As part of our new build, we plan to install a photovoltaic system on the roof. The roof area is approximately 160sqm (1,720 sq ft), with a pitch of 25 degrees, a gable roof with one side facing northeast and the other southwest. Since we are both civil servants and income from photovoltaic systems requires approval and may later be counted towards our pension, feed-in is not an option for us.
The system is intended solely to reduce our electricity consumption. We will have a ground-source heat pump with a borehole, a 300l (80 gallons) hot water storage tank, and a ventilation system for heating. The house is designed to meet KFW 55 standard (higher efficiency is no longer possible due to the basement).
Since I am home starting at midday, appliances such as the washing machine, dryer, dishwasher, and others will mainly be used during the day.
Additionally, we live in an area with above-average sunshine and fewer cloudy days, even in winter.
We do not want a battery storage system yet, even though this means we will occasionally export surplus electricity. Once batteries become more affordable, we plan to add one later.
How should the system be sized for our needs?
The system is intended solely to reduce our electricity consumption. We will have a ground-source heat pump with a borehole, a 300l (80 gallons) hot water storage tank, and a ventilation system for heating. The house is designed to meet KFW 55 standard (higher efficiency is no longer possible due to the basement).
Since I am home starting at midday, appliances such as the washing machine, dryer, dishwasher, and others will mainly be used during the day.
Additionally, we live in an area with above-average sunshine and fewer cloudy days, even in winter.
We do not want a battery storage system yet, even though this means we will occasionally export surplus electricity. Once batteries become more affordable, we plan to add one later.
How should the system be sized for our needs?
T
toxicmolotof4 Mar 2017 13:14We are basically rotated 45°, no matter how you would orient East-West.
With an East/West setup, the “advantage” is that the curve becomes wider and flatter... at least in theory.
In practice, however, this comes with a more expensive mounting system and a significantly costlier inverter. Overall, it will never be worthwhile. If you’re really interested, have two systems of the same size calculated—one facing south and one East-West.
East-West always delivers less yield despite higher investment costs. And it doesn’t matter whether you use the electricity yourself or feed it into the grid. Self-consumption does not make photovoltaics more profitable.
East-West systems with batteries are even more nonsensical. All I can do then is shake my head.
The only advantage of an East-West setup is that you can install more modules to create a larger system (if space and budget allow) and thereby reduce the cost per kilowatt-peak (kWp).
With an East/West setup, the “advantage” is that the curve becomes wider and flatter... at least in theory.
In practice, however, this comes with a more expensive mounting system and a significantly costlier inverter. Overall, it will never be worthwhile. If you’re really interested, have two systems of the same size calculated—one facing south and one East-West.
East-West always delivers less yield despite higher investment costs. And it doesn’t matter whether you use the electricity yourself or feed it into the grid. Self-consumption does not make photovoltaics more profitable.
East-West systems with batteries are even more nonsensical. All I can do then is shake my head.
The only advantage of an East-West setup is that you can install more modules to create a larger system (if space and budget allow) and thereby reduce the cost per kilowatt-peak (kWp).
Hmn, in what way is the inverter supposed to get more expensive? For east/west orientations, no special features are really needed, right? Or would shading have been an issue for you? You will be mounting the system on the south side anyway.
But yes. If I can buy one kWh from the public grid at 26 cents and instead consume a self-generated kWh from the roof with 4-5 cents in sales tax, that gives a price advantage of 21 cents. If I feed this kWh into the grid instead (currently 12.3 cents for new installations), the price advantage decreases accordingly. Self-consumption is therefore a very important factor in the profitability of a photovoltaic system.
I think that depends on the system size, the battery capacity, and usage patterns. But yes, generally it doesn't make much sense.
toxicmolotow schrieb:
Self-consumption does not make a photovoltaic system more profitable.
But yes. If I can buy one kWh from the public grid at 26 cents and instead consume a self-generated kWh from the roof with 4-5 cents in sales tax, that gives a price advantage of 21 cents. If I feed this kWh into the grid instead (currently 12.3 cents for new installations), the price advantage decreases accordingly. Self-consumption is therefore a very important factor in the profitability of a photovoltaic system.
toxicmolotow schrieb:
East-west systems with batteries are even more contradictory. I just shake my head at that.
I think that depends on the system size, the battery capacity, and usage patterns. But yes, generally it doesn't make much sense.
T
toxicmolotof4 Mar 2017 14:37I’m not sure how you generate your electricity, but my system doesn’t do it for free. The investment has to be paid off. I produce kWh for about 13 cents, plus 4 cents VAT, making it 16 cents. When feeding into the grid, I receive the same price.
Electricity can also be purchased for 21 cents. This significantly lowers your calculation. Therefore, I maintain that whether self-consumption or feed-in, currently there is hardly any difference financially. That’s why the focus should be on maximizing power yield through orientation and minimizing investment costs.
This does not consider possible taxation of the free value transfer. But the same may apply to feed-in remuneration, so I’m ignoring that for now.
For an east-west setup, you definitely need an inverter that can independently convert two separate strings. This is not necessarily required for a purely south-facing system. East-west installations always yield less without shading. Also, the east-west mounting system costs more per module than a south-facing one. At least that was the case here.
Electricity can also be purchased for 21 cents. This significantly lowers your calculation. Therefore, I maintain that whether self-consumption or feed-in, currently there is hardly any difference financially. That’s why the focus should be on maximizing power yield through orientation and minimizing investment costs.
This does not consider possible taxation of the free value transfer. But the same may apply to feed-in remuneration, so I’m ignoring that for now.
For an east-west setup, you definitely need an inverter that can independently convert two separate strings. This is not necessarily required for a purely south-facing system. East-west installations always yield less without shading. Also, the east-west mounting system costs more per module than a south-facing one. At least that was the case here.
T
toxicmolotof5 Mar 2017 20:28If you compare directly, it’s a difference of a few hundred euros. However, this cannot be answered generally. The question is whether it makes sense to cover both sides of the roof.
Yes, I will probably have to. Each individual roof section of this pyramid roof is only about 28 m2 (300 square feet)... that would be too little for me with only one side covered since I am installing a heat pump and want to feed as much photovoltaic electricity in over the course of the year as possible. In the summer, it also provides cooling.
Similar topics