May 21, 2019


Combination of economy

We combine a 6 kW photovoltaic system with a heat pump and we get free heating and power forever! Net Metering enables the consumer to generate the electricity needed by his home, helping him to get rid of electricity costs (the price of kWh has an increasing trend). By adding environmental and energy extensions, installing photovoltaic systems besides being particularly interesting helps to eliminate the energy footprint of our home or business environment.

On the other hand, heat pumps use cooling fluids that have the property of absorbing heat from the environment and yielding it multiplied to a second (final) medium e.g. air or water. 75% of the energy required is absorbed by the “free” energy of the environment and the remaining 25% is taken in the form of electricity. They are, therefore, an extremely economical but also environmentally friendly heating medium.


The heating and cooling design data The present study presents the annual electricity consumption for a 140m2 dwelling with modest 3cm thick insulation and underfloor heating system. Annual electricity consumption also includes electricity (kWh) consumed by a heat pump, which is used to heat the house during the winter season and cooling it during the summer season. The thermal capacity of the heat pump is 14.8 kW, while its cooling capacity is 16.5 kW and the absorbed power is 5 kW.

Based on the indications of the external electricity meter (kilometer) which records exclusively the consumption of the heat pump, the total annual energy consumed for its operation amounts to 5,242 kWh. More specifically:



Period Energy consumption in kWh
Winter 3.667
Summer 1.575

More specifically, during the winter and the period from January to April 2014, the energy consumed for heating the house was 2,200 kWh, while for October to December 2014 the corresponding energy was 1,466 kWh .

The operating costs Below we present the calculation of the operating costs to cover the heating needs of the heat pump and the comparison with the various sources of energy used for space heating, based on the thermal and cooling requirements presented in the above table.

The energy values ​​used for the above calculations are those shown in Table 2:

Energy source Energy price € / kWh
Electricity 0.18 (kWh + other charges)
Petroleum 0.157 (price 2014-2015)
Natural Gas 0,069 (price 2015-2016)

The savings achieved in relation to oil amounted to € 1016 (60%).

The technical description

The interconnected photovoltaic system will be mounted on a sloping roof. The photovoltaic panels will be placed on aluminum bases following the slope of the roof. The photovoltaic system consists of 24 AmeriSolar 24 polycrystalline photovoltaic modules of 255Wp power. The dimensions of each frame are 1640 mm x 992 mm x 40 mm. The photovoltaic panels and the support bases are followed by multi-year guarantees and are essentially free of maintenance. The photovoltaic station will consist of 2 photovoltaic strings and will be connected to the MPPT of the Zeversolar 6kW inverter. Alternatively, an ABB inverter can be used. The inverters are followed with all the necessary credentials and security codes and have internal DC switches. The installation will create a low-voltage switchboard with ABB C204 C25 miniature circuit-breakers for magneto-thermal protection and lightning protection ABB OVR T2 40-275 for lightning protection and overvoltage protection. The aim of selecting the materials and method of installation is to optimally exploit its sunshine area with as little loss as possible due to shading, cables, etc. For the latest in all our installations we use high quality DC and AC cables, tested and certified by the most demanding VDE and TUV Laboratories in Germany, certified for a long service life according to IE C 60216 (with manufacturer’s warranty), and .a. Particular emphasis is placed on the quality of the installation, both in the choice of materials and in the selection of collaborators and technical solutions planned in the implementation study.

The performance of the system

A detailed study of shading and annual performance and simulation with related software has been done. The performance of the system, taking into account all the shades over time and the orientation of the installation. Consumption of the plant was simulated in monthly load, simulating household electrical heating models (in this case heat pump). The total consumption of the plant (heat pump and photovoltaic system) amounts to 8,738 kWh / year.

Savings in numbers

According to the customer invoice (and the simulation software calculations for electricity consumption.

It follows from the above that the annual benefit to a consumer who has installed a Net Metering system and produces his own energy consumed amounts to € 1,164.09 (0.1361 € x 8.553 kWh).

The Initial Total Investment Capital for the photovoltaic system, which amounts to € 8,601.06. The increase in the increase in the energy saving prices results from the increase in the cost of PPC over time (increase of the price kWh, VAT, fees, etc.), while the operating expenses mentioned in the table include the maintenance and the insurance of the photovoltaic system . Based on the above, the depreciation of the system takes place at 7.5 years

Conclusion: Why should I do it? In short, in 25 years, Net Metering will provide us with net profits of € 25,514.54, resulting from the deduction of initial capital (€ 8,601.06) and operating expenses (€ 2,213.71) of total savings energy (€ 36,329.31). Therefore, investing in a self-produced photovoltaic system has an annual return of 10 times a term deposit (on favorable terms) at the bank.