Solar Hot Water Systems

Sometimes I’ll get someone asking to write a guest post that starts off with “Hi, I’m a recent college graduate looking to expand my writing portfolio …” That’s translation for: “Hi, I work for a search engine optimization company writing blog posts for companies that have hired us to build back links to their site.” Most times the writing is generic and written with little understanding of our audience.

Today’s post is sort of like that. But in this case I sent it back to them for 3 revisions. They kept revising and sending back. Following is the result. Tell me what you think of it.

– Ranger Man


Solar energy is one of the buzz-phrases of the moment, and given the rising costs of fossil fuels, one of the most relevant to the man (and woman) on the street. Solar water heating systems are about the easiest way for people to get on the renewable energy band wagon; they’re not as expensive as they once were and the returns are remarkable. But, how do you know how big your system needs to be to meet your family’s needs.

The average person uses approximately 19.8 gallons of water per day (24 hours). To determine the size of the solar water storage tank you’ll need you simply multiply this by the number of people living in your house. A family of four would therefore need an 80 gallon tank – technically speaking they’ll only need 79.2 gallons but no one makes tanks to those incredibly specific specifications.

Some people recommend that you get a bigger solar water tank than you actually need. This is to ensure that you have an adequate supply of hot water on cold and overcast days. As costs increase with size this decision will depend entirely on your budget.

Solar hot water systems

There are several types of hot water systems available:

  • Thermosyphon systems rely on that old age tendency for hot water (or air) to raise and cold water (or air) to sink. In this system, the tank is always placed above the collector, so that it is always filled with hot water. As water cools it moves down a series of pipes, collects heat and rises back to the tank. The systems require very little maintenance.A 20-tube system for families up to seven people will require approximately 32 square feet.
  • Evacuated tubes are perhaps the most efficient solar collectors. The collectors comprise a row of glass tubes with all the air removed – hence the vacuum. The tubes collect heat, which cannot escape outward through the vacuum insulation, and is transferred via the heat-transfer liquid to the storage tank. They can get very hot, are highly freeze resistant and are therefore well suited to cold climates. Evacuated tube systems are more efficient per square metre, making them the system of choice where roof space is an issue. A 20-tube system will take up approximately 45.2 square feet; a 30-tube system will take up 67.3 square feet.

Generally speaking you’ll need a 20-tube system for a medium size family and a 30-tube system for large families.

  • Flat plate collectors are the kind people are most familiar with. They comprise a dark flat plate which absorbs heat, a transparent cover to limit heat loss, a heat-transport fluid, and insulated backing. In very cold areas where frost and snow are common, it’s recommended that homeowners get polymer flat plate collectors, as opposed to the traditional metal kind.A flat plate collector will need around 21 to 27 square feet.


The cost of solar water tanks is decreasing as systems are more in demand across the United States, not to mention the rest of the world.

Currently, you’ll pay anything from $700 for an 80 gallon tank to $4000 for a 200 gallon tank.

(Much bigger tanks, edging into industrial size, such as 1000 gallon tanks go for around $20 000).

Evacuated tubes: tubes for medium families cost between $470 and $650. Kits for medium sized families cost around $1800.

Thermosyphon systems: a system for four people will set you back roughly $1600.

Flat plate solar collector: costs in the region of $1200.

It’s possible to buy kits complete with collectors and tanks for around $5000.

Pay back

By and large, solar water heating systems should meet between 80% and 100% of your household’s hot water needs. This equates to savings of between 50% and 80% on your heating bill.

The pay back period – the time it takes to recover the initial cost of the system – should be between two and three years.

After that your hot water is absolutely free. Or almost, as there will occasional maintenance costs, but these are miniscule compared to what you would have been paying for on-grid energy.

Increase savings

You can maximise the amount of money and energy you save by the way in which you install your solar hot water system.

You need to orientate your solar collectors (panels) so that they catch the most sun. You should also tilt your collectors at an angle to truly get optimum solar coverage. This is even more important in winter, when the number of daylight hours decreases.


Written by Sandy Cosser. Sandy writes for a range of online publications relating to green energy and solar water heating.
Image by mydogivana Attribution Creative Commons 2.0 Generic (CC BY 2.0)