extc2020
2014-11-07 15:07:17
- #1
Hello dear forum!
I am planning a new build of 140 sqm (KfW 70 heating demand) and wonder if this would be possible.
In the center of the ground floor of the house, there should be a wood stove with 8 to 10 kW. (Coal + wood)
It stands in the 3-meter-wide passage to the 40 sqm living room and can optionally be separated from the hallway with a ceiling-mounted sliding door (no step), so that the heat from the stove can be varied and partially reach upstairs through the hallway and also distribute throughout the entire ground floor.
Additionally, convector heaters (electric) should provide base heat if needed.
Hot water:
Instantaneous water heater with a small upstream storage tank that preheats the drinking water in winter and heats it up to the maximum supply temperature of the instantaneous heater when there is a lot of solar power.
KfW and the Energy Saving Ordinance 2009
will probably throw a wrench in the works, even though I would only need about 700 kWh heating electricity from the grid, produce electricity myself, and use coal and wood with an efficiency of at least 85 percent. Maybe you have an idea how my plan could still work without losing sight of the financial aspect.
If needed, you can read at the end of my explanations how I arrive at which numbers.
Plan:
Electric heating + wood stove (just for comparison)
or
Electric heating + photovoltaic system + wood stove (priority 1)
Calculation:
9000 kWh total demand
6300 kWh heating demand
700 kWh hot water heating (approx. 2 kWh per day per year)
2000 kWh household electricity
Heating period from around October to April: 180 days
(Heating demand: 6300 kWh : 180 days heating period = 35 kWh per day)
Electric heating + photovoltaic system + wood stove:
9000 kWh total consumption
minus 1350 kWh self-consumption in the heating period (photovoltaic system)
minus 1000 kWh self-consumption household electricity (photovoltaic system)
9000 kWh - 2325 kWh = 6650 kWh remaining demand
minus 1000 kWh household electricity to buy at 25 cents = 250 euros
minus 700 kWh x 25 cents (20 days electric heating absence + water + buffer) = 200 euros
minus 4950 kWh from stove (wood I have for free) coal = 270 euros
Costs of 720 euros per year + photovoltaic system 1200 repayment - 300 euros profit
1920 euros total costs – 300 euros income = 1620 euros total costs per year
135 euros per month
Gas heating + wood stove
9000 kWh total consumption
2000 kWh household electricity purchase: 2000 x 0.25 = 500 euros
7000 kWh gas x 8 cents = 560 euros
2000 kWh wood x 8 cents = minus 160 euros
Tank rental yearly = 135 euros
Maintenance yearly 100 euros
1135 yearly : 12 = 95 euros per month
For comparison: (but I do not want this)
Electric heating + wood stove
9000 kWh total consumption
minus 5000 stove = coal 270 euros
4000 kWh x 0.25 euros = 1000 euros
1270 euros per year : 12 = 105 euros per month
Gas heating system 12,000 euros/electric heating 4,500 euros
7,500 euros that I would have to “burn” first.
Gas heating would save me 120 euros per year
1,200 euros in 10 years
4,800 euros in 40 years
Result
I pay 40 euros more every month than with gas for 10 years and have then paid off the photovoltaic system.
10 years x 12 months x 40 euros extra costs = 4,800 euros
(System loan KfW for 11,000 euros at 1.55 percent)
After 10 years
I assume gas and electricity rise equally and therefore keep the numbers.
Ongoing costs with electric heating + photovoltaics per year =
720 euros - 300 profit - 100 euros taxes = 520 euros : 12 = 43.3 euros x 12 = 520
Ongoing costs with gas: 95 euros x 12 = 1,140
Ongoing costs with electric heating: = 105 euros x 12 = 1,260
Electricity + photovoltaics cost 520 euros
Gas costs 620 euros more
Only electricity costs 740 euros more
Price for electric heating and photovoltaics: 11,000 + 4,500 = 15,500
Price for gas heating with radiators and installation: 12,000
After about 18 years I start to make a profit. After 10 years, I have about 620 euros less ongoing costs per year.
Questions:
Is an electric heating system as described above sensibly implementable?
I would probably have to build at least a house with a heating energy demand for heating and water of 5,500 kWh.
(Exactly KfW 40)
Is this calculation correct? House with 5,500 kWh x eP 2.6 - 4,500 kWh solar power : 140 sqm living space =
70 kWh per sqm of primary energy and thus permissible according to KfW 100.
Which system efficiency factor (eP) must I calculate? (2.6)
Is it possible with electric heating as above to achieve a KfW 70 standard without unrealistic amounts of investment?
Giving up the 5,000 euro subsidy (KfW 40) and the interest advantage and at the same time investing 10,000 euros more in the KfW 40 standard makes no sense.
Explanations (how I arrive at numbers etc.)
Photovoltaic system
5 kWp SOUTH (50 sqm) with about 4,500 kWh yield. Approximately 11,000 euros purchase price complete.
10 years repayment at 1.55 percent is 100 euros per month.
The system generates only about 30 percent in the heating period 1,350 kWh, which I use completely myself.
Additionally, over the year I will consume about 1,000 kWh of household electricity and for hot water myself.
Feed-in 2,500 kWh at 12 cents = 300 euros profit minus 30 percent tax. On average, about 110 euros interest expenses oppose the profit.
Energy demand
A KfW 70 house uses about 7,000 kWh for heating and water per year. (2 persons)
With KfW 40 it would probably make even more sense, as even less heating electricity would be needed.
I operate the wood stove with wood (free) and brown coal briquettes from the hardware store. In the morning before leaving and in the evening before going to bed about 6 briquettes or more or less as needed. These last about 9 hours and you can immediately add wood and briquettes again.
Coal / wood has a value of 4 kWh minus the stove’s efficiency (-15 percent) = 3.4 kWh per kilo. Coal = 3 euros per 10 kg = 0.3 euros per 1 kg. 1 kWh coal costs 0.088 euros.
150 days x 6 kilos of coal = 900 kg coal x 0.3 euros = 270 euros
150 days x 5 kilos of wood = 750 kg wood
900 kg coal x 3.4 kWh = 3,060 kWh
750 kg wood x 3.4 kWh = 2,550 kWh
Electricity demand:
20 days when the stove cannot be operated (absence)
20 x 35 kWh = 700 kWh x 0.25 euros = 175 euros + number x times the heater kicks in + 25 euros
Since only the base temperature is needed during absence, it will probably save costs.
Number X: the electric heating switches on because the temperature falls below 15 or in the bedroom below 18 degrees.
Further advantages
- Hardly any technology that needs maintenance or breaks down (if self-exchange)
- No heating pipes in the house
- No replacement after 20 or 30 years
- No aging or replacement after 20 or 30 years and when again significantly cheaper than gas/oil
- Efficiency of stove (coal + wood) at least 85 percent (power plants Germany approx. 50)
Disadvantages
- Labor-intensive
- Wood must be purchased if no source is available or physically not possible
- High ongoing costs without wood and coal
- Probably no KfW subsidy or loan
What do you think of these thoughts? Possibilities? Suggestions?
Best regards Matthias
I am planning a new build of 140 sqm (KfW 70 heating demand) and wonder if this would be possible.
In the center of the ground floor of the house, there should be a wood stove with 8 to 10 kW. (Coal + wood)
It stands in the 3-meter-wide passage to the 40 sqm living room and can optionally be separated from the hallway with a ceiling-mounted sliding door (no step), so that the heat from the stove can be varied and partially reach upstairs through the hallway and also distribute throughout the entire ground floor.
Additionally, convector heaters (electric) should provide base heat if needed.
Hot water:
Instantaneous water heater with a small upstream storage tank that preheats the drinking water in winter and heats it up to the maximum supply temperature of the instantaneous heater when there is a lot of solar power.
KfW and the Energy Saving Ordinance 2009
will probably throw a wrench in the works, even though I would only need about 700 kWh heating electricity from the grid, produce electricity myself, and use coal and wood with an efficiency of at least 85 percent. Maybe you have an idea how my plan could still work without losing sight of the financial aspect.
If needed, you can read at the end of my explanations how I arrive at which numbers.
Plan:
Electric heating + wood stove (just for comparison)
or
Electric heating + photovoltaic system + wood stove (priority 1)
Calculation:
9000 kWh total demand
6300 kWh heating demand
700 kWh hot water heating (approx. 2 kWh per day per year)
2000 kWh household electricity
Heating period from around October to April: 180 days
(Heating demand: 6300 kWh : 180 days heating period = 35 kWh per day)
Electric heating + photovoltaic system + wood stove:
9000 kWh total consumption
minus 1350 kWh self-consumption in the heating period (photovoltaic system)
minus 1000 kWh self-consumption household electricity (photovoltaic system)
9000 kWh - 2325 kWh = 6650 kWh remaining demand
minus 1000 kWh household electricity to buy at 25 cents = 250 euros
minus 700 kWh x 25 cents (20 days electric heating absence + water + buffer) = 200 euros
minus 4950 kWh from stove (wood I have for free) coal = 270 euros
Costs of 720 euros per year + photovoltaic system 1200 repayment - 300 euros profit
1920 euros total costs – 300 euros income = 1620 euros total costs per year
135 euros per month
Gas heating + wood stove
9000 kWh total consumption
2000 kWh household electricity purchase: 2000 x 0.25 = 500 euros
7000 kWh gas x 8 cents = 560 euros
2000 kWh wood x 8 cents = minus 160 euros
Tank rental yearly = 135 euros
Maintenance yearly 100 euros
1135 yearly : 12 = 95 euros per month
For comparison: (but I do not want this)
Electric heating + wood stove
9000 kWh total consumption
minus 5000 stove = coal 270 euros
4000 kWh x 0.25 euros = 1000 euros
1270 euros per year : 12 = 105 euros per month
Gas heating system 12,000 euros/electric heating 4,500 euros
7,500 euros that I would have to “burn” first.
Gas heating would save me 120 euros per year
1,200 euros in 10 years
4,800 euros in 40 years
Result
I pay 40 euros more every month than with gas for 10 years and have then paid off the photovoltaic system.
10 years x 12 months x 40 euros extra costs = 4,800 euros
(System loan KfW for 11,000 euros at 1.55 percent)
After 10 years
I assume gas and electricity rise equally and therefore keep the numbers.
Ongoing costs with electric heating + photovoltaics per year =
720 euros - 300 profit - 100 euros taxes = 520 euros : 12 = 43.3 euros x 12 = 520
Ongoing costs with gas: 95 euros x 12 = 1,140
Ongoing costs with electric heating: = 105 euros x 12 = 1,260
Electricity + photovoltaics cost 520 euros
Gas costs 620 euros more
Only electricity costs 740 euros more
Price for electric heating and photovoltaics: 11,000 + 4,500 = 15,500
Price for gas heating with radiators and installation: 12,000
After about 18 years I start to make a profit. After 10 years, I have about 620 euros less ongoing costs per year.
Questions:
Is an electric heating system as described above sensibly implementable?
I would probably have to build at least a house with a heating energy demand for heating and water of 5,500 kWh.
(Exactly KfW 40)
Is this calculation correct? House with 5,500 kWh x eP 2.6 - 4,500 kWh solar power : 140 sqm living space =
70 kWh per sqm of primary energy and thus permissible according to KfW 100.
Which system efficiency factor (eP) must I calculate? (2.6)
Is it possible with electric heating as above to achieve a KfW 70 standard without unrealistic amounts of investment?
Giving up the 5,000 euro subsidy (KfW 40) and the interest advantage and at the same time investing 10,000 euros more in the KfW 40 standard makes no sense.
Explanations (how I arrive at numbers etc.)
Photovoltaic system
5 kWp SOUTH (50 sqm) with about 4,500 kWh yield. Approximately 11,000 euros purchase price complete.
10 years repayment at 1.55 percent is 100 euros per month.
The system generates only about 30 percent in the heating period 1,350 kWh, which I use completely myself.
Additionally, over the year I will consume about 1,000 kWh of household electricity and for hot water myself.
Feed-in 2,500 kWh at 12 cents = 300 euros profit minus 30 percent tax. On average, about 110 euros interest expenses oppose the profit.
Energy demand
A KfW 70 house uses about 7,000 kWh for heating and water per year. (2 persons)
With KfW 40 it would probably make even more sense, as even less heating electricity would be needed.
I operate the wood stove with wood (free) and brown coal briquettes from the hardware store. In the morning before leaving and in the evening before going to bed about 6 briquettes or more or less as needed. These last about 9 hours and you can immediately add wood and briquettes again.
Coal / wood has a value of 4 kWh minus the stove’s efficiency (-15 percent) = 3.4 kWh per kilo. Coal = 3 euros per 10 kg = 0.3 euros per 1 kg. 1 kWh coal costs 0.088 euros.
150 days x 6 kilos of coal = 900 kg coal x 0.3 euros = 270 euros
150 days x 5 kilos of wood = 750 kg wood
900 kg coal x 3.4 kWh = 3,060 kWh
750 kg wood x 3.4 kWh = 2,550 kWh
Electricity demand:
20 days when the stove cannot be operated (absence)
20 x 35 kWh = 700 kWh x 0.25 euros = 175 euros + number x times the heater kicks in + 25 euros
Since only the base temperature is needed during absence, it will probably save costs.
Number X: the electric heating switches on because the temperature falls below 15 or in the bedroom below 18 degrees.
Further advantages
- Hardly any technology that needs maintenance or breaks down (if self-exchange)
- No heating pipes in the house
- No replacement after 20 or 30 years
- No aging or replacement after 20 or 30 years and when again significantly cheaper than gas/oil
- Efficiency of stove (coal + wood) at least 85 percent (power plants Germany approx. 50)
Disadvantages
- Labor-intensive
- Wood must be purchased if no source is available or physically not possible
- High ongoing costs without wood and coal
- Probably no KfW subsidy or loan
What do you think of these thoughts? Possibilities? Suggestions?
Best regards Matthias