Solar Electricity

Our solar electric power system is made up of four main parts

1. Solar panels on three roof faces
2. Hybrid Inverter
3. Battery storage
4. Battery charger(s)

Solar Panels

Since we don’t have a south facing roof we have to compromise and have panels facing in two directions, the South East will get more sunshine in the morning and the South West in the afternoon. We will probably get more overall power this way unless we had had a very large south facing roof. The nominal output of the solar is 2.8kW (7 x 405W) for the ‘P’ roof, 4kW (10 x 405W) for the ‘M’ roof and 2.2kW (22 x 100W) for Skylight. We could actually get more than this but only for a short time in on a perfectly clear day in midsummer!

The ‘M’ & ‘P’ roof’s panels are connected together in series to make two  300-400V feeds to the hybrid inverter in the Utility room. The skylight panels will wired in series/parallel to feed the solar battery chargers.

The 405W panels are Trina vertex S 405W black.

Hybrid Inverter

The main function of this unit is to convert the high voltage DC from the solar panels to either 230V AC for general use or 50V DC to charge the battery. It can convert 2 independent strings of solar panels and continuously adjust the conversion so as to maximise the output of the panels (This is called Maximum Power Point Tracking [MPPT]). The unit has a total of 5kW of capacity which is shared between the solar inputs so if we had very bright sunshine the unit will have to degrade the solar output.

The unit has battery storage attached which is charged from excess solar (i.e. when the house is not using all the power generated) and is discharged to power the house when there is insufficient solar (at night!). The unit will charge/discharge the battery @ up to 100A (i.e. all the solar power is charging the battery or full 5kW is coming from the battery).

The Hybrid inverter is a Solis S5-EH1P5K-L.

Battery Storage

Since most of the Solar power is produced when the house is idling at background power levels we need to store all the power to use later… Thus the system has a large battery!

The current battery system has a capacity of 32kWh, which is made up of 2 x 50V batteries having 14kWh each and a 12V battery @ 4kWh. The system limits the usage to 90% of capacity to improve longevity (Full capacity is available in an emergency).

The batteries are stored in draws built into the tech cupboard (1 extra draw for expansion).

Each draw contains the individual 280Ah 3.2V LiFePo4 cells (16 for 50V and 4 for 12V) connected with copper bus bars and a Battery management system (BMS) to oversee the cell health and report the battery state. There is a disconnect switch between the battery and the system bus bars.

Battery chargers

The system can charge the batteries from both solar and grid power. The 50V system has 3 charging sources, hybrid inverter (from external solar), solar charger(s) (from skylight solar) and 10kW of grid chargers. The 12V battery has a solar charger (from skylight solar) and a 1kW of grid charger.

We will have intelligent control of when the battery is charged from the grid so to use only off peak power and to leave enough capacity to accept tomorrows anticipated solar excess.