Brooks’ family solar house
Technical summary by Chris Brooks

Summary
The Brooks’ family house, a 3-bed detached house in Hady, has 8 solar panels (mostly 230 W) connected to batteries which are used to power all the low-energy LED lighting in the house. Monitoring enables lights to be turned off when the stored power drops too low.

In addition the family have installed 4 kW solar panels (16 Panels) connected to the grid which are used to help power the family home and charge a Renault Twizy electric car.

Solar panels No. Watts Use
Off grid 8 230ea (1.8 kW) Linked to 8 x 110 amp hr leisure batteries which power all the LED lighting
Grid-tied 16 250ea (4 kW) Charges family electric car as well as other appliances

Technical details

Off-grid solar lighting
Initially the family started simple by installing an 80 W Solar Panel, Charge Controller and Leisure Battery in their Motorhome (RV). We then changed all the internal lights to low energy LED strips. The savings were considerable: all the LEDs combined consumed less electricity than one of the 12 x 8 W fluorescent tubes.

After 7 years the RV battery was still working well and solar panels had dropped in price (the original 80w panel cost £250 while new 230 W panels now cost £100). They started to look at the house. We had already changed most of the bulbs to mains LED ones but the early LEDs didn’t last as long as expected but we used them to work out what colour light we liked for particular rooms: cool light in the bathroom, kitchen and office and warm white in the bedroom and lounge.

Brooks LEDIn our large conservatory we installed 12 V, 3 x 5m long white LED strips up the centre and similar multi coloured (mainly set to blue now) strips around the edge. See more pictures at http://1drv.ms/1s7HXbe

We also installed some coloured LEDs in the bedroom and under cupboard LEDs in the kitchen. These were powered from a couple of Leisure batteries (2 x 125 amp lead acid) charged by 2 x 230 W Solar panels mounted on a south facing Porch roof. It worked for a winter but we concluded the batteries needed to be bigger.

The next step was to add 6 more 230 W panels and 6 more 110 amp batteries now all running at 24 V. ie 8 panels feeding 8 batteries in four pairs. The 24 V is then stepped down to 12 V to power all the lighting. Using 24 V allowed the use of a cheaper solar chargers to handle the current. For safety, fuses were installed in all cable runs.

The house has 3 separate lighting circuits and we were able to phase the change over by pulling the wires out of the consumer unit (fuse box or breaker box) and attaching them to the 12.4 V adapter. We then went round and changed all the bulbs on that circuit to 12 V 7 W, 9 W, 10 W LED Corn bulbs or MR12/GU5.3 spots 4 W. We also added a Voltage display on the Battery bank and 12 V circuits. This is good to do sanity checks on the battery bank without finding out a multimeter. All this meant no change to any light fitting or light switches, so minimum disruption. The house is now lit completely off grid so in a power cut the lights stay on.

Remote control of lighting/mains battery charging
Next we used the output from the solar charge controller to control a Mains Battery charger. ie. Should the battery bank voltage drop to 50% (see later as to why 50%) it turns on the mains powered battery charger. This only occurs after several days of no sun in winter.

We also have an Arduino (open source electronics platform) attached to the battery bank to monitor the voltage which gives a web page with a nice dial gauge. On a test bed we have a relay bank that is also attached to an Arduino along with the software mocked up. The Arduino will monitor the voltage and if the bank gets too low it turns off unnecessary circuits (coloured conservatory LEDS, bedroom coloured LEDS, under kitchen cupboard LEDS, garage lights etc). We also have the ability to control circuits via the web page so we can remotely turn the lights on/off (for energy and security reasons).

Electric car
The family also owns a Renault Twizy all electric car which is generally charged using 4 kW of grid-tied solar panels.

Battery details
The battery bank consists of 8 x 110 amp leisure batteries in pairs. Wiith lead acid it is recommended you only discharge to 50%. This means the battery bank is rated at 5.2 kWh.

It runs at 24 V nominal therefore we charge at 27.8 V, maintain at 27.2 V and expect off charge voltage to be 25.4 V (100%) and 24.4 V (50%) all measured at no load.

A lot depends on how fast the discharge is, the quality of the battery (not all will last at 50% state of charge (SOC) for many cycles) and how quick they can be charged after discharge. However we believe our batteries will do 1,000 discharges to 50% SOC, so should last approx 8 years. Therefore at present this may not be a viable money saving exercise. However during powercuts it will allow us to still watch TV as well as keeping the lights on.

We opted for leisure batteries because they deliver low current for long periods unlike car starter batteries which deliver high currents for short periods. Batteries weaken when they go flat and the more often it goes completely flat the weaker the battery becomes. Lead Acid, unlike Lithium batteries; become damaged if taken below a round 50%. This is why the G-WIZ and Aixam EV’s (Electric Vehicles) need to change the batteries often. Leisure battery construction will withstand a higher discharge (not high current) when compared to starter batteries, however they will still suffer the same damage. Leisure batteries are rated on a C rating (usually C20) and this gives the capacity the battery when new can supply ie. an 80 amp hour battery will supply 4 amps for 20 hours (C20) before becoming empty (and damaged). The same battery cannot supply 8 amps for 10 hours it would be nearer 8 hours.

While we would have preferred to use lithium based batteries, there is a big leap in costs and availability of the chargers etc.
For more information contact Chris Brooks via hello@transitionchesterfield.org.uk