“combine”

It is important to consider multiple combinations of renewable components when planning in order to undertand and harness the NPV synergies between them.

The effect on NPV from adding a component is not necessarily additive. Suppose a heat pump and solar PV improve the NPV by £HP and £PV respectively when installed alone. Implementing both, however, does not necessarily result in £(HP+PV). Sometimes there is a synergy, but sometimes there isn’t.

In our case, batteries and heat pumps made virtually no financial sense together or on their own, but both can pay off if combined with sufficient solar pv. We were able oversize our solar install to the limit with 40 panels: these become a significant “free” source of electricity for the heat pump, even in winter: see graphs below. Your mileage may vary.

For these reasons it is important to simulate renewables together: specify in “combine”¹ up to four renewable components² to combine by adding them the JSON description³.

"combine": {
 "battery",
 "solar_pv",
 "heat_pump"
},

The above example tells the simulator to simulate each of the combinations of battery (B), solar_pv (PV) and heat pump (HP) as follows:

• none: no components at all⁴;
• PV: keep the boiler and just add solar PV panels;
• HP: just replace the boiler with a heat pump;
• HP, PV: replace the boiler with a heat pump and add solar PV;
• B: keep the boiler and just add a battery;
• B, PV: keep the boiler and add both a battery and solar PV;
• B, HP: add a battery and replace the boiler with a heat pump;
• B, HP, PV: add a battery, replace the boiler with a heat pump and add solar PV.

Two plots of NPV vs project duration are displayed :

• absolute NPV for each combination, including none;
• NPV for each combination relative to none.

Here’s are the absolute NPV for each combination for our house, including the NPV for “none” (staying with our 2 year old oil boiler):

… and here are the NPVs compared to doing nothing for each combination:

Note:

1. If you omit “combine” or leave it empty, a single combination of the components marked for inclusion are simulated. ↩︎
2. You can use up to four renewable components in “combine”: “battery”, “heat_pump”, “insulation”, “solar_pv” and “solar_thermal”. ↩︎
3. When not added to “combine”, other renewable components are included in the simulation of the combinations if their component is marked to be included (i.e. “include”: true). ↩︎
4. It’s always necessary to compare with the NPV if we do nothing, i.e. stay with our old boiler, insulation etc and continued with our existing energy consumption profile (e.g. oil and electricity). The simulator refers to this as the “none” project, where no renewable component is included. ↩︎