Financial Analysis - Net Zero Site 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 Site 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:

  • 24 PVs (6 kW) + Electric Heaters
  • 18 PVs (4.5 kW) + Biomass
  • 18 PVs (4.5 kW) + ASHP
  • 18 PVs (4.5 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.


Graph 1: Capital Costs – Net Zero Site Energy Building

The cheapest option as derived from Graph 1 is the first one which includes the addition of six PVs (and therefore extra 1.5 kW) together with electric heaters where the main reason for that is that most equipment already exists. On the other hand, the most expensive option is the last one presented on the above graph which utilises the existing PVs and a GSHP where the total capital cost derives only from the GSHP’s cost.

Graph 2 presents the annual costs and revenues of 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.


Graph 2: Costs & Revenues - Net Zero Site Energy Building

Comparing the findings in the bar chart above, the annual running costs for the first three combinations are about the same and the overall lowest ones occur when implementing a GSHP. The revenues though worked out the opposite way, with the use of the GSHP having the highest ones and the other three combinations having revenues ranging from around £600 to £800 per year. It should be highlighted that in all three cases where the electric heaters were replaced by a more efficient heating system, eligible for the RHI scheme, total revenues outweighed total running expenses.

Up to this point of the financial analysis and having in mind both results presented above, the combination including the electric heaters has the lowest capital cost but when costs and revenues are combined result to an overall net cost of £19 per year. At the right side of the graphs, the combination including the GSHP has the highest capital cost but also a very high overall revenue of £652 when both annual costs and revenues are accounted.

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.


Graph 3: Payback periods - Net Zero Site Energy Building

Reviewing all the financial results including Graph 3 above, direct to the point that the combination with the highest capital cost has the least years for payback due to high annual revenues (mainly due to RHI payments) whereas the lowest capital cost combination has negative payback period. This means that the equipment installed can never be paid back as the combined result from costs and revenues was negative and therefore net payments occur on an annual basis despite the payments from FITs. The combinations including biomass and ASHP as a heating option take nearly 76 years and 48 years respectively to be paid back.