Picture of a toonie.
Net Metering
Net metering concept diagram.
Off-grid solar
An off grid house with solar panels on the roof
Solar DHW
Closeup of a vacuum tube solar hot water collector
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Eastern Ontario
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Solar Hot Water Heating Questions
A picture of a solar hot water installation at a dairy farm

What is Solar Hot Water Heating?

A system of thermal collectors that use a liquid working fluid to collect heat energy from the sun. With the exception of swimming pool heaters, the products that we offer use an anti-freeze working fluid. A water-to-water heat exchanger transfers heat to a hot water heater tank. A circulation pump regulates the flow of fluid in the system. In the picture the farm's dairy building has vacuum tube collectors to produce high temperature hot water for cleaning and sterilizing the dairy's equipment.

Can Thermal Solar Hot Water Heating Panels be Used for Building Heating?

It can be used as a supplemental heat source in a hydronic heating system. It should not be the only source of heat, as the amount of heat produced is the least in the winter, when the most heat is needed. It is possible to supply all the heat required, but it is definitely not an economically viable approach.

It can provide supplemental heat for both radiant heat and for hot water systems with baseboard or tall convectors.

There are systems that provide hot water for both DHW and for heating from the same set of thermal solar collectors.

Can Thermal Solar Panels provide Air Conditioning?

Yes, the heat collected can power absorbtion type refrigeration. Look up Oxford Gardens in Woodstock ON for an example of this application at work. During the summer of 2013 this provided 100% of the air conditioning load for this retirement home facility.

Flat Plate or Vacuum Tube?

For some people which is best question is similar to a chevy vs Ford topic. The best answer is that it depends on the project details. We offer both types. Some of the considerations are:

  • Temperature required for the hot water supply
  • Climate (flat plate collectors are more efficient in warm climates)
  • Orientation of the mounting surface

How Many Collectors will I Need For My House

For domestic hot water heating, some of the factors to consider are:

  • Number of occupants of the house users of hot water
  • Temperature of the cold water supply
  • If your family members are above or below average in their use of hot water.
  • Without doing a specific assessment, no exact answer is possible. Two is a typical value for a small family.

Can you Determine How Much Hot Water We Use?

This is an excellent question, and an accurate answer is required to correctly size your system without resorting to rules of thumb. For a couple of types of hot water heaters we can use a non-invasive methods to track your water use. For the majority of water heaters, the only accurate way is by inserting a flow meter into one of your pipes. This will require shutting of the water for a few minutes. For more details call us, or we can discuss this during a site visit. A diary method will give some useful information if you are willing to do it diligently for a week or longer.

What Type of Water Sources Are Acceptable For Solar DHW?

Hard water is water that has high mineral content (as opposed to "soft water"). Calcium is the most common mineral associated with water hardness. The concern is formation of limescale on heat exchanger surfaces. The other type of concern is that some water contents can be corrosive, and could attack the metal of the heat exchanger.

The standard Enerworks pump station highly integrated DHW appliance has a very compact plate heat exchanger, that is designed for use on municipal water systems that draw their water from a lake or river. Well water or similar hard water supplies tend to deposit minerals on any hot surface, and may over time clog small heat exchanger passages in this type of heat exchanger. If water hardness exceeds 12 GPG (200 ppm), a water-softener must be in line before the EnerWorks Appliance.

For installations with hard water that exceeds 12 GPG (200 ppm), the same type of panels are used but with a coil inside tank type of heat exchanger. This is a stainless steel tank with a 40´ long x 1.25″ diameter stainless steel coil heat exchanger. Even if this type of heat exchanger builds up some mineral deposits, they are on the outside of the heat exchange coil, and the mineral does not block the potable water flow. The buildup is simialr to the way it occurs in an electric hot water heater tank or kettle. The only impact of mineral buildup is a drop in heat exchanger efficiency. The Enerworks Super Solar Combi Tank has a cleanout opening to permit scale removal.

Net Metering or Solar Water Heating?

Hot water heating accounts for approximately 22 percent of total household energy consumption (NRCan data from 2004). This energy may come from low cost sources such as natural gas, or wood. If it comes from high cost sources such as propane, oil or electric resistance heating, this is a considerable target for savings.

If your household has electric heat and electric hot water heating, which can offer the most savings by using solar energy? From one study which can be found at www.cbeedac.com. an average Canadian household using 236l of hot water per household per day is using 4775 kWh of electricity, or other fuel a year to heat the water. The mean household size was calculated at 2.55 persons from the 2001 Census, (Statistics Canada, 2001). For larger households with greater than 2.55 members, such as a 5 person household the energy input for hot water heating could be estimated to be twice this value or 9550 kWh.

The average Canadian household uses 19 kWh of electrical energy per day, according to a recent study. With electric heating and electric hot water you will be considerably above average. Therefore if your target is to reduce your current energy expenses, there is a bigger opportunity for savings with a net metering installation than with solar hot water heating. Another conclusion is that the opportunities of savings with solar hot water heating increase as the family size increases.

If a solar hot water heater was installed only to lower the utility bills of a family size of 2.55 people, it could avoid purchasing up to 4775 kWh, while with a solar PV net-metering system, it could avoid purchasing up to 11980 kWh per year. Therefore if there has to be a choice of only one system, and both systems have paid back the initial investment, the net metering system has the potential ability to reduce spending a little more than twice the amount of money relative to solar hot water heating.

If your annual electricity use is over approximately 11980 kWh per year, then in Ontario a net metering system will not bring your hydro bill to zero kWh. Then net metering plus a solar hot water heater will provide additional electrical energy bill reductions.

If you only have a limited roof area to use, solar DHW usually uses less area for the given amount of solar energy captured.

Commercial uses of hot water such as a restaurant or dairy use a far greater amount of hot water, and the economics are quite different. There is no 10kW limit for solar hot water, since the energy is not exported to a utility, but consumed on the site where it is captured.

Heat Pump Domestic Hot Water Heater

Another idea that works for some locations, use a heat pump based water heater, and just use net-metering for your energy input. It does not work if your heating source is electricity, but could make sense if you heat with wood or other low cost fuel. There are at least 6 companies making these for the Canadian market. Note that they cool and dehumidify your basement when they are running, not exactly ideal during the winter, but nice in the summer. This approaxch is much more attractive is the USA where humidity is a problem, and there is a much lower requirement for heating in the winter.

Drain Water Heat Recovery

A drain water heat recovery can lower hot water heating bills dramatically if your household mainly takes showers and not baths. It costs nothing to operate, and can be up to 50% efficient. These are relatively inexpensive. Visit NRCan's web page on drain water heat recovery for more information.