Thermo-Economic Viability Analysis of a Photovoltaic Heat Pump System for Space Heating Purposes in Cold Climates of Northern USA - Literature Review

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The objective of this project is to analyse the viability of using photovoltaic heat pumps for space heating requirements in the cold climates of northern USA, look into the policy implications and discern whether there could be a potential subsidy for consumers who wish to purchase new PV-HP systems.


Below is the literature review for the same.


Ji, J., Pei, G., Chow, T., Liu, K., He, H., Lu, J., & Han, C. (2008). Experimental study of photovoltaic solar assisted heat pump system. Solar Energy, 82(1), 43–52. https://doi.org/10.1016/j.solener.2007.04.006

  • study analysed a novel photovoltaic solar-assisted heat pump (PV-SAHP) under different condenser water supply temperatures over a time frame of 4 days with fairly constant weather conditions
  • studies indicated that the PV-SAHP system has greater value of coefficient of performance (COP) than a conventional heat pump, and also has higher photovoltaic efficiency than a standard PV-HP system
  • authors used a solar-assisted heat pump, in which the conventional air-source evaporator of the heat pump was replaced by direct-expansion solar collectors
  • solar heating effect increased the temperature at the evaporator, which consequently increased the COP of the HP. This can also prevent potential frosting at very cold climates
  • because of the direct expansion, the refrigerant R22 (working fluid) undergoes phase change at relatively lower temperature, which lowers operating temperature of PV cells and thus leads to increased energy conversion efficiency
  • the standard air-cooled evaporator and PV evaporator were connected in parallel, so that normally the PV evaporator would remain in service, but when solar radiation is weak, and evaporating temperature falls below ambient temperature, then the air evaporator would start to operate as a backup
  • entire PV evaporator constituted of 9 PV evaporator modules. Total aperture area was 5.49 m2 and total PV cell area was 4.59 m2. A single PV evaporator module was 1.01 m x 0.73 m
  • PV cells were of single-crystalline silicon type, with following characteristics: 0.63 V open circuit voltage, 5.12 A short-circuit current, 2.40 W maximum power, 0.53 V and 4.58 A at maximum power point, and 15.4% electrical efficiency (under sample testing conditions of 1000 W/m2 solar irradiation, 25°C ambient temperature, and 156.25 cm2 cell area)

Observations and conclusions:

  • condenser capacity increased with increasing solar irradiation
  • compressor power required decreases slightly for increasing solar irradiation
  • COP of the HP increased with increasing solar irradiation
  • photovoltaic power output increased with increasing solar irradiation
  • photovoltaic efficiency generally increases with solar irradiation but is also influenced to a large extent by angle of incidence


Ji, J., Liu, K., Chow, T., Pei, G., He, W., & He, H. (2008). Performance analysis of a photovoltaic heat pump. Applied Energy, 85(8), 680–693. https://doi.org/10.1016/j.apenergy.2008.01.003

  • authors proposed a novel heat pump system in which the PV/T collector was coupled with a solar-assisted heat pump and it operated as an evaporator of a refrigeration cycle
  • cooling effect due to evaporation reduces operating temperature of PV cells, which leads to increase in efficiency
  • authors developed a mathematical model and performed numerical simulations based on the “distributed parameters” approach
  • experimental prototype was constructed and tested, and performance compared with simulated results
  • PV-SAHP was found to have better COP than a conventional heat pump, and also had better photovoltaic efficiency


Helsen, L. (2010). Modelling and simulation of a grid connected photovoltaic heat pump system with thermal energy storage using Modelica. 21.

  • objective of this study was to reduce the peak load demand on the grid in case of grid-connected PV-HP systems
  • maintaining the balance between production and consumption, while making sure that grid load demand does not become too high, can be done in two ways – either by using energy storage, or by demand side management (DSM)
  • authors focus on one particular way of achieving DSM – by using thermal energy storage (TES)
  • they developed an integrated model consisting of a grid-connected PV system, a conventional heat pump, a hot water storage tank and a control strategy – using the object-oriented, open source programming language Modelica
  • solar irradiance and metrological data were considered for Uccle, Belgium
  • simulations were done for a period of 6 weeks starting from 1st Jan, so as to include the heating requirements of winter season

Observations and conclusions:

  • increasing the size of the hot water storage tank would increase overall energy consumption and decrease the system performance factor (SPF)
  • daytime priority control strategy (taking less power from the grid when solar irradiance is available) worked optimally to produce energy savings, but only when the storage tank was properly insulated
  • grid load control strategy – keep the storage tank SOC (state of charge) at an intermediate level so that it could turn the heat pump on or off as and when necessary – found to be most effective and reduced the peak loads by almost 50%


Chua, K. J., Chou, S. K., & Yang, W. M. (2010). Advances in heat pump systems: A review. Applied Energy, 87(12), 3611–3624. https://doi.org/10.1016/j.apenergy.2010.06.014


Chen, H., Riffat, S. B., & Fu, Y. (2011). Experimental study on a hybrid photovoltaic/heat pump system. Applied Thermal Engineering, 31(17), 4132–4138. https://doi.org/10.1016/j.applthermaleng.2011.08.027

  • authors explore the possibilities of using R-134a refrigerant as a cooling medium to cool the PV panel in a PV-HP system
  • experimental prototype of a hybrid micro PV panel based heat pump system was constructed for performance testing in a laboratory at University of Nottingham
  • PV panel was constructed using 6 glass vacuum tubes, PV modules, aluminium sheet, and copper tube (GPAC) sandwiches connected in series, to act as the evaporator. This was coupled with a small heat pump system
  • glass vacuum tubes reduced the heat loss from the PV panel to the ambient atmosphere, which resulted in improvement of thermal performance
  • 3 different testing modes were conducted to observe the effects of solar irradiation, condenser water flow rate and condenser water supply temperature on performance characteristics
  • for a base reference state, solar irradiation of 600 W/m2, water flow rate of 2 lit/min and condenser supply temperature of 35°C were considered, without any form of cooling mechanism for the PV panels

Observations and conclusions:

  • Overall COP of the system, PV power output and electrical efficiency increased with increasing solar irradiation when condenser water supply temperature and flow rate were constant. The increase in electrical efficiency was 1.9% as compared to a system without cooling
  • COP of the system decreased with increasing condenser water supply temperature when solar irradiation and water flow rate were constant. But changing the condenser water supply temperature had negligible effect on PV power output and electrical efficiency
  • Increasing condenser water flow rate under constant solar irradiation and water supply temperature decreased COP of the system, but had almost no effect on PV power output and electrical efficiency


Calise, F., Dentice d’Accadia, M., Figaj, R. D., & Vanoli, L. (2016). A novel solar-assisted heat pump driven by photovoltaic/thermal collectors: Dynamic simulation and thermoeconomic optimization. Energy, 95, 346–366. https://doi.org/10.1016/j.energy.2015.11.071

  • provides a dynamic simulation model of a novel poly-generation system comprising of a solar-assisted heat pump and an adsorption chiller, both driven by PV/T collectors
  • system also consists of two tanks which serve as thermal storage system
  • during winter, heat generated by the PV/T’s would be primarily used by the HP for space heating and the remaining part can be used for domestic hot water (DHW) production
  • in summer, majority portion of the PV/T-generated heat can be supplied to hot side of adsorption chiller for space cooling, while the rest of the heat can be used for DHW generation
  • system was modelled using TRNSYS and simulated for operation for one year in a one-storey residential building
  • base case for reference was taken using metrological data and solar irradiation for Naples, Italy
  • results of the simulations showed that the entire space heating requirements of the modelled house during winter could be supplied by the SAHP (solar-assisted heat pump), while the adsorption chiller can provide 70% of the cooling requirements of summer season
  • thermo-economic analysis showed that without public incentive, the system is not profitable and has an SPB (simple payback) of over 16 years. But with 50% capital cost subsidy and solar collector area of 24.25 m2, the system becomes profitable and SPB drops to 14.38 years


Pearce, J., & Kantamneni, A. (2016). Emerging Economic Viability of Grid Defection in a Northern Climate Using Solar Hybrid Systems. https://www.academia.edu/25363058/Emerging_Economic_Viability_of_Grid_Defection_in_a_Northern_Climate_Using_Solar_Hybrid_Systems


Huang, W., Ji, J., Xu, N., & Li, G. (2016). Frosting characteristics and heating performance of a direct-expansion solar-assisted heat pump for space heating under frosting conditions. Applied Energy, 171, 656–666. https://doi.org/10.1016/j.apenergy.2016.03.048

  • authors analysed the operation of a direct-expansion solar-assisted heat pump (DX-SAHP) under frosting conditions
  • protoype was constructed (DX-SAHP with bare solar collectors for space heating) and tested in lab

Experimental conditions: ambient temperatures ranging from -3°C to 7°C; relative humidity (RH) values of 50%, 70% & 90%; solar irradiances of 0 W/m2, 100 W/m2, 200 W/m2 and 300 W/m2

Observations:

  • minimum solar irradiance of 100 W/m2 was required to prevent frosting when ambient temperature was -3°C and RH 70%. If ambient temperature is lower or if humidity is higher, then higher value of solar irradiation would be required to prevent frosting
  • increased value of solar irradiation also increases the heating capacity and COP of the heat pump
  • frosting process in DX-SAHP was slower than a conventional fin-and-tube type heat exchanger. Evaporator was not frosted even after 360 min (6 hours) of continuous operation and system performance was also not affected


Poppi, S., Sommerfeldt, N., Bales, C., Madani, H., & Lundqvist, P. (2018). Techno-economic review of solar heat pump systems for residential heating applications. Renewable and Sustainable Energy Reviews, 81, 22–32. https://doi.org/10.1016/j.rser.2017.07.041

  • reviewed the existing literature on all kinds of solar heat pump (SHP) systems – photovoltaic, thermal, and hybrid thermal-photovoltaic – in order to try to provide a common ground for comparative economic analysis of different types of SHPs
  • economic comparison showed that payback time of SHPs varies inversely with solar irradiance and directly with heating degree-days
  • payback time was found to be longer than 30 years at high latitude places (solar irradiance of 850–1200 kW-h/m2·year and heating degree-days over 3000), while it was shorter than 21 years in places closer to the equator (solar irradiance over 1500 kW-h/m2·year and heating degree-days smaller than 700)
  • authors suggest the use of NPV (net present value) or an annualised adaptation rather than SPB for economic comparison


Prehoda, E., Pearce, J., & Schelly, C. (2019). Policies to Overcome Barriers for Renewable Energy Distributed Generation: A Case Study of Utility Structure and Regulatory Regimes in Michigan. Energies, 12(4), 674.


Besagni, G., Croci, L., Nesa, R., & Molinaroli, L. (2019). Field study of a novel solar-assisted dual-source multifunctional heat pump. Renewable Energy, 132, 1185–1215. https://doi.org/10.1016/j.renene.2018.08.076


Ammar, A. A., Sopian, K., Alghoul, M. A., Elhub, B., & Elbreki, A. M. (2019). Performance study on photovoltaic/thermal solar-assisted heat pump system. Journal of Thermal Analysis and Calorimetry, 136(1), 79–87. https://doi.org/10.1007/s10973-018-7741-6

  • energy and exergy analysis conducted for a photovoltaic-thermal solar-assisted heat pump (PV/T-SAHP) system under varying conditions of solar irradiation
  • R-134a was used in a refrigeration cycle and the PV/T panel was used as evaporator for that, so that the temperature drop owing to evaporation of R-134a can decrease the temperature of the PV modules and enhance their performance
  • model simulated and analysed using Engineering Equation Solver (EES)
  • metrological and solar irradiation data were considered for Kuala Lumpur, Malaysia; ambient temperature was taken as 28°C

Observations and conclusions:

  • COP of the system increased with increasing solar irradiation
  • average value of overall COP was 6.14 and the average exergetic COP (COPex) was 1.49
  • electrical efficiency and thermal efficiency both decreased with increasing solar irradiation
  • average values of electrical and thermal efficiency were 11.77% and 80.97% respectively
  • average thermal exergy efficiency was 51.64% and the overall exergetic efficiency was 61.29%


Shi, G.-H., Aye, L., Li, D., & Du, X.-J. (2019). Recent advances in direct expansion solar assisted heat pump systems: A review. Renewable and Sustainable Energy Reviews, 109, 349–366. https://doi.org/10.1016/j.rser.2019.04.044


Vaishak, S., & Bhale, P. V. (2019). Photovoltaic/thermal-solar assisted heat pump system: Current status and future prospects. Solar Energy, 189, 268–284. https://doi.org/10.1016/j.solener.2019.07.051

  • authors explain the working principle of a PV/T-SAHP system, advantages over conventional HP, and limitations
  • past work reviewed. Certain important works were selected and their (experimental and simulated) data was analysed
  • suggestions provided for future improvement of PV-SAHP (use of phase change materials as intermediate heat storage unit, using variable speed DC compressor directly coupled with the PV modules)


Ozakin, A. N., Yakut, K., & Khalaji, M. N. (2019). Performance Analysis of Photovoltaic-Heat Pump (PV/T) Combined Systems: A Comparative Numerical Study. Journal of Solar Energy Engineering, 142(021010). https://doi.org/10.1115/1.4045313


Sakellariou, E. I., Wright, A. J., Axaopoulos, P., & Oyinlola, M. A. (2019). PVT based solar assisted ground source heat pump system: Modelling approach and sensitivity analyses. Solar Energy, 193, 37–50. https://doi.org/10.1016/j.solener.2019.09.044

  • authors modelled a PV/T-based, solar-assisted, ground-source heat pump using TRNSYS, and simulated sensitivity & feasibility analysis
  • for the PV/T collectors, an experimentally verified transient model was used
  • for the geothermal energy source, a shallow borefield was installed with 16 U-shaped borehole heat exchangers (BHE)
  • performance data for the heat pump were taken from a German manufacturer
  • system was modelled for space heating and hot water requirements of a standard house under weather conditions of Birmingham, UK

Observations:

  • among all variable parameters, angle of inclination or tilt of the PV modules had the most impact on electricity generation
  • large inclination angle (70°) caused 3.47% increase (as compared to the base case of 30° inclination) of the specific heat productivity (SP) of the entire system
  • increased flow rate of 100 Kg/h (from the base value of 50 Kg/h) increased the SP of the PV/T module by 26%, and also increased thermal efficiency


Wang, X., Xia, L., Bales, C., Zhang, X., Copertaro, B., Pan, S., & Wu, J. (2020). A systematic review of recent air source heat pump (ASHP) systems assisted by solar thermal, photovoltaic and photovoltaic/thermal sources. Renewable Energy, 146, 2472–2487. https://doi.org/10.1016/j.renene.2019.08.096

  • authors do a comparative analysis of the available literature on the various kinds of solar-assisted air-source heat pump (ASHP) systems – solar-thermal (ST), photovoltaic (PV) and hybrid photovoltaic-thermal (PV/T)

Observations:

  • PV-ASHP had the best techno-economic performance – with a high COP (coefficient of performance) of 3.75, with moderate cost and moderate payback time
  • ST-ASHP system had relatively low COP at mean value of 2.90, but requires much smaller investment or capital cost, with 3.5-10 years payback time
  • PV/T-ASHP had moderate COP of 3.03, but needs large capital cost, which means longer payback time, also requires more complex control strategy


Obalanlege, M. A., Mahmoudi, Y., Douglas, R., Ebrahimnia-Bajestan, E., Davidson, J., & Bailie, D. (2020). Performance assessment of a hybrid photovoltaic-thermal and heat pump system for solar heating and electricity. Renewable Energy, 148, 558–572. https://doi.org/10.1016/j.renene.2019.10.061

  • analysed a PV/T heat pump system that served dual purpose of space heating + electricity generation for a small home for weather conditions of Belfast, Ireland
  • system comprised of a photovoltaic-thermal panel connected through a PV/T water tank to a heat pump
  • quasi-steady state assumptions made
  • simulations done using MATLAB to account for space heating a volume of 5x3x3 cubic metres

Observations:

  • increasing the solar irradiation increases temperature of PV panels, which decreases their electrical efficiency. At irradiation of 750 W/m2, thermal efficiency of the PV/T panels decreased by 0.5%, and for 1000 W/m2 the decrease was 2%. Conversely, low irradiation levels caused the thermal efficiency to gradually increase over time – 3.5% under 500 W/m2 and 14% under 250 W/m2
  • increasing irradiation from 250 to 1000 W/m2 increased overall COP of the system although it had negligible effect on COP of the heat pump itself
  • increasing volume of the water tank from 1 litre to 100 litres caused a 17% decrease of temperature of the PV panel, which increased overall efficiency (electrical+thermal) by 6.1%. But this increase in tank size had no effect on COP of the system
  • increasing water flow rate from 3 lit/min (laminar) to 17 lit/min (turbulent) decreased the PV panel temperature by 2.9°C, which increased the total efficiency by 3.25%


Badiei, A., Golizadeh Akhlaghi, Y., Zhao, X., Shittu, S., Xiao, X., Li, J., Fan, Y., & Li, G. (2020). A chronological review of advances in solar assisted heat pump technology in 21st century. Renewable and Sustainable Energy Reviews, 132, 110132. https://doi.org/10.1016/j.rser.2020.110132


Duhirwe, P. N., Hwang, J. K., Ngarambe, J., Kim, S., Kim, K., Song, K., & Yun, G. Y. (n.d.). A novel deep learning-based integrated photovoltaic, energy storage system and electric heat pump system: Optimising energy usage and costs. International Journal of Energy Research, n/a(n/a). https://doi.org/10.1002/er.6462

  • proposes a novel integrated energy-efficient system for PV, ESS (energy storage system) and electric heat pump (EHP), that maximises the usage of PV energy, optimises ESS usage and reduces EHP energy consumption costs
  • components of the system are connected to a deep learning (DL) based algorithm that forecasts the PV energy generation and energy demand of the EHP, and accordingly schedules the charging/discharging time of ESS depending on peak load times
  • authors developed an integrated cascade algorithm (ICA) as an optimization method, that incorporates two DL forecasting methods for EHP energy consumption and photovoltaic energy generation
  • depending on the forecasting results, the PV-generated energy is balanced between the heat pump and the ESS in order to decrease energy consumption from the main grid
  • proposed model was field tested in operation for 10 months from late 2017 to 2018 for space heating one particular retail shop inside a commercial building complex in Cheonan, South Korea
  • authors claim that the proposed integrated system can provide annual savings of 12% by saving electricity as compared to a standard PV-HP system


Pearce, J. (n.d.). Economics of Grid-Tied Solar Photovoltaic Systems Coupled to Heat Pumps: The Case of Northern Climates of the U.S. and Canada. Energies. Retrieved February 5, 2021, from https://www.academia.edu/45058034/Economics_of_Grid_Tied_Solar_Photovoltaic_Systems_Coupled_to_Heat_Pumps_The_Case_of_Northern_Climates_of_the_U_S_and_Canada

  • objective was to analyse PV-HP to completely replace natural gas heat pumps in USA & Canada
  • numerical simulations and economic analysis done using SAM
  • local electricity and natural gas rates considered for twin cities of Sault Ste Marie in both USA & Canada
  • simulations done for 6 scenarios
    1. ground mounted, fixed-tilt PV, grid-tied to match 100% of electric load in Sault Ste Marie, MI
    2. ground mounted, fixed-tilt PV, grid-tied to match 100% of electric load in Sault Ste Marie, Ontario
    3. air source heat pump to meet all thermal load with grid electricity in Sault Ste Marie, MI
    4. air source heat pump to meet all thermal load with grid electricity in Sault Ste Marie, Ontario
    5. ground mounted, fixed-tilt PV, grid tied to match 100% of electric load and electrified thermal load assuming air source heat pump in Sault Ste Marie, MI
    6. ground mounted, fixed-tilt PV, grid tied to match 100% of electric load and electrified thermal load assuming air source heat pump in Sault Ste Marie, Ontario
  • monthly average space heating requirements were taken by averaging from 10-year data

Observations and conclusions:

  • in both USA & Canada, PV systems could be sized for 6.9 kW for systems without a heat pump, and 20.6 kW for those with heat pump. Annually they would produce 9,130 kWh and 20,611 kWh energy, respectively
  • total system cost would be $3.30/W in Ontario and $3.10/W in Michigan
  • gross cost estimated to be $43,854 in the U.S. and $49,029 in Canada
  • all of the systems have a simple payback time (SPB) shorter than the lifetime under warranty, which means that all cases provide a positive return
  • internal rate of return (IRR) for PV+HP systems in the US was 3.4%, and in Canada 0.6%
  • inclusion of ITC (federal income tax credit) in the USA increases IRR by more than 1.7% and decreases payback time by 3.8 years


Websites/blogs/links:

  1. Electricity Local – Houghton Electricity Rates
  2. The Balance Small Business – Most Expensive and Cheapest Electricity by State
  3. Electric Choice – Electricity Rates by State