ᐅ Roof with photovoltaic system or alternative investments – experiences?

Hi,

I am currently planning to renovate our 29-year-old house. Apart from recurring maintenance work, no major modernization measures have been carried out so far. We have insulated the walls ourselves in the past, but nothing else.

This means the house:
- still has the original roof
- the original gas heating system
- the original windows on the ground floor

What is already decided and will be done in late summer/early autumn is a roof renovation according to KFW standards. The roof will be completely rebuilt and insulated.

Additionally, I have budgeted around 13,000 euros for a photovoltaic system. However, I am still unsure how practical installing a photovoltaic system really is. The company I am in contact with recommended using the electricity ourselves and feeding the surplus into the grid. My initial thought was to include a storage system to use electricity at night or during bad weather. The location would actually be ideal for a photovoltaic system, as our roof faces southeast.

That’s why I am now considering whether I should invest the money in a new heating system instead. Our heating has been in use since the house was built and has never caused any problems. However, I believe that new gas boilers operate more efficiently and should reduce gas consumption (hopefully). I would probably also have a bit of extra money left over to possibly replace some radiators, if that can contribute to better efficiency...

Maybe you have some advice or would like to share what you would do.

Regards

I'll start. Not too much on the technical side. A new gas boiler, I think that’s a good idea. New radiators – why? Or are the old radiators heavily rusted? New Danfoss thermostatic valves, yes, those make sense. Those valves tend to close poorly over time. Photovoltaic panels are a waste of money; better insulate the side walls and roof. The house is about 30 years old, so from 1987–1988. Are all the windows still in good condition? Are the roof tiles intact? Is the base waterproofing still sound? Karsten

Have an energy consultant develop a concept.

Advice: The gas boiler has potential since it doesn’t have condensing technology yet, right?

Photovoltaic panels can also provide a return, but as always, it depends heavily on the purchase price. Storage systems are more of a hobby; even with a lot of effort, they’re not very efficient.

Photovoltaic systems generally are not a waste of money. This is more often the case with thermal systems.

The gas boiler might need to be replaced. However, I would first try to optimize the existing one. Heating behavior, settings, and insulation can make a big difference here.
Since you still plan to work on the roof, I would also mention the windows. Additionally, thermal bridges like roller shutter boxes, for example, should be considered.
I would avoid changing the radiators for now.
My approach would be to insulate whatever is possible first (basement ceiling?) and only at the very end install a suitable gas boiler if the old one breaks down.
Without more detailed information, a ground-source heat pump might also be an option. But that’s just speculation.

After the first paragraph, I would have said: Insulate the roof! But you’ve already done that.

Yes, I agree with the previous comments:
- Check the gas boiler and replace it if necessary
- Use electronic thermostats
- Check the windows and replace them if needed (from this point onward, don’t proceed without consulting an expert to avoid moisture or mold issues)
- Assess the overall condition of the house and determine what else needs to be done now or within the next few years

I would consider the photovoltaic system purely as an investment. Honestly evaluate the (personal time) effort involved and the concentration risk. Personally, I would probably invest in a broadly diversified stock ETF and skip the photovoltaic system. But your situation might be different...

Photovoltaic systems become more worthwhile the more of the generated electricity you can use yourself. Heat pumps and electric vehicles complement this well. Gas heating and combustion-engine cars less so.