I've looked into solar water heating several times recently for my home but, for me at least, the costs just don't balance up at the moment.

Based on my gas bills and research I've read online, I estimate that I currently spend around £170-£190 per year heating water in our home. The lowest quote I've had so far for a solar heating system which will, to quote the installer, "provide 'most' of my hot water needs" was around the £3700 mark. This gives me, at best, a pay-back time of roughly 19 years before I start to get my "free" hot water.

I guess as solar technology develops, and demand for this technology grows, we'll hopefully see prices come down but for the time-being at least, while I'd really love to be harnessing the world's natural energy resources rather than paying my monthly gas bill, it just doesn't financially stack up for me.

As you correctly conclude, solar water heating is too expensive to make financial sense. I hope all elderly and vulnerable people get this point, so that they won't be confused by sales talk into spending their hard-earned money.

A friend has solar water heating. It does work, even in winter, but he would have have been better off putting his money in a building society - the savings he gets are minuscule. For one thing, they only work during daylight; that may be obvious, but it means they will only provide hot water during daylight hours.

Also, though they do work, you will never heat your home with one - they will provide some, but by no means all, of your hot water requirements, and will draw some electricity that must be factored into the running costs.

For what they are, I can't see why they cost so much. They comprise black tubing, simple pipework, a couple of electric pumps, basic electronics and water mixed with anti-freeze. How can suppliers justify thousands of pounds for this? Smoke and mirrors.

Don't forget that energy prices are currently on the increase. If you make a one-off investment, that is also a fixed cost and every year you are likely to be saving more.

If you take your lower rate (170) and take the current government rate of inflation - 3%, £170 is the equivalent of £250 by 2020 and by 2023 you will have spent £3700 almost exactly. So 15 years is a fair maximum.

If we take your upper rate and assume inflation of 6%, you pay off by 2020 - only 12 years. Even 6% isn't exactly run-away inflation. With current market conditions, higher rates could be possible. The following shows rates of 15% between 2002 and 2006 (hope my maths is right!) here. That rate continuing would give you pay back by 2017 (assuming £170 level)!

Alan mentioned savings accounts. You will probably never get more than 2% real interest in a cash savings account. Inflation of energy prices is almost guaranteed to be higher than this.

On balance, I think the financial viability will increase exponentially every year as energy prices increase and technology costs fall. Meanwhile, technology should improve making the devices more efficient.

That's not even mentioning the environmental benefit. Has anyone considered ground-source heat pumps? That solves the daylight problem.

By the way, I'm not a solar-hot-water salesman although this started to sound like a sales pitch!

Henry