Hello,
I want to have a house built— a single-family home with 112m² (1,206 sq ft) of living space. I assume that, according to the 2009 Energy Saving Ordinance, all houses are very well insulated. Since I’m not a fan of throwing my money away to big energy companies, the house will be equipped with an air-to-water heat pump, a ventilation system with heat recovery, and a photovoltaic system on the roof.
My simple thinking is this: the photovoltaic system generates electricity, the air-to-water heat pump uses electricity, and the ventilation system helps prevent mold and, because it operates with heat recovery, I won’t need as much electricity to keep the house warm.
I’m open to being convinced otherwise!
Best regards
I want to have a house built— a single-family home with 112m² (1,206 sq ft) of living space. I assume that, according to the 2009 Energy Saving Ordinance, all houses are very well insulated. Since I’m not a fan of throwing my money away to big energy companies, the house will be equipped with an air-to-water heat pump, a ventilation system with heat recovery, and a photovoltaic system on the roof.
My simple thinking is this: the photovoltaic system generates electricity, the air-to-water heat pump uses electricity, and the ventilation system helps prevent mold and, because it operates with heat recovery, I won’t need as much electricity to keep the house warm.
I’m open to being convinced otherwise!
Best regards
S
Slimjim8115 Oct 2011 14:48Hi,
It’s clear that you can’t reduce additional costs like operating expenses to zero, but the goal—at least I think this applies to everyone—is to keep operating costs as low as possible.
So, I tried to calculate some average values.
A photovoltaic system with 23m² (248 square feet) of module area and 30 kWp (peak power), facing south with a roof pitch of 45°, is expected to generate around 2700 kWh per year. At 25 cents per kWh, that equals €675.
If you both feed electricity into the grid and consume electricity from it, you pay 16 cents per kWh but also receive 25 cents per kWh for the feed-in. However, if electricity flows only in one direction (1. feed-in / 2. consumption), then you either get 25 cents for feed-in or pay 25 cents for consumption.
An average household of three people consumes about 3200 kWh per year. At 25 cents per kWh, that amounts to €800 annually.
The air-to-water heat pump consumes on average 5000 kWh. At 16 cents per kWh, that costs €800.
Summary:
€800 for the heat pump
+ €800 for household electricity
= €1600
- €675 credited from the photovoltaic system (feed-in earnings)
= €925 annual electricity cost,
which is about €77 per month.
Would this theoretical calculation be correct?
If anyone has real figures, an example would be appreciated.
Best regards
It’s clear that you can’t reduce additional costs like operating expenses to zero, but the goal—at least I think this applies to everyone—is to keep operating costs as low as possible.
So, I tried to calculate some average values.
A photovoltaic system with 23m² (248 square feet) of module area and 30 kWp (peak power), facing south with a roof pitch of 45°, is expected to generate around 2700 kWh per year. At 25 cents per kWh, that equals €675.
If you both feed electricity into the grid and consume electricity from it, you pay 16 cents per kWh but also receive 25 cents per kWh for the feed-in. However, if electricity flows only in one direction (1. feed-in / 2. consumption), then you either get 25 cents for feed-in or pay 25 cents for consumption.
An average household of three people consumes about 3200 kWh per year. At 25 cents per kWh, that amounts to €800 annually.
The air-to-water heat pump consumes on average 5000 kWh. At 16 cents per kWh, that costs €800.
Summary:
€800 for the heat pump
+ €800 for household electricity
= €1600
- €675 credited from the photovoltaic system (feed-in earnings)
= €925 annual electricity cost,
which is about €77 per month.
Would this theoretical calculation be correct?
If anyone has real figures, an example would be appreciated.
Best regards
R
ralph1234521 Nov 2011 13:04Forget that approach. You are overlooking the initial investment costs. What good would it do you to have operating costs of zero if you had to invest hundreds of thousands for it?
The photovoltaic system generates income for you. (The electricity goes to the utility company, not to you). So, forget about your electricity consumption for a moment and consider the photovoltaic system on its own.
The photovoltaic system is a huge financial expense. Economically speaking, your investment in the photovoltaic system yields a return of about 5-7%, depending on subsidies, purchase price, and repair costs. You would have to look up the current figures. It is profitable, but the question is whether, as a homebuilder, you have that much money available to turn your roof into an investment asset. Usually, when building a house, people sell their assets to use the capital for construction.
As a power supplier, the system is not very useful to you, as mentioned, the electricity does not go to your appliances but to the utility. The electricity is produced in summer, mostly around midday. The air-source heat pump uses electricity when heating water, so in the morning and evening during bathing times, and for heating in winter. It’s not enough for cooking anyway. You would need batteries. Large ones...
If you want to save even more energy, then heat your water differently: geothermal heat pump or solar thermal system with heating assistance. But an air-source heat pump combined with controlled ventilation with heat recovery is already a very good approach.
More efficient appliances like a fridge, washing machine, induction stove, etc., also still offer potential.
The photovoltaic system generates income for you. (The electricity goes to the utility company, not to you). So, forget about your electricity consumption for a moment and consider the photovoltaic system on its own.
The photovoltaic system is a huge financial expense. Economically speaking, your investment in the photovoltaic system yields a return of about 5-7%, depending on subsidies, purchase price, and repair costs. You would have to look up the current figures. It is profitable, but the question is whether, as a homebuilder, you have that much money available to turn your roof into an investment asset. Usually, when building a house, people sell their assets to use the capital for construction.
As a power supplier, the system is not very useful to you, as mentioned, the electricity does not go to your appliances but to the utility. The electricity is produced in summer, mostly around midday. The air-source heat pump uses electricity when heating water, so in the morning and evening during bathing times, and for heating in winter. It’s not enough for cooking anyway. You would need batteries. Large ones...
If you want to save even more energy, then heat your water differently: geothermal heat pump or solar thermal system with heating assistance. But an air-source heat pump combined with controlled ventilation with heat recovery is already a very good approach.
More efficient appliances like a fridge, washing machine, induction stove, etc., also still offer potential.
M
Micha&Dany22 Nov 2011 06:06Hello
Well, the numbers are not quite correct:
(1) With 23m² (248 sq ft) you definitely can’t reach 30 kWp – 3 kWp is much more realistic (depending on the modules used)
(2) There is no such thing as “maximum something” in photovoltaics – the “limits” are the available area and the available budget – nothing else 😉
(3) How much electricity you can generate with a certain system size depends mainly on your location. Here in the Ruhr area you can assume about 850 kWh/kWp (which means on average 2550 kWh/year for a 3 kWp system), in Munich you can expect around 980 kWh/kWp (= 2940 kWh/year). The feed-in tariff in 2011 is 28.74 cents/kWh (= 733 euros/year in the Ruhr area / 845 euros/year in Munich)
16 cents? Where do you still get electricity at this price?
Here we pay 21 cents and have already received notification that electricity prices will increase again starting 1.1.2012...
😕
Yes, this calculation is roughly correct. What is missing: self-consumption.
You have the option to use the electricity you generate yourself. If you consume up to 30% of your own generated electricity, you get 12.36 cents per kWh for that, and if you use more than 30% yourself, you get 16.74 cents.
Whether self-consumption regulations pay off depends on your individual situation. For us, very little electricity is used during the day because nobody is at home. However, if you have a home office and work during the day, your daytime consumption will be higher… So simply analyze your own usage behavior.
You can find an example profitability analysis here as well:
https://www.hausbau-forum.de/solar-energiefragen/4781-Viebrockhaus-haus-photovoltaikanlage.html#post28568
@Gartenbau:
What do “zero” operating costs mean for me? Well, if I have to spend 100 euros per month on energy (electricity, heating) and my photovoltaic system brings 100 euros per month into the account but cost me 10,000 euros, then the system pays for itself after 8.3 years and from then on I start saving – namely 100 euros per month = 1200 euros per year
I find that very appealing 😀
Regards
Micha 😎
Slimjim81 schrieb:
Hi,
So I tried to calculate some average values.
The photovoltaic system with 23m² (248 sq ft) of module area and a 30kWp (maximum something), south-facing and 45° roof pitch is supposed to generate about 2700 kWh per year.
Well, the numbers are not quite correct:
(1) With 23m² (248 sq ft) you definitely can’t reach 30 kWp – 3 kWp is much more realistic (depending on the modules used)
(2) There is no such thing as “maximum something” in photovoltaics – the “limits” are the available area and the available budget – nothing else 😉
(3) How much electricity you can generate with a certain system size depends mainly on your location. Here in the Ruhr area you can assume about 850 kWh/kWp (which means on average 2550 kWh/year for a 3 kWp system), in Munich you can expect around 980 kWh/kWp (= 2940 kWh/year). The feed-in tariff in 2011 is 28.74 cents/kWh (= 733 euros/year in the Ruhr area / 845 euros/year in Munich)
Slimjim81 schrieb:
At 25 cents/kWh this means 675 euros.
If I both feed electricity into the grid and draw electricity from the grid at the same time, I pay 16 cents/kWh, but also get 25 cents.
16 cents? Where do you still get electricity at this price?
Here we pay 21 cents and have already received notification that electricity prices will increase again starting 1.1.2012...
Slimjim81 schrieb:
But if the electricity only flows in one direction (1. feed-in / 2. consumption) I get either 1. 25 cents or 2. pay 25 cents.
😕
Slimjim81 schrieb:
A household of three people consumes about 3200 kWh on average. That’s 800 euros per year at 25 cents.
The air-to-water heat pump consumes on average 5000 kWh at 16 cents, which is 800 euros.
Summary:
800 euros heat pump
+ 800 euros household electricity
= 1600 euros
- 675 euros offset from the photovoltaic system (revenue from grid feed-in)
= 925 euros electricity costs per year
which is about 77 euros per month
Would this theoretical calculation be correct?
If anyone has data, an example would be helpful.
Best regards
Yes, this calculation is roughly correct. What is missing: self-consumption.
You have the option to use the electricity you generate yourself. If you consume up to 30% of your own generated electricity, you get 12.36 cents per kWh for that, and if you use more than 30% yourself, you get 16.74 cents.
Whether self-consumption regulations pay off depends on your individual situation. For us, very little electricity is used during the day because nobody is at home. However, if you have a home office and work during the day, your daytime consumption will be higher… So simply analyze your own usage behavior.
You can find an example profitability analysis here as well:
https://www.hausbau-forum.de/solar-energiefragen/4781-Viebrockhaus-haus-photovoltaikanlage.html#post28568
@Gartenbau:
What do “zero” operating costs mean for me? Well, if I have to spend 100 euros per month on energy (electricity, heating) and my photovoltaic system brings 100 euros per month into the account but cost me 10,000 euros, then the system pays for itself after 8.3 years and from then on I start saving – namely 100 euros per month = 1200 euros per year
I find that very appealing 😀
Regards
Micha 😎
Slimjim81 schrieb:
...The air-to-water heat pump consumes on average 5000kWh How do you arrive at that?? Both the demand and consumption depend on the specific individual conditions. With insufficient planning, the difference between demand and consumption is unfortunately much smaller than expected for air-source heat pumps. Only with precisely and thoroughly planned systems can you achieve an annual performance factor of about 3.5!Best regards.
Micha&Dany schrieb:
...You can also find an example of a cost-effectiveness analysis here:... There are entirely different issues underlying this that are hardly offset by optimistic assumptions about photovoltaic systems! Best regards
R
ralph1234522 Nov 2011 16:39Micha&Dany schrieb:
@Gartenbau:
What do zero operating costs get me? Well, if I spend 100 euros per month on energy (electricity, heating) and my photovoltaic system generates 100 euros per month in savings and cost me 10,000 euros, then the system pays for itself after 8.3 years, and from that point on, I start saving—100 euros per month equals 1,200 euros per year.
I find that very tempting 😀
Regards,
Micha 😎To achieve zero operating costs requires more than just a photovoltaic system. At least some heating method like a ground-source heat pump is needed. Those don’t come for free. The photovoltaic system that covers your entire electricity demand also requires more than just a few panels for 10,000 euros. You could practically cover your entire roof and fill your basement with batteries for the rainy season. The problem with renewable energy is that everyone believes that investing a few thousand euros will save a fortune. The opposite is true. That doesn’t mean it is bad. Ecologically, it can make sense. Financially, only rarely.
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