What does EVIE and the mechanical and electrical engineer Mr. P. Michalopoulos claim and what does Mr. A. Efthymiadis, curator of the scientific committee of the specialty of mechanical engineers of the TEE, answer.
Objections and the need for clarifications were caused by the article of Mr. Apostolos Efthymiadis (Dr. article concerned the cost of producing hot water for use in boilers, depending on the heating medium.
The prices mentioned in the article by Mr. Efthymiadis referred to the cost of production of hot water with natural gas, with heat pump, with biomass boilers, pellets and wood chips, as well as with solar water heaters.
According to the Union of Solar Energy Industries (EBEE), for almost all systems, the cost of hot water was calculated by Mr. Efthymiadis only the cost of fuel, while this did not apply to solar systems, which have zero fuel costs, but It was chosen to calculate the cost of equipment 230 euros per sq.m., with depreciation in 5 years and efficiency of 550 kWh / year, raising the cost of production of hot water for the use of solar systems to 8.3 minutes per kWh and thus creating a false picture.
The calculations did not take into account, according to EBIE, the heat losses in any of the systems except the solar one, as a result of which their efficiency and operation conditions are idealized. For example, in the heat pump the COP was used to calculate the efficiency.
The seasonal efficiency (SPF, which shows the annual efficiency of the heat pump in an ideal installation) would be significantly lower, according to EBHE, while the usual power of the pump is higher or lower than required in each building (under-dimensioning or over-dimensioning), so that in practice the efficiency is even lower.
The same goes for gas or oil boilers, according to EBIE, which considers that the most appropriate way to compare alternatives is the total cost of heat (LCOH). Following the internationally recognized method proposed by the IEA-SHC (International Energy Agency-Solar Heating and Cooling), EBHE states that the cost of kWh of solar water heater in our country is between 0.02 - 0.04 euros per kWh, depending on the size and type (natural flow or accelerated flow). This value has been calculated with a system life of 20 years and an energy gain of 683 kWh / m2 per year, as claimed by EBHE.
Contrary to EBIE's remarks, the columnist Mr. A. Efthymiadis argued that the restriction of space prevented the extensive analysis of the cost of producing hot water, limiting it primarily to the price of fuel, while the size of the capital was considered only in the case of solar water heaters (since in this case there is no fuel price) and heat pumps (since capital is important and can not be ignored).
As far as solar water heating systems are concerned, the price necessarily, according to Mr. A. Efthymiadis, included only the capital component, since there is no fuel component. In this case, a consumer loan with interest rate ε = 9% for a repayment period N = 7 years was taken into account, ie with interest arrears given by the formula:
ΤΚ = Δ ε. (1+ε)Ν /[(1+ε)Ν – 1] = 0,2 Δ.
Also, an annual solar gain of 550 kWh / m2 was taken into account against an average value of 630 kWh / m2, taking into account both the partial use of solar during the year and the colder climates in northern Greece.
Apart from EBHE, however, Mr. Panagiotis Michalopoulos, MBA electrical engineer, from Newton Solar Systems, also expressed his question in a letter to "TH", because Mr. A. Efthymiadis refers to the cost of borrowing the solar water heater. and not the heat pump.
According to Mr. A. Efthymiadis, the prices reported by EBHE 2 to 4 minutes per kWh for the production of hot water from solar are too low and unproven. Even if the annual solar gain of 683 kWh / m2 reported by EBIE is accepted, the price of the produced kilowatt hour of hot water is estimated at 6.7 minutes / kWh.
As for the heat pump, according to Mr. A. Efthymiadis, a seasonal efficiency grade (SCOP) of 3.4 was obtained, which corresponds to a high temperature heat pump. According to Mr. Efthymiadis, he avoided the use of the term SCOP and resorted to the use of the term COP not out of ignorance but for reasons of space economy and limitation of explanations, while the value of 3.4 is correct and is not easy to improve further.
Finally, according to Mr. A. Efthymiadis, with a careful observation of his article published in the November issue "I", it is found that the solar thermal system is economically superior to the rest, since the final value of 8.3 minutes / kWh is clearly more competitive than the heat pump, which was estimated at 10 to 15 minutes / kWh, when the supply includes not only the boiler but also the heat pump itself.
