A hot topic for hard times
The use of the sun to replace dirty electricity can work a number of ways. I focus here on options for your home or organisation.
The first and most popular option is solar hot water. Incoming radiation from the sun converts directly to heat; storage is through having a relatively large tank that can be heated to a higher temperature than you actually need. For safety, you should have a tempering valve that mixes in cold water so you do not get scalded. Most solar systems have an overflow that releases hot water if the system overheats. This is an essential safety feature.
Another option is a heat pump, which works on the same physics as an air conditioner or refrigerator except it uses the hot side and discards the cool side.
A heat pump is the better option if you have a lot of hot water use after dark when a solar heater would be wasted. Heat pumps are also preferable for large-scale heating with continuous demand, for example, heating a pool.
If used as designed, a solar hot water system with electric backup should use about 90% less electricity than a purely electrical system. A heat pump saves about 80%.
Another option is to install solar panels. Photovoltaic systems can only generate electricity when the sun is shining. In cloudy weather, even where there is enough radiation to heat water, they are ineffective. For this reason, such systems are best used either coupled with the grid or with batteries.
With batteries, you can be independent of the grid or at least have the option to keep going for a while when the grid is off. Batteries are expensive and only really an option if you have frequent power outages or if you are far from the grid.
The major components are photovoltaic panels and an inverter, a device that converts the DC voltage from the panels to AC at the same voltage as the mains, and synchronised to the mains AC signal. A grid-tied system comes in two flavours: purely a top-up of your grid-based supply and a system that exports to the grid.
In South Africa, a few municipalities give credit for exported electricity; in Makana that is not an option. The big obstacle here to such a system is the reliance of our municipality on its slice of electricity tariffs to balance its budget (to the extent that it does). It is fair that electricity users who are on the grid should contribute something to infrastructure costs; the government should consider how that should work as solar power gets less expensive.
How inexpensive is it? About a year ago, I priced a system and it would have taken about six years to re- cover the cost. A photovoltaic system lasts about 25 years, mostly without maintenance costs (the inverter may need to be replaced sooner than that). That’s pretty good, so why didn’t I do it?
The main obstacle for home use is that the best hours of solar generation are not a great fit to home usage. Unless you work from home, as long as feeding to the grid is not an option, only a very small-scale system that feeds things you do not turn off makes sense.
If you are running a business or educational organisation that is busy during the day, it’s a different story.
Finally, a few words on gridscale solar power. Photovoltaics are cost-effective when the sun is shining. To get the best out of them, they need to be deployed in areas with little cloud and ideally across a big enough geographic range that some operate when others are under cloud. My calculated payback time assumes an average of 10 hours per day of sunshine; there are parts of the country with more.
However, without storage, photovoltaics have to be part of a pool that can generate power even without sunshine. Storage is expensive. The largest-scale bulk storage on our grid is called pumped storage – hydro schemes that can run in reverse, pumping water uphill when there is an oversupply of electricity and running the usual way with downhill flow over turbines to generate power.
There is another form of solar generation that includes storage: solar thermal, also known as concentrated solar power (CSP). In this type of system, heat of the sun is stored, often in a molten salt mix, allowing electricity generation during non-sunlit hours. We have three small trial-scale plants in South Africa. More here: https:// www.eia.gov/energyexplained/?page=solar_thermal_power_plants
Find us Online: www.grocotts. co.za/environews
Contacts for Makana Environews
Nikki Köhly: firstname.lastname@example.org, 046 603 7205 Tim Bull: email@example.com, 076 289 5122 Jenny Gon: firstname.lastname@example.org, 046 622 5822 Nick James: email@example.com, 082 575 9781 Philip Machanick: firstname.lastname@example.org, 046 603 8635.