Solar Panels to heat house - For Beginners

prospect

Hi All,

Now before anyone gives out to me, I have looked at old threads on this, and on the internet and I have to say they have confused me even further, so please go easy on me.

I have a 3 year old house that is 290sqM. By floor space it is 50% UFH and 50% rads. It is currently heated by an oil bolier.

I would love to install as much solar panels as possible to provide hot water for both the taps, and the UFH/Rads. I understand that I will need to keep the oil to boost the heat, but I currently only heat to about 60oC anyway.

I have a large roof that is S-S-W facing. It is a hipped roof and is 9.5m long at the top, and 13.5m long at the bottom. It is 3.8m from the ridge to the gutters and is a 40 degree pitch.

Is it feasible? What product should I be looking for. Whom should I be talking to?

Thanks.

hotlips_h

prospect. I'm interested in the answer to this too as it's related in a way to my problem.

We are just about to install 4m2 solar evacuated tube panels for hot water on a west-south-west facing roof. We also want to run one towel heater in a new bathroom off solar. Even if it only heats up in the summer, that's fine. We just want it to dry towels in the summer when the other heating is off. We're happy to put 2 towel heaters in the bathroom, one run off the normal heating (gas boiler & radiators) and one run off solar, if that's necessary.

I'm being told that it's not really feasible as we might just end up with lukewarm water in the cylinder if we heat a radiator on the way from the panel to the cylinder. (I'm talking to Glas, who sell Thermomax panels and are based in Kilkenny.) Now, this does not make a huge amount of sense to me.

So, I'm wondering if anyone has done this?

air

I think that this is a feasible if expensive option.
The way to go about it would probably to install a large insulated thermal store (a very large water tank) that has twin coils in it.
You could use normal thermal controllers to control the flow from the panels to the store and route your central heating loop through the second coil.
By placing panels in series you could probably attain a temperature in the store of whatever you want to run through your heating system (60 - 70 degrees?) although you would have to be careful to design within the operating limits of the panels / tanks etc.

Assuming you were aiming to heat the water from 10degrees (incoming) to 70 degrees (for heating system), then you would need approximately 10.7 litres of water storage for every kilowatt hour of solar energy that you want to capture in the day and release at night.

As far as I know a 20 tube solar panel is rated around 2Kw.

Now, by combining those figure, the number of sunshine hours per day at your location and the figures on your energy consumption you should be able to calculate:
a) How many solar collectors you need
b) How large your insulated storage system needs to be

NB. I'd multiply the 10.7 figure by 1.5 to account for system losses and because it will allow you a bit of overhead.

Bear in mind though that your peak heating load is likely to be in the winter months when the sun doesnt shine very much! You will still need a backup for those days.

air

Just read this on the ecologics site (which incidentially is the most impressive commercial Irish renewable energy site I've come across)
"Although solar space heating is great for solar panel sales, we aren’t pushing it as an option. It works best when you need it least. Unless your house is one which requires some heat all through the summer, to get enough panels to give meaningful heat in the winter will require a huge heat dump for surplus heat in the summer. We doubt it is worthwhile in most cases.
"
From (http://www.ecologics.ie/grants/)
I'd tend to agree with them.

On the other hand there is some info on annualised heat storage here - http://www.earthshelters.com/Index.html a little on the extreme side though.

prospect

Thank you for the information and that link.
I appreciate the time and effort you put in to help me.

Fergus Wheatley

Hello,

With regard to the amount of power a solar panel produces. I have installed quite a few systems and my favourite in terms of price and amount of hot water the customer gets is a 2 x 24 tube panels + 210 litre insulated tank. The panels drive the tank way over 60C on a hot day (so a dump rad is needed), and provide good hot water even on crap days. Anyway please see attached for the simulated outputs.

If anybody wants to email me for docs on solar space or water heating I will gladly send information on. (too big for forum rules)

Fergus
www.alliedsolar.ie

prospect

Sorry, but what is a 'dump rad'?

Is this a radiator that is left switched on, like in a hotpress?

air

Its a radiator that is connected to the output from your solar panel (s).
A controller determines when the heat store has reached capacity and then opens a valve to direct the excess heat to the radiator.
Its a regulation mechanism to prevent damage / danger from over heating/pressure caused by gathering more energy than your tank can store.
For example if you had one hot day that you were away from your house and your tanks were at peak temperature, they might over heat the following day if the water wasnt used. The controller senses this situation and directs the excess heat to the radiator instead of the tank.

derekhandforth

I have UFH/3 towel rads powered by a Gerkross 30KW woodpellet boiler, and intend to use solar to supplement this.

I have just purchased a 750 L buffer tank from solar energy Ireland in Sligo. http://www.solarenergyireland.com/ This is a direct cylinder with a tank within a tank for DHW. The DHW inner tank is 200L. The boiler will heat the outer tank directly (ie no coil) which is the most efficient method, which in turn heats the inner DHW. This arragement is the most suitable for solar DHW rather than heating coils or flat plate heat exchangers which both require the entire buffer tank to be nearly full before give decent DHW. The bottom of the tank has a solar coil.

I am going to put 3 * 30 Navitron 47mm tubes up to supply this. In summer this should give me all the DHW I need and supply some energy during the winter months.

As the DHW mixing valve is set to 50 deg C and the UFH runs at 45 deg C I only need the tank to be at 55 deg C with a weekly boost to 60 deg C to prevent legionella. Any excess energy is supplied by the woodpellet boiler.

Some people argue that this is overkill as I will have too much heat in the summer which I will have to dump. This is true, but it can be dumped through the 3 towel rads, and as it is free energy it is not wasteful. The opposite side of the story is that it will give some support to the UFH during the winter months as the operating temperatures are low.

I would rather dump free energy during the summer and have the benefit of free space heating in the winter!

Irish_Army01

Here is another Renewable Energy Site that has every Alternative energy available.

badmanjam

Anyone interested in Renewables like solar hot water and Wood Pellet boilers should check out Donabate Bathroom & Heating Centre or www.dbh.ie. They have a full working Pellet Boiler in their showroom along with solar and cylinders...Well worth a visit if considering it. Got the whole job myself and now getting 65% of my hot water for free !!