CANADIAN RESEARCH and DEVELOPMENT ACTIVITIES

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THE CASE FOR SOLAR DOMESTIC HOT WATER

The classic solar domestic hot water pre-heating appliance is considered a mature technology in Canada yet is has barely scratched the surface of its market potential. This straightforward system can tackle 40% of the home's hot water bill in Canada and every home could have one. That potential has spurred many demonstration programs proving the technology reliable and functional so why aren't they selling?

System Description

A typical residential solar hot water heater usually consists of 6 sq m of glass covered solar collectors (two 4'x8' solar panels), a storage tank of about 450l (120 gallons), a pump and solar controller and insulated piping. Current plumbing codes in BC require a double walled heat exchanger (dumb rule that needs to be changed) and backflow prevention as well as leak detection all adding to the costs. Water is pre-heated on its way to a hot water tank reducing the work the hot water tank has to do.

The Numbers

If we look at solar radiation data for Toronto or Vancouver we find that there is about 30 GJ of solar energy available on a 6 sq m surface facing the sun each year based on typical weather data. In BC solar domestic hot water heaters generally are displacing natural gas and natural gas is cheap! The cost of natural gas as of March 2012 is $10.4/GJ including the carbon tax soon to be $30/tonne. The Energuide top rated hot water tank is 67% efficient including standby losses so for comparison to solar heated water the cost of natural gas in mainland BC is $10.4/.67= $15.51/GJ if you have the top of the line most efficienct hot water tank. A solar domestic hot water heater that is 6 sq m in collector area can collect $465 worth of energy in natural gas dollars/year if it collects 100% of the solar radiation that is available. It is impossible to do better because that is all that is available. Actually its not "impossible". If the air is warmer than the water being heated in the collector and the collector is not insulated as in the case of an unglazed swimming pool heating type solar collector the collector can collect the solar radiation plus heat from the air itself for an efficiency greater than 100% but that's not going to happen in the case of the higher temperature collectors typically specified for this application. So what portion of what is available can we expect to collect? You have to remember that in BC there is a lot more solar radiation available in the summer compared to winter and many days the solar tank will be fully heated up and solar will shut off because the high temperature limit is reached. There's no way anyone can expect any solar device to collect 100% of what is available. Typical operating collector efficiencies are no better than 75% over their operating range in this application. We believe 50% is optimistic. If one of these systems collects and delivers 50% of the solar resource that is available then it saves $233/year against natural gas in BC (lower mainland prices) at 2012 prices.

These systems sell for $14,000 in an immature market (Canada) down to as little as $5000 after rebates and incentives (of which currently there is very little available). We've seen bulk purchases where the installed cost gets down to $8000 before incentives. If you can buy one for $8000 installed then you can expect a simple payback period of 34 to 64 years based on an expected savings of $124-233/year. We would expect the price to come down to the $5000 level if the market was stronger. That would get the simple payback down to 21-40 year range. Where natural gas is double the cost as in many regions of BC including Colwood BC where a major demonstration program is underway the payback improves by a factor of 2. In BC electricity is $0.10/kwhr or more and rising. This translates to $28/GJ equalling the effective energy cost of natural gas at Colwood BC. Against fuel or electricity at this cost it becomes possible to finance the capital cost with the energy savings. We haven't included any maintenance costs but these are fairly minor. We also have not included any environmental considerations. These are not so minor.

The Case for Solar Hot Water

We can't often make a solid case for residential solar hot water heating based on the energy savings numbers alone in regions with the lowest natural gas prices. At the low price of natural gas today that should not come as a surprize to anyone. We are mortgaging the future of the planet to allow us to pig out on cheap energy today. Proponents of solar thermal hot water systems for the home should not apologize for the reality of the numbers. The fossil fuel industry and the government should be apologizing for using our atmosphere as a free dumping ground for the carbon and pollutants directly resulting from the burning of fossil fuels.

Realistic Solar Thermal Markets in Canada Without Incentives

What is happening is municipalities are deciding to reduce their footprints themselves but municipalities have to justify their tax dollar investments to their constituents. It comes down to what value is placed on the carbon and other pollutants. In BC the carbon is $30/ tonne. Experts have cited that the carbon tax needs to be $150/tonne to affect any real change. In natural gas dollars $30/tonne represents about $1.50/GJ. Its about 15% of what we currently pay in BC. If we consider the value of the carbon or the environmental cost of the carbon to really be $150/tonne then we can add 75% to the cost of the natural gas. Now we're at a 16-32 year payback potential for our example residential system of 6 square meters of solar collector and 120 gallons storage at the bargain price of $8000 installed. In regions on electricity or higher natural gas costs like Vancouver Island the payback drops almost in half and solar looks quite attractive.

We can do large scale solar hot water systems at better than a 15 year payback period when the loads are huge. Huge loads mean we can do all our work at the low end of the temperature range where unglazed solar collectors are more efficient and far less expensive as in this 2011 installed solar hot water heater pre-heating 16 showers at the Minoru Aquatic Center in Richmond BC. 15 years seems like a long payback but the typical solar thermal investment has been closer to 50 years at best historically and 15 years is a payback where the capital cost can be financed with the energy savings and the end result is an awful lot of carbon reduction at no cost to the taxpayer.

Solar DHW Preheater Conclusions

In conclusion solar dhw can be justified on the numbers in BC even without a significant price tag for carbon but against low cost mainland BC natural gas costing $10.4/GJ its not easy. We need to go even further to justify this. We need to look at what governments have done and continue to do to support the natural gas industry. They take all the risk of exploration away. The thinking is that we all need cheap fuel to finance our growing economy. When you add all these factors together it does justify the decision to solar heat your hot water. Check out our facebook page for what we're doing in solar thermal today. We can set you up to be sustainable but we're not going to sugar coat anything so don't waste your time. Its not magic. If fossil fuels cost included what it would cost to put the carbon back in the ground we'd have a huge solar industry. Instead here in BC we focus on natural gas and as a result we sacrifice a sustainable future.

A typical evacuated tube style solar hot water heating solar panel

A large scale solar hot water system using low cost low pressure evacuated tubes

Solar hot water heaters belong on every rooftop

Hot Sun employee Pat Welish works on an old boxed and glazed solar heater