“combinations”

It is important to consider synergies between renewable components.

The effect on NPV of adding components 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 the sum is greater than the sum or their parts … and sometimes it is less.

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 components when combined together.

The “combinations” tag allows up to four renewable components¹ to be combined by adding them the JSON description². s together: specify in “combine”³ .

"combinations": {
  "Boiler": ["boiler"],
  "Boiler+Solar": ["boiler","solar_pv" ],
  "Boiler+Battery": ["battery","boiler"],
  "Boiler+Battery+Solar": ["battery","boiler",   "solar_pv"],
 "Heatpump": ["heat_pump"],
 "Heatpump+Battery": ["battery", "heat_pump"],
 "Heatpump+Solar": ["heat_pump",  "solar_pv"],
 "Heatpump+Battery+Solar": 
["battery","heat_pump","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. You can specify up to three renewable components from “battery”, “heat_pump”, “insulation”, “solar_pv” and “solar_thermal”. ↩︎
2. Components not added to “combinations” are still included in the simulation if they are marked to be included (i.e. “include”: true). ↩︎
3. A single simulation is performed including only the components marked to be included (i.e. “include”: true) if “combinations” is omitted or empty. ↩︎