Practical Home Energy Saving
Updated: 12-Oct-2013
Glass Of Water

Stage 1: A Simple Inverter/Battery Set Up

Inverter/Battery Set Up Schematic

The arrangement shown was used to carry out the initial feasibility study. The system was used to power the garage, side passage, utility room and outside toilet lights. The load consisted of 2 * 22W Bulbs controlled by a PIR, 2 individually switched 36W neons plus a pair of 50W halogen lights. All the items apart from the PIR are relatively low usage and were chosen because they were not particularly important and are easy to get to for wiring. The results obtained plus assumptions and comments are shown below.

<

Caution: Electricity can be dangerous. Modifications to any electrical apparatus or wiring should only be carried out by a competent person.

It is important the inverter neutral is isolated from mains neutral otherwise there will be around 800V between mains live and inverter live due to the voltages being out of phase. The inverter must be properly connected to mains earth.

 

Inverter

Average
Time On
(Hrs Daily)

Inverter
Input
(Amps)

Inverter
Input
(Watts)

Inverter
Output
(Watts)

Inverter
Efficiency

No Load

0

0.30

3.6

0

0.0%

PIR/Light Detector

24

0.24

2.9

2

30.9%

36W Neon

2

3.78

45.4

38

77.6

2 * 36W Neon

0.1

6.51

78.1

74

90.6

2 * 11W Lo Energy

0.3

2.26

27.1

24

78.1

2 * 50W Halogen

0.5

8.58

103

100

93.8

 

Charger

Time

Switch
(Watts)

Charger
Input
(Watts)

Charger
Current
(Amps)

Charger
Output
(Watts)

Charger
Efficiency
(%)

Battery
Input
(KWHr/day)

Total
Power
(KWHr/day)

On 4.3 Hrs/day (Cheap Rate)

24.0

119.0

6.4

76.5

64.3

0.510

0.312

 

System Efficiency

System
Input
(KWHr/day)

Power
Supplied
(KWHr/day)

Overall
Efficiency
(%)

Totals

0.510

0.187

36.8

 

Cost Comparison

Cheap
Rate
(p/KWHr)

Normal
Rate
(p/KWHr)

Cheap
Rate
(KWHr/day)

Normal
Rate
(KWHr/day)

Cost
(per Day)

Cost
(per Qtr)

Original

4.40

10.50

0.012

0.175

£0.019

£1.71

Inverter System

4.40

10.50

0.510

0.0

£0.022

£2.02

Assumptions
1. Inverter system uses only cheap rate electricity.
2. Originally items used only on normal rate electricity.
3. Assumes battery energy conversion 100%.
4. Assumes stable battery voltage of 12V which it isn't but the variations should average out.
5. Usage averaged over whole year for simplicity.
6. The time switch consumption of 1W has been added to the battery charger input power.
7. Battery charger reverse leakage current of 70mA included in inverter input current and power figures.

Comments
1. Efficiency is very low.
2. Time Switch on time has to be adjusted to suit load - probably fairly regularly.
3. Battery charger efficiency is lower than expected.
4. Cost using this setup is slightly more expensive than without it.

Legal Disclaimer
Site History
Privacy Policy
Site Map
Copyright © 2005-2014 A. J. Shadlock All Rights Reserved Worldwide