Solar Tubes - options

[contadino]

There are big problems with putting solar heating systems on the roof. The weight(especially for a hot water system), the possibility of roof leaks, the lack of accessibility for maintenance, the inability to change the angle of the collector with the seasons, and the costs involved with installation. That's also assuming you have a section of roof which is oriented in the proper direction.

You would be better off with a collector that's at ground level, for all of those reasons. It can run directly into the side of the house (or basement). You can always plant a line of bushes along it to hide it from view. You could also do the installation yourself when the system is at ground level, instead of using an expensive roofing contractor.

Another advantage of having the panels lower than the tank is that you can use a thermosiphon to get the circulation. No pump maintenance, no worries about powercuts on sunny days, no running costs....

[JakeR]

I looked at the sales page that began this post. It describes an evacuated tube system, but I didn't see anything that looked special about theirs.

In general evacuated air collectors are more efficient and heat the water to higher temperatures. The vacume in th4e tube insulates the same way a vacuum thermos bottle insulates so more heat is retained.

I take issue with the idea of doing without a tank. Most of us would like to be able to take warm showers when the sun isn't shining.

Solar hot water generally has reasonably short payback times so I think it's wise to consider money spent on it as an investment that will be returned. Look for dealers in your area who have clients that have been living with their systems for a few years that you can talk to.

Unless you're completely committed to a zero carbon footprint, I'd look for a system with a storage tank and back-up heating.

[solarcooker]

I looked at the sales page that began this post. It describes an evacuated tube system, but I didn't see anything that looked special about theirs.

In general evacuated air collectors are more efficient and heat the water to higher temperatures. The vacume in th4e tube insulates the same way a vacuum thermos bottle insulates so more heat is retained.

I take issue with the idea of doing without a tank. Most of us would like to be able to take warm showers when the sun isn't shining.

Solar hot water generally has reasonably short payback times so I think it's wise to consider money spent on it as an investment that will be returned. Look for dealers in your area who have clients that have been living with their systems for a few years that you can talk to.

Unless you're completely committed to a zero carbon footprint, I'd look for a system with a storage tank and back-up heating.

Good point. You need an expansion tank with a recirculating water system anyway, right? It might as well be big enough to store at least some heated water. Could a regular water heater be used, somehow, for an expansion tank, storage, and backup heat source?

[swiftnick]

I installed a 20 tube system in 2007 and then added a further 20 tubes in 2008. Total cost DIY was about £1150 with about 5 days labour involved (this years staycation )

Mounted on the gable end as this is the south facing side of house (see picture)

Pressurised the system using a expansion vessel and filling kit. I recommend pressurising - they perform much better than the pressure provided by a header tank.

I reckon the system will reduce gas consumption by about 3200kwh. My gas bill for August to October was £18!

[xone]

I installed a 20 tube system in 2007 and then added a further 20 tubes in 2008. Total cost DIY was about £1150 with about 5 days labour involved (this years staycation )

Mounted on the gable end as this is the south facing side of house (see picture)

Pressurised the system using a expansion vessel and filling kit. I recommend pressurising - they perform much better than the pressure provided by a header tank.

I reckon the system will reduce gas consumption by about 3200kwh. My gas bill for August to October was £18!

Hi swiftnick, just a query. How come you didn't put both the panels on the roof, one east, one west? You'd have tracked the sun as it went over your house and you'd still have the same efficiency. Not that there's anything wrong with what you've done.

[Big Al]

I installed a 20 tube system in 2007 and then added a further 20 tubes in 2008. Total cost DIY was about £1150 with about 5 days labour involved (this years staycation )

Mounted on the gable end as this is the south facing side of house (see picture)

Pressurised the system using a expansion vessel and filling kit. I recommend pressurising - they perform much better than the pressure provided by a header tank.

I reckon the system will reduce gas consumption by about 3200kwh. My gas bill for August to October was £18!

this is what is putting me off solar thermal because for the same period as you quote £18 for my gas was only £37 so for me to spend that amount of money means a long payback time. Still more power to your plans for actually doing it.... I widh I had the spare capital to do it also.

big al.

[xone]

I installed a 20 tube system in 2007 and then added a further 20 tubes in 2008. Total cost DIY was about £1150 with about 5 days labour involved (this years staycation )

Mounted on the gable end as this is the south facing side of house (see picture)

Pressurised the system using a expansion vessel and filling kit. I recommend pressurising - they perform much better than the pressure provided by a header tank.

I reckon the system will reduce gas consumption by about 3200kwh. My gas bill for August to October was £18!

this is what is putting me off solar thermal because for the same period as you quote £18 for my gas was only £37 so for me to spend that amount of money means a long payback time. Still more power to your plans for actually doing it.... I widh I had the spare capital to do it also.

big al.

This is true, but what if he has a familiy of 4 and his original bill was £45 + a month??

[Odsox]

this is what is putting me off solar thermal because for the same period as you quote £18 for my gas was only £37 so for me to spend that amount of money means a long payback time. Still more power to your plans for actually doing it.... I widh I had the spare capital to do it also.

Yes me too. I got all enthusiastic a few months back until I did the maths.
My hot water is by immersion heater on off peak supply and going through a year's bills I found all my HW costed me €90.
It would ever so many years for a solar system to start paying it's way, even with no backup for cloudy days.
Nice eco friendly idea, but there are better ways to spend my limited funds.

[Green Aura]

I've just discovered that where I live doesn't have the infrastructure to send electricity to the grid. We've just had plans for a village wind farm shelved because of this.

So, my question to all you knowledgeable bods out there is - can we still have pv leccy and how do you work out how much storage capacity (batteries) you'd need? I know it must be do-able because off-gridders do it.

I hope that makes sense because I've just confused myself writing it!

[Annpan]

You don't need to sell excess back to the grid anyway (the prices are ludicrous, something like 0.5p a unit ) You just need a bank of 12v batteries, like a cupboard of car batteries...

Someone much more knowledgeable will be along in a minute... I'll shut-up now.

[Odsox]

I'll shut-up now.

It's even better here, first you need a certificate which cost €100 three or four years ago, so almost certainly a lot more now.
Then they will connect you to the grid.
Then you can feed any amount of electricity ... FOR FREE i.e. they won't pay you anything at all.

You're right Ann, batteries are the way to go, but that's what makes it unattractive as the batteries cost an arm and a leg and only have a lifetime of 4 or 5 years.

[Big Al]

I'll shut-up now.

It's even better here, first you need a certificate which cost €100 three or four years ago, so almost certainly a lot more now.
Then they will connect you to the grid.
Then you can feed any amount of electricity ... FOR FREE i.e. they won't pay you anything at all.

You're right Ann, batteries are the way to go, but that's what makes it unattractive as the batteries cost an arm and a leg and only have a lifetime of 4 or 5 years.

I'm lucky in that respect because in england we can export to the grid via the power companies. There is currently a lot of fighting between the companies for micro generators such as us. Generally the power companies will instal an import / export meter free of charge then every six months you give them the readings and they work out the bills. Some will allow you to cash in the roc's and pay a cheaper price per unit or others will keep the roc's and pay a higher price per unit. The uk governmnet has in April of this year recently shelved plans for a large payment scheme where power companies are made to pay micro gnerators something like 40p per unit.
Sfter a lot of whinging by a lot of people it is back in the new energy bill so if it comes off this would make PV panels more cost effective and shorten the payback time because me for instance would use electric at 11p per unit and sell it for 40 p per unit.