Category: Planning

Use “panels” to describe each type of panel you use. Here’s an example of a solar pv “panel” description:

"panel": {
   "panel": "AIKO 455W",
   "width_m": 1.134,
   "height_m": 1.722,
   "cost": {
     "per_panel_gbp": 0.0,
     "maintenance_per_panel_pa_gbp": 5.00
   },
   "efficiency": {
     "spec": 
     "percent": 23.1,
     "loss_percent_pa": 0.3,
     "loss_percent_per_celsius": 0.29,
     "temperature_reference_celsius": 25
    },
    "power_max_w": 455.0,
    "lifetime_years": 25,                 "thermal_inertia_m2_second_per_w_celsius": 1000
},

If more than one panel type is used, describe each type within a “panels” array using the format example below:

    "panels": [
      {
        "panel": "AIKO 455W",
        "#": "AIK-A-MAH54-445-AB Gen 2 All Black",
        "cost": {
          "gbp" : 100.0,
          "gbp_per_year" : 1.0
        },
        "width_m": 1.134,
        "height_m": 1.722,
        "power_max_w": 455.0,
        "lifetime_years": 25,
        "thermal_inertia_m2_second_per_w_celsius": 1000,
        "efficiency": {
          "percent": 23.1,
          "loss_percent_per_year": 0.3,
          "loss_percent_per_celsius": 0.29,
          "temperature_reference_celsius": 25
        }
      },
      {
        "panel": "AIKO 470W",
        "#": "Aiko Neostar 3S+ 470W N-Type ABC, Gen 3, 54 Cell, All Black",
        "cost": {
          "gbp" : 110.0,
          "gbp_per_year" : 1.0
        },
        "width_m": 1.134,
        "height_m": 1.722,
        "power_max_w": 470.0,
        "lifetime_years": 25,
        "thermal_inertia_m2_second_per_w_celsius": 1000,
        "efficiency": {
          "percent": 24.3,
          "loss_percent_per_year": 0.3,
          "loss_percent_per_celsius": 0.29,
          "temperature_reference_celsius": 25
        }
      }
    ],

Within each collector, reference the relevant type using “panel” and the number of panels “panels_number” inside each collector description in “collectors”, for example:

"collectors": {
   "collector A": {
      . . . 
      "panel": "AIKO 455W",
      "panels_number": 16,
      . . . 
   },
   "collector B": {
      . . . 
      "panel": "AIKO 470W",
      "panels_number": 12,
      . . . 
   },
   "collector C": {
      . . . 
      "panel": "AIKO 470W",
      "panels_number": 8,
      . . . 
   }
},

“gbp” and “gbp_per_year” specifies initial and ongoing per unit costs. These are multiplied by “panels_number” and summed.

A collector can specify only a single type of panel. Create another collector if you want to include an additional panel type.

A collector is a plane on which solar panels of a particular type are mounted. A house can have multiple collectors. For example, a collector on a south facing roof and another on a south-west facing roof. Give each collector a name, e.g. “collector A” and “collector B” in the below example.

For multiple panel types within a same plane, create a separate collector for each type.

For each collector:

• name your collector using “name” (optional);
• use “include” to include it in the simulation;
• if the collector is shaded, express in “shading_factor” its average shading across the year as a fractional factor corresponding to the average proportion of light that reaches it¹;
• give the number of panels in “panels_number” if you know it. Alternately give in “area”:
  • “border_m”: the width of a border area where panels cannot be placed;
  • dimensions of the collector’s ground footprint along the tilt axis (“tilt_m”) and line of slope (“other_m”) to allow the simulator to use the maximum number that will fit from the panel dimensions;
• give its “orientation” by stating its “type” as “tilted” giving the angle of tilt above the horizontal in “tilt_degrees”, and tilt direction from true north in “azimuth_degrees”;
• specify initial and on-going costs in “costs” under “gbp” and “gbp_per_year” respectively;
• identify the type of panel in “panel”: see also here.

See example below:

    "collectors": {
      "collector A": {
        "include": true,
        "panel": "AIKO 455W",
        "panels_number" : 0.9,
        "shading_factor": 1.0,
        "area": {
           "dimensions_footprint_axis": {
              "tilt_m": 6.0,
              "other_m": 1.9
              },
           "orientation": {
              "type": "tilted",
              "tilt_degrees": 35,
              "azimuth_degrees": 185
              }
           }
        },        
      "collector B": {
        "include": false,  
        "panel": "AIKO 470W",  
        "shading_factor": 0.7,
        "panels_number": 5
        "cost": {
          "gbp": 1500.0,
          "gbp_per_year": 0.0      
        },
        "orientation": {
          "type": "tilted",
          "tilt_degrees": 45,
          "azimuth_degrees": 270
        }
      }
    }
  },

Costs can be itemised, for example:

        "cost": {
          "gbp": {
             "materials" : 500.0
             "labour" : 1000",
          "gbp_per_year": 0.0      
        },

1. Ranging from 0 (fully obscured) to 1 (no shading). ↩︎

Heat pumps move thermal energy from outside to inside, and in reverse when cooling.

A heat pump outputs cop kilowatt hours of thermal energy for space and hot water heating for every 1 kilowatt hour of electrical energy it consumes. The great attraction of heat pumps is that cop is usually much greater than 1. In other words, they output more energy heat energy than is input as electrical energy. This much more efficient than electrical heaters (cop is 1) or oil/gas boilers (cop typically between 0.5 and 0.95).

In theory cop can be large (see above) but is usually between 2 and 6, influenced mainly by:

• engineering limitations;
• the temperate and climate where your home is located;
• the number, efficiency, size and condition of radiators in your home;
• the diameter and length of the central heating plumbing connecting the heat pump to your radiators;
• how well insulated your home is;
• the flow capacity of your central heating pipes.

To describe your heat pump:

• use the “include” flag to include it;
• give an accurate average for cop over a year: scop (“seasonal coefficient of performance”) in “scop”. To obtain this reliably, ask a qualified installer to conduct a heat loss survey on your home and include (and preferably guarantee) the scop figure as part of its quotation;
• in “power” include the maximum heat power output for your heatpump “output_kw”, and its background power consumption “background_w” when not running;
• in “cost” include in “gbp” the initial costs (including necessary preparatory works, heat pump installation, radiator resizings, buffer tank if fitted), and annual costs (e.g. maintenance) in “gbp_per_year”.

    "heat_pump": {
        "include": true,
        "scop": 4.0,        
        "power": {
           "output_kw": 10.0,
           "background_w": 20
        },
        "cost": {
          "gbp": {
             "install": 15000.0,
             "grant": -7500
             },
          "gbp_per_year": {
             "maintenance": 250.0
             }
          },
        "design": {
           "internal_temp_max_c" : 24.0,
           "outside_temp_min_c" : -3.0,
           "cops": {
                "0": 5.1,
                "5": 5.0,
               "10": 4.9,
               "20": 4.5,
               "30": 4.0,
               "40": 3.0,
               "50": 2.0,
               "60": 1.5,
               "70": 1.2,
               "80": 1.1,
               "90": 1.0,
              "100": 0.95
           }
        }   
    },

The optional “design” tag fine tunes heat pump performance:

• “internal_temp_max_c” is the maximum room temperature that can be reached when the outside temperature is at its lowest, see below;
• “outside_temp_min_c” is the lowest outside temperature at which the heat pump can maintain “internal_temp_max_c”;
• “cops” is how cop varies with temperature expressed as an array of temperature – cop values. These are sometimes included in heat pump datasheets but accuracy is not critical and it can be omitted, especially if you know “scop”.

Batteries store energy for later use or export at a profit:

"battery": {
    "include": true,
    "initial_raw_capacity_kwh": 13.5,
    "cost_install_gbp": 5000.0,
    "max_charge_kw": 6.4,
    "max_discharge_kw": 6.4,
    "cost_maintenance_pa_gbp": 0,
    "round_trip_efficiency_percent": 93,
    "projection": {
      "cycles_to_reduced_capacity": 7500,
      "reduced_capacity_percent": 20
    }    
  },

“initial_raw_capacity_kwh” gives the battery’s initial capacity at the beginning of the project.

Include your battery’s maximum charge in discharge powers in “max_charge_kw” and “max_discharge_kw” respectively. All batteries, especially those couple to AC inverters, lose some power when charging and discharging, so you need to state the round trip efficiency in “round_trip_efficiency_percent”.

“gbp” is the intial cost including installation. If your battery requires annual maintenance (few do) put this in “gbp_per_year”.

The simulator assumes battery capacity reduces linearly with charge-discharge cycles. For your stated “initial_raw_capacity_kwh”, state the “reduced_capacity_percent” and “cycles_to_reduced_capacity”. I.e. in the above example, capacity reduces to 0.8 * 13.5 kWh (10.8 kWh) after 7,500 cycles.

Behaviour

The simulator attempts to satisfy the house load:

• from the battery, then

• from the grid.

The simulator assumes the battery charges as much as possible:

• from solar generation, then

• from the grid during off peak periods

The insulation component achieves a percentage reduction in space heating energy demand:

"insulation": {
  "include": true,
  "cost": {
    "gbp": 2500.0,
    "gbp_per_year": 0.0 
  },
  "energy_saving_percent": 20
}

The above example is for adding cavity insulation to a typical 5 bedroom house: initial costs only of £2,500 and achieves a 20% reduction to its space heating energy demand.

Insulation investments should be your first until they result in diminishing returns.

It pays to stop at some point, and your house doesn’t have to be a passive house for adding more not to make sense. For example, after adding a little extra loft insulation to our wall cavity filled 1960s house, there was relatively little we could do to improve it further beyond paying another £30k to clad it, inside or out: far less financially attractive compared to installing solar PV with a heat pump and battery.