Office UPS Powered by Solar Energy

[box]Executive Summary[/box]

Navgathi on a strong foundation of solar installation on boats turned towards land based installation. The first test case was the computer UPS system in Navgathi office. A suitable grid-tie inverter was selected; however to utilize the solar energy during grid outage a relay system with charge controller that works under this scenario was proposed. This ensure that all the energy produced by the solar panels can be utilized.

Solar Panels installed on roof of Navgathi office

[box]Scenario Before Installation[/box] The office computers, 15 in number in one floor, were powered through in-line UPS (Liebert 3 kVA), that ensures un-interrupted power supply when KSEB (State Electricity Board) grid fails. The overall consumption of the office top floor was around 40 units per day including air-conditioners and other loads.

The objective was to reduce this electricity consumption by means of solar installation. Since most of the consumption is in day-light hours (8:30 AM – 6:00 PM) and that we had a dedicated UPS for computers and lights/fans, it made sense to install grid- tie system without batteries.

[box]First Stage: Grid-tie Inverter[/box]

We experimented on the angle of the solar panel installation. Initially we placed then horizontally and noted the power generation. Once the structure was completed for placing them at 10 degrees South facing, the energy produced increase by 25%. On a average we could generate 19 kWh in a day (February in Kochi).

Solar Panels: 17 panels of 230 W each = 3910 W
Make: VEGA
Grid Tie-Inverter: 3000 W
Make: SMA Sunny Boy 3000 TL

[box]Second Stage: Charge Controller and Relay[/box]

The solution was add a charge controller to connect the solar panels with the battery bank of the UPS. This connection would be activated when the grid fails. This was made possible by means of a relay system that will automatically change over the connection from grid-tie inverter to charge controller.

A big challenge in this relay system was that when the solar panels are connected with the grid-tie inverter then it is in series connection whereas when it is connected with the charge controller the solar panels have three groups of panels in parallel – six each in two sets and five in other based on the limitation of input voltage.

Charge Controller: 5000 W @ 96 V
Make: Midnite Solar
Relay & Controls: In-house

[box]Benefits[/box]

The system give the following benefits:

First Stage:

Drastic reduction in electricity bill

Second Stage:

Increased back-up time of UPS in the day time (when is grid fails)
Complete utilization of solar energy from panels

All equipments, cable, junction box etc. are IEC approved.

[box]Costing[/box]

First Stage: 5.5 lakhs
Second Stage: 1 lakh
Total System: 6.5 lakhs

Above prices are excluding MNRE subsidy. Firms making profit can also get the benefit of depreciation up to 70%.