I have spent the last ten years of my career in the renewable energy and wider energy technology area. I have managed a renewable fund. I have advised global investors on where to invest their money and today I am advising companies on strategy, fund raising and M&A in the energy area.
I am convinced that our energy world is radically changing thanks to technologies such as solar, horizontal drilling, demand response, LEDs, batteries as well as exciting new business models from companies such as SolarCity in the power market or Tesla in the electric car area. And we have already seen, particularly in Europe, a huge build out of renewables which has forever changed our power markets.
And there’s me buying a house on the German-Polish border surrounded by trees, fields and water. A beautiful and tranquil place in the flood plains of the river Oder and I am surrounded by renewable energy, nature and eco-farmers.
We have a biogas power station outside the village. Most farmers have solar on their roofs. Most people use wood for heating purposes, and there are a large amount of wind turbines in the area. And a ten minute drive and I am at Neuhardenberg which is home to Germany’s biggest solar PV plant (145MW).
The house itself needs to be renovated and I have followed on from Denmark by banning the use of fossil fuels for heating systems.
That narrows my choices down to using biomass such as wood or geothermal/solar heat pumps or full electricity for heating and hot water. I looked at putting in a small CHP unit. I looked at wood pellets. I even looked at fuel cells. In the end I have decided to go fully renewable.
I will use solar thermal and a heat pump for my hot water and I will also put 10kW of PV solar on my roof. My goal is to buy as little power as possible from the grid and I am going to put intelligence and storage around it so that I use as much of that power as possible.
Storage will come in three forms, hot water in a tank, an electric car and if needed an extra battery system. I am also going to flexibilise the demand side to meet that solar production. I am also going to buy a BMW i3 (assuming BMW can actually organise charging stations in both Berlin airports) and again to charge it during the day.
I want an intelligent system that works automatically without my intervention but that I can also control with my mobile phone. And any electricity I do buy from the grid will be renewable.
I am also going to put in highly efficient devices in the home. The lighting will be LEDs and we will also put an infrared electric heating system which produces radiant heat just like the sun. And my wife is happy because she says that it produces a healthy and comfortable heat.
They also look good. They can be hidden behind pictures or as what we are going to do in the kitchen they can be made to look like black boards. I will also put in a wood fired heating range which will provide direct heat for the living room as well as heat for hot water.
Probably the most radical thing I am going to do is to wire the house for direct current (DC) purposes. It just makes no sense to me that we generated DC with solar panels, convert that energy to alternating current (AC) and then convert them back to DC so we can power the whole range of digital devices that make up our modern lives.
And the power losses are up to 20% as a result. I am also fed up having all those black transformer boxes around my house. What I want is to plug everything in as one does a mobile phone into a computer. A simple USB port for everything. I would go fully DC but the issue is that there are still a whole range of devices such as washing machines that need AC. But I know they are coming and I will be ready!
Source: Energy and Carbon. Reproduced with permission.
This post was published on March 22, 2016 3:08 pm
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DC is a bit of a catch-cry here. A good question to ask, but one which Thomas Edison and Nikola Tesla tussled-out, over 120 years ago. Some of the conclusions then would pretty much still hold today - namely that AC distribution is safer and cheaper than DC distribution. Although in this case it is within a house, rather than without. Also, what you make up for in losses in practice, would tend to be far outweighed by the cost of doing so safely. Protecting against DC arcing in case of a fault is more involved that protection against faults in AC systems. In short, a DC fault is more likely to create a fire than an AC fault.
I would also question the 20% losses in DC-AC-DC conversion. Modern switch-mode power supplies are extremely efficient. You can also get into micro-solar these days - eg solar powered small devices such as clocks etc using tiny 1W-class solar panels and tiny regulators. Much safer and less messy than reticulated fixed DC voltage that you have to convert up and down anyway to things like 3V, 6V 12V 18V etc - which BTW use the same efficient switch-mode technology used for AC to DC conversion in the first place.
At the end of the day, if a person is really concerned about 10 or 20% perceived losses in their power system, why not just install 10 or 20% more solar on your roof?
Couldn't of said it better myself.
Have you thought about the price of inverters?
Why spend $5000 to push the voltage to 240 when you can buy appliances that will run from 12 volt and there are less losses..
Stepping out of the norm requires some innovative thinking but you dont have to build or design anything, the low voltage equipment is already available..
My experience comes from living in an RV/motorhome where I have everything I need (except a washing machine because I use a laundry as necessary) including satellite TV...
I agree with RV/motorhome/caravan/trailer/cruising vessel situations, that 12V or 24V will do for small numbers of small-ish appliances. But each case on its merits. Above a certain sized dwelling, a central DC-AC inverter makes a lot of sense, as it gives you access to cheaper mass-produced 240V appliances, AND the ability to run your cables tens of metres. 12V can't do that - its cable losses become too great.
Fantastic that you can live an ultra-low power lifestyle.
In Edison and Tesla's time there was no way to convert DC from one voltage to another. This is the only reason AC became the power of choice. DC is more efficient by any measure available and is the power of choice for long haul transmission. AC is safer because it is easy to interrupt AC current. A DC circuit needs special breakers and DC switches should have a special circuit, or magnet to extinguish the arc. With these things factored into the equation DC can be made available quite safely.
Yes, so while it is possible to install DC reticulation today, it is still not anywhere near as economic as AC. Consider DC runs for PV - they have to be installed in heavy-duty conduit all the way - not so AC for the same power carrying capacity. And you still need voltage conversion, as you also do for AC. DC still has it's place.
Any exposed cable needs to be installed in conduit. AC or DC. DC current has better carrying capacity than AC on a given cable size. DC to DC conversion is also more efficient. Up to 99.5% If you use a 240V battery bank all the cable sizes will be quite small and losses minimal. With some investment DC switches could be used and all your appliances could run from 240V DC no conversion needed.
I=V/R; and for AC root-mean-square (RMS) is used to equate the same power as DC, and assuming all other things equal, and skin-effect conductance of AC is negligible, the equation yields the same result for AC or DC - for small scale systems.
(For HV transmission - it's a different story. Capacitance, inductance and corona effects really come into play - HVDC is eminently preferable above 500kV)
DC conversion efficiency varies with difference in V's converted (as does AC). At the grid side of things, it still is the case that high power voltage conversion is most economically done via transformer-based technology - 100kW and up switch-mode distribution inverters would be far more expensive for capital, maintenance and reliability than transformers.
DC is inherently worse in failure mode- usually due to directional corrosion on connecting parts - the polarised current corrodes and transfers material much faster than AC, leading to more stringent design and construction engineering - read more expense than AC.
Interestingly, "large amount of wind turbines in the area" do not appear to be causing the local residence any health issues.
Yes. Because the Germans made sure that some of the money earned with those turbine flows (through company tax) to the local council / community. When this is the case, nearly all suspected health impacts mysteriously disappear, or rather, are never observed in the first place.
YES... YES... I have spoken to friends about the weird situation of converting 12 or 24 volt to 240 volt just to drive a washing machine and fridge.. Those appliances can both be run off 12 volt. Worse case scenario you instal a small inverter for that machine. Lighting can easily be 12 volt, water heating solar and cooking gas... Heating if needed can be done with solar heaters... Once again we need to step away from the model which has come at us from that created by the past...
If you live in a bus or caravan, maybe. But solar PV on a typical house runs at anything from 120V DC to 600V DC. It all needs to be converted anyway. 12V is *NOT* an economic option for typical house appliances due to large losses in cabling caused by the currents needed for running anything but a small-power appliance at 12V. Believe me a typical house running on 12V is a nightmare for safety and reliability.
I'm working on a solar powered DC washing machine, particularly to try and make this dream of a fully DC house viable. If one can avoid the cost of the inverter, that's a big saving. Email me at stewart@villageinfrastructure.org if this is of more interest. We've already done solar agricultural mills for village farmers for food processing - rice hulling, flour grinding, vegetable grating, etc etc.
Fantastic stuff for no-grid, less-developed places. Make it reliable as you can!
I appreciate the dream. And many off grid people live on DC...but usually in little cabins. I have lived off grid for 15 years in a large house with an average of 15 adults in community. I have been through the arithmetic...DC is not worth it. Face the music, spend $5000 on a quality inverter. It may last 20 years ($250 a year). By the time you replace it the same inverter power will cost $1000. Inverters now hit 98% efficiency. DC appliances cost twice what AC does. The other suggestion is to use PV instead of Solar hotwater panels. Solar hot water is dead at the present price of PV in Germany.
Gerald, I agree that IR panels 'feel' better for heating. You need to look at the Heat pump systems for water and interior heating and cooling as well. IR has a COP of 1. Heat pumps can run up to a COP of 3 or 4. That means they are 3 or 4 times as efficient, which might be an issue if you wanted to use less electricity overall.
Reducing the number of electric 'bricks' is in part an ascetic issue. I have decided that nearly everything 'small' that I buy in the future will run off of 5VDC, with a USB plug.
As an electronics technician it is easy to see DC is everywhere in the house already, and only the grid and a few exceptional appliances (cooking and washing machines) run on AC. Mobile applications like yachts and motorhomes predominantly use DC. Developing countries use extensive DC. For a time, solar systems developed an industry standard around 12V as a single lead acid battery was 12V. However some trucks and larger engines with larger electrical systems needed two batteries or 24V, so DC appliances needed to auto-select between a 12V and a 24V source voltage. As a result, todays DC appliances run on 12V and 24V, although 24V is better for reducing cable diameter. The current industry standard for solar battery banks is 48V, which more than halves cable diameter again, though unfortunately DC appliances are not currently available running 48V. DC will undoubtedly evolve and we don't know what industry standard the world will settle on, and hence what DC voltage will develop in economies of scale. Makita runs most of their power tools on a single 18V Lithium battery, although some higher power tools need two batteries hence running on 36V. At the present day, using 24V DC in a house requires consciously locating the battery bank close to medium and higher power electrical appliances. Since the solar panels, solar regulator and batteries all run on DC, DC will always be a choice as well as adding the $2k - $8k inverter/charger for AC appliances as well. DC will always be simple and reliable as thats what comes directly out of the battery and solar panels. As large centralised grids are replaced by more targeted grids around population centres, DC will naturally evolve in smaller remote areas or areas with a thin grid.
To see the cable diameter issue, the box in the LHS top of this picture is the isolator switch for the solar panels and its wires are 6mm2. I wired this DC circuit board yesterday. Reading left to right, the second box is space left spare for a future solar array. Then the third box is the circuit breaker for the Solar Controller which steps the voltage down to 24V so these wires are 16mm2. I left room for future additional Solar Controllers and any other unforeseen gear. The next box is the DC circuit breakers for any future DC appliances and the wire feeding it is also 16mm2. So the DC comes from our Solar Panels, through our Isolator Switch, through our Solar Controller and its circuit breaker, then into our DC circuits and batteries. Looking at the large box on the LHS, this is the large battery disconnect switch, which has 50mm2 wires feeding the inverter/charger. The inverter/charger runs our high current appliances so the wires are thick. The round component in the middle is a battery meter which measures the % battery charge and the midpoint voltages of a battery bank, to check all batteries are charging effectively. The blue box is a battery balancer which makes sure the batteries charge equally. This granny flat uses a 24V battery bank, which also gives the choice to run the 24V DC circuit breakers. In the future, this building may need a DC water pump and our local electrician also does AC to DC fridge conversion. This solar install is a compact design, placing the circuit breakers and meters in this DC cabinet and the expensive and temperature sensitive components, like the Solar Regulator, Batteries and Inverter/Charger inside.
This picture shows the back of a DC circuit board. As the voltage steps down from our solar array, the wires get bigger. The large components like the Solar Controller, Inverter/Charger and Batteries are on the inside wall. The wiring loom is brought across to the RHS with the heaviest wire gauge components mounted on the back RHS of the board, enabling our largest wires to have a larger turning diameter, with spare wire for any future changes in configuration. Typically, installers will build the circuit board at their workshop and install it at our homes and connect the wires. It's good to think ahead, about how many PV arrays we wish to begin with, where we have space for the switching gear, inverter/charger and batteries. Each install is unique and this one has provision of both AC and DC appliances.
I am with you. DC is the future. Now you have to ask only 1 question:
1. Which appliances wont run on 240V DC? Most modern appliances including fridges, washing machines, heaters, Airconditioners all run better on DC than AC.
So lucky you, living in Germany, the home of great engineers, all you need is to develop some general power outlets GPO's that will safely interrupt DC power. There are lots of easy ways to do this.. Than why not go to a 240V battery bank and run everything from that? I have designed my home in Australia 14kW off grid using a 240V battery bank so that when the switches become available I can bypass the inverter and save that 20%.. If you feel inclined to develop a DC power outlet, look me up. http://www.livingnatural.com.au