system does not require any electricity or pumps for its operation. These types of systems are known as “passive” solar heaters because of the relative simplicity in design. Rather than placing the solar storage tank next to your existing water heater, a thermosiphon solar heater has a storage tank installed above the solar collectors (panels). In operation, the collector and tank create a loop of heat flow:

1. Cold water from the bottom of the tank flows into the bottom of the collectors
2. Sun on the collectors heats the water and causes it to rise through the panel
3. Hot water exits through the top of the panel and flows into the top of the tank.
4. A heat exchanger inside the tank extracts heat for hot water use.

While it is definitely the least expensive option, thermosiphon systems are not very common in colder climates. During the coldest months of the year, it is best to have the storage tank inside in a well insulated place, rather than on the roof. Thermosiphon systems are much more common in warmer climates where freezing temperatures are not an issue. Some summer cottages or summer homes could benefit from these systems since they are ideally suited for the warmest months of the year.

For more information, see:
Canadian Renewable Energy Network (CanREN):Applications of Solar Heating
Canadian Renewable Energy Network (CanREN): An Introduction to Solar Water Heating Systems

Water Heating System Buyer’s Guide from NRCan:
http://canmetenergy-canmetenergie.nrcan-rncan.gc.ca/eng/publications.html?ISBN:0-662-28486-0

Read about Solar Pool Heating

What Is Photovoltaic
Sunlight changed directly into electricity is known as photovoltaic (PV) energy. The DC (direct current) electricity created by PV panels is converted to AC (alternating current) – the same current used in your home and transmitted on the power grid – by an inverter installed with your PV system. This power is then fed directly into your home’s overall electricity supply by connecting to the main circuit breaker panel. This is "parallel generated electricity" that works in conjunction with the existing utility-grid supply (grid-tied). During times when the PV system is generating less than the building’s demand, the additional required power will be automatically drawn from the grid. As PV production increases, the electricity meter will slow down depending on how much solar power is being generated. When the solar PV system is producing more electricity than is being consumed, the excess will flow on to the grid, making the meter run backwards. This electricity will be effectively "stored" in the electrical grid for later consumption (Net Metering). An alternate connection program, Ontario’s Standard Offer Program, will pay homeowners for the total amount of renewable energy being produced by an installed solar PV system (called micro-embedded generation). For more information about these programs for photovoltaic, go to the Incentives page.

For more information, see:
Canadian Renewable Energy Network (CanREN): Integrating Photovoltaic Arrays in Buildings
Canadian Renewable Energy Network (CanREN): An Introduction to Photovoltaic Systems

Payback Periods or Return on Investment (ROI)
Solar retrofits for the typical Ontario household can average $6,000 for a solar water heater and $12,000 for small scale photovoltaic. Custom designed and installed solar energy systems can be scaled up to increase energy output – depending on a household’s energy needs. Greater cost savings are usually realized through an economy of scale: meaning the larger the solar energy system, the lower the cost of energy delivered for the money invested. Keep in mind that after the initial investment, solar energy can be much more economical than other energy alternatives since the resource needed to power the solar energy systems – sunshine – is free and unlimited.

Individual payback periods for residential solar energy systems are calculated by a variable equation of:
• Size and cost of system
• Carrying cost (or interest rate) of purchasing loans
• Purchasing incentives (rebates, grants, zero-interest loans)
• Participation in a feed-in tariff (Standard Offer Contract) which pays generator for the power being produced
• Current and future prices of conventional energy
• Saved cost of reduced energy consumption

Solar Water Heaters
25-30% of the total energy consumed in the average Ontario household goes to heating hot water. Estimated payback periods for a solar water heater range from 6-13 years for water heated by electricity, and 12-20 years for natural gas heating based on the factors in the equation above. Custom installed solar water heaters range from 4,000 and up installed for flat plate and evacuated tube collectors.

Photovoltaic Systems
PV systems can cost from $12,000 and up for a basic entry level system that will reduce the average Ontarian’s demand by about 20-30% (depending on your home’s energy consumption patterns and efficiency). Based on the factors in the equation above, the payback period is approximately 15-25 years.

There are many purchases we make that are not based on ROI, but on other concerns. Cars, entertainment systems and furniture are generally not purchased with ROI in mind. Solar energy systems should be seen as an investment, not only in economic returns but in a healthy environment. Since a solar energy system is an improvement to your home (like a renovated kitchen or bathroom) you can expect that the value of your home will increase as will your quality of life. Real estate studies have shown that homes with installed renewable energy systems actually sell faster and sell at a premium.

Benefits of Solar Energy

• A more sustainable, clean energy source than fossil fuels or nuclear energy
• Reduces greenhouse gas emissions and air pollutants and decreases our impact on climate change. This, in turn, increases the traditionally non-quantitative ‘quality of life’ measures such as better respiratory health, decreased work or school absenteeism from smog-related asthma, and mitigating the broader personal and socio-economic impacts of climate change.
• Helps citizens develop an energy conservation ethic, increasing their independence from outside energy sources and decreasing their annual energy costs
• Reduces the need to import energy from abroad and is an energy source unaffected by global price fluctuations
• Creates employment opportunities and new sources of income for Ontario manufacturers and trades

How to Go Solar

Are you interested in getting started on a home solar installation. This resource outlines 7 easy steps to "Go Solar" and receive rebates for homeowners in Ontario.

How to Go Solar (248KB PDF)

What Would it Take For You to Go Solar?

The Ontario Solar Task Force Report has been released! The Solar Task Force has provided an informative and detailed report that outlines a plan for how Ontario can reach its ambitious target of 100,000 solar rooftops in 15 years.

Packed with information and analysis, the report explores the great potential for where the solar industry can go in Ontario.
Solar Task Force Report – October 2008 (400KB PDF)

Solar Times Newsletter – Keep Up-to-Date on Solar Initiatives in Ontario

Read the Solar Times Winter 2008 newsletter (600 KB PDF)