Financial Analysis - Net Zero Source Energy Building

Following on from the financial data section, in this section a more detailed and project specific information is presented regarding the Net Zero Source Energy Building strategies examined. Data are provided mainly in graphs to allow for a comparison to be made between these strategies. The combinations analysed are:

• 18 PVs (4.5 kW) + 1 WT (6 kW) + Electric Heaters
• 24 PVs (6 kW) + 1 WT (2.5 kW) + Biomass
• 30 PVs (7.5 kW) + 1 WT (2.5 kW) + ASHP
• 30 PVs (7.5 kW) + 1 WT (2.5 kW) + GSHP

Below, a graph showing the capital costs for the selected four combinations is presented where a clear comparison can be made. The capital costs for the supply equipment already installed at the building are not included in the below graph. The systems already installed are 18 PV panels (4.5 kW), electric heaters and a solar thermal unit.

The cheapest option as derived from Graph 1 is the first one which includes a PV installation of 4.5 kW, a 6 kW wind turbine and electric heaters; the only cost for this supply mix stems from the wind turbine. On the other hand, the most expensive combination with a capital cost of £32,000 is the last one shown above, which comprises 30 PVs, a 2.5 kW wind turbine and a GSHP.

Graph 2 presents the costs and revenues from the same four combinations. The costs include maintenance and operation expenses of equipment whereas revenues include payments from Feed-in-Tariffs and the Renewable Heat Incentive scheme as calculated according to each combination’s on-site energy generation and exports.

Comparing the findings in the bar chart above, annual running costs for all four combinations range from about £430 to £590, with the second and fourth options having the highest and cheapest respectively. In detail, annual operational costs are minimized at only £430 when implementing a 7.5 kW PV array, a 2.5 kW wind turbine and a GSHP. This combination is also the best in terms of maintenance expenses. As can be seen, in all four Source NZEB combinations presented, funding revenues were significantly increased compared to the respective of the Site NZEB operation, which is mainly attributed to the larger installed capacity required. It is also noteworthy that total revenues outweighed by far total running expenses.

Up to this point of the financial analysis and having in mind both results presented above, the combination using the electric heaters as the heating option requires the lowest capital (only £25,000 for the 6 kW wind turbine). Additionally, when costs and revenues are accounted together they result to an overall net revenue of £1816 per year, which is the highest among the combinations reviewed.

The graph below presents the payback periods for each supply mix resulting from the combined data from Graphs 1 & 2. They were calculated as their capital cost divided by either their overall annual running cost or revenue.

Reviewing all the financial results including Graph 3 above, it can be seen that although the three first options had approximately the same capital costs, the payback period for the first combination was significantly shorter, about 14 years, due to the very high net annual revenues. Indeed, the second combination which involves a biomass boiler has greater than triple payback period than the best one recorded (first combination). Finally, comparing the results presented above with the ones for a Net Zero Site Energy Building it can be clearly seen that even though the capital costs are much higher for this case, the payback periods are much shorter.