The cost of generating electricity through a residential or commercial rooftop PV installation is approximately half of ESKOM’s cost for generation from burning coals. Likewise the average household or commercial building has access to technology that enables it to harvest most of its household water, safe for human consumption, from rainwater. Both electricity and water are dependent on storage capacity that will increase their effectiveness.
AWPower engineers have designed and installed multiple rooftop energy and water efficiency systems during the past year, and judging from the results, we believe that we are on the verge of the rooftop revolution as outlined by Arnaud Dabancourt in his research submitted for an Executive Masters in Business Administration at the Graduate School of Business at the University of Cape Town (2016). In his thesis, Dabancourt predicts a “leapfrog effect” similar to that of the mobile phone, where previously there had been few or no telecommunications in parts of Africa. It is predicted that this phenomenon could lead to a “death spiral” for traditional power utilities all over the world.
Rooftop generation of electricity and rainwater harvesting becomes even more significant when one studies statistics that show that up to 40% of water is lost through infrastructure collapse. The same collapse is noticeable for electrical infrastructure through lack of preventative maintenance and cable theft, or even more serious incidences of load shedding.
Typical rooftop energy and water systems may look like the following:
Typical Rainwater Harvesting System:
A typical fully integrated rainwater harvesting system would supply the entire building (residential or commercial) with drinkable (potable) water. The system consists of water tanks that are fed from multiple gutters collecting from most, if not all, of the roof area. From the tanks the water is pumped with an energy-efficient 850W variable speed drive pump through a 3-stage particle filter system with a UV-filter to ensure that the water is purified.
The energy efficient variable speed drive (VSD) pump has the functionality to gradually increase its power draw to maintain the pressure set for the system, rather than being a conventional 1.5kW pump with constant 1.5kW power draw. The system includes, as backup, a municipal supply into the tanks with a ball valve that will collect municipal water should the rainwater supply run low. Provision is made for expanding the water tank capacity, for example underground tanks of 6,000L can be added to the existing system, as shown in the images below.
Typical installed cost incl. VAT: R 67,000
Typical Solar PV System:
Solar PV installations could be modular, and a 6kW Off-Grid heavy-duty Inverter, together with 3,24kWp (12 x 270Wp) of rooftop mounted PV modules would be a good starting point. Recommended storage would be a bank of 4 x 240Ah AGM/Gel Hybrid batteries that store up to 11.5kWh of generated electricity. The system is suitable for supporting the full load of a building, including the conventional geyser which is fitted with a 2kW or 1.5kW element, managed by a geyser controller. The inverter has the functionality to automatically connect to the grid when running low on PV or battery power.
Typical installed cost incl. VAT: R 154,000