CANADIAN RESEARCH and DEVELOPMENT ACTIVITIES

Phone: 778 300 1803

info@powerstripsolar.com

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! If natural gas costs $10/GJ and the hot water tank is 70% efficient and we displace 40% of the load then the annual savings are $171

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 46 years. That's why conventional old school solar thermal using expensive boxed and glazed and evacuated tube type collectors is DEAD! It took forever for this basic reality to set in as governments and NGO's pushed and pushed for more and more incentives to do solar dhw.

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 but in many regions energy is a lot more expensive, there's more sun but not in BC. Not yet.

Realistic Solar Thermal Markets in Canada Without Incentives

We can do large scale solar hot water systems at better than a 10 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.

Today (2023) the focus seems to be on electrification and heat pumps are being toutaed as the holy grail BUT the heat pump industry isn't being too forthcoming with their actual numbers. Try to look up the effect of humidity on COP for any heat pump of any kind. You'd think there would be some transparency there. Does it make sense to tun a heat pump (for pool heating or air conditioning) from photovoltaics? No it doesn't. Here is a blurb on that topic on our US web site. In California this question comes up a lot because the roof space is dominated by PV

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